Sample records for largest dune field
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Modeling aeolian dune and dune field evolution
Diniega, Serina
Aeolian sand dune morphologies and sizes are strongly connected to the environmental context and physical processes active since dune formation. As such, the patterns and measurable features found within dunes and dune fields can be interpreted as records of environmental conditions. Using mathematical models of dune and dune field evolution, it should be possible to quantitatively predict dune field dynamics from current conditions or to determine past field conditions based on present-day observations. In this dissertation, we focus on the construction and quantitative analysis of a continuum dune evolution model. We then apply this model towards interpretation of the formative history of terrestrial and martian dunes and dune fields. Our first aim is to identify the controls for the characteristic lengthscales seen in patterned dune fields. Variations in sand flux, binary dune interactions, and topography are evaluated with respect to evolution of individual dunes. Through the use of both quantitative and qualitative multiscale models, these results are then extended to determine the role such processes may play in (de)stabilization of the dune field. We find that sand flux variations and topography generally destabilize dune fields, while dune collisions can yield more similarly-sized dunes. We construct and apply a phenomenological macroscale dune evolution model to then quantitatively demonstrate how dune collisions cause a dune field to evolve into a set of uniformly-sized dunes. Our second goal is to investigate the influence of reversing winds and polar processes in relation to dune slope and morphology. Using numerical experiments, we investigate possible causes of distinctive morphologies seen in Antarctic and martian polar dunes. Finally, we discuss possible model extensions and needed observations that will enable the inclusion of more realistic physical environments in the dune and dune field evolution models. By elucidating the qualitative and
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Southern high latitude dune fields on Mars: Morphology, aeolian inactivity, and climate change
Fenton, L.K.; Hayward, R.K.
2010-01-01
fields, which can provide a lower age limit through crater counting: assuming all relatively stabilized dune fields represent a single noncontiguous surface of uniform age, their estimated crater retention age is climate conditions are responsible for the observed degradation and reduced level of aeolian activity. A lack of observed transport pathways and the absence of large dune fields in the largest basins (Hellas and Argyre Planitiae) are consistent with the previously proposed idea that dune sands are not typically transported far from their source regions on Mars. ?? 2009 Elsevier B.V.
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Size distribution and structure of Barchan dune fields
Directory of Open Access Journals (Sweden)
O. Durán
2011-07-01
Full Text Available Barchans are isolated mobile dunes often organized in large dune fields. Dune fields seem to present a characteristic dune size and spacing, which suggests a cooperative behavior based on dune interaction. In Duran et al. (2009, we propose that the redistribution of sand by collisions between dunes is a key element for the stability and size selection of barchan dune fields. This approach was based on a mean-field model ignoring the spatial distribution of dune fields. Here, we present a simplified dune field model that includes the spatial evolution of individual dunes as well as their interaction through sand exchange and binary collisions. As a result, the dune field evolves towards a steady state that depends on the boundary conditions. Comparing our results with measurements of Moroccan dune fields, we find that the simulated fields have the same dune size distribution as in real fields but fail to reproduce their homogeneity along the wind direction.
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Ewing, Ryan C.; Peyret, Aymeric-Pierre B.; Kocurek, Gary; Bourke, Mary
2010-01-01
High-Resolution Imaging Science Experiment (HiRISE) imagery of the central Olympia Undae Dune Field in the north polar region of Mars shows a reticulate dune pattern consisting of two sets of nearly orthogonal dune crestlines, with apparent slipfaces on the primary crests, ubiquitous wind ripples, areas of coarse-grained wind ripples, and deflated interdune areas. Geomorphic evidence and dune field pattern analysis of dune crest length, spacing, defect density, and orientation indicates that ...
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Ewing, Ryan C.; Peyret, Aymeric-Pierre B.; Kocurek, Gary; Bourke, Mary
2010-08-01
High-Resolution Imaging Science Experiment (HiRISE) imagery of the central Olympia Undae Dune Field in the north polar region of Mars shows a reticulate dune pattern consisting of two sets of nearly orthogonal dune crestlines, with apparent slipfaces on the primary crests, ubiquitous wind ripples, areas of coarse-grained wind ripples, and deflated interdune areas. Geomorphic evidence and dune field pattern analysis of dune crest length, spacing, defect density, and orientation indicates that the pattern is complex, representing two constructional generations of dunes. The oldest and best-organized generation forms the primary crestlines and is transverse to circumpolar easterly winds. Gross bed form-normal analysis of the younger pattern of crestlines indicates that it emerged with both circumpolar easterly winds and NE winds and is reworking the older pattern. Mapping of secondary flow fields over the dunes indicates that the most recent transporting winds were from the NE. The younger pattern appears to represent an influx of sediment to the dune field associated with the development of the Olympia Cavi reentrant, with NE katabatic winds channeling through the reentrant. A model of the pattern reformation based upon the reconstructed primary winds and resulting secondary flow fields shows that the development of the secondary pattern is controlled by the boundary condition of the older dune topography.
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Multi-spatial analysis of aeolian dune-field patterns
Ewing, Ryan C.; McDonald, George D.; Hayes, Alex G.
2015-07-01
Aeolian dune-fields are composed of different spatial scales of bedform patterns that respond to changes in environmental boundary conditions over a wide range of time scales. This study examines how variations in spatial scales of dune and ripple patterns found within dune fields are used in environmental reconstructions on Earth, Mars and Titan. Within a single bedform type, different spatial scales of bedforms emerge as a pattern evolves from an initial state into a well-organized pattern, such as with the transition from protodunes to dunes. Additionally, different types of bedforms, such as ripples, coarse-grained ripples and dunes, coexist at different spatial scales within a dune-field. Analysis of dune-field patterns at the intersection of different scales and types of bedforms at different stages of development provides a more comprehensive record of sediment supply and wind regime than analysis of a single scale and type of bedform. Interpretations of environmental conditions from any scale of bedform, however, are limited to environmental signals associated with the response time of that bedform. Large-scale dune-field patterns integrate signals over long-term climate cycles and reveal little about short-term variations in wind or sediment supply. Wind ripples respond instantly to changing conditions, but reveal little about longer-term variations in wind or sediment supply. Recognizing the response time scales across different spatial scales of bedforms maximizes environmental interpretations from dune-field patterns.
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Xu, Zhiwei; Mason, Joseph A.; Lu, Huayu
2015-01-01
The response of dune fields to changing environmental conditions can be better understood by investigating how changing vegetation cover affects dune morphodynamics. Significant increases in vegetation and widespread dune stabilization over the years 2000-2012 are evident in high-resolution satellite imagery of the Mu Us dune field in north-central China, possibly a lagged response to changing wind strength and temperature since the 1970s. These trends provide an opportunity to study how dune morphology changes with increasing vegetation stabilization. Vegetation expansion occurs mainly by expansion of pre-existing patches in interdunes. As vegetation spreads from interdunes onto surrounding dunes, it modifies their shapes in competition with wind-driven sand movement, primarily in three ways: 1) vegetation anchoring horns of barchans transforms them to parabolic dunes; 2) vegetation colonizes stoss faces of barchan and transverse dunes, resulting in lower dune height and an elongated stoss face, with shortening of barchan horns; and 3) on transverse dunes, the lee face is fixed by plants that survive sand burial. Along each of these pathways of stabilization, dune morphology tends to change from more barchanoid to more parabolic forms, but that transformation is not always completed before full stabilization. Artificial stabilization leads to an extreme case of "frozen" barchans or transverse dunes with original shapes preserved by rapid establishment of vegetation. Observations in the Mu Us dune field emphasize the point that vegetation growth and aeolian sand transport not only respond to external factors such as climate but also interact with each other. For example, some barchans lose sand mass during vegetation fixation, and actually migrate faster as they become smaller, and vegetation growth on a barchan's lower stoss face may alter sand transport over the dune in a way that favors more rapid stabilization. Conceptual models were generalized for the
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Origin of the late quaternary dune fields of northeastern Colorado
Muhs, D.R.; Stafford, T.W.; Cowherd, S.D.; Mahan, S.A.; Kihl, R.; Maat, P.B.; Bush, C.A.; Nehring, J.
1996-01-01
Stabilized eolian deposits, mostly parabolic dunes and sand sheets, cover much of the landscape of northeastern Colorado and adjacent parts of southwestern Nebraska in four geographically distinct dune fields. Stratigraphic and soil-geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka, possibly between 11 ka and 4 ka, and within the past 1.5 ka. Thus, eolian sand deposition took place under both glacial and interglacial climatic conditions. In the youngest episodes of eolian sand movement, Holocene parabolic dunes partially buried Pleistocene sand sheet deposits. Late Holocene sands in the Fort Morgan and Wray dune fields, to the south of the South Platte River, have trace element ratios that are indistinguishable from modern South Platte River sands, but different from Ogallala Formation bedrock, which has previously been cited as the main source of dune sand on the Great Plains. Sands in the Greeley dune field, to the north of the South Platte River, have trace element concentrations that indicate a probable Laramie Formation source. Measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields, in good agreement with resultant drift directions calculated for nearby weather stations. Thus, paleowinds were probably not significantly different from present-day winds, and are consistent with a South Platte River source for the Fort Morgan and Wray dune fields, and a Laramie Formation source for the Greeley dune field. Sand accumulated downwind of the South Platte River to form the Fort Morgan dune field. In addition, sand was also transported farther downwind over the upland formed by the calcrete caprock of the Ogallala Formation, and deposited in die lee of the upland on the southeast side. Because of high wind energy, the upland itself served as a zone of sand transport, but little or no sand accumulation took place on this surface. These
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Latitudinal and altitudinal controls of Titan's dune field morphometry
Le Gall, A.; Hayes, A. G.; Ewing, R.; Janssen, M. A.; Radebaugh, J.; Savage, C.; Encrenaz, P.; the Cassini Radar Team
2012-01-01
Dune fields dominate ˜13% of Titan's surface and represent an important sink of carbon in the methane cycle. Herein, we discuss correlations in dune morphometry with altitude and latitude. These correlations, which have important implications in terms of geological processes and climate on Titan, are investigated through the microwave electromagnetic signatures of dune fields using Cassini radar and radiometry observations. The backscatter and emissivity from Titan's dune terrains are primarily controlled by the amount of interdune area within the radar footprint and are also expected to vary with the degree of the interdunal sand cover. Using SAR-derived topography, we find that Titan's main dune fields (Shangri-La, Fensal, Belet and Aztlan) tend to occupy the lowest elevation areas in Equatorial regions occurring at mean elevations between ˜-400 and ˜0 m (relative to the geoid). In elevated dune terrains, we show a definite trend towards a smaller dune to interdune ratio and possibly a thinner sand cover in the interdune areas. A similar correlation is observed with latitude, suggesting that the quantity of windblown sand in the dune fields tends to decrease as one moves farther north. The altitudinal trend among Titan's sand seas is consistent with the idea that sediment source zones most probably occur in lowlands, which would reduce the sand supply toward elevated regions. The latitudinal preference could result from a gradual increase in dampness with latitude due to the asymmetric seasonal forcing associated with Titan's current orbital configuration unless it is indicative of a latitudinal preference in the sand source distribution or wind transport capacity.
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Optical Dating of Holocene Dune Sands in the Ferris Dune Field, Wyoming
Stokes, Stephen; Gaylord, David R.
1993-05-01
Optical dating of late Quaternary quartz dune sands from the Clear Creek portion of Ferris dune field, Wyoming, demonstrates the considerable potential of the technique as a chronostratigraphic tool. A sequence of radiocarbon-dated Holocene interdune strata permit optical dating of the intercalated dune sand to be tested; the concordance is good. The optical dates for the aeolian deposits not datable by radiocarbon suggest that aeolian sedimentation at Clear Creek peaked during two relatively short phases at ca. 8500 and 4000 yr B.P. The dates indicate that aeolian accumulation maxima (at least in the Clear Creek area) may not be synchronous with previously defined phases of marked aridity.
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Trickle-down boundary conditions in aeolian dune-field pattern formation
Ewing, R. C.; Kocurek, G.
2015-12-01
One the one hand, wind-blown dune-field patterns emerge within the overarching boundary conditions of climate, tectonics and eustasy implying the presence of these signals in the aeolian geomorphic and stratigraphic record. On the other hand, dune-field patterns are a poster-child of self-organization, in which autogenic processes give rise to patterned landscapes despite remarkable differences in the geologic setting (i.e., Earth, Mars and Titan). How important are climate, tectonics and eustasy in aeolian dune field pattern formation? Here we develop the hypothesis that, in terms of pattern development, dune fields evolve largely independent of the direct influence of 'system-scale' boundary conditions, such as climate, tectonics and eustasy. Rather, these boundary conditions set the stage for smaller-scale, faster-evolving 'event-scale' boundary conditions. This 'trickle-down' effect, in which system-scale boundary conditions indirectly influence the event scale boundary conditions provides the uniqueness and richness of dune-field patterned landscapes. The trickle-down effect means that the architecture of the stratigraphic record of dune-field pattern formation archives boundary conditions, which are spatially and temporally removed from the overarching geologic setting. In contrast, the presence of an aeolian stratigraphic record itself, reflects changes in system-scale boundary conditions that drive accumulation and preservation of aeolian strata.
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Holocene eolian activity in the Minot dune field, North Dakota
Muhs, D.R.; Stafford, Thomas W.; Been, J.; Mahan, S.A.; Burdett, J.; Skipp, G.; Rowland, Z.M.
1997-01-01
Stabilized eolian sand is common over much of the Great Plains region of the United States and Canada, including a subhumid area of ??? 1500 km2 near Minot, North Dakota. Eolian landforms consist of sand sheets and northwest-trending parabolic dunes. Dunes and sand sheets in the Minot field are presently stabilized by a cover of prairie grasses or oak woodland. Stratigraphic studies and accelerator mass spectrometry radiocarbon dating of paleosols indicate at least two periods of eolian sand movement in the late Holocene. Pedologic data suggest that all of the dune field has experienced late Holocene dune activity, though not all parts of the dune field may have been active simultaneously. Similar immobile element (Ti, Zr, La, Ce) concentrations support the interpretation that eolian sands are derived from local glaciofluvial and glaciolacustrine sediments. However, glaciolacustrine and glaciofluvial source sediments have high Ca concentrations from carbonate minerals, whereas dune sands are depleted in Ca. Because noneolian-derived soils in the area are calcareous, these data indicate that the Minot dune field may have had extended periods of activity in the Holocene, such that eolian abrasion removed soft carbonate minerals. The southwest-facing parts of some presently stabilized dunes were active during the 1930s drought, but were revegetated during the wetter years of the 1940s. These observations indicate that severe droughts accompanied by high temperatures are the most likely cause of Holocene eolian activity.
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Equinoctial Activity Over Titan Dune Fields Revealed by Cassini/vims
Rodriguez, S.; Le Mouelic, S.; Barnes, J. W.; Hirtzig, M.; Rannou, P.; Sotin, C.; Brown, R. H.; Bow, J.; Vixie, G.; Cornet, T.; Bourgeois, O.; Narteau, C.; Courrech Du Pont, S.; Le Gall, A.; Reffet, E.; Griffith, C. A.; Jaumann, R.; Stephan, K.; Buratti, B. J.; Clark, R. N.; Baines, K. H.; Nicholson, P. D.; Coustenis, A.
2012-12-01
Titan, the largest satellite of Saturn, is the only satellite in the solar system with a dense atmosphere. The close and continuous observations of Titan by the Cassini spacecraft, in orbit around Saturn since July 2004, bring us evidences that Titan troposphere and low stratosphere experience an exotic, but complete meteorological cycle similar to the Earth hydrological cycle, with hydrocarbons evaporation, condensation in clouds, and rainfall. Cassini monitoring campaigns also demonstrate that Titan's cloud coverage and climate vary with latitude. Titan's tropics, with globally weak meteorological activity and widespread dune fields, seem to be slightly more arid than the poles, where extensive and numerous liquid reservoirs and sustained cloud activity have been discovered. Only a few tropo-spheric clouds have been observed at Titan's tropics during the southern summer. As equinox was approaching (in August 2009), they occurred more frequently and appeared to grow in strength and size. We present here the observation of intense brightening at Titan's tropics, very close to the equinox. These detections were conducted with the Visual and Infrared Mapping Spectrometer (VIMS) onboard Cassini. We will discuss the VIMS images of the three individual events detected so far, observed during the Titan's flybys T56 (22 May 2009), T65 (13 January 2010) and T70 (21 June 2010). T56, T65 and T70 observations show an intense and transient brighten-ing of large regions very close to the equator, right over the extensive dune fields of Senkyo, Belet and Shangri-La. They all appear spectrally and morphologically different from all transient surface features or atmospheric phenomena previously reported. Indeed, these events share in particular a strong brightening at wavelengths greater than 2 μm (especially at 5 μm), making them spectrally distinct from the small tropical clouds observed before the equinox and the large storms observed near the equator in September and October
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Mars Global Digital Dune Database; MC-1
Hayward, R.K.; Fenton, L.K.; Tanaka, K.L.; Titus, T.N.; Colaprete, A.; Christensen, P.R.
2010-01-01
The Mars Global Digital Dune Database presents data and describes the methodology used in creating the global database of moderate- to large-size dune fields on Mars. The database is being released in a series of U.S. Geological Survey (USGS) Open-File Reports. The first release (Hayward and others, 2007) included dune fields from 65 degrees N to 65 degrees S (http://pubs.usgs.gov/of/2007/1158/). The current release encompasses ~ 845,000 km2 of mapped dune fields from 65 degrees N to 90 degrees N latitude. Dune fields between 65 degrees S and 90 degrees S will be released in a future USGS Open-File Report. Although we have attempted to include all dune fields, some have likely been excluded for two reasons: (1) incomplete THEMIS IR (daytime) coverage may have caused us to exclude some moderate- to large-size dune fields or (2) resolution of THEMIS IR coverage (100m/pixel) certainly caused us to exclude smaller dune fields. The smallest dune fields in the database are ~ 1 km2 in area. While the moderate to large dune fields are likely to constitute the largest compilation of sediment on the planet, smaller stores of sediment of dunes are likely to be found elsewhere via higher resolution data. Thus, it should be noted that our database excludes all small dune fields and some moderate to large dune fields as well. Therefore, the absence of mapped dune fields does not mean that such dune fields do not exist and is not intended to imply a lack of saltating sand in other areas. Where availability and quality of THEMIS visible (VIS), Mars Orbiter Camera narrow angle (MOC NA), or Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) images allowed, we classified dunes and included some dune slipface measurements, which were derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification. It was beyond the scope of this report to look at the detail needed to discern subtle dune modification. It was also
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Control parameters of the martian dune field positions at planetary scale: tests by the MCD
allemand, pascal
2016-04-01
The surface of Mars is occupied by more than 500 dunes fields mainly located inside impact craters of the south hemisphere and near the north polar cap. The questions of the activity of martian dunes and of the localization of the martian dune fields are not completely solved. It has been demonstrated recently by image observation and image correlation that some of these dune fields are clearly active. The sand flux of one of them has been even estimated. But there is no global view of the degree of activity of each the dune fields. (2)The topography of impact craters in which dune fields are localized is an important factor of their position. But there is no consensus of the effect of global atmospheric circulation on dune field localization. These two questions are addressed using the results of Mars Climate Database 5.2 (MCD) (Millour, 2015; Forget et al., 1999). The wind fields of the MCD have been first validated against the observations made on active dune fields. Using a classical transport law, the Drift Potential (DP) and the Relative Drift Potential (RDP) have been computed for each dune fields. A good correlation exists between the position of dune fields and specific values of these two parameters. The activity of each dune field is estimated from these parameters and tested on some examples by image observations. Finally a map of sand flow has been computed at the scale of the planet. This map shows that sand and dust is trapped in specific regions. These regions correspond to the area of dune field concentration.
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Hoover, R. H.; Gaylord, D. R.; Cooper, C. M.
2018-05-01
The St. Anthony Dune Field (SADF) is a 300 km2 expanse of active to stabilized transverse, barchan, barchanoid, and parabolic sand dunes located in a semi-arid climate in southeastern Idaho. The northeastern portion of the SADF, 16 km2, was investigated to examine meteorological influences on dune mobility. Understanding meteorological predictors of sand-dune migration for the SADF informs landscape evolution and impacts assessment of eolian activity on sensitive agricultural lands in the western United States, with implications for semi-arid environments globally. Archival aerial photos from 1954 to 2011 were used to calculate dune migration rates which were subsequently compared to regional meteorological data, including temperature, precipitation and wind speed. Observational analyses based on aerial photo imagery and meteorological data indicate that dune migration is influenced by weather for up to 5-10 years and therefore decadal weather patterns should be taken into account when using dune migration rates as proxies from climate fluctuation. Statistical examination of meteorological variables in this study indicates that 24% of the variation of sand dune migration rates is attributed to temperature, precipitation and wind speed, which is increased to 45% when incorporating lag time.
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Kim, Jungrack; Kim, Younghwi; Park, Minseong
2016-10-01
At the present time, arguments continue regarding the migration speeds of Martian dune fields and their correlation with atmospheric circulation. However, precisely measuring the spatial translation of Martian dunes has succeeded only a very few times—for example, in the Nili Patera study (Bridges et al. 2012) using change-detection algorithms and orbital imagery. Therefore, in this study, we developed a generic procedure to precisely measure the migration of dune fields with recently introduced 25-cm resolution orbital imagery specifically using a high-accuracy photogrammetric processor. The processor was designed to trace estimated dune migration, albeit slight, over the Martian surface by 1) the introduction of very high resolution ortho images and stereo analysis based on hierarchical geodetic control for better initial point settings; 2) positioning error removal throughout the sensor model refinement with a non-rigorous bundle block adjustment, which makes possible the co-alignment of all images in a time series; and 3) improved sub-pixel co-registration algorithms using optical flow with a refinement stage conducted on a pyramidal grid processor and a blunder classifier. Moreover, volumetric changes of Martian dunes were additionally traced by means of stereo analysis and photoclinometry. The established algorithms have been tested using high-resolution HIRISE time-series images over several Martian dune fields. Dune migrations were iteratively processed both spatially and volumetrically, and the results were integrated to be compared to the Martian climate model. Migrations over well-known crater dune fields appeared to be almost static for the considerable temporal periods and were weakly correlated with wind directions estimated by the Mars Climate Database (Millour et al. 2015). As a result, a number of measurements over dune fields in the Mars Global Dune Database (Hayward et al. 2014) covering polar areas and mid-latitude will be demonstrated
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Adnani, M.; Azzaoui, M. A.; Elbelrhiti, H.; Ahmamou, M.; Masmoudi, L.
2015-12-01
Dunes around Khnifiss lagoon (28° 3'N, 12°13'W) show different colors ranging from black at the beach, whitish yellow in transverse dunes near the beach to reddish at the mega barchans situated few kilometers in the SW. The scientific question is about the abundance of different dunes in the same environmental conditions. The present work aims to investigate the factors that influence dunes color change, and then at which degree these factors could control dunes stability. To highlight the difference in color observed at the dune fields then to characterize dunes mineralogy, Landsat TM images were used in addition to mineralogical analysis that was carried out for the black grains samples originated from megabarchans. Optic Microscope and SEM- EDS data was adopted, in addition to physico-chemical analysis provided by Electronic Microprobe. Grain size and shape analysis were conducted to characterize the different types of grains of sand. 3/1 Landsat image band ratio allowed iron oxide distinction, the results revealed the importance of iron oxide concentration. Furthermore, mineralogical and physico-chemical analysis revealed (i) a high grade of oxides (Rutile, Ilmenite, Magnetite, Ulvöspinel) in samples, (ii) silicates (Quartz, Clinopyroxene, feldspar, Zircon), (iii) phosphate (apatite) and (iv) carbonate (calcite). The grain size analysis of the sand originated from the megabarchans reveals that there are three populations of sand. Black grains with a diameter less than 100μm and dominated by the magnetite, red ones composed mainly by the quartz with diameter between 100 and 180 μm and grains with diameter more than 180 μm are white and composed by carbonates. The threshold of motion of these different grains was calculated. It shows that these different grains have the same threshold of motion, which means that the grain size compensates the density. This explains the abundance of different populations of sand in the same environment. The dominance of iron
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Beveridge, C.; Kocurek, G.; Ewing, R.C.; Lancaster, N.; Morthekai, P.; Singhvi, A.K.; Mahan, S.A.
2006-01-01
The pattern of dunes within the Gran Desierto of Sonora, Mexico, is both spatially diverse and complex. Identification of the pattern components from remote-sensing images, combined with statistical analysis of their measured parameters demonstrate that the composite pattern consists of separate populations of simple dune patterns. Age-bracketing by optically stimulated luminescence (OSL) indicates that the simple patterns represent relatively short-lived aeolian constructional events since ???25 ka. The simple dune patterns consist of: (i) late Pleistocene relict linear dunes; (ii) degraded crescentic dunes formed at ???12 ka; (iii) early Holocene western crescentic dunes; (iv) eastern crescentic dunes emplaced at ???7 ka; and (v) star dunes formed during the last 3 ka. Recognition of the simple patterns and their ages allows for the geomorphic backstripping of the composite pattern. Palaeowind reconstructions, based upon the rule of gross bedform-normal transport, are largely in agreement with regional proxy data. The sediment state over time for the Gran Desierto is one in which the sediment supply for aeolian constructional events is derived from previously stored sediment (Ancestral Colorado River sediment), and contemporaneous influx from the lower Colorado River valley and coastal influx from the Bahia del Adair inlet. Aeolian constructional events are triggered by climatic shifts to greater aridity, changes in the wind regime, and the development of a sediment supply. The rate of geomorphic change within the Gran Desierto is significantly greater than the rate of subsidence and burial of the accumulation surface upon which it rests. ?? 2006 The Authors. Journal compilation 2006 International Association of Sedimentologists.
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Ewing, R. C.
2011-12-01
Wind blown landscapes are a default geomorphic and sedimentary environment in our solar system. Wind sand dunes are ubiquitous features on the surfaces of Earth, Mars and Titan and prevalent within the aeolian rock records of Earth and Mars. Dunes are sensitive to environmental and climatic changes and a complete understanding of this system promises a unique, robust and quantitative record of paleoclimate extending to the early histories of these worlds. However, our understanding of how aeolian dune landscapes evolve and how the details of the wind are recorded in cross-strata is limited by our lack of understanding of three-dimensional dune morphodynamics related to changing boundary conditions such as wind direction and magnitude and sediment source area. We use airborne LiDAR datasets over 40 km2 of White Sands Dune Field collected from June 2007, June 2008, January 2009, September 2009 and June 2010 to quantify 1) three-dimensional dune geometries, 2) annual and seasonal patterns of erosion and deposition across dune topography, 3) spatial changes in sediment flux related to position within the field, 4) spatial changes in sediment flux across sinuous crestlines and 5) morphologic changes through dune-dune interactions. In addition to measurements, we use the LiDAR data along with wind data from two near-by weather stations to develop a simple model that predicts depositional and stratigraphic patterns on dune lee slopes. Several challenges emerged using time series LiDAR data sets at White Sands Dune Field. The topography upon which the dunes sit is variable and rises by 16 meters over the length of the dune field. In order to compare individual dune geometries across the field and between data sets a base surface was interpolated from local minima and subtracted from the dune topography. Co-registration and error calculation between datasets was done manually using permanent vegetated features within the active dune field and structures built by the
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Hayes, A. G.; Ewing, R. C.; Cassini Radar Science Team, T.
2011-12-01
Fields of bedform patterns persist across many orders of magnitude, from cm-scale sub-aqueous current ripples to km-scale aeolian dunes, and form with surprisingly little difference in expression despite a range of formative environments. Because of the remarkable similarity between and among patterns, extracting information about climate and environment from these patterns is a challenge. For example, crest orientation is not diagnostic of a particular flow regime; similar patterns form under many different flow configurations. On Titan, these challenges have played out with many attempts to reconcile dune-field patterns with modeled and expected wind regimes. We propose that thinking about the change in dune orientation, rather than the orientation itself, can provide new insights on the long-term stability of the dune-field patterns and the formative wind regime. In this work, we apply the re-orientation model presented by Werner and Kocurek [Geology, 1997] to the equatorial dune fields of Titan. We measure variations in pattern parameters (crest spacing, crest length and defect density, which is the number of defect pairs per total crest length) both within and between Titan's dune fields to describe pattern maturity and identify areas where changes in dune orientation are likely to occur (or may already be occurring). Measured defect densities are similar to Earth's largest linear dune fields, such as the Namib Sand Sea and the Simpson Desert. We use measured defect densities in the Werner and Kocurek model to estimate crestline reorientation rates. We find reorientation timescales varying from ten to a hundred thousand times the average migration timescale (time to migrate a bedform one meter, ~1 Titan year according to Tokano (Aeolian Research, 2010)). Well organized patterns have the longest reorientation time scales (~10^5 migration timescales), while the topographically or spatially isolated patches of dunes show the shortest reorientation times (~10
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Thompson, L. M.; O'Connell-Cooper, C.; Spray, J. G.; Gellert, R.; Boyd, N. I.; Desouza, E.
2017-12-01
The MSL-APXS has analyzed a variety of unconsolidated sediments within the Gale impact crater, including soils, sands from barchan [High, Namib dunes], and linear dunes [Nathan Bridges, Mount Desert dunes], within the active Bagnold dune field, and sands from two smaller ripple fields ("mega-ripples"). The Gale "soils" (unsorted, unconsolidated sediments, ranging from fine-grained particles (including dust) to coarser "pebbly" material [>2 mm]), are, to a large degree, similar to Martian basaltic soils quantified by APXS, at Gusev crater (MER-A_Spirit) and Meridiani Planum (MER-B_Opportunity). Some local contributions are indicated by, for example, the enriched K levels (relative to a martian average basaltic soil [ABS]) within coarser Gale soil samples, and a Cr, Mn, Fe enrichment within finer-grained samples. Sands (grain size 62 µm to 2 mm) of the Bagnold dunes, generally, exhibit elevated Mg and Ni, indicating enrichment from olivine and pyroxene, but depleted S, Cl and Zn, indicating high activity levels and low dust. Compositional differences, related both to position within a dune (i.e., crest versus off-crest sand), and type of dune (linear versus barchan), are identified. Off-crest sands have Na, Al, Si, K, P contents similar to (or slightly depleted, relative to) the ABS, enrichment in Mg, and low dust content, whilst crest sands contain very high Mg and Ni (relative to the ABS), low felsic elemental concentrations and very low dust content. Cr is significantly enriched (and, to a lesser degree, Mn, Fe, Ti) in the off-crest sands of the linear dunes. In contrast, barchan dunes off-crest sands have Cr, Mn, Fe, and Ti abundances similar to those in the Gale soils. Additionally, Ni concentrations in barchan dunes off-crest sands are enriched relative to the linear dunes. Analyses from a small, isolated "mega-ripple" reveal a composition similar to that of the Gale soils, including a high dust content. The second mega-ripple, within a larger ripple field, is
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Kim, J.; Park, M.; Baik, H. S.; Choi, Y.
2016-12-01
At the present time, arguments continue regarding the migration speeds of Martian dune fields and their correlation with atmospheric circulation. However, precisely measuring the spatial translation of Martian dunes has rarely conducted only a very few times Therefore, we developed a generic procedure to precisely measure the migration of dune fields with recently introduced 25-cm resolution High Resolution Imaging Science Experimen (HIRISE) employing a high-accuracy photogrammetric processor and sub-pixel image correlator. The processor was designed to trace estimated dune migration, albeit slight, over the Martian surface by 1) the introduction of very high resolution ortho images and stereo analysis based on hierarchical geodetic control for better initial point settings; 2) positioning error removal throughout the sensor model refinement with a non-rigorous bundle block adjustment, which makes possible the co-alignment of all images in a time series; and 3) improved sub-pixel co-registration algorithms using optical flow with a refinement stage conducted on a pyramidal grid processor and a blunder classifier. Moreover, volumetric changes of Martian dunes were additionally traced by means of stereo analysis and photoclinometry. The established algorithms have been tested using high-resolution HIRISE images over a large number of Martian dune fields covering whole Mars Global Dune Database. Migrations over well-known crater dune fields appeared to be almost static for the considerable temporal periods and were weakly correlated with wind directions estimated by the Mars Climate Database (Millour et al. 2015). Only over a few Martian dune fields, such as Kaiser crater, meaningful migration speeds (>1m/year) compared to phtotogrammetric error residual have been measured. Currently a technical improved processor to compensate error residual using time series observation is under developing and expected to produce the long term migration speed over Martian dune
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Mars Global Digital Dune Database (MGD3): Global dune distribution and wind pattern observations
Hayward, Rosalyn K.; Fenton, Lori; Titus, Timothy N.
2014-01-01
The Mars Global Digital Dune Database (MGD3) is complete and now extends from 90°N to 90°S latitude. The recently released south pole (SP) portion (MC-30) of MGD3 adds ∼60,000 km2 of medium to large-size dark dune fields and ∼15,000 km2 of sand deposits and smaller dune fields to the previously released equatorial (EQ, ∼70,000 km2), and north pole (NP, ∼845,000 km2) portions of the database, bringing the global total to ∼975,000 km2. Nearly all NP dunes are part of large sand seas, while the majority of EQ and SP dune fields are individual dune fields located in craters. Despite the differences between Mars and Earth, their dune and dune field morphologies are strikingly similar. Bullseye dune fields, named for their concentric ring pattern, are the exception, possibly owing their distinctive appearance to winds that are unique to the crater environment. Ground-based wind directions are derived from slipface (SF) orientation and dune centroid azimuth (DCA), a measure of the relative location of a dune field inside a crater. SF and DCA often preserve evidence of different wind directions, suggesting the importance of local, topographically influenced winds. In general however, ground-based wind directions are broadly consistent with expected global patterns, such as polar easterlies. Intriguingly, between 40°S and 80°S latitude both SF and DCA preserve their strongest, though different, dominant wind direction, with transport toward the west and east for SF-derived winds and toward the north and west for DCA-derived winds.
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Wiggs, Giles F. S.; Livingstone, Ian; Warren, Andrew
1996-09-01
Field measurements on an unvegetated, 10 m high barchan dune in Oman are compared with measurements over a 1:200 scale fixed model in a wind tunnel. Both the field and wind tunnel data demonstrate similar patterns of wind and shear velocity over the dune, confirming significant flow deceleration upwind of and at the toe of the dune, acceleration of flow up the windward slope, and deceleration between the crest and brink. This pattern, including the widely reported upwind reduction in shear velocity, reflects observations of previous studies. Such a reduction in shear velocity upwind of the dune should result in a reduction in sand transport and subsequent sand deposition. This is not observed in the field. Wind tunnel modelling using a near-surface pulse-wire probe suggests that the field method of shear velocity derivation is inadequate. The wind tunnel results exhibit no reduction in shear velocity upwind of or at the toe of the dune. Evidence provided by Reynolds stress profiles and turbulence intensities measured in the wind tunnel suggest that this maintenance of upwind shear stress may be a result of concave (unstable) streamline curvature. These additional surface stresses are not recorded by the techniques used in the field measurements. Using the occurrence of streamline curvature as a starting point, a new 2-D model of dune dynamics is deduced. This model relies on the establishment of an equilibrium between windward slope morphology, surface stresses induced by streamline curvature, and streamwise acceleration. Adopting the criteria that concave streamline curvature and streamwise acceleration both increase surface shear stress, whereas convex streamline curvature and deceleration have the opposite effect, the relationships between form and process are investigated in each of three morphologically distinct zones: the upwind interdune and concave toe region of the dune, the convex portion of the windward slope, and the crest-brink region. The
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The Single-Phase ProtoDUNE Technical Design Report
Energy Technology Data Exchange (ETDEWEB)
Abi, B. [Univ. of Padova (Italy); et al.
2017-06-21
ProtoDUNE-SP is the single-phase DUNE Far Detector prototype that is under construction and will be operated at the CERN Neutrino Platform (NP) starting in 2018. ProtoDUNE-SP, a crucial part of the DUNE effort towards the construction of the first DUNE 10-kt fiducial mass far detector module (17 kt total LAr mass), is a significant experiment in its own right. With a total liquid argon (LAr) mass of 0.77 kt, it represents the largest monolithic single-phase LArTPC detector to be built to date. It's technical design is given in this report.
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O'Shea, P. M.; Putzig, N. E.; Van Kooten, S.; Fenton, L. K.
2015-12-01
We analyzed the effects of slopes on the thermal properties of three dune fields in Mars' southern hemisphere. Although slope has important thermal effects, it is not the main driver of observed apparent thermal inertia (ATI) for these dunes. Comparing the ATI seasonal behavior as derived from Thermal Emission Spectrometer (TES) data with that modeled for compositional heterogeneities, we found that TES results correlate best with models of duricrust overlying and/or horizontally mixing with fines. We measured slopes and aspects in digital terrain models created from High Resolution Imaging Science Experiment (HiRISE) images of dunes within Proctor, Kaiser, and Wirtz craters. Using the MARSTHERM web toolset, we incorporated the slopes and aspects together with TES albedo, TES thermal inertia, surface pressure, and TES dust opacity, into models of seasonal ATI. Models that incorporate sub-pixel slopes show seasonal day and night ATI values that differ from the TES results by 0-300 J m-2 K-1 s-½. In addition, the models' day-night differences are opposite in sign from those of the TES results, indicating that factors other than slope are involved. We therefore compared the TES data to model results for a broad range of horizontally mixed and two-layered surfaces to seek other possible controls on the observed data, finding that a surface layer of higher thermal inertia is a likely contributor. However, it is clear from this study that the overall composition and morphology of the dune fields are more complex than currently available models allow. Future work will combine slopes with other model parameters such as multi-layered surfaces and lateral changes in layer thickness. Coupling these improvements with broader seasonal coverage from the Thermal Emission Imaging System (THEMIS) at more thermally favorable times of day would allow more accurate characterization of dune thermal behavior.
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Ewing, R. C.; Hayes, A. G.; McCormick, C.; Ballard, C.; Troy, S. A.
2012-04-01
Fields of bedform patterns persist across many orders of magnitude, from cm-scale sub-aqueous current ripples to km-scale aeolian dunes, and form with surprisingly little difference in expression despite a range of formative environments. Because of the remarkable similarity among bedform patterns, extracting information about climate and environment from these patterns is a challenge. For example, crestline orientation is not diagnostic of a particular flow regime; similar patterns form under many different flow configurations. On Titan, these challenges have played out with many attempts to reconcile dune crestline orientation with modeled and expected wind regimes. We propose that thinking about the time-scale of the change in dune orientation, rather than the orientation itself, can provide new insights on the long-term stability of the dune-field patterns and the formative wind regime. In this work, we apply the crestline re-orientation model developed by Werner and Kocurek [Geology, 1997] to the equatorial dune fields of Titan. We use Cassini Synthetic Aperture Radar images processed through a de-noising algorithm recently developed by Lucas et al. [LPSC, 2012] to measure variations in pattern parameters (crest spacing, crest length and defect density, which is the number of defect pairs per total crest length) both within and between Titan's dune fields to describe pattern maturity and identify areas where changes in dune orientation are likely to occur (or may already be occurring). Measured defect densities are similar to Earth's largest linear dune fields, such as the Namib Sand Sea and the Simpson Desert. We use measured defect densities in the Werner and Kocurek model to estimate crestline reorientation rates. We find reorientation timescales varying from ten to a hundred thousand times the average migration timescale (time to migrate a bedform one meter, ~1 Titan year according to Tokano (Aeolian Research, 2010)). Well-organized patterns have the
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The Sources of Moisture in the Sand Dunes – The Example of the Western Sahara Dune Field
Directory of Open Access Journals (Sweden)
Żmudzka Elwira
2014-09-01
Full Text Available Climatic and meteorological conditions may limit the aeolian transport within barchans. An explanation of that issue was the main goal of the investigation held in Western Sahara dune fields located around Tarfaya and Laâyoune. Particular attention was paid to the factors causing the moisture content rising of the sand dune surface layer, which could influence the wind threshold shear velocity in the aeolian transport. The wetted surface layer of sand, when receiving moisture from precipitation or suspensions, reduces the aeolian transport, even in case of wind velocity above 4-5 m s-1. Fog and dew condensation does not affect the moisture of deeper sand layers, what occurs after rainfall.
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Airflow over Barchan dunes: field measurements, mathematical modelling and wind tunnel testing
Wiggs, G. F. S.
1992-01-01
There are few empirical measurements of velocity, shear velocity, sand transport, morphological change on the windward slopes of dunes.This thesis compares field measurements on a barchan dune in Oman with calculations using a mathematical model (FLOWSTAR) and measurements in a wind tunnel. All three techniques demonstrate similar patterns of velocity, confirming the acceleration of flow up the windward slope, deceleration between the crest and brink and significant flow decele...
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Field measurements of mean and turbulent airflow over a barchan sand dune
Weaver, Corinne M.; Wiggs, Giles F. S.
2011-05-01
Advances in our knowledge of the aeolian processes governing sand dune dynamics have been restricted by a reliance on measures of time-averaged airflow, such as shear velocity ( u*). It has become clear that such measures are incapable of explaining the complete dynamics of sediment transport across dune surfaces. Past evidence from wind tunnel and modelling studies has suggested that in some regions on a dune's surface the sediment transport might be better explained through investigations of the turbulent nature of the airflow. However, to date there have been no field studies providing data on the turbulent characteristics of the airflow around dunes with which to support or refute such hypotheses. The field investigation presented here provides mean and turbulent airflow measurements across the centre-line of a barchan sand dune in Namibia. Data were collected using arrays of sonic anemometers and were compared with sand flux data measured using wedge-shaped traps. Results support previously published data derived from wind tunnels and numerical models. The decline in mean wind velocity at the upwind toe of the dune is shown to coincide with a rise in turbulence, whilst mean velocity acceleration on the upper slope corresponds with a general decline in measured turbulence. Analysis of the components of Reynold shear stress ( -u'¯w'¯) and normal stresses ( u¯ and w2 ¯) supports the notion that the development of flow turbulence along the dune centre-line is likely to be associated with the interplay between streamline curvature and mean flow deceleration/acceleration. It is suggested that, due to the nature of its calculation, turbulence intensity is a measure of less practical use than direct assessments of the individual components of Reynolds stress, particularly the instantaneous horizontal streamwise component ( u2 ¯) and shear stress ( -uw¯). Whilst, increases in Reynolds shear stress and the horizontal streamwise component of stress in the toe
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The Geologic Exploration of the Bagnold Dune Field at Gale Crater by the Curiosity Rover.
Chojnacki, Matthew; Fenton, Lori K
2017-11-01
The Mars Science Laboratory rover Curiosity engaged in a monthlong campaign investigating the Bagnold dune field in Gale crater. What represents the first in situ investigation of a dune field on another planet has resulted in a number of discoveries. Collectively, the Curiosity rover team has compiled the most comprehensive survey of any extraterrestrial aeolian system visited to date with results that yield important insights into a number of processes, including sediment transport, bed form morphology and structure, chemical and physical composition of aeolian sand, and wind regime characteristics. These findings and more are provided in detail by the JGR-Planets Special Issue Curiosity's Bagnold Dunes Campaign, Phase I.
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Lopez Valencia, Oliver Miguel; Jadoon, Khan; Missimer, Thomas
2015-01-01
Planning for use of a dune field aquifer for managed aquifer recharge (MAR) requires that hydraulic properties need to be estimated over a large geographic area. Saturated hydraulic conductivity of dune sands is commonly estimated from grain size
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Cavanna, F; Touramanis, C
2017-01-01
ProtoDUNE-SP is the single-phase DUNE Far Detector prototype that is under construction and will be operated at the CERN Neutrino Platform (NP) starting in 2018. It was proposed to the CERN SPSC in June 2015 (SPSC-P-351) and was approved in December 2015 as experiment NP04 (ProtoDUNE). ProtoDUNE-SP, a crucial part of the DUNE effort towards the construction of the first DUNE 10-kt fiducial mass far detector module (17 kt total LAr mass), is a significant experiment in its own right. With a total liquid argon (LAr) mass of 0.77 kt, it represents the largest monolithic single phase LArTPC detector to be built to date. It is housed in an extension to the EHN1 hall in the North Area, where the CERN NP is providing a new dedicated charged-particle test beamline. ProtoDUNE-SP aims to take its first beam data before the LHC long shutdown (LS2) at the end of 2018. ProtoDUNE-SP prototypes the designs of most of the single-phase DUNE far detector module (DUNE-SP) components at a 1:1 scale, with an extrapolation of abo...
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Vriend, Nathalie
"Booming" sand dunes are able to produce low-frequency sound that resembles a pure note from a music instrument. The sound has a dominant audible frequency (70-105 Hz) and several higher harmonics and may be heard from far distances away. A natural or induced avalanche from a slip face of the booming dune triggers the emission that may last for several minutes. There are various references in travel literature to the phenomenon, but to date no scientific explanation covered all field observations. This thesis introduces a new physical model that describes the phenomenon of booming dunes. The waveguide model explains the selection of the booming frequency and the amplification of the sound in terms of constructive interference in a confined geometry. The frequency of the booming is a direct function of the dimensions and velocities in the waveguide. The higher harmonics are related to the higher modes of propagation in the waveguide. The experimental validation includes quantitative field research at the booming dunes of the Mojave Desert and Death Valley National Park. Microphone and geophone recordings of the acoustic and seismic emission show a variation of booming frequency in space and time. The analysis of the sensor data quantifies wave propagation characteristics such as speed, dispersion, and nonlinear effects and allows the distinction between the source mechanism of the booming and the booming itself. The migration of sand dunes results from a complicated interplay between dune building, wind regime, and precipitation. The morphological and morphodynamical characteristics of two field locations are analyzed with various geophysical techniques. Ground-penetrating radar images the subsurface structure of the dunes and reveal a natural, internal layering that is directly related to the history of dune migration. The seismic velocity increases abruptly with depth and gradually increases with downhill position due to compaction. Sand sampling shows local
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Sand dune movement in the Victoria Valley, Antarctica
Bourke, Mary C.; Ewing, Ryan C.; Finnegan, David; McGowan, Hamish A.
2009-08-01
We use vertical aerial photographs and LiDAR topographic survey data to estimate dune migration rates in the Victoria Valley dunefield, Antarctica, between 1961 and 2001. Results confirm that the dunes migrated an average of 1.5 m/year. These values are consistent with other estimates of dune migration from cold climate deserts and are significantly lower than estimates from warm deserts. Dune migration rates are retarded by the presence of entrained ice, soil moisture and a reversing wind regime. Dune absorption, merging and limb extension are apparent from the time-series images and account for significant changes in dune form and the field-scale dune pattern. Dune-field pattern analysis shows an overall increase in dune-field organization with an increase in mean dune spacing and a reduction in total crest length and defect density. These data suggest that dunes in other cold desert environments on Earth, Mars or Titan, that may also have inter-bedded frozen laminae, still have the potential to migrate and organize, albeit at lower rates than dunes in warm deserts.
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Ewing, R. C.; Lapotre, M. G. A.; Lewis, K. W.; Day, M. D.; Stein, N.; Rubin, D. M.; Sullivan, R. J., Jr.; Banham, S.; Thomas, N. M.; Lamb, M. P.; Gupta, S.; Fischer, W. W.
2017-12-01
Wind-blown sand dunes are ubiquitous on the surface of Mars and are a recognized component of the martian stratigraphic record. Our current knowledge of the aeolian sedimentary processes that determine dune morphology, drive dune dynamics, and create aeolian cross-stratification are based upon orbital studies of ripple and dune morphodynamics, rover observations of stratification on Mars, Earth analogs, and experimental and theoretical studies of sand movement under martian conditions. Exploration of the Bagnold Dunes by the Curiosity Rover in Gale Crater, Mars provided the first opportunity to make in situ observations of martian dunes from the grain-to-dune scale. We used the suite of cameras on Curiosity, including Navigation Camera, Mast Camera, and Mars Hand Lens Imager. We measured grainsize and identified sedimentary processes similar to processes on terrestrial dunes, such as grainfall, grainflow, and impact ripples. Impact ripple grainsize had a median of 0.103 mm. Measurements of grainflow slopes indicate a relaxation angle of 29° and grainfall slopes indicate critical angles of at least 32°. Dissimilar to terrestrial dunes, large, meter-scale ripples form on all slopes of the dunes. The ripples form both sinuous and linear crestlines, have symmetric and asymmetric profiles, range in height between 12cm and 28cm, and host grainfall, grainflow, and impact ripples. The largest ripples are interpreted to integrate the annual wind cycle within the crater, whereas smaller large ripples and impact ripples form or reorient to shorter term wind cycling. Assessment of sedimentary processes in combination with dune type across the Bagnold Dunes shows that dune-field pattern development in response to a complex crater-basin wind regime dictates the distribution of geomorphic processes. From a stratigraphic perspective, zones of highest potential accumulation correlate with zones of wind convergence, which produce complex winds and dune field patterns thereby
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Reconstruction of the coastal morphodynamics of the Fulong-beach dune field in north-eastern Taiwan
Dörschner, Nina; Böse, Margot; Frechen, Manfred
2010-05-01
The Fulong-beach dune field is located at the north-eastern coast of Taiwan. Built up of medium and fine grained quartz rich sand, it represents a unique feature of only few kilometres along the east coast of Taiwan. This unique sedimentological regime makes the area most perfectly suitable for age estimations by optically stimulated luminescence (OSL). The dune field is crossed by the Shuangsi-river, which flows into the Pacific Ocean. The coastal area is subjected to very dynamic conditions in the transition zone between land and sea. Due to the constant force of marine and aeolian processes from tides, weather and sediment accumulation by rivers, it is a continuously changing area. Taiwan is located in a very active tectonic zone with high elevation rates, which reach from 4 mm per year at the east coast up to 7 mm per year in the southern parts of the island. Furthermore Taiwan is affected by medial 3.8 typhoons per year and minor earthquakes nearly occur every day (LIN ET AL. 2006). The consequences are high rates of erosion and sediment transport during very short time periods. The Fulong-beach coastal area is densely populated and proud for being a tourism destination. At the northern end of the dune field the Lungmen nuclear power plant is currently under construction. Four separate dune ridges could be identified from a digital elevation model and from field mapping. During the field campaign in October and November 2009 17 samples were taken for OSL-dating (MURRAY ET AL. 1995) out of the four dune ridges as well as out of a more than 30 m high elevated outcrop cut by the Shuangsi-river. The measurement and the evaluation of the OSL-samples will provide us an insight into the duration and intensity of the processes affecting the coastal area of Taiwan during the Holocene. We will give an outline during the poster presentation of the methodical approach and the morphodynamical processes affecting the Fulong-beach dune field in north-eastern Taiwan
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Composition And Geometry Of Titan'S Dunes
Le Gall, Alice; Janssen, M. A.; Wye, L. C.; Lorenz, R. D.; Radebaugh, J.; Cassini RADAR Team
2009-09-01
Fields of linear dunes cover a large portion of Titan's equatorial regions. As the Cassini mission continues, more of them are unveiled and examined by the microwave Titan RADAR Mapper both in the active and passive modes of operation of the instrument and with an increasing variety of observational geometries. In this presentation, we will show that the joint analysis of the SAR (Synthetic Aperture Radar) and radiometry observations of the dunes at closest approach supports the idea of different composition between the dunes and the interdunes. It suggests that the icy bedrock of Titan may be exposed, or partially exposed, in the interdunes. We also see regional differences among dune fields. Dunes are highly directional features; their visibility is controlled by the look direction and the incidence angle. We have developed a backscatter and emissivity model that takes into account the topography of the dunes relative to the geometry of observation as well as the composition of the dunes and interdunes. Compared to observations and, in particular, to multiple observations of areas at the overlap of several swaths, we argue the need for a diffuse scattering mechanism. The presence of ripples in the dunes and/or interdunes might account for the recorded backscatter. In this presentation we will also report the results of the T61 experiment. The T61 HiSAR sequence (on August 25, 2009) was designed to examine a small region of the Shangri-La dune field with a substantial sampling of incidence angles around the direction perpendicular to the dunes long axis. The spot in question was already observed during the T55 SAR swath and the T61 experiment should allow us to determine the slope of the dunes.
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Directory of Open Access Journals (Sweden)
Oliver M. Lopez
2015-11-01
Full Text Available Planning for use of a dune field aquifer for managed aquifer recharge (MAR requires that hydraulic properties need to be estimated over a large geographic area. Saturated hydraulic conductivity of dune sands is commonly estimated from grain size distribution data by employing some type of empirical equation. Over 50 samples from the Wadi Khulays dune field in Western Saudi Arabia were collected and the grain size distribution, porosity, and hydraulic conductivity were measured. An evaluation of 20 existing empirical equations showed a generally high degree of error in the predicted compared to the measured hydraulic conductivity values of these samples. Statistical analyses comparing estimated versus measured hydraulic conductivity demonstrated that there is a significant relationship between hydraulic conductivity and mud percentage (and skewness. The modified Beyer equation, which showed a generally low prediction error, was modified by adding a second term fitting parameter related to the mud concentration based on 25 of the 50 samples analyzed. An inverse optimization process was conducted to quantify the fitting parameter and a new empirical equation was developed. This equation was tested against the remaining 25 samples analyzed and produced an estimated saturated hydraulic conductivity with the lowest error of any empirical equation. This methodology can be used for large dune field hydraulic conductivity estimation and reduce planning costs for MAR systems.
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Lopez Valencia, Oliver Miguel
2015-11-12
Planning for use of a dune field aquifer for managed aquifer recharge (MAR) requires that hydraulic properties need to be estimated over a large geographic area. Saturated hydraulic conductivity of dune sands is commonly estimated from grain size distribution data by employing some type of empirical equation. Over 50 samples from the Wadi Khulays dune field in Western Saudi Arabia were collected and the grain size distribution, porosity, and hydraulic conductivity were measured. An evaluation of 20 existing empirical equations showed a generally high degree of error in the predicted compared to the measured hydraulic conductivity values of these samples. Statistical analyses comparing estimated versus measured hydraulic conductivity demonstrated that there is a significant relationship between hydraulic conductivity and mud percentage (and skewness). The modified Beyer equation, which showed a generally low prediction error, was modified by adding a second term fitting parameter related to the mud concentration based on 25 of the 50 samples analyzed. An inverse optimization process was conducted to quantify the fitting parameter and a new empirical equation was developed. This equation was tested against the remaining 25 samples analyzed and produced an estimated saturated hydraulic conductivity with the lowest error of any empirical equation. This methodology can be used for large dune field hydraulic conductivity estimation and reduce planning costs for MAR systems.
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Possibility of star (pyramid) dune development in the area of bimodal wind regime
Biejat, K.
2012-04-01
Star (pyramid) dunes are the largest aeolian landforms. They can occur in three types - simple, complex and compound. Development of this type of dunes is usually connected with multidirectional or complex wind regimes. The aim of this study was to verify a hypothesis that the star dunes can also develop by a bimodal wind regime and by local modifications of nearsurface wind flow directions. Field study was performed on Erg Chebbi, in southern Morocco. Several star and transverse dunes were selected for the study of their shape. The star dunes were analysed concerning their type and position in the dune field. This erg contains all of three types of star dunes together with transverse dunes. The regional wind data show that there are two dominant wind directions - NE (Chergui) and SW (Saheli). To determine the difference in shape of star dunes, we performed topographic surveying by GPS RTK. The results allowed to create 3D models of star dunes. The models were used to determine metric characteristics of star dunes, including area of dune basis, volume, and slope angles. On the basis of 3D models, primary, secondary and, on the compound dunes, tertiary arms were determined. Primary arms on each type of star dunes, as well as crestlines of transverse dunes, have dominant orientation NW-SE, perpendicular to two dominant wind directions. This clearly confirms that star dunes of Erg Chebbi develop by a bimodal wind regime In contrast to primary arms, subsidiary (secondary and tertiary) arms are not connected to general wind regime. The secondary arms of star dunes occur to be differentially developer. There are more subsidiary arms on SW sides in comparison to the E sides of the dunes where inclination of slopes is constant. It can be therefore inferred that sand has been supplied predominantly from SW direction. This is supported by distribution of the dunes on the erg. Most compound star dunes compose a chain along the E margin of the erg. Comparison of compound star
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Mapping gullies, dunes, lava fields, and landslides via surface roughness
Korzeniowska, Karolina; Pfeifer, Norbert; Landtwing, Stephan
2018-01-01
Gully erosion is a widespread and significant process involved in soil and land degradation. Mapping gullies helps to quantify past, and anticipate future, soil losses. Digital terrain models offer promising data for automatically detecting and mapping gullies especially in vegetated areas, although methods vary widely measures of local terrain roughness are the most varied and debated among these methods. Rarely do studies test the performance of roughness metrics for mapping gullies, limiting their applicability to small training areas. To this end, we systematically explored how local terrain roughness derived from high-resolution Light Detection And Ranging (LiDAR) data can aid in the unsupervised detection of gullies over a large area. We also tested expanding this method for other landforms diagnostic of similarly abrupt land-surface changes, including lava fields, dunes, and landslides, as well as investigating the influence of different roughness thresholds, resolutions of kernels, and input data resolution, and comparing our method with previously published roughness algorithms. Our results show that total curvature is a suitable metric for recognising analysed gullies and lava fields from LiDAR data, with comparable success to that of more sophisticated roughness metrics. Tested dunes or landslides remain difficult to distinguish from the surrounding landscape, partly because they are not easily defined in terms of their topographic signature.
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Sediment Source Fingerprinting of the Lake Urmia Sand Dunes.
Ahmady-Birgani, Hesam; Agahi, Edris; Ahmadi, Seyed Javad; Erfanian, Mahdi
2018-01-09
Aeolian sand dunes are continuously being discovered in inner dry lands and coastal areas, most of which have been formed over the Last Glacial Maximum. Presently, due to some natural and anthropogenic implications on earth, newly-born sand dunes are quickly emerging. Lake Urmia, the world's second largest permanent hypersaline lake, has started shrinking, vast lands comprising sand dunes over the western shore of the lake have appeared and one question has been playing on the minds of nearby dwellers: where are these sand dunes coming from, What there was not 15 years ago!! In the present study, the determination of the source of the Lake Urmia sand dunes in terms of the quantifying relative contribution of each upstream geomorphological/lithological unit has been performed using geochemical fingerprinting techniques. The findings demonstrate that the alluvial and the fluvial sediments of the western upstream catchment have been transported by water erosion and they accumulated in the lower reaches of the Kahriz River. Wind erosion, as a secondary agent, have carried the aeolian sand-sized sediments to the sand dune area. Hence, the Lake Urmia sand dunes have been originating from simultaneous and joint actions of alluvial, fluvial and aeolian processes.
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Corridors of barchan dunes: Stability and size selection
DEFF Research Database (Denmark)
Hersen, P.; Andersen, Ken Haste; Elbelrhiti, H.
2004-01-01
state. Second, the propagation speed of dunes decreases with the size of the dune: this leads, through the collision process, to a coarsening of barchan fields. We show that these phenomena are not specific to the model, but result from general and robust mechanisms. The length scales needed...... for these instabilities to develop are derived and discussed. They turn out to be much smaller than the dune field length. As a conclusion, there should exist further, yet unknown, mechanisms regulating and selecting the size of dunes....
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Controls on desert dune activity - a geospatial approach
Lancaster, N.; Hesse, P. P.
2017-12-01
Desert and other inland dunes occur on a wide spectrum of activity (defined loosely as the proportion of the surface area subject to sand movement) from unvegetated to sparsely vegetated "active" dunes through discontinuously vegetated inactive dunes to completely vegetated and degraded dunes. Many of the latter are relicts of past climatic conditions. Although field studies and modeling of the interactions between winds, vegetation cover, and dune activity can provide valuable insights, the response of dune systems to climate change and variability past, present, and future has until now been hampered by the lack of pertinent observational data on geomorphic and climatic boundary conditions and dune activity status for most dune areas. We have developed GIS-based approach that permits analysis of boundary conditions and controls on dune activity at a range of spatial scales from dunefield to global. In this approach, the digital mapping of dune field and sand sea extent has been combined with systematic observations of dune activity at 0.2° intervals from high resolution satellite image data, resulting in four classes of activity. 1 km resolution global gridded datasets for the aridity index (AI); precipitation, satellite-derived percent vegetation cover; and estimates of sand transport potential (DP) were re-sampled for each 0.2° grid cell, and dune activity was compared to vegetation cover, sand transport potential, precipitation, and the aridity index. Results so far indicate that there are broad-scale relationships between dunefield mean activity, climate, and vegetation cover. However, the scatter in the data suggest that other local factors may be at work. Intra-dune field patterns are complex in many cases. Overall, much more work needs to be done to gain a full understanding of controls at different spatial and temporal scales, which can be faciliated by this spatial database.
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2004-01-01
31 May 2004 Springtime for the martian northern hemisphere brings defrosting spots and patterns to the north polar dune fields. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example located near 76.7oN, 250.4oW. In summer, these dunes would be darker than their surroundings. However, while they are still covered by frost, they are not any darker than the substrate across which the sand is slowly traveling. Dune movement in this case is dominated by winds that blow from the southwest (lower left) toward the northeast (upper right). The picure covers an area about 3 km (1.9 mi) across and is illuminated by sunlight from the lower left.
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Exploring inner structure of Titan's dunes from Cassini Radar observations
Sharma, P.; Heggy, E.; Farr, T. G.
2013-12-01
Linear dunes discovered in the equatorial regions of Titan by the Cassini-Huygens mission are morphologically very similar to many terrestrial linear dune fields. These features have been compared with terrestrial longitudinal dune fields like the ones in Namib desert in western Africa. This comparison is based on the overall parallel orientation of Titan's dunes to the predominant wind direction on Titan, their superposition on other geomorphological features and the way they wrap around topographic obstacles. Studying the internal layering of dunes has strong implications in understanding the hypothesis for their origin and evolution. In Titan's case, although the morphology of the dunes has been studied from Cassini Synthetic Aperture Radar (SAR) images, it has not been possible to investigate their internal structure in detail as of yet. Since no radar sounding data is available for studying Titan's subsurface yet, we have developed another technique to examine the inner layering of the dunes. In this study, we utilize multiple complementary radar datasets, including radar imaging data for Titan's and Earth's dunes and Ground Penetrating Radar (GPR)/radar sounding data for terrestrial dunes. Based on dielectric mixing models, we suggest that the Cassini Ku-band microwaves should be able to penetrate up to ~ 3 m through Titan's dunes, indicating that the returned radar backscatter signal would include contributions from both surface and shallow subsurface echoes. This implies that the shallow subsurface properties can be retrieved from the observed radar backscatter (σ0). In our analysis, the variation of the radar backscatter as a function of dune height is used to provide an insight into the layering in Titan's dunes. We compare the variation of radar backscatter with elevation over individual dunes on Titan and analogous terrestrial dunes in three sites (Great Sand Sea, Siwa dunes and Qattaniya dunes) in the Egyptian Sahara. We observe a strong, positive
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Rip Currents, Mega-Cusps, and Eroding Dunes
Thornton, E.B.; MacMahan, J.; Sallenger, A.H.
2006-01-01
Submitted to Marine Geology 1 November 2006 Dune erosion is shown to occur at the embayment of beach mega-cusps O(200m alongshore) that are associated with rip currents. The beach is the narrowest at the embayment of the mega-cusps allowing the swash of large storm waves coincident with high tides to reach the toe of the dune, to undercut the dune and to cause dune erosion. Field measurements of dune, beach, and rip current morphology are acquired along an 18 km shoreline in southern Mont...
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Measurements of Dune Parameters on Titan Suggest Differences in Sand Availability
Stewart, Brigitte W.; Radebaugh, Jani
2014-11-01
The equatorial region of Saturn’s moon Titan has five large sand seas with dunes similar to large linear dunes on Earth. Cassini Radar SAR swaths have high enough resolution (300 m) to measure dune parameters such as width and spacing, which helps inform us about formation conditions and long-term evolution of the sand dunes. Previous measurements in locations scattered across Titan have revealed an average width of 1.3 km and spacing of 2.7 km, with variations by location. We have taken over 1200 new measurements of dune width and spacing in the T8 swath, a region on the leading hemisphere of Titan in the Belet Sand Sea, between -5 and -9 degrees latitude. We have also taken over 500 measurements in the T44 swath, located on the anti-Saturn hemisphere in the Shangri-La Sand Sea, between 0 and 20 degrees latitude. We correlated each group of 50 measurements with the average distance from the edge of the dune field to obtain an estimate of how position within a dune field affects dune parameters. We found that in general, the width and spacing of dunes decreases with distance from the edge of the dune field, consistent with similar measurements in sand seas on Earth. We suggest that this correlation is due to the lesser availability of sand at the edges of dune fields. These measurements and correlations could be helpful in determining differences in sand availability across different dune fields, and along the entire equatorial region of Titan.
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Overview of Initial Results From Studies of the Bagnold Dune Field on Mars by the Curiosity Rover
Bridges, Nathan; Ehlmann, Bethany; Ewing, Ryan; Newman, Claire; Sullivan, Robert; Conrad, Pamela; Cousin, Agnes; Edgett, Kenneth; Fisk, Martin; Fraeman, Abigail; Johnson, Jeffrey; Lamb, Michael; Lapotre, Mathieu; Le Mouélic, Stéphane; Martinez, German; Meslin, Pierre-Yves; Thompson, Lucy; van Beek, Jason; Vasavada, Ashwin; Wiens, Roger
2016-04-01
The Curiosity Rover is currently studying the Bagnold Dunes in Gale Crater. Here we provide a general overview of results and note that other EGU presentations will focus on specific aspects. The in situ activities have not yet occurred as of this writing, but other analyses have been performed approaching and within the dunefield. ChemCam passive spectra of Bagnold Dune sands are consistent with the presence of olivine. Two APXS spots on the High Dune stoss slope margin, and two others in an engineering test sand patch, show less inferred dust, greater Si, and higher Fe/Mn than other "soils" in Gale Crater. ChemCam analyses of more than 300 soils along the Curiosity traverse show that both fine and coarse soils have increasing iron and alkali content as the Bagnold Dunes are approached, a trend that may reflect admixtures of local rocks (alkalis + iron) to the fines, but also a contribution of Bagnold-like sand (iron) that increases toward the dunefield. MAHLI images of sands on the lower east stoss slope of High Dune show medium and coarse sand in ripple forms, and very fine and fine sand in ripple troughs. Most grains are dark gray, but some are also brick-red/brown, white, green translucent, yellow, brown" colorless translucent, or vitreous spheres HiRISE orbital images show that the Bagnold Dunes migrate on the order of decimeters or more per Earth year. Prior to entering the dune field, wind disruption of dump piles and grain movement was observed over multi-sol time spans, demonstrating that winds are of sufficient strength to mobilize unconsolidated material, either through direct aerodynamic force or via the action of smaller impacting grains. Within the dune field, we are, as of this writing, engaged in change detection experiments with Mastcam and ChemCam's RMI camera. Data we have so far, spanning 8 sols from the same location, shows no changes. Mastcam and RMI images of the stoss sides of Namib, Noctivaga, and High Dune show that the "ripples" seen
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van Puijenbroek, Marinka E. B.; Nolet, Corjan; de Groot, Alma V.; Suomalainen, Juha M.; Riksen, Michel J. P. M.; Berendse, Frank; Limpens, Juul
2017-12-01
Dune development along highly dynamic land-sea boundaries is the result of interaction between vegetation and dune size with sedimentation and erosion processes. Disentangling the contribution of vegetation characteristics from that of dune size would improve predictions of nebkha dune development under a changing climate, but has proven difficult due to the scarcity of spatially continuous monitoring data. This study explored the contributions of vegetation and dune size to dune development for locations differing in shelter from the sea. We monitored a natural nebkha dune field of 8 ha, along the coast of the island Texel, the Netherlands, for 1 year using an unmanned aerial vehicle (UAV) with camera. After constructing a digital surface model and orthomosaic we derived for each dune (1) vegetation characteristics (species composition, vegetation density, and maximum vegetation height), (2) dune size (dune volume, area, and maximum height), (3) degree of shelter (proximity to other nebkha dunes and the sheltering by the foredune). Changes in dune volume over summer and winter were related to vegetation, dune size and degree of shelter. We found that a positive change in dune volume (dune growth) was linearly related to initial dune volume over summer but not over winter. Big dunes accumulated more sand than small dunes due to their larger surface area. Exposed dunes increased more in volume (0.81 % per dune per week) than sheltered dunes (0.2 % per dune per week) over summer, while the opposite occurred over winter. Vegetation characteristics did not significantly affect dune growth in summer, but did significantly affect dune growth in winter. Over winter, dunes dominated by Ammophila arenaria, a grass species with high vegetation density throughout the year, increased more in volume than dunes dominated by Elytrigia juncea, a grass species with lower vegetation density (0.43 vs. 0.42 (m3 m-3) week-1). The effect of species was irrespective of dune size or
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Changes of Bulgarian Coastal Dune Landscape under Anthropogenic Impact
Palazov, A.; Young, R.; Stancheva, M.; Stanchev, H.
2012-04-01
At one time large sand dune formations were widely distributed along the Bulgarian coast. However, due to increased urbanization in the coastal zone, the areas of total dune landscape has been constantly reduced. Dunes presently comprise only 10% of the entire 412 km long coastline of Bulgaria: they embrace a total length of 38.57 km and a total area of 8.78 km2 Important tasks in dune protection are identification of landscape changes for a certain period of time and accurate delineation of sand dune areas. The present research traces sand dune changes along the Bulgarian Black Sea coast over a 27 year period (1983-2010). This period includes also the time of expanded tourist boom and overbuilding of the coastal zone, and respectively presents the largest dune changes and reductions. Based on the landscape change analyst in GIS environment the study also aims to explore the importance of different natural and human factors in driving the observed dune alterations and destruction. To detect and assess dune changes during the last 3 decades, we used data for sand dunes derived from several sources at different time periods in order to compare changes in shoreline positions, dune contours and areas: i) Topographic maps in 1:5,000 scale from 1983; ii) Modern Very High Resolution orthophotographs from 2006 and 2010; iii) QuickBird Very High Resolution satellite images from 2009; iv) Statistical information for population and tourist infrastructure is also used to consider the influence of human pressure and hotel developments on the dune dynamics. In addition, for more detailed description and visualization of main dune types, digital photos have been taken at many parts of the Bulgarian coast. The study was performed in GIS environment. Based on the results obtained the dunes along the Bulgarian coast were divided into three main groups with relation to the general factors responsible for their alterations: i) Dunes that have decreased in result of shoreline retreat
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Dune growth under multidirectional wind regimes
Gadal, C.; Rozier, O.; Claudin, P.; Courrech Du Pont, S.; Narteau, C.
2017-12-01
Under unidirectional wind regimes, flat sand beds become unstable to produce periodic linear dunes, commonly called transverse dunes because their main ridges are oriented perpendicular to the air flow. In areas of low sediment availability, the same interactions between flow, transport and topography produce barchan dunes, isolated sand-pile migrating over long distances with a characteristic crescentic shape. For the last fifteen years, barchan dunes and the instability at the origin of transverse dunes have been the subject of numerous studies that have identified a set of characteristic length and time scales with respect to the physical properties of both grains and fluid. This is not the case for dunes developing under multidirectional wind regimes. Under these conditions, dune orientation is measured with respect to the direction of the resultant sand flux. Depending on the wind regime, dunes do not always line up perpendicularly to the resultant sand flux, but can also be at an oblique angle or even parallel to it. These oblique and longitudinal dunes are ubiquitous in all deserts on Earth and planetary bodies because of the seasonal variability of wind orientation. They are however poorly constrained by observations and there is still no complete theoretical framework providing a description of their orientation and initial wavelength. Here, we extend the linear stability analysis of a flat sand of bed done in two dimensions for a unidirectional flow to three dimensions and multidirectional flow regimes. We are able to recover transitions from transverse to oblique or longitudinal dune patterns according to changes in wind regimes. We besides give a prediction for the initial dune wavelength. Our results compare well to previous theory of dune orientation and to field, experimental and numerical data.
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Annual monsoon rains recorded by Jurassic dunes.
Loope, D B; Rowe, C M; Joeckel, R M
2001-07-05
Pangaea, the largest landmass in the Earth's history, was nearly bisected by the Equator during the late Palaeozoic and early Mesozoic eras. Modelling experiments and stratigraphic studies have suggested that the supercontinent generated a monsoonal atmospheric circulation that led to extreme seasonality, but direct evidence for annual rainfall periodicity has been lacking. In the Mesozoic era, about 190 million years ago, thick deposits of wind-blown sand accumulated in dunes of a vast, low-latitude desert at Pangaea's western margin. These deposits are now situated in the southwestern USA. Here we analyse slump masses in the annual depositional cycles within these deposits, which have been described for some outcrops of the Navajo Sandstone. Twenty-four slumps, which were generated by heavy rainfall, appear within one interval representing 36 years of dune migration. We interpret the positions of 20 of these masses to indicate slumping during summer monsoon rains, with the other four having been the result of winter storms. The slumped lee faces of these Jurassic dunes therefore represent a prehistoric record of yearly rain events.
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Cohn, N.; Ruggiero, P.; de Vries, S.
2016-12-01
Dunes provide the first line of defense from elevated water levels in low-lying coastal systems, limiting potentially major flooding, economic damages, and loss of livelihood. Despite the well documented importance of healthy dunes, our predictive ability of dune growth, particularly following erosive storm events, remains poor - resulting in part from traditionally studying the wet and dry beach as separate entities. In fact, however, dune recovery and growth is closely tied to the subtidal morphology and the nearshore hydrodynamic conditions, necessitating treating the entire coastal zone from the shoreface to the backshore as an integrated system. In this context, to further improve our understanding of the physical processes allowing for beach and dune growth during fair weather conditions, a large field experiment, the Sandbar-aEolian Dune EXchange EXperiment, was performed in summer 2016 in southwestern Washington, USA. Measurements of nearshore and atmospheric hydrodynamics, in-situ sediment transport, and morphology change provide insight into the time and space scales of nearshore-beach-dune exchanges along a rapidly prograding stretch of coast over a 6 week period. As part of this experiment, the hypothesis that dune growth is limited by the welding of intertidal sandbars to the shoreline (Houser, 2009) was tested. Using laser particle counters, bed elevation sensors (sonar altimeters and Microsoft Kinect), continuously logging sediment traps, RGB and IR cameras, and repeat morphology surveys (terrestrial lidar, kite based structure from motion, and RTK GPS), spatial and temporal trends in aeolian sediment transport were assessed in relation to the synoptic onshore migration and welding of intertidal sandbars. Observations from this experiment demonstrate that (1) the intertidal zone is the primary source of sediment to the dunes during non-storm conditions, (2) rates of saltation increase during later stages of bar welding but equivalent wind conditions
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Future DUNE constraints on EFT
Falkowski, Adam; Grilli di Cortona, Giovanni; Tabrizi, Zahra
2018-04-01
In the near future, fundamental interactions at high-energy scales may be most efficiently studied via precision measurements at low energies. A universal language to assemble and interpret precision measurements is the so-called SMEFT, which is an effective field theory (EFT) where the Standard Model (SM) Lagrangian is extended by higher-dimensional operators. In this paper we investigate the possible impact of the DUNE neutrino experiment on constraining the SMEFT. The unprecedented neutrino flux offers an opportunity to greatly improve the current limits via precision measurements of the trident production and neutrino scattering off electrons and nuclei in the DUNE near detector. We quantify the DUNE sensitivity to dimension-6 operators in the SMEFT Lagrangian, and find that in some cases operators suppressed by an O(30) TeV scale can be probed. We also compare the DUNE reach to that of future experiments involving atomic parity violation and polarization asymmetry in electron scattering, which are sensitive to an overlapping set of SMEFT parameters.
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Dune and ripple migration along Curiosity's traverse in Gale Crater on Mars
Silvestro, S.; Vaz, D.; Ewing, R. C.; Fenton, L. K.; Michaels, T. I.; Ayoub, F.; Bridges, N. T.
2013-12-01
The NASA Mars Science Laboratory (MSL) rover, Curiosity, has safely landed near a 35-km-long dark dune field in Gale Crater on Mars. This dune field lies along Curiosity's traverse to Aeolis Mons (Mt. Sharp). Here we present new evidence of aeolian activity and further estimate wind directions within the dune field through analysis of ripple migration with the COSI-Corr technique, which provides precise measurements of ripple displacement at the sub-pixel scale.The area analyzed is located ~10 km southwest of rover Curiosity's current position and ~4 km SW of its selected path through Aeolis Mons (Mt. Sharp) (Fig. 1a). Here barchan dunes with elongated horns and seif dunes coexist with more typical barchan and dome dunes (Fig. 1a, b), with slopes sculpted by two intersecting ripple crestline orientations trending at 45° and 330°. The range of dune types and ripple orientations indicate the dune field morphology is influenced by at least two winds from the NW and the NE. The direction of migration is toward the SW, suggesting the most recent sand transporting winds were from the NE (Fig. 1c). These results match previous predictions and can be used to forecast the wind conditions close to the entry point to Mt. Sharp. Fig. 1: a-b) Study area c) Ripple migration direction computed using the COSI-Corr technique
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Bogle, Rian; Redsteer, Margaret Hiza; Vogel, John M.
2015-01-01
Aeolian sand covers extensive areas of the Navajo Nation in the southwestern United States. Much of this sand is currently stabilized by vegetation, although many drier parts of these Native lands also have active and partly active dunes. Current prolonged drought conditions that started in the mid-1990s are producing significant changes in dune mobility. Reactivation of regional aeolian deposits due to drought or increasing aridity from rising temperatures resulting from climate change could have serious consequences for human and animal populations, agriculture, grazing, and infrastructure. To understand and document the current and future potential for mobility, seasonally repeated surveys were used to track the location of multiple active barchan dunes. By utilizing Real-Time Kinematic GPS field surveys and simultaneously collecting in-situ meteorological data, it is possible to examine climatic parameters and seasonal variations that affect dune mobility and their relative influences. Through analysis of the recorded data, we examined the fit of various climate parameters, and demonstrate that under the current prolonged drought, wind power is the dominant factor controlling dune mobility.
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Minimal size of a barchan dune
Parteli, E. J. R.; Durán, O.; Herrmann, H. J.
2007-01-01
Barchans are dunes of high mobility which have a crescent shape and propagate under conditions of unidirectional wind. However, sand dunes only appear above a critical size, which scales with the saturation distance of the sand flux [P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. 89, 264301 (2002); B. Andreotti, P. Claudin, and S. Douady, Eur. Phys. J. B 28, 321 (2002); G. Sauermann, K. Kroy, and H. J. Herrmann, Phys. Rev. E 64, 31305 (2001)]. It has been suggested by P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. 89, 264301 (2002)] that this flux fetch distance is itself constant. Indeed, this could not explain the protosize of barchan dunes, which often occur in coastal areas of high litoral drift, and the scale of dunes on Mars. In the present work, we show from three-dimensional calculations of sand transport that the size and the shape of the minimal barchan dune depend on the wind friction speed and the sand flux on the area between dunes in a field. Our results explain the common appearance of barchans a few tens of centimeter high which are observed along coasts. Furthermore, we find that the rate at which grains enter saltation on Mars is one order of magnitude higher than on Earth, and is relevant to correctly obtain the minimal dune size on Mars.
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Fernandez-Cascales, Laura; Lucas, Antoine; Rodriguez, Sébastien; Gao, Xin; Spiga, Aymeric; Narteau, Clément
2018-05-01
Dunes provide unique information about wind regimes on planetary bodies where there is no direct meteorological data. At the eastern margin of Olympia Undae on Mars, dune orientation is measured from satellite imagery and sediment cover is estimated using the high contrast between the dune material and substrate. The analysis of these data provide the first quantification of relationship between sediment availability and dune orientation. Abrupt and smooth dune reorientations are associated with inward and outward dynamics of dunes approaching and ejecting from major sedimentary bodies, respectively. These reorientation patterns along sediment transport pathways are interpreted using a new generation dune model based on the coexistence of two dune growth mechanisms. This model also permits solving of the inverse problem of predicting the wind regime from dune orientation. For bidirectional wind regimes, solutions of this inverse problem show substantial differences in the distributions of sediment flux orientation, which can be attributed to atmospheric flow variations induced by changes in albedo at the boundaries of major dune fields. Then, we conclude that relationships between sediment cover and dune orientation can be used to constrain wind regime and dune field development on Mars and other planetary surfaces.
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Parabolic dune reactivation and migration at Napeague, NY, USA: Insights from aerial and GPR imagery
Girardi, James D.; Davis, Dan M.
2010-02-01
Observations from mapping since the 19th century and aerial imagery since 1930 have been used to study changes in the aeolian geomorphology of coastal parabolic dunes over the last ~ 170 years in the Walking Dune Field, Napeague, NY. The five large parabolic dunes of the Walking Dune Field have all migrated across, or are presently interacting with, a variably forested area that has affected their migration, stabilization and morphology. This study has concentrated on a dune with a particularly complex history of stabilization, reactivation and migration. We have correlated that dune's surface evolution, as revealed by aerial imagery, with its internal structures imaged using 200 MHz and 500 MHz Ground Penetrating Radar (GPR) surveys. Both 2D (transect) and high-resolution 3D GPR imagery image downwind dipping bedding planes which can be grouped by apparent dip angle into several discrete packages of beds that reflect distinct decadal-scale episodes of dune reactivation and growth. From aerial and high resolution GPR imagery, we document a unique mode of reactivation and migration linked to upwind dune formation and parabolic dune interactions with forest trees. This study documents how dune-dune and dune-vegetation interactions have influenced a unique mode of blowout deposition that has alternated on a decadal scale between opposite sides of a parabolic dune during reactivation and migration. The pattern of recent parabolic dune reactivation and migration in the Walking Dune Field appears to be somewhat more complex, and perhaps more sensitive to subtle environmental pressures, than an idealized growth model with uniform deposition and purely on-axis migration. This pattern, believed to be prevalent among other parabolic dunes in the Walking Dune Field, may occur also in many other places where similar observational constraints are unavailable.
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Yan, Na; Baas, Andreas
2015-04-01
Parabolic dunes are one of a few common aeolian landforms which are highly controlled by eco-geomorphic interactions. Parabolic dunes, on the one hand, can be developed from highly mobile dune landforms, barchans for instance, in an ameliorated vegetation condition; or on the other hand, they can be reactivated and transformed back into mobile dunes due to vegetation deterioration. The fundamental mechanisms and eco-geomorphic interactions controlling both dune transformations remain poorly understood. To bridge the gap between complex processes involved in dune transformations on a relatively long temporal scale and real world monitoring records on a very limited temporal scale, this research has extended the DECAL model to incorporate 'dynamic' growth functions and the different 'growth' of perennial shrubs between growing and non-growing seasons, informed by field measurements and remote sensing analysis, to explore environmental controls and eco-geomorphic interactions of both types of dune transformation. A non-dimensional 'dune stabilising index' is proposed to capture the interactions between environmental controls (i.e. the capabilities of vegetation to withstand wind erosion and sand burial, the sandy substratum thickness, the height of the initial dune, and the sand transport potential), and establish the linkage between these controls and the geometry of a stabilising dune. An example demonstrates how to use the power-law relationship between the dune stabilising index and the normalised migration distance to assist in extrapolating the historical trajectories of transforming dunes. The modelling results also show that a slight increase in vegetation cover of an initial parabolic dune can significantly increase the reactivation threshold of climatic impact (both drought stress and wind strength) required to reactivate a stabilising parabolic dune into a barchan. Four eco-geomorphic interaction zones that govern a barchan-to-parabolic dune transformation
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Provenance of Coastal dune sands along Red Sea, Egypt
Indian Academy of Sciences (India)
26
accumulation of sands behind vegetation or any other obstacles. ... The study areas Safaga (SF) and Quseir (QS) field dunes (Fig. 1) ..... coastal dune sands were deposited in a passive margin of a synrift .... Sed Petrol 63(6), 1110-1117.
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Numerical modelling of flow structures over idealized transverse aeolian dunes of varying geometry
Parsons, Daniel R.; Walker, Ian J.; Wiggs, Giles F. S.
2004-04-01
A Computational Fluid Dynamics (CFD) model (PHOENICS™ 3.5) previously validated for wind tunnel measurements is used to simulate the streamwise and vertical velocity flow fields over idealized transverse dunes of varying height ( h) and stoss slope basal length ( L). The model accurately reproduced patterns of: flow deceleration at the dune toe; stoss flow acceleration; vertical lift in the crest region; lee-side flow separation, re-attachment and reversal; and flow recovery distance. Results indicate that the flow field over transverse dunes is particularly sensitive to changes in dune height, with an increase in height resulting in flow deceleration at the toe, streamwise acceleration and vertical lift at the crest, and an increase in the extent of, and strength of reversed flows within, the lee-side separation cell. In general, the length of the separation zone varied from 3 to 15 h from the crest and increased over taller, steeper dunes. Similarly, the flow recovery distance ranged from 45 to >75 h and was more sensitive to changes in dune height. For the range of dune shapes investigated in this study, the differing effects of height and stoss slope length raise questions regarding the applicability of dune aspect ratio as a parameter for explaining airflow over transverse dunes. Evidence is also provided to support existing research on: streamline curvature and the maintenance of sand transport in the toe region; vertical lift in the crest region and its effect on grainfall delivery; relations between the turbulent shear layer and downward forcing of flow re-attachment; and extended flow recovery distances beyond the separation cell. Field validation is required to test these findings in natural settings. Future applications of the model will characterize turbulence and shear stress fields, examine the effects of more complex isolated dune forms and investigate flow over multiple dunes.
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protoDUNE-Single Phase and protDUNE-DualPhase
Brice, Maximilien
2016-01-01
At the EHN1 two big 8m x 8m x8m detector prototypes (protoDUNE-Single Phase and protDUNE-DualPhase) are being constructed. The aim is to test technologies and detector performances for DUNE, a new generation of LBN neutr
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Johnson, Jeffrey R.; Achilles, Cherie; Bell, James F.; Bender, Steve; Cloutis, Edward; Ehlmann, Bethany; Fraeman, Abigail; Gasnault, Olivier; Hamilton, Victoria E.; Le Mouélic, Stéphane; Maurice, Sylvestre; Pinet, Patrick; Thompson, Lucy; Wellington, Danika; Wiens, Roger C.
2017-12-01
As part of the Bagnold Dune campaign conducted by Mars Science Laboratory rover Curiosity, visible/near-infrared reflectance spectra of dune sands were acquired using Mast Camera (Mastcam) multispectral imaging (445-1013 nm) and Chemistry and Camera (ChemCam) passive point spectroscopy (400-840 nm). By comparing spectra from pristine and rover-disturbed ripple crests and troughs within the dune field, and through analysis of sieved grain size fractions, constraints on mineral segregation from grain sorting could be determined. In general, the dune areas exhibited low relative reflectance, a weak 530 nm absorption band, an absorption band near 620 nm, and a spectral downturn after 685 nm consistent with olivine-bearing sands. The finest grain size fractions occurred within ripple troughs and in the subsurface and typically exhibited the strongest 530 nm bands, highest relative reflectances, and weakest red/near-infrared ratios, consistent with a combination of crystalline and amorphous ferric materials. Coarser-grained samples were the darkest and bluest and exhibited weaker 530 nm bands, lower relative reflectances, and stronger downturns in the near-infrared, consistent with greater proportions of mafic minerals such as olivine and pyroxene. These grains were typically segregated along ripple crests and among the upper surfaces of grain flows in disturbed sands. Sieved dune sands exhibited progressive decreases in reflectance with increasing grain size, as observed in laboratory spectra of olivine size separates. The continuum of spectral features observed between the coarse- and fine-grained dune sands suggests that mafic grains, ferric materials, and air fall dust mix in variable proportions depending on aeolian activity and grain sorting.
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Pasquon, K.; Gargani, J.; Nachon, M.; Conway, S. J.; Massé, M.; Jouannic, G.; Balme, M. R.; Costard, F.; Vincendon, M.
2017-12-01
Diverse gully morphologies are seen on Mars and differences are often neglected for simplification. Here we describe in detail the morphology and present-day activity of two gully-systems on the Kaiser dune field in the southern hemisphere of Mars. We then compare their activity with that of the morphologically distinct linear dune gullies present on the same dunes. The studied gully-systems have large depositional aprons (named "large apron gullies") and occur on dune faces oriented westward. They are active from mid-autumn to late winter (i.e. from Ls 50° to Ls 180°) coinciding with CO2 ice condensation/sublimation cycles. Sandy material collapses from the alcove flanks onto the alcove floor sporadically throughout this period. This accumulated sand is remobilized by punctuated mass flows which we estimate to be up to 7100 m3 in volume. These flows run out on to the apron and occur between Ls 120° and Ls 160°. These mass flow events occur when the number of "digitate flows" is at its seasonal maximum. Digitate flows are characterized by long-narrow zig-zagging low-albedo tracks and do not seem to transport appreciable sediment, and they can number in the hundreds. Small pits appear at their termini or midway along and sometimes these pits are re-deepened by subsequent flows. These events repeat every year and using volume balance calculations we find that the whole system could be built on a timescale of hundreds of martian ears. These large apron gullies differ in morphology and timing from the linear dune gullies. The linear dune gullies are active in late winter, or beginning of spring when the CO2 frost finally sublimates, which occurs after the activity of the large apron gullies. Due to the difference of orientation between large apron gullies and linear dune as well as timing, we infer that insolation, which may influence (i) the depth to ground ice, (ii) the amount of volatiles deposits, is the main cause their differences. Sediment transport by CO2
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Advanced InSAR imaging for dune mapping
Havivi, Shiran; August, Yitzhak; Blumberg, Dan G.; Rotman, Stanley R.
2015-04-01
extensively in the field. High resolution TerraSAR-X (TSX) images, covering the entire research area were acquired for the period of October 2011 to July 2012 (15 images in total). All images were co-registreted, the first image was used as the master image. A coherence index was calculated for all the images. Analysis was performed in GIS software. The results display minor changes (coherence index in range of 0.4-0.65) on dune crests depending on the dune location relative to its distance from the sea and distance from the city. In addition, field results indicate erosion / deposition of sand in a cumulatively amount of approximately 30mm annually. The results of this study confirm that it is possible to monitor subtle changes in dunes and to identify dune stability or instability, only by the use of SAR images.
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Grain-size variations on a longitudinal dune and a barchan dune
Watson, Andrew
1986-01-01
The grain-size characteristics of the sand upon two dunes—a 40 m high longitudinal dune in the central Namib Desert and a 6.0 m high barchan in the Jafurah sand sea of Saudi Arabia—vary with position on the dunes. On the longitudinal dune, median grain size decreases, sorting improves and the grain-size distributions are less skewed and more normalized toward the crest. Though sand at the windward toe is distinct, elsewhere on the dune the changes in grain-size characteristics are gradual. An abrupt change in grain size and sorting near the crest—as described by Bagnold (1941, pp. 226-229)—is not well represented on this dune. Coarse grains remain as a lag on concave slope units and small particles are winnowed from the sand on the steepest windward slopes near the crest. Avalanching down slipfaces at the crest acts only as a supplementary grading mechanism. On the barchan dune median grain size also decreases near the crest, but sorting becomes poorer, though the grain-size distributions are more symmetric and more normalized. The dune profile is a Gaussian curve with a broad convex zone at the apex upon which topset beds had accreted prior to sampling. Grain size increases and sorting improves down the dune's slipface. However, this grading mechanism does not influence sand on the whole dune because variations in wind regime bring about different modes of dune accretion. On both dunes, height and morphology appear to influence significantly the grain-size characteristics.
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Rip currents, mega-cusps, and eroding dunes
Thornton, E.B.; MacMahan, J.; Sallenger, A.H.
2007-01-01
Dune erosion is shown to occur at the embayment of beach mega-cusps O(200 m alongshore) that are associated with rip currents. The beach is the narrowest at the embayment of the mega-cusps allowing the swash of large storm waves coincident with high tides to reach the toe of the dune, to undercut the dune and to cause dune erosion. Field measurements of dune, beach, and rip current morphology are acquired along an 18 km shoreline in southern Monterey Bay, California. This section of the bay consists of a sandy shoreline backed by extensive dunes, rising to heights exceeding 40 m. There is a large increase in wave height going from small wave heights in the shadow of a headland, to the center of the bay where convergence of waves owing to refraction over the Monterey Bay submarine canyon results in larger wave heights. The large alongshore gradient in wave height results in a concomitant alongshore gradient in morphodynamic scale. The strongly refracted waves and narrow bay aperture result in near normal wave incidence, resulting in well-developed, persistent rip currents along the entire shoreline. The alongshore variations of the cuspate shoreline are found significantly correlated with the alongshore variations in rip spacing at 95% confidence. The alongshore variations of the volume of dune erosion are found significantly correlated with alongshore variations of the cuspate shoreline at 95% confidence. Therefore, it is concluded the mega-cusps are associated with rip currents and that the location of dune erosion is associated with the embayment of the mega-cusp.
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Estimation of sand dune thickness using a vertical velocity profile
International Nuclear Information System (INIS)
Al-Shuhail, Abdullatif A.
2004-01-01
Previous field and mathematical studies have shown that sand dunes may have vertical velocity profiles (i.e. continuous increase of velocity with depth). Therefore, computing the dunes thickness using conventional seismic refraction methods that assume a vertically homogeneous layer will likely produce some errors. The purpose of this study is to quantify the effect of the vertical velocity profile in a sand dune on the process of thickness estimation using seismic refraction data. First, the time distance (T-X) data of the direct wave in the dune is calculated using a vertical velocity profile, V (z), derived from Hertz-Mindlin contact theory. Then the thickness is estimated from the calculated T-X data, intercept time and velocity of the refractor at the dune's base assuming a constant velocity in the dune. The error in the estimated thickness due to the constant-velocity assumption increases with increasing thickness and decreasing porosity of the dune. For sand dunes with porosities greater than 0.2 and thickness less than 200 meter, the error is less than 15%. (author)
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Aeolian dune sediment flux heterogeneity in Meridiani Planum, Mars.
Chojnacki, Matthew; Urso, Anna; Fenton, Lori K; Michaels, Timothy I
2017-06-01
It is now known unambiguously that wind-driven bedform activity is occurring on the surface of Mars today, including early detections of active sand dunes in Meridiani Planum's Endeavour crater. Many of these reports are only based on a few sets of observations of relatively isolated bedforms and lack regional context. Here, we investigate aeolian activity across central Meridiani Planum and test the hypothesis that dune sites surrounding Endeavour crater are also active and part of region-wide sediment migration driven by northwesterly winds. All 13 dune fields investigated clearly showed evidence for activity and the majority exhibited dune migration (average rates of 0.6 m/Earth-year). Observations indicate substantial geographic and temporal heterogeneity of dune crest fluxes across the area and per site. Locations with multiple time steps indicate dune sand fluxes can vary by a factor of five, providing evidence for short periods of rapid migration followed by near-stagnation. In contrast, measurements at other sites are nearly identical, indicating that some dunes are in a steady-state as they migrate. The observed sediment transport direction was consistent with a regional northeasterly-to-northwesterly wind regime, revealing more variations than were appreciated from earlier, more localized studies. Craters containing shallow, degraded, flat-floored interiors tended to have dunes with high sediment fluxes/activity, whereas local kilometer-scale topographic obstructions (e.g., central peaks, yardangs) were found to be inversely correlated with dune mobility. Finally, the previous, more limited detections of dune activity in Endeavour crater have been shown to be representative of a broader, region-wide pattern of dune motion.
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The role of vegetation in shaping dune morphology
Duran Vinent, O.; Moore, L. J.; Young, D.
2012-12-01
. Consistent with field observations, we find that basic dune morphology is primarily determined by grass species, with linear or hummocky dunes being built by some species, while others may prevent dune formation. We also find that the evolution of coastal dune morphology is controlled by at least two bio-geomorphic couplings: (1) between vegetation growth and sand transport, which leads to a positive feedback for dune growth, as certain beach grasses maximize growth under sand accretion, which means that an ever denser vegetation implies an ever higher accretion rate; and (2) between vegetation growth and shoreline position through the sand influx. While the first coupling is responsible for dune formation, the second one determines when dunes stop growing and thus controls final dune size. This is particularly relevant for accreting/eroding coastlines where we find that dune size, and thus coastal protection, is maximized for relatively small accretion rates while larger accretion rates lead to formation of a new, smaller dune ridge at the beach.
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Modeling Megacusps and Dune Erosion
Orzech, M.; Reniers, A. J.; Thornton, E. B.
2009-12-01
Megacusps are large, concave, erosional features of beaches, of O(200m) alongshore wavelength, which sometimes occur when rip channel bathymetry is present. It is commonly hypothesized that erosion of the dune and back beach will be greater at the alongshore locations of the megacusp embayments, principally because the beach width is narrower there and larger waves can more easily reach the dune toe (e.g., Short, J. Geol., 1979, Thornton, et al., Mar. Geol., 2007). At present, available field data in southern Monterey Bay provide some support for this hypothesis, but not enough to fully confirm or refute it. This analysis utilizes XBeach, a 2DH nearshore sediment transport model, to test the above hypothesis under a range of wave conditions over several idealized rip-megacusp bathymetries backed by dunes. Model results suggest that while specific wave conditions may result in erosional hot spots at megacusp embayments, other factors such as tides, wave direction, and surf zone bathymetry can often play an equal or stronger role.
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Sand transportation and reverse patterns over leeward face of sand dune
Jiang, Hong; Dun, Hongchao; Tong, Ding; Huang, Ning
2017-04-01
Sand saltation has complex interactions with turbulent flow and dune form. Most models of wind-blown sand consider ideal circumstances such as steady wind velocity and a flat surface, and the bulk of data on wind flow and sand transport over an individual dune has focused mostly on the influence of dune shape or inter-dune space on the wind flow, neglecting the effect of morphology on sand saltation, particularly airflow and sand transportation over the leeward slope. Wind flow structures over the leeward slope of sand dunes have a fundamental influence on the organization of sand dunes. In order to understand sand dune dynamics, lee face airflow and sediment transportation should be paid more attention. Previous field observations could not measure turbulent flow structure well because of the limited observation points and the influence of experiment structure on wind field. In addition, the reverse sand particles over leeward face could not be collected by sand trap in field. Numerous field observations could not measure turbulent flow structure because of the limited observation points and the influence of experimental structures on the wind field. In addition, the reverse transport of sand particles over leeward face could not be collected by sand traps in field. Therefore, this paper aims to investigate the turbulent flow structure and sand transport pattern over the leeward slope. A numerical model of sand saltation over slope terrain is constructed, which also considers the coupling effects between air flow and sand particles. The large eddy simulation method is used to model turbulent flow. Sand transport is simulated by tracking the trajectory of each sand particle. The results show that terrain significantly alters the turbulent air flow structure and wind-blown sand movement, especially over the leeward slope. Here, mass flux increases initially and then decreases with height in the reversed flow region in the direction of wind flow, and the mass flux
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Mineralogy of an active eolian sediment from the Namib dune, Gale crater, Mars
Achilles, C. N.; Downs, R. T.; Ming, D. W.; Rampe, E. B.; Morris, R. V.; Treiman, A. H.; Morrison, S. M.; Blake, D. F.; Vaniman, D. T.; Ewing, R. C.; Chipera, S. J.; Yen, A. S.; Bristow, T. F.; Ehlmann, B. L.; Gellert, R.; Hazen, R. M.; Fendrich, K. V.; Craig, P. I.; Grotzinger, J. P.; Des Marais, D. J.; Farmer, J. D.; Sarrazin, P. C.; Morookian, J. M.
2017-11-01
The Mars Science Laboratory rover, Curiosity, is using a comprehensive scientific payload to explore rocks and soils in Gale crater, Mars. Recent investigations of the Bagnold Dune Field provided the first in situ assessment of an active dune on Mars. The Chemistry and Mineralogy (CheMin) X-ray diffraction instrument on Curiosity performed quantitative mineralogical analyses of the history of the dune material and offers an important opportunity for ground truth of orbital observations. CheMin's analysis of the mineralogy and phase chemistry of modern and ancient Gale crater dune fields, together with other measurements by Curiosity's science payload, provides new insights into present and past eolian processes on Mars.
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Mineralogy and Genesis of Heavy Minerals in Coastal Dune Sands, South Eastern Qatar
Nasir, Sobhi J. [صبحي جابر نصر; El-Kassas, Ibrahim A.; Sadiq, A. Ali M.
1999-01-01
Large amounts of aeolian sand occur in the southeastern coastal zone of Qatar Peninsula as sand dunes accumulated in a vast sand field locally called " Niqyan Qatar ". The present work, carried out on a sand dune belt of this field near Mesaied Industrial City, revealed the distribution of heavy minerals shows a regional variability induced by provenance and local variability reflecting genetic differences. The studied dune sands are rich in shells of pelecypods, with the light mineral assemb...
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Source-to-Sink: An Earth/Mars Comparison of Boundary Conditions for Eolian Dune Systems
Kocurek, Gary; Ewing, Ryan C.
2012-01-01
Eolian dune fields on Earth and Mars evolve as complex systems within a set of boundary conditions. A source-to-sink comparison indicates that although differences exist in sediment production and transport, the systems largely converge at the dune-flow and pattern-development levels, but again differ in modes of accumulation and preservation. On Earth, where winds frequently exceed threshold speeds, dune fields are sourced primarily through deflation of subaqueous deposits as these sediments...
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Bridges, N.; Sullivan, R. J., Jr.; Ewing, R. C.; Newman, C. E.; Ayoub, F.; Lapotre, M. G. A.; van Beek, J.
2016-12-01
In early 2016, the Mars Science Laboratory rover completed the first in situ investigation of an active dune field on another planetary body, the "Bagnold Dunes" in Gale Crater. During the campaign, a series of Mastcam and RMI time-series images of local sand patches, dump piles, ripples, and the lee face and margin of Namib Dune (a barchan in the Bagnold field) were acquired. These were at cadences of a sol or more that were generally at nearly the same local time, and intra-sol imaging bridged by continuous wind measurements from REMS. The dune field has also been imaged 16 times by HiRISE since 2008. By combining the two datasets, long term dune dynamics over the whole field can be compared to small-scale and short-term observations on the surface. From HiRISE, Namib Dune and other barchans and longitudinal dunes to the south and west migrate generally toward the south to southeast. The most active sand deposits are the longitudinal and barchans dunes, with the highest ripple migration rates found on the highest elevations. Rippled sand patches exhibit little of no motion. From MSL, the scrambling of grains on the surfaces of local rippled sand patches and Namib Dune is obvious over periods as short as a single sol, with light-toned grains showing the greatest tendency. On the lee face of Namib, images show grain scrambling, one case of modification to a secondary grainflow, and possibly ripple motion over 3-16 sols. At the dune margin, grain scrambling and one major slump on the lee face of a dune ripple are seen. The daytime REMS record shows wind speeds up to 20 m/s with confidence. As yet, we do not have a demonstrable correlation between measured wind speeds and changes, suggesting that short term gusts or non-aeolian processes acting as triggers may precede significant activity. The changes, occurring in a low flux season based on HiRISE analysis and global circulation models, indicate an active surface at all times of the year to some degree.
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Largest US oil and gas fields, August 1993
Energy Technology Data Exchange (ETDEWEB)
1993-08-06
The Largest US Oil and Gas Fields is a technical report and part of an Energy Information Administration (EIA) series presenting distributions of US crude oil and natural gas resources, developed using field-level data collected by EIA`s annual survey of oil and gas proved reserves. The series` objective is to provide useful information beyond that routinely presented in the EIA annual report on crude oil and natural gas reserves. These special reports also will provide oil and gas resource analysts with a fuller understanding of the nature of US crude oil and natural gas occurrence, both at the macro level and with respect to the specific subjects addressed. The series` approach is to integrate EIA`s crude oil and natural gas survey data with related data obtained from other authoritative sources, and then to present illustrations and analyses of interest to a broad spectrum of energy information users ranging from the general public to oil and gas industry personnel.
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Largest US oil and gas fields, August 1993
International Nuclear Information System (INIS)
1993-01-01
The Largest US Oil and Gas Fields is a technical report and part of an Energy Information Administration (EIA) series presenting distributions of US crude oil and natural gas resources, developed using field-level data collected by EIA's annual survey of oil and gas proved reserves. The series' objective is to provide useful information beyond that routinely presented in the EIA annual report on crude oil and natural gas reserves. These special reports also will provide oil and gas resource analysts with a fuller understanding of the nature of US crude oil and natural gas occurrence, both at the macro level and with respect to the specific subjects addressed. The series' approach is to integrate EIA's crude oil and natural gas survey data with related data obtained from other authoritative sources, and then to present illustrations and analyses of interest to a broad spectrum of energy information users ranging from the general public to oil and gas industry personnel
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What is a Dune: Developing AN Automated Approach to Extracting Dunes from Digital Elevation Models
Taylor, H.; DeCuir, C.; Wernette, P. A.; Taube, C.; Eyler, R.; Thopson, S.
2016-12-01
Coastal dunes can absorb storm surge and mitigate inland erosion caused by elevated water levels during a storm. In order to understand how a dune responds to and recovers from a storm, it is important that we can first identify and differentiate the beach and dune from the rest of the landscape. Current literature does not provide a consistent definition of what the dune features (e.g. dune toe, dune crest) are or how they can be extracted. The purpose of this research is to develop enhanced approaches to extracting dunes from a digital elevation model (DEM). Manual delineation, convergence index, least-cost path, relative relief, and vegetation abundance were compared and contrasted on a small area of Padre Island National Seashore (PAIS), Preliminary results indicate that the method used to extract the dune greatly affects our interpretation of how the dune changes. The manual delineation method was time intensive and subjective, while the convergence index approach was useful to easily identify the dune crest through maximum and minimum values. The least-cost path method proved to be time intensive due to data clipping; however, this approach resulted in continuous geomorphic landscape features (e.g. dune toe, dune crest). While the relative relief approach shows the most features in multi resolution, it is difficult to assess the accuracy of the extracted features because extracted features appear as points that can vary widely in their location from one meter to the next. The vegetation approach was greatly impacted by the seasonal and annual fluctuations of growth but is advantageous in historical change studies because it can be used to extract consistent dune formation from historical aerial imagery. Improving our ability to more accurately assess dune response and recovery to a storm will enable coastal managers to more accurately predict how dunes may respond to future climate change scenarios.
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Szynkiewicz, A.; Ewing, R. C.; Fishbaugh, K. E.; Bourke, M. C.; Bustos, D.; Pratt, L. M.
2009-03-01
New morphological features (e.g., cross-bedding strata, bright patches), revealed by HiRISE for the gypsum-rich Olympia Undae Dune Field, appear to indicate the change(s) in paleoenvironmental conditions likely controlled by climate fluctuations in the North Pole of Mars.
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Dune-slope activity due to frost and wind throughout the north polar erg, Mars.
Diniega, Serina; Hansen, Candice J; Allen, Amanda; Grigsby, Nathan; Li, Zheyu; Perez, Tyler; Chojnacki, Matthew
2017-01-01
Repeat, high-resolution imaging of dunes within the Martian north polar erg have shown that these dune slopes are very active, with alcoves forming along the dune brink each Mars year. In some areas, a few hundred cubic metres of downslope sand movement have been observed, sometimes moving the dune brink 'backwards'. Based on morphological and activity-timing similarities of these north polar features to southern dune gullies, identifying the processes forming these features is likely to have relevance for understanding the general evolution/modification of dune gullies. To determine alcove-formation model constraints, we have surveyed seven dune fields, each over 1-4 Mars winters. Consistent with earlier reports, we found that alcove-formation activity occurs during the autumn-winter seasons, before or while the stable seasonal frost layer is deposited. We propose a new model in which alcove formation occurs during the autumn, and springtime sublimation activity then enhances the feature. Summertime winds blow sand into the new alcoves, erasing small alcoves over a few Mars years. Based on the observed rate of alcove erasure, we estimated the effective aeolian sand transport flux. From this, we proposed that alcove formation may account for 2-20% of the total sand movement within these dune fields.
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Modeling river dune development and dune transition to upper stage plane bed
Naqshband, Suleyman; van Duin, Olav; Ribberink, Jan S.; Hulscher, Suzanne J.M.H.
2016-01-01
Large asymmetric bedforms known as dunes commonly dominate the bed of sand rivers. Due to the turbulence generation over their stoss and lee sides, dunes are of central importance in predicting hydraulic roughness and water levels. During floods in steep alluvial rivers, dunes are observed to grow
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Franzetti, M.; Le Roy, P.; Garlan, T.; Delacourt, C.; Thibaud, R.; Cancouet, R.; Graindorge, D.; Prunier, C.; Sukhovich, A.; Deschamps, A.
2013-12-01
The deep sandwave dynamics is still in debate. Understanding the migration processes and the resulting evolution of their 3D internal architecture are scientifically challenging. To address these questions we realized two swath bathymetry surveys complemented with seismic reflection across the large sandwaves field named 'Banc du Four'. It is located offshore the Western Brittany and is composed of more 500 dunes. Some of the dunes' wavelengths and heights exceed 1000m and 30m respectively placing them among the largest dunes ever described. Equilibrium laws obtained from our morphological analysis are not completely in agreement with those described in previous studies of similar structures in shallow waters. Relatively high migration velocities on deep continental shelves (from 3 to 20m.yr-1) attest of their still present dynamical equilibrium. Internal-external morphological and kinematical analyses show the existence of two different dynamic regimes. Interpretation of the seismic reflection data allowed reconstructing long-term evolution of the sandbank and the establishment of progressive connections between stepped submarine channels and tidal dynamics during the last sea-level rise.
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CFD evaluation of erosion rate around a bridge near a sand dune
He, Wei; Huang, Ning; Dun, Hongchao; Wang, Wenbo
2017-04-01
This study performs a series of simulations through solving the Navier-Stokes equations and the RNG k-ε turbulence model to investigate the wind erosion rates around a bridge in a desert area with sand dunes. The digital elevation model of sand dunes and the bridge model are obtained respectively from hypsographic map and construction drawings. Through combining them into the CFD software of Fluent the simulation zone was formed. The data of wind speed obtained from field observation is fitted into a logarithm format, which was imported into Fluent model as a inlet wind speed condition. Then, the effect of Dun-Go railway on wind-blown sand movement of the neighbouring environment is simulated. The results exhibit that affected by both the sand dune and bridge, the flow field is in a complex condition. It is also shown that the bridge in upstream of the sand dune will not increase the sand transport rate intensively, but change both wind velocity gradient and turbulence kinetic energy over surface of sand dune. On the other hand, when the bridge is built downstream the sand dune, simulation results show that sand deposition rate would be decreased in reference region downstream the pier.
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Monitoring of desert dune topography by multi angle sensors
Yun, J.; Kim, J.; Choi, Y.; Yun, H.
2011-12-01
Nowadays, the sandy desert is rapidly expanding world widely and results in a lot of risks in the socio-econimical aspects as well as the anthropogenic activities. For example, the increasing occurrences of mineral dust storm which presumably originated from the sandy deserts in northwest China become a serious threat in human activities as well as public health over Far East Asian area as the interpretation by the MODIS analysis (Zhang et al., 2007) and the particle trajectory simulation with HYSPLYT (HYbrid Single-Particle Lagrangian Integrated Trajectory) (Kim et al., 2011) identified. Since the sand dune activity has been recognized as an essential indicator of the progressive desertification, it is important to establish the monitoring method for the variations of topographic properties by the dune activities such as local roughness. Thus it will provide the crucial data about the extent and the transition of sandy desert. For example, it is well known the aerodynamic roughness lengths Zo which can be driven from the specialized sensor such as POLDER (POLarization and Directionality of the Earth's Reflectances) is essential to understand desert dune characteristics. However, for the multi temporal observation of dune fields, the availability of data set to extract Zo is limited. Therefore, we employed MISR (Multi angle imaging Spectro Radiometer) image sequence to extract multi angle topographic parameters such as NDAI (Normalized Difference Angular Index) or the variation of radiance with the viewing geometry which are representing the characteristics of target desert topography instead of Zo. In our approach, NDAI were expanded to the all viewing angles and then compared over the target sandy desert and the surrounding land covers. It showed very strong consistencies according to the land cover type and especially over the dynamic dune fields. On the other hands, the variation of NDAIs of sandy desert combining with the metrological observations were
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Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars
Ewing, R. C.; Lapotre, M. G. A.; Lewis, K. W.; Day, M.; Stein, N.; Rubin, D. M.; Sullivan, R.; Banham, S.; Lamb, M. P.; Bridges, N. T.; Gupta, S.; Fischer, W. W.
2017-12-01
The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large-ripple lee slopes. Lee slopes were 29° where grainflows were present and 33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter-scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune-field pattern dynamics and basin-scale boundary conditions will dictate the style and distribution of sedimentary processes.
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Deep learning for the detection of barchan dunes in satellite images
Azzaoui, A. M.; Adnani, M.; Elbelrhiti, H.; Chaouki, B. E. K.; Masmoudi, L.
2017-12-01
Barchan dunes are known to be the fastest moving sand dunes in deserts as they form under unidirectional winds and limited sand supply over a firm coherent basement (Elbelrhiti and Hargitai,2015). They were studied in the context of natural hazard monitoring as they could be a threat to human activities and infrastructures. Also, they were studied as a natural phenomenon occurring in other planetary landforms such as Mars or Venus (Bourke et al., 2010). Our region of interest was located in a desert region in the south of Morocco, in a barchan dunes corridor next to the town of Tarfaya. This region which is part of the Sahara desert contained thousands of barchans; which limits the number of dunes that could be studied during field missions. Therefore, we chose to monitor barchan dunes with satellite imagery, which can be seen as a complementary approach to field missions. We collected data from the Sentinel platform (https://scihub.copernicus.eu/dhus/); we used a machine learning method as a basis for the detection of barchan dunes positions in the satellite image. We trained a deep learning model on a mid-sized dataset that contained blocks representing images of barchan dunes, and images of other desert features, that we collected by cropping and annotating the source image. During testing, we browsed the satellite image with a gliding window that evaluated each block, and then produced a probability map. Finally, a threshold on the latter map exposed the location of barchan dunes. We used a subsample of data to train the model and we gradually incremented the size of the training set to get finer results and avoid over fitting. The positions of barchan dunes were successfully detected and deep learning was an effective method for this application. Sentinel-2 images were chosen for their availability and good temporal resolution, which will allow the tracking of barchan dunes in future work. While Sentinel images had sufficient spatial resolution for the
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Brice, Maximilien
2017-01-01
The protoDUNE experimental program is designed to test and validate the technologies and design that will be applied to the construction of the DUNE Far Detector at the Sanford Underground Research Facility (SURF). The protoDUNE detectors will be run in a dedicated beam line at the CERN SPS accelerator complex. The rate and volume of data produced by these detectors will be substantial and will require extensive system design and integration effort. As of Fall 2015, "protoDUNE" is the official name for the two apparatuses to be used in CERN beam test: single-phase and dual-phase LArTPC detectors. Each received a formal CERN experiment designation: NP02 for the dual-phase detector. NP04 for single-phase detector.
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Rasmussen, K. R.
2012-12-01
Morphological changes during more than 100 years have been investigated for a cliff-top dune complex at Rubjerg at the Danish North Sea coast. Here the lower 50 m of the cliff front is composed of Pleistocene steeply inclined floes of silt and clay with coarse sand in between which gives it a saw-tooth appearance. On top of this the dunes are found for several kilometres along the coastline. Due to erosion by the North Sea the cliff has retreated about 120 m between approximately 1880 and 1970 as indicated from two national surveys, and recent GPS-surveys indicate that erosion is continuing at a similar rate. Nevertheless the cliff top dune complex has survived, but its morphology has undergone some changed. The old maps indicate that around 1880 the dune complex was composed of several up to about 20 m high dunes streamlined in the East-West direction which is parallel to the prevailing wind direction. When protective planting started during the first half of the 20th Century the cliff top dunes gradually merged together forming a narrow, tall ridge parallel to the shore line with the highest part reaching about 90 m near 1970. In 1993 the highest points along the ridge was almost 95 m high, but then the protective planting was considerably reduced and recent annual GPS-surveys indicate that the dunes respond quickly to this by changing their morphology towards the original appearance. It is remarkable that despite the mass wasting caused by the constant erosion of the cliff front the dunes have remained more or less intact. Theoretical studies of hill flow indicate given the proper geometry of the cliff then suspension of even coarse grains can be a very effective agent for carrying sand from the exposed parts of the cliff front to and beyond the cliff-top. Mostly the sand grains are deposited within some hundred meters downwind of the cliff dune while silt is often carried more than 10 km inland. Field observations indicate that where the dislodged floes and
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Parker Gay, S.
1999-03-01
Significant studies of sand dunes and sand movement made in coastal southern Peru in 1959-1961 [Gay, S.P., 1962. Origen, distribución y movimiento de las arenas eólicas en el área de Yauca a Palpa. Boletin de la Sociedad Geologica del Perú 37, 37-58] have never been published in the English language and consequently have never been referred to in the standard literature. These studies contain valuable information, not developed by later workers in this field, that may be of broad general interest. For example, using airphotos of barchan dunes and plotting the rates of movement vs. dune widths, the author quantified the deduction of Bagnold [Bagnold, R.A., 1941. The Physics of Blown Sand and Desert Dunes. Methuen, London.] that the speed of barchan movement is inversely proportional to barchan size (as characterized by height or width). This led to the conclusion that all barchans in a given dune field, regardless of size, sweep out approximately equal areas in equal times. Another conclusion was that collisions between smaller, overtaking dunes and larger dunes in front of them do not result in destruction or absorption of the smaller dunes if the collision is a `sideswipe'. The dunes simply merge into a compound dune for a time, and the smaller dune then moves on intact, i.e., passes, the larger dune, whilst retaining its approximate original size and shape. Another result of the 1959-1961 studies was a map that documents the Pacific coast beaches as the source of the sand ( Fig. 1), which is then blown inland through extensive dune fields of barchans and other dune forms in great clockwise-sweeping paths, to its final resting place in huge sand masses, sometimes called `sand seas' [Lancaster, N., 1995. Geomorphology of Desert Dunes. Routledge, London], at higher elevations 20 to 60 km from the coast. A minor, but nevertheless interesting, discovery was a small heavy mineral dune located directly in the lee of a large barchan, evidently formed by the winnowing
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Van Thiel de Vries, J.S.M.
2012-01-01
In a situation with a narrow dune, the dune base can be protected with a revetment to reduce dune erosion during extreme events. To quantify the effects of a revetment on storm impact, the functionality of the numerical storm impact model XBeach (Roelvink et al., 2009) is extended to account for the
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Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars.
Ewing, R C; Lapotre, M G A; Lewis, K W; Day, M; Stein, N; Rubin, D M; Sullivan, R; Banham, S; Lamb, M P; Bridges, N T; Gupta, S; Fischer, W W
2017-12-01
The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large-ripple lee slopes. Lee slopes were ~29° where grainflows were present and ~33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter-scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune-field pattern dynamics and basin-scale boundary conditions will dictate the style and distribution of sedimentary processes.
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Advanced Interferometric Synthetic Aperture Imaging Radar (InSAR) for Dune Mapping
Havivi, Shiran; Amir, Doron; Schvartzman, Ilan; August, Yitzhak; Mamman, Shimrit; Rotman, Stanely R.; Blumberg, Dan G.
2016-04-01
varying levels of stability and vegetation cover and have been monitored meteorologically, geomorphologically, and studied extensively in the field. High resolution TerraSAR-X (TSX) images covering the entire research area were acquired for the period of 2011 to 2012. Analysis was performed in imaging processing and GIS software. The coherence results display minor changes on the dune crest (0.42-0.49), compared to bigger changes in windward slope (0.31-0.37). The level of change depends on the dune location relative to its distance from the sea. Furthermore, the coherence results show decreasing over time. Field results indicate erosion/deposition of sand ranging from -99 to 137 mm/year. The results of this study confirm that it is possible to monitor subtle changes in sand dunes and to identify dune stability or instability, only by the use of SAR images, even in areas characterized by low coherence.
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Fenton, Lori K.; Hayward, Rosalyn K.; Horgan, Briony H.N.; Rubin, David M.; Titus, Timothy N.; Bishop, Mark A.; Burr, Devon M.; Chojnacki, Matthew; Dinwiddie, Cynthia L.; Kerber, Laura; Gall, Alice Le; Michaels, Timothy I.; Neakrase, Lynn D.V.; Newman, Claire E.; Tirsch, Daniela; Yizhaq, Hezi; Zimbelman, James R.
2013-01-01
The Third International Planetary Dunes Workshop took place in Flagstaff, AZ, USA during June 12–15, 2012. This meeting brought together a diverse group of researchers to discuss recent advances in terrestrial and planetary research on aeolian bedforms. The workshop included two and a half days of oral and poster presentations, as well as one formal (and one informal) full-day field trip. Similar to its predecessors, the presented work provided new insight on the morphology, dynamics, composition, and origin of aeolian bedforms on Venus, Earth, Mars, and Titan, with some intriguing speculation about potential aeolian processes on Triton (a satellite of Neptune) and Pluto. Major advancements since the previous International Planetary Dunes Workshop include the introduction of several new data analysis and numerical tools and utilization of low-cost field instruments (most notably the time-lapse camera). Most presentations represented advancement towards research priorities identified in both of the prior two workshops, although some previously recommended research approaches were not discussed. In addition, this workshop provided a forum for participants to discuss the uncertain future of the Planetary Aeolian Laboratory; subsequent actions taken as a result of the decisions made during the workshop may lead to an expansion of funding opportunities to use the facilities, as well as other improvements. The interactions during this workshop contributed to the success of the Third International Planetary Dunes Workshop, further developing our understanding of aeolian processes on the aeolian worlds of the Solar System.
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Understanding river dune splitting through flume experiments and analysis of a dune evolution model
Warmink, Jord Jurriaan; Dohmen-Janssen, Catarine M.; Lansink, Jord; Naqshband, Suleyman; van Duin, Olav; Paarlberg, Andries; Termes, A.P.P.; Hulscher, Suzanne J.M.H.
2014-01-01
Forecasts of water level during river floods require accurate predictions of the evolution of river dune dimensions, because the hydraulic roughness of the main channel is largely determined by the bed morphology. River dune dimensions are controlled by processes like merging and splitting of dunes.
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Stability of isolated Barchan dunes
Fourrière, Antoine; Charru, François
2010-11-01
When sand grains are entrained by an air flow over a non-erodible ground, or with limited sediment supply from the bed, they form isolated dunes showing a remarkable crescentic shape with horns pointing downstream. These dunes, known as Barchan dunes, are commonly observed in deserts, with height of a few meters and velocity of a few meters per year (Bagnold 1941). These dunes also exist under water, at a much smaller, centimetric size (Franklin & Charru 2010). Their striking stability properties are not well understood yet. Two phenomena are likely to be involved in this stability: (i) relaxation effects of the sand flux which increases from the dune foot up to the crest, related to grain inertia or deposition, and (ii) a small transverse sand flux due to slope effects and the divergence of the streamlines of the fluid flow. We reproduced aqueous Barchan dunes in a channel, and studied their geometrical and dynamic properties (in particular their shape, velocity, minimum size, and rate of erosion). Using coloured glass beads (see the figure), we were then able to measure the particle flux over the whole dune surface. We will discuss the stability of these dunes in the light of our measurements.
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CSIR Research Space (South Africa)
Tinley, KL
1985-01-01
Full Text Available . The descriptive section is divided into geographic setting, physical features, ecological features and dune dynamics. Emphasis is placed on the factors affecting dune formation and erosion and the biogeography and dynamics of dune vegetation. Current use...
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Characteristics of dune-paleosol-sequences in Fuerteventura. - What should be questioned?
Faust, Dominik; Willkommen, Tobias; Yanes, Yurena; Richter, David; Zöller, Ludwig
2013-04-01
Characteristics of dune-paleosol-sequences in Fuerteventura. - What should be questioned? Dominik Faust, TU Dresden, Germany Tobias Willkommen, TU Dresden, Germany Yurena Yanes, CSIC Granada/Cincinatti, Spain/USA David Richter, TU Dresden, Germany Ludwig Zöller, Uni Bayreuth, Germany The northern part of Fuerteventura is characterized by large dune fields. We investigated dune-paleosol-sequences in four pits to establish a robust stratigraphy and to propose a standard section. An interaction of processes like dune formation, soil formation and redeposition of soils and sand are most important to understand the principles of landscape development in the study area. To our mind a process cycle seem to be important: First climbing-dunes are formed by sand of shelf origin. Then soil formation could have taken place. Soil and/or sand were then eroded and deposited at toe slope position. This material in turn is the source of new sand supply and dune formation. The described cycle may be repeated several times and this ping-pong-process holds on. The results are sections composed of dune layers, paleosols and colluvial material interbedded. Fundamental questions still remain unanswered: Is climate change responsable for changes in process combination (e.g. from dune formation to soil formation)? Or are these features due to divergence phenomenon, where different effects/results (dune and soils) may be linked to similar causes (here: climate)? Assuming that different features (soils and dunes) were formed under one climate, increasing soil forming intensity could be mainly a function of decreasing sand supply. This in turn could be caused by reduced sand production (s. ZECH et al. accepted). However geochemical data and mollusc assemblages point to changing environments in space and even climate modifications in time.
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Hardin, E.; Mitasova, H.; Overton, M.
2010-12-01
In barrier islands where communities are subjected to hazards including storm surge and high wave height, coastal dunes offer the first line of defense to property and vital infrastructure. When dunes are over-washed, substantial damage, including complete destruction of buildings and roads can occur. For this reason, dunes are an integral aspect of coastal hazard management. As new, more efficient mapping and analysis technologies evolve, currently used methodologies should be regularly be reexamined in order to ensure the development of the most effective coastal management strategies. Currently, topographical parameters, such as dune height, are usually measured along evenly spaced, shore-perpendicular beach profiles. In previous studies, profile spacing has varied from 20m to over 500m, however, it has been shown that dune height can vary substantially over tens of meters. Profile spacing is a compromise between the resources needed to perform high-resolution measurements and ensuring the capture of meaningful dune features. While it is often clear how the choice of profile spacing will affect the resources needed to perform the analysis, it is often unclear how spacing affects the ability to capture significant dune variation and prevent omission of a narrow dune breach that can open the way for significant flooding. In this study, the structure of alongshore variation in dune height is investigated. The studied dune ridge is located in the Outer Banks, North Carolina, USA and stretches 18km from south of Oregon Inlet (75:31:19W, 35:46:03N) to Rodanthe (75:27:56W, 35:36:31N). The dune ridge is extracted from a 0.5m resolution Digital Elevation Model (DEM) that was interpolated from airborne lidar data using regularized spline with tension. The lidar data was collected in March 2008 by the National Oceanic and Atmospheric Administration. A dune ridge is usually identified as the highest elevation along a shore-perpendicular profile or where ocean-facing slope
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Large-eddy simulations of unidirectional water flow over dunes
Grigoriadis, D. G. E.; Balaras, E.; Dimas, A. A.
2009-06-01
The unidirectional, subcritical flow over fixed dunes is studied numerically using large-eddy simulation, while the immersed boundary method is implemented to incorporate the bed geometry. Results are presented for a typical dune shape and two Reynolds numbers, Re = 17,500 and Re = 93,500, on the basis of bulk velocity and water depth. The numerical predictions of velocity statistics at the low Reynolds number are in very good agreement with available experimental data. A primary recirculation region develops downstream of the dune crest at both Reynolds numbers, while a secondary region develops at the toe of the dune crest only for the low Reynolds number. Downstream of the reattachment point, on the dune stoss, the turbulence intensity in the developing boundary layer is weaker than in comparable equilibrium boundary layers. Coherent vortical structures are identified using the fluctuating pressure field and the second invariant of the velocity gradient tensor. Vorticity is primarily generated at the dune crest in the form of spanwise "roller" structures. Roller structures dominate the flow dynamics near the crest, and are responsible for perturbing the boundary layer downstream of the reattachment point, which leads to the formation of "horseshoe" structures. Horseshoe structures dominate the near-wall dynamics after the reattachment point, do not rise to the free surface, and are distorted by the shear layer of the next crest. The occasional interaction between roller and horseshoe structures generates tube-like "kolk" structures, which rise to the free surface and persist for a long time before attenuating.
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2005-01-01
18 March 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark dunes on a crater floor during the southern spring. Some of the dunes have frost on their south-facing slopes. Location near: 52.3oS, 326.7oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring
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Mineralogy of an Active Eolian Sediment from the Namib Dune, Gale Crater, Mars
Achilles, C. N.; Downs, R. T.; Ming, D. W.; Rampe, E. B.; Morris, R. V.; Treiman, A. H.; Morrison, S. M.; Blake, D. F.; Vaniman, D. T.; Ewing, R. C.; Chipera, S. J.; Yen, A. S.; Bristow, T. F.; Ehlmann, B. L.; Gellert, R.
2017-01-01
The Mars Science Laboratory rover, Curiosity, is using a comprehensive scientific payload to explore rocks and soils in Gale crater, Mars. Recent investigations of the Bagnold Dune Field provided the first in situ assessment of an active dune on Mars. The Chemistry and Mineralogy (CheMin) X-ray diffraction instrument on Curiosity performed quantitative mineralogical analyses of the
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The morphology and morphodynamics of sand-gravel subaquatic dunes: the Raba River estuary, Poland
Directory of Open Access Journals (Sweden)
Artur RADECKI-PAWLIK
2012-08-01
Full Text Available In the outlet of the Raba River to the Vistula, the biggest river in Poland, the morphology and morphodynamics of sand and fine-gravel subaquatic dunes were investigated. The site is situated in highland region just about the entrance to Polish Carpathians. The dunes formed on the Raba River bed estuary are composed of sand and fine gravel (d50 up to 11 mm. Systematic observation (within the 2000-2005 were made of geometry, sediment composition and hydraulic climate under which the dunes grew and decomposed. The investigation focuses here mostly on the geometrical parameters of these bed forms such as height, length, as well as granulometric characteristics of the sediment. Based on in-site measurements different hydraulic parameters were calculated such as shear stresses, resistant coefficient, Froude and Reynolds numbers and roughness coefficient. It was found that the relation between height (H and length (L of the Raba estuary dunes describes the formula: H = 0.05L0.35. Also these dunes are steeper and flatter then classical H/L index is: H/L = 0.0518L0.622. During the field campaign, when the foot access to the estuary was possible and dunes were spotted on the river bed the range of measured water velocity was from v = 0.39 m∙s-1 to v = 0.81 m∙s-1 with the highest velocity over the dune crest. At the same time the measured range of shear stresses within the dune field formation were from t = 0.115 N×m-2 to t = 1.59 N×m-2. On the field investigations the CCHE2D - two-dimensional unsteady flow and sediment transport model for non-equilibrium transport of non-uniform sediment mixtures – was applied. The model was used to simulate the morphodynamic changes along the outlet of the Raba River basing on field observations of the 2005 summer flood as well as calculate hydraulics parameters. It was also used to test and confirm the range of morphodynamic changes, which take place along the research reach where the dunes are being developed
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Sports, genre et developpement durable : l'heritage d'une ...
African Journals Online (AJOL)
Sports, genre et developpement durable : l'heritage d'une distribution ... to new populations in situation of confrontation with the difference that Goffman (1975) ... and women (gender), maintain the sports field and behind the appearance of a ...
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A case study on dune response to infragravity waves
Li, Wenshan; Wang, Hui; Li, Huan; Wu, Shuangquan; Li, Cheng
2017-08-01
A series of numerical simulations were conducted using the process-based model XBeach to investigate dune response under normal and getting rid of infragravity wave conditions with different slopes. Erosion volume upside the dune toe and dune top recession are set as indicators for dune vulnerability as well as defence capacity for its front-beach. Results show that both dune erosion volume and dune top recession decrease with gentler dune slopes. Of all the simulation cases, dune with a face slope of 1/1 lost most sand and supplied most sand for lower-bed. The presence of infragravity waves is validated to be crucial to dune vulnerability. The dune erosion volume is shown to decrease by 44.5%∼61.5% and the dune top recession decreased by 0%∼45.5% correspondingly, in the case that infragravity motion is not taken into account during simulation for different dune slopes.
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Ecogeomorphology of Sand Dunes Shaped by Vegetation
Tsoar, H.
2014-12-01
Two dune types associated with vegetation are known: Parabolic and Vegetated Linear Dunes (VLDs), the latters are the dominant dune type in the world deserts. Parabolic dunes are formed in humid, sub-humid and semi-arid environments (rather than arid) where vegetation is nearby. VLDs are known today in semiarid and arid lands where the average yearly rainfall is ≥100 mm, enough to support sparse cover of vegetation. These two dune types are formed by unidirectional winds although they demonstrate a different form and have a distinct dynamics. Conceptual and mathematical models of dunes mobility and stability, based on three control parameters: wind power (DP), average annual precipitation (p), and the human impact parameter (μ) show that where human impact is negligible the effect of wind power (DP) on vegetative cover is substantial. The average yearly rainfall of 60-80 mm is the threshold of annual average rainfall for vegetation growth on dune sand. The model is shown to follow a hysteresis path, which explains the bistability of active and stabilized dunes under the same climatic conditions with respect to wind power. We have discerned formation of parabolic dunes from barchans and transverse dunes in the coastal plain of Israel where a decrease in human activity during the second half of the 20th century caused establishment of vegetation on the crest of the dunes, a process that changed the dynamics of these barchans and transverse dunes and led to a change in the shape of the windward slope from convex to concave. These dunes gradually became parabolic. It seems that VLDs in Australia or the Kalahari have always been vegetated to some degree, though the shrubs were sparser in colder periods when the aeolian erosion was sizeable. Those ancient conditions are characterized by higher wind power and lower rainfall that can reduce, but not completely destroy, the vegetation cover, leading to the formation of lee (shadow) dunes behind each shrub. Formation of
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Zbigniew Pruszak; Rafal Ostrowski; Jan Schönhofer
2011-01-01
The paper analyses the results of field investigations into the evolution of the shoreline and dune toe positions in a multi-bar,dissipative coastal zone. The correlations between the changes in the shoreline and the dune toe range from -0.4 to 0.8. It is most often the case that the dune toe is stable while the shoreline moves. Consistent cross-shore migration is slightly more likelyto happen than the divergent or convergent movements of both lines. Shoreline retreat and advance attain resp...
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Experiment Simulation Configurations Used in DUNE CDR
Energy Technology Data Exchange (ETDEWEB)
Alion, T. [Univ. of South Carolina, Columbia, SC (United States); Black, J. J. [Univ. of Warwick, Coventry (United Kingdom); Bashyal, A. [Oregon State Univ., Corvallis, OR (United States); Bass, M. [Univ. of Oxford (United Kingdom); Bishai, M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Cherdack, D. [Colorado State Univ., Fort Collins, CO (United States); Diwan, M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Djurcic, Z. [Argonne National Lab. (ANL), Argonne, IL (United States); Evans, J. [Univ. of Manchester (United Kingdom); Fernandez-Martinez, E. [Madrid Autonama Univ. (Spain); Fields, L. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Fleming, B. [Yale Univ., New Haven, CT (United States); Gran, R. [Univ. of Minnesota, Duluth, MN (United States); Guenette, R. [Univ. of Oxford (United Kingdom); Hewes, J. [Univ. of Manchester (United Kingdom); Hogan, M. [Colorado State Univ., Fort Collins, CO (United States); Hylen, J. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Junk, T. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Kohn, S. [Univ. of California, Berkeley, CA (United States); LeBrun, P. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lundberg, B. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Marchionni, A. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Morris, C. [Univ. of California, Berkeley, CA (United States); Papadimitriou, V. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Rameika, R. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Rucinski, R. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Soldner-Rembold, S. [Univ. of Manchester (United Kingdom); Sorel, M. [Spanish National Research Council (CSIC), Valencia (Spain). Univ. of Valencia (UV), Inst. de Fisica Corpuscular; Urheim, J. [Indiana Univ., Bloomington, IN (United States); Viren, B. [Brookhaven National Lab. (BNL), Upton, NY (United States); Whitehead, L. [Univ. of Houston, TX (United States); Wilson, R. [Colorado State Univ., Fort Collins, CO (United States); Worcester, E. [Brookhaven National Lab. (BNL), Upton, NY (United States); Zeller, G. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
2016-06-30
The LBNF/DUNE CDR describes the proposed physics program and experimental design at the conceptual design phase. Volume 2, entitled The Physics Program for DUNE at LBNF, outlines the scientific objectives and describes the physics studies that the DUNE collaboration will perform to address these objectives. The long-baseline physics sensitivity calculations presented in the DUNE CDR rely upon simulation of the neutrino beam line, simulation of neutrino interactions in the far detector, and a parameterized analysis of detector performance and systematic uncertainty. The purpose of this posting is to provide the results of these simulations to the community to facilitate phenomenological studies of long-baseline oscillation at LBNF/DUNE. Additionally, this posting includes GDML of the DUNE single-phase far detector for use in simulations. DUNE welcomes those interested in performing this work as members of the collaboration, but also recognizes the benefit of making these configurations readily available to the wider community.
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Impact d'une modulation duale sur les performances d'une liaison ...
African Journals Online (AJOL)
Le présent document présente la technique de modulation duale Fréquence - Amplitude dans le cas d'une liaison optique du type IM-DD. Ce travail révèle que la modulation duale Fréquence - Amplitude permet de générer un signal à bande latérale unique. Les performances d'une liaison optique IM-DD basée sur cette ...
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Bridges, Nathan T.; Ehlmann, Bethany L.
2018-01-01
The Bagnold dunes in Gale Crater, Mars, are the first active aeolian dune field explored in situ on another planet. The Curiosity rover visited the Bagnold dune field to understand modern winds, aeolian processes, rates, and structures; to determine dune material composition, provenance, and the extent and type of compositional sorting; and to collect knowledge that informs the interpretation of past aeolian processes that are preserved in the Martian sedimentary rock record. The Curiosity rover conducted a coordinated campaign of activities lasting 4 months, interspersed with other rover activities, and employing all of the rover's science instruments and several engineering capabilities. Described in 13 manuscripts and summarized here, the major findings of the Bagnold Dunes Campaign, Phase I, include the following: the characterization of and explanation for a distinctive, meter-scale size of sinuous aeolian bedform formed in the high kinetic viscosity regime of Mars' thin atmosphere; articulation and evaluation of a grain splash model that successfully explains the occurrence of saltation even at wind speeds below the fluid threshold; determination of the dune sands' basaltic mineralogy and crystal chemistry in comparison with other soils and sedimentary rocks; and characterization of chemically distinctive volatile reservoirs in sand-sized versus dust-sized fractions of Mars soil, including two volatile-bearing types of amorphous phases.
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On the Internal Structure of Mobile Barchan Sand Dunes due to Granular Processes
Vriend, N. M.; Arran, M.; Louge, M. Y.; Hay, A. G.; Valance, A.
2017-12-01
In this work, we visualize the internal structure of mobile barchan desert dunes at the avalanche scale. We reveal an intriguing history of dune building using a novel combination of local sand sampling and advanced geophysical techniques resulting in high resolution measurements of individual avalanche events. Due to progressive rebuilding, granular avalanching, erosional and depositional processes, these marching barchan dunes are reworked every few years and a characteristic zebra-pattern (figure 1a), orientated parallel to the slipface at the angle of repose, appears at regular intervals. We present scientific data on the structure obtained from several mobile barchan dunes of different sizes during recent desert field campaigns (2014, 2015, 2017) in a mobile barchan dune field in Qatar (25.01°N, 51.34°E in the AlWakrah municipality). The site has been equipped with a weather station and has been regularly visited by a multidisciplinary research team in recent years (e.g. [1]). By applying high-frequency (1200 MHz) ground penetrating radar (GPR) transects across the midline (figure 1b) we map the continuous evolution of this cross-bedding at high resolution deep within the dune. The GPR reveals a slope reduction of the slipface near the base of the dune; evidence of irregular wind reversals; and the presence of a harder aeolian cap around the crest and extending to the brink. The data is supplemented with granulometry from layers stabilized by dyed water injection and uncovered by excavating vertical walls perpendicular to old buried avalanches. We attribute visible differences in water penetration between adjacent layers to fine particle segregation processes in granular avalanches. This work was made possible by the support of NPRP grant 6-059-2-023 from the Qatar National Research Fund to MYL and AGH, and a Royal Society Dorothy Hodgkin Research Fellowship to NMV. We thank Jean-Luc Métayer for performing detailed particle size distribution measurements
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Sand dune tracking from satellite laser altimetry
Dabboor, Mohammed
Substantial problems arise from sand movement in arid and semi-arid countries. Sand poses a threat to infrastructure, agricultural and urban areas. These issues are caused by the encroachment of sand on roads and railway tracks, farmland, towns and villages, and airports, to name a few. Sand movement highly depends on geomorphology including vegetation cover, shape and height of the terrain, and grain size of the sand. However, wind direction and speed are the most important factors that affect efficient sand movement. The direction of the movement depends on the main direction of the wind, but it has been shown that a minimum wind speed is required, e.g. wind gusts, to initiate sand transport. This fact prevents a simple calculation of sand transport from conventional wind data as wind records rarely contain sub-minute intervals masking out any wind gusts. An alternative of predicting sand transport is the direct observation of sand advance by in situ measurements or via satellite. Until recently, satellite imagery was the only means to compare dune shape and position for predicting dune migration over several years. In 2003, the NASA laser altimetry mission ICESat became operational and monitors elevations over all surface types including sand dunes with an accuracy of about 10-20 cm. In this study, ICESat observations from repeat tracks (tracks overlapping eachother within 50 m) are used to derive sand dune advance and direction. The method employs a correlation of the elevation profiles over several dunes and was sucessfully validated with synthetic data. The accuracy of this method is 5 meters of dune advance. One of the most active areas exhibiting sand and dune movement is the area of the Arabian Peninsula. Approximately one-third of the Arabian Peninsula is covered by sand dunes. Different wind regimes (Shamal, Kaus) cause sand dune movement in the selected study area in the eastern part of the Arabian Peninsula between 20-25 degrees North and 45-55 degrees
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Microbial Characterization of Qatari Barchan Sand Dunes.
Directory of Open Access Journals (Sweden)
Sara Abdul Majid
Full Text Available This study represents the first characterization of sand microbiota in migrating barchan sand dunes. Bacterial communities were studied through direct counts and cultivation, as well as 16S rRNA gene and metagenomic sequence analysis to gain an understanding of microbial abundance, diversity, and potential metabolic capabilities. Direct on-grain cell counts gave an average of 5.3 ± 0.4 x 105 cells g-1 of sand. Cultured isolates (N = 64 selected for 16S rRNA gene sequencing belonged to the phyla Actinobacteria (58%, Firmicutes (27% and Proteobacteria (15%. Deep-sequencing of 16S rRNA gene amplicons from 18 dunes demonstrated a high relative abundance of Proteobacteria, particularly enteric bacteria, and a dune-specific-pattern of bacterial community composition that correlated with dune size. Shotgun metagenome sequences of two representative dunes were analyzed and found to have similar relative bacterial abundance, though the relative abundances of eukaryotic, viral and enterobacterial sequences were greater in sand from the dune closer to a camel-pen. Functional analysis revealed patterns similar to those observed in desert soils; however, the increased relative abundance of genes encoding sporulation and dormancy are consistent with the dune microbiome being well-adapted to the exceptionally hyper-arid Qatari desert.
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Bourke, Mary; Nield, Jo; Diniega, Serina; Hansen, Candy; McElwaine, Jim
2016-04-01
The seasonal sublimation of CO2 ice is an active driver of present-day surface change on Mars. Diniega et al (2013) proposed that a discrete type of Martian gully, found on southern hemisphere dunes, were formed by the movement of CO2 seasonal ice blocks. These 'Linear Gullies' consist primarily of long (100 m - 2.5 km) grooves with near-uniform width (few-10 m wide), and typical depth of nudge it moved downslope. The dynamics of the block movement were recorded using a pair of high resolution video cameras. Geomorphological observations were noted and topographic change was quantified using a Leica P20 terrestrial laser scanner with a resolution of 0.8 mm at 10 m, and change detection limits less than 3 mm. The block run was repeated a total of 10 times and launched from the same location at the dune brink. The experiment ran for 45 minutes. The block size was reduced to (45 x 190 x 195 mm) by the end of the run series. The resultant geomorphology shows that the separate block runs occupied different tracks leading to a triangular plan form shape with a maximum width of 3.5 m. This is different from the findings in Arizona where a narrower track span was recorded (1.7m) (Bourke et al, 2016). Similar block dynamics were observed at both sites (as blocks moved straight, swiveled and bounced downslope). Distinctive pits with arcuate rims on their downslope edge were formed where blocks bounced on the surface. These pits are at an almost equidistant spacing. Despite a longer slope (16 m as opposed to 8m at Grand Falls), no depositional apron was formed. Levee development was less consistent compared to the Arizona site, but a pronounced unpaired-levee formed towards the base of the lee slope. These data show that sublimating blocks of CO2 ice leave signatures of transport paths and are capable of eroding and transporting sediment. Diniega,S. et al (2013) A new dry hypothesis for the formation of Martian linear gullies. Icarus. Vol. 225, 1, p. 526-537. Bourke, M.C. et
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Guan, Chao; Hasi, Eerdun; Zhang, Ping; Tao, Binbin; Liu, Dan; Zhou, Yanguang
2017-10-01
Since the 1970s, parabolic dunes at the southern fringe of the Hobq Desert, Inner Mongolia, China have exhibited many different shapes (V-shaped, U-shaped, and palmate) each with a unique mode of development. In the study area, parabolic dunes are mainly distributed in Regions A, B, and C with an intermittent river running from the south to the north. We used high-resolution remote-sensing images from 1970 to 2014 and RTK-GPS measurements to study the development modes of different dune shapes; the modes are characterized by the relationship between the intermittent river and dunes, formation of the incipient dune patterns, the predominant source supply of dunes, and the primary formation of different shapes (V-shaped, U-shaped, and palmate). Most parabolic dunes in Region A are V-shaped and closer to the bank of the river. The original barchans in this region exhibit "disconnected arms" behavior. With the sand blown out of the riverbed through gullies, the nebkhas on the disconnected arms acquire the external sand source through the "fertile island effect", thereby developing into triangular sand patches and further developing into V-shaped parabolic dunes. Most parabolic dunes in Regions B and C are palmate. The residual dunes cut by the re-channelization of river from transverse dune fields on the west bank are the main sand source of Region B. The parabolic dunes in Region C are the original barchans having then been transformed. The stoss slopes of V-shaped parabolic dunes along the riverbank are gradual and the dunes are flat in shape. The dune crest of V-shaped parabolic dune is the deposition area, which forms the "arc-shaped sand ridge". Their two arms are non-parallel; the lateral airflow of the arms jointly transport sand to the middle part of dunes, resulting in a narrower triangle that gradually becomes V-shaped. Palmate parabolic dunes have a steeper stoss slope and height. The dune crest of the palmate parabolic dune is the erosion area, which forms
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The influence of groundwater depth on coastal dune development at sand flats close to inlets
Silva, Filipe Galiforni; Wijnberg, Kathelijne M.; de Groot, Alma V.; Hulscher, Suzanne J. M. H.
2018-05-01
A cellular automata model is used to analyze the effects of groundwater levels and sediment supply on aeolian dune development occurring on sand flats close to inlets. The model considers, in a schematized and probabilistic way, aeolian transport processes, groundwater influence, vegetation development, and combined effects of waves and tides that can both erode and accrete the sand flat. Next to three idealized cases, a sand flat adjoining the barrier island of Texel, the Netherlands, was chosen as a case study. Elevation data from 18 annual LIDAR surveys was used to characterize sand flat and dune development. Additionally, a field survey was carried out to map the spatial variation in capillary fringe depth across the sand flat. Results show that for high groundwater situations, sediment supply became limited inducing formation of Coppice-like dunes, even though aeolian losses were regularly replenished by marine import during sand flat flooding. Long dune rows developed for high sediment supply scenarios which occurred for deep groundwater levels. Furthermore, a threshold depth appears to exist at which the groundwater level starts to affect dune development on the inlet sand flat. The threshold can vary spatially depending on external conditions such as topography. On sand flats close to inlets, groundwater is capable of introducing spatial variability in dune growth, which is consistent with dune development patterns found on the Texel sand flat.
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Directory of Open Access Journals (Sweden)
Serge Suanez
2015-07-01
Full Text Available Monitoring of dune erosion and accretion on the high-energy macrotidal Vougot beach in North Brittany (France over the past decade (2004–2014 has revealed significant morphological changes. Dune toe erosion/accretion records have been compared with extreme water level measurements, defined as the sum of (i astronomic tide; (ii storm surge; and (iii vertical wave runup. Runup parameterization was conducted using swash limits, beach profiles, and hydrodynamic (Hm0, Tm0,–1, and high tide water level—HTWL data sets obtained from high frequency field surveys. The aim was to quantify in-situ environmental conditions and dimensional swash parameters for the best calibration of Battjes [1] runup formula. In addition, an empirical equation based on observed tidal water level and offshore wave height was produced to estimate extreme water levels over the whole period of dune morphological change monitoring. A good correlation between this empirical equation (1.01Hmoξo and field runup measurements (Rmax was obtained (R2 85%. The goodness of fit given by the RMSE was about 0.29 m. A good relationship was noticed between dune erosion and high water levels when the water levels exceeded the dune foot elevation. In contrast, when extreme water levels were below the height of the toe of the dune sediment budget increased, inducing foredune recovery. These erosion and accretion phases may be related to the North Atlantic Oscillation Index.
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Coastal Dunes of the Baltic Sea Shores: A Review
Directory of Open Access Journals (Sweden)
Łabuz Tomasz Arkadiusz
2018-03-01
Full Text Available The article summarises results of studies conducted along the Baltic Sea sandy coasts by scientists involved in coastal dune research, and presents an attempt to describe the types and distribution of dune coasts. The Baltic Sea coasts feature lower and higher foredunes. The lowland behind the coastal dune belt is covered by wandering or stabilised inland dunes – transgressive forms, mainly parabolic or barchans. The source of sediment for dune development includes fluvioglacial sands from eroded coasts, river-discharged sand, and older eroded dunes. Due to the ongoing erosion and coastal retreat, many dunes have been eroded, and some are withdrawing onto the adjacent land. There are visible differences between the south-eastern, western, and northern parts of the Baltic Sea coast with respect to dune development. The entire southern and eastern coast abounds in sand, so the coastal dunes are large, formerly or currently wandering formations. The only shifting dunes are found at the Polish and the Russian–Lithuanian coasts on the Łebsko Lake Sandbar as well as on the Vistula and Curonian Spits. The very diverse shoreline of the south-western coast experiences a scarcity of larger sandy formations. Substantial parts of the Baltic Sea sandy coasts have been eroded or transformed by humans. The northern part of the Baltic Sea coast features mainly narrow and low sandy coasts (e.g. in Estonia. Further north, sandy dunes are virtually absent.
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Ludwig, J.; Lindhorst, S.; Betzler, C.; Bierstedt, S. E.; Borówka, R. K.
2017-08-01
It is shown that coastal dunes bear a so far unread archive of annual wind intensity. Active dunes at the Polish coast near Łeba consist of two genetic units: primary dunes with up to 18 m high eastward-dipping foresets, temporarily superimposed by smaller secondary dunes. Ground-penetrating radar (GPR) data reveal that the foresets of the primary dunes are bundled into alternating packages imaged as either low- or high-amplitude reflections. High-amplitude packages are composed of quartz sand with intercalated heavy-minerals layers. Low-amplitude packages lack these heavy-mineral concentrations. Dune net-progradation is towards the east, reflecting the prevalence of westerly winds. Winds blowing parallel to the dune crest winnow the lee slope, leaving layers enriched in heavy minerals. Sediment transport to the slip face of the dunes is enhanced during the winter months, whereas winnowing predominantly takes place during the spring to autumn months, when the wind field is bi-directional. As a consequence of this seasonal shift, the sedimentary record of one year comprises one low- and one high-amplitude GPR reflection interval. This sedimentary pattern is a persistent feature of the Łeba dunes and recognized to resemble a sedimentary "bar code". To overcome hiatuses in the bar code of individual dunes and dune-to-dune variations in bar-code quality, dendrochronological methods were adopted to compile a composite bar code from several dunes. The resulting data series shows annual variations in west-wind intensity at the southern Baltic coast for the time period 1987 to 2012. Proxy-based wind data are validated against instrumental based weather observations.
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Ewing, Ryan C.; Bridges, Nathan T.; Sullivan, Rob; Lapotre, Mathieu G. A.; Fischer, Woodward W.; Lamb, Mike P.; Rubin, David M.; Lewis, Kevin W.; Gupta, Sanjeev
2016-04-01
Wind-blown sand dunes are ubiquitous on the surface of Mars and are a recognized component of the martian stratigraphic record. Our current knowledge of the aeolian sedimentary processes that determine dune morphology, drive dune dynamics, and create aeolian cross-stratification are based upon orbital studies of ripple and dune morphodynamics, rover observations of stratification on Mars, Earth analogs, and experimental and theoretical studies of sand movement under Martian conditions. In-situ observations of sand dunes (informally called the Bagnold Dunes) by Curiosity Rover in Gale Crater, Mars provide the first opportunity to make observations of dunes from the grain-to-dune scale thereby filling the gap in knowledge between theory and orbital observations and refining our understanding of the martian aeolian stratigraphic record. We use the suite of cameras on Curiosity, including Navigation Camera (Navcam), Mast Camera (Mastcam) and Mars Hand Lens Imager (MAHLI), to make observations of the Bagnold Dunes. Measurements of sedimentary structures are made where stereo images are available. Observations indicate that structures generated by gravity-driven processes on the dune lee slopes, such as grainflow and grainfall, are similar to the suite of aeolian sedimentary structures observed on Earth and should be present and recognizable in Mars' aeolian stratigraphic record. Structures formed by traction-driven processes deviate significantly from those found on Earth. The dune hosts centimeter-scale wind ripples and large, meter-scale ripples, which are not found on Earth. The large ripples migrate across the depositional, lee slopes of the dune, which implies that these structures should be present in Mars' stratigraphic record and may appear similar to compound-dune stratification.The Mars Science Laboratory Curiosity Rover Team is acknowledged for their support of this work.
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Modeling the effect of dune sorting on the river long profile
Blom, A.
2012-12-01
of sediment supply from upstream. By definition the sum of the exposure of both layers equals unity. The model accounts for vertical sediment fluxes due to grain flows down the bedform lee face and the formation of a less mobile coarse layer. The model with its vertical sediment fluxes is validated against earlier flume experiments. It deals well with the transition between a plane bed and a bedform-dominated bed. Applying the model to field scale confirms that dune sorting increases river profile concavity.
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Boundary Conditions and the Aeolian Sediment State of the Olympia Undae Dune Field, Mars
Middlebrook, W.; Ewing, R. C.; Ayoub, F.; Bridges, N. T.; Smith, I.; Spiga, A.
2015-05-01
We evaluate the boundary conditions in Olympia Undae. We map two and three dimensional dune parameters from two locations proximal and distal to Planum Boreum and constrain sediment fluxes. We compare our results with a mesoscale atmospheric model.
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Modeling river dune evolution using a parameterization of flow separation
Paarlberg, Andries J.; Dohmen-Janssen, C. Marjolein; Hulscher, Suzanne J.M.H.; Termes, Paul
2009-01-01
This paper presents an idealized morphodynamic model to predict river dune evolution. The flow field is solved in a vertical plane assuming hydrostatic pressure conditions. The sediment transport is computed using a Meyer-Peter–Müller type of equation, including gravitational bed slope effects and a
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Interdisciplinary Research Produces Results in the Understanding of Planetary Dunes
Titus, Timothy N.; Hayward, Rosalyn Kay; Bourke, Mary C.
2010-08-01
Second International Planetary Dunes Workshop: Planetary Analogs—Integrating Models, Remote Sensing, and Field Data; Alamosa, Colorado, 18-21 May 2010; Dunes and other eolian bed forms are prominent on several planetary bodies in our solar system. Despite 4 decades of study, many questions remain regarding the composition, age, and origins of these features, as well as the climatic conditions under which they formed. Recently acquired data from orbiters and rovers, together with terrestrial analogs and numerical models, are providing new insights into Martian sand dunes, as well as eolian bed forms on other terrestrial planetary bodies (e.g., Titan). As a means of bringing together terrestrial and planetary researchers from diverse backgrounds with the goal of fostering collaborative interdisciplinary research, the U.S. Geological Survey (USGS), the Carl Sagan Center for the Study of Life in the Universe, the Desert Research Institute, and the U.S. National Park Service held a workshop in Colorado. The small group setting facilitated intensive discussion of problems and issues associated with eolian processes on Earth, Mars, and Titan.
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Water Use for Cultivation Management of Watermelon in Upland Field on Sand Dune
Hashimoto, Iwao; Senge, Masateru; Itou, Kengo; Maruyama, Toshisuke
Early-maturing cultivation of watermelon in a plastic tunnel was invetigated in upland field on sand dune on the coast of the Japan Sea to find water use to control blowing sand and to transplant seedlings. This region has low precipitation, low humidity, and strong wind in March and April, when sand is readily blown in the field. Water is used to control blowing sand on days with precipitation below 5 mm, minimum humidity below the meteorological average in April, and maximum wind velocity above the meteorological average in April. For the rooting and growth of watermelon seedlings, soil temperature needs to be raised because it is low in April. Ridges are mulched with transparent, porous polyethylene films 10 or more days before transplanting the seedlings and irrigated with sprinklers on fine days for the thermal storage of solar energy. The stored heat steams the mulched ridges to raise soil temperature to 15°C or higher on the day of transplanting the seedlings. The total amount of irrigation water used for watermelon cultivation was 432.7 mm, of which 23.6 mm was for blowing sand control and 26.6 mm was for transplanting the seedlings. The combined amount, 50.2 mm, is 11.6% of the total amount of water used for cultivation management.
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Very large dune formation along the Ebro outer continental shelf (Western Mediterranean)
Lo Iacono, Claudio; Guillén, Jorge; Puig, Pere; Ribó, Marta; Ballesteros, Maria; Palanques, Albert; Farrán, Marcelli; Acosta, Juan
2010-05-01
observed along the studied region are amongst the largest ever recognized on an outer shelf setting. Morphologic characters and the orientation towards SW and W directions suggest the Liguro-Provenzal-Catalan geostrophic current as the primary forcing factor in their formation. Contemporary hydrodynamic measurement at the Ebro continental shelf-edge show that near-bottom wave action is negligible in this area, whereas maximum shear stresses induced by currents are able to resuspend fine sand particles and prevent the relict transgressive deposits from being covered by mud. However, recorded nearbottom currents generate shear stresses below the critical value for transport the relict coarse sands found in the study area and form large bedforms. The comparison of successive bathymetric images and the relation wavelength/height suggest that the described very large dunes are inactive features over long periods, as observed in similar environments along several continental margins. Thus, the morphological configuration of the Columbretes outer shelf must have played a crucial role in enhancing the southward flowing bottom currents during energetic hydrodynamic events, giving them the potential to generate such bedforms.
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2004-01-01
9 May 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a suite of frost-covered sand dunes in the north polar region of Mars in early spring, 2004. The dunes indicate wind transport of sand from left to right (west to east). These landforms are located near 78.1oN, 220.8oW. This picture is illuminated by sunlight from the lower left and covers an area about 3 km (1.9 mi) across.
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Invasive plants on disturbed Korean sand dunes
Kim, Kee Dae
2005-01-01
The sand dunes in coastal regions of South Korea are important ecosystems because of their small size, the rare species found in this habitat, and the beautiful landscapes they create. This study investigated the current vegetative status of sand dunes on three representative coasts of the Korean peninsula, and on the coasts of Cheju Island, and assessed the conditions caused by invasive plants. The relationships between the degree of invasion and 14 environmental variables were studied. Plots of sand dunes along line transects perpendicular to the coastal lines were established to estimate vegetative species coverage. TWINSPAN (Two-Way Indicator Species Analysis), CCA (Canonical Correspondence Analysis), and DCCA (Detrended Canonical Correspondence Analysis) were performed to classify communities on sand dunes and assess species composition variation. Carex kobomugi, Elymus mollis, and Vitex rotundifolia were found to be the dominant species plotted on the east, the west, and the peripheral coasts of Cheju Island, respectively. Vegetation on the south coast was totally extinct. The 19 communities, including representative C. kobomugi, C. kobomugi- Ixeris repens, C. kobomugi- Oenothera biennis, E. mollis, Lolium multiflorum- Calystegia soldanella, and V. rotundifolia- C. kobomugi, were all classified according to TWINSPAN. Oenothera biennis and L. multiflorum were exotics observed within these native communities. CCA showed that invasive native and exotic species distribution was segregated significantly, according to disturbance level, exotic species number, gravel, sand and silt contents, as well as vegetation size. It further revealed that human disturbance can strongly favor the settlement of invasive and exotic species. Restoration options to reduce exotic plants in the South Korean sand dune areas were found to be the introduction of native plant species from one sand dune into other sand dune areas, prohibition of building and the introduction of exotic
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Quantifying energy and water fluxes in dry dune ecosystems of the Netherlands
Voortman, B. R.; Bartholomeus, R. P.; van der Zee, S. E. A. T. M.; Bierkens, M. F. P.; Witte, J. P. M.
2015-09-01
Coastal and inland dunes provide various ecosystem services that are related to groundwater, such as drinking water production and biodiversity. To manage groundwater in a sustainable manner, knowledge of actual evapotranspiration (ETa) for the various land covers in dunes is essential. Aiming at improving the parameterization of dune vegetation in hydrometeorological models, this study explores the magnitude of energy and water fluxes in an inland dune ecosystem in the Netherlands. Hydrometeorological measurements were used to parameterize the Penman-Monteith evapotranspiration model for four different surfaces: bare sand, moss, grass and heather. We found that the net longwave radiation (Rnl) was the largest energy flux for most surfaces during daytime. However, modeling this flux by a calibrated FAO-56 Rnl model for each surface and for hourly time steps was unsuccessful. Our Rnl model, with a novel submodel using solar elevation angle and air temperature to describe the diurnal pattern in radiative surface temperature, improved Rnl simulations considerably. Model simulations of evaporation from moss surfaces showed that the modulating effect of mosses on the water balance is species-dependent. We demonstrate that dense moss carpets (Campylopus introflexus) evaporate more (5 %, +14 mm) than bare sand (total of 258 mm in 2013), while more open-structured mosses (Hypnum cupressiforme) evaporate less (-30 %, -76 mm) than bare sand. Additionally, we found that a drought event in the summer of 2013 showed a pronounced delayed signal on lysimeter measurements of ETa for the grass and heather surfaces, respectively. Due to the desiccation of leaves after the drought event, and their feedback on the surface resistance, the potential evapotranspiration in the year 2013 dropped by 9 % (-37 mm) and 10 % (-61 mm) for the grass and heather surfaces, respectively, which subsequently led to lowered ETa of 8 % (-29 mm) and 7 % (-29 mm). These feedbacks are of importance for
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Directory of Open Access Journals (Sweden)
Zbigniew Pruszak
2011-03-01
Full Text Available The paper analyses the results of field investigations into the evolution of the shoreline and dune toe positions in a multi-bar,dissipative coastal zone. The correlations between the changes in the shoreline and the dune toe range from -0.4 to 0.8. It is most often the case that the dune toe is stable while the shoreline moves. Consistent cross-shore migration is slightly more likelyto happen than the divergent or convergent movements of both lines. Shoreline retreat and advance attain respective rates of 0.7 m day-1 and 0.4 m day-1. Deep-water wave energy of about 50 kJ m-1 constitutes the boundary between shore accumulation and erosion.
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Matter Density Profile Shape Effects at DUNE
Energy Technology Data Exchange (ETDEWEB)
Kelly, Kevin J. [Northwestern U.; Parke, Stephen J. [Fermilab
2018-02-19
Quantum mechanical interactions between neutrinos and matter along the path of propagation, the Wolfenstein matter effect, are of particular importance for the upcoming long-baseline neutrino oscillation experiments, specifically the Deep Underground Neutrino Experiment (DUNE). Here, we explore specifically what about the matter density profile can be measured by DUNE, considering both the shape and normalization of the profile between the neutrinos' origin and detection. Additionally, we explore the capability of a perturbative method for calculating neutrino oscillation probabilities and whether this method is suitable for DUNE. We also briefly quantitatively explore the ability of DUNE to measure the Earth's matter density, and the impact of performing this measurement on measuring standard neutrino oscillation parameters.
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DEFF Research Database (Denmark)
Becker, Marius; Schrottke, Kerstin; Bartholomä, Alexander
2013-01-01
25 g/L below the lutocline to 70 g/L at the river bed, whereas the gelling concentration was below 70 g/L. Sites of fluid mud formation coincided with the location of the estuarine turbidity zone during slack water. On average, near-bed density gradients were initially observed in dune troughs 1.2 h...... before slack water, and all fluid mud layers were entrained 2.3 h after slack water. No shear instabilities occurred until 1.8 h after slack water. While the flow was oriented in the dune direction, rapid entrainment was related to the development of the turbulent flow field behind dunes and is explained...... to be induced by advection of strong turbulence during accelerating currents. Fluid mud layers in dune troughs were entrained at an earlier point in time after slack water, compared to adjacent layers formed on a comparatively flat bed, where dune crests did not protrude from the lutocline....
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Dune-Yardang Interactions in Becquerel Crater, Mars
Urso, Anna; Chojnacki, Matthew; Vaz, David A.
2018-02-01
Isolated landscapes largely shaped by aeolian processes can occur on Earth, while the majority of Mars' recent history has been dominated by wind-driven activity. Resultantly, Martian landscapes often exhibit large-scale aeolian features, including yardang landforms carved from sedimentary-layered deposits. High-resolution orbital monitoring has revealed that persistent bedform activity is occurring with dune and ripple migration implying ongoing abrasion of the surface. However, little is known about the interaction between dunes and the topography surrounding them. Here we explore dune-yardang interactions in Becquerel crater in an effort to better understand local landscape evolution. Dunes there occur on the north and south sides of a 700 m tall sedimentary deposit, which displays numerous superposed yardangs. Dune and yardang orientations are congruent, suggesting that they both were formed under a predominantly northerly wind regime. Migration rates and sediment fluxes decrease as dunes approach the deposit and begin to increase again downwind of the deposit where the effect of topographic sheltering decreases. Estimated sand abrasion rates (16-40 μm yr-1) would yield a formation time of 1.8-4.5 Myr for the 70 m deep yardangs. This evidence for local aeolian abrasion also helps explain the young exposure ages of deposit surfaces, as estimated by the crater size-frequency distribution. Comparisons to terrestrial dune activity and yardang development begin to place constraints on yardang formation times for both Earth and Mars. These results provide insight into the complexities of sediment transport on uneven terrain and are compelling examples of contemporary aeolian-driven landscape evolution on Mars.
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Dune-Yardang Interactions in Becquerel Crater, Mars.
Urso, Anna; Chojnacki, Matthew; Vaz, David A
2018-01-01
Isolated landscapes largely shaped by aeolian processes can occur on Earth, while the majority of Mars' recent history has been dominated by wind-driven activity. Resultantly, Martian landscapes often exhibit large-scale aeolian features, including yardang landforms carved from sedimentary-layered deposits. High-resolution orbital monitoring has revealed that persistent bedform activity is occurring with dune and ripple migration implying ongoing abrasion of the surface. However, little is known about the interaction between dunes and the topography surrounding them. Here we explore dune-yardang interactions in Becquerel crater in an effort to better understand local landscape evolution. Dunes there occur on the north and south sides of a 700 m tall sedimentary deposit, which displays numerous superposed yardangs. Dune and yardang orientations are congruent, suggesting that they both were formed under a predominantly northerly wind regime. Migration rates and sediment fluxes decrease as dunes approach the deposit and begin to increase again downwind of the deposit where the effect of topographic sheltering decreases. Estimated sand abrasion rates (16-40 μm yr -1 ) would yield a formation time of 1.8-4.5 Myr for the 70 m deep yardangs. This evidence for local aeolian abrasion also helps explain the young exposure ages of deposit surfaces, as estimated by the crater size-frequency distribution. Comparisons to terrestrial dune activity and yardang development begin to place constraints on yardang formation times for both Earth and Mars. These results provide insight into the complexities of sediment transport on uneven terrain and are compelling examples of contemporary aeolian-driven landscape evolution on Mars.
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Large-eddy simulation of unidirectional turbulent flow over dunes
Omidyeganeh, Mohammad
We performed large eddy simulation of the flow over a series of two- and three-dimensional dune geometries at laboratory scale using the Lagrangian dynamic eddy-viscosity subgrid-scale model. First, we studied the flow over a standard 2D transverse dune geometry, then bedform three-dimensionality was imposed. Finally, we investigated the turbulent flow over barchan dunes. The results are validated by comparison with simulations and experiments for the 2D dune case, while the results of the 3D dunes are validated qualitatively against experiments. The flow over transverse dunes separates at the dune crest, generating a shear layer that plays a crucial role in the transport of momentum and energy, as well as the generation of coherent structures. Spanwise vortices are generated in the separated shear; as they are advected, they undergo lateral instabilities and develop into horseshoe-like structures and finally reach the surface. The ejection that occurs between the legs of the vortex creates the upwelling and downdrafting events on the free surface known as "boils". The three-dimensional separation of flow at the crestline alters the distribution of wall pressure, which may cause secondary flow across the stream. The mean flow is characterized by a pair of counter-rotating streamwise vortices, with core radii of the order of the flow depth. Staggering the crestlines alters the secondary motion; two pairs of streamwise vortices appear (a strong one, centred about the lobe, and a weaker one, coming from the previous dune, centred around the saddle). The flow over barchan dunes presents significant differences to that over transverse dunes. The flow near the bed, upstream of the dune, diverges from the centerline plane; the flow close to the centerline plane separates at the crest and reattaches on the bed. Away from the centerline plane and along the horns, flow separation occurs intermittently. The flow in the separation bubble is routed towards the horns and leaves
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Testing model parameters for wave‐induced dune erosion using observations from Hurricane Sandy
Overbeck, Jacquelyn R.; Long, Joseph W.; Stockdon, Hilary F.
2017-01-01
Models of dune erosion depend on a set of assumptions that dictate the predicted evolution of dunes throughout the duration of a storm. Lidar observations made before and after Hurricane Sandy at over 800 profiles with diverse dune elevations, widths, and volumes are used to quantify specific dune erosion model parameters including the dune face slope, which controls dune avalanching, and the trajectory of the dune toe, which controls dune migration. Wave‐impact models of dune erosion assume a vertical dune face and erosion of the dune toe along the foreshore beach slope. Observations presented here show that these assumptions are not always valid and require additional testing if these models are to be used to predict coastal vulnerability for decision‐making purposes. Observed dune face slopes steepened by 43% yet did not become vertical faces, and only 50% of the dunes evolved along a trajectory similar to the foreshore beach slope. Observations also indicate that dune crests were lowered during dune erosion. Moreover, analysis showed a correspondence between dune lowering and narrower beaches, smaller dune volumes, and/or longer wave impact.
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Testing model parameters for wave-induced dune erosion using observations from Hurricane Sandy
Overbeck, J. R.; Long, J. W.; Stockdon, H. F.
2017-01-01
Models of dune erosion depend on a set of assumptions that dictate the predicted evolution of dunes throughout the duration of a storm. Lidar observations made before and after Hurricane Sandy at over 800 profiles with diverse dune elevations, widths, and volumes are used to quantify specific dune erosion model parameters including the dune face slope, which controls dune avalanching, and the trajectory of the dune toe, which controls dune migration. Wave-impact models of dune erosion assume a vertical dune face and erosion of the dune toe along the foreshore beach slope. Observations presented here show that these assumptions are not always valid and require additional testing if these models are to be used to predict coastal vulnerability for decision-making purposes. Observed dune face slopes steepened by 43% yet did not become vertical faces, and only 50% of the dunes evolved along a trajectory similar to the foreshore beach slope. Observations also indicate that dune crests were lowered during dune erosion. Moreover, analysis showed a correspondence between dune lowering and narrower beaches, smaller dune volumes, and/or longer wave impact.
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Formation of aeolian dunes on Anholt, Denmark since AD 1560
DEFF Research Database (Denmark)
Clemmensen, Lars B; Bjørnsen, Mette; Murray, Andrew
2007-01-01
Sand dunes on the island of Anholt (Denmark) in the middle of Kattegat form a relatively barren, temperate climate Aeolian system, locally termed the "Desert". The dunes have developed on top of a raised beach ridge system under the influence of dominant winds from westerly directions. They are r......Sand dunes on the island of Anholt (Denmark) in the middle of Kattegat form a relatively barren, temperate climate Aeolian system, locally termed the "Desert". The dunes have developed on top of a raised beach ridge system under the influence of dominant winds from westerly directions....... They are relatively coarse-grained with an average mean grain size of 480 µm. The last phase of aeolian activity and dune formation on Anholt started after AD 1560, when the local pine forest was removed. Historical sources report intense sand mobilization in the 17th century, and new optically stimulated...... in the beginning of the 20th century probably records a temporary decrease in storminess. Ground-penetrating radar mapping of the internal structures in two dunes in the western part of the Desert (a parabolic dune and a linear dune) indicates the importance of north-westerly (storm) winds during dune formation...
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Jacobberger, P. A.; Hooper, D. M.
1991-01-01
Seasonal reflectance variations in semigrid environments provide a means of assessing vegetation health and density as well as monitoring landform processes. Multitemporal Landsat Thematic Mapper scenes with field measurements are used to map geomorphology and vegetation density in a stabilized dune environment and to measure seasonal reflectance changes for a series of ten geomorphological and vegetation units on the Kalahari-age linear dunes. Units were chosen based on differences in landform and proportion of trees, forbs and bare soil. Reflectance curves and normalized-difference vegetation indices (NDVI) show that dune crests have the strongest seasonal variability in color and brightness. The geomorphological link with reflectance and NDVI values are linked to biomass production and zoning of vegetation with slope, drainage and subtle soil differences.
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Fan, Baoli; McHugh, Allen David; Guo, Shujiang; Ma, Quanlin; Zhang, Jianhui; Zhang, Xiaojuan; Zhang, Weixing; Du, Juan; Yu, Qiushi; Zhao, Changming
2018-03-01
Calligonum mongolicum is a successful pioneer shrub to combat desertification, which is widely used for vegetation restoration in the desert regions of northwest China. In order to reveal the limitations to natural regeneration of C. mongolicum by asexual and sexual reproduction, following the process of sand dune stabilization, we assessed clonal shoots, seedling emergence, soil seed bank density, and soil physical characteristics in mobile and stabilized sand dunes. Controlled field and pot experiments were also conducted to assess germination and seedling emergence in different dune soil types and seed burial depths. The population density of mature C. mongolicum was significantly different after sand dune stabilization. Juvenile density of C. mongolicm was much lower in stabilized sand dunes than mobile sand dune. There was no significant difference in soil seed bank density at three soil depths between mobile and stabilized sand dunes, while the emergence of seedlings in stabilized dunes was much lower than emergence in mobile dunes. There was no clonal propagation found in stabilized dunes, and very few C. mongolicum seedlings were established on stabilized sand dunes. Soil clay and silt content, air-filled porosity, and soil surface compaction were significantly changed from mobile sand dune to stabilized dunes. Seedling emergence of C. mongolicm was highly dependent on soil physical condition. These results indicated that changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural regeneration in stabilized sand dunes. Therefore, clonal propagation may be the most important mode for population expansion in mobile sand dunes. As a pioneer species C. mongolicum is well adapted to propagate in mobile sand dune conditions, it appears unlikely to survive naturally in
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Coexistence of Dunes and Humid Conditions at Titan's Tropics
Radebaugh, Jani; Lorenz, R. D.; Lunine, J. I.; Kirk, R. L.; Ori, G. G.; Farr, T. G.; Malaska, M.; Le Gall, A.; Liu, Z. Y. C.; Encrenaz, P. J.; Paillou, P.; Hayes, A.; Lopes, R. M. C.; Turtle, E. P.; Wall, S. D.; Stofan, E. R.; Wood, C. A.; Cassini RADAR Team
2012-10-01
At Titan's equatorial latitudes there are tens of thousands of dunes, a landform typical of desert environments where sand does not become anchored by vegetation or fluids. Model climate simulations predict generally dry conditions at the equator and humid conditions near the poles of Titan, where lakes of methane/ethane are found. However, moderate relative methane humidity was observed at the Huygens landing site, recent rainfall was seen by Cassini ISS near the Belet Sand Sea, and a putative transient lake in Shangri-La was observed by Cassini VIMS, all of which indicate abundant fluids may be present, at least periodically, at Titan's equatorial latitudes. Terrestrial observations and studies demonstrate dunes can exist and migrate in conditions of high humidity. Active dunes are found in humid climates, indicating the movement of sand is not always prohibited by the presence of fluids. Sand mobility is related to precipitation, evaporation and wind speed and direction. If dune surfaces become wetted by rainfall or rising subsurface fluids, they can become immobilized. However, winds can act to dry the uppermost layers, freeing sands for saltation and enabling dune migration in wet conditions. Active dunes are found in tropical NE Brazil and NE Australia, where there are alternating dry and wet periods, a condition possible for Titan's tropics. Rising and falling water levels lead to the alteration of dune forms, mainly from being anchored by vegetation, but also from cementation by carbonates or clays. Studies of Titan's dunes, which could undergo anchoring of organic sediments by hydrocarbon fluids, could inform the relative strength of vegetation vs. cementation at humid dune regions on Earth. Furthermore, a comprehensive survey of dune morphologies near regions deemed low by SARTopo and stereo, where liquids may collect in wet conditions, could reveal if bodies of liquid have recently existed at Titan's tropics.
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Forman, S. L.; Spaeth, M.; Marín, L.; Pierson, J.; Gómez, J.; Bunch, F.; Valdez, A.
2006-07-01
The Great Sand Dunes National Park and Preserve (GSDNPP) in the San Luis Valley, Colorado, contains a variety of eolian landforms that reflect Holocene drought variability. The most spectacular is a dune mass banked against the Sangre de Cristo Mountains, which is fronted by an extensive sand sheet with stabilized parabolic dunes. Stratigraphic exposures of parabolic dunes and associated luminescence dating of quartz grains by single-aliquot regeneration (SAR) protocols indicate eolian deposition of unknown magnitude occurred ca. 1290-940, 715 ± 80, 320 ± 30, and 200-120 yr ago and in the 20th century. There are 11 drought intervals inferred from the tree-ring record in the past 1300 yr at GSDNPP potentially associated with dune movement, though only five eolian depositional events are currently recognized in the stratigraphic record. There is evidence for eolian transport associated with dune movement in the 13th century, which may coincide with the "Great Drought", a 26-yr-long dry interval identified in the tree ring record, and associated with migration of Anasazi people from the Four Corners areas to wetter areas in southern New Mexico. This nascent chronology indicates that the transport of eolian sand across San Luis Valley was episodic in the late Holocene with appreciable dune migration in the 8th, 10-13th, and 19th centuries, which ultimately nourished the dune mass against the Sangre de Cristo Mountains.
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Directory of Open Access Journals (Sweden)
Diana G Cuadrado
2012-03-01
Full Text Available Se estudió la morfología de un campo de dunas submarinas desarrollado en una entrada de marea que conecta la plataforma continental argentina con bahía Anegada (sur de la provincia de Buenos Aires. Se infiere la circulación sedimentaria a partir del desplazamiento diferencial de las geoformas medido en relevamientos consecutivos. Como parte de la metodología se utilizó un ecosonda y un sistema batimétrico por medición de fase (SBMF denominado GeoSwath que permitieron obtener la morfología submarina en detalle. Se observaron dunas grandes sobre el límite sur del campo de dunas con altura entre 4,5 y 5,0 m y espaciamiento entre 100 y 120 m, a profundidades de 24 m, que se desplazan hacia el exterior del canal a una rapidez entre 18 y 75 m año-1. Hacia el límite norte del campo, a 21 m de profundidad las dunas eran de menor magnitud, entre 2,0 y 2,5 m de altura y espaciamiento entre 40 y 80 m, y se desplazaron a una rapidez entre 18 y 36 m año-1 hacia el interior de bahía Anegada. Se obtuvo la distribución del flujo de agua en toda la columna, en un perfil perpendicular al canal relevado, mediante ADCP. Los valores máximos de rapidez de corriente fueron durante la marea creciente, alcanzando 2,0 m s-1. Los resultados obtenidos permiten definir un modelo circulatorio de transporte de sedimentos arenosos, con la formación de un delta de marea de flujo en la cabecera de la entrada de marea y un delta de reflujo en el límite del dominio oceánico, unidos por una garganta de marea profunda, exenta de sedimentos inconsolidados.The morphology of a submarine dune field developed in a tidal inlet that connects the Argentinean continental shelf with Anegada Bay (southern Buenos Aires province was studied. The sediment circulation was inferred from the differential displacements of the bedforms evaluated by comparing consecutive surveys. An echosounder and a Phase Measuring Bathymetric System (PMBS called GeoSwath were used to obtain a
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Energy Technology Data Exchange (ETDEWEB)
Strait, James [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); McCluskey, Elaine [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Lundin, Tracy [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Willhite, Joshua [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Hamernik, Thomas [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Papadimitriou, Vaia [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Marchionni, Alberto [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Kim, Min Jeong [National Inst. of Nuclear Physics (INFN), Frascati (Italy). National Lab. of Frascati (INFN-LNF); Nessi, Marzio [Univ. of Geneva (Switzerland); Montanari, David [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Heavey, Anne [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
2016-01-21
This volume of the LBNF/DUNE Conceptual Design Report covers the Long-Baseline Neutrino Facility for DUNE and describes the LBNF Project, which includes design and construction of the beamline at Fermilab, the conventional facilities at both Fermilab and SURF, and the cryostat and cryogenics infrastructure required for the DUNE far detector.
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Large-eddy simulation of sand dune morphodynamics
Khosronejad, Ali; Sotiropoulos, Fotis; St. Anthony Falls Laboratory, University of Minnesota Team
2015-11-01
Sand dunes are natural features that form under complex interaction between turbulent flow and bed morphodynamics. We employ a fully-coupled 3D numerical model (Khosronejad and Sotiropoulos, 2014, Journal of Fluid Mechanics, 753:150-216) to perform high-resolution large-eddy simulations of turbulence and bed morphodynamics in a laboratory scale mobile-bed channel to investigate initiation, evolution and quasi-equilibrium of sand dunes (Venditti and Church, 2005, J. Geophysical Research, 110:F01009). We employ a curvilinear immersed boundary method along with convection-diffusion and bed-morphodynamics modules to simulate the suspended sediment and the bed-load transports respectively. The coupled simulation were carried out on a grid with more than 100 million grid nodes and simulated about 3 hours of physical time of dune evolution. The simulations provide the first complete description of sand dune formation and long-term evolution. The geometric characteristics of the simulated dunes are shown to be in excellent agreement with observed data obtained across a broad range of scales. This work was supported by NSF Grants EAR-0120914 (as part of the National Center for Earth-Surface Dynamics). Computational resources were provided by the University of Minnesota Supercomputing Institute.
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DETECTION OF BARCHAN DUNES IN HIGH RESOLUTION SATELLITE IMAGES
Directory of Open Access Journals (Sweden)
M. A. Azzaoui
2016-06-01
Full Text Available Barchan dunes are the fastest moving sand dunes in the desert. We developed a process to detect barchans dunes on High resolution satellite images. It consisted of three steps, we first enhanced the image using histogram equalization and noise reduction filters. Then, the second step proceeds to eliminate the parts of the image having a texture different from that of the barchans dunes. Using supervised learning, we tested a coarse to fine textural analysis based on Kolomogorov Smirnov test and Youden’s J-statistic on co-occurrence matrix. As an output we obtained a mask that we used in the next step to reduce the search area. In the third step we used a gliding window on the mask and check SURF features with SVM to get barchans dunes candidates. Detected barchans dunes were considered as the fusion of overlapping candidates. The results of this approach were very satisfying in processing time and precision.
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2006-01-01
[figure removed for brevity, see original site] Context image for PIA03291 Frost-free Dunes These dark dunes are frost covered for most of the year. As southern summer draws to a close, the dunes have been completely defrosted. Image information: VIS instrument. Latitude -66.6N, Longitude 37.0E. 34 meter/pixel resolution. Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.
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Siegal, Z.; Tsoar, H.; Karnieli, A.
2013-06-01
Luminescence dating of stable sand dunes in the large deserts of the world has shown several episodes of mobility during the last 30 k years. The logical explanation for the mobility of fixed dunes is severe drought. Though drought length can be estimated, the level of precipitation drop is unknown. The stabilized sand dunes of the northwestern Negev Desert, Israel have been under an unprecedented prolonged drought since 1995. This has resulted in a vast decrease of shrubs cover on the fixed sand dunes, which changes along the rainfall gradient. In the north, an average of 27% of the shrubs had wilted by 2009, and in the drier southern area, 68% of the shrubs had withered. This loss of shrubbery is not expected to induce dune remobilization because the existing bio-crust cover is not negatively affected by the drought. Eleven aerial photographs taken over the drier southern area from 1956 to 2005 show the change in shrub cover due to human impact and the recent severe drought.
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Mughal, Iqra
2013-05-01
In arid lands, a major contribution to water loss is by soil water evaporation. Desert sand dunes in arid regions are devoid of runoff and have high rates of infiltration. Rainwater is commonly stored within them because of the low permeability soils in the underlying desert pavement. In such cases, moisture is confined in the sand dune below a depth, termed as the “extinction depth”, where it is protected from evaporation during long dry periods. Moreover, desert sand dunes have sparse vegetation, which results in low transpiration losses from the stored water. The water accumulated below the extinction depth of the sand dunes can be utilized for various purposes such as in irrigation to support desert agriculture. In this study, field experiments were conducted in Western Saudi Arabia to monitor the soil moisture gradients and determine the diffusive extinction depth of dune sand. The dune sand was saturated with water and was exposed to natural conditions (evaporation and precipitation). The decline of the water level in the sand column was continuously recorded using transducers and sensors installed at different depths monitored the temporal variation of temperature and moisture content within the sand. The hydrological simulator HYDRUS-1D was used to construct the vertical profiles of soil water content and temperature and the results obtained from HYDRUS-1D were compared to the gradients monitored by the sensors.
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Chiu, Pin-Jung
In search of answers to the biggest missing puzzle in the field of neutrino physics, large- scale Liquid Argon Time Projection Chambers (LAr-TPCs) have been postulated to be the most attractive instruments for next generation neutrino observations. A state-of-the- art experiment, the Deep Underground Neutrino Experiment (DUNE), which will utilize this LAr-TPC technology for the studies of neutrino science and proton decay, is currently in the stage of design and prototyping. This thesis reports on the behavior studies of a 6 × 6 × 6 m^3 prototype, ProtoDUNE, in the context of DUNE from the electrostatic’s point of view. Electrostatic simulations had been performed on the whole detector in order to verify the uniformity of the electric field, and to assure that all local electric fields within the detector are below a certain value to avoid any electrical breakdown phenomena. Additionally, to characterize the performance of the 2D anode used for charge readout in the experiment, some simulations and measur...
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Probabilistic estimation of dune retreat on the Gold Coast, Australia
Palmsten, Margaret L.; Splinter, Kristen D.; Plant, Nathaniel G.; Stockdon, Hilary F.
2014-01-01
Sand dunes are an important natural buffer between storm impacts and development backing the beach on the Gold Coast of Queensland, Australia. The ability to forecast dune erosion at a prediction horizon of days to a week would allow efficient and timely response to dune erosion in this highly populated area. Towards this goal, we modified an existing probabilistic dune erosion model for use on the Gold Coast. The original model was trained using observations of dune response from Hurricane Ivan on Santa Rosa Island, Florida, USA (Plant and Stockdon 2012. Probabilistic prediction of barrier-island response to hurricanes, Journal of Geophysical Research, 117(F3), F03015). The model relates dune position change to pre-storm dune elevations, dune widths, and beach widths, along with storm surge and run-up using a Bayesian network. The Bayesian approach captures the uncertainty of inputs and predictions through the conditional probabilities between variables. Three versions of the barrier island response Bayesian network were tested for use on the Gold Coast. One network has the same structure as the original and was trained with the Santa Rosa Island data. The second network has a modified design and was trained using only pre- and post-storm data from 1988-2009 for the Gold Coast. The third version of the network has the same design as the second version of the network and was trained with the combined data from the Gold Coast and Santa Rosa Island. The two networks modified for use on the Gold Coast hindcast dune retreat with equal accuracy. Both networks explained 60% of the observed dune retreat variance, which is comparable to the skill observed by Plant and Stockdon (2012) in the initial Bayesian network application at Santa Rosa Island. The new networks improved predictions relative to application of the original network on the Gold Coast. Dune width was the most important morphologic variable in hindcasting dune retreat, while hydrodynamic variables, surge and
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Late Pleistocene dune activity in the central Great Plains, USA
Mason, J.A.; Swinehart, J.B.; Hanson, P.R.; Loope, D.B.; Goble, R.J.; Miao, X.; Schmeisser, R.L.
2011-01-01
Stabilized dunes of the central Great Plains, especially the megabarchans and large barchanoid ridges of the Nebraska Sand Hills, provide dramatic evidence of late Quaternary environmental change. Episodic Holocene dune activity in this region is now well-documented, but Late Pleistocene dune mobility has remained poorly documented, despite early interpretations of the Sand Hills dunes as Pleistocene relicts. New optically stimulated luminescence (OSL) ages from drill cores and outcrops provide evidence of Late Pleistocene dune activity at sites distributed across the central Great Plains. In addition, Late Pleistocene eolian sands deposited at 20-25 ka are interbedded with loess south of the Sand Hills. Several of the large dunes sampled in the Sand Hills clearly contain a substantial core of Late Pleistocene sand; thus, they had developed by the Late Pleistocene and were fully mobile at that time, although substantial sand deposition and extensive longitudinal dune construction occurred during the Holocene. Many of the Late Pleistocene OSL ages fall between 17 and 14 ka, but it is likely that these ages represent only the later part of a longer period of dune construction and migration. At several sites, significant Late Pleistocene or Holocene large-dune migration also probably occurred after the time represented by the Pleistocene OSL ages. Sedimentary structures in Late Pleistocene eolian sand and the forms of large dunes potentially constructed in the Late Pleistocene both indicate sand transport dominated by northerly to westerly winds, consistent with Late Pleistocene loess transport directions. Numerical modeling of the climate of the Last Glacial Maximum has often yielded mean monthly surface winds southwest of the Laurentide Ice Sheet that are consistent with this geologic evidence, despite strengthened anticyclonic circulation over the ice sheet. Mobility of large dunes during the Late Pleistocene on the central Great Plains may have been the result of
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Non-equilibrium flow and sediment transport distribution over mobile river dunes
Hoitink, T.; Naqshband, S.; McElroy, B. J.
2017-12-01
Flow and sediment transport are key processes in the morphodynamics of river dunes. During floods in several rivers (e.g., the Elkhorn, Missouri, Niobrara, and Rio Grande), dunes are observed to grow rapidly as flow strength increases, undergoing an unstable transition regime, after which they are washed out in what is called upper stage plane bed. This morphological evolution of dunes to upper stage plane bed is the strongest bed-form adjustment during non-equilibrium flows and is associated with a significant change in hydraulic roughness and water levels. Detailed experimental investigations, however, have mostly focused on fixed dunes limited to equilibrium flow and bed conditions that are rare in natural channels. Our understanding of the underlying sedimentary processes that result into the washing out of dunes is therefore very limited. In the present study, using the Acoustic Concentration and Velocity Profiler (ACVP), we were able to quantify flow structure and sediment transport distribution over mobile non-equilibrium dunes. Under these non-equilibrium flow conditions average dune heights were decreasing while dune lengths were increasing. Preliminary results suggest that this morphological behaviour is due to a positive phase lag between sediment transport maximum and topographic maximum leading to a larger erosion on the dune stoss side compared to deposition on dune lee side.
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van Puijenbroek, Marinka E B; Teichmann, Corry; Meijdam, Noortje; Oliveras, Imma; Berendse, Frank; Limpens, Juul
2017-09-01
Rising sea levels threaten coastal safety by increasing the risk of flooding. Coastal dunes provide a natural form of coastal protection. Understanding drivers that constrain early development of dunes is necessary to assess whether dune development may keep pace with sea-level rise. In this study, we explored to what extent salt stress experienced by dune building plant species constrains their spatial distribution at the Dutch sandy coast. We conducted a field transplantation experiment and a glasshouse experiment with two dune building grasses Ammophila arenaria and Elytrigia juncea . In the field, we measured salinity and monitored growth of transplanted grasses in four vegetation zones: (I) nonvegetated beach, (II) E. juncea occurring, (III) both species co-occurring, and (IV) A. arenaria dominant. In the glasshouse, we subjected the two species to six soil salinity treatments, with and without salt spray. We monitored biomass, photosynthesis, leaf sodium, and nutrient concentrations over a growing season. The vegetation zones were weakly associated with summer soil salinity; zone I and II were significantly more saline than zones III and IV. Ammophila arenaria performed equally (zone II) or better (zones III, IV) than E. juncea , suggesting soil salinity did not limit species performance. Both species showed severe winter mortality. In the glasshouse, A. arenaria biomass decreased linearly with soil salinity, presumably as a result of osmotic stress. Elytrigia juncea showed a nonlinear response to soil salinity with an optimum at 0.75% soil salinity. Our findings suggest that soil salinity stress either takes place in winter, or that development of vegetated dunes is less sensitive to soil salinity than hitherto expected.
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Impacts of storm chronology on the morphological changes of the Formby beach and dune system, UK
Dissanayake, P.; Brown, J.; Karunarathna, H.
2015-07-01
Impacts of storm chronology within a storm cluster on beach/dune erosion are investigated by applying the state-of-the-art numerical model XBeach to the Sefton coast, northwest England. Six temporal storm clusters of different storm chronologies were formulated using three storms observed during the 2013/2014 winter. The storm power values of these three events nearly halve from the first to second event and from the second to third event. Cross-shore profile evolution was simulated in response to the tide, surge and wave forcing during these storms. The model was first calibrated against the available post-storm survey profiles. Cumulative impacts of beach/dune erosion during each storm cluster were simulated by using the post-storm profile of an event as the pre-storm profile for each subsequent event. For the largest event the water levels caused noticeable retreat of the dune toe due to the high water elevation. For the other events the greatest evolution occurs over the bar formations (erosion) and within the corresponding troughs (deposition) of the upper-beach profile. The sequence of events impacting the size of this ridge-runnel feature is important as it consequently changes the resilience of the system to the most extreme event that causes dune retreat. The highest erosion during each single storm event was always observed when that storm initialised the storm cluster. The most severe storm always resulted in the most erosion during each cluster, no matter when it occurred within the chronology, although the erosion volume due to this storm was reduced when it was not the primary event. The greatest cumulative cluster erosion occurred with increasing storm severity; however, the variability in cumulative cluster impact over a beach/dune cross section due to storm chronology is minimal. Initial storm impact can act to enhance or reduce the system resilience to subsequent impact, but overall the cumulative impact is controlled by the magnitude and number
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Dune Morphodynamics on a Semi-Arid, Wave-Dominated Barrier Island: South Padre Island, Texas
Del Angel, D. C.; Gibeaut, J. C.
2012-12-01
Spatial and temporal dune accretion along the barrier island of South Padre Island (SPI),Texas was examined using a combination of field measurements and lidar elevation data. Volume change rates derived from the data were compared to potential sediment transport rates derived from Hsu's (1974 & 1977) model using local wind-gauge data. A statistical model was then used to investigate controls on foredune accretion. Dune volume change was estimated from cross-shore profile measurements acquired during the summer of 2009, spring of 2010, and fall of 2010. For summer 2009 to spring 2010, dune volume change ranged from -18 to 12.5 m^3/m. The onshore potential drift for the same time period was estimated to be 6.6 m^3/m. In comparison, volume change ranged from -5.5 to 5.3 m^3/m for spring to fall 2010 with most dunes experiencing erosion. The estimated onshore drift was much higher at 22.5 m^3/m. The high drift potential associated with the spring and summer months is attributed to the predominant wind direction and the occurrence of tropical storms. Dune volume change was also observed on a longer time scale using lidar DEMs for the years 2000, 2005, and 2009. From 2000 to 2005, most natural dunes experienced accretion with a mean of 17.67 m^3/m, whereas between 2005 and 2009, the majority of dunes experienced volume loss with a mean change of -4.16 m^3/m. Overall, the mean volume change from 2000 to 2009 was 13.51 m^3/m. Onshore drift for 2000 to 2005 was estimated to be 16.44 m^3/m, which is a good approximation to the observed volume change. In contrast, onshore drift for 2000 to 2009 was estimated to be 80.4 m^3/m, which is substantially higher than the mean volume change observed during the period. The discrepancy between the modeled and observe value is partly due to dune volume loss from storm surge erosion. In addition, there was a significant increase in onshore drift potential from 2006 to 2008. Stepwise backward regression was used to find significant
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Delgado-Fernandez, I.; Jackson, D.; Cooper, J. A.; Baas, A. C.; Lynch, K.; Beyers, M.
2010-12-01
Airflow separation, lee-side eddies and secondary flows play an essential role on the formation and maintenance of sand dunes. Downstream from dune crests the flow surface layer detaches from the ground and generates an area characterised by turbulent eddies in the dune lee slope (the wake). At some distance downstream from the dune crest, flow separates into a reversed component directed toward the dune toe and an offshore “re-attached” component. This reattachment zone (RZ) has been documented in fluvial and desert environments, wind tunnel experiments and numerical simulations, but not yet characterised in coastal dunes. This study examines the extent and temporal evolution of the RZ and its implications for beach-dune interaction at Magilligan, Northern Ireland. Wind parameters were measured over a profile extending from an 11 m height dune crest towards the beach, covering a total distance of 65 m cross-shore. Data was collected using an array of nine ultrasonic anemometers (UAs) deployed in April-May 2010, as part of a larger experiment to capture airflow data under a range of incident wind velocities and offshore directions. UAs were located along the profile (5 m tower spacing) over the beach, which allowed a detailed examination of the RZ with empirical data. Numerical modelling using Computational Fluid Dynamics (CFD) software was also conducted with input data from anemometer field measurements, running over a surface mesh generated from LiDAR and DGPS surveys. Results demonstrate that there is a wind threshold of approximately 5-6 ms-1 under which no flow separation exists with offshore winds. As wind speed increases over the threshold, a flow reversal area is quickly formed, with the maximum extent of the RZ at approximately 3.5 dune heights (h). The maximum extent of the RZ increases up to 4.5h with stronger wind speeds of 8-10 ms-1 and remains relatively constant as wind speed further increases. This suggests that the spatial extent of the RZ is
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Quantifying thresholds for significant dune erosion along the Sefton Coast, Northwest England
Esteves, Luciana S.; Brown, Jennifer M.; Williams, Jon J.; Lymbery, Graham
2012-03-01
Field and model hindcast data are used to establish a critical dune erosion threshold for the Sefton Coast (NW England). Events are classified as causing significant erosion if they result in: (a) a mean dune retreat along the entire study area of > 2 m; (b) a dune retreat of ≥ 5 m along a coastal segment ≥ 2 km in length; and (c) an eroded area ≥ 20,000 m2. For the period 1996 to 2008, individual storms were characterised using hindcast results from a POLCOMS-WAM model and measured data from the Liverpool Bay Coastal Observatory. Results show that combined extreme surge levels (> 1.5 m) and wave heights (> 4 m), or tidal water levels above 9.0 m Chart Datum (CD), do not always result in significant dune erosion. Evidence suggests that erosion is more likely to occur when wave heights are > 2.6 m, peak water level is > 10.2 m CD at Liverpool and when consecutive tidal cycles provide 10 h or more of water levels above 9.4 m CD. However, lower water levels and wave heights, and shorter events of sustained water levels, can cause significant erosion in the summer. While the return period for events giving rise to the most severe erosion in the winter is > 50 years, significant erosion in the summer can be caused by events with return periods dune toe elevation c. 30 cm. Although the study shows it might be possible to characterise objectively storm events based on oceanographic conditions, the resultant morphological change at the coast is demonstrated to depend on the time and duration of events, and on other variables which are not so easy to quantify. Further investigation is needed to understand the influence of alongshore and seasonal variability in beach/dune morphology in determining the response to the hydrodynamic and meteorological conditions causing significant erosion. Improved monitoring pre- and post-storm of changes in beach/dune morphology is required to develop reliable proxies that can be used to establish early warning systems to mitigate the
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Turbulence and sediment transport over sand dunes and ripples
Bennis, A.; Le Bot, S.; lafite, R.; Bonneton, P.; Ardhuin, F.
2013-12-01
Several bedforms are present near to the surfzone of natural beaches. Dunes and ripples are frequently observed. Understanding the turbulence over these forms is essential for the sediment transport. The turbulent flow and the suspended sand particles interact with each other. At the moment, the modelling strategy for turbulence is still a challenge. According to the spatial scales, some different methods to model the turbulence are employed, in particular the RANS (Reynolds Averaged Navier-Stokes) and the LES (Large Eddy Simulation). A hybrid method combining both RANS and LES is set up here. We have adapted this method, initially developed for atmospheric flow, to the oceanic flow. This new method is implemented inside the 3D hydrodynamic model, MARS 3D, which is forced by waves. LES is currently the best way to simulate turbulent flow but its higher cost prevents it from being used for large scale applications. So, here we use RANS near the bottom while LES is set elsewhere. It allows us minimize the computational cost and ensure a better accuracy of the results than with a fully RANS model. In the case of megaripples, the validation step was performed with two sets of field data (Sandy Duck'97 and Forsoms'13) but also with the data from Dune2D model which uses only RANS for turbulence. The main findings are: a) the vertical profiles of the velocity are similar throughout the data b) the turbulent kinetic energy, which was underestimated by Dune2D, is in line with the observations c) the concentration of the suspended sediment is simulated with a better accuracy than with Dune2D but this remains lower than the observations.
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Rupert, Michael G.; Plummer, Niel
2004-01-01
Great Sand Dunes National Monument is located in south-central Colorado along the eastern edge of the San Luis Valley. The Great Sand Dunes National Monument contains the tallest sand dunes in North America; some rise up to750 feet. Important ecological features of the Great Sand Dunes National Monument are palustrine wetlands associated with interdunal ponds and depressions along the western edge of the dune field. The existence and natural maintenance of the dune field and the interdunal ponds are dependent on maintaining ground-water levels at historic elevations. To address these concerns, the U.S. Geological Survey conducted a study, in collaboration with the National Park Service, of ground-water flow direction, water quality, recharge sources, and age at the Great Sand Dunes National Monument. A shallow unconfined aquifer and a deeper confined aquifer are the two principal aquifers at the Great Sand Dunes National Monument. Ground water in the unconfined aquifer is recharged from Medano and Sand Creeks near the Sangre de Cristo Mountain front, flows underneath the main dune field, and discharges to Big and Little Spring Creeks. The percentage of calcium in ground water in the unconfined aquifer decreases and the percentage of sodium increases because of ionic exchange with clay minerals as the ground water flows underneath the dune field. It takes more than 60 years for the ground water to flow from Medano and Sand Creeks to Big and Little Spring Creeks. During this time, ground water in the upper part of the unconfined aquifer is recharged by numerous precipitation events. Evaporation of precipitation during recharge prior to reaching the water table causes enrichment in deuterium (2H) and oxygen-18 (18O) relative to waters that are not evaporated. This recharge from precipitation events causes the apparent ages determined using chlorofluorocarbons and tritium to become younger, because relatively young precipitation water is mixing with older waters
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Zooming in on neutrino oscillations with DUNE
Srivastava, Rahul; Ternes, Christoph A.; Tórtola, Mariam; Valle, José W. F.
2018-05-01
We examine the capabilities of the DUNE experiment as a probe of the neutrino mixing paradigm. Taking the current status of neutrino oscillations and the design specifications of DUNE, we determine the experiment's potential to probe the structure of neutrino mixing and C P violation. We focus on the poorly determined parameters θ23 and δC P and consider both two and seven years of run. We take various benchmarks as our true values, such as the current preferred values of θ23 and δC P, as well as several theory-motivated choices. We determine quantitatively DUNE's potential to perform a precision measurement of θ23, as well as to test the C P violation hypothesis in a model-independent way. We find that, after running for seven years, DUNE will make a substantial step in the precise determination of these parameters, bringing to quantitative test the predictions of various theories of neutrino mixing.
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1999-01-01
MOC image of dunes in Chasma Boreale, a giant trough in the north polar cap. This September 1998 view shows dark sand emergent from beneath a veneer of bright frost left over from the northern winter that ended in July 1998.
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International Nuclear Information System (INIS)
Remke, Eva; Brouwer, Emiel; Kooijman, Annemieke; Blindow, Irmgard; Esselink, Hans; Roelofs, Jan G.M.
2009-01-01
Coastal dunes around the Baltic Sea have received small amounts of atmospheric nitrogen and are rather pristine ecosystems in this respect. In 19 investigated dune sites the atmospheric wet nitrogen deposition is 3-8 kg N ha -1 yr -1 . The nitrogen content of Cladonia portentosa appeared to be a suitable biomonitor of these low to medium deposition levels. Comparison with EMEP-deposition data showed that Cladonia reflects the deposition history of the last 3-6 years. With increasing nitrogen load, we observed a shift from lichen-rich short grass vegetation towards species-poor vegetation dominated by the tall graminoid Carex arenaria. Plant species richness per field site, however, does not decrease directly with these low to medium N deposition loads, but with change in vegetation composition. Critical loads for acidic, dry coastal dunes might be lower than previously thought, in the range of 4-6 kg N ha -1 yr -1 wet deposition. - Even low to medium nitrogen deposition impacts Baltic dune vegetation promoting a dominance of taller graminoids
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Dating pleistocene fossil coastal sand dunes by thermoluminescence
International Nuclear Information System (INIS)
Poupeau, G.; Souza, J.H.; Soliani Junior, E.; Loss, E.L.
1983-01-01
It was shown recently that sunlight exposure is able to bleach most of the geological thermoluminescence (TL) of wind transported sediments. This property has been used in an attempt to date dunes from the well developed recent quaternary coastal dunes system of Rio Grande do Sul. Preliminary results presented here, show that TL dating on fossil sand dunes from Rio Grande do Sul should be possible in a time range from present to at least 50.000 yr and possibly more than 100.000 yr. (Author) [pt
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Natural versus Urban dunes along the Emilia-Romagna coast, Northern Adriatic (Italy)
Corbau, Corinne; Simeoni, Umberto
2014-05-01
Beach-dune interaction models can be precious tools for land managers and policymakers. However, if the models are inaccurate, land use policies may be designed based on false pretences or assumptions leading to poor land management, long-term erosion and sustainability issues, and increased difficulties in maintaining the dynamic coastal systems. From the literature, it appears that even the most reliable beach-dunes interactions models are not applicable to all coastal systems (Short and Hesp, 1982; Psuty, 1988; Sherman and Bauer, 1993). The study aims to identify the morphological evolution of the Emilia-Romagna coastal dunes according to its natural and "human" characteristics and to classify groups of dunes with similar evolutionary patterns. The coastal area consists essentially of 130 km of low sandy coast, interrupted by vast lagoon areas, harbor jetties and numerous hard coastal defense structures that were built during the first half of the 20th century to protect the Emilia-Romagna coast against erosion. Today about 57% of the littoral is protected by hard defenses, which have modified the morphodynamic characteristics of the beach without inverting the negative coastal evolution's trend. From recent aerial photographs (2011), 62 coastal dunes have been identified and mapped. Furthermore, the dune analysis shows a variability of the "physical characteristics" of coastal-dune systems along the Emilia-Romagna coast. The dune height varies from 1 to 7 meters, the width of the beach and of the active dunes range respectively from 10 to 150 m and from 10 to 65 m. Three main factors may explain the variability of the "physical characteristics": 1- Firstly the frontal dunes may be of different states according to the classification of Hesp (2002) since they correspond to incipient foredunes, well-developed foredunes, blowouts, residual foredunes as well as reactivated relict foredunes, 2- This could also be related to a different orientation of the coastline
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Insect biodiversity of the Algodones Dunes of California
Directory of Open Access Journals (Sweden)
Lynn Kimsey
2017-11-01
Full Text Available Over a nine year period beginning in 2007 we surveyed the insects of the Algodones Dunes, Imperial Count, California, as part of a study undertaken for the U.S. Bureau of Land Management. In a series of 22 collecting trips ranging in duration from 2 to 8 days we thus far have accumulated records of 1,840 species, 21 orders and 244 families from the dunes. Hymenoptera constituted the most diverse order, comprising about 45% of all the species recovered. Insect diversity and abundance peaked during the hottest part of the year between the months of May and September. Life history traits of the insects sampled included herbivores (29.6%, parasitoids (28.7%, predators (18.1%, pollen/nectar feeders (10.9%, detritivores (6.2% and scavengers (2.4%. Seventy-nine or 4% of the insect species collected in the dunes have been solely recorded from there, and 3% of the species almost certainly derive from adjacent aquatic habitats or agricultural ecosystems, as their life histories could not be completed in Algodones Dunes habitat. The insect fauna of the Algodones Dunes is unexpectedly rich and diverse.
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Linking restoration ecology with coastal dune restoration
Lithgow, D.; Martínez, M. L.; Gallego-Fernández, J. B.; Hesp, P. A.; Flores, P.; Gachuz, S.; Rodríguez-Revelo, N.; Jiménez-Orocio, O.; Mendoza-González, G.; Álvarez-Molina, L. L.
2013-10-01
Restoration and preservation of coastal dunes is urgently needed because of the increasingly rapid loss and degradation of these ecosystems because of many human activities. These activities alter natural processes and coastal dynamics, eliminate topographic variability, fragment, degrade or eliminate habitats, reduce diversity and threaten endemic species. The actions of coastal dune restoration that are already taking place span contrasting activities that range from revegetating and stabilizing the mobile substrate, to removing plant cover and increasing substrate mobility. Our goal was to review how the relative progress of the actions of coastal dune restoration has been assessed, according to the ecosystem attributes outlined by the Society of Ecological Restoration: namely, integrity, health and sustainability and that are derived from the ecological theory of succession. We reviewed the peer reviewed literature published since 1988 that is listed in the ISI Web of Science journals as well as additional references, such as key books. We exclusively focused on large coastal dune systems (such as transgressive and parabolic dunefields) located on natural or seminatural coasts. We found 150 articles that included "coastal dune", "restoration" and "revegetation" in areas such as title, keywords and abstract. From these, 67 dealt specifically with coastal dune restoration. Most of the studies were performed in the USA, The Netherlands and South Africa, during the last two decades. Restoration success has been assessed directly and indirectly by measuring one or a few ecosystem variables. Some ecosystem attributes have been monitored more frequently (ecosystem integrity) than others (ecosystem health and sustainability). Finally, it is important to consider that ecological succession is a desirable approach in restoration actions. Natural dynamics and disturbances should be considered as part of the restored system, to improve ecosystem integrity, health and
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Leicht-Young, S. A.; Pavlovic, N.B.; Grundel, R.; Frohnapple, K.J.
2009-01-01
In habitats where disturbance is frequent, seed banks are important for the regeneration of vegetation. Sand dune systems are dynamic habitats in which sand movement provides intermittent disturbance. As succession proceeds from bare sand to forest, the disturbance decreases. At Indiana Dunes National Lakeshore, we examined the seed banks of three habitat types across a successional gradient: foredunes, secondary dunes, and oak savanna. There were differences among the types of species that germinated from each of the habitats. The mean seed bank density increased across the successional gradient by habitat, from 376 to 433 to 968 seeds m-2, but with foredune and secondary dune seed bank densities being significantly lower than the savanna seed bank density. The number of seeds germinated was significantly correlated with soil organic carbon, demonstrating for this primary successional sequence that seed density increases with stage and age. The seed bank had much lower species richness than that of the aboveground vegetation across all habitats. Among sites within a habitat type, the similarity of species germinated from the seed banks was very low, illustrating the variability of the seed bank even in similar habitat types. These results suggest that restoration of these habitats cannot rely on seed banks alone. ?? 2008 Springer Science+Business Media B.V.
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Energy Technology Data Exchange (ETDEWEB)
Acciarri, R. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); et al.
2016-01-22
This document presents the Conceptual Design Report (CDR) put forward by an international neutrino community to pursue the Deep Underground Neutrino Experiment at the Long-Baseline Neutrino Facility (LBNF/DUNE), a groundbreaking science experiment for long-baseline neutrino oscillation studies and for neutrino astrophysics and nucleon decay searches. The DUNE far detector will be a very large modular liquid argon time-projection chamber (LArTPC) located deep underground, coupled to the LBNF multi-megawatt wide-band neutrino beam. DUNE will also have a high-resolution and high-precision near detector.
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Acciarri, R.; Adamowski, M.; Adams, C.; Adamson, P.; Adhikari, S.; Ahmad, Z.; Albright, C.H.; Alion, T.; Amador, E.; Anderson, J.; Anderson, K.; Andreopoulos, C.; Andrews, M.; Andrews, R.; Anghel, I.; Anjos, J. d.; Ankowski, A.; Antonello, M.; Aranda Fernandez, A.; Ariga, A.; Ariga, T.; Aristizabal, D.; Arrieta-Diaz, E.; Aryal, K.; Asaadi, J.; Asner, D.; Athar, M.S.; Auger, M.; Aurisano, A.; Aushev, V.; Autiero, D.; Avila, M.; Back, J.J.; Bai, X.; Baibussinov, B.; Baird, M.; Balantekin, B.; Baller, B.; Ballett, P.; Bambah, B.; Bansal, M.; Bansal, S.; Barker, G.J.; Barletta, W.A.; Barr, G.; Barros, N.; Bartosz, B.; Bartoszek, L.; Bashyal, A.; Bass, M.; Bay, F.; Beacom, J.; Behera, B.R.; Bellettini, G.; Bellini, V.; Beltramello, O.; Benekos, N.; Benetti, P.A.; Bercellie, A.; Bergevin, M.; Berman, E.; Berns, H.; Bernstein, R.; Bertolucci, S.; Bhandari, B.; Bhatnagar, V.; Bhuyan, B.; Bian, J.; Biery, K.; Bishai, M.; Blackburn, T.; Blake, A.; Blaszczyk, F. d. M.; Blaufuss, E.; Bleakley, B.; Blucher, E.; Bocean, V.; Boffelli, F.; Boissevain, J.; Bolognesi, S.; Bolton, T.; Bonesini, M.; Boone, T.; Booth, C.; Bordoni, S.; Borysova, M.; Bourguille, B.; Boyd, S.B.; Brailsford, D.; Brandt, A.; Bremer, J.; Brice, S.; Bromberg, C.; Brooijmans, G.; Brown, G.; Brown, R.; Brunetti, G.; Bu, X.; Buchanan, N.; Budd, H.; Bugg, B.; Calafiura, P.; Calligarich, E.; Calvo, E.; Camilleri, L.; Campanelli, M.; Cantini, C.; Carls, B.; Carr, R.; Cascella, M.; Castromonte, C.; Mur, E.Catano; Cavanna, F.; Centro, S.; Cervera Villanueva, A.; Chalifour, M.; Chandratre, V.B.; Chatterjee, A.; Chattopadhyay, S.; Chattopadhyay, S.; Chaussard, L.; Chembra, S.; Chen, H.; Chen, K.; Chen, M.; Cherdack, D.; Chi, C.; Childress, S.; Choubey, S.; Choudhary, B.C.; Christodoulou, G.; Christofferson, C.; Church, E.; Cianci, D.; Cline, D.; Coan, T.; Cocco, A.; Coelho, J.; Cole, P.; Collin, G.; Conrad, J.M.; Convery, M.; Corey, R.; Corwin, L.; Cranshaw, J.; Crivelli, P.; Cronin-Hennessy, D.; Curioni, A.; Cushing, J.; Adams, D.L.; Dale, D.; Das, S.R.; Davenne, T.; Davies, G.S.; Davies, J.; Dawson, J.; De, K.; de Gouvea, A.; de Jong, J.K.; de Jong, P.; De Lurgio, P.; Decowski, M.; Delbart, A.; Densham, C.; Dharmapalan, R.; Dhingra, N.; Di Luise, S.; Diamantopoulou, M.; Diaz, J.S.; Diaz Bautista, G.; Diwan, M.; Djurcic, Z.; Dolph, J.; Drake, G.; Duchesneau, D.; Duvernois, M.; Duyang, H.; Dwyer, D.A.; Dye, S.; Dytman, S.; Eberly, B.; Edgecock, R.; Edmunds, D.; Elliott, S.; Elnimr, M.; Emery, S.; Endress, E.; Eno, S.; Ereditato, A.; Escobar, C.O.; Evans, J.; Falcone, A.; Falk, L.; Farbin, A.; Farnese, C.; Farzan, Y.; Fava, A.; Favilli, L.; Felde, J.; Felix, J.; Fernandes, S.; Fields, L.; Finch, A.; Fitton, M.; Fleming, B.; Forest, T.; Fowler, J.; Fox, W.; Fried, J.; Friedland, A.; Fuess, S.; Fujikawa, B.; Gago, A.; Gallagher, H.; Galymov, S.; Gamble, T.; Gandhi, R.; Garcia-Gamez, D.; Gardiner, S.; Garvey, G.; Gehman, V.M.; Gendotti, A.; Geronimo, G. d.; Ghag, C.; Ghoshal, P.; Gibin, D.; Gil-Botella, I.; Gill, R.; Girardelli, D.; Giri, A.; Glavin, S.; Goeldi, D.; Golapinni, S.; Gold, M.; Gomes, R.A.; Gomez Cadenas, J.J.; Goodman, M.C.; Gorbunov, D.; Goswami, S.; Graf, N.; Graf, N.; Graham, M.; Gramelini, E.; Gran, R.; Grant, C.; Grant, N.; Greco, V.; Greenlee, H.; Greenler, L.; Greenley, C.; Groh, M.; Grullon, S.; Grundy, T.; Grzelak, K.; Guardincerri, E.; Guarino, V.; Guarnaccia, E.; Guedes, G.P.; Guenette, R.; Guglielmi, A.; Habig, A.T.; Hackenburg, R.W.; Hackenburg, A.; Hadavand, H.; Haenni, R.; Hahn, A.; Haigh, M.D.; Haines, T.; Hamernik, T.; Handler, T.; Hans, S.; Harris, D.; Hartnell, J.; Hasegawa, T.; Hatcher, R.; Hatzikoutelis, A.; Hays, S.; Hazen, E.; Headley, M.; Heavey, A.; Heeger, K.; Heise, J.; Hennessy, K.; Hewes, J.; Higuera, A.; Hill, T.; Himmel, A.; Hogan, M.; Holanda, P.; Holin, A.; Honey, W.; Horikawa, S.; Horton-Smith, G.; Howard, B.; Howell, J.; Hurh, P.; Huston, J.; Hylen, J.; Imlay, R.; Insler, J.; Introzzi, G.; Ioanisyan, D.; Ioannisian, A.; Iwamoto, K.; Izmaylov, A.; Jackson, C.; Jaffe, D.E.; James, C.; James, E.; Jediny, F.; Jen, C.; Jhingan, A.; Jimenez, S.; Jo, J.H.; Johnson, M.; Johnson, R.; Johnstone, J.; Jones, B.J.; Joshi, J.; Jostlein, H.; Jung, C.K.; Junk, T.; Kaboth, A.; Kadel, R.; Kafka, T.; Kalousis, L.; Kamyshkov, Y.; Karagiorgi, G.; Karasavvas, D.; Karyotakis, Y.; Kaur, A.; Kaur, P.; Kayser, B.; Kazaryan, N.; Kearns, E.; Keener, P.; Kemboi, S.; Kemp, E.; Kettell, S.H.; Khabibullin, M.; Khandaker, M.; Khotjantsev, A.; Kirby, B.; Kirby, M.; Klein, J.; Kobilarcik, T.; Kohn, S.; Koizumi, G.; Kopylov, A.; Kordosky, M.; Kormos, L.; Kose, U.; Kostelecky, A.; Kramer, M.; Kreslo, I.; Kriske, R.; Kropp, W.; Kudenko, Y.; Kudryavtsev, V.A.; Kulagin, S.; Kumar, A.; Kumar, G.; Kumar, J.; Kumar, L.; Kutter, T.; Laminack, A.; Lande, K.; Lane, C.; Lang, K.; Lanni, F.; Learned, J.; Lebrun, P.; Lee, D.; Lee, H.; Lee, K.; Lee, W.M.; Leigui de Oliveira, M.A.; Li, Q.; Li, S.; Li, S.; Li, X.; Li, Y.; Li, Z.; Libo, J.; Lin, C.S.; Lin, S.; Ling, J.; Link, J.; Liptak, Z.; Lissauer, D.; Littenberg, L.; Littlejohn, B.; Liu, Q.; Liu, T.; Lockwitz, S.; Lockyer, N.; Loew, T.; Lokajicek, M.; Long, K.; Lopes, M.D.L.; Lopez, J.P.; Losecco, J.; Louis, W.; Lowery, J.; Luethi, M.; Luk, K.; Lundberg, B.; Lundin, T.; Luo, X.; Lux, T.; Lykken, J.; Machado, A.A.; Macier, J.R.; Magill, S.; Mahler, G.; Mahn, K.; Malek, M.; Malhotra, S.; Malon, D.; Mammoliti, F.; Mancina, S.; Mandal, S.K.; Mandodi, S.; Manly, S.L.; Mann, A.; Marchionni, A.; Marciano, W.; Mariani, C.; Maricic, J.; Marino, A.; Marshak, M.; Marshall, C.; Marshall, J.; Marteau, J.; Martin-Albo, J.; Martinez, D.; Matsuno, S.; Matthews, J.; Mauger, C.; Mavrokoridis, K.; Mayilyan, D.; Mazzucato, E.; McCauley, N.; McCluskey, E.; McConkey, N.; McDonald, K.; McFarland, K.S.; McGowan, A.M.; McGrew, C.; McKeown, R.; McNulty, D.; McTaggart, R.; Mefodiev, A.; Mehrian, M.; Mehta, P.; Mei, D.; Mena, O.; Menary, S.; Mendez, H.; Menegolli, A.; Meng, G.; Meng, Y.; Mertins, D.; Merritt, H.; Messier, M.; Metcalf, W.; Mewes, M.; Meyer, H.; Miao, T.; Milincic, R.; Miller, W.; Mills, G.; Mineev, O.; Miranda, O.; Mishra, C.S.; Mishra, S.R.; Mitrica, B.; Mladenov, D.; Mocioiu, I.; Mohanta, R.; Mokhov, N.; Montanari, C.; Montanari, D.; Moon, J.; Mooney, M.; Moore, C.; Morfin, J.; Morgan, B.; Morris, C.; Morse, W.; Moss, Z.; Mossey, C.; Moura, C.A.; Mousseau, J.; Mualem, L.; Muether, M.; Mufson, S.; Murphy, S.; Musser, J.; Musser, R.; Nakajima, Y.; Naples, D.; Napolitano, J.; Navarro, J.; Navas, D.; Nelson, J.; Nessi, M.; Newcomer, M.; Ng, Y.; Nichol, R.; Nicholls, T.C.; Nikolics, K.; Niner, E.; Norris, B.; Noto, F.; Novakova, P.; Novella, P.; Nowak, J.; Nunes, M.S.; O'Keeffe, H.; Oldeman, R.; Oliveira, R.; Olson, T.; Onishchuk, Y.; Osta, J.; Ovsjannikova, T.; Page, B.; Pakvasa, S.; Pal, S.; Palamara, O.; Palazzo, A.; Paley, J.; Palomares, C.; Pantic, E.; Paolone, V.; Papadimitriou, V.; Park, J.; Parke, S.; Parsa, Z.; Pascoli, S.; Patterson, R.; Patton, S.; Patzak, T.; Paulos, B.; Paulucci, L.; Pavlovic, Z.; Pawloski, G.; Peeters, S.; Pennacchio, E.; Perch, A.; Perdue, G.N.; Periale, L.; Perkin, J.D.; Pessard, H.; Petrillo, G.; Petti, R.; Petukhov, A.; Pietropaolo, F.; Plunkett, R.; Pordes, S.; Potekhin, M.; Potenza, R.; Potukuchi, B.; Poudyal, N.; Prokofiev, O.; Pruthi, N.; Przewlocki, P.; Pushka, D.; Qian, X.; Raaf, J.L.; Raboanary, R.; Radeka, V.; Radovic, A.; Raffelt, G.; Rakhno, I.; Rakotondramanana, H.T.; Rakotondravohitra, L.; Ramachers, Y.A.; Rameika, R.; Ramsey, J.; Rappoldi, A.; Raselli, G.; Ratoff, P.; Rebel, B.; Regenfus, C.; Reichenbacher, J.; Reitzner, D.; Remoto, A.; Renshaw, A.; Rescia, S.; Richardson, M.; Rielage, K.; Riesselmann, K.; Robinson, M.; Rochester, L.; Rodrigues, O.B.; Rodrigues, P.; Roe, B.; Rosen, M.; Roser, R.M.; Ross-Lonergan, M.; Rossella, M.; Rubbia, A.; Rubbia, C.; Rucinski, R.; von Rohr, C.Rudolph; Russell, B.; Ruterbories, D.; Saakyan, R.; Sahu, N.; Sala, P.; Samios, N.; Sanchez, F.; Sanchez, M.; Sands, B.; Santana, S.; Santorelli, R.; Santucci, G.; Saoulidou, N.; Scaramelli, A.; Schellman, H.; Schlabach, P.; Schmitt, R.; Schmitz, D.; Schneps, J.; Scholberg, K.; Schukraft, A.; Schwehr, J.; Segreto, E.; Seibert, S.; Sepulveda-Quiroz, J.A.; Sergiampietri, F.; Sexton-Kennedy, L.; Sgalaberna, D.; Shaevitz, M.; Shahi, J.; Shahsavarani, S.; Shanahan, P.; Shankar, S.U.; Sharma, R.; Sharma, R.K.; Shaw, T.; Shrock, R.; Shyrma, I.; Simos, N.; Sinev, G.; Singh, I.; Singh, J.; Singh, J.; Singh, V.; Sinnis, G.; Sippach, W.; Smargianaki, D.; Smy, M.; Snider, E.; Snopok, P.; Sobczyk, J.; Sobel, H.; Soderberg, M.; Solomey, N.; Sondheim, W.; Sorel, M.; Sousa, A.; Soustruznik, K.; Spitz, J.; Spooner, N.J.; Stancari, M.; Stancu, I.; Stefan, D.; Steiner, H.M.; Stewart, J.; Stock, J.; Stoica, S.; Stone, J.; Strait, J.; Strait, M.; Strauss, T.; Striganov, S.; Sulej, R.; Sullivan, G.; Sun, Y.; Suter, L.; Sutera, C.M.; Svoboda, R.; Szczerbinska, B.; Szelc, A.; Soldner-Rembold, S.; Talaga, R.; Tamsett, M.; Tariq, S.; Tatar, E.; Tayloe, R.; Taylor, C.; Taylor, D.; Terao, K.; Thiesse, M.; Thomas, J.; Thompson, L.F.; Thomson, M.; Thorn, C.; Thorpe, M.; Tian, X.; Tiedt, D.; Timm, S.C.; Tonazzo, A.; Tope, T.; Topkar, A.; Torres, F.R.; Torti, M.; Tortola, M.; Tortorici, F.; Toups, M.; Touramanis, C.; Tripathi, M.; Tropin, I.; Tsai, Y.; Tsang, K.V.; Tsenov, R.; Tufanli, S.; Tull, C.; Turner, J.; Tzanov, M.; Tziaferi, E.; Uchida, Y.; Urheim, J.; Usher, T.; Vagins, M.; Vahle, P.; Valdiviesso, G.A.; Valerio, L.; Vallari, Z.; Valle, J.; Van Berg, R.; Van de Water, R.; Van Gemmeren, P.; Varanini, F.; Varner, G.; Vasseur, G.; Vaziri, K.; Velev, G.; Ventura, S.; Verdugo, A.; Viant, T.; Vieira, T.V.; Vignoli, C.; Vilela, C.; Viren, B.; Vrba, T.; Wachala, T.; Wahl, D.; Wallbank, M.; Walsh, N.; Wang, B.; Wang, H.; Wang, L.; Wang, T.; Warburton, T.K.; Warner, D.; Wascko, M.; Waters, D.; Watson, T.B.; Weber, A.; Weber, M.; Wei, W.; Weinstein, A.; Wells, D.; Wenman, D.; Wetstein, M.; White, A.; Whitehead, L.; Whittington, D.; Wilking, M.; Willhite, J.; Wilson, P.; Wilson, R.J.; Winslow, L.; Wittich, P.; Wojcicki, S.; Wong, H.H.; Wood, K.; Worcester, E.; Worcester, M.; Wu, S.; Xin, T.; Yanagisawa, C.; Yang, S.; Yang, T.; Yarritu, K.; Ye, J.; Yeh, M.; Yershov, N.; Yonehara, K.; Yu, B.; Yu, J.; Zalesak, J.; Zalewska, A.; Zamorano, B.; Zang, L.; Zani, A.; Zani, A.; Zavala, G.; Zeller, G.; Zhang, C.; Zhang, C.; Zimmerman, E.D.; Zito, M.; Zwaska, R.
2016-01-01
This document presents the Conceptual Design Report (CDR) put forward by an international neutrino community to pursue the Deep Underground Neutrino Experiment at the Long-Baseline Neutrino Facility (LBNF/DUNE), a groundbreaking science experiment for long-baseline neutrino oscillation studies and for neutrino astrophysics and nucleon decay searches. The DUNE far detector will be a very large modular liquid argon time-projection chamber (LArTPC) located deep underground, coupled to the LBNF multi-megawatt wide-band neutrino beam. DUNE will also have a high-resolution and high-precision near detector.
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Modelling dune evolution and dynamic roughness in rivers
Paarlberg, Andries
2008-01-01
Accurate river flow models are essential tools for water managers, but these hydraulic simulation models often lack a proper description of dynamic roughness due to hysteresis effects in dune evolution. To incorporate the effects of dune evolution directly into the resistance coefficients of
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Taniguchi, Keisuke; Endo, Noritaka
2007-10-01
It is generally considered that barchans, isolated crescentic-shaped dunes, develop where wind is unidirectional and the available sand is insufficient to cover the entire dune field; however, Bishop [Bishop, M.A., 2001. Seasonal variation of crescentic dune morphology and morphometry, Strzelecki Simpson desert, Australia. Earth Surface Process and Landforms 26, 783 791.] observed barchans that developed in areas where winds blow seasonally in opposite directions and described a peculiar deformation feature, the “rear slipface,” that is not found in ordinary barchans. Barchans under such bidirectional flows are poorly understood, and it is necessary to study barchans that formed under many different flow conditions. We conducted flume experiments to investigate the deformation of barchans under alternating water flow, and observed new deformation features in addition to rear slipfaces. We conclude that the deformation of barchans can be categorized into four types, one of which shows morphologies similar to barchans within Proctor Crater, Mars. The deformation type depends on the strength of the reverse flow relative to the forward flow and the absolute velocity of the forward flow. Comparison of our results with barchan dunes within Proctor Crater enable us to qualitatively estimate the wind strength and direction related to dune formation on Mars. These results are in agreement with those of Fenton et al. [Fenton, L.K., Toigo, A.D., Richardson, M.I., 2005. Aeolian processes in Proctor Crater on Mars: Mesoscale modeling of dune-forming winds. Journal of Geophysical Research 110 (E6), E06005.].
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Effects of sand fences on coastal dune vegetation distribution
Grafals-Soto, Rosana
2012-04-01
Sand fences are important human adjustments modifying the morphology of developed shores. The effects of sand fences on sediment transport and deposition in their initial stages have been well studied, but little is known about the effect of deteriorated sand fences that have become partially buried low scale barriers within the dune, potentially benefiting vegetation growth by protecting it from onshore stress. Data on vegetation, topography and fence characteristics were gathered at three dune sites in Ocean City, New Jersey on September 2007 and March 2008 to evaluate the effect of fences within the dune on vegetation distribution. Variables include: distance landward of dune toe, degree of sheltering from onshore stressors, net change in surface elevation (deposition or erosion), vegetation diversity and density, presence of remnant fence, and distance landward of fence. Results for the studied environment reveal that 1) vegetation diversity or density does not increase near remnant fences because most remnants are lower than average vegetation height and can not provide shelter; but 2) vegetation distribution is related to topographic variables, such as degree of sheltering, that are most likely the result of sand accretion caused by fence deployment. Fence deployment that prioritizes the creation of topographically diverse dunes within a restricted space may increase the diversity and density of the vegetation, and the resilience and value of developed dunes. Managers should consider the benefits of using sand fences on appropriately wide beaches to create a protective dune that is also diverse, functional and better able to adapt to change.
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Hydro-geochemical analysis of a degraded dune slack
Grootjans, AP; Sival, FP; Stuyfzand, PJ
A hydrochemical analysis of the groundwater composition was carried out in a degraded dune slack complex in order to assess the prospects for regeneration of low productivity, basiphilous vegetation types, typical of natural dune slacks. Two hundred and fifty water samples, most of them obtained
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Flemming, Burghard W.; Kudrass, Hermann-Rudolf
2018-02-01
The existence of a continuously flowing Mozambique Current, i.e. a western geostrophic boundary current flowing southwards along the shelf break of Mozambique, was until recently accepted by oceanographers studying ocean circulation in the south-western Indian Ocean. This concept was then cast into doubt based on long-term current measurements obtained from current-meter moorings deployed across the northern Mozambique Channel, which suggested that southward flow through the Mozambique Channel took place in the form of successive, southward migrating and counter-clockwise rotating eddies. Indeed, numerical modelling found that, if at all, strong currents on the outer shelf occurred for not more than 9 days per year. In the present study, the negation of the existence of a Mozambique Current is challenged by the discovery of a large (50 km long, 12 km wide) subaqueous dune field (with up to 10 m high dunes) on the outer shelf east of the modern Zambezi River delta at water depths between 50 and 100 m. Being interpreted as representing the current-modified, early Holocene Zambezi palaeo-delta, the dune field would have migrated southwards by at least 50 km from its former location since sea level recovered to its present-day position some 7 ka ago and after the former delta had been remoulded into a migrating dune field. Because a large dune field composed of actively migrating bedforms cannot be generated and maintained by currents restricted to a period of only 9 days per year, the validity of those earlier modelling results is questioned for the western margin of the flow field. Indeed, satellite images extracted from the Perpetual Ocean display of NASA, which show monthly time-integrated surface currents in the Mozambique Channel for the 5 month period from June-October 2006, support the proposition that strong flow on the outer Mozambican shelf occurs much more frequently than postulated by those modelling results. This is consistent with more recent modelling
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The Mediterranean Coastal Dunes in Egypt: An Endangered Landscape
Batanouny, K. H.
1999-08-01
The Mediterranean coast in Egypt extends almost 900 km, the major part of which is bordered by sand dunes of different natures and types. Along the coastline between Alexandria and El-Alamein, a distance of some 100 km, the sand dunes represent a particular landscape with special characteristics and features, and consequently plants with particular attributes. In this area, the belt of sand dunes has developed immediately south of the shore and these dunes may rise up to 10 m in height and extend about 0·5-1·5 km inland from the shore. These dunes are famous as a habitat for the fig (Ficus carica L.) cultivation depending on the irregular rainfall. They also represent a landing station and a cross-road for birds such as quail migrating from Europe in the north. In the past, summer resort areas were confined to limited areas with few people, these same areas support the growth of some important plant species, for example, sand binders, medicinal and range plants. For more than two decades, there has been considerable socio-economic change and an open-door policy in the economy of the country has been adopted. One of the consequences of this change is that a great part of the coastal dune belt west of Alexandria till El-Alamein, has been subjected to destruction, due to the continuous construction of summer resort villages. These were built at a distance of about 100 m of the shoreline, extending 400-600 m inland and a breadth of 400 m or more along the shoreline. The area already covered by the dunes is now almost occupied by new buildings, gardens and other infrastructure. The consequences of these human activities are numerous and include impacts on the soil, water resources, the flora and the fauna, migrating birds, trends of the indigenous people, and the cultural environment. The present paper gives a concise environmental setting of the dune belt before the advent of the new activities, and the socio-economic and political attitudes which threaten the dunes
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The largest subsea hot tap (future tap flange) at Angel Field, Australia
Energy Technology Data Exchange (ETDEWEB)
Lad, Deepak; Drysdale, Colin [T.D. Williamson (United States); Naidoo, Sashie [T.D. Williamson (Australia)
2008-07-01
A subsea hot tap was conducted near the gas production platforms in Angel Field, Australia in September 2007 and verified as the largest no. 900 subsea hot tap by Australian authorities. This paper outlines the subsea tapping process, risks and safety issues in deep water environment, including the need to ensure 100% system accuracy and that the machine fluids used to operate the subsea tapping machines were environmentally friendly. The testing phase included land and water testing. In the land tests, issues relating to metal hardness, temperature, pressure and ocean currents that affected machine stability, torque and cutting rate were considered. All preliminary design and testing focused on being able to mount the tapping machine to a pre-existing hot-tap flange and conduct the tapping operation, start to finish, preferably without changing the cutter. The water depth tests took place inside a pressurized, underwater hyperbaric chamber. The equipment repeated the land testing process in conditions duplicating that of the actual project site. Timing was also measured in multiple climatic conditions (except water depth) to obtain an estimation of various scenarios. The field tapping process was conducted without problems in over six hours with a single cutter and without any stalls. (author)
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Planetary dune workshop expands to include subaqueous processes
Titus, Timothy N.; Bryant, Gerald; Rubin, David M.
2018-01-01
Dune-like structures appear in the depths of Earth’s oceans, across its landscapes, and in the extremities of the solar system beyond. Dunes rise up under the thick dense atmosphere of Venus, and they have been found under the almost unimaginably ephemeral atmosphere of a comet.
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TUMEUR ORBITAIRE: MANIFESTATION INITIALE D'UNE MALADIE ...
African Journals Online (AJOL)
L'hétérogénéité et la rareté des formes multicentriques de la maladie de Castleman font que leurs traitements soient très disparates. La maladie de Castleman doit être considérée comme un diagnostic possible d'une adénopathie cervicale particulièrement chez les patients souffrant d'une maladie inflammatoire chronique.
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Dune Erosion Models and Swash Zone Kinematics from Remote Video Observations
2010-12-09
system. Thus, successful prediction of dune erosion requires knowledge of the expected trajectory of the eroding dune toe . If we describe the... dune toe trajectory as following a slope, βT, two end member retreat trajectories exist. The first would be direct landward erosion so that zb never...changes 0 0 T bb ztz (2.24) The second end member trajectory is that erosion moves the dune toe directly up the foreshore slope
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Hu, Hao; Wei, Taoyuan; Yang, Zhongyong; Hackney, Christopher R.; Parsons, Daniel R.
2018-05-01
It has long been highlighted that important feedbacks exist between river bed morphology, sediment transport and the turbulent flow field and that these feedbacks change in response to forcing mechanisms. However, our current understanding of bedform dynamics is largely based on studies of steady flow environments and cohesionless bed conditions. Few investigations have been made under rapidly changing flows. Here, we examine flow and sediment dynamics over low-angle dunes in unsteady flows in the Changjiang (Yangtze) Estuary, China. Topography, flow and sediment data were collected over a reach ca 1.8 km long through a semi-diurnal tidal cycle in a moderate tide of flood season. The results show that: (1) roughness length derived from the upper flow changes little with the flow reversing and displays the same value on both the ebb and flood tide. Moreover, the variability of individual bedform features plays an important role in roughness length variation. (2) Shear stress over the crest of low-angle dunes roughly represents the total spatially averaged stress over dunes in this study area, which has significant implications for advancing numerical models. (3) Changes in morphology, flow and sediment dynamics over dunes through time reveal how low-angle dunes evolve within a tidal cycle. (4) The clockwise hysteresis loops between flow dynamics and bedform features (height and aspect ratio) are also observed. The combination of suspended sediment transport and bedload transport on dune transformation and migration attributes to the clockwise hysteresis. The specific sediment composition of the riverbed, in some extent, affects the mechanism of sediment transport related to the exchange between suspended sediment and riverbed, but further investigation is needed to figure out the mechanism behind this for extended series of tides, such as spring/neap tide and tides in flooding and dry season.
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Dune management challenges on developed coasts
Elko, Nicole A.; Brodie, Kate; Stockdon, Hilary F.; Nordstrom, Karl F.; Houser, Chris; McKenna, Kim; Moore, Laura; Rosati, Julie D.; Ruggiero, Peter; Thuman, Roberta; Walker, Ian J.
2015-01-01
From October 26-28, 2015, nearly 100 members of the coastal management and research communities met in Kitty Hawk, NC, USA to bridge the apparent gap between the coastal dune research of scientists and engineers and the needs of coastal management practitioners. The workshop aimed to identify the challenges involved in building and managing dunes on developed coasts, assess the extent to which scientific knowledge can be applied to the management community, and identify approaches to provide means to bridge the gap between needs and potential solutions.
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The role of bathymetry, wave obliquity and coastal curvature in dune erosion prediction
Den Heijer, C.
2013-01-01
This study aims at reducing uncertainty in dune erosion predictions, in particular at complex dune coasts, in order to improve the assessment method for dune safety against flooding. To that end, state-of-the-art process-based dune erosion models are employed to further investigate issues
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O'Keeffe, Nicholas; Delgado-Fernandez, Irene; Aplin, Paul; Jackson, Derek; Marston, Christopher
2017-04-01
Coastal dunes are natural buffers against the threat of climate change-induced sea level rise. Their evolution is largely controlled by sediment exchanges between the geomorphic sub-units of the nearshore, beach, foredune and dune field. Coastlines characterised by multiple blowouts at the beach-dune interface may be more susceptible to coastline retreat through the enhanced landwards transport of beach and foredune sediment. This study, based in Sefton, north-west England, exploits an unprecedented temporal coverage of LIDAR surveys spanning 15 years (1999, 2008, 2010, 2013 and 2014). Established GIS techniques have been utilised to extract both the coastline (foredune toe) and the foredune crest from each LIDAR derived DTM (Digital Terrain Model). Migration of the foredune toe has been tracked over this period. Analysis of differentials between the height of the dune toe and dune crest have been used to locate the alongshore position of blowouts within the foredune. Dune sediment budgets have then been calculated for each DTM and analysis of the budgets conducted, with the coastline being compartmentalised alongshore, based on presence of blowouts within the foredune. Results indicate that sections of the coastline where blowouts are present within the foredune may be most vulnerable to coastline retreat. Temporal changes in the sediment budget within many of these sections also provides evidence that, if blowouts are present, coastline retreat continues to be a possibility even when the dune sediment budget remains positive.
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CERN tests largest superconducting solenoid magnet
2006-01-01
"CERN's Compacts Muon Solenoid (CMS) - the world's largest superconducting solenoid magnet - has reached full field in testing. The instrument is part of the proton-proton Large Hadron Collider (LHC) project, located in a giant subterranean chamber at Cessy on the Franco-Swiss border." (1 page)
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International Nuclear Information System (INIS)
Tani, Takashi; Nakanishi, Yuji; Horita, Tsuyoshi; Kawase, Chiharu; Oyabu, Isao; Kishimoto, Takeshi.
1996-01-01
Mitsubishi Electric has delivered the world's largest DC generator for the toroidal field coil power supply of the JFT-2M Tokamak at the Japan Atomic Energy Research Institute. The unit rotates at 225 or 460 rpm, providing a maximum rated output of 2,700 V, 19,000 A and 51.3 MW. The toroidal field is a DC field, so use of a DC generator permits a simpler design consuming less floor space than an AC drive system. The generator was manufactured following extensive studies on commutation, mechanical strength and insulation. (author)
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Indian Academy of Sciences (India)
ble low-frequency (s. 75–105 Hz), that can some- times be heard up to 10 km away. Scientific in- vestigations suggest that the sustained low fre- quency sound of sand dunes that resembles a pure note from a musical instrument, is due to the synchronized motion of well-sorted dry sand grains when they spontaneously ...
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Farrell, E.; Lynch, K.; Wilkes Orozco, S.; Castro Camba, G.; Scullion, A.
2017-12-01
This two year field monitoring project examines the response and recovery of 1.2km of a coastal beach-dune system in the west coast of Ireland (The Maharees, Brandon Bay, Co. Kerry) to storms. The results from this project initiated a larger scale study to assess the long term evolution of Brandon Bay (12km) and patterns of meso-scale rotation. On a bay scale historic shoreline analyses were completed using historic Ordnance Survey maps, aerial photography, and DGPS surveys inputted to the Digital Shoreline Analysis System. These were coupled with a GSTA-wavemeter experiment that collected 410 sediment samples along the beach and nearshore to identify preferred sediment transport pathways along the bay. On a local scale (1.2km) geomorphological changes of the beach and nearshore were monitored using repeated monthly DGPS surveys and drone technology. Topographical data were correlated with atmospheric data obtained from a locally installed automatic weather station, oceanographic data from secondary sources, and photogrammetry using a camera installed at the site collecting pictures every 10 minutes during daylight hours. Changes in surface elevation landward of the foredune from aeolian processes were measured using five pin transects across the dune. The contribution of local blowout dynamics were measured using drone imagery and structure-from-motion technology. The results establish that the average shoreline recession along the 1.2 km site is 72 m during the past 115 years. The topographic surveys illustrate that natural beach building processes initiate system recovery post storms including elevated foreshores and backshores and nearshore sand bar migration across the entire 1.2 km stretch of coastline. In parallel with the scientific work, the local community have mobilized and are working closely with the lead scientists to implement short term coastal management strategies such as signage, information booklets, sand trap fencing, walkways, wooden
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Upstream sediment input effects on experimental dune trough scour in sediment mixtures
Kleinhans, M.G.
2005-01-01
Understanding causes of dune irregularity, especially dune trough scour, is important for the modeling of vertical sorting of sediment mixtures in morphological models of rivers with sediment mixtures. Sediment in dunes is generally sorted in a fining-upward manner, which affects the sediment
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A Sharp View on River Dune Transition to Upper Stage Plane Bed
Naqshband, S.; Hoitink, A.J.F.; Mcelroy, B.; Hurther, D.; Hulscher, S.J.M.H.
2017-01-01
Sandy river beds are dominated by rhythmic features known as dunes. Experimental investigations of turbulent flow and sediment transport over dunes have predominantly focused on equilibrium flows that are rare in natural rivers. Using a novel acoustic instrument over migrating dunes in a laboratory
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A sharp view on river dune transition to upper stage plane bed
Naqshband, S.; Hoitink, A.J.F.; Mcelroy, B.; Hurther, D.; Hulscher, S.J.M.H.
2017-01-01
Sandy river beds are dominated by rhythmic features known as dunes. Experimental investigations of turbulent flow and sediment transport over dunes have predominantly focused on equilibrium flows that are rare in natural rivers. Using a novel acoustic instrument over migrating dunes in a laboratory
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Latorre, Claudio; GonzáLez, AngéLica L.; Quade, Jay; FariñA, José M.; Pinto, Raquel; Marquet, Pablo A.
2011-09-01
Extensive dune fields made up exclusively of the bromeliad Tillandsia landbeckii thrive in the Atacama Desert, one of the most extreme landscapes on earth. These plants survive by adapting exclusively to take in abundant advective fog and dew as moisture sources. Although some information has been gathered regarding their modern distribution and adaptations, very little is known about how these dune systems actually form and accumulate over time. We present evidence based on 20 radiocarbon dates for the establishment age and development of five different such dune systems located along a ˜215 km transect in northern Chile. Using stratigraphy, geochronology and stable C and N isotopes, we (1) develop an establishment chronology of these ecosystems, (2) explain how the unique T. landbeckii dunes form, and (3) link changes in foliar δ15N values to moisture availability in buried fossil T. landbeckii layers. We conclude by pointing out the potential that these systems have for reconstructing past climate change along coastal northern Chile during the late Holocene.
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Responses of woody species to spatial and temporal ground water changes in coastal sand dune systems
Máguas, C.; Rascher, K. G.; Martins-Loução, A.; Carvalho, P.; Pinho, P.; Ramos, M.; Correia, O.; Werner, C.
2011-12-01
In spite of the relative importance of groundwater in costal dune systems, studies concerning the responses of vegetation to ground water (GW) availability variations, particularly in Mediterranean regions, are scarce. Thus, the main purpose of this study is to compare the responses of co-occurring species possessing different functional traits, to changes in GW levels (i.e. the lowering of GW levels) in a sand dune ecosystem. For that, five sites were established within a 1 km2 area in a meso-mediterranean sand dune ecosystem dominated by a Pinus pinaster forest. Due to natural topographic variability and anthropogenic GW exploitation, substantial variability in depth to GW between sites was found. Under these conditions it was possible to identify the degree of usage and dependence on GW of different plant species (two deep-rooted trees, a drought adapted shrub, a phreatophyte and a non-native woody invader) and how GW dependence varied seasonally and between the heterogeneous sites. Results indicated that the plant species had differential responses to changes in GW depth according to specific functional traits (i.e. rooting depth, leaf morphology, and water use strategy). Species comparison revealed that variability in pre-dawn water potential (Ψpre) and bulk leaf δ13C was related to site differences in GW use in the deep-rooted (Pinus pinaster, Myrica faya) and phreatophyte (Salix repens) species. However, such variation was more evident during spring than during summer drought. The exotic invader, Acacia longifolia, which does not possess a very deep root system, presented the largest seasonal variability in Ψpre and bulk leaf δ13C. In contrast, the response of Corema album, an endemic understory drought-adapted shrub, seemed to be independent of water availability across seasons and sites. Thus, the susceptibility to lowering of GW due to anthropogenic exploitation, in plant species from sand dunes, is variable, being particularly relevant for deep
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Long, Hao; Shen, Ji; Chen, Jianhui; Tsukamoto, Sumiko; Yang, Linhai; Cheng, Hongyi; Frechen, Manfred
2017-10-01
Arid central Asia (ACA) is one of the largest arid (desert) areas in the world, and its climate is dominated by the westerlies. In this study, we examined sand dune evolution from the Bayanbulak Basin in the Tian Shan (Xinjiang, NW China), aiming to infer the Holocene moisture history of the ACA. Combined with stratigraphic observation and environmental proxies analysis (grain size, magnetic susceptibility and total organic content), large numbers of luminescence ages from multiple sites (eight sections, 79 samples) were applied to reconstruct the evolution of the sand dune accumulation in the study basin. The overall results imply very dry conditions characterized by sand dune accumulation at ∼12-6.5 ka, a wet interval between ∼6.5 and 0.8 ka when soil formation occurred, and decreased moisture during the last 0.8 ka. This moisture variation pattern is generally consistent with that inferred from many lacustrine records in the core zone of ACA, suggesting a widespread dry period in the early-to-middle Holocene and relatively wet middle-to-late Holocene. Thus, the moisture history derived from the current sand dune system contrasts with that in Asian monsoon areas, which are characterized by a strong monsoon (high precipitation) in the early and mid-Holocene and a weak monsoon (low precipitation and dry climate) during the late Holocene. Our results strongly suggest that the winter solar insolation and the external boundary conditions such as atmospheric CO2 concentration, ice sheets, and meltwater fluxes, have been major influential factors triggering the Holocene moisture evolution in the core zone of ACA.
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36 CFR 7.80 - Sleeping Bear Dunes National Lakeshore.
2010-07-01
... 36 Parks, Forests, and Public Property 1 2010-07-01 2010-07-01 false Sleeping Bear Dunes National Lakeshore. 7.80 Section 7.80 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE INTERIOR SPECIAL REGULATIONS, AREAS OF THE NATIONAL PARK SYSTEM § 7.80 Sleeping Bear Dunes National...
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Last Glacial Maximum Development of Parna Dunes in Panhandle Oklahoma, USA
Johnson, W. C.; Halfen, A. F.; McGowen, S.; Carter, B.; Fine, S.; Bement, L. C.; Simms, A. R.
2012-12-01
Though dunefields are a ubiquitous feature of the North American Great Plains, those studied to date have consisted primarily of sand grains. In Beaver County of the Oklahoma panhandle, however, upland dune forms consist of sand-sized aggregates of silt and clay. These aptly named parna dunes occur in two swarms, range in height from 10-15 m, and have asymmetrical dome morphologies with approximate north-south dune orientations. Despite their morphological similarities to sand dunes of the region, their origin and evolution is unknown. Documenting parna dune formation in the Oklahoma panhandle will help improve our understanding of prehistoric landscape instability and climate change, particularly in the central Great Plains where such records are limited. Panhandle parna dunes are typified by Blue Mound, our best documented parna dune thus far. Coring has documented a basal paleosol buried at a depth equivalent to the surrounding landscape—14C ages from this soil indicate its formation about 25-21 ka. The paleosol is a hydric Mollisol with a pronounced C3 isotopic signature reflecting hydric plant communities, rather than the regionally dominated C4 prairie vegetation. Hydric soils are associated with many of the playas on the surrounding landscape today, which suggests that they may have been more prevalent during the LGM. The overlying 8-10 m of parna is low in organic C and high in calcite, with indications of up to ten major episodes of sediment flux, which are documented with magnetic, isotope, soil-stratigraphic, particle-size, and color data. Near-surface luminescence (OSL) ages from Blue Mound are similar to the 14C ages from the basal paleosol, indicating rapid dune construction, with little or no Holocene accumulation of sediment. Marine isotope stage (MIS) 3 loess records indicate that upland areas of the region were relatively stable with attendant widespread pedogenesis prior to development of the parna dunes. At the onset of the LGM, however, the
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Martian Dune Ripples as Indicators of Recent Surface Wind Patterns
Johnson, M.; Zimbelman, J. R.
2015-12-01
Sand dunes have been shown to preserve the most recent wind patterns in their ripple formations. This investigation continues the manual documentation of ripples on Martian dunes in order to assess surface wind flow. Study sites investigated must have clear HiRISE frames and be able to represent diverse locations across the surface, decided primarily by their spread of latitude and longitude values. Additionally, frames with stereo pairs are preferred because of their ability to create digital terrain models. This will assist in efforts to relate dune slopes and obstacles to ripple patterns. The search and analysis period resulted in 40 study sites with mapped ripples. Lines were drawn perpendicular to ripple crests across three adjacent ripples in order to document both ripple wavelength from line length and inferred wind direction from azimuth. It is not possible to infer a unique wind direction from ripple orientation alone and therefore these inferred directions have a 180 degree ambiguity. Initial results from all study sites support previous observations that the Martian surface has many dune types in areas with adequate sand supply. The complexity of ripple patterns varies greatly across sites as well as within individual sites. Some areas of uniform directionality for hundreds of kilometers suggest a unimodal wind regime while overlapping patterns suggest multiple dominant winds or seasonally varying winds. In most areas, form flow related to dune shape seems to have a large effect on orientation and must be considered along with the dune type. As long as the few steep slip faces on these small dunes are avoided, form flow can be considered the dominant cause of deviation from the regional wind direction. Regional results, wind roses, and comparisons to previous work will be presented for individual sites.
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Fitterman, David V.; de Sozua Filho, Oderson A.
2009-01-01
Time-domain electromagnetic (TEM) soundings were made near Great Sand Dunes National Park and Preserve in the San Luis Valley of southern Colorado to obtain subsurface information of use to hydrologic modeling. Seventeen soundings were made to the east and north of the sand dunes. Using a small loop TEM system, maximum exploration depths of about 75 to 150 m were obtained. In general, layered earth interpretations of the data found that resistivity decreases with depth. Comparison of soundings with geologic logs from nearby wells found that zones logged as having increased clay content usually corresponded with a significant resistivity decrease in the TEM determined model. This result supports the use of TEM soundings to map the location of the top of the clay unit deposited at the bottom of the ancient Lake Alamosa that filled the San Luis Valley from Pliocene to middle Pleistocene time.
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Sediment flux and airflow on the stoss slope of a barchan dune
Lancaster, N.; Nickling, W. G.; Neuman, C. K. McKenna; Wyatt, V. E.
1996-09-01
Measurements of sediment flux on the windward slope of an isolated barchan using an array of 30 sand traps provide new data that can constrain models of dune dynamics. The data show that at low wind incident speeds, flux increases up the dune exponentially, whereas at higher wind speeds the increase with distance approaches linearity. Wind profile measurements, conducted at the same time as the flux measurements, indicate that, although wind speed at a given height increases by 1.2 times from dune toe to brinkline, wind shear velocity derived from the profile data decreases up the dune and is in many cases below transport threshold values. This demonstrates that conventional wind profiles, derived from anemometry on dunes, do not measure the part of the boundary layer that is significant for sediment transport.
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Ehlmann, B L; Edgett, K S; Sutter, B; Achilles, C N; Litvak, M L; Lapotre, M G A; Sullivan, R; Fraeman, A A; Arvidson, R E; Blake, D F; Bridges, N T; Conrad, P G; Cousin, A; Downs, R T; Gabriel, T S J; Gellert, R; Hamilton, V E; Hardgrove, C; Johnson, J R; Kuhn, S; Mahaffy, P R; Maurice, S; McHenry, M; Meslin, P-Y; Ming, D W; Minitti, M E; Morookian, J M; Morris, R V; O'Connell-Cooper, C D; Pinet, P C; Rowland, S K; Schröder, S; Siebach, K L; Stein, N T; Thompson, L M; Vaniman, D T; Vasavada, A R; Wellington, D F; Wiens, R C; Yen, A S
2017-12-01
The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine to medium sized (~45-500 μm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si enriched relative to other soils at Gale crater, and H 2 O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by visible/near-infrared spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or H 2 O- or OH-bearing impact or volcanic glasses and (2) amorphous components in the fine fraction (<40 μm; represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H 2 O.
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Zellman, Kristine L.
2014-01-01
San Miguel Island is the westernmost of the California Channel Islands and one of the windiest areas on the west coast of North America. The majority of the island is covered by coastal sand dunes, which were stripped of vegetation and subsequently mobilized due to droughts and sheep ranching during the late 19th century and early 20th century. Since the removal of grazing animals, vegetation and biological soil crusts have once again stabilized many of the island's dunes. In this study, historical aerial photographs and field surveys were used to develop a chronosequence of the pattern of change in vegetation communities and biological soil crust levels of development (LOD) along a gradient of dune stabilization. Historical aerial photographs from 1929, 1954, 1977, and 2009 were georeferenced and used to delineate changes in vegetation canopy cover and active (unvegetated) dune extent among 5 historical periods (pre-1929, 1929–1954, 1954–1977, 1977–2009, and 2009–2011). During fieldwork, vegetation and biological soil crust communities were mapped along transects distributed throughout San Miguel Island's central dune field on land forms that had stabilized during the 5 time periods of interest. Analyses in a geographic information system (GIS) quantified the pattern of changes that vegetation and biological soil crust communities have exhibited on the San Miguel Island dunes over the past 80 years. Results revealed that a continuing increase in total vegetation cover and a complex pattern of change in vegetation communities have taken place on the San Miguel Island dunes since the removal of grazing animals. The highly specialized native vascular vegetation (sea rocket, dunedelion, beach-bur, and locoweed) are the pioneer stabilizers of the dunes. This pioneer community is replaced in later stages by communities that are dominated by native shrubs (coastal goldenbush, silver lupine, coyote-brush, and giant coreopsis), with apparently overlapping or
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Effects of Trampling Limitation on Coastal Dune Plant Communities
Santoro, Riccardo; Jucker, Tommaso; Prisco, Irene; Carboni, Marta; Battisti, Corrado; Acosta, Alicia T. R.
2012-03-01
Sandy coastlines are sensitive ecosystems where human activities can have considerable negative impacts. In particular, trampling by beach visitors is a disturbance that affects dune vegetation both at the species and community level. In this study we assess the effects of the limitation of human trampling on dune vegetation in a coastal protected area of Central Italy. We compare plant species diversity in two recently fenced sectors with that of an unfenced area (and therefore subject to human trampling) using rarefaction curves and a diversity/dominance approach during a two year study period. Our results indicate that limiting human trampling seems to be a key factor in driving changes in the plant diversity of dune systems. In 2007 the regression lines of species abundance as a function of rank showed steep slopes and high Y-intercept values in all sectors, indicating a comparable level of stress and dominance across the entire study site. On the contrary, in 2009 the regression lines of the two fenced sectors clearly diverge from that of the open sector, showing less steep slopes. This change in the slopes of the tendency lines, evidenced by the diversity/dominance diagrams and related to an increase in species diversity, suggests the recovery of plant communities in the two fences between 2007 and 2009. In general, plant communities subject to trampling tended to be poorer in species and less structured, since only dominant and tolerant plant species persisted. Furthermore, limiting trampling appears to have produced positive changes in the dune vegetation assemblage after a period of only two years. These results are encouraging for the management of coastal dune systems. They highlight how a simple and cost-effective management strategy, based on passive recovery conservation measures (i.e., fence building), can be a quick (1-2 years) and effective method for improving and safeguarding the diversity of dune plant communities.
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Coastal dune dynamics in response to excavated foredune notches
Ruessink, B. G.; Arens, S. M.; Kuipers, M.; Donker, J. J. A.
2018-04-01
Dune management along developed coasts has traditionally focussed on the suppression of the geomorphic dynamics of the foredune to improve its role in sea defence. Because a stabilized foredune acts as an almost total barrier to aeolian transport from the beach, the habitat diversity in the more landward dunes has degraded. With the overarching objective to mitigate this undesirable loss in biodiversity, dune management projects nowadays increasingly intend to restore aeolian dynamics by reconnecting the beach-dune system with notches excavated through the foredune. Here, we use repeat topographic survey data to examine the geomorphic response of a coastal dune system in the Dutch National Park Zuid-Kennemerland to five notches excavated in 2012-2013 within an 850-m stretch of the 20-m high established foredune. The notches were dug in a V-shape (viewed onshore), with a width between approximately 50 and 100 m at the top, a (cross-dune) length between 100 and 200 m, and excavation depths between 9 and 12.5 m. The 1 × 1 m digital terrain models, acquired with airborne Lidar and UAV photogrammetry, illustrate that during the 3-year survey period the notches developed into a U-shape because of wall deflation, and that up to 8-m thick and 150-m long depositional lobes formed landward of the notches. Sand budget computations showed that the sand volume of the entire study area increased by about 22,750 m3/year, which, given the 850-m width of the study area, corresponds to an aeolian input from the beach of approximately 26.5 m3/m/year. Between 2006 and 2012 all wind-blown beach sand deposited on the seaward side of the foredune; since 2013, the notches have caused 75% of the sand to be deposited landward of the foredune. This highlights that the notches are highly effective conduits for aeolian transport into the back dunes. Future monitoring is required to determine for how long the notches will stimulate aeolian dynamics and if (and when) vegetation eventually
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Pomar, F.; del Valle, L.; Fornós, J. J.; Gómez-Pujol, L.
2018-05-01
Aeolian-alluvial sedimentary interaction results in the formation of deposits characterized by typical alluvial sedimentary structures, but is composed of conspicuous amounts of aeolian sediments. The literature on this topic is limited and most works relate more with continental aeolian dunes or fluvial dune interference with fan bodies. Furthermore, there is a lack of examples of aeolian-alluvial sedimentary interference in coastal settings. In the western Mediterranean, there are many Pleistocene alluvial fan deposits built up partly by sediment originating from coastal dunes dismantled by alluvial streams. Very often, these deposits show a continuous sedimentary sequence through which we can derive the contribution and predominance of coastal, alluvial-colluvial and aeolian processes and their controls on landscape formation. This is an outstanding feature within coastal systems since it shows marine sediments reworked and integrated within coastal dune fields by aeolian transport, and the latter built up into alluvial fan bodies. In this sense, aeolian-alluvial interaction is the geomorphic-sedimentary expression of the coexistence and overlapping of alluvial and aeolian environments resulting in deposits sharing sedimentary features from both environments. The aim of this paper is to unravel the contribution of coastal dunes in the construction of alluvial fans bodies and identify the main sedimentary facies that constitute these deposits, as well as their climatic controls. For this reason, Es Caló fan (northern Mallorca) has been selected due to its well-exposed deposits exhibiting the alternation of aeolian, alluvial and colluvial deposits. Sedimentological and stratigraphic analyses based on 33 logs and complementary analyses demonstrate that most of the facies constituting the fan body are made up completely of marine bioclastic sands. These deposits record an alluvial fan sedimentary environment characterized by sediments inputs that do not proceed
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Dune recovery after storm erosion on a high-energy beach: Vougot Beach, Brittany (France)
Suanez, Serge; Cariolet, Jean-Marie; Cancouët, Romain; Ardhuin, Fabrice; Delacourt, Christophe
2012-02-01
On 10th March 2008, the high energy storm Johanna hit the French Atlantic coast, generating severe dune erosion on Vougot Beach (Brittany, France). In this paper, the recovery of the dune of Vougot Beach is analysed through a survey of morphological changes and hydrodynamic conditions. Data collection focused on the period immediately following storm Johanna until July 2010, i.e. over two and a half years. Results showed that the dune retreated by a maximum of almost 6 m where storm surge and wave attack were the most energetic. Dune retreat led to the creation of accommodation space for the storage of sediment by widening and elevating space between the pre- and post-storm dune toe, and reducing impacts of the storm surge. Dune recovery started in the month following the storm event and is still ongoing. It is characterised by the construction of "secondary" embryo dunes, which recovered at an average rate of 4-4.5 cm per month, although average monthly volume changes varied from - 1 to 2 m 3.m - 1 . These embryo dunes accreted due to a large aeolian sand supply from the upper tidal beach to the existing foredune. These dune-construction processes were facilitated by growth of vegetation on low-profile embryo dunes promoting backshore accretion. After more than two years of survey, the sediment budget of the beach/dune system showed that more than 10,000 m 3 has been lost by the upper tidal beach. We suggest that seaward return currents generated during the storm of 10th March 2008 are responsible for offshore sediment transport. Reconstitution of the equilibrium beach profile following the storm event may therefore have generated cross-shore sediment redistribution inducing net erosion in the tidal zone.
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International Nuclear Information System (INIS)
Brook, F.J.
1999-01-01
At least four depositional episodes, each involving cycles of dune instability and sand accumulation followed by stabilisation and soil formation, are represented in a Holocene dune sequence at Tokerau Beach. The first depositional episode followed the maximum post-glacial sea level rise at 6500 years BP, probably with formation of a narrow dune belt landward of the present coastline. The second depositional episode resulted in extensive progradation of the dune belt to about the present coastline from c. 3000-2000 years BP, followed by dune stabilisation and soil formation from c. 2000-900 years BP. The third depositional episode involved vertical dune accretion at c. 900-600 years BP, followed by stabilisation and soil formation after c. 600 years BP. The fourth depositional episode, after 240 years BP, resulted in further vertical dune accretion and localised extensive erosion and reworking of pre-existing dune deposits. Fossil landsnail faunas indicate that there was patchy sandfield and shrubland vegetation of the dune belt from c. 3000-2000 years BP, followed by a mosaic of shrubland and forest from c. 2000-900 years BP. After 900 years BP there was a progressive reversion to patchy shrubland vegetation, but an extensive shrubland cover again became established at c. 600 years BP and persisted until c. 450 years BP, when it was replaced by patchy shrubland and sandfield vegetation. Dune progradational phases in the first two depositional episodes correlate with and probably developed primarily in response to changes in sea level, whereas subsequent alternating phases of dune stabilisation and build-up are inferred to have resulted in part from the influence of long term cyclical variation in prevailing local wind and wave regimes in Doubtless Bay. Two stratigraphically distinct, exotic, sea-rafted pumice units are represented in the Tokerau dune sequence: Tokerau pumice (new), which has a primary depositional age of c. 3000 years BP, and Loisels pumice, which
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Boterenbrood, A.J.; Donsellaar-Ten Bokkel Huinink, van W.A.E.; Donselaar, van J.
1956-01-01
Dans la végétation des dunes du Languedoc J. BRAUN-BLANQUET (1952) distingue trois associations, à savoir; 1) l’Agropyretum mediterraneum parmi et sur les premières dunes basses; 2) l’Ammophiletum arundinaceae sur les dunes plus hautes; et 3) le Crucianelletum maritimae dans les dépressions et en
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Performances d'une nouvelle approche dans l'estimation au champ
African Journals Online (AJOL)
ACSS
Elle possède cependant des limitations, dues à l'organisation temporaire d'une .... Performances d'une nouvelle approche dans l'estimation au champ utilisant le principe de la ... différents types de résidus (soja, luzerne, haricot et maïs) et ...
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3D visualization of liquefaction-induced dune collapse in the Navajo Sandstone, Utah, USA
Ford, Colby; Nick, Kevin; Bryant, Gerald
2015-04-01
The eolian Navajo Sandstone outcrop on the Canyon Overlook Trail in Zion National Park in Southern Utah is dissected by modern erosion in a way which reveals a great deal of the three-dimensional architecture of a major soft-sediment deformation event. The feature is bounded below by a well-developed interdune complex made up of two superimposed carbonate lenses, above by an irregular truncational surface, and incorporates 3 - 10 m of sandstone over an approximately 2 km area. The material above the deformed interval is undeformed cross-bedded sandstone, with crossbeds downlapping onto the surface of truncation. The stratigraphic confinement of deformation and the irregularity of the upper bounding surface suggests a deformation process which created topography, which was in turn covered by the next upwind dune before it could be eroded flat. The deformed material itself is laterally segmented by a stacked succession of shear surfaces, which all strike approximately perpendicular to the paleo-wind direction and dip at decreasing angles in the down paleo-wind direction. These factors point to the collapse of a major dune into the downwind interdune area, likely initiated by liquefaction in the interdune complex. The foundering of the dune's toe into the liquefied area created a powerful lateral stress field which did not extend significantly into the subsurface. The dune collapse process has been used in the past to describe other soft-sediment deformation features in the Navajo Sandstone, but this site provides a wealth of physical details which were not previously associated with dune collapse. Shear surfaces originate in the interdune deposit as slip between laminae, then the cohesive muds provided support as they were thrust upward to angles of up to 50 degrees. The margins of the site also contain important paleoenvironmental indicators. Dinosaur tracks are exposed both at the extreme upwind and downwind margins of the interdune deposit in and slightly above
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Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars
Ewing, R. C.; Lapotre, M. G. A.; Lewis, K. W.; Day, M.; Stein, N.; Rubin, D. M.; Sullivan, R.; Banham, S.; Lamb, M. P.; Bridges, N. T.; Gupta, S.; Fischer, W. W.
2017-01-01
The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were pre...
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Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars
Ewing, R. C.; Lapotre, M. G. A.; Lewis, K. W.; Day, M.; Stein, N.; Rubin, D. M.; Sullivan, R.; Banham, S.; Lamb, M. P.; Bridges, N. T.; Gupta, S.; Fischer, W. W.
2017-01-01
Abstract The Mars Science Laboratory rover Curiosity visited two active wind‐blown sand dunes within Gale crater, Mars, which provided the first ground‐based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial‐like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples...
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Variability of sediment transport in beach and coastal dune environments, Brittany, France
Regnauld, Hervé; Louboutin, Roland
2002-06-01
On the coasts of Brittany (English Channel and Bay of Biscay), barrier systems were surveyed between 1995 and 2000. The beach profiles have a very high variability, which cannot be statistically explained by linear correlation with the wind, the waves, or the tides. The behaviour of the profile is represented on a phase diagram (speed of profile change: Y-axis, thickness of the profile: X-axis). The points in the center of the profile "rotate" around an average equilibrium which is seldom measured in the field. The seaward edge of the beaches oscillates between loss and gain, but with a net positive budget. The landward top of the beach displays a range of oscillations. The dunes always have a positive budget. The whole behaviour of the system is explained if the precise succession of anticyclonic and cyclonic winds is taken into account. Long periods of easterly winds (offshorewards) tend to produce a calm sea and to increase tidal sediment settling on the seafloor. If an onshore westerly storm occurs just after such a period, it hits a sediment-rich environment and produces a net accumulation on both the beach and the dunes. Periods of westerly calm to moderate winds do not help accumulation: a full going storm will hit a depleted environment and produce erosion. The speed of dune accretion and the budget of the beaches seem to partly depend on the ratio of cyclonic to anticyclonic conditions.
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Topographically-controlled site conditions drive vegetation pattern on inland dunes in Poland
Sewerniak, Piotr; Jankowski, Michał
2017-07-01
The inland dunes of Central Europe are commonly overplanted by Scots pine (Pinus sylvestris) monocultures in which the primary occurrence of the natural vegetation pattern is obliterated. We hypothesize that on naturally revegetated inland dunes the pattern is clear and driven by topographically-controlled site conditions. To test this hypothesis, we addressed the following research questions: (1) Does topography drive vegetation patterns on inland dunes and if so, what are main differences between vegetation in varying relief positions? (2) To what extent does topography involve the variability of microclimates and of soil properties, and how does the topographically-induced differentiation of these site conditions control vegetation patterns? We conducted interdisciplinary studies (applying floristic, pedological and microclimatic research techniques) on a naturally revegetated inland dune area situated on a military artillery training ground near Toruń, northern Poland. We investigated vegetation patterns with reference to three topographical position variants (north-facing slopes, south-facing slopes, and intra-dune depressions). We found distinct differences in vegetation characteristics covering the aforementioned topographical positions. This primarily concerned species composition of ground vegetation: Calluna vulgaris was dominant species on north-facing slopes, Corynephorus canescens on south-facing slopes, while Calamagrostis epigejos in intra-dune depressions. In comparison to dune slopes, the depressions were characterized by much higher biodiversity of vascular plant species. This followed the most favorable soil conditions for the existence of plants (higher moisture and nutrient pools) occurring in low topographical positions. However, tree succession was most advanced not in depressions, where the competitive impact of tall grasses on seedlings was recognized, but on north-facing slopes. Based on our results, we formulated some suggestions, which
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SHEAR STRENGTH, COLLAPSIBILITY AND COMPRESSIBILITY CHARACTERISTICS OF COMPACTED BAIJI DUNE SOILS
Directory of Open Access Journals (Sweden)
ABBAS JAWAD AL-TAIE
2017-03-01
Full Text Available Baiji city is a vital industrial centre in Iraq since it has the biggest oil refinery. Therefore, Baiji has become an attractive site for strategic construction projects. Dune sand covers about 220 km2 of the area of Baiji city. However, few researches had attempted to study its behaviour. In this study laboratory tests were conducted to determine the shear strength, collapsibility and compressibility of the dune sand at its natural and compacted status. The effect of dry unit weight, moisture content, relative density and soaking on mechanical properties of dune soil was investigated. The results demonstrated that dry and soaked dune specimens tested at their in-situ condition exhibited similar volume changes during shear and identical friction angles. The results of shear tests of both of compacted soaked and unsoaked samples were identical. The collapse potential of dune soil is inversely proportional with the relative density. The minimum axial strain is observed when the samples are compacted to modified effort. The compression index of the compacted specimens is affected by moulding water content, while the rebound index is less sensitive.
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Carling, P. A.; Radecki-Pawlik, A.; Williams, J. J.; Rumble, B.; Meshkova, L.; Bell, P.; Breakspear, R.
2006-01-01
In the macrotidal Severn estuary, UK, the dynamics of intertidal fine-gravel dunes were investigated. These dunes are migrating across a bedrock platform. Systematic observations were made of hydraulic climate, geometry, migration rates and internal sedimentary structures of the dunes. During spring tides, the ebb flow is dominant, dunes grow in height and have ebb orientated geometry with bedrock floors in the troughs. During neap tides, a weak flood flow may dominate. Dunes then are flood orientated or symmetrical. Neap dune heights decrease and the eroded sediment is stored in the dune troughs where the bedrock becomes blanketed by muddy gravel. During spring tides, instantaneous bed shear stresses reach 8 N m - 2 , sufficient to disrupt a 9 mm-gravel armour layer. However, a sustained bed shear stress of 4 N m - 2 is required to initiate dune migration at which time the critical depth-mean velocity is 1 m s - 1 . Ebb and flood inequalities in the bed shear stress explain the changes in dune asymmetry and internal structures. During flood tides, the crests of the dunes reverse such that very mobile sedimentary 'caps' overlie a more stable dune 'core'. Because ebb tides dominate, internal structures of the caps often are characterised by ebb orientated steep open-work foresets developed by strong tidal currents and some lower angle crossbeds deposited as weaker currents degrade foresets. The foresets forming the caps may be grouped into cosets (tidal bundles) and are separated from mud-infused cores of crossbeds that lie below, by reactivation and erosion surfaces blanketed by discontinuous mud drapes. The cores often exhibit distinctive muddy toe sets that define the spacing of tidal cosets.
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Demography and monitoring of Welsh's milkweed (Asclepias welshii) at Coral Pink Sand Dunes
Brent C. Palmer; L. Armstrong
2001-01-01
Results are presented of a 12-year monitoring program on the Coral Pink Sand Dunes and Sand Hills populations of the threatened Welsh's milkweed, Asclepias welshii N & P Holmgren. The species is an early sera1 member of the dune flora, colonizing blowouts and advancing with shifting dunes. When an area stabilizes and other vegetation encroaches, A. welshii is...
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Erosion of Coastal Foredunes: A Review on the Effect of Dune Vegetation
2017-02-01
inhabited by vegetation (Figure 2).The collision regime occurs when the total storm water level exceeds the elevation of the dune toe but is lower than the...of Dune Vegetation by Duncan B. Bryant, Mary A. Bryant, and Alison S. Grzegorzewski PURPOSE: The purpose of this Coastal and Hydraulics...Engineering Technical Note (CHETN) is to identify the potential roles of vegetation in mitigating coastal dune erosion during storm events by presenting a
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2011-10-06
...] Draft Conservation Plan and Draft Environmental Assessment; Dunes Sagebrush Lizard, Texas AGENCY: Fish... draft Texas Conservation Plan for the Dunes Sagebrush Lizard (TCP). The draft TCP will function as a... the Applicant for the dunes sagebrush lizard (Sceloporus arenicolus) throughout its range in Texas...
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Responses of woody species to spatial and temporal ground water changes in coastal sand dune systems
Directory of Open Access Journals (Sweden)
C. Máguas
2011-12-01
Full Text Available In spite of the relative importance of groundwater in costal dune systems, studies concerning the responses of vegetation to ground water (GW availability variations, particularly in Mediterranean regions, are scarce. Thus, the main purpose of this study is to compare the responses of co-occurring species possessing different functional traits, to changes in GW levels (i.e. the lowering of GW levels in a sand dune ecosystem. For that, five sites were established within a 1 km2 area in a meso-mediterranean sand dune ecosystem dominated by a Pinus pinaster forest. Due to natural topographic variability and anthropogenic GW exploitation, substantial variability in depth to GW between sites was found. Under these conditions it was possible to identify the degree of usage and dependence on GW of different plant species (two deep-rooted trees, a drought adapted shrub, a phreatophyte and a non-native woody invader and how GW dependence varied seasonally and between the heterogeneous sites. Results indicated that the plant species had differential responses to changes in GW depth according to specific functional traits (i.e. rooting depth, leaf morphology, and water use strategy. Species comparison revealed that variability in pre-dawn water potential (Ψpre and bulk leaf δ13C was related to site differences in GW use in the deep-rooted (Pinus pinaster, Myrica faya and phreatophyte (Salix repens species. However, such variation was more evident during spring than during summer drought. The exotic invader, Acacia longifolia, which does not possess a very deep root system, presented the largest seasonal variability in Ψpre and bulk leaf δ13C. In contrast, the response of Corema album, an endemic understory drought-adapted shrub, seemed to be independent of water availability across seasons and sites. Thus, the susceptibility to lowering of GW due to anthropogenic
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Is succession in wet calcareous dune slacks affected by free sulfide?
Adema, EB; van Gemerden, H; Grootjans, AP; Adema, Erwin B.; Grootjans, Ab P.; Rapson, G.
Consequences of sulfide toxicity on succession in wet calcareous dune slacks were investigated. Sulfide may exert an inhibitory effect on dune slack plants, but several pioneer species exhibit ROL (Radial Oxygen Loss) and thereby protect themselves against free sulfide. Under oxic conditions free
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Neutrinos, DUNE and the world best bound on CPT invariance
Barenboim, G.; Ternes, C. A.; Tórtola, M.
2018-05-01
CPT symmetry, the combination of Charge Conjugation, Parity and Time reversal, is a cornerstone of our model building strategy and therefore the repercussions of its potential violation will severely threaten the most extended tool we currently use to describe physics, i.e. local relativistic quantum fields. However, limits on its conservation from the Kaon system look indeed imposing. In this work we will show that neutrino oscillation experiments can improve this limit by several orders of magnitude and therefore are an ideal tool to explore the foundations of our approach to Nature. Strictly speaking testing CPT violation would require an explicit model for how CPT is broken and its effects on physics. Instead, what is presented in this paper is a test of one of the predictions of CPT conservation, i.e., the same mass and mixing parameters in neutrinos and antineutrinos. In order to do that we calculate the current CPT bound on all the neutrino mixing parameters and study the sensitivity of the DUNE experiment to such an observable. After deriving the most updated bound on CPT from neutrino oscillation data, we show that, if the recent T2K results turn out to be the true values of neutrino and antineutrino oscillations, DUNE would measure the fallout of CPT conservation at more than 3σ. Then, we study the sensitivity of the experiment to measure CPT invariance in general, finding that DUNE will be able to improve the current bounds on Δ (Δ m312) by at least one order of magnitude. We also study the sensitivity to the other oscillation parameters. Finally we show that, if CPT is violated in nature, combining neutrino with antineutrino data in oscillation analysis will produce imposter solutions.
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CONTRIBUTION TO THE STUDY OF DUNES FIXATION IN THE SEMI-ARIDE ENVIRONMENT: ALGERIA
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Saida Akkouche
2017-05-01
Full Text Available In our study,of dune fixation , spontaneous vegetation was installed inside the grid. Over the years, plant diversity has improved with74 species in 2009 (22 families and 61 genera, demonstrating a significant reduction of troubles, caused especially by the erosive action of winds and other microclimate factors. Indeed, in non-fixed dunes (mechanical and biological fixation vegetation is particularly present in the lower slopes of the dunes shelter where humidity is relatively high and the soil fertile. But in fixed environments, vegetation climbs to the top of dunes, improving: I The Microclimate; creating a gentle atmosphere under the effect of shade and transpiration; II Floor; increasing its humidity and improving its fertility through the provision of litter. On all of the fixed dunes and under the feet of planted species a surface layer of soil , sometimes reduced in a few centimeters, is formed by fine particles of clays and acting as a shield which reduces evaporation and therefore allows a relatively large water retention preserved for a longer period of the year. This layer is called "Self-mulching" is a colloidal material which sticks the sand after a biological dune fixation.
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Laboratory studies of dune sand for the use of construction industry in Sri Lanka
de Silva Jayawardena, Upali; Wijesuriya, Roshan; Abayaweera, Gayan; Viduranga, Tharaka
2015-04-01
With the increase of the annual sand demand for the construction industry the excessive excavation of river sand is becoming a serious environmental problem in Sri Lanka. Therefore, it is necessary to explore the possibility for an alternative to stop or at least to minimize river sand mining activities. Dune sand is one of the available alternative materials to be considered instead of river sand in the country. Large quantities of sand dunes occur mainly along the NW and SE coastal belt which belong to very low rainfall Dry Zone coasts. The height of dune deposits, vary from 1m to about 30 meters above sea level. The objective of this paper is to indicate some studies and facts on the dune sand deposits of Sri Lanka. Laboratory studies were carried out for visual observations and physical properties at the initial stage and then a number of tests were carried out according to ASTM standards to obtain the compressive strength of concrete cylinders and mortar cubes mixing dune sand and river sand in different percentages keeping a constant water cement ratio. Next the water cement ratio was changed for constant dune sand and river sand proportion. Microscopic analysis shows that the dune sand consist of 95 % of quartz and 5 % of garnet, feldspar, illmenite and other heavy minerals with clay, fine dust, fine shell fragments and organic matters. Grains are sub-rounded to angular and tabular shapes. The grain sizes vary from fine to medium size of sand with silt. The degree of sorting and particle size observed with dune sands are more suited with the requirement of fine aggregates in the construction industry. The test result indicates that dune sand could be effectively used in construction work without sieving and it is ideal for wall plastering due to its'-uniformity. It could also be effectively used in concrete and in mortars mixing with river sand. The best mixing ratio is 75% dune sand and 25% river sand as the fine aggregate of concrete. For mortar the mixing
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Restoration of Dune Habitats in Østerild Klitplantage - Baseline Monitoring 2011
DEFF Research Database (Denmark)
Nygaard, Bettina; Wind, Peter; Ejrnæs, Rasmus
will lead to clear-felling of up to 266 ha coniferous dune plantations. The agreement parties decided that the vegetation development from coniferous forest to open dune habitats should be monitored. The monitoring programme includes a recording of soil conditions and plant species composition pr...
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Linking marine resources to ecotonal shifts of water uptake by terrestrial dune vegetation.
Greaver, Tara L; Sternberg, Leonel L da S
2006-09-01
As evidence mounts that sea levels are rising, it becomes increasingly important to understand the role of ocean water within terrestrial ecosystem dynamics. Coastal sand dunes are ecosystems that occur on the interface of land and sea. They are classic ecotones characterized by zonal distribution of vegetation in response to strong gradients of environmental factors from the ocean to the inland. Despite the proximity of the dune ecosystem to the ocean, it is generally assumed that all vegetation utilizes only freshwater and that water sources do not change across the ecotone. Evidence of ocean water uptake by vegetation would redefine the traditional interpretation of plant-water relations in the dune ecosystem and offer new ideas for assessing maritime influences on function and spatial distribution of plants across the dune. The purpose of this study was to identify sources of water (ocean, ground, and rain) taken up by vegetation using isotopic analysis of stem water and to evaluate water uptake patterns at the community level based on the distribution and assemblage of species. Three coastal dune systems located in southern Florida, USA, and the Bahamian bank/platform system were investigated. Plant distributions across the dune were zonal for 61-94% of the 18 most abundant species at each site. Species with their highest frequency on the fore dune (nearest the ocean) indicate ocean water uptake as evidenced by delta 18O values of stem water. In contrast, species most frequent in the back dune show no evidence of ocean water uptake. Analysis of species not grouped by frequency, but instead sampled along a transect from the ocean toward the inland, indicates that individuals from the vegetation assemblage closest to the ocean had a mixed water-harvesting strategy characterized by plants that may utilize ocean, ground-, and/or rainwater. In contrast, the inland vegetation relies mostly on rainwater. Our results show evidence supporting ocean water use by dune
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Quantification of Dune Response over the Course of a 6-Day Nor'Easter, Outer Banks, NC
Brodie, K. L.; Spore, N.; Swann, C.
2014-12-01
The amount and type of foredune morphologic change during a storm event primarily scales with the level of inundation during that event. Specifically, external hydrodynamic forcing (total water level) can be compared with antecedent beach and foredune morphology to predict an impact regime that relates to the type of expected morphologic evolution of the system. For example, when total water levels are above the dune toe, but below the dune crest, the impact regime is classified as "collision" and the expected morphology response is slumping or scarping of the dune face. While the amount of dune retreat scales largely with the duration of wave attack to the dune face, characteristics of the dune other than its crest or toe elevation may also enhance or impede rates of morphologic change. The aftermath of Hurricane Sandy provided a unique opportunity to observe alongshore variations in dune response to a 6-day Nor'Easter (Hs >4 m in 6 m depth), as a variety of dunes were constructed (or not) by individual home owners in preparation for the winter storm season. Daily terrestrial lidar scans were conducted along 20 km of coastline in Duck, NC using Coastal Lidar And Radar Imaging System (CLARIS) during the first dune collision event following Sandy. Foredunes were grouped by their pre-storm form (e.g. vegetated, pushed, scarped, etc) using automated feature extraction tools based on surface curvature and slope, and daily rates of morphologic volume change were calculated. The highest dune retreat rates were focused along a 1.5 km region where cross-shore erosion of recently pushed, un-vegetated dunes reached 2 m/day. Variations in dune response were analyzed in relation to their pre-storm morphology, with care taken to normalize for alongshore variations in hydrodynamic forcing. Ongoing research is focused on identifying specific metrics that can be easily extracted from topographic DEMs to aid in dune retreat predictions.
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Giambastiani, Beatrice M. S.; Greggio, Nicolas; Sistilli, Flavia; Fabbri, Stefano; Scarelli, Frederico; Candiago, Sebastian; Anfossi, Giulia; Lipparini, Carlo A.; Cantelli, Luigi; Antonellini, Marco; Gabbianelli, Giovanni
2016-10-01
Coastal dunes play an important role in protecting the coastline. Unfortunately, in the last decades dunes have been removed or damaged by human activities. In the Emilia- Romagna region significant residual dune systems are found only along Ravenna and Ferrara coasts. In this context, the RIGED-RA project “Restoration and management of coastal dunes along the Ravenna coast” (2013-2016) has been launched with the aims to identify dynamics, erosion and vulnerability of Northern Adriatic coast and associated residual dunes, and to define intervention strategies for dune protection and restoration. The methodology is based on a multidisciplinary approach that integrates the expertise of several researchers and investigates all aspects (biotic and abiotic), which drive the dune-beach system. All datasets were integrated to identify test sites for applying dune restoration. The intervention finished in April 2016; evolution and restoration efficiency will be assessed.
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Nolet, Corjan; van Puijenbroek, Marinka; Suomalainen, Juha; Limpens, Juul; Riksen, Michel
2018-04-01
Vegetated coastal dunes have the capacity to keep up with sea-level rise by accumulating and stabilizing wind-blown sand. In Europe, this is attributed to marram grass (Ammophila arenaria), a coastal grass species that combines two unique advantages for dune-building: (1) a very high tolerance to burial by wind-blown sand, and (2) more vigorous growth due to positive feedback to sand burial. However, while these vegetation characteristics have been demonstrated, observational data has not been used to model a function to describe the growth response of Ammophila to sand burial. Studies that model coastal dune development by incorporating positive feedback, as a result, may be hampered by growth functions that are unvalidated against field data. Therefore, this study aims to parameterize an empirical relationship to model the growth response of Ammophila to burial by wind-blown sand. A coastal foredune along a nourished beach in the Netherlands was monitored from April 2015 to April 2016. High-resolution geospatial data was acquired using an Unmanned Aerial Vehicle (UAV). Growth response of Ammophila, expressed by changes in Normalized Difference Vegetation Index (Δ NDVI) and vegetation cover (Δ Cover), is related to a sand burial gradient by fitting a Gaussian function using nonlinear quantile regression. The regression curves indicate an optimal burial rate for Ammophila of 0.31 m of sand per growing season, and suggest (by extrapolation of the data) a maximum burial tolerance for Ammophila between 0.78 (for Δ Cover) and 0.96 m (for Δ NDVI) of sand per growing season. These findings are advantageous to coastal management: maximizing the potential of Ammophila to develop dunes maximizes the potential of coastal dunes to provide coastal safety.
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Qian, F.; Lee, D. B.; Bodek, S.; Roberts, S.; Topping, T. T.; Robele, Y.; Koditschek, D. E.; Jerolmack, D. J.
2017-12-01
Understanding the parameters that control the spatial variation in aeolian soil erodibility is crucial to the development of sediment transport models. Currently, in-situ measurements of erodibility are time consuming and lack robustness. In an attempt to remedy this issue, we perform field and laboratory tests to determine the suitability of a novel mechanical shear strength method to assess soil erodibility. These tests can be performed quickly ( 1 minute) by a semi-autonomous robot using its direct-drive leg, while environmental controls such as soil moisture and grain size are simultaneously characterized. The robot was deployed at White Sands National Monument to delineate and understand erodibility gradients at two different scales: (1) from dry dune crest to moist interdune (distance 10s m), where we determined that shear strength increases by a factor of three with increasing soil moisture; and (2) from barren barchan dunes to vegetated and crusted parabolics downwind (distance 5 km), where we found that shear strength was enhanced by a factor of two relative to loose sand. Interestingly, shear strength varied little from carbonate-crusted dune surfaces to bio-crust covered interdunes in the downwind parabolic region, indicating that varied surface crusts contribute similarly to erosion resistance. To isolate the control of soil moisture on erodibility, we performed laboratory experiments in a sandbox. These results verify that the observed increase in soil erodibility from barchan crest to interdune at White Sands is dominated by soil moisture, and the variation in parabolic dune and barchan interdune areas results from a combination of soil moisture, bio-activity, and crust development. This study highlights that spatial variation of soil erodibility in arid environments is large enough to significantly affect sediment transport, and that probing soil erodibility with a robot has the potential to improve our understanding of this multifaceted problem.
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2011-04-07
... for Dunes Sagebrush Lizard AGENCY: Fish and Wildlife Service, Interior. ACTION: Proposed rule... list the dunes sagebrush lizard (Sceloporus arenicolus) under the Endangered Species Act of 1973, as... dunes sagebrush lizard (Sceloporus arenicolus) that was published in the Federal Register on December 14...
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The primary opinion on the formation mechanisms of mega dunes and lakes in the Badain jaran desert
International Nuclear Information System (INIS)
Guo Yonghai; Li Yawei
2010-01-01
Badain Jaran Desert is famous in distribution of many lakes and mega dunes in the world. Up to now, there are several different opinions about formation problems of lakes and mega dunes. Actually, these problems are directly correlated to the groundwater circulation and alternation in the area. Refering to the prevenient research results and combining with the current hydrogeological investigation in the desert, the paper discussed the problems about the formation mechanisms of lakes and mega dunes. The Primary cognition is that: the lakes in the desert were formed mainly by the lateral recharge of groundwaters both from Yabulai mountain and mega dunes. The formation of the mega dunes was related nearly to the rainfall and groundwater in the area. The formation and coexistence relationship between lakes and mega dunes is that: the mega dunes were formed firstly, and then the lakes. That is to say the mega dunes are the basic conditions for the lake formation. (authors)
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Martian aeolian activity at the Bagnold Dunes, Gale Crater: The view from the surface and orbit
Bridges, N. T.; Sullivan, R.; Newman, C. E.; Navarro, S.; van Beek, J.; Ewing, R. C.; Ayoub, F.; Silvestro, S.; Gasnault, O.; Le Mouélic, S.; Lapotre, M. G. A.; Rapin, W.
2017-10-01
The first in situ investigation of an active dune field on another planetary surface occurred in 2015-2016 when the Mars Science Laboratory Curiosity rover investigated the Bagnold Dunes on Mars. High Resolution Imaging Science Experiment images show clear seasonal variations that are in good agreement with atmospheric model predictions of intra-annual sand flux and migration directions that together indicate that the campaign occurred during a period of low wind activity. Curiosity surface images show that limited changes nevertheless occurred, with movement of large grains, particularly on freshly exposed surfaces, two occurrences of secondary grain flow on the slip face of Namib Dune, and a slump on a freshly exposed surface of a large ripple. These changes are seen at Martian solar day (sol)-to-sol time scales. Grains on a rippled sand deposit and unconsolidated dump piles show limited movement of large grains over a few hours during which mean friction speeds are estimated at 0.3-0.4 m s-1. Overall, the correlation between changes and peak Rover Environmental Monitoring Station (REMS) winds is moderate, with high wind events associated with changes in some cases, but not in others, suggesting that other factors are also at work. The distribution of REMS 1 Hz wind speeds shows a significant tail up to the current 20 m s-1 calibration limit, indicating that even higher speed winds occur. Nonaeolian triggering mechanisms are also possible. The low activity period at the dunes documented by Curiosity provides clues to processes that dominated in the Martian past under conditions of lower obliquity.
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Sand Dunes in Steady Flow at Low Froude Numbers: Dune Height Evolution and Flow Resistance
DEFF Research Database (Denmark)
Niemann, S. L.; Fredsøe, Jørgen; Jacobsen, Niels Gjøl
2011-01-01
equilibrium shape. The flow modeling is based on a k-ω turbulence closure. The sediment transport is assumed to be bed-load only, with an avalanche-like movement on the steep dune front. The model is also found capable of predicting the growth in wavelength if the initially prescribed wavelength...
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Doermann, L.; Kaminsky, G. M.; Ruggiero, P.
2006-12-01
Beach topographic data have been collected along the 160 km-long Columbia River Littoral Cell in southwest Washington and northwest Oregon, USA as part of the Southwest Washington Coastal Erosion Study and a NANOOS pilot project. The monitoring program includes the collection of cross-shore beach profiles at 49 sites for each of the 34 seasons since 1997 (with few exceptions), enabling the investigation of the seasonal to interannual morphological variability of this high-energy coast. We focus here on the dunes backing the beaches, aiming to quantitatively describe the wide variety of characteristics they exhibit, as well as to relate dune evolution to shoreline change. To analyze the large volume of high-quality data, we use automated algorithms and systematic processes to identify the location of the dune toe, crest, and face, and calculate a volume (where enough data are available) and beach width for each survey. We define the position of the dune face as the elevation half-way between the average dune toe and average dune crest elevations at each profile location, and beach width as the horizontal distance between the 2-m contour (~MSL) and the dune toe. Much like shoreline proxies lower on the beach profile, (e.g., the 3-m contour), the location of the dune toe shows large seasonal variability with onshore deposition of sand in summer months and offshore sand transport in the winter. However, the location of the dune face and the elevation of the dune crest are much less variable and are useful in describing the evolution of the dune/beach system in the horizontal and vertical directions, respectively, over interannual time scales. On beaches with the highest shoreline change rates in the study area, the dune face follows the progradational trend of the shoreline with the dune face prograding at approximately 25-50% of the rate of the shoreline. Along many of these beaches that experienced severe erosion during the El Niño of 1997/98, the dune face
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Yang, Haotian; Li, Xinrong; Wang, Zengru; Jia, Rongliang; Liu, Lichao; Chen, Yongle; Wei, Yongping; Gao, Yanhong; Li, Gang
2014-04-15
Reconstructing vegetation in arid and semiarid areas has become an increasingly important management strategy to realize habitat recovery, mitigate desertification and global climate change. To assess the carbon sequestration potential in areas where sand-binding vegetation has been established on shifting sand dunes by planting xeric shrubs located near the southeastern edge of the Tengger Desert in northern China, we conducted a field investigation of restored dune regions that were established at different times (20, 30, 47, and 55 years ago) in the same area. We quantified the total organic carbon (TOC) in each ecosystem by summing the individual carbon contributions from the soil (soil organic carbon; SOC), shrubs, and grasses in each system. We found that the TOC, as well as the amount of organic carbon in the soil, shrubs, and grasses, significantly increased over time in the restored areas. The average annual rate of carbon sequestration was highest in the first 20 years after restoration (3.26 × 10(-2)kg·m(-2) ·year(-1)), and reached a stable rate (2.14 × 10(-2) kg·m(-2) ·year(-1)) after 47 years. Organic carbon storage in soil represented the largest carbon pool for both restored systems and a system containing native vegetation, accounting for 67.6%-85.0% of the TOC. Carbon in grass root biomass, aboveground grass biomass, litter, aboveground shrub biomass, and shrub root biomass account for 10.0%-21.0%, 0.2%-0.6%, 0.1%-0.2%, 1.7%-12.1% and 0.9%-6.2% of the TOC, respectively. Furthermore, we found that the 55-year-old restored system has the capacity to accumulate more TOC (1.02 kg·m(-2) more) to reach the TOC level found in the natural vegetation system. These results suggest that restoring desert ecosystems may be a cost-effective and environmentally friendly way to sequester CO2 from the atmosphere and mitigate the effects of global climate change. Copyright © 2014 Elsevier B.V. All rights reserved.
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Petrology of dune sand derived from basalt on the Ka'u Desert, Hawaii
Gooding, J. L.
1982-01-01
Dune sand from the Ka'u Desert, southwest flank of Kilauea volcano, Hawaii, is moderately well-sorted (median = 1.60 Phi, deviation = 0.60, skewness = 0.25, kurtosis = 0.68) and composed mostly of frosted subangular particles of basalt glass ('unfractionated' olivine-normative tholeitte), olivine, lithic fragments (subophitic and intersertal basalts; magnetite-ilmenite-rich basalts), reticular basalt glass, magnetite, ilmenite, and plagioclase, in approximately that order of abundance. Quantitative lithological comparison of the dune sand with sand-sized ash from the Keanakakoi Formation supports suggestions that the dune sand was derived largely from Keanakakoi ash. The dune sand is too well sorted to have been emplaced in its present form by base-surge but could have evolved by post-eruption reworking of the ash.
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Nourishment of perched sand dunes and the issue of erosion control in the Great Lakes
Marsh, William M.
1990-09-01
Although limited in coverage, perched sand dunes situated on high coastal bluffs are considered the most prized of Great Lakes dunes. Grand Sable Dunes on Lake Superior and Sleeping Bear Dunes on Lake Michigan are featured attractions of national lakeshores under National Park Service management. The source of sand for perched dunes is the high bluff along their lakeward edge. As onshore wind crosses the bluff, flow is accelerated upslope, resulting in greatly elevated levels of wind stress over the slope brow. On barren, sandy bluffs, wind erosion is concentrated in the brow zone, and for the Grand Sable Bluff, it averaged 1 m3/yr per linear meter along the highest sections for the period 1973 1983. This mechanism accounts for about 6,500 m3 of sand nourishment to the dunefield annually and clearly has been the predominant mechanism for the long-term development of the dunefield. However, wind erosion and dune nourishment are possible only where the bluff is denuded of plant cover by mass movements and related processes induced by wave erosion. In the Great Lakes, wave erosion and bluff retreat vary with lake levels; the nourishment of perched dunes is favored by high levels. Lake levels have been relatively high for the past 50 years, and shore erosion has become a major environmental issue leading property owners and politicians to support lake-level regulation. Trimming high water levels could reduce geomorphic activity on high bluffs and affect dune nourishment rates. Locally, nourishment also may be influenced by sediment accumulation associated with harbor protection facilities and by planting programs aimed at stabilizing dunes.
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Seasonal geomorphic processes and rates of sand movement at Mount Baldy dune in Indiana, USA
Kilibarda, Zoran; Kilibarda, Vesna
2016-12-01
Winds are very strong, frequent, and have high energy (annual DP ∼800 VU) along the southern shores of Lake Michigan, allowing the coexistence of fixed and active dunes. Six years (2007-13) of monitoring Mount Baldy in the Indiana Dunes National Lakeshore reveals that this is the most active coastal dune in the Great Lakes region. This paper documents aeolian processes and changes in the dune's morphology that occur temporarily, following storms, or seasonally, due to weather (climate) variations. Most of the sand transport in this area takes place during strong storms with gale force (>17.5 m/s) winds, which occur in the autumn and winter months. A single storm, such as the October 28-31, 2013 event, can contribute 25% of the annual sand transport and dune movement inland. In its most active year (June 1, 2011 through May 31, 2012), Mount Baldy moved inland on average 4.34 m, with a maximum of 6.52 m along the blowout's axis (155° azimuth). During this particularly active season, there were six storms with sustained gale force winds, winter air temperatures were warmer than average, and shelf ice on Lake Michigan lasted only one day. The dune is least active during the summer season, when the winds are weakest. The late fall and winter winds are the strongest. But in a typical year, most of the dune's advance inland takes place during the spring thaw when sand is released from over-steepened and lumpy slip face, allowing it to avalanche to the toe of the slip face. However, with a warming air temperatures, a reduction in the duration of winter shelf ice, and rising Lake Michigan levels, the annual rates of sand transport and dune movement may increase. The recent Mount Baldy management strategy, which includes planting vegetation and installing wind barriers on the dune's stoss side in an effort to fix the dune and stop its further movement inland, may potentially cause the destruction of the mobile sand, open dune habitat, resulting in the extinction of rare
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Energy Technology Data Exchange (ETDEWEB)
Camprubi, A.; Calvet, C.; Cabot, P.; Pitet, M.; Estaun, V.
2010-07-01
This study was conducted in order to characterize the natural albacore's mycorrhizal (AM) biodiversity from Mediterranean sand dune ecosystems and to protect in a collection this biodiversity. The occurrence of AM fungi associated with sand dune plant species in three Mediterranean locations on the north-eastern coast of Spain was examined in one well preserved coastal sand dune and in two embrionary dunes recently protected from public access. Traditional taxonomy and molecular techniques were used to identify the AM fungal species present in these ecosystems. The species identified and isolated were: Scutellospora persica (Kiosk and Walker) Walker and Sanders, Glomus ambisporum Smith and Schenck, Glomus diaphanum Morton and Walker, Glomus clarum Nicolson and Schenck, Glomus intraradices Schenck and Smith, Glomus microaggregatum Koske, Gemma and Olexia and Gigaspora margarita Becker and Hall. Spores of Glomus were the most abundant in the direct soil extraction samples. The molecular analysis indicates that the most abundant fungi forming AM in the roots belonged to the Gigasporaceae group followed by fungi of Glomus group A and Glomus group B. The highest diversity of fungi and abundance of the AM fungal spores was found in the well preserved and undisturbed dune systems. (Author) 26 refs.
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Sand Dune Ridge Alignment Effects on Surface BRF over the Libya-4 CEOS Calibration Site
Directory of Open Access Journals (Sweden)
Yves M. Govaerts
2015-02-01
Full Text Available The Libya-4 desert area, located in the Great Sand Sea, is one of the most important bright desert CEOS pseudo-invariant calibration sites by its size and radiometric stability. This site is intensively used for radiometer drift monitoring, sensor intercalibration and as an absolute calibration reference based on simulated radiances traceable to the SI standard. The Libya-4 morphology is composed of oriented sand dunes shaped by dominant winds. The effects of sand dune spatial organization on the surface bidirectional reflectance factor is analyzed in this paper using Raytran, a 3D radiative transfer model. The topography is characterized with the 30 m resolution ASTER digital elevation model. Four different regions-of-interest sizes, ranging from 10 km up to 100 km, are analyzed. Results show that sand dunes generate more backscattering than forward scattering at the surface. The mean surface reflectance averaged over different viewing and illumination angles is pretty much independent of the size of the selected area, though the standard deviation differs. Sun azimuth position has an effect on the surface reflectance field, which is more pronounced for high Sun zenith angles. Such 3D azimuthal effects should be taken into account to decrease the simulated radiance uncertainty over Libya-4 below 3% for wavelengths larger than 600 nm.
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A bright intra-dune feature on Titan and its implications for sand formation and transport
MacKenzie, Shannon; Barnes, Jason W.; Rodriguez, Sebastien; Cornet, Thomas; Brossier, Jeremy; Soderblom, Jason M.; Le Mouélic, Stephane; Sotin, Christophe; Brown, Robert H.; Buratti, Bonnie J.; Clark, Roger Nelson; Nicholson, Philip D.; Baines, Kevin
2017-10-01
Organic sands cover much of Titan’s equatorial belt, gathered into longitudinal dunes about a kilometer wide and hundreds of kilometers long. At the end of the Cassini era, questions of how such a vast volume of saltable material is or was created on Titan remain unanswered. At least two possible mechanisms suggested for forming sand-sized particles involve liquids: (1) evaporite deposition and erosion and (2) flocculation of material within a lake. Transporting sand from the lakes and seas of Titan’s poles to the equatorial belt is not strongly supported by Cassini observations: the equatorial belt sits higher than the poles and no sheets or corridors of travelling sand have been identified. Thus, previous sites of equatorial surface liquids may be of interest for understanding sand formation, such as the suggested paleoseas Tui and Hotei Regio. A newly identified feature in the VIMS data sits within the Fensal dune field but is distinct from the surrounding sand. We investigate this Bright Fensal Feature (BFF) using data from Cassini VIMS and RADAR. Specifically, we find spectral similarities between the BFF and both sand and Hotei Regio. The RADAR cross sectional backscatter is similar to neighboring dark areas, perhaps sand covered interdunes. We use this evidence to constrain the BFF’s formation history and discuss how this intra-dune feature may contribute to the processes of sand transport and supply.
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Marconi, V.; Antonellini, M.; Balugani, E.; Minchio, A.; Gabbianelli, G.
2009-04-01
Due to climate changes and to anthropogenic interventions, saltwater intrusion is affecting the aquifers and the surface water of the Po plain along the Adriatic coast. During the last decade, we recognized in this area a pattern of climate change: precipitations are less frequent and the yearly amount of rain is concentrated in a few strong storm events. This pattern results in an increase of gales strength during the winter, which causes shoreline retreat and an erosion of the coastal dunes. The coastal part of the Po plain consists of a low-lying and mechanically-drained farmland further from the sea and of a narrow belt of dunes and pine forests in the backshore area. The wide sandy beaches are now retreating and the dune system (only a few meters in height) is almoust destroyed, because of tourism development and of disaggregated rivers and shorelines management. A still active dune system is preserved in our study area, a coastal plain included between the Fiumi Uniti and Bevano rivers near the city of Ravenna. As a result of an intensive exploitation of coastal aquifers for agricultural, industrial, and civil uses, both the phreatic aquifer and the surface waters have been contaminated by seawater. Despite its value for the natural ecosystem and the agricultural soil, the phreatic aquifer is not considered of interest by the regional authorities responsible for water management. A detailed hydrogeological survey was performed by our research group during the Summer 2008 within the framework of the CIRCLE-ERANET project WATERKNOW on the effects of climate change on the mediterranean catchments. In this survey 29 auger holes with an average spacing of 350 m where drilled with the objective of determining the top groundwater quality in the coastal aquifer. At the same time, we measured the chemical and physical parameters of the surface waters. The data collected in the field show that a fresh groundwater lens is still present in the aquifer of the backshore
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Natural and anthropogenic factors affecting freshwater lenses in coastal dunes of the Adriatic coast
Cozzolino, Davide; Greggio, Nicolas; Antonellini, Marco; Giambastiani, Beatrice Maria Sole
2017-08-01
This study characterizes the near-shore portion of the shallow coastal aquifer included in the Ravenna area (Northern Italy) with special attention to the roles of coastal dunes as freshwater reservoirs and their buffer on groundwater salinity. The paper focuses on the presence and evolution of freshwater lenses below coastal dunes and highlights the existing differences between preserved natural dunes and dunes strongly affected by human intervention. The influence that multiple natural and anthropogenic factors, such as land cover, local drainage network, and beach erosion have on the presence, size and evolution of the freshwater lenses in the aquifer is quantified and discussed. The methodology includes multiple seasonal monitoring and sampling campaigns of physical (water level, salinity, and temperature) and chemical (major cations and anions) groundwater parameters. Results indicate that freshwater lenses, where existing, are limited in thickness (about 1-2 m). Proximity to drainage ditches as well as limited dune elevation and size do not allow the formation and permanent storage of large freshwater lenses in the aquifer below the dunes. The pine forest land cover, that replaced the typical bush or sand cover, intensifies evapotranspiration reducing net infiltration and freshwater storage. The cation species distribution in the water shows that a freshening process is ongoing in preserved natural sites with stable or advancing beaches, whereas a salinization process is ongoing in anthropogenic-impacted areas with strongly-fragmented dune systems. Currently, the thin freshwater lenses in the shallow Ravenna coastal aquifer are limited in space and have no relevance for irrigation or any other human activity. The dune-beach system, however, is the recharge zone of the coastal aquifer and its protection is important to reduce water and soil salinization, which in turn control the health of the whole coastal ecosystem.
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Creating dune landscapes for nature and housing - how to assess the designs?
van den Ancker, J.; Jungerius, P. D.; Hartman, J.
2012-04-01
Over the last decades landscape and nature organisations in The Netherlands initiated discussions about safeguarding characteristic historical landscapes, as well as improving nature and landscape quality. In these discussions they were supported by Dutch government agencies and newspapers. As a consequence, architects, landscape architects and building firms in the Netherlands try to upgrade the quality of houses and build-up areas by creating special landscape settings. Dunes are one of the landscapes that appeal to the designers, and several projects make use of dunes to create a quality living environment. Also nature manager construct dunes in what is called 'new nature'. This contribution evaluates several projects creating dune landscapes. Criteria for the evaluation are: - the subsequent geomorphology, - the materials used for construction, - the resulting internal structure, - the soil profile, - the relationship with the vegetation, - the historical integrity of the location. These examples indicate that engaging earth-scientific knowhow would substantially improve the authenticity of the designs.
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Application of the ERICA Integrated Approach to the Drigg coastal sand dunes
International Nuclear Information System (INIS)
Wood, M.D.; Marshall, W.A.; Beresford, N.A.; Jones, S.R.; Howard, B.J.; Copplestone, D.; Leah, R.T.
2008-01-01
The EC-funded project 'Environmental Risks from Ionising Contaminants: Assessment and Management' (ERICA) developed an 'Integrated Approach' for assessing the impact of ionising radiation on ecosystems. This paper presents the application of the ERICA Integrated Approach, supported by a software programme (the ERICA Tool) and guidance documentation, to an assessment of the Drigg coastal sand dunes (Cumbria, UK). Targeted sampling provided site-specific data for sand dune biota, including amphibians and reptiles. Radionuclides reported included 90 Sr, 99 Tc, 137 Cs, 238 Pu, 239+240 Pu and 241 Am. Site-specific data were compared to predictions derived using the ERICA Tool. Some under- and over-predictions of biota activity concentrations were identified but can be explained by the specific ecological characteristics and contamination mechanism of the dunes. Overall, the results indicated no significant impact of ionising radiation on the sand dune biota and the Integrated Approach was found to be a flexible and effective means of conducting a radiation impact assessment
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Modelling the impact of the climatic changes on the dune erosion. The case of the Camargue
International Nuclear Information System (INIS)
Sabatier, F.
2008-01-01
Three climatic changes scenarios were investigated by an increase of energy and by the duration of an extreme storm. The wave characteristics properties and the sea level time series of the referenced storm were increased of about 5, 10 and 20 % in order to define the dune erosion. We evidenced that the wave height displays more influence on the dune erosion than the sea level. Moreover, the storm duration, over 4 days, does not play an important role on the dune erosion. However, there is no proportional relationships between a weak storm energy increase and/or duration, and dune erosion. A small increase of storm will have a large impact on dune erosion in the future. (author)
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Newman, Claire E.; Gomez-Elvira, Javier; Marin, Mercedes; Navarro, Sara; Torres, Josefina; Richardson, Mark I.; Battalio, J. Michael; Guzewich, Scott D.; Sullivan, Robert; de la Torre, Manuel;
2016-01-01
A high density of REMS wind measurements were collected in three science investigations during MSL's Bagnold Dunes Campaign, which took place over approx. 80 sols around southern winter solstice (Ls approx. 90deg) and constituted the first in situ analysis of the environmental conditions, morphology, structure, and composition of an active dune field on Mars. The Wind Characterization Investigation was designed to fully characterize the near-surface wind field just outside the dunes and confirmed the primarily upslope/downslope flow expected from theory and modeling of the circulation on the slopes of Aeolis Mons in this season. The basic pattern of winds is 'upslope' (from the northwest, heading up Aeolis Mons) during the daytime (approx. 09:00-17:00 or 18:00) and 'downslope' (from the southeast, heading down Aeolis Mons) at night (approx. 20:00 to some time before 08:00). Between these times the wind rotates largely clockwise, giving generally westerly winds mid-morning and easterly winds in the early evening. The timings of these direction changes are relatively consistent from sol to sol; however, the wind direction and speed at any given time shows considerable intersol variability. This pattern and timing is similar to predictions from the MarsWRF numerical model, run at a resolution of approx. 490 m in this region, although the model predicts the upslope winds to have a stronger component from the E than the W, misses a wind speed peak at approx. 09:00, and under-predicts the strength of daytime wind speeds by approx. 2-4 m/s. The Namib Dune Lee Investigation reveals 'blocking' of northerly winds by the dune, leaving primarily a westerly component to the daytime winds, and also shows a broadening of the 1 Hz wind speed distribution likely associated with lee turbulence. The Namib Dune Side Investigation measured primarily daytime winds at the side of the same dune, in support of aeolian change detection experiments designed to put limits on the saltation
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Ortega, Beatriz; Schaaf, Peter; Murray, Andrew; Caballero, Margarita; Lozano, Socorro; Ramirez, Angel
2013-12-01
Records of past climatic changes in desert environments are scarce due to the poor preservation of biological proxies. To overcome this lack we consider the paleoenvironmental significance and age of a lunette dune at the eastern rim of Playa San Bartolo (PSB) in the Sonoran Desert (Mexico). Thermoluminescence and optical stimulated luminescence (TL and OSL) provide the chronology of lunette dune development. Mineralogical, geochemical (major, trace and REE element concentrations) and rock magnetic analyses allow for the assessment of sediment provenance and changes in the composition of the PSB dune over time. The upper 6 m of dune accumulation occurred over the past 1.5 ka, largely during AD 500-1200, a period that correlates with the Medieval climatic anomaly (AD 300-1300). Variability in composition of dune sediments is attributed to changes in sediment sources. Sand sized deposits are mainly eroded from granitoids from nearby outcrops. Sandy silt deposits, rich in evaporative minerals, resulted after the flooding of PSB, later deflation and accumulation of both detritic and authigenic components in the dune. These findings suggest that main dune accretion occurred during regionally extended drought conditions, disrupted by sporadic heavy rainfall.
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Energy Technology Data Exchange (ETDEWEB)
Bottiglioni, F; Coutant, J; Gadda, E; Prevot, F [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires
1966-12-01
A plasma column is created in a magnetic field by longitudinal diffusion from a low-pressure pulsed discharge in hydrogen. Depending on the discharge conditions, two regimes are obtained in which the gas pumping speed has a different effect upon the plasma density in the column. Calculations are presented which can explain this effect by a difference in the transverse diffusion coefficient. (authors) [French] On forme une colonne de plasma dans un champ magnetique par diffusion longitudinale a partir d'une decharge puisee dans l'hydrogene a basse pression. Selon les conditions de la decharge on observe deux regimes differents pour lesquels le pompage du gaz neutre a un effet different sur la densite resultante du plasma dans la colonne. On presente des calculs qui peuvent expliquer cet effet par une difference dans la diffusion transversale du plasma. (auteurs)
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Plant functional traits and diversity in sand dune ecosystems across different biogeographic regions
Mahdavi, P.; Bergmeier, E.
2016-07-01
Plant species of a functional group respond similarly to environmental pressures and may be expected to act similarly on ecosystem processes and habitat properties. However, feasibility and applicability of functional groups in ecosystems across very different climatic regions have not yet been studied. In our approach we specified the functional groups in sand dune ecosystems of the Mediterranean, Hyrcanian and Irano-Turanian phytogeographic regions. We examined whether functional groups are more influenced by region or rather by habitat characteristics, and identified trait syndromes associated with common habitat types in sand dunes (mobile dunes, stabilized dunes, salt marshes, semi-wet sands, disturbed habitats). A database of 14 traits, 309 species and 314 relevés was examined and trait-species, trait-plot and species-plot matrices were built. Cluster analysis revealed similar plant functional groups in sand dune ecosystems across regions of very different species composition and climate. Specifically, our study showed that plant traits in sand dune ecosystems are grouped reflecting habitat affiliation rather than region and species pool. Environmental factors and constraints such as sand mobility, soil salinity, water availability, nutrient status and disturbance are more important for the occurrence and distribution of plant functional groups than regional belonging. Each habitat is shown to be equipped with specific functional groups and can be described by specific sets of traits. In restoration ecology the completeness of functional groups and traits in a site may serve as a guideline for maintaining or restoring the habitat.
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Impact of invasive Rosa rugosa on the arthropod fauna of Danish yellow dunes
DEFF Research Database (Denmark)
Elleriis, Pernille; Pedersen, Morten Lauge; Toft, Søren
2015-01-01
monospecific shrubbery rich in large flowers. We predicted faunal responses according to the changes in resource availability and environmental conditions promoted by this particular invasive plant: increased populations of flower-visiting insects and species of the phytophagous and detritivorous guilds...... and diversity and increased dominance in the rose patches, due to reductions among xerotherm species. The results indicate that considerable faunistic impoverishment of thermophilic dune specialist species can be expected in the future if R. rugosa is allowed to continue its invasion across the dune habitat.......We compared the arthropod fauna of Rosa rugosa patches to the adjacent native yellow dune vegetation by pitfall trapping in the National Park Thy at the Danish North Sea coast. R. rugosa changes the vegetation from a dune grassland (dominated by Ammophila arenaria) poor in flowering plants to a low...
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DEFF Research Database (Denmark)
Vestergaard, Peter
2006-01-01
with F. rubra and the invasive alien Rosa rugosa. It was concluded, that the main trends in the geomorphological and vegetational development of the man-made beach-dune system is similar to the development in natural dunes. In the future, further accretion and seaward dune formation may be expected...
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Energy Technology Data Exchange (ETDEWEB)
Keil, Deborah, E-mail: Deborah.Keil@montana.edu [Department of Microbiology and Immunology, Montana State University, Bozeman, MT 59717 (United States); Buck, Brenda [Department of Geoscience, University of Nevada, Las Vegas, NV 89154 (United States); Goossens, Dirk [Department of Geoscience, University of Nevada, Las Vegas, NV 89154 (United States); Geography Research Group, Department of Earth and Environmental Sciences, KU Leuven (Belgium); Teng, Yuanxin [Department of Geoscience, University of Nevada, Las Vegas, NV 89154 (United States); Leetham, Mallory; Murphy, Lacey [Department of Microbiology and Immunology, Montana State University, Bozeman, MT 59717 (United States); Pollard, James [Department of Geoscience, University of Nevada, Las Vegas, NV 89154 (United States); Eggers, Margaret [Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717 (United States); McLaurin, Brett [Department of Environmental, Geographical, and Geological Sciences, Bloomsburg University of Pennsylvania, Bloomsburg, PA 17815 (United States); Gerads, Russell [Brooks Rand Labs, LLC, Bothell, WA 98011 (United States); DeWitt, Jamie [Department of Pharmacology and Toxicology, East Carolina University, Greenville, NC 27834 (United States)
2016-01-15
Exposure to geogenic particulate matter (PM) comprised of mineral particles has been linked to human health effects. However, very little data exist on health effects associated with geogenic dust exposure in natural settings. Therefore, we characterized particulate matter size, metal chemistry, and health effects of dust collected from the Nellis Dunes Recreation Area (NDRA), a popular off-road vehicle area located near Las Vegas, NV. Adult female B6C3F1 mice were exposed to several concentrations of mineral dust collected from active and vegetated sand dunes in NDRA. Dust samples (median diameter: 4.4 μm) were suspended in phosphate-buffered saline and delivered at concentrations ranging from 0.01 to 100 mg dust/kg body weight by oropharyngeal aspiration. ICP-MS analyses of total dissolution of the dust resulted in aluminum (55,090 μg/g), vanadium (70 μg/g), chromium (33 μg/g), manganese (511 μg/g), iron (21,600 μg/g), cobalt (9.4 μg/g), copper (69 μg/g), zinc (79 μg/g), arsenic (62 μg/g), strontium (620 μg/g), cesium (13 μg/g), lead 25 μg/g) and uranium (4.7 μg/g). Arsenic was present only as As(V). Mice received four exposures, once/week over 28-days to mimic a month of weekend exposures. Descriptive and functional assays to assess immunotoxicity and neurotoxicity were performed 24 h after the final exposure. The primary observation was that 0.1 to 100 mg/kg of this sand dune derived dust dose-responsively reduced antigen-specific IgM antibody responses, suggesting that dust from this area of NDRA may present a potential health risk. - Graphical abstract: During periods of heavy wind erosion, dense dust clouds of locally emitted geogenic dust enrobe the central Nellis Dune Recreation Area dunes. - Highlights: • Toxicological effects were characterized specific to geogenic dust exposure from a recreational sand dune site in Nevada. • The geogenic dust is a mixture of many metals and crystalline silica. • Exposure to geogenic dust dose
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Le syndrome de Tunnel tarsien : à propos d'une observation au ...
African Journals Online (AJOL)
Les auteurs présentent un fait clinique d'une douleur subaiguë de la face médiale du pied gauche, explorée par l'imagerie par résonance magnétique, en complément d'une échographie Doppler. Ces explorations ont permis de faire le diagnostic du syndrome de tunnel tarsien par aponévrosite plantaire secondaire à une ...
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Arens, Sebastiaan M.; Mulder, Jan P. M.; Slings, Quirinus L.; Geelen, Luc H. W. T.; Damsma, Petra
2013-10-01
This paper discusses and compares results of management interventions to remobilise dunes and obtain more autonomous changes in foredunes resulting from a change in coastal defence policy. In recent decades, nature conservation managers tried to restore aeolian dynamics and dune mobility landward of foredunes to maintain threatened, rare pioneer species. Results indicate that destabilisation activities yielded an important increase of blowing sand and its effects on ecology but with a limited effect on the desired integral remobilization of dunes. Roots remaining in the sand after removal of vegetation and soil is one of the main problems. Follow up removal of roots for 3 to 5 years seems to be essential, but it is not clear whether the dunes will remain mobile in the long term. In 1990 the Dutch government decided to maintain the position of the coastline by artificial sand nourishment. An intensive management of the foredunes was no longer required. Consequently, natural processes in the foredunes revived, and the sediment budget of the beach-dune system changed. Two main types of responses are visible. In some areas, increased input of sand resulted in the development of embryonic dunes seaward of the former foredunes, leading to increased stabilisation of the former foredunes. In other areas, development of embryonic dunes was insignificant despite the increased sand input, but wind erosion features developed in the foredunes, and the environment was more dynamic. The reasons for the differences are not clear, and the interaction between shoreface, beach and dunes is still poorly understood. Until now, attempts to mobilise the inner dunes were independent of changes made to the foredunes. We argue that an integrated, dynamic approach to coastal management, taking account of all relevant functions (including safety and natural values) and the dune-beach system as a whole, may provide new and durable solutions. An integrated approach would ideally provide fresh
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Snow Dunes: A Controlling Factor of Melt Pond Distribution on Arctic Sea Ice
Petrich, Chris; Eicken, Hajo; Polashenski, Christopher M.; Sturm, Matthew; Harbeck, Jeremy P.; Perovich, Donald K.; Finnegan, David C.
2012-01-01
The location of snow dunes over the course of the ice-growth season 2007/08 was mapped on level landfast first-year sea ice near Barrow, Alaska. Landfast ice formed in mid-December and exhibited essentially homogeneous snow depths of 4-6 cm in mid-January; by early February distinct snow dunes were observed. Despite additional snowfall and wind redistribution throughout the season, the location of the dunes was fixed by March, and these locations were highly correlated with the distribution of meltwater ponds at the beginning of June. Our observations, including ground-based light detection and ranging system (lidar) measurements, show that melt ponds initially form in the interstices between snow dunes, and that the outline of the melt ponds is controlled by snow depth contours. The resulting preferential surface ablation of ponded ice creates the surface topography that later determines the melt pond evolution.
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Energy Technology Data Exchange (ETDEWEB)
Handelmann, D.; Klittmann, T.; Badenhop, J.; Folger, M.
2000-07-01
Coastal dunes have an important function as unique habitats for plants and animals as well as natural barriers against storm tides. Thus, they are of special value for nature conservation and coastal defence issues. Facing their potential endangering due to accelerated climate change profound knowledge of stabilty of coastal dunes is essential. In this context the presented study deals with the impact of climate change on biogenic sand stabilization in coastal dunes, which have to be conceived as an ecosystemic process. Questions of climate affected reactions of organism groups involved in this process (plants, soil microflora, soil fauna) and alterations in soil structure were followed up. Within the scope of a 2-years-lasting field experiment conducted on the Eastfrisian Island Norderney the microclimate near the soil surface was modified by gauze covering, which was set up on field plots. (orig.) [German] In ihrer Funktion als Lebensraum fuer Pflanzen und Tiere sowie als natuerlicher Schutzwall bei Sturmfluten wird den Kuestenduenen eine wichtige Bedeutung im Natur- und Kuestenschutz beigemessen. Angesichts ihrer potentiellen Gefaehrdung durch einen beschleunigten Klimawandel ist ein fundierter Kenntnisstand zur Stabilitaet von Kuestenduenen von elementarem Interesse. Vor diesem Hintergrund befasst sich die vorliegende Studie mit dem Einfluss von Klimaaenderungen auf die biogene Sandstabilisierung in Kuestenduenen, die aufgrund des bestehenden organismischen Beziehungsgeflechtes als oekosystemarer Prozess aufzufassen ist. Dabei wurden Fragen nach klimaabhaengigen Reaktionen der an diesem Prozess beteiligten Organismengruppen (Pflanzen, Bodenmikroflora, Bodenfauna) und Veraenderungen des Bodengefueges bearbeitet. Im Rahmen eines 2-jaehrigen Freilandexperimentes auf der Ostfriesischen Insel Norderney wurde das bodennahe Mikroklima mittels einer Gazeueberspannung auf 4 m{sup 2} grossen und mit Strandhafer (Calammophila baltica) bepflanzten Parzellen experimentell
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Application of the ERICA Integrated Approach to the Drigg coastal sand dunes
Energy Technology Data Exchange (ETDEWEB)
Wood, M.D. [Institute for Sustainable Water Integrated Management and Ecosystem Research (SWIMMER)/School of Biological Sciences, Nicholson Building, University of Liverpool, Liverpool, Merseyside L69 3GP (United Kingdom)], E-mail: mwood@liv.ac.uk; Marshall, W.A. [Westlakes Scientific Consulting Ltd., Princess Royal Building, Westlakes Science and Technology Park, Moor Row, Cumbria CA24 3LN (United Kingdom); Beresford, N.A. [Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster, Lancashire LA1 4AP (United Kingdom); Jones, S.R. [Westlakes Scientific Consulting Ltd., Princess Royal Building, Westlakes Science and Technology Park, Moor Row, Cumbria CA24 3LN (United Kingdom); Howard, B.J. [Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster, Lancashire LA1 4AP (United Kingdom); Copplestone, D. [Environment Agency, P.O. Box 12, Richard Fairclough House, Knutsford Road, Latchford, Warrington, Cheshire WA4 1HG (United Kingdom); Leah, R.T. [Institute for Sustainable Water Integrated Management and Ecosystem Research (SWIMMER)/School of Biological Sciences, Nicholson Building, University of Liverpool, Liverpool, Merseyside L69 3GP (United Kingdom)
2008-09-15
The EC-funded project 'Environmental Risks from Ionising Contaminants: Assessment and Management' (ERICA) developed an 'Integrated Approach' for assessing the impact of ionising radiation on ecosystems. This paper presents the application of the ERICA Integrated Approach, supported by a software programme (the ERICA Tool) and guidance documentation, to an assessment of the Drigg coastal sand dunes (Cumbria, UK). Targeted sampling provided site-specific data for sand dune biota, including amphibians and reptiles. Radionuclides reported included {sup 90}Sr, {sup 99}Tc, {sup 137}Cs, {sup 238}Pu, {sup 239+240}Pu and {sup 241}Am. Site-specific data were compared to predictions derived using the ERICA Tool. Some under- and over-predictions of biota activity concentrations were identified but can be explained by the specific ecological characteristics and contamination mechanism of the dunes. Overall, the results indicated no significant impact of ionising radiation on the sand dune biota and the Integrated Approach was found to be a flexible and effective means of conducting a radiation impact assessment.
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Turbulent flow structures and aeolian sediment transport over a barchan sand dune
Wiggs, G. F. S.; Weaver, C. M.
2012-03-01
The turbulent structure of airflow over a barchan sand dune is determined using quadrant analysis of wind velocity data derived from sonic anemometers. Results indicate an increased frequency of ejection and sweep events in the toe region of the dune, characteristic of the turbulent bursting process. In contrast, at the crest there was a significant increase in the occurrence of outward interactions. Combined with high frequency saltation data our analyses show that turbulent structures characterised by a positive streamwise fluctuating velocity (+u‧ sweeps at the toe and outward interactions at the crest) have a dominant influence on sand transport on the dune, together accounting for up to 83% and 95% of transporting events at the toe and crest respectively.
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Dune advance into a coastal forest, equatorial Brazil: A subsurface perspective
Buynevich, Ilya V.; Filho, Pedro Walfir M. Souza; Asp, Nils E.
2010-06-01
A large active parabolic dune along the coast of Pará State, northern Brazil, was analyzed using aerial photography and imaged with high-resolution ground-penetrating radar (GPR) to map the subsurface facies architecture and point-source anomalies. Most high-amplitude (8-10 dB) subsurface anomalies are correlated with partially buried mangrove trees along the leading edge (slipface) of the advancing dune. Profiles along a 200-m long basal stoss side of the dune reveal 66 targets, most of which lie below the water table and are thus inaccessible by other methods. Signal amplitudes of point-source anomalies are substantially higher than those associated with the reflections from continuous subsurface features (water table, sedimentary layers). When complemented with exposures and excavations, GPR provides the best means of rapid continuous imaging of the geological record of complex interactions between vegetation and aeolian deposition.
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Photon detection system for ProtoDUNE dual phase
Cuesta, C. (on behalf of DUNE collaboration)
2017-01-01
The Deep Underground Neutrino Experiment (DUNE) is a 40-kton underground liquid argon time-projection-chamber (LAr TPC) detector, for long-baseline neutrino oscillation studies and for neutrino astrophysics and nucleon decay searches. Photon detector systems embedded within the LAr TPC add precise timing capabilities for non-beam events. The ProtoDUNE dual phase detector will consist of a 6x6x6 m3 liquid argon time-projection chamber placed at CERN and the light readout will be formed by 8-inch cryogenic photomultipliers from Hamamatsu. The characterization of the 36 photomultipliers, the base design, and the light calibration system are described. In addition, preliminary results from a 3x1x1 m3 LAr double phase detector operating at CERN are presented.
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Hayes, Alexander G.
2018-06-01
Before NASA's New Horizons mission, the surface of Pluto was shrouded in mystery. No one knew what to expect from its surface and most scientists shied away from detailed speculation, except to say that the one thing we should expect is to be surprised (1). On page 992 of this issue, Telfer et al. (2) present such a surprise by describing features interpreted as dunes on Pluto's surface.
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Ruocco, Matteo; Bertoni, Duccio; Sarti, Giovanni; Ciccarelli, Daniela
2014-08-01
Mediterranean coastal dunes are dynamic and heterogeneous ecosystems characterised by a strong interaction between abiotic and biotic factors. The present study aimed to adopt a multidisciplinary approach - integrating data on dune morphology, sediment texture and soil parameters as well as shoreline trend - in order to define which are the abiotic factors that most affect the distribution and composition of Mediterranean plant dune communities. The study was carried out in two protected areas, located in central Italy, subjected to different shoreline trends in recent years. 75 plots were identified along eleven randomly positioned cross-shore transects, starting from the beach continuing up to the plant communities of the backdunes. In each plot floristic and environmental data - such as distance to the coastline, plot altitude, inclination, shoreline trend, mean grain-size, sorting, pH, conductivity and organic matter concentration - were collected. The analyses revealed significant changes of vegetational cover, dune morphology and geopedological features along the coast-to-inland gradient. Relationships between vegetation composition and environmental factors were investigated through Canonical Correspondence Analysis (CCA). Four factors - distance to the coastline, mean grain-size, shoreline trend and organic matter - were found to be closely correlated with the floristic composition of plant communities. Finally, soil properties were highlighted as the most determinant factors of community zonation in these Mediterranean coastal dune ecosystems. These results could be taken into account by local managers in conservation actions such as protecting the eroding foredunes as well as in artificial dune reconstructions.
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International Nuclear Information System (INIS)
Allen, Debbie; Darling, W. George; Williams, Peter J.; Stratford, Charlie J.; Robins, Nick S.
2014-01-01
Highlights: • Braunton Burrows is an alkaline rain-fed system with no saline intrusion. • Marine aerosols and shell dissolution dominate unsaturated zone water quality. • Hydrochemical evolution in the unsaturated zone is rapid. • Slower evolutionary processes contribute to water quality in the saturated zone. • High dune groundwaters were 13–16 yr old and dune slack groundwater 5–7 yr old. - Abstract: An improved knowledge of the hydrology of coastal dune systems is desirable for successful management of their diverse ecology under a changing climate. As a near-pristine coastal dune spit system, Braunton Burrows (SW England) is an ideal location for the study of the natural processes governing recharge to the dune groundwater system and the evolution of its water quality. Whereas previous investigations have tended to focus on inter-dune slacks, this study has also given attention to infiltration through the high dunes. Cores were taken through dunes and the resulting sand samples processed to provide information on grain size distribution and porewater chemistry. Groundwater samples were obtained from beneath dunes and slacks. A variety of geochemical techniques were applied including hydrochemistry, stable isotopes and residence time indicators. The unsaturated zone profiles indicate the existence of piston flow recharge with an infiltration rate of 0.75–1 m/yr, although faster rates probably also occur locally. Groundwater beneath the high dunes gave ages in the range 13–16 yr, compared to the dune slack groundwater ages of 5–7 yr, and an age of 22 yr for groundwater from the underlying mudstone aquifer. The chemistry of waters in both unsaturated and saturated zones is dominated by Ca and HCO 3 , supplemented by variable amounts of other ions derived from marine aerosols and limited reaction with sand grains and their coatings. The main chemical evolution of the porewaters occurs rapidly through the mobilisation of surface salt crusts and
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Rewriting the Landform History of One of Africa's Three Largest Basins
Wilkinson, Justin
2014-01-01
The Kalahari Basin in southern Africa - one of the largest basins in Africa, along with the Congo and Chad basins - has attracted attention since David Livingstone traveled through the area in the 1840s. It is a semiarid desert with a large freshwater swampland known as the Okavango Swamp (150 km radius). This prominent megafan (a fan with radii >100 km), with its fingers of dark green forests projecting into the dun colors of the dunes of the Kalahari semi-desert, has been well photographed by astronauts over the years. The study area in the northern Kalahari basin is centered on the Okavango megafan of northwest Botswana, whose swampland has become well known as an African wildlife preserve of importance to biology and tourism alike. The Okavango River is unusual because it has deposited not one but two megafans along its course: the Okavango megafan and the Cubango megafan. The Okavango megafan is one of only three well-known megafans in Africa. Megafans on Earth were once thought to be rare, but recent research has documented 68 in Africa alone. Eleven megafans, plus three more candidates, have been documented in the area immediately surrounding the Okavango feature. These 11 megafans occupy the flattest and smoothest terrains adjacent to the neighboring upland and stand out as the darkest areas in the roughness map of the area. Megafan terrains occupy at least 200,000 sq km of the study area. The roughness map shown is based on an algorithm used first on Mars to quantify topographic roughness. Research of Earth's flattest terrains is just beginning with the aid of such maps, and it appears that these terrains are analogous to the flattest regions of Mars. Implications: 1. The variability in depositional style in each subbasin may apply Africa-wide: rift megafan length is dominated by rift width, whereas Owambo subbasin megafans are probably controlled by upland basin size; Zambezi subbasin megafans appear more like foreland basin types, with the position of
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Sarti, Giovanni; Bertoni, Duccio; Bini, Monica; Ciccarelli, Daniela; Ribolini, Adriano; Ruocco, Matteo; Pozzebon, Alessandro; Alquini, Fernanda; Giaccari, Riccardo; Tordella, Stefano
2014-05-01
Coastal dune systems are arguably one of the most dynamic environments because their evolution is controlled by many factors, both natural and human-related. Hence, they are often exposed to processes leading to erosion, which in turn determine serious naturalistic and economic losses. Most recent studies carried out on different dune fields worldwide emphasized the notion that a better definition of this environment needs an approach that systematically involves several disciplines, striving to merge every data collected from any individual analyses. Therefore, a new multidisciplinary method to study coastal dune systems has been conceived in order to integrate geology, biology, and modern wireless technologies. The aim of the work is threefold: i) to check the reliability of this new approach; ii) to provide a dataset as complete as ever about the factors affecting the evolution of coastal dunes; and iii) to evaluate the influence of any biotic and abiotic factors on plant communities. The experimentation site is located along the Pisa coast within the Migliarino - S. Rossore - Massaciuccoli Regional Park, a protected area where human influence is low (Tuscany, Italy). A rectangle of 100 x 200 m containing 50 grids of 20 x 20 m was established along the coastal dune systems from the coastline to the pinewood at the landward end of the backdune area. Sampling from each grid determined grain-size analysis carried out on surface sediment samples such as geologic aspects; topographic surveys performed by means of DGPS-RTK instruments; geophysical surveys conducted with a GPR equipment, which will be matched with core drilling activities; digital image analysis of high definition pictures taken by means of a remote controlled aircraft drone flying over the study area; biological data obtained by percent cover of each vascular plant species recorded in the sampling unit. Along with geologic and biologic methodologies, this research implemented the use of informatics
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Grootjans, AP; Everts, H; Bruin, K; Fresco, L; Grootjans, Ab P.
The effects of sod cutting were studied in a dune area on the Dutch Wadden Sea Island of Texel. Sod cutting was carried out in a range of different dune slacks in order to restore dune slack vegetation with many endangered Red List species. Sod cutting removed approximately 96% of the soil seed
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Grootjans, A.P.; Everts, H.; Bruin, K.; Fresco, L.
2011-01-01
The effects of sod cutting were studied in a dune area on the Dutch Wadden Sea Island of Texel. Sod cutting was carried out in a range of different dune slacks in order to restore dune slack vegetation with many endangered Red List species. Sod cutting removed approximately 96% of the soil seed
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Groundwater variables and vegetation in dune slacks
Lammerts, E.J.; Maas, C.; Grootjans, A.P.
Basiphilous pioneer plant communities, influenced by phreatic groundwater, are endangered in The Netherlands. In dune slacks of the Dutch Wadden Sea islands, their area has also declined, though they still occur fairly frequently. For purposes of nature conservancy it is important to know how to
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Directory of Open Access Journals (Sweden)
J. Honrado
2010-02-01
Full Text Available Understanding dune ecosystem responses to multi-scale environmental changes can provide the framework for reliable forecasts and cost-efficient protocols for detecting shifts in prevailing coastal dynamics. Based on the hypothesis that stress and disturbance interact as primary community controls in coastal dunes, we studied the fine-scale floristic assembly of foredune vegetation, in its relation to topography, along regional and local environmental gradients in the 200 km long coastline of northern Portugal, encompassing a major biogeographic transition in western Europe. Thirty topographic profiles perpendicular to the shoreline were recorded at ten sites along the regional climate gradient, and vegetation was sampled by recording the frequency of plant species along those profiles. Quantitative topographic attributes of vegetated dune profiles (e.g. length or height exhibited wide variations relatable to differences in prevailing coastal dynamics. Metrics of taxonomic diversity (e.g. total species richness and its additive beta component and of the functional composition of vegetation were highly correlated to attributes of dune topography. Under transgressive dynamics, vegetation profiles have fewer species, increased dominance, lower turnover rates, and lower total vegetation cover. These changes may drive a decrease in structural and functional diversity, with important consequences for resistance, resilience and other ecosystem properties. Moreover, differences in both vegetation assembly (in meta-stable dunes and response to increased disturbance (in eroding dunes between distinct biogeographic contexts highlight a possible decline in facilitation efficiency under extreme physical stress (i.e. under Mediterranean climate and support the significance of functional approaches in the study of local ecosystem responses to disturbance along regional gradients. Our results strongly suggest that assessing fine-scale community assembly can
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Sand mining impacts on long-term dune erosion in southern Monterey Bay
Thornton, E.B.; Sallenger, Abby; Sesto, Juan Conforto; Egley, L.; McGee, Timothy; Parsons, Rost
2006-01-01
Southern Monterey Bay was the most intensively mined shoreline (with sand removed directly from the surf zone) in the U.S. during the period from 1906 until 1990, when the mines were closed following hypotheses that the mining caused coastal erosion. It is estimated that the yearly averaged amount of mined sand between 1940 and 1984 was 128,000 m3/yr, which is approximately 50% of the yearly average dune volume loss during this period. To assess the impact of sand mining, erosion rates along an 18 km range of shoreline during the times of intensive sand mining (1940–1990) are compared with the rates after sand mining ceased (1990–2004). Most of the shoreline is composed of unconsolidated sand with extensive sand dunes rising up to a height of 46 m, vulnerable to the erosive forces of storm waves. Erosion is defined here as a recession of the top edge of the dune. Recession was determined using stereo-photogrammetry, and LIDAR and GPS surveys. Long-term erosion rates vary from about 0.5 m/yr at Monterey to 1.5 m/yr in the middle of the range, and then decrease northward. Erosion events are episodic and occur when storm waves and high tides coincide, allowing swash to undercut the dune and resulting in permanent recession. Erosion appears to be correlated with the occurrence of El Niños. The calculated volume loss of the dune in southern Monterey Bay during the 1997–98 El Niño winter was 1,820,000 m3, which is almost seven times the historical annual mean dune erosion of 270,000 m3/yr. The alongshore variation in recession rates appears to be a function of the alongshore gradient in mean wave energy and depletions by sand mining. After cessation of sand mining in 1990, the erosion rates decreased at locations in the southern end of the bay but have not significantly changed at other locations.
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Stockdon, H.F.; Doran, K.S.; Sallenger, A.H.
2009-01-01
The morphology of coastal sand dunes plays an important role in determining how a beach will respond to a hurricane. Accurate measurements of dune height and position are essential for assessing the vulnerability of beaches to extreme coastal change during future landfalls. Lidar topographic surveys provide rapid, accurate, high-resolution datasets for identifying the location, position, and morphology of coastal sand dunes over large stretches of coast. An algorithm has been developed for identification of the crest of the most seaward sand dune that defines the landward limit of the beach system. Based on changes in beach slope along cross-shore transects of lidar data, dune elevation and location can automatically be extracted every few meters along the coastline. Dune elevations in conjunction with storm-induced water levels can be used to predict the type of coastal response (e.g., beach erosion, dune erosion, overwash, or inundation) that may be expected during hurricane landfall. The vulnerability of the beach system at Fire Island National Seashore in New York to the most extreme of these changes, inundation, is assessed by comparing lidar-derived dune elevations to modeled wave setup and storm surge height. The vulnerability of the beach system to inundation during landfall of a Category 3 hurricane is shown to be spatially variable because of longshore variations in dune height (mean elevation 5.44 m, standard deviation 1.32 m). Hurricane-induced mean water levels exceed dune elevations along 70 of the coastal park, making these locations more vulnerable to inundation during a Category 3 storm. ?? 2009 Coastal Education and Research Foundation.
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The fate of threatened coastal dune habitats in Italy under climate change scenarios.
Prisco, Irene; Carboni, Marta; Acosta, Alicia T R
2013-01-01
Coastal dunes worldwide harbor threatened habitats characterized by high diversity in terms of plant communities. In Italy, recent assessments have highlighted the insufficient state of conservation of these habitats as defined by the EU Habitats Directive. The effects of predicted climate change could have dramatic consequences for coastal environments in the near future. An assessment of the efficacy of protection measures under climate change is thus a priority. Here, we have developed environmental envelope models for the most widespread dune habitats in Italy, following two complementary approaches: an "indirect" plant-species-based one and a simple "direct" one. We analyzed how habitats distribution will be altered under the effects of two climate change scenarios and evaluated if the current Italian network of protected areas will be effective in the future after distribution shifts. While modeling dune habitats with the "direct" approach was unsatisfactory, "indirect" models had a good predictive performance, highlighting the importance of using species' responses to climate change for modeling these habitats. The results showed that habitats closer to the sea may even increase their geographical distribution in the near future. The transition dune habitat is projected to remain stable, although mobile and fixed dune habitats are projected to lose most of their actual geographical distribution, the latter being more sensitive to climate change effects. Gap analysis highlighted that the habitats' distribution is currently adequately covered by protected areas, achieving the conservation target. However, according to predictions, protection level for mobile and fixed dune habitats is predicted to drop drastically under the climate change scenarios which we examined. Our results provide useful insights for setting management priorities and better addressing conservation efforts to preserve these threatened habitats in future.
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Analyse cognitive d'une politique publique : justice ...
African Journals Online (AJOL)
Analyse cognitive d'une politique publique : justice environnementale et « marchés ruraux » de bois-énergie. ... energy sources to poor urban dwellers; and to reduce the poverty of rural households by promoting sustainable forest management including income generation through producing and marketing charcoal.
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Puijenbroek, van M.E.B.; Teichmann, C.; Meijdam, Noortje; Oliveras Menor, I.; Berendse, F.; Limpens, J.
2017-01-01
Rising sea levels threaten coastal safety by increasing the risk of flooding. Coastal dunes provide a natural form of coastal protection. Understanding drivers that constrain early development of dunes is necessary to assess whether dune development may keep pace with sea-level rise. In this study,
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Rizzo, Angela; Aucelli, Pietro P. C.; Gracia, Javier F.; Anfuso, Giorgio; Rosskopf, Carmen M.
2016-04-01
considered by taking into account the medium term evolution (approx. 30 years) of the dune toe and dune vegetation cover. The proposed methodology was tested for two coastal sectors with different physiographic and marine conditions and different land use characteristics: the Valdelagrana beach and the Campomarino beach that are respectively located in the eastern part of the Gulf of Cadiz (Spain) and in the southern part of the Molise coastal stretch (Italy). Preliminary results show that the methodology allows identifying within the studied coastal sectors coast stretches with different degree of susceptibility. It is furthermore very advantageous as it requires parameters mostly already available through photo-interpretation, therefore it is easy to apply without requiring field surveys as do many other index-based methods.
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Loope, D. B.; Zlotnik, V. A.; Kettler, R. M.; Pederson, D. T.
2012-12-01
dune lee slope through a pipe, the erupted sand dried and was buried by climbing wind-ripple strata as the large dune continued to advance downwind. The mapped cluster recording eight distinct seismic events lies within thin-laminated sediment that was deposited by wind ripples during 1 m (~ 1 year) of southeastward dune migration. We conclude that the small pipes and dikes of our study sites are products of numerous >MM 5 earthquakes, some of which recurred at intervals of less than 2 months. We interpret one small cluster of pipes and dikes with well-defined upward terminations as a distinct shock-aftershock sequence. Because the largest modern earthquakes can produce surface liquefaction only up to about 175 km from their epicenters, the Jurassic epicenters must have been well within that distance. The tendency of modern plate boundaries to produce high-frequency aftershocks suggests that the epicenter for this Jurassic sequence lay to the southwest, within the plate boundary zone (not within continental rocks to the east). As eolian dunes steadily migrate over interdune surfaces underlain by water-saturated dune cross-strata, the thin, distinct laminae produced by the wind ripples that occupy dune toes can faithfully record high-frequency seismic events.
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Erosion reasons and rate on accumulative Polish dune coast caused by the January 2012 storm surge
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Tomasz A. Łabuz
2014-03-01
Full Text Available The Polish coast is a non-tidal area; its shores are affected mainly by autumn-winter storm surges. Those of 6 and 14 January 2012 are representative of the forces driving the erosion of normally accumulative sections of coastal dunes, monitored by the author since 1997. The sea level maximum during these two storm surges reached 1.2 to 1.5 m amsl along the Polish coast. Land forms up to 3 m amsl were inundated. Beaches and low parts of the coast up to this height were rebuilt by sea waves attacking the coast for almost 12 days. Quantitative analyses of the morphological dynamics of the coastal dunes are presented for 57 profiles located along the coast. Only those accumulative sections of the Polish coast are analysed where sand accumulation did occur and led to new foredune development. The mean rate of dune erosion was 2.5 m3 per square metre with an average toe retreat of 1.4 m. Erosion understood as dune retreat was greater when a beach was lower (correlation coefficient 0.8. Dune erosion did not occur on coasts with beaches higher than 3.2 m or on lower ones covered by embryo dunes.
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Digital Repository Service at National Institute of Oceanography (India)
Rodrigues, R.S.
Coastal Sand Dune flora (CSD) forms a specialized group of plants commonly referred as psammophytes. Goa has limited natural resources including beaches and sand dunes. The state is globally known for its tourism activities, which pressurize...
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Wang, Yongcui; Alberto, Busso Carlos; Jiang, Deming; Ala, Musa; Li, Xuehua; Zhou, Quanlai; Lin, Jixiang; Ren, Guohua; Jia, Lian
2016-04-01
Artemisia wudanica is an endemic, perennial, pioneering psammophyte species in the sand dune ecosystems of western Horqin Sand Land in northern China. However, no studies have addressed how sexual and asexual reproduction modes of A. wudanica perform at the transitional zones between active dune inter-dune lowlands and active dunes. In early spring, quadrats were randomly set up in the study area to monitor surviving seedling and/or ramet density and frequency coming from sexual/asexual reproduction of A. wudanica. Iron sticks were inserted near each quadrat to determine wind erosion intensity (WE). Additionally, soil samples were collected nearby each quadrat to test for soil moisture (SM), organic matter (OM) and pH. Surviving seedlings of A. wudanica showed an inverse response in comparison with ramets to SM, OM and WE. Soil moisture showed the most positive effect, and WE the negative effect, on surviving, sexual reproduction seedlings. Contrarily, WE had the most positive effect, and SM the negative effect, on asexual reproduction ramets. This suggests that increases in SM and decreases in WE should benefit recruitment of A. wudanica seedlings. On the contrary, ramets coming from asexual reproduction showed a different response to environmental factors in transition zone habitats. While SM was not a key constraint for the survival of seedlings, they showed a better, positive response to wind erosion environments. Overall, various study environmental parameters could be improved to foster A. wudanica invasion and settlement in the plant community through different reproductive modes, thereby promoting vegetation restoration and rehabilitation.
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Can nonstandard interactions jeopardize the hierarchy sensitivity of DUNE?
Deepthi, K. N.; Goswami, Srubabati; Nath, Newton
2017-10-01
We study the effect of nonstandard interactions (NSIs) on the propagation of neutrinos through the Earth's matter and how it affects the hierarchy sensitivity of the DUNE experiment. We emphasize the special case when the diagonal NSI parameter ɛe e=-1 , nullifying the standard matter effect. We show that if, in addition, C P violation is maximal then this gives rise to an exact intrinsic hierarchy degeneracy in the appearance channel, irrespective of the baseline and energy. Introduction of the off diagonal NSI parameter, ɛe τ, shifts the position of this degeneracy to a different ɛe e. Moreover the unknown magnitude and phases of the off diagonal NSI parameters can give rise to additional degeneracies. Overall, given the current model independent limits on NSI parameters, the hierarchy sensitivity of DUNE can get seriously impacted. However, a more precise knowledge of the NSI parameters, especially ɛe e, can give rise to an improved sensitivity. Alternatively, if a NSI exists in nature, and still DUNE shows hierarchy sensitivity, certain ranges of the NSI parameters can be excluded. Additionally, we briefly discuss the implications of ɛe e=-1 (in the Earth) on the Mikheyev-Smirnov-Wolfenstein effect in the Sun.
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Wet dune slacks : decline and new opportunities
Dijk, H.W.J. van; Grootjans, A.P.
1993-01-01
For a number of infiltrated coastal dune areas it is discussed to what extent artificial infiltration for the public water supply affects the quality of soil, groundwater and vegetation around pools and ponds, and what its effect is on the vegetation. Further, the results of investigations into the
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Directory of Open Access Journals (Sweden)
M. Ghadiry
2012-06-01
Full Text Available The movements of the sand dunes are considered as a threat for roads, irrigation networks, water resources, urban areas, agriculture and infrastructures. The main objectives of this study are to develop a new GIS-based model for automated extraction of sand dune encroachment using remote sensing data and to assess the rate of sand dune movement. To monitor and assess the movements of sand dunes in Dakhla oases area, multi-temporal satellite images and a GIS-developed model, using Python script in Arc GIS, were used. The satellite images (SPOT images, 1995 and 2007 were geo-rectified using Erdas Imagine. Image subtraction was performed using spatial analyst in Arc GIS, the result of image subtraction obtains the sand dune movement between the two dates. The raster and vector shape of sand dune migration was automatically extracted using spatial analyst tools. The frontiers of individual dunes were measured at different dates and movement rates were analyzed in GIS. The ModelBuilder in Arc GIS was used in order to create a user friendly tool. The custom built model window is easy to handle by any user who wishes to adapt the model in his work. It was found that the rate of sand dune movement ranged between 3 and 9 m per year. The majority of sand dunes have a rate movement between 0 and 6 m and very few dunes had a movement rate between 6 and 9 m. Integrating remote sensing and GIS provided the necessary information for determining the minimum, maximum, mean, rate and area of sand dune migration.
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Justin O. Schmidt
2013-01-01
A large artificial sand dune composed of finely crushed mine tailings was produced by deep mining operations at Ruby, Arizona. Today, the ghost town of Ruby is an important historical location and biodiversity refuge, with the newly formed dune forming the core of the refuge. The dune provides ideal nesting habitat for at least 13 species of sand-loving wasps,...
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Castanho, Camila de Toledo; Lortie, Christopher J; Zaitchik, Benjamin; Prado, Paulo Inácio
2015-01-01
Empirical studies in salt marshes, arid, and alpine systems support the hypothesis that facilitation between plants is an important ecological process in severe or 'stressful' environments. Coastal dunes are both abiotically stressful and frequently disturbed systems. Facilitation has been documented, but the evidence to date has not been synthesized. We did a systematic review with meta-analysis to highlight general research gaps in the study of plant interactions in coastal dunes and examine if regional and local factors influence the magnitude of facilitation in these systems. The 32 studies included in the systematic review were done in coastal dunes located in 13 countries around the world but the majority was in the temperate zone (63%). Most of the studies adopt only an observational approach to make inferences about facilitative interactions, whereas only 28% of the studies used both observational and experimental approaches. Among the factors we tested, only geographic region mediates the occurrence of facilitation more broadly in coastal dune systems. The presence of a neighbor positively influenced growth and survival in the tropics, whereas in temperate and subartic regions the effect was neutral for both response variables. We found no evidence that climatic and local factors, such as life-form and life stage of interacting plants, affect the magnitude of facilitation in coastal dunes. Overall, conclusions about plant facilitation in coastal dunes depend on the response variable measured and, more broadly, on the geographic region examined. However, the high variability and the limited number of studies, especially in tropical region, indicate we need to be cautious in the generalization of the conclusions. Anyway, coastal dunes provide an important means to explore topical issues in facilitation research including context dependency, local versus regional drivers of community structure, and the importance of gradients in shaping the outcome of net
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A meta-analysis of plant facilitation in coastal dune systems: responses, regions, and research gaps
Directory of Open Access Journals (Sweden)
Camila de Toledo Castanho
2015-02-01
Full Text Available Empirical studies in salt marshes, arid, and alpine systems support the hypothesis that facilitation between plants is an important ecological process in severe or ‘stressful’ environments. Coastal dunes are both abiotically stressful and frequently disturbed systems. Facilitation has been documented, but the evidence to date has not been synthesized. We did a systematic review with meta-analysis to highlight general research gaps in the study of plant interactions in coastal dunes and examine if regional and local factors influence the magnitude of facilitation in these systems. The 32 studies included in the systematic review were done in coastal dunes located in 13 countries around the world but the majority was in the temperate zone (63%. Most of the studies adopt only an observational approach to make inferences about facilitative interactions, whereas only 28% of the studies used both observational and experimental approaches. Among the factors we tested, only geographic region mediates the occurrence of facilitation more broadly in coastal dune systems. The presence of a neighbor positively influenced growth and survival in the tropics, whereas in temperate and subartic regions the effect was neutral for both response variables. We found no evidence that climatic and local factors, such as life-form and life stage of interacting plants, affect the magnitude of facilitation in coastal dunes. Overall, conclusions about plant facilitation in coastal dunes depend on the response variable measured and, more broadly, on the geographic region examined. However, the high variability and the limited number of studies, especially in tropical region, indicate we need to be cautious in the generalization of the conclusions. Anyway, coastal dunes provide an important means to explore topical issues in facilitation research including context dependency, local versus regional drivers of community structure, and the importance of gradients in shaping
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L'infiltration d'une dilution ideale des solutions avec epineph rine au ...
African Journals Online (AJOL)
L'auteur rapporte un procédé simplifié de dilution d'une solution anesthésique avec épinéphrine passant d'une concentration de 1/100 000 à 1/800 000 pour rechercher une hémostase locale effective sans compromettre dans l'immédiat la vitalité de la vascularisation périphérique des lambeaux cutanés levés. The author ...
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SPINIFICI-SCAEVOLETEA SERICEAE, A NEW VEGETATION CLASS FOR PSAMMOPHYTIC DUNE VEGETATION IN THAILAND
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S. PIGNATII
1996-04-01
Full Text Available This is a short account on the coastal dune vegetation of the Gulf of Siam in Thailand. Vegetation is mainly composed by succulent creeping plants with herbaceous habit as to Canavalia maritima (Papilionaceae and Iponwea pes-caprae (Convolvulaceae and the robust stoloniferous grass Spinijex littoreus, the last having an important function for the fonnation of coastal dunes.
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SPINIFICI-SCAEVOLETEA SERICEAE, A NEW VEGETATION CLASS FOR PSAMMOPHYTIC DUNE VEGETATION IN THAILAND
Directory of Open Access Journals (Sweden)
S. PIGNATII
1996-01-01
Full Text Available This is a short account on the coastal dune vegetation of the Gulf of Siam in Thailand. Vegetation is mainly composed by succulent creeping plants with herbaceous habit as to Canavalia maritima (Papilionaceae and Iponwea pes-caprae (Convolvulaceae and the robust stoloniferous grass Spinijex littoreus, the last having an important function for the fonnation of coastal dunes.
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Walker, Ian J.; Hesp, Patrick A.; Davidson-Arnott, Robin G. D.; Bauer, Bernard O.; Namikas, Steven L.; Ollerhead, Jeff
2009-04-01
This study reports the responses of three-dimensional near-surface airflow over a vegetated foredune to variations in the conditions of incident flow during an 8-h experiment. Two parallel measurement transects were established on morphologically different dune profiles: i) a taller, concave-convex West foredune transect with 0.5-m high, densely vegetated (45%), seaward incipient foredune, and ii) a shorter, concave-straight East foredune transect with lower, sparsely vegetated (14%) seaward incipient foredune. Five stations on each transect from the incipient dune to the crest were equipped with ultrasonic anemometers at 0.6 and 1.65 m height and logged at 1 Hz. Incident conditions were recorded from a 4-m tower over a flat beach. Winds increased from 6 m s - 1 to > 20 m s - 1 and were generally obliquely onshore (ENE, 73°). Three sub-events and the population of 10-minute averages of key properties of flow ( U, W, S, CV U) from all sample locations on the East transect ( n = 235) are examined to identify location- and profile-specific responses over 52° of the incident direction of flow (from 11 to 63° onshore). Topographic steering and forcing cause major deviations in the properties and vectors of near-surface flow from the regional wind. Topographic forcing on the concave-straight dune profile increases wind speed and steadiness toward the crest, with speed-up values to 65% in the backshore. Wind speed and steadiness of flow are least responsive to changes in incident angle in the backshore because of stagnation of flow and are most responsive at the lower stoss under pronounced streamline compression. On the steeper concave-convex profile, speed and steadiness decrease toward the crest because of stagnation of flow at the toe and flow expansion at the slope inflection point on the lower stoss. Net downward vertical velocity occurs over both profiles, increases toward the crest, and reflects enhanced turbulent momentum conveyance toward the surface. All of
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Shumack, Samuel; Hesse, Paul; Turner, Liam
2017-12-01
This study aims to determine the common response of coastal sand dunes in Western Australia (WA) to fire on decadal time-scales, in terms of ecological-geomorphic-climatic interactions to test the hypothesis that fire plays a role in coastal dune destabilisation. Fires are commonly suggested to have contributed to widespread dune reactivation in Australia and globally, a hypothesis that is relatively untested. We used data from the Landsat Thematic Mapper, Enhanced Thematic Mapper Plus, and Operational Land Imager missions to monitor changes in surface coverage on coastal sand dunes in south-west WA after fires. We analysed 31 fire scars from 1988 to 2016 in two Landsat scenes on the west and south coast of WA. Recovery ratios derived from the Normalised Difference Vegetation Index (NDVI) were used to monitor patterns in post-fire biomass and surface cover. Recovery ratios are correlated with indices of burn severity, and meteorological data to investigate relationships. We also used Maximum Likelihood Classification to monitor changes in bare sand area. Results suggest that recovery followed a strongly consistent pattern, and is characterised by rapid vegetation cover re-establishment within six to twelve months. Prior to this, some aeolian activity may have occurred but without substantial surface changes. Initial germination and/or resprouting were followed by steady growth up to seven years, where NDVI typically neared pre-fire values. Some variation in early recovery occurred between the west and south coast, possibly owing to relative proportions of reseeding and resprouting plants. A log regression explained 75% of the recovery pattern (79% on the south coast). Precipitation had some ability to explain recovery up to nine months post-fire (r2 = 0.29 to 0.54). No relationships were observed between estimates of burn severity and recovery. After nine months, the biggest cause of spatial variation in recovery was the pre-fire community composition and related
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Lorenz, Ralph; Radebaugh, Jani; Barnes, Jason; Turtle, Elizabeth
2016-04-01
The term megabarchans, referring to large crescentic dunes, might be thought to suggest a link to common barchans. However, the spatial arrangement of megabarchans, such as those at Liwa in the United Arab Emirates where the recent Star Wars movie was filmed, is quite distinct from that found in barchan corridors, and the mechanism by which winds in a unidirectional regime might cause dunes to grow to such large sizes is not at all obvious. Instead, we suggest that the growth and regular arrangement of megabarchans results from their prior accumulation as large linear dunes in a bidirectional wind regime, and the subsequent reduction in frequency or intensity of one of the wind directions. The more unidirectional wind then results in preferential slip face development on one side, and slow migration (slow, since the dunes are large - we report measurements of 50-80m high dunes at Liwa of ~0.1m/yr). The continuum of linear to hooked barchan forms in the Rub Al'Khali south of Liwa supports this paradigm. The Badain Jaran desert similarly has rather large dunes with a regular arrangement, but may have evolved further, with generally more well-developed crescentic slip faces. The relevance of this evolution to Titan, where some hooked barchan forms have been identified, will be discussed. Another feature of Liwa and the Badain Jaran, that may also have a counterpart on Titan, is the existence of interdune sabkhas due to a near-surface water table. In the Badain Jaran these are quite often water-filled, and similarly in the Lençóis Maranhenses barchanoid dunes in Brazil, seasonal flooding of the interdunes occurs. The possible role of water on sand mobility and the resultant dune morphology will be discussed.
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Architectural evidence of dune collapse in the Navajo Sandstone, Zion National Park, Utah
Ford, Colby; Bryant, Gerald; Nick, Kevin E.
2016-10-01
The Canyon Overlook Trail of Zion National Park follows an outcrop of Navajo Sandstone, which displays a uniquely well-exposed assemblage of features associated with failure of the lee face of a large eolian dune, and run-out over an expanse of interdune sediments downwind of that bedform. Exposed features include dramatic folds in the interdune succession and a stacked series of thrust sheets incorporating both interdune and overlying dune deposits. Thrust surfaces display consistent strikes, parallel to those of undeformed foresets, and incorporate zones of brittle failure and fluid deformation, including folds overturned in the direction of foreset dip. These features correspond to predictions made by a previous researcher's model of dune collapse, formulated from less fortuitously exposed architectures in the Navajo Sandstone. Unlike the previous model, however, this site preserves distinct indications that the bulk of deformed material accumulated above the level of the contemporary interdune surface, in an aggradational succession. Paleotopographic reconstruction, based on preserved facies relationships at this site, indicates the presence of a large dune, partially encroached upon a well-developed wet interdune succession, made up of two half-meter carbonate mud layers, separated by a meter of medium-grained sand. Trapping of pore water pressure between these mud layers during liquefaction reduced shear strength in this interval, facilitating the collapse of the lee face of the upwind dune into the interdune area, and transmitted resultant shear forces to distal portions of the interdune expanse, in the shallow subsurface. Shear failure developed along bedding planes in the horizontally laminated carbonate muds, which provided both lubrication of the shear surfaces and structural support for the preservation of coherent thrust sheets during production of an imbricated succession of shear zones in the toe portion of the slump. Individual shear surfaces
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Lynch, K.; Jackson, D.; Delgado-Fernandez, I.; Cooper, J. A.; Baas, A. C.; Beyers, M.
2010-12-01
This study examines sand transport and wind speed across a beach at Magilligan Strand, Northern Ireland, under offshore wind conditions. Traditionally the offshore component of local wind regimes has been ignored when quantifying beach-dune sediment budgets, with the sheltering effect of the foredune assumed to prohibit grain entrainment on the adjoining beach. Recent investigations of secondary airflow patterns over coastal dunes have suggested this may not be the case, that the turbulent nature of the airflow in these zones enhances sediment transport potential. Beach sediment may be delivered to the dune toe by re-circulating eddies under offshore winds in coastal areas, which may explain much of the dynamics of aeolian dunes on coasts where the dominant wind direction is offshore. The present study investigated aeolian sediment transport patterns under an offshore wind event. Empirical data were collected using load cell traps, for aeolian sediment transport, co-located with 3-D ultrasonic anemometers. The instrument positioning on the sub-aerial beach was informed by prior analysis of the airflow patterns using computational fluid dynamics. The array covered a total beach area of 90 m alongshore by 65 m cross-shore from the dune crest. Results confirm that sediment transport occurred in the ‘sheltered’ area under offshore winds. Over short time and space scales the nature of the transport is highly complex; however, preferential zones for sand entrainment may be identified. Alongshore spatial heterogeneity of sediment transport seems to show a relationship to undulations in the dune crest, while temporal and spatial variations may also be related to the position of the airflow reattachment zone. These results highlight the important feedbacks between flow characteristics and transport in a complex three dimensional surface.
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The role of the reef–dune system in coastal protection in Puerto Morelos (Mexico
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G. L. Franklin
2018-04-01
Full Text Available Reefs and sand dunes are critical morphological features providing natural coastal protection. Reefs dissipate around 90 % of the incident wave energy through wave breaking, whereas sand dunes provide the final natural barrier against coastal flooding. The storm impact on coastal areas with these features depends on the relative elevation of the extreme water levels with respect to the sand dune morphology. However, despite the importance of barrier reefs and dunes in coastal protection, poor management practices have degraded these ecosystems, increasing their vulnerability to coastal flooding. The present study aims to theoretically investigate the role of the reef–dune system in coastal protection under current climatic conditions at Puerto Morelos, located in the Mexican Caribbean Sea, using a widely validated nonlinear non-hydrostatic numerical model (SWASH. Wave hindcast information, tidal level, and a measured beach profile of the reef–dune system in Puerto Morelos are employed to estimate extreme runup and the storm impact scale for current and theoretical scenarios. The numerical results show the importance of including the storm surge when predicting extreme water levels and also show that ecosystem degradation has important implications for coastal protection against storms with return periods of less than 10 years. The latter highlights the importance of conservation of the system as a mitigation measure to decrease coastal vulnerability and infrastructure losses in coastal areas in the short to medium term. Furthermore, the results are used to evaluate the applicability of runup parameterisations for beaches to reef environments. Numerical analysis of runup dynamics suggests that runup parameterisations for reef environments can be improved by including the fore reef slope. Therefore, future research to develop runup parameterisations incorporating reef geometry features (e.g. reef crest elevation, reef lagoon width, fore
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The role of the reef-dune system in coastal protection in Puerto Morelos (Mexico)
Franklin, Gemma L.; Torres-Freyermuth, Alec; Medellin, Gabriela; Allende-Arandia, María Eugenia; Appendini, Christian M.
2018-04-01
Reefs and sand dunes are critical morphological features providing natural coastal protection. Reefs dissipate around 90 % of the incident wave energy through wave breaking, whereas sand dunes provide the final natural barrier against coastal flooding. The storm impact on coastal areas with these features depends on the relative elevation of the extreme water levels with respect to the sand dune morphology. However, despite the importance of barrier reefs and dunes in coastal protection, poor management practices have degraded these ecosystems, increasing their vulnerability to coastal flooding. The present study aims to theoretically investigate the role of the reef-dune system in coastal protection under current climatic conditions at Puerto Morelos, located in the Mexican Caribbean Sea, using a widely validated nonlinear non-hydrostatic numerical model (SWASH). Wave hindcast information, tidal level, and a measured beach profile of the reef-dune system in Puerto Morelos are employed to estimate extreme runup and the storm impact scale for current and theoretical scenarios. The numerical results show the importance of including the storm surge when predicting extreme water levels and also show that ecosystem degradation has important implications for coastal protection against storms with return periods of less than 10 years. The latter highlights the importance of conservation of the system as a mitigation measure to decrease coastal vulnerability and infrastructure losses in coastal areas in the short to medium term. Furthermore, the results are used to evaluate the applicability of runup parameterisations for beaches to reef environments. Numerical analysis of runup dynamics suggests that runup parameterisations for reef environments can be improved by including the fore reef slope. Therefore, future research to develop runup parameterisations incorporating reef geometry features (e.g. reef crest elevation, reef lagoon width, fore reef slope) is warranted.
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Properties of dune sand concrete containing coffee waste
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Mohamed Guendouz
2018-01-01
Full Text Available In the last years, an increase of coffee beverages consumption has been observed all over the world; and its consumption increases the waste coffee grounds which will become an environmental problems. Recycling of this waste to produce new materials like sand concrete appears as one of the best solutions for reduces the problem of pollution. This work aims to study the possibility of recycling waste coffee grounds (Spent Coffee Grounds (SCG as a fine aggregate by replacing the sand in the manufacturing of dune sand concrete. For this; sand concrete mixes were prepared with substitution of sand with the spent coffee grounds waste at different percentage (0%, 5%, 10%, 15% and 20% by volume of the sand in order to study the influence of this wastes on physical (Workability, bulk density and porosity, mechanical (compressive and flexural strength and Thermal (Thermal conductivity and thermal diffusivity properties of dune sand concrete. The results showed that the use of spent coffee grounds waste as partial replacement of natural sand contributes to reduce workability, bulk density and mechanical strength of sand concrete mixes with an increase on its porosity. However, the thermal characteristics are improved and especially for a level of 15% and 20% of substitution. So, it is possible to obtain an insulating material which can be used in the various types of structural components. This study ensures that reusing of waste coffee grounds in dune sand concrete gives a positive approach to reduce the cost of materials and solve some environmental problems.
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Uavs to Assess the Evolution of Embryo Dunes
Taddia, Y.; Corbau, C.; Zambello, E.; Russo, V.; Simeoni, U.; Russo, P.; Pellegrinelli, A.
2017-08-01
The balance of a coastal environment is particularly complex: the continuous formation of dunes, their destruction as a result of violent storms, the growth of vegetation and the consequent growth of the dunes themselves are phenomena that significantly affect this balance. This work presents an approach to the long-term monitoring of a complex dune system by means of Unmanned Aerial Vehicles (UAVs). Four different surveys were carried out between November 2015 and November 2016. Aerial photogrammetric data were acquired during flights by a DJI Phantom 2 and a DJI Phantom 3 with cameras in a nadiral arrangement. GNSS receivers in Network Real Time Kinematic (NRTK) mode were used to frame models in the European Terrestrial Reference System. Processing of the captured images consisted in reconstruction of a three-dimensional model using the principles of Structure from Motion (SfM). Particular care was necessary due to the vegetation: filtering of the dense cloud, mainly based on slope detection, was performed to minimize this issue. Final products of the SfM approach were represented by Digital Elevation Models (DEMs) of the sandy coastal environment. Each model was validated by comparison through specially surveyed points. Other analyses were also performed, such as cross sections and computing elevation variations over time. The use of digital photogrammetry by UAVs is particularly reliable: fast acquisition of the images, reconstruction of high-density point clouds, high resolution of final elevation models, as well as flexibility, low cost and accuracy comparable with other available techniques.
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UAVS TO ASSESS THE EVOLUTION OF EMBRYO DUNES
Directory of Open Access Journals (Sweden)
Y. Taddia
2017-08-01
Full Text Available The balance of a coastal environment is particularly complex: the continuous formation of dunes, their destruction as a result of violent storms, the growth of vegetation and the consequent growth of the dunes themselves are phenomena that significantly affect this balance. This work presents an approach to the long-term monitoring of a complex dune system by means of Unmanned Aerial Vehicles (UAVs. Four different surveys were carried out between November 2015 and November 2016. Aerial photogrammetric data were acquired during flights by a DJI Phantom 2 and a DJI Phantom 3 with cameras in a nadiral arrangement. GNSS receivers in Network Real Time Kinematic (NRTK mode were used to frame models in the European Terrestrial Reference System. Processing of the captured images consisted in reconstruction of a three-dimensional model using the principles of Structure from Motion (SfM. Particular care was necessary due to the vegetation: filtering of the dense cloud, mainly based on slope detection, was performed to minimize this issue. Final products of the SfM approach were represented by Digital Elevation Models (DEMs of the sandy coastal environment. Each model was validated by comparison through specially surveyed points. Other analyses were also performed, such as cross sections and computing elevation variations over time. The use of digital photogrammetry by UAVs is particularly reliable: fast acquisition of the images, reconstruction of high-density point clouds, high resolution of final elevation models, as well as flexibility, low cost and accuracy comparable with other available techniques.
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Thermoluminescence dating of sand dunes at Roonka, South Australia
International Nuclear Information System (INIS)
Prescott, J.R.
1983-01-01
Thermoluminescence has been used to date sediments associated with the archaeological excavations at Roonka. An age of 65,000 +- 12,000 years has been found for the terra rossa soil immediately underlying the oldest 14 C dated feature at the main site (18,000 years). At the East Bank site, an age of 2700 +- 300 years is found for the top of the dune at a depth of 30 cm. An age of 14,500 +- 2000 years is found for a stratigraphically distinct and sealed layer at a depth of 1 m. A similar (or possibly older) date is found at 1.7 m. These ages are consistent with the archaeological and geomorphological evidence. There is some evidence that bleaching of sediments by daylight may not be complete in the field. If this is confirmed the ages will need to be revised downwards. (author)
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Cas d'une loi exponentielle Bayesian predict
African Journals Online (AJOL)
DK
Avec des données groupées : Cas d'une loi exponentielle. Bayesian predictions of order statistics with grouped data: The case of an exponential law. Assia Chadli* & Asma Meradji. Laboratoire LaPS, Département de Mathématiques, Faculté des Sciences. Université Badji Mokhtar Annaba, BP 12, 23000, Annaba, Algérie.
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Reliability of dune erosion assessment along curved coastlines
Hoonhout, B.M.; Den Heijer, C.
2010-01-01
The dune assessment methods used to ensure the safety of the lower areas in The Netherlands are based on simple empirical relations that are, strictly speaking, only valid for infinitely long, uniform and straight coasts. The wide application of these relations is mainly justified due to intentional
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Morphology and mechanism of the very large dunes in the tidal reach of the Yangtze River, China
Shuwei, Zheng; Heqin, Cheng; Shuaihu, Wu; Shengyu, Shi; Wei, Xu; Quanping, Zhou; Yuehua, Jiang
2017-05-01
High-resolution multibeam data was used to interpret the surface morphology of very large dunes (VLDs) in the tidal reach of the Yangtze River, China. These VLDs can be divided into three categories according to their surface morphological characteristics. (1) VLDs-I: those with a smooth surface and cross-section; (2) VLDs-II: those accompanied by secondary dunes; (3) VLDs-III: those accompanied by secondary dunes and numerous elliptical pits. Parameters and spatial distribution of VLDs, and bed surface sediment were analyzed in the laboratory. Overall, channel morphology is an important factor affecting the development of VLDs, and channels with narrow and straight and certain water surface slope are facilitating the development of VLDs by constraining stream power. Meanwhile, distribution density of VLDs depicts a decreasing trend from Chizhou towards the estuary, are probably influenced by channel morphology and width. Associated pits in VLDs-III change the 3D dune morphology by distributing in secondary dunes as beads. The Three Gorges Dam project (TGP) leads to the bed surface sediment activity frequently and leads to the riverbed surface sediment coarsens, which promotes the further development of dunes. Moreover, other human activities, such as river regulation project, sand mining and Deep Water Channel Regulation Project have changed the regional river boundary conditions and hydrodynamic conditions are influential on the development of VLDs.
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Djebbi, M.; Gabtni, H.
2018-01-01
As it is located in a very particular and complex domain within the Tellian fold and thrust belt zone in northwestern Tunisia, the Nefza area has always been challenging. Geological, hydrogeological and geophysical studies were conducted in the region. A multidisciplinary study was performed by combining geological and geophysical techniques. Gravity data processing revealed the continuity of the outcropping series of Argoub Er Romane and Jebel Hamra underneath the dune deposits building a high zone separating the dune of Zouaraa and Ouchtata into two asymmetric basins. It forms a threshold zone that controls the geometry of the dune reservoir in the area. The distribution of the gravity anomaly along the dune of Zouaraa proved the heterogeneity of this dune reservoir. Gravity data modeling for this area confirmed these results and showed a preferential tendency of subsidence to the northwest and thus the thickening of Zouaraa dune sequence as compared to that of Ouchtata.
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Roskin, Joel; Bookman, Revital; Friesem, David; Vardi, Jacob
2017-04-01
The paper presents a late Pleistocene aeolian-fluvial record within a linear dune-like structure that partway served as a dune dam. Situated along the southern fringe of the northwestern Negev desert dunefield (Israel) the structure's morphology, orientation, and some of its stratigraphic units partly resemble adjacent west-east extending vegetated linear dunes. Uneven levels of light-colored, fine-grained fluvial deposits (LFFDs) extend to the north and south from the flanks of the studied structure. Abundant Epipalaeolithic sites line the fringes of the LFFDs. The LFFD microstructures of fine graded bedding and clay blocky peds indicate sorting and shrinking of saturated clays in transitional environments between low energy flows to shallow standing water formed by dunes damming a mid-sized drainage system. The structure's architecture of interchanging units of sand with LFFDs indicates interchanging dominances between aeolian sand incursion and winter floods. Sand mobilization associated with powerful winds during the Heinrich 1 event led to dune damming downstream of the structure and within the structure to in-situ sand deposition, partial fluvial erosion, reworking of the sand, and LFFD deposition. Increased sand deposition led to structure growth and blockage of its drainage system that in turn accumulated LFFD units up stream of the structure. Extrapolation of current local fluvial sediment yields indicate that LFFD accretion up to the structure's brim occurred over a short period of several decades. Thin layers of Geometric Kebaran (c. 17.5-14.5 ka cal BP) to Harifian (12-11 ka BP) artifacts within the structure's surface indicates intermittent, repetitive, and short term camping utilizing adjacent water along a timespan of 4-6 kyr. The finds directly imply that the NW Negev LFFDs formed in dune-dammed water bodies which themselves were formed following events of vegetated linear dune elongation. LFFD accumulation persisted as a result of dune dam
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Dew Measurements along a Longitudinal Sand Dune Transect
Jacobs, A.F.G.; Heusinkveld, B.G.; Berkowicz, S.
2000-01-01
In a desert environment dew can serve as an important source of moisture for plants, biological crusts, insects and small animals. A measurement programme was carried out within a sand dune belt situated in the northwestern Negev desert, Israel, to measure daily amounts of dew deposition as well as
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Lorenz, R. D.; Radebaugh, J.; Wall, S. D.; Kirk, R.; Le Gall, A.; Janssen, M. A.; Zebker, H.; Paganelli, F.; Wye, L.; Lunine, J.
2008-12-01
Recent flybys (T43, T44 - and just prior to this meeting, T48) provide SAR imagery of northern Shangri-La, the large dark region just to the WNW of Xanadu. Previous imaging of SE Shangri-La (T13) showed that dunes there take a pronounced southward dip compared with the E-W direction seen elsewhere. The new data show rather different directions for dunes in northern Shangri-La, and confirm a blocking or divergent influence of Xanadu. Application of monopulse radar methods to retrieve elevations from Cassini SAR images ('SARTopo') now allows us to explore the influence of topography on the local dune (and by implication, wind) patterns, and the relationship between elevation and sediment accumulation. The lack of large positive relief at Xanadu makes its influence on the dunes somewhat surprising. We consider the possible mechanisms of Xanadu's effect on the winds, using terrestrial analogs as a guide. We review the global pattern of dune orientations and their implications for atmospheric circulation: this orientation map presents a challenging constraint for modelers. We note preliminary indications that scatterometry of Titan's dunefields yields azimuth-dependent radar cross-sections (as is the case for terrestrial sand seas) and note future plans for dune studies on Titan with multi-angle observations that will provide constraints on dune-scale slopes and duneforms too small to resolve.
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Dark material in the polar layered deposits and dunes on Mars
Herkenhoff, Ken E.; Vasavada, Ashwin R.
1999-07-01
Viking infrared thermal mapping and bistatic radar data suggest that the bulk density of the north polar erg material is much lower than that of the average Martian surface or of dark dunes at lower latitudes. We have derived a thermal inertia of 245-280Jm-2s-1/2K-1(5.9-6.7×10-3calcm-2s-1/2K-1) for the Proctor dune field and 25-150Jm-2s-1/2K-1(0.6-3.6×10-3calcm-2s-1/2K-1) for the north polar erg. The uniqueness of the thermophysical properties of the north polar erg material may be due to a unique polar process that has created them. The visible and near-infrared spectral reflectance of the erg suggests that the dark material may be composed of basalt or ferrous clays. These data are consistent with the dark material being composed of basaltic ash or filamentary sublimate residue (FSR) particles derived from erosion of the layered deposits. Dark dust may be preferentially concentrated at the surface of the layered deposits by the formation of FSR particles upon sublimation of water ice. Further weathering and erosion of these areas of exposed layered deposits may form the dark, saltating material that is found in both polar regions. Dark FSR particles may saltate for great distances before eventually breaking down into dust grains, re-mixing with the global dust reservoir, and being recycled into the polar layered deposits via atmospheric suspension.
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Directory of Open Access Journals (Sweden)
Tomasz A. Łabuz
2014-01-01
Full Text Available The Polish coast is a non-tidal area; its shores are affected mainly by autumn-winter storm surges. Those of 6 and 14 January 2012 are representative of the forces driving the erosion of normally accumulative sections of coastal dunes, monitored by the author since 1997. The sea level maximum during these two storm surges reached 1.2 to 1.5 m amsl along the Polish coast. Land forms up to 3 m amsl were inundated. Beaches and low parts of the coast up to this height were rebuilt by sea waves attacking the coast for almost 12 days. Quantitative analyses of the morphological dynamics of the coastal dunes are presented for 57 profiles located along the coast. Only those accumulative sections of the Polish coast are analysed where sand accumulation did occur and led to new foredune development. The mean rate of dune erosion was 2.5 m3 per square metre with an average toe retreat of 1.4 m. Erosion understood as dune retreat was greater when a beach was lower (correlation coefficient 0.8. Dune erosion did not occur on coasts with beaches higher than 3.2 m or on lower ones covered by embryo dunes.
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Dynamics of Unusual Debris Flows on Martian Sand Dunes
Miyamoto, Hideaki; Dohm, James M.; Baker, Victor R.; Beyer, Ross A.; Bourke, Mary
2004-01-01
Gullies that dissect sand dunes in Russell impact crater often display debris flow-like deposits in their distal reaches. The possible range of both the rheological properties and the flow rates are estimated using a numerical simulation code of a Bingham plastic flow to help explain the formation of these features. Our simulated results are best explained by a rapid debris flow. For example, a debris flow with the viscosity of 10(exp 2) Pa s and the yield strength of 10(exp 2) Pa can form the observed deposits with a flow rate of 0.5 cu m/s sustained over several minutes and total discharged water volume on the order of hundreds of cubic meters, which may be produced by melting a surface layer of interstitial ice within the dune deposits to several centimeters depth.
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Quantifying spatial and temporal trends in beach-dune volumetric changes using spatial statistics
Eamer, Jordan B. R.; Walker, Ian J.
2013-06-01
Spatial statistics are generally underutilized in coastal geomorphology, despite offering great potential for identifying and quantifying spatial-temporal trends in landscape morphodynamics. In particular, local Moran's Ii provides a statistical framework for detecting clusters of significant change in an attribute (e.g., surface erosion or deposition) and quantifying how this changes over space and time. This study analyzes and interprets spatial-temporal patterns in sediment volume changes in a beach-foredune-transgressive dune complex following removal of invasive marram grass (Ammophila spp.). Results are derived by detecting significant changes in post-removal repeat DEMs derived from topographic surveys and airborne LiDAR. The study site was separated into discrete, linked geomorphic units (beach, foredune, transgressive dune complex) to facilitate sub-landscape scale analysis of volumetric change and sediment budget responses. Difference surfaces derived from a pixel-subtraction algorithm between interval DEMs and the LiDAR baseline DEM were filtered using the local Moran's Ii method and two different spatial weights (1.5 and 5 m) to detect statistically significant change. Moran's Ii results were compared with those derived from a more spatially uniform statistical method that uses a simpler student's t distribution threshold for change detection. Morphodynamic patterns and volumetric estimates were similar between the uniform geostatistical method and Moran's Ii at a spatial weight of 5 m while the smaller spatial weight (1.5 m) consistently indicated volumetric changes of less magnitude. The larger 5 m spatial weight was most representative of broader site morphodynamics and spatial patterns while the smaller spatial weight provided volumetric changes consistent with field observations. All methods showed foredune deflation immediately following removal with increased sediment volumes into the spring via deposition at the crest and on lobes in the lee
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On Beam Matching and the Space-Charge Effect in protoDUNE-SP
Mandalia, Jesal Paresh
2017-01-01
In this project simulations using LArSoft have been analysed in particular looking at how the space-charge effect will affect the matching of particle tracks from the beam line monitor to the TPC and the TPC's performance measuring $\\frac{dE}{dx}$ in protoDUNE-SP. The analysis here provides some preliminary calibrations for protoDUNE-SP to account for the impact the space charge effect will have. Many areas of pion cross section analysis will be affected by the space charge effect so it is vital for a calibration to be developed.
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Species diversity of abuscular mycorrhizal fungi (AMF) was assessed along a dunes stabilization gradient (embyonic dune, foredune and fixed dune) at Praia da Joaquina (Joaquina Beach), Ilha de Santa Catarina. These dunes served as a case study to assess whether diversity and myc...
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Escobar, Indra Elena C; Santos, Vilma M; da Silva, Danielle Karla A; Fernandes, Marcelo F; Cavalcante, Uided Maaze T; Maia, Leonor C
2015-06-01
The aim of this study was to describe the impact of re-vegetation on the restoration of microbial community structure and soil microbiological properties in sand dunes that had been affected by mining activity. Soil samples were collected during the dry and rainy seasons from a chronosequence (1, 9, 21 years) of re-vegetated dunes using a single preserved dune as a reference. The composition of the fatty acid methyl esters and soil microbial properties were evaluated. The results showed that the changes in microbial community structure were related to seasonal variations: biomarkers of Gram-positive bacteria were higher than Gram-negative bacteria during the dry season, showing that this group of organisms is more tolerant to these stressful conditions. The microbial community structure in the natural dune was less affected by seasonal variation compared to the re-vegetated areas, whereas the opposite was observed for microbiological properties. Thus, in general, the proportion of saprobic fungi was higher in the natural dune, whereas Gram-negative bacteria were proportionally more common in the younger areas. Although over time the re-vegetation allows the recovery of the microbial community and the soil functions, these communities and functions are different from those found in the undisturbed areas.
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Technique originale de relèvement enclouage à foyer fermé d'une ...
African Journals Online (AJOL)
Le relèvement enclouage à foyer fermé (R.E.F.F) est une technique originale de traitement des fractures thalamiques du calcanéum. Il s'agit d'un patient âgé de 40 ans sans antécédents, victime d'une chute domestique sur le talon droit, d'une hauteur de 3 mètres. Le patient présentait un 'dème et une ecchymose du talon ...
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Bierstedt, Svenja E.; Hünicke, Birgit; Zorita, Eduardo; Ludwig, Juliane
2017-07-01
We statistically analyse the relationship between the structure of migrating dunes in the southern Baltic and the driving wind conditions over the past 26 years, with the long-term aim of using migrating dunes as a proxy for past wind conditions at an interannual resolution. The present analysis is based on the dune record derived from geo-radar measurements by Ludwig et al. (2017). The dune system is located at the Baltic Sea coast of Poland and is migrating from west to east along the coast. The dunes present layers with different thicknesses that can be assigned to absolute dates at interannual timescales and put in relation to seasonal wind conditions. To statistically analyse this record and calibrate it as a wind proxy, we used a gridded regional meteorological reanalysis data set (coastDat2) covering recent decades. The identified link between the dune annual layers and wind conditions was additionally supported by the co-variability between dune layers and observed sea level variations in the southern Baltic Sea. We include precipitation and temperature into our analysis, in addition to wind, to learn more about the dependency between these three atmospheric factors and their common influence on the dune system. We set up a statistical linear model based on the correlation between the frequency of days with specific wind conditions in a given season and dune migration velocities derived for that season. To some extent, the dune records can be seen as analogous to tree-ring width records, and hence we use a proxy validation method usually applied in dendrochronology, cross-validation with the leave-one-out method, when the observational record is short. The revealed correlations between the wind record from the reanalysis and the wind record derived from the dune structure is in the range between 0.28 and 0.63, yielding similar statistical validation skill as dendroclimatological records.
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INLAND DUNE VEGETATION OF THE NETHERLANDS
Directory of Open Access Journals (Sweden)
R. HAVEMAN
2003-01-01
Full Text Available Drifting sands in the Netherlands are the result of human over-exploitation (sod-cutting, over-grazing of woodlands and heathlands. The most important association of inland sand dune areas is the Spergulo-Corynephoretum (Corynephorion canescentis, which is poor in vascular plants, but in it older stager rich in mosses and especially lichens. In the Netherlands, the area of drifting sand is reduced dramatically in the last 70 years. mainly by afforestation and spontaneous succession.
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Dunes on planet Tatooine: Observation of barchan migration at the Star Wars film set in Tunisia
Lorenz, Ralph D.; Gasmi, Nabil; Radebaugh, Jani; Barnes, Jason W.; Ori, Gian G.
2013-11-01
Sand dune migration is documented with a readily-available tool (Google Earth) near Chott El Gharsa, just north-west of Tozeur, Tunisia. As fiducial markers we employ a set of buildings used to portray the fictional city Mos Espa. This set of ~ 20 buildings over roughly a hectare was constructed in 1997 for the movie Star Wars Episode 1 - The Phantom Menace. The site now lies between the arms of a large “pudgy” barchan dune, which has been documented via satellite imaging in 2002, 2004, 2008 and 2009 to have moved from ~ 140 m away to only ~ 10 m away. Visits by the authors to the site in 2009 and 2011 confirm the barchan to be in a threatening position: a smaller set nearby was substantially damaged by being overrun by dunes circa 2004. The migration rate of ~ 15 m/yr decreases over the observation period, possibly as a result of increased local rainfall, and is consistent with barchan migration rates observed at other locations worldwide. The migration rate of this and two other barchans suggests sand transport of ~ 50 m3/m/yr, somewhat higher than would be suggested by traditional wind rose calculations: we explore possible reasons for this discrepancy. Because of the link to popular science fiction, the site may be of pedagogical interest in teaching remote sensing and geomorphic change. We also note that nearby playa surfaces and agricultural areas have a time-variable appearance. The site's popularity as a destination for Star Wars enthusiasts results in many photographs being posted on the internet, providing a rich set of in-situ imagery for continued monitoring in the absence of dedicated field visits.
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Nitrogen deposition and grass encroachment in calcareous and acidic Grey dunes (H2130) in NW-Europe
Kooijman, A.M.; van Til, M.; Noordijk, E.; Remke, E.; Kalbitz, K.
We present an overview of high nitrogen deposition effects on coastal dune grasslands in NW-Europe (H2130), especially concerning grass encroachment in calcareous and acidic Grey Dunes. The problem is larger than previously assumed, because critical loads are still too high, and extra N-input from
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Mason, J.A.; Swinehart, J.B.; Lu, H.; Miao, X.; Cha, P.; Zhou, Y.
2008-01-01
The climatic controls on dune mobility, especially the relative importance of wind strength, remain incompletely understood. This is a key research problem in semi-arid northern China, both for interpreting past dune activity as evidence of paleoclimate and for predicting future environmental change. Potential eolian sand transport, which is approximately proportional to wind power above the threshold for sand entrainment, has decreased across much of northern China since the 1970s. Over the same period, effective moisture (ratio of precipitation to potential evapotranspiration) has not changed significantly. This "natural experiment" provides insight on the relative importance of wind power as a control on dune mobility in three dunefields of northern China (Mu Us, Otindag, and Horqin), although poorly understood and potentially large effects of human land use complicate interpretation. Dune forms in these three regions are consistent with sand transport vectors inferred from weather station data, suggesting that wind directions have remained stable and the stations adequately represent winds that shaped the dunes. The predicted effect of weaker winds since the 1970s would be dune stabilization, with lower sand transport rates allowing vegetation cover to expand. Large portions of all three dunefields remained stabilized by vegetation in the 1970s despite high wind power. Since the 1970s, trends in remotely sensed vegetation greenness and change in mobile dune area inferred from sequential Landsat images do indicate widespread dune stabilization in the eastern Mu Us region. On the other hand, expansion of active dunes took place farther west in the Mu Us dunefield and especially in the central Otindag dunefield, with little overall change in two parts of the Horqin dunes. Better ground truth is needed to validate the remote sensing analyses, but results presented here place limits on the relative importance of wind strength as a control on dune mobility in the
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Ukstins, I.; Sara, M.; Riishuus, M.; Schmidt, M. E.; Yingst, R. A.; Berger, J.
2017-12-01
Examining the compositional effect of aeolian transport and sorting processes on basaltic sands is significant for understanding the evolution of the Bagnold dune field, as well as other martian soils and sedimentary units. We use the Askja sand sheet, Iceland, as a testbed to quantify the nature of soil production and aeolian transport processes in a mafic system. Basalts from Askja and surrounding volcanic units, which can have high MgO (5-18 wt %) and high Fe2O3 (5-18 wt %), have been weathered to form mafic volcaniclastic deposits which are incorporated into a 40-km long sand sheet to the E-SE of the caldera, ranging from 10 cm to 10 m thick, and covering 240 km2. Ash and lava from the 2014-2015 Holuhraun eruption were emplaced onto the southeastern part of the sand sheet. The SW section is deflationary and defined by very fine to medium grained basaltic sand with ventifact cobbles and boulders. The central part is inflating and dominated by very fine-grained sand, relict lava fields, and small to large sand ripples (1 to 30 cm). The NE portion is also inflating but accumulation is limited to topographic depressions. Bulk chemistry of >200 sand samples are similar to Martian crust (SiO2: 48-52 wt %, MgO: 5-8 wt %, Fe2O3: 13-15 wt %). MgO concentrations vary with distance along the sand sheet, increasing by 1.5% over 10 km in the downwind direction (E, NE), then maintaining a relatively consistent concentration of 6.75 wt % over 18 km. Mean equancy of grains decreases 15 % to the E over 10 km followed by a plateau at 65 to 75 %. Material at depth tends to be of higher sphericity than material on or near the surface. Notably, MgO increases while the sphericity decreases and both data sets level off at 10 km, which suggests these two variables are related. These indicate input of material with prismoidal morphology around 10 km, and may be due to the Holuhraun eruption.
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Waichel, Breno L.; Scherer, Claiton M. S.; Frank, Heinrich T.
2008-03-01
Burial of active aeolian dunes by lava flows can preserve the morphology of the dunes and generate diverse features related to interaction between unconsolidated sediments and lavas. In the study area, located in southern Brazil, burial of aeolian deposits by Cretaceous basaltic lava flows completely preserved dunes, and generate sand-deformation features, sand diapirs and peperite-like breccia. The preserved dunes are crescentic and linear at the main contact with basalts, and smaller crescentic where interlayered with lavas. The various feature types formed on sediment surfaces by the advance of the flows reflect the emplacement style of the lavas which are compound pahoehoe type. Four feature types can be recognized: (a) type 1 features are related to the advance of sheet flows in dune-interdune areas with slopes > 5°, (b) type 2 is formed where the lava flows advance in lobes and climb the stoss slope of crescentic dunes (slopes 8-12°), (c) type 3 is generated by toes that descend the face of linear dunes (slopes 17-23°) and (d) type 4 occurs when lava lobes descend the stoss slope of crescentic dunes (slopes 10-15°). The direction of the flows, the disposition and morphology of the dunes and the ground slope are the main factors controlling formation of the features. The injection of unconsolidated sand in lava lobes forms diapirs and peperite-like breccias. Sand diapirs occur at the basal portion of lobes where the lava was more solidified. Peperite-like breccias occur in the inner portion where lava was more plastic, favoring the mingling of the components. The generation of both features is related to a mechanical process: the weight of the lava causes the injection of sand into the lava and the warming of the air in the pores of the sand facilitates this process. The lava-sediment interaction features presented here are consistent with previous reports of basalt lavas with unconsolidated arid sediments, and additional new sand-deformation features
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Optical dating of dune ridges on Rømø
DEFF Research Database (Denmark)
Madsen, Anni Tindahl; Murray, A. S.; Andersen, Thorbjørn Joest
2007-01-01
The application of optically stimulated luminescence (OSL) to the dating of recent aeolian sand ridges on Rømø, an island off the southwest coast of Denmark, is tested. These sand ridges began to form approximately 300 years ago, and estimates of the ages are available from historical records....... Samples for OSL dating were taken ~0.5 m below the crests of four different dune ridges; at least five samples were recovered from each ridge to test the internal consistency of the ages. Additional samples were recovered from the low lying areas in the swales and from the scattered dune formations......-defined building phases separated by inactive periods and the first major ridge formed ~235 years ago. This study demonstrates that optical dating can be successfully applied to these young aeolian sand deposits, and we conclude that OSL dating is a powerful chronological tool in studies of coastal change....
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A unifying model for planform straightness of ripples and dunes in air and water
Rubin, David M.
2012-01-01
Geologists, physicists, and mathematicians have studied ripples and dunes for more than a century, but despite considerable effort, no general model has been proposed to explain perhaps the most fundamental property of their morphology: why are some bedforms straight, continuous, parallel, and uniform in planform geometry (i.e. two-dimensional) whereas others are irregular (three-dimensional)? Here we argue that physical coupling along the crest of a bedform is required to produce straight crests and that along-crest flow and sand transport provide effective physical mechanisms for that coupling. Ripples and dunes with the straightest and most continuous crests include longitudinal and oblique dunes in unidirectional flows, wave ripples, dunes in reversing flows, wind ripples, and ripples migrating along a slope. At first glance, these bedforms appear quite different (ripples and dunes; air and water; transverse, oblique, and longitudinal orientations relative to the net sand-transport direction), but they all have one property in common: a process that increases the amount of along-crest sand transport (that lengthens and straightens their crests) relative to the across-crest transport (that makes them migrate and take the more typical and more three-dimensional planform geometry). In unidirectional flows that produce straight bedforms, along-crest transport of sand is caused by along-crest flow (non-transverse bedform orientation), gravitational transport along an inclined crest, or ballistic splash in air. Bedforms in reversing flows tend to be straighter than their unidirectional counterparts, because reverse transport across the bedform crest reduces the net across-crest transport (that causes the more typical irregular geometry) relative to the along-crest transport (that smoothes and straightens planform geometry).
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Remke, E.; Brouwer, E.; Kooijman, A.; Blindow, I.; Esselink, H.; Roelofs, J.G.M.
2009-01-01
Coastal dunes around the Baltic Sea have received small amounts of atmospheric nitrogen and are rather pristine ecosystems in this respect. In 19 investigated dune sites the atmospheric wet nitrogen deposition is 3-8 kg N ha−1 yr−1. The nitrogen content of Cladonia portentosa appeared to be a
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Reconstruction and Analysis for the DUNE 35-ton Liquid Argon Prototype
Energy Technology Data Exchange (ETDEWEB)
Wallbank, Michael James [Sheffield U.
2018-01-01
Neutrino physics is approaching the precision era, with current and future experiments aiming to perform highly accurate measurements of the parameters which govern the phenomenon of neutrino oscillations. The ultimate ambition with these results is to search for evidence of CP-violation in the lepton sector, currently hinted at in the world-leading analyses from present experiments, which may explain the dominance of matter over antimatter in the Universe. The Deep Underground Neutrino Experiment (DUNE) is a future long-baseline experiment based at Fermi National Accelerator Laboratory (FNAL), with a far detector at the Sanford Underground Research Facility (SURF) and a baseline of 1300 km. In order to make the required precision measurements, the far detector will consist of 40 kton liquid argon and an embedded time projection chamber. This promising technology is still in development and, since each detector module is around a factor 15 larger than any previous experiment employing this design, prototyping the detector and design choices is critical to the success of the experiment. The 35-ton experiment was constructed for this purpose and will be described in detail in this thesis. The outcomes of the 35-ton prototype are already influencing DUNE and, following the successes and lessons learned from the experiment, confidence can be taken forward to the next stage of the DUNE programme. The main oscillation signal at DUNE will be electron neutrino appearance from the muon neutrino beam. High-precision studies of these νe interactions requires advanced processing and event reconstruction techniques, particularly in the handling of showering particles such as electrons and photons. Novel methods developed for the purposes of shower reconstruction in liquid argon are presented with an aim to successfully develop a selection to use in a νe charged-current analysis, and a first-generation selection using the new techniques is presented.
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Roskin, Joel; Katra, Itzhak; Blumberg, Dan G.
2013-04-01
The study of the effects of past climates on ancient cultures is usually based on geologic records pertaining to rainfall and temperature fluctuations and shifts. This study proposes a paradigm of anthropogenic activity and windiness fluctuations to explain aeolian sedimentation and dune mobilization in the northwestern (NW) Negev Desert dunefield (Israel). The proposed paradigm contributes a different approach to estimating the effect of climate changes on the unprecedented agricultural and urban settlement expansion during the late Roman to Early Islamic period in the northern and central Negev Desert. This study builds upon the late Holocene cluster of luminescence ages of Roskin et al. (Age, origin and climatic controls on vegetated linear dunes in the northwestern Negev Desert (Israel), Quaternary Science Reviews 30 (2011), 1649-1674) coupled with analysis of archaeological finds and historical texts. We suggest that whereas the NW Negev dunefield was generally stable during the Holocene, intermittent dune mobilization during the late Holocene, at ~1.8 ka and mostly 1.4-1.1 ka (~600-900 CE), are linked to periods of human occupation. The idea that the last glacial dune encroachments alone that formed the NW Negev dunefield is connected to cold-event windy climates that may have intensified East Mediterranean cyclonic winter storms, cannot explain the late Holocene dune mobilizations. We conceptually model a connection between late Holocene dune mobilization, widespread anthropogenic occupation and activity, and windiness. We maintain that historic grazing and uprooting shrubs for fuel in the past by nomads and sedentary populations led to decimation of dune stabilizers, biogenic soil crusts and vegetation, causing dune erodibility and low-grade activity. Short-term events of amplified wind power in conjunction with periods of augmented anthropogenic activity that triggered major events of dune mobilization (elongation) and accretion have been preserved in the
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Neutrino versus antineutrino oscillation parameters at DUNE and Hyper-Kamiokande experiments
de Gouvêa, André; Kelly, Kevin J.
2017-11-01
Testing, in a nontrivial, model-independent way, the hypothesis that the three-massive-neutrinos paradigm properly describes nature is among the main goals of the current and the next generation of neutrino oscillation experiments. In the coming decade, the DUNE and Hyper-Kamiokande experiments will be able to study the oscillation of both neutrinos and antineutrinos with unprecedented precision. We explore the ability of these experiments, and combinations of them, to determine whether the parameters that govern these oscillations are the same for neutrinos and antineutrinos, as prescribed by the C P T -theorem. We find that both DUNE and Hyper-Kamiokande will be sensitive to unexplored levels of leptonic C P T -violation. Assuming the parameters for neutrino and antineutrino oscillations are unrelated, we discuss the ability of these experiments to determine the neutrino and antineutrino mass-hierarchies, atmospheric-mixing octants, and C P -odd phases, three key milestones of the experimental neutrino physics program. Additionally, if the C P T -symmetry is violated in nature in a way that is consistent with all present neutrino and antineutrino oscillation data, we find that DUNE and Hyper-Kamiokande have the potential to ultimately establish leptonic C P T -invariance violation.
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Interactions between hyporheic flow produced by stream meanders, bars, and dunes
Stonedahl, Susa H.; Harvey, Judson W.; Packman, Aaron I.
2013-01-01
Stream channel morphology from grain-scale roughness to large meanders drives hyporheic exchange flow. In practice, it is difficult to model hyporheic flow over the wide spectrum of topographic features typically found in rivers. As a result, many studies only characterize isolated exchange processes at a single spatial scale. In this work, we simulated hyporheic flows induced by a range of geomorphic features including meanders, bars and dunes in sand bed streams. Twenty cases were examined with 5 degrees of river meandering. Each meandering river model was run initially without any small topographic features. Models were run again after superimposing only bars and then only dunes, and then run a final time after including all scales of topographic features. This allowed us to investigate the relative importance and interactions between flows induced by different scales of topography. We found that dunes typically contributed more to hyporheic exchange than bars and meanders. Furthermore, our simulations show that the volume of water exchanged and the distributions of hyporheic residence times resulting from various scales of topographic features are close to, but not linearly additive. These findings can potentially be used to develop scaling laws for hyporheic flow that can be widely applied in streams and rivers.
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Spring foraging resources and the behaviour of pollinating insects in fixed dune ecosystems
Directory of Open Access Journals (Sweden)
Aoife T. O'Rourke
2014-08-01
Full Text Available In temperate climates, foraging resources for pollinating insects are especially important in early spring when animals emerge from hibernation and initiate annual life cycles. One habitat, protected under EU law, which provides resources for a range of pollinating insects, but has received little research attention, is fixed (grey dunes. Fixed dunes often contain creeping willow (Salix repens, Salicaceae, which may be an important early season resource for obligate flower visitors. We examined the springtime activity of flower visitors in fixed dune ecosystems in relation to sugar concentration and composition in nectar, composition of essential amino acids in pollen, and floral abundance. We also investigated whether the presence or absence of S. repens influenced the abundance and species richness of three obligate flower visiting guilds (solitary bees, bumblebees and hoverflies in eight sites along the eastern and southern coasts of Ireland. Higher insect visitation rates were observed to species whose nectar contained greater concentrations of glucose and fructose. Solitary bee visitation rates were related to % Essential Amino Acid (EAA in pollen and floral species richness. Ulex europeaus, and S. repens were the most abundant flowering species, but visitation rates were not related to floral abundance. Higher abundances of bumblebees and hoverflies were discovered at sites where S. repens was present. This study raises further questions about the nutritional requirements and preferences of obligate flower visitors in fixed dune ecosystems in spring time.
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How extensive is the effect of modern farming on bird communities in a sand dune desert?
Directory of Open Access Journals (Sweden)
Faris Khoury
2009-12-01
Full Text Available Bird community structure and diversity measures in sand dune habitats far from and close to modern farms in Wadi Araba, south-west Jordan, were compared using 52 line transects for breeding birds and habitat variables. A change in the bird community of sand dunes surrounding farming projects was measured to a distance of 1 km, but could neither be related to changes in habitat structure nor to the activity of op- portunistic predators (Red Fox as these did not vary significantly between the two samples. The farms included lines of trees and offered a constant source of water, which attracted a variety of opportunistic species, thus increasing bird diversity and total bird abundances. The absence of characteristic ground-dwelling species of open sand dune habitats in the structurally intact sand dunes surrounding farms was likely to be the result of localized, but effectively far-reaching habitat modification (farms acting as barriers and/or competition with some of the opportunistic species, which were common around farms.
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Strien, van A.J.; Dekker, J.J.A.; Straver, M.; Meij, van der T.; Soldaat, L.L.; Ehrenburg, A.; Loon, van E.
2011-01-01
Context: Wild rabbits are considered a key species in the coastal dunes of the Netherlands, but populations have collapsed as a result of viral diseases. Aim: We studied to what extent population collapse led to local extinction and whether recolonisation of empty patches in the dunes happened.
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van Strien, A.J.; Dekker, J.J.A.; Straver, M.; van der Meij, T.; Soldaat, L.L.; Ehrenburg, A.; van Loon, E.
2011-01-01
Context: Wild rabbits are considered a key species in the coastal dunes of the Netherlands, but populations have collapsed as a result of viral diseases. Aim: We studied to what extent population collapse led to local extinction and whether recolonisation of empty patches in the dunes happened.
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Turbulent Flow and Sand Dune Dynamics: Identifying Controls on Aeolian Sediment Transport
Weaver, C. M.; Wiggs, G.
2007-12-01
Sediment transport models are founded on cubic power relationships between the transport rate and time averaged flow parameters. These models have achieved limited success and recent aeolian and fluvial research has focused on the modelling and measurement of sediment transport by temporally varying flow conditions. Studies have recognised turbulence as a driving force in sediment transport and have highlighted the importance of coherent flow structures in sediment transport systems. However, the exact mechanisms are still unclear. Furthermore, research in the fluvial environment has identified the significance of turbulent structures for bedform morphology and spacing. However, equivalent research in the aeolian domain is absent. This paper reports the findings of research carried out to characterise the importance of turbulent flow parameters in aeolian sediment transport and determine how turbulent energy and turbulent structures change in response to dune morphology. The relative importance of mean and turbulent wind parameters on aeolian sediment flux was examined in the Skeleton Coast, Namibia. Measurements of wind velocity (using sonic anemometers) and sand transport (using grain impact sensors) at a sampling frequency of 10 Hz were made across a flat surface and along transects on a 9 m high barchan dune. Mean wind parameters and mass sand flux were measured using cup anemometers and wedge-shaped sand traps respectively. Vertical profile data from the sonic anemometers were used to compute turbulence and turbulent stress (Reynolds stress; instantaneous horizontal and vertical fluctuations; coherent flow structures) and their relationship with respect to sand transport and evolving dune morphology. On the flat surface time-averaged parameters generally fail to characterise sand transport dynamics, particularly as the averaging interval is reduced. However, horizontal wind speed correlates well with sand transport even with short averaging times. Quadrant
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Loy Yang A - Australia's largest privatisation
International Nuclear Information System (INIS)
Yenckin, C.
1997-01-01
The recent A$4,746 million privatisation of the 2000MW Loy Yang A power station and the Loy Yang coal mine by the Victorian Government is Australia's largest privatisation and one of 1997's largest project financing deals. (author)
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Probabilistic estimation of dune erosion and coastal zone risk
Li, F.
2014-01-01
Coastal erosion has gained global attention and has been studied for many decades. As a soft sea defence structure, coastal sandy dunes protect coastal zones all over the world, which usually are densely populated areas with tremendous economic value. The coastal zone of the Netherlands, one of the
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Activité insecticide d'une souche marocaine de Bacillus ...
African Journals Online (AJOL)
endotoxines et β -exotoxines) extraites à partir d'une souche de Bacillus thuringiensis (Bt A9) isolée d'un sol au Maroc sur la mouche Ceratitis capitata Wied (Diptera ; Tephritidae). les endotoxines de Bt A9 agissent sur la mortalité des larves et la ...
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The integration of Workload Management Systems for the ProtoDUNE Software and Computing cluster
Oniciuc, Oriana-Maria
2017-01-01
The protoDUNE experimental program is designed to test and validate the technologies for DUNE. All of the many elements in the chain of data acquisition, storage, distribution and processing are critically important to derive physics results from the data. To achieve these, a software stack has been chosen to implement automatic propagation of configurations across all the nodes in the NP cluster. This report presents the architecture of the system and the operations through which the cluster features can be scaled.
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2012-06-19
... dunes sagebrush lizard is still at the park, but the negative survey data from 2007 suggests they may be... harm from solar energy development. Our Response: We acknowledge that solar energy development may be a..., and should be resurveyed to determine if dunes sagebrush lizards are still present, though BLM's 2011...
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Sand dunes development of Vistula River mouth during May 2014 flood
Lisimenka, Aliaksandr; Rudowski, Stanisław; Kałas, Maciej; Szefler, Kazimierz
2015-04-01
The Vistula, Poland's primary river, is the largest river of the southern Baltic Sea and is one of the least regulated amongst large rivers in Europe. The Vistula has a vast delta with the main mouth in the form of an artificial cross-cut channel of about 3000 m length, 400 m width and up to 10 m depth. The comprehensive riverbed morphology in the area is characterized by the set of both 2D and 3D sandy bedforms of various orientations (Lisimenka et al., 2013). About 95% of total Vistula water, with the long-term average annual water discharge of 1081 m3/s, outflows into the Baltic Sea through this channel, which also plays a crucial role in sediment delivery processes into the Vistula External Delta, coast and neighbouring marine waters. Results of bathymetry measurements which were carried out in the main Vistula river mouth during the 23-26 May 2014 flood are presented. Echosounding records were made using boat mounted high-resolution Reson Seabat 7101 multibeam echosounder system (MBES) operating at 240 kHz. The measurements set includes data from: (1) the central part of the river channel with a wide band width for the first and last days of the experiment; (2) the riverbed elevation along axis longitudinal profile obtained on a daily basis with a twice per day registration at the final stage of the rising limb of a flood wave. During the considered period of time, extremely high magnitudes of water level and water discharge values changed from 2590 m3/s up to 4110 m3/s were observed. Estimated based on positioning system data, water flow velocity amounted to about 2 m/s and exceeded a long-term average conditions in more than two times. Based on bedform tracking tool proposed by Van der Mark and Blom (2007), the geometric variables of individual bedforms for each elevation profiles were extracted and histograms of the dune height and length were obtained. The results revealed significant changes in bedform geometry with a counterclockwise hysteresis effect as
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A study of invisible neutrino decay at DUNE and its effects on θ 23 measurement
Choubey, Sandhya; Goswami, Srubabati; Pramanik, Dipyaman
2018-02-01
We study the consequences of invisible decay of neutrinos in the context of the DUNE experiment. We assume that the third mass eigenstate is unstable and decays to a light sterile neutrino and a scalar or a pseudo-scalar. We consider DUNE running in 5 years neutrino and 5 years antineutrino mode and a detector volume of 40 kt. We obtain the expected sensitivity on the rest-frame life-time τ 3 normalized to the mass m 3 as τ3 /m 3 > 4 .50 × 10-11 s/eV at 90% C.L. for a normal hierarchical mass spectrum. We also find that DUNE can discover neutrino decay for τ3 /m 3 > 4 .27 × 10-11 s/eV at 90% C.L. In addition, for an unstable ν3 with an illustrative value of τ3 /m 3 = 1 .2 × 10-11 s/eV, the no decay case could get disfavoured at the 3 σ C.L. At 90% C.L. the expected precision range for this true value is obtained as 1 .71 × 10-11 > τ3 /m 3 > 9 .29 × 10-12 in units of s/eV. We also study the correlation between a non-zero τ3 /m 3 and standard oscillation parameters and find an interesting correlation in the appearance and disappearance channels with the mixing angle θ 23. This alters the octant sensitivity of DUNE, favorably (unfavorably) for true θ 23 in the lower (higher) octant. The effect of a decaying neutrino does not alter the hierarchy or CP violation discovery sensitivity of DUNE in a discernible way.
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Energy Technology Data Exchange (ETDEWEB)
Canobbio, E [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires. Services de Physique Appliquee, Service d' Ionique Generale, Section d' Etudes des Interactions Ondes Plasmas; Finzi, U [Institut de Physique Theorique de Milan (Italy)
1966-07-01
The motion of a charged particle in an axial uniform steady magnetic field, under the action of a radial space charge is calculated. A cylindrical symmetric charge distribution similar to the one which is observed in HF plasma accelerators is assumed. The particle motion is discussed with the method of effective potentials. A radial acceleration of ions is shown to be possible if the space charge density is sufficiently high. The displacement of the turning points of the trajectories due to the electrostatic field is calculated in the low plasma density approximation. Finally a HF circularly polarized electric field is introduced, the shift in cyclotron resonance is calculated and a low frequency resonance is found to be possible. (authors) [French] On etudie le mouvement d'une particule dans un champ magnetique axial uniforme et constant en presence d'un champ de charge d'espace radial. On considere une distribution de charge a symetrie cylindrique, semblable a celle qu'on observe dans les accelerateurs de plasma a H.F. On se sert des potentiels effectifs pour discuter les caracteristiques du mouvement. Une acceleration radiale des ions est possible lorsque la densite de charge est assez elevee. On calcule aussi les deplacements des points de rebroussement des trajectoires produits par un champ electrostatique faible. On introduit enfin un champ electrique HF polarise circulairement et on calcule le deplacement de la resonance de cyclotron du au champ de charge d'espace. En meme temps on voit apparaitre dans l'energie cinetique de la particule une resonance a basse frequence. (auteurs)
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O'Connell-Cooper, C. D.; Spray, J. G.; Thompson, L. M.; Gellert, R.; Berger, J. A.; Boyd, N. I.; Desouza, E. D.; Perrett, G. M.; Schmidt, M.; VanBommel, S. J.
2017-12-01
We present Alpha-Particle X-ray Spectrometer (APXS) data for the active Bagnold dune field within the Gale impact crater (Mars Science Laboratory (MSL) mission). We derive an APXS-based average basaltic soil (ABS) composition for Mars based on past and recent data from the MSL and Mars Exploration Rover (MER) missions. This represents an update to the Taylor and McLennan (2009) average Martian soil and facilitates comparison across Martian data sets. The active Bagnold dune field is compositionally distinct from the ABS, with elevated Mg, Ni, and Fe, suggesting mafic mineral enrichment and uniformly low levels of S, Cl, and Zn, indicating only a minimal dust component. A relationship between decreasing grain size and increasing felsic content is revealed. The Bagnold sands possess the lowest S/Cl of all Martian unconsolidated materials. Gale soils exhibit relatively uniform major element compositions, similar to Meridiani Planum and Gusev Crater basaltic soils (MER missions). However, they show minor enrichments in K, Cr, Mn, and Fe, which may signify a local contribution. The lithified eolian Stimson Formation within the Gale impact crater is compositionally similar to the ABS and Bagnold sands, which provide a modern analogue for these ancient eolian deposits. Compilation of APXS-derived soil data reveals a generally homogenous global composition for Martian soils but one that can be locally modified due to past or extant geologic processes that are limited in both space and time.
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Jones, Fábio Herbert; Scherer, Claiton Marlon dos Santos; Kuchle, Juliano
2016-05-01
The Permian Caldeirão Member (Santa Brígida Formation), located in the Tucano Central Basin, northeast region of Brazil, is characterized by a sandstone succession of aeolian origin that comprises the preserved deposits of dunes and interdunes. Grainflow and translatent wind-ripple strata, and frequent presence of reactivation surface, compose the cross-bedding of crescent aeolian dune deposits. The aeolian cross-strata show a mean dip toward the ENE. In places, interlayered with dune cross-beds, occur interdune units composed of facies indicative of dry, damp and wet condition of the substrate, suggesting spatial and/or temporal variations in the moisture content of the interdune accumulation surface. The presence of NNW current ripple cross-lamination in wet interdune areas indicates streamflows confined to interdune corridors and oriented perpendicular to aeolian transport direction. Lenses of damp and wet interdune strata exhibit mainly interdigitated and transitional relationships with the toe-sets of overlying aeolian dune units in sections parallel to aeolian transport, indicating that dune migration was contemporaneous with accumulation in adjacent interdunes. Lateral variations in the preserved thickness of the interdune units and the associated rare occurrence of abrupt and erosive contacts between interdune and overlying dune sets, suggest temporal variations in the angle of dune and interdune climb that may be related to high-frequency changes in water table position. Four stratigraphic intervals in the Caldeirão Member can be identified, two intervals showing cross-bedding of aeolian dunes without wet interdune areas and two intervals exhibiting aeolian dunes separated by wet interdune areas, marking the transition between dry aeolian systems (Intervals I and III) and wet aeolian systems (Intervals II and IV). The temporal alternations between dry and wet aeolian systems reflect changes in the availability of dry sand and/or the rate in the water
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DEFF Research Database (Denmark)
Nielsen, Knud Erik; Degn, Hans Jørgen; Damgaard, Christian
2011-01-01
A new species has recently invaded coastal dune ecosystems in North West Europe. The native and expansive inland grass, Deschampsia flexuosa, progressively dominating inland heaths, has recently invaded coastal dunes in Denmark, occasionally even as a dominant species. A total of 222 coastal loca...
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Jungerius, P.D.; Witter, J.V.; van Boxel, J.H.
1991-01-01
Blowouts are the main features of aeolian activity in many dune areas. To assess the impact of future climatic change on the geomorphological processes prevailing in a dune landscape it is essential to understand blowout formation and identify the meteorological parameters which are important. The
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Looking Back at 'Purgatory Dune'
2005-01-01
The wheels of NASA's Mars Exploration Rover Opportunity dug more than 10 centimeters (4 inches) deep into the soft, sandy material of a wind-shaped ripple in Mars' Meridiani Planum region during the rover's 446th martian day, or sol (April 26, 2005). Getting the rover out of the ripple, dubbed 'Purgatory Dune,' required more than five weeks of planning, testing, and carefully monitored driving. Opportunity used its navigation camera to capture this look back at the ripple during sol 491 (June 11, 2005), a week after the rover drove safely onto firmer ground. The ripple that became a sand trap is about one-third meter (one foot) tall and 2.5 meters (8 feet) wide.
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Vegetative and reproductive phenological patterns in coastal dunes in S Spain
Directory of Open Access Journals (Sweden)
Rodríguez-Gallego, Carmen
2015-06-01
Full Text Available The phenology of Mediterranean plant species has been extensively studied in different types of ecosystems. However, very little research has been conducted on dune ecosystems. The aim of this research is the phenological characterization and comparison among phenological patterns in three coastal dunes areas in S Spain. For this purpose, we apply the methodology proposed by Orshan (1989 and NLPCA phenological indexes. Our results show that seasonality of species from coastal dunes in S Spain follows the pattern observed in dry and warm Mediterranean ecosystems. The maximum phenological activity occurs for a period of 7-9 months, mainly in spring and late winter, whereas summer is clearly the most inactive period of the year. Vegetative phenophases predominate over the reproductive. Flowering is mainly early (March-May, but it may extend to summer. Flowering duration has been identified as a key index in the differentiation among coastal dunes with different conditions of Mediterranean macroclimate, whereas the importance of the phenophase sequence index has been shown in order to discriminate sectors within dunes. Using the NLPCA analysis based on phenological indexes, four phenological groups of species have been determined. From a conservation perspective, the identification of these groups point out the utility of developing different strategies of management according to the high diversity of eco- and phenomorphological variability that characterize the coastal dunes.La fenología de las especies vegetales mediterráneas ha sido ampliamente estudiada en diferentes tipos de ecosistemas. Sin embargo, es poco lo que se conoce sobre fenología de dunas costeras. El objetivo del presente trabajo es la caracterización y comparación de patrones fenológicos en tres áreas de dunas costeras del Sur de España. Para ello, se ha aplicado la metodología propuesta por Orshan (1989 así como índices fenológicos NLPCA. Nuestros resultados muestran
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Stuyfzand, Pieter J; van der Schans, Martin L
2018-07-15
In the coastal dunes of the Western Netherlands, managed aquifer recharge (MAR) is applied for drinking water supply since 1957. The MAR systems belong to the Aquifer Transfer Recovery (ATR) type, because recharge and recovery are operated without interruption. This makes these systems very vulnerable to intake interruptions, which are expected to increase in frequency and duration due to climate change. Such interruptions are problematic, because: (i) groundwater recovery from dunes needs to continue to supply fresh drinking water to the Western Netherlands; (ii) risks of salt water intrusion are high, and (iii) MAR bordering wet dune slacks with an EU Natura 2000 status cannot survive for long without MAR. In this paper, effects of intake stops are discussed and quantified. The hydrological effects consist of the decline of water tables, disappearance of flow-through dune lakes, reservoir depletion, salt water intrusion, disruption of rainwater lenses, and entrapped air hampering a rapid refill of the groundwater reservoir. Water quality effects include changes in (i) redox environment of the flushed aquifer, impacting the behavior of nutrients, calcium, sulfate and organic micro-pollutants, and (ii) the mixing ratio of water types. The main ecological impacts comprise the dying of organisms in recharge ponds and dune lakes, and a decline of biodiversity. Effects of very long intake interruptions (years) are predicted via historical observations during the long overexploitation period (1900-1957) prior to MAR. A closed form analytical solution for safe yield of a semiconfined aquifer is proposed, together with a related upconing risk index. Both also apply to the pumping from any fresh water lens without MAR. Some mitigation strategies are discussed, such as a dual intake, raising the storage capacity, earlier mud removal, and accelerated refilling of the reservoir. A magnitude scale for intake stops (MIS) is proposed. Copyright © 2018 Elsevier B.V. All rights
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Directory of Open Access Journals (Sweden)
Eric H. Metzler
2014-03-01
Full Text Available The white sands formation, a snow-white gypsum dunes system, is the world's largest gypsum dune field. White Sands National Monument protects about 40% of the dunes; the dunes formation as it is known today was formed ca. 8,000 years BP. Prior to 8,000 years BP, the area covered by the dunes was a wet cool forest of the last glacial maximum in North America. The dunes were formed as a result of the hypsithermal, a warming and drying period which followed the most recent glacial maximum. The white sands formation is located in south central New Mexico in the Tularosa Basin of southwestern United States. A 10-year study of moths at the dunes was commissioned by the U. S. National Park Service in 2006. Almost immediately species new to science were detected. In the period of 6 years, 30 new species were discovered in the dunes. Several of the new species are white or very pale in color, and are endemic to the dunes. The focus of the 10 year project was modified to emphasize naming the undescribed species which helps the National Park Service catalog and manage the habitats. The data should encourage other researchers to explore the interactions of the animals with the plants and the harsh desert environment, to study DNA and evolution, and to study the rapid adaptation which seems to be occurring.
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SiPMs characterization and selection for the DUNE far detector photon detection system
Sun, Y.; Maricic, J.
2016-01-01
The Deep Underground Neutrino Experiment (DUNE) together with the Long Baseline Neutrino Facility (LBNF) hosted at the Fermilab will provide a unique, world-leading program for the exploration of key questions at the forefront of neutrino physics and astrophysics. CP violation in neutrino flavor mixing is one of its most important potential discoveries. Additionally, the experiment will determine the neutrino mass hierarchy and precisely measure the neutrino mixing parameters which may potentially reveal new fundamental symmetries of nature. Moreover, the DUNE is also designed for the observation of nucleon decay and supernova burst neutrinos. The photon detection (PD) system in the DUNE far detector provides trigger for cosmic backgrounds, enhances supernova burst trigger efficiency and improves the energy resolution of the detector. The DUNE adopts the technology of liquid argon time projection chamber (LArTPC) that requires the PD sensors, silicon photomultipliers (SiPM), to be carefully chosen to not only work properly in LAr temperature, but also meet certain specifications for the life of the experiment. A comprehensive testing of SiPMs in cryostat is necessary since the datasheet provided by the manufactures in the market does not cover this temperature regime. This paper gives the detailed characterization results of SenSL C-Series 60035 SiPMs, including gain, dark count rate (DCR), cross-talk and after-pulse rate. Characteristic studies on SiPMs from other vendors are also discussed in order to avoid any potential problems associated with using a single source. Moreover, the results of the ongoing mechanical durability tests are shown for the current candidate, SenSL B/C-Series 60035 SiPMs.
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2013-12-06
...-FF08R00000] Guadalupe-Nipomo Dunes National Wildlife Refuge, San Luis Obispo County, CA: Intent To Prepare a...) for the Guadalupe-Nipomo Dunes National Wildlife Refuge located in San Luis Obispo County of... (Refuge) in San Luis Obispo County, California. This notice complies with our CCP policy to (1) advise...
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Nutrient limitation and vegetation changes in a coastal dune slack
Lammerts, EJ; Pegtel, DM; Grootjans, AP; van der Veen, A.
Basiphilous pioneer species are among the most endangered plant species in The Netherlands. They find most of their refuges in young coastal dune slacks, especially on the Wadden Sea islands. For the purpose of nature management it is important to know which processes control the presence of
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Stefansdottir, G.; Aradottir, A. L.; Sigurdsson, B. D.
2014-05-01
The volcanic island of Surtsey has been a natural laboratory where the primary succession of flora and fauna has been monitored, since it emerged from the N-Atlantic Ocean in 1963. We quantified the accumulation rates of nitrogen (N) and soil organic matter (SOM) in a 37 year long chronosequence of Leymus arenarius dunes in order to illuminate the spatiotemporal patterns in their build-up in primary succession. The Leymus dune area, volume and height grew exponentially over time. Aboveground plant biomass, cover or number of shoots per unit area did not change significantly with time, but root biomass accumulated with time, giving a root-shoot ratio of 19. The dunes accumulated on average 6.6 kg N ha-1 year-1, which was 3.5 times more than is received annually by atmospheric deposition. The extensive root system of Leymus seems to effectively retain and accumulate large part of the annual N deposition, not only deposition directly on the dunes but also from the adjacent unvegetated areas. SOM per unit area increased exponentially with dune age, but the accumulation of roots, aboveground biomass and SOM was more strongly linked to soil N than time: 1 g m-2 increase in soil N led on the average to 6 kg C m-2 increase in biomass and SOM. The Leymus dunes, where most of the N has been accumulated, will therefore probably act as hot-spots for further primary succession of flora and fauna on the tephra sands of Surtsey.
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Zhou, X.; Wang, G.; Yan, B.; Kearns, T.
2016-12-01
Terrestrial laser scanning (TLS) techniques have been proven to be efficient tools to collect three-dimensional high-density and high-accuracy point clouds for coastal research and resource management. However, the processing and presenting of massive TLS data is always a challenge for research when targeting a large area with high-resolution. This article introduces a workflow using shell-scripting techniques to chain together tools from the Generic Mapping Tools (GMT), Geographic Resources Analysis Support System (GRASS), and other command-based open-source utilities for automating TLS data processing. TLS point clouds acquired in the beach and dune area near Freeport, Texas in May 2015 were used for the case study. Shell scripts for rotating the coordinate system, removing anomalous points, assessing data quality, generating high-accuracy bare-earth DEMs, and quantifying beach and sand dune features (shoreline, cross-dune section, dune ridge, toe, and volume) are presented in this article. According to this investigation, the accuracy of the laser measurements (distance from the scanner to the targets) is within a couple of centimeters. However, the positional accuracy of TLS points with respect to a global coordinate system is about 5 cm, which is dominated by the accuracy of GPS solutions for obtaining the positions of the scanner and reflector. The accuracy of TLS-derived bare-earth DEM is primarily determined by the size of grid cells and roughness of the terrain surface for the case study. A DEM with grid cells of 4m x 1m (shoreline by cross-shore) provides a suitable spatial resolution and accuracy for deriving major beach and dune features.
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He, Wei; Huang, Ning; Xu, Bin; Wang, Wenbo
2018-04-23
A bridge built inside the reversed flow region of a sand dune will change the characteristics of wind-sand movement in this region. The Reynolds-averaged Navier-Stokes simulation and discrete particle tracing are used to simulate the wind-sand movement around a sand dune with a bridge built inside the reversed region. Three cases with different bridge positions are studied. The results show that 1) compared with the isolated dune case, a tall bridge built at the leeward toe leads to an increase in the deposition rate on the leeward slope and a longer reversed flow region downstream of the sand dune; meanwhile, the high speed of crosswind on the bridge indicates that some measures should be taken to protect trains from strong crosswind; 2) a low bridge at the leeward toe has little effect on the sand deposition and reversed flow region of the dune; however, low sand transport rate and crosswind speed on the bridge show that anti-crosswind/sand measures should be taken according to the actual situation and 3) a low bridge on the leeward slope has little effect on the length of reversed flow region, however, high crosswind speed and sand flux on the bridge reveal the need of anti-crosswind/sand measures on the bridge. Moreover, the bridges in the reversed flow region increase the sand flux near the leeward crest; as a result, the moving patterns of the sand dune are changed.
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International Nuclear Information System (INIS)
Klõšeiko, J.
2003-01-01
The fraction of photosynthetically active radiation transmitted through the canopy (FPAR) on a forested dune was measured at different locations with a ceptometer, and the correlations of carbohydrates in Scots pine needles with FPAR were studied. The hypothesis was that the sucrose content is relatively stable in different light environments and the main effect of the location on the dune is expressed on the glucose content in needles assuming that glucose regulates the balance between the light environment and nutritional conditions influencing the carbohydrate production and demand processes in trees. The contents of the investigated carbohydrates did not correlate with the FPAR, which was significantly elevated at the higher locations on the dune (500 per cent on top) relative to the locations on the foot. The concentrations of hexoses varied substantially between the individual branches or trees from the same plots and between plots, while sucrose levels on single plots were relatively constant. Analysis of variance indicated the effect of the location on the concentrations of sucrose and excess bound fructose, and on the total content of carbohydrates in current-year needles in which the investigated parameters were positively correlated with the respective parameters in one-year-old needles. The results indicate that the content of carbohydrates does not directly depend on the light environment on the dune, though the large variance in the content of hexoses possibly requires increasing the number of samples on each plot to reveal the differences in needles between the locations on the dune
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Czuba, John A.; Oberg, Kevin A.; Best, Jim L.; Parsons, Daniel R.; Simmons, S. M.; Johnson, K.K.; Malzone, C.
2009-01-01
This paper investigates the flow in the lee of a large sand dune located at the confluence of the Mississippi and Missouri Rivers, USA. Stationary profiles collected from an anchored boat using an acoustic Doppler current profiler (ADCP) were georeferenced with data from a real-time kinematic differential global positioning system. A multibeam echo sounder was used to map the bathymetry of the confluence and provided a morphological context for the ADCP measurements. The flow in the lee of a low-angle dune shows good correspondence with current conceptual models of flow over dunes. As expected, quadrant 2 events (upwellings of low-momentum fluid) are associated with high backscatter intensity. Turbulent events generated in the lower lee of a dune near the bed are associated with periods of vortex shedding and wake flapping. Remnant coherent structures that advect over the lower lee of the dune in the upper portion of the water column, have mostly dissipated and contribute little to turbulence intensities. The turbulent events that occupy most of the water column in the upper lee of the dune are associated with periods of wake flapping.
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INVESTIGATION OF GEOTECHNICAL SPECIFICATIONS OF SAND DUNE SOIL: A CASE STUDY AROUND BAIJI IN IRAQ
Directory of Open Access Journals (Sweden)
Abbas J. Al-Taie
2013-11-01
Full Text Available ABSTRACT: While more than half the land surface of Iraq consists of deserts covered mainly with sand dunes, little research has taken place to study the characteristics and the behavior of dune soils. This paper directed toward studying the geotechnical properties of dune sands taken from Baiji city (northwest of Iraq. A vast laboratory testing program was carried out to achieve the purpose of this paper. The physical tests, chemical tests, X-ray diffraction analysis, permeability test, compaction characteristics, compressibility and collapsibility tests; and shear strength tests were included in this program. The results indicate that soil of Baiji sand dune exhibits prefer engineering properties according to their state. As such, this soil is considered suitable for use in geotechnical constructions. ABSTRAK: Walaupun lebih separuh daripada bumi Iraq terdiri daripada gurun yang dipenuhi dengan bukit-bukit pasir, tidak banyak penyelidikan dijalankan untuk mengkaji sifat-sifat dan ciri-ciri tanah pasir tersebut. Kertas kerja ini menyelidik sifat geoteknikal bukit pasir yang diambil dari pekan Baiji (di bahagian barat utara Iraq. Program penyelidikan makmal yang menyeluruh telah dijalankan bagi mencapai objektif kajian ini. Ujian fizikal, ujian kimia, analisis belauan sinar-x, ujian kebolehtelapan, ciri pemadatan, faktor ketermampatan, ujian keruntuhan dan ujian kekuatan ricih diambilkira dalam program ini. Keputusan menunjukkan bahawa tanih bukit pasir Baiji mengutamakan ciri kejuruteraan berdasarkan keadaannya. Oleh itu, tanah ini dianggap sesuai untuk kegunaan pembinaan geoteknikal.
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Directory of Open Access Journals (Sweden)
Takafumi Miyasaka
2016-07-01
Full Text Available Previous field research on the Horqin Sandy Land (China, which has suffered from severe desertification during recent decades, revealed how land use on a sand-dune topography affects both land degradation and restoration. This study aimed to depict the spatial distribution of local land use in order to shed more light on previous field findings regarding policies on a broader scale. We performed the following analyses with Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM and Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2 images of Advanced Land Observing Satellite (ALOS: (1 object-based classification to discriminate preliminary classification of land-use types that were approximately differentiated by ordinary pixel-based analysis with spectral information; (2 digital photogrammetry to generate a digital surface model (DSM with adequately high accuracy to represent undulating sand-dune topography; (3 geographic information system (GIS analysis to classify major topographic types with the digital surface model (DSM; and (4 overlay of the two classification results to depict the local land-use types. The overall accuracies of the object-based and GIS-based classifications were high, at 93% (kappa statistic: 0.84 and 89% (kappa statistic: 0.81, respectively. The resultant local land-use map represents areas covered in previous field studies, showing where and how land degradation and restoration are likely to occur. This research can contribute to future environmental surveys, models, and policies in the study area.
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Emery, Sarah M; Bell-Dereske, Lukas; Rudgers, Jennifer A
2015-04-01
Ecosystem engineer species influence their community and ecosystem by creating or altering the physical structure of habitats. The function of ecosystem engineers is variable and can depend on both abiotic and biotic factors. Here we make use of a primary successional system to evaluate the direct and interactive effects of climate change (precipitation) and fungal endophyte symbiosis on population traits and ecosystem function of the ecosystem engineering grass species, Ammophila breviligulata. We manipulated endophyte presence in A. breviligulata in combination with rain-out shelters and rainfall additions in a factorial field experiment established in 2010 on Lake Michigan sand dunes. We monitored plant traits, survival, growth, and sexual reproduction of A. breviligulata from 2010-2013, and quantified ecosystem engineering as the sand accumulation rate. Presence of the endophyte in A. breviligulata increased vegetative growth by up to 19%, and reduced sexual reproduction by up to 46% across all precipitation treatments. Precipitation was a less significant factor than endophyte colonization for A. breviligulata growth. Reduced precipitation increased average leaf number per tiller but had no other effects on plant traits. Changes in A. breviligulata traits corresponded to increases in sand accumulation in plots with the endophyte as well as in plots with reduced precipitation. Sand accumulation is a key ecosystem function in these primary successional habitats, and so microbial symbiosis in this ecosystem engineer could lead to direct effects on the value of these dune habitats for humans.
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Compaction and Collapse Characteristics of Dune Sand Stabilized with Lime-Silica Fume Mix
Directory of Open Access Journals (Sweden)
Mohammed Y. Fattah
2016-04-01
Full Text Available The purpose of this research is to assess the suitability of dune sands as construction materials. Moreover, such a goal is considered beneficial in determining appropriate methods for soil stabilization or ground improvement and to assessing the suitability of dune sands as subgrade layer for carrying roads and rail foundation. Dune sand samples were collected from a region in Baiji area in Salah-Aldeen governorate, North of Iraq. A grey-colored densified silica fume (SF and lime (L are used. Three percentages are used for lime (3%, 6%, and 9%, and four rates are used for silica fume (3%, 6%, 9% and 12% and the maximum percentage of silica fume is mixed with the proportions of lime. Unsoaked California Bearing Ratio (CBR on compacted dune sands treated dune sands with L-SF by mixing and cured for one day. The increasing in CBR ranged between 443 – 707% at 2.54 mm penetration and 345 – 410% at 5.08 mm penetration. Resumen El propósito de esta investigación es evaluar el uso de arena de dunas como materiales de construcción. Además, este objetivo permite determinar los métodos apropiados para la estabilización del suelo, el mejoramiento del terreno y la evaluación de pertinencia de la arena de dunas en capas subbase para carreteras y cimientos férreos. Se recolectaron muestras de arena de dunas en el área de Baiji, del comisionado Salah-Aldeen, al norte de Irak. Se utilizó vapor de óxido de silicio (SF, en inglés, grisáceo y densificado, y óxido de calcio (L. Se utilizaron tres porcentajes para el óxido de calcio (3 %, 6 % y 9 %, y cuatro para el óxido de silicio (3 %, 6 %, 9% y 12% y el máximo porcentaje del óxido de silicio se mezcló con las proporciones de óxido de calcio. Se realizó en seco el Ensayo de Relación de Soporte de California (del inglés California Bearing Ratio, CBR en arena de dunas compactada y tratada con la mezcla L-SF curada durante un día. El incremento en el ensayo CBR osciló entre 443
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La neurotoxoplasmose congenitale du nourrisson : a propos d'une ...
African Journals Online (AJOL)
Les auteurs rapportent un cas isolé d'une Toxoplasmose cérébrale congénitale chez un enfant de 02 ans hospitalisé dans le service de neurologie du centre hospitalouniversitaire (C.H.U) Campus de Lomé. La revue de la littérature permet d'insister sur les formes cliniques, l'imagerie médicale, la biologie ainsi que les ...
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The Influences of a Clay Lens on the Hyporheic Exchange in a Sand Dune
Directory of Open Access Journals (Sweden)
Chengpeng Lu
2018-06-01
Full Text Available A laboratory flume simulating a riverbed sand dune containing a low-permeability clay lens was constructed to investigate its influence on the quality and quantity of hyporheic exchange. By varying the depths and spatial locations of the clay lens, 24 scenarios and one blank control experiment were created. Dye tracers were applied to visualize patterns of hyporheic exchange and the extent of the hyporheic zone, while NaCl tracers were used to calculate hyporheic fluxes. The results revealed that the clay lens reduces hyporheic exchange and that the reduction depends on its spatial location. In general, the effect was stronger when the lens was in the center of the sand dune. The effect weakened when the lens was moved near the boundary of the sand dune. A change in horizontal location had a stronger influence on the extent of the hyporheic zone compared with a change in depth. The size of the hyporheic zone changed with the depth and position of the clay lens. There was a maximum of hyporheic extent with the lens at a depth of 0.1 m caused by changes of water flow paths.
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Augmenter la production alimentaire de subsistance en vue d'une ...
International Development Research Centre (IDRC) Digital Library (Canada)
Augmenter la production alimentaire de subsistance en vue d'une meilleure nutrition au Cambodge (FCRSAI, phase II). L'insécurité alimentaire des familles, les pénuries de vivres saisonnières et les carences nutritionnelles chez les femmes et les enfants sont chose courante au Cambodge. Ce projet peaufinera les ...
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Mycorrhizal status of Lycium europaeum in the coastal dunes of ...
African Journals Online (AJOL)
SARAH
2013-11-30
Nov 30, 2013 ... to fix the mobile dunes and to protect the reserve of Sidi Boughaba threatened by the progress of sand. Mycorrhization probably .... 90°C in the water bath until the roots became white. Roots were then rinsed, after this; ..... early in the vegetation succession on degraded soil and promote subsequently the ...
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Lapotre, M. G. A.; Ehlmann, B. L.; Minson, S. E.; Arvidson, R. E.; Ayoub, F.; Fraeman, A. A.; Ewing, R. C.; Bridges, N. T.
2017-12-01
During its ascent up Mount Sharp, the Mars Science Laboratory Curiosity rover traversed the Bagnold Dune Field. We model sand modal mineralogy and grain size at four locations near the rover traverse, using orbital shortwave infrared single-scattering albedo spectra and a Markov chain Monte Carlo implementation of Hapke's radiative transfer theory to fully constrain uncertainties and permitted solutions. These predictions, evaluated against in situ measurements at one site from the Curiosity rover, show that X-ray diffraction-measured mineralogy of the basaltic sands is within the 95% confidence interval of model predictions. However, predictions are relatively insensitive to grain size and are nonunique, especially when modeling the composition of minerals with solid solutions. We find an overall basaltic mineralogy and show subtle spatial variations in composition in and around the Bagnold Dunes, consistent with a mafic enrichment of sands with cumulative aeolian-transport distance by sorting of olivine, pyroxene, and plagioclase grains. Furthermore, the large variations in Fe and Mg abundances ( 20 wt %) at the Bagnold Dunes suggest that compositional variability may be enhanced by local mixing of well-sorted sand with proximal sand sources. Our estimates demonstrate a method for orbital quantification of composition with rigorous uncertainty determination and provide key constraints for interpreting in situ measurements of compositional variability within Martian aeolian sandstones.
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Lapotre, Mathieu G.A.; Ehlmann, B. L.; Minson, Sarah E.; Arvidson, R. E.; Ayoub, F.; Fraeman, A. A.; Ewing, R. C.; Bridges, N. T.
2017-01-01
During its ascent up Mount Sharp, the Mars Science Laboratory Curiosity rover traversed the Bagnold Dune Field. We model sand modal mineralogy and grain size at four locations near the rover traverse, using orbital shortwave infrared single scattering albedo spectra and a Markov-Chain Monte Carlo implementation of Hapke's radiative transfer theory to fully constrain uncertainties and permitted solutions. These predictions, evaluated against in situ measurements at one site from the Curiosity rover, show that XRD-measured mineralogy of the basaltic sands is within the 95% confidence interval of model predictions. However, predictions are relatively insensitive to grain size and are non-unique, especially when modeling the composition of minerals with solid solutions. We find an overall basaltic mineralogy and show subtle spatial variations in composition in and around the Bagnold dunes, consistent with a mafic enrichment of sands with cumulative transport distance by sorting of olivine, pyroxene, and plagioclase grains during aeolian saltation. Furthermore, the large variations in Fe and Mg abundances (~20 wt%) at the Bagnold Dunes suggest that compositional variability induced by wind sorting may be enhanced by local mixing with proximal sand sources. Our estimates demonstrate a method for orbital quantification of composition with rigorous uncertainty determination and provide key constraints for interpreting in situ measurements of compositional variability within martian aeolian sandstones.
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Hacker, D. B.; Biek, R. F.; Rowley, P. D.
2015-12-01
The newly discovered Miocene Markagunt gravity slide (MGS; Utah, USA) represents the largest volcanic landslide structure on Earth. Recent geologic mapping of the MGS indicates that it was a large contiguous volcanic sheet of allochthonous andesitic mudflow breccias and lava flows, volcaniclastic rocks, and intertonguing regional ash-flow tuffs that blanketed an area of at least 5000 km2 with an estimated volume of ~3000 km3. From its breakaway zone in the Tushar and Mineral Mountains to its southern limits, the MGS is over 95 km long and at least 65 km wide. The MGS consists of four distinct structural segments: 1) a high-angle breakaway segment, 2) a bedding-plane segment, ~60 km long and ~65 km wide, typically located within the volcaniclastic Eocene-Oligocene Brian Head Formation, 3) a ramp segment ~1-2 km wide where the slide cuts upsection, and 4) a former land surface segment where the upper-plate moved at least 35 km over the Miocene landscape. The presence of basal and lateral cataclastic breccias, clastic dikes, jigsaw puzzle fracturing, internal shears, pseudotachylytes, and the overall geometry of the MGS show that it represents a single catastrophic emplacement event. The MGS represents gravitationally induced collapse of the southwest sector of the Oligocene to Miocene Marysvale volcanic field. We suggest that continuous growth of the Marysvale volcanic field, loading more volcanic rocks on a structurally weak Brian Head basement, created conditions necessary for gravity sliding. In addition, inflation of the volcanic pile due to multiple magmatic intrusions tilted the strata gently southward, inducing lateral spreading of the sub-volcanic rocks prior to failure. Although similar smaller-scale failures have been recognized from individual volcanoes, the MGS represents a new class of low frequency but high impact hazards associated with catastrophic sector collapse of large volcanic fields containing multiple volcanoes. The relationship of the MGS to
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Adams, P. N.; Conlin, M. P.; Johnson, H. A.; Paniagua-Arroyave, J. F.; Woo, H. B.; Kelly, B. P.
2017-12-01
During energetic coastal storms, surge from low atmospheric pressure, high wave set-up, and increased wave activity contribute to significant morphologic change within the dune and upper beach environments of barrier island systems. Hurricane Irma made landfall on the southwestern portion of the Florida peninsula, as a category 4 storm on Sept 10th, 2017 and tracked northward along the axis of the Florida peninsula for two days before dissipating over the North American continent. Observations along the North Florida Atlantic coast recorded significant wave heights of nearly 7 m and water levels that exceeded predictions by 2 meters on the early morning of Sept. 11th. At Fort Matanzas National Monument, the dune and upper beach adjacent to Matanzas Inlet experienced landward retreat during the storm, diminishing the acreage of dune and scrub habitat for federally-listed endangered and threatened animal species, including the Anastasia beach mouse, gopher tortoises, and several protected shore birds. Real Time Kinematic (RTK) GPS surveys, conducted prior to the passage of the storm (Sept. 8) and immediately after the storm (Sept. 13) document dune scarp retreat >10 m in places and an average retreat of 7.8 m (+/- 5.2 m) of the 2-m beach contour, attributable to the event, within the study region. Although it is typical to see sedimentary recovery at the base of dunes within weeks following an erosive event of this magnitude, our follow up RTK surveys, two weeks (Sept. 26) and five weeks (Oct. 19) after the storm, document continued dune retreat and upper beach lowering. Subsequent local buoy observations during the offshore passage of Hurricanes Jose, Maria (Sept. 17 and 23, respectively) and several early-season Nor'easters recorded wave heights well above normal (2-3 meters) from the northeast. The lack of recovery may reveal a threshold vulnerability of the system, in which the timing of multiple moderate-to-high wave events, in the aftermath of a land falling
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Digital Repository Service at National Institute of Oceanography (India)
Mascarenhas, A.
by regular tides which raise or lower water levels by 2 or 3 meters daily. It is these geomorphic features which support mangrove thickets which are today visible far into the hinterland along river banks, distributary channels, creeks and lagoons. Several... the maximum brunt of this "development". The beach - dune environment is a highly organized system. Sand dunes which generally back wide beaches, are features of extreme fragility and sensitive to anthropogenic stress. Sand dunes are Nature's line of defense...
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Schulz, Karoline; Mikhailyuk, Tatiana; Dreßler, Mirko; Leinweber, Peter; Karsten, Ulf
2016-01-01
Biological soil crusts (BSCs) are known as "ecosystem-engineers" that have important, multifunctional ecological roles in primary production, in nutrient and hydrological cycles, and in stabilization of soils. These communities, however, are almost unstudied in coastal dunes of the temperate zone. Hence, for the first time, the biodiversity of cyanobacterial and algal dominated BSCs collected in five dunes from the southern Baltic Sea coast on the islands Rügen and Usedom (Germany) was investigated in connection with physicochemical soil parameters. The species composition of cyanobacteria and algae was identified with direct determination of crust subsamples, cultural methods, and diatom slides. To investigate the influence of soil properties on species composition, the texture, pH, electrical conductivity, carbonate content, total contents of carbon, nitrogen, phosphorus, and the bioavailable phosphorus-fraction (PO4 (3-)) were analyzed in adjacent BSC-free surface soils at each study site. The data indicate that BSCs in coastal dunes of the southern Baltic Sea represent an ecologically important vegetation form with a surprisingly high site-specific diversity of 19 cyanobacteria, 51 non-diatom algae, and 55 diatoms. All dominant species of the genera Coleofasciculus, Lyngbya, Microcoleus, Nostoc, Hydrocoryne, Leptolyngbya, Klebsormidium, and Lobochlamys are typical aero-terrestrial cyanobacteria and algae, respectively. This first study of coastal sand dunes in the Baltic region provides compelling evidence that here the BSCs were dominated by cyanobacteria, algae, or a mixture of both. Among the physicochemical soil properties, the total phosphorus content of the BSC-free sand was the only factor that significantly influenced the cyanobacterial and algal community structure of BSCs in coastal dunes.
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Commande adaptive d'une machine asynchrone
Slama-Belkhodja, I.; de Fornel, B.
1996-06-01
The paper deals with an indirect self-tuning speed control for an induction motor supplied by a chopper-filter-inverter system. Input/Output models are identified with the recursive least squares algorithm and the controller adaptation is based on a pole assignement strategy. Emphasis is put on the evaluation of the parameter identification in order to avoid instabilities because of disturbances or insufficient excitations. This is especially of importance when the adaptive control is carried out in closed loop systems and without additional test signals. Simulation results show the improvement of the dynamic responses and the robustness against load variations or parameters variations (rotor resistance, inertia). Cat article décrit une stratégie de commande adaptive indirecte à Placement de Pôles (PP), appliquée à la commande en vitesse d'une machine asynchrone alimentée par un ensemble hacheur-filtre-onduleur de tension. L'algorithme des Moindres Carrés Récursifs (MCR) est utilisé pour l'identification des modèles de comportement type entrées/sorties. Un intérêt particulier est porté à la mise en oeuvre de cet algorithme et à la discussion de ses résultats, tenant compte des erreurs de modélisation et de la nature peu riche en excitations des entrées du processus. Différents régimes transitoires ont été simulés pour apprécier l'apport de cette association (MCR-PP) : démarrages et inversion des sens de rotation, à vide et en charges, applications d'échelons de couple résistant, variations paramétriques. Les résultats permettent d'illustrer, tant au niveau des performances que de la robustesse, l'apport d'une telle commande adaptive pour des entraînements électriques avec une machine asynchrone.
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Miller, Thomas E
2015-01-12
Coastal geomorphology and vegetation are expected to be particularly sensitive to climate change, because of disturbances caused by sea-level rise and increased storm frequency. Dunes have critical reciprocal interactions with vegetation; dunes create habitats for plants, while plants help to build dunes and promote geomorphological stability. These interactions are also greatly affected by disturbances associated with sand movement, either in accretion (dune building) or in erosion. The magnitude and intensity of disturbances are expected to vary with habitat, from the more exposed and less stable foredunes, to low-lying and flood-prone interdunes, to the protected and older backdunes. Permanent plots were established at three different spatial scales on St George Island, FL, USA, where the vegetation and dune elevation were quantified annually from 2011 to 2013. Change in elevation, either through accretion or erosion, was used as a measure of year-to-year disturbance over the 2 years of the study. At the scale of different dune habitats, foredunes were found to have the greatest disturbance, while interdunes had the least. Elevation and habitat (i.e. foredune, interdune, backdune) were significantly correlated with plant community composition. Generalized linear models conducted within each habitat show that the change in elevation (disturbance) is also significantly correlated with the plant community, but only within foredunes and interdunes. The importance of disturbance in exposed foredunes was expected and was found to be related to an increasing abundance of a dominant species (Uniola paniculata) in eroding areas. The significant effect of disturbance in the relatively stable interdunes was surprising, and may be due to the importance of flooding associated with small changes in elevation in these low-lying areas. Overall, this study documents changes in the plant community associated with elevation, and demonstrates that the foredune and interdune
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Hantson, W.P.R.; Kooistra, L.; Slim, P.A.
2012-01-01
Questions Does remote sensing improve classification of invasive woody species in dunes, useful for shrub management? Does additional height information and an object-based classifier increase woody species classification accuracy? Location The dunes of Vlieland, one of the Wadden Sea Islands, the
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Azoogh, Liela; Khalili moghadam, Bijan; Jafari, Siroos
2018-06-01
In the past half-century, petroleum mulching-biological fixation (PM-BF) practices have been employed to stabilize sand dunes in Iran. However, the effects of PM-BF practices on the attributes of sand dunes and the dispersion of heavy metals of mulch have been poorly understood. To this end, three regions treated with PM-BF for 5, 20, and 40 years and a control region with no PM-BF were studied. Samples of soil properties were taken at the depths of 0-10 cm and 10-50 cm, with three replications, in Khuzestan Province. The results showed that PM-BF practices promoted the restoration of vegetation cover in the sand dunes. In addition, these practices increased the deposition of dust particles, gradually increasing the magnitudes of palygorskite and smectite clays over time. The interactions between dust deposition and PM-BF practices significantly altered the chemical and physical properties of the dunes. PM-BF practices increased soil organic matter (184-287%), cation exchangeable capacity (142-209%), electrical conductivity (144-493%), clay content (134-196%), and penetration resistance (107-170%) compared to the region with no PM-BF practices. Furthermore, petroleum mulching significantly increased the amount of Ni (1.19%), Cd (1.55%), Pb (1.08%), Cu (1.34%), Zn (1.38%), Mn (1.66%), and Fe (1.15%). However, in the long term, these elements will probably leach linearly as a consequence of an increase in organic matter and soil salinity in the light texture of sand dunes.
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Le socle d'une œuvre, invisible mais essentiel
Huguenin, Daniel
2015-01-01
Tiré du site internet du blog des Musées d'art et d'histoire (http://blog.mahgeneve.ch): "Le support se faisant aujourd'hui le plus discret possible, voire invisible. Sa réalisation nécessite une étroite collaboration entre les différents acteurs d'une exposition car le socleur doit allier les besoins de la conservation et de la muséographie.".
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TERATOME MATURE DE LA PAROTIDE : A PROPOS D'UNE ...
African Journals Online (AJOL)
Le tératome de la parotide est une malformation tumorale vestigiale rare contenant des dérivés plus ou moins différenciés, des trois feuillets embryonnaires. A la lumière d'une nouvelle observation et des données de la littérature, on se propose de mettre l'accent sur les aspects cliniques, histologiques et thérapeutiques de ...
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Birnbaum, G.; Freitag, J.; Brauner, R.; König-Langlo, G.; Schulz, E.; kipfstuhl, J.; Oerter, H.; Reijmer, C.H.; Schlosser, E.; Faria, S.H.; Ries, H.; Loose, B.; Herber, A.; Duda, M. G.; Powers, J. G.; Manning, K. W.; van den Broeke, M.R.
2010-01-01
Analyses of shallow cores obtained at the European Project for Ice Coring in Antarctica (EPICA) drilling site Kohnen station (758000 S, 008040 E; 2892ma.s.l.) on the plateau of Dronning Maud Land reveal the presence of conserved snow dunes in the firn. In situ observations during three dune
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Suanez , Serge ,; Cancouët , Romain; Floc'h , France; Blaise , Emmanuel; Ardhuin , Fabrice; Filipot , Jean-François; Cariolet , Jean-Marie; Delacourt , Christophe
2015-01-01
Monitoring of dune erosion and accretion on the high-energy macrotidal Vougot beach in North Brittany (France) over the past decade (2004–2014) has revealed significant morphological changes. Dune toe erosion/accretion records have been compared with extreme water level measurements, defined as the sum of (i) astronomic tide; (ii) storm surge; and (iii) vertical wave runup. Runup parameterization was conducted using swash limits, beach profiles, and hydrodynamic (Hm0, Tm0,–1, and high tide wa...
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Leary, K. P.; Buscombe, D.; Schmeeckle, M.; Kaplinski, M. A.
2017-12-01
Bedforms are ubiquitous in sand-bedded rivers, and understanding their morphodynamics is key to quantifying bedload transport. As such, mechanistic understanding of the spatiotemporal details of sand transport through and over bedforms is paramount to quantifying total sediment flux in sand-bedded river systems. However, due to the complexity of bedform field geometries and migration in natural settings, our ability to relate migration to bedload flux, and to quantify the relative role of tractive and suspended processes in their dynamics, is incomplete. Recent flume and numerical investigations indicate the potential importance of cross-stream transport, a process previously regarded as secondary and diffusive, to the three-dimensionality of bedforms and spatially variable translation and deformation rates. This research seeks to understand and quantify the importance of cross-stream transport in bedform three-dimensionality in a field setting. This work utilizes a high-resolution (0.25 m grid) data set of bedforms migrating in the channel of the Colorado River in Grand Canyon National Park. This data set comprises multi-beam sonar surveys collected at 3 different flow discharges ( 283, 566, and 1076 m3/s) along a reach of the Colorado River just upstream of the Diamond Creek USGS gage. Data were collected every 6 minutes almost continuously for 12 hours. Using bed elevation profiles (BEPs), we extract detailed bedform geometrical data (i.e. bedform height, wavelength) and spatial sediment flux data over a suite of bedforms at each flow. Coupling this spatially extensive data with a generalized Exner equation, we conduct mass balance calculations that evaluate the possibility, and potential importance, of cross-stream transport in the spatial variability of translation and deformation rates. Preliminary results suggest that intra-dune cross-stream transport can partially account for changes in the planform shape of dunes and may play an important role in spatially
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Brantley, Steven T; Bissett, Spencer N; Young, Donald R; Wolner, Catherine W V; Moore, Laura J
2014-01-01
Barrier islands are complex and dynamic systems that provide critical ecosystem services to coastal populations. Stability of these systems is threatened by rising sea level and the potential for coastal storms to increase in frequency and intensity. Recovery of dune-building grasses following storms is an important process that promotes topographic heterogeneity and long-term stability of barrier islands, yet factors that drive dune recovery are poorly understood. We examined vegetation recovery in overwash zones on two geomorphically distinct (undisturbed vs. frequently overwashed) barrier islands on the Virginia coast, USA. We hypothesized that vegetation recovery in overwash zones would be driven primarily by environmental characteristics, especially elevation and beach width. We sampled species composition and environmental characteristics along a continuum of disturbance from active overwash zones to relict overwash zones and in adjacent undisturbed environments. We compared species assemblages along the disturbance chronosequence and between islands and we analyzed species composition data and environmental measurements with Canonical Correspondence Analysis to link community composition with environmental characteristics. Recovering and geomorphically stable dunes were dominated by Ammophila breviligulata Fernaud (Poaceae) on both islands while active overwash zones were dominated by Spartina patens (Aiton) Muhl. (Poaceae) on the frequently disturbed island and bare sand on the less disturbed island. Species composition was associated with environmental characteristics only on the frequently disturbed island (p = 0.005) where A. breviligulata was associated with higher elevation and greater beach width. Spartina patens, the second most abundant species, was associated with larger sediment grain size and greater sediment size distribution. On the less frequently disturbed island, time since disturbance was the only factor that affected community
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Directory of Open Access Journals (Sweden)
Steven T Brantley
Full Text Available Barrier islands are complex and dynamic systems that provide critical ecosystem services to coastal populations. Stability of these systems is threatened by rising sea level and the potential for coastal storms to increase in frequency and intensity. Recovery of dune-building grasses following storms is an important process that promotes topographic heterogeneity and long-term stability of barrier islands, yet factors that drive dune recovery are poorly understood. We examined vegetation recovery in overwash zones on two geomorphically distinct (undisturbed vs. frequently overwashed barrier islands on the Virginia coast, USA. We hypothesized that vegetation recovery in overwash zones would be driven primarily by environmental characteristics, especially elevation and beach width. We sampled species composition and environmental characteristics along a continuum of disturbance from active overwash zones to relict overwash zones and in adjacent undisturbed environments. We compared species assemblages along the disturbance chronosequence and between islands and we analyzed species composition data and environmental measurements with Canonical Correspondence Analysis to link community composition with environmental characteristics. Recovering and geomorphically stable dunes were dominated by Ammophila breviligulata Fernaud (Poaceae on both islands while active overwash zones were dominated by Spartina patens (Aiton Muhl. (Poaceae on the frequently disturbed island and bare sand on the less disturbed island. Species composition was associated with environmental characteristics only on the frequently disturbed island (p = 0.005 where A. breviligulata was associated with higher elevation and greater beach width. Spartina patens, the second most abundant species, was associated with larger sediment grain size and greater sediment size distribution. On the less frequently disturbed island, time since disturbance was the only factor that affected
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Energy Technology Data Exchange (ETDEWEB)
Kortsenshtein, V.N.
1977-01-01
A description is given of water-pressure systems in a number of the largest gas and gas-condensate fields of the Soviet Union, whose industrial reserves exceed 500 billion cubic meters. These include fields located in the concluding stage of development with sharply reduced recovery (Shebelinsk), fields that have just begun to operate and are characterized by increasing production (Vuktyl, Medved, Orenburg, Shatlyk, Urengoisk), and fields that are not yet developed (Yamburg and Zapolyar). Problems in the theory and practice of studying water-pressure systems of the largest gas and gas-condensate fields are analyzed primarily in connection with conditions required for their rational development which would provide for a maximum extraction of hydrocarbons from the interior. Importance is also given to the hydrogeological aspects of the formation of large hydrocarbon deposits and their distribution in the earth's crust. The most reliable factual materials on hydrogeology are utilized. The book is designed for personnel in the gas and oil industries, hydrogeologists, and scientists interested in problems of the formation, survey, and development of the largest hydrocarbon deposits. 92 references, 65 figures, 71 tables.
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Maximilien Brice
2008-01-01
STRING 2008 hold at CERN -- the largest and most important conference on String Theory with the mostly active researchers in the field. The main purpose of the conference is to review the latest developments for experts.
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Roskin, J.; Sivan, D.; Shtienberg, G.; Roskin, E.; Porat, N.; Bookman, R.
2015-12-01
The study focuses on the Holocene appearance, chronology and drivers of beach sand deposition and inland aeolian sand transport around the Roman-Byzantine ruins of Caesarea, Israel. Beach sand, sand sheets, nebkha, linear and transverse dunes as well as parabolic and transverse interdunes along two transects were sampled in the current study down to their substrate. Sixteen new optically stimulated luminescence ages cluster at ∼5.9-3.3 ka, ∼1.2-1.1 ka (800-900 AD) and ∼190-120 years ago (1825-1895 AD) indicating times of middle and late Holocene sand sheet depositions and historical dune stabilization. The first age cluster indicates that beach sand accumulated when rates of global sea level rise declined around 6-5 ka. Until ∼4 ka sand sheets encroached up to 2.5 km inland. Historical and archaeological evidence points to sand mobilization since the first century AD. Sand sheets dating to 1.2-1.1 ka, coevally found throughout the dunefield represent sand stabilization due to vegetation reestablishment attributed to gradual and fluctuating decline in human activity from the middle Early Islamic period until the 10th century. Historical and chronological evidence of the existence of transverse and coppice dunes from the 19th century suggest that dunes only formed in the last few centuries. The study illustrates the initial role of natural processes, in this case decline in global sea level rise and the primary and later role of fluctuating human activity upon coastal sand mobility. The study distinguishes between sand sheets and dunes and portrays them as sensors of environmental changes.
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Laboratory coupling tests for optimum land streamer design over sand dunes surface
Almalki, Hashim; Alata, Mohanad; Alkhalifah, Tariq Ali
2012-01-01
The cost of data acquisition in land is becoming a major issue as we strive to cover larger areas with seismic surveys at high resolution. Over sand dunes the problem is compounded by the week coupling obtain using geophones, which often forces us
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Lapotre, M. G. A.; Ehlmann, B. L.; Minson, S. E.; Arvidson, R. E.; Ayoub, F.; Fraeman, A. A.; Ewing, R. C.; Bridges, N. T.
2017-01-01
During its ascent up Mount Sharp, the Mars Science Laboratory Curiosity rover traversed the Bagnold Dune Field. We model sand modal mineralogy and grain size at four locations near the rover traverse, using orbital shortwave infrared single-scattering albedo spectra and a Markov chain Monte Carlo implementation of Hapke's radiative transfer theory to fully constrain uncertainties and permitted solutions. These predictions, evaluated against in situ measurements at one site from the Curiosity ...
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Water repellency and infiltration of biological soil crusts on an arid and a temperate dunes
Fischer, Thomas; Yair, Aaron; Geppert, Helmut; Veste, Maik
2014-05-01
Biological soil crusts (BSCs) play an important role in many ecosystems and in all climates. We studies hydrological properties of BSCs under arid and temperate climates. The arid study site was located near Nizzana, in the northwestern Negev, Israel and the temperate site was near Lieberose, Brandenburg, Germany. BSCs were sampled at each site near the dune crest, at the center of the dune slope and at the dune base. Using principal component analysis (PCA), we studied the relationships between hydraulic properties and the molecular structure of organic matter using repellency indices, microinfiltrometry, and 13C-CP/MAS-NMR. The soil texture was finer and water holding capacities (WHCs) were higher in Nizzana, whereas surface wettability was reduced in Lieberose. At both sites, BSCs caused extra WHC compared to the mineral substrate. Infiltration after wetting along both catenas generally reached a maximum after 10 min and decreased after 30 min. Carbohydrates were the dominating components in all of the BSCs studied, where the relative peak areas of carbohydrate-derived structures (60-110 ppm) amounted to 28-46% and to 10-14% of total C-peak areas, respectively. PCA revealed that the WHC of the substrate was closely related to the amount of silt and clay, whereas the BSC induced extra WHC was closely related to carbohydrates. It was further found that water repellency was positively related to carbohydrate C, but negatively related to alkyl C. Infiltration kinetics was attributed to polysaccharide hydration and swelling. Our findings support the hypothesis that hydraulic properties of BSCs are determined by extracellular polymeric substances (EPS) and soil texture. Hydraulic properties in BSCs result from the combination of chemical properties related to C compounds mainly dominated by carbohydrates and physical surface properties related to texture, porosity and water holding capacity. References Fischer, T., Yair, A., Veste, M., Geppert, H. (2013) Hydraulic
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Assessment of Ni, Cu, Zn and Pb levels in beach and dune sands from Havana resorts, Cuba.
Díaz Rizo, Oscar; Buzón González, Fran; Arado López, Juana O
2015-11-15
Concentrations of nickel (Ni), copper (Cu), zinc (Zn) and lead (Pb) in beach and dune sands from thirteen Havana (Cuba) resorts were estimated by X-ray fluorescence analysis. Determined mean metal contents (in mg·kg(-1)) in beach sand samples were 28±12 for Ni, 35±12 for Cu, 31±11 for Zn and 6.0±1.8 for Pb, while for dune sands were 30±15, 38±22, 37±15 and 6.8±2.9, respectively. Metal-to-iron normalization shows moderately severe and severe enrichment by Cu. The comparison with sediment quality guidelines shows that dune sands from various resorts must be considered as heavily polluted by Cu and Ni. Almost in every resort, the Ni and Cu contents exceed their corresponding TEL values and, in some resorts, the Ni PEL value. The comparison with a Havana topsoil study indicates the possible Ni and Cu natural origin. Copyright © 2015 Elsevier Ltd. All rights reserved.
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Largest College Endowments, 2011
Chronicle of Higher Education, 2012
2012-01-01
Of all endowments valued at more than $250-million, the UCLA Foundation had the highest rate of growth over the previous year, at 49 percent. This article presents a table of the largest college endowments in 2011. The table covers the "rank," "institution," "market value as of June 30, 2011," and "1-year change" of institutions participating in…
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Dune communities of SE Colorado: Patterns of rarity, disjunction and succession
T. Kelso; N. Bower; P. Halteman; K. Tenney; S. Weaver
2007-01-01
Dune communities occur across the western Great Plains and in isolated spots in eastern Colorado. They are biologically important due to their endemic nature, their rapid succession, and their ephemeral abundance in response to climate, grazing practices, and ranchland management. The abundance of these terrestrial islands has changed considerably over scales from tens...
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Water-use dynamics of a peat swamp forest and a dune forest in Maputaland, South Africa
Directory of Open Access Journals (Sweden)
A. D. Clulow
2013-05-01
Full Text Available Peat swamp forests are the second rarest forest type found in South Africa while dune forests have been under severe threat through mining and agriculture. Both forest types exist in the conservation area, and World Heritage site, known as the iSimangaliso Wetland Park on the East coast of South Africa. The area is prone to severe droughts (Taylor et al., 2006 and recent attempts to understand the local water balance revealed that there was insufficient information on the water use of the indigenous forests of the area. The peat swamp forest and dune forest sites studied in this research were located within close proximity to each other, yet, are characterised by different landscape positions in terms of water availability. The coastal dune forest soil profile was generally dry and sandy and the tree roots did not have access to the water table. In contrast the peat swamp forest is located in an interdunal wetland where the trees have permanent access to water. The climate at both sites is subtropical with a mean annual precipitation of 1200 mm yr−1. However, over 20 months of measurement, the first summer (October 2009 to March 2010 was drier (424 versus 735 mm than the second summer (October 2010 to March 2011 emphasising the variability of the rainfall in the area and providing a wide range of conditions measured. The sap flow of an evergreen, overstory Syzygium cordatum and a semi-deciduous, understory Shirakiopsis elliptica were measured in the peat swamp forest using the heat ratio method. The Syzygium cordatum water use was not highly seasonal and the daily maximum water use ranged from approximately 30 L d−1 in winter to 45 L d−1 in summer whereas the extit{Shirakiopsis elliptica} water use was more seasonal at 2 L d−1 in winter and 12 L d−1 in summer. The water use of the Syzygium cordatum was not influenced by seasonal rainfall variations and was actually higher in the drier summer (October 2009 to March 2010. Three trees of
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Dune associated calcretes, Rhizoliths and Paleosols from the western continental shelf of India
Digital Repository Service at National Institute of Oceanography (India)
Rao, V.P.; Thamban, M.
detrital/carbonate sands with thin heavy mineral laminations are found. Textural studies indicate that the detrital sands are derived from dunes. Drusy calcite and neomorphic calcite cements are associated with the sands. Sheet deposits contain coarse...
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Sand erosion at the toe of a gabion-protected dune face
Chapman, A.
1992-01-01
The purpose of this research project was to study the manner in which erosion takes place the the toe of a dune slope protected by gabions, and to examine the response of the gabions to this erosion. A sand slope overlaid by model gabions was subjected to wave attack in a hydraulic flume, and
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Field Note: Threatening Tonle Sap: Challenges for Southeast-Asia’s largest Freshwater Lake
Directory of Open Access Journals (Sweden)
Kuenzer, Claudia
2013-09-01
Full Text Available The Tonle Sap ecosystem in Cambodia is Southeast Asia’s largest freshwater lake; strongly impacted by the Mekong river flood pulse. The lake is home to exceptional biodiversity, and rural communities living in free floating villages on the lake and on its shores. The fragile niche ecosystems as well as the rural livelihoods of Tonle Sap are under severe threat. Overfishing, illegal wood harvesting, further resource exploitation, and water quality deterioration all impact the stability of the socio-ecological system of Tonle Sap. At the same time, expected flood pulse changes due to regulatory measures in the context of hydropower development upstream on the Mekong are a severe threat for Tonle Sap’s ecosystem stability. The area needs to shift into the focus of attention of national and international re-searchers, stakeholders, and decision makers, to find suitable pathways for a future sustainable development of this unique and pristine region.
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Anderson, C. P.; Carter, G. A.; Mooneyhan, D.
2013-12-01
Carlton P. Anderson, Gregory Carter, and David Mooneyhan University of Southern Mississippi Gulf Coast Geospatial Center Department of Geography and Geology Carlton.p.anderson@eagles.usm.edu The Mississippi-Alabama (MS-AL) barrier island chain consist of dynamic depositional landforms that constantly undergo changes in their evolutionary processes through changes in sea level, sediment supply, and weather events. These complex landscapes of the Northern Gulf of Mexico (NGOM) provide a chance to study their geomorphological progressions, which have been produced by sea level rise and fluvial processes throughout the Holocene. Studies on the freshwater lens of barriers have mainly concentrated on carbonate island settings with minimal focus to barriers with siliciclastic geology. The purpose of this study is to examine the relationship beach dune topography plays in the development and sustainability of the fresh water lens of Cat Island, Mississippi. Cat Island offers the opportunity to research a siliciclastic barrier along the NGOM where minimal anthropogenic activities have taken place. To determine the effect dune topography has on the fresh water lens, a transect of permanent water wells were used in conjunction with test wells at different sites throughout the north spit of the island, to establish the water table height above the ellipsoid (WGS 84), with vertical accuracies of 2 cm. Cross-sectional profiles of the dunes were also performed utilizing purposeful transects that intersected fresh water ponds in the dune-swale systems. These ponds provide water table elevations at the surface which were interpolated across the dunes for areas that lacked permanent well sites. To obtain survey-grade accuracies, a Trimble TSC3 receiver coupled with a R8 antennae RTK system were used. Salinity measurements were taken at test sites to determine the salt-to-freshwater interface. Results provide insights into how dune topography influences the fresh water lens of a
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Largest particle detector nearing completion
2006-01-01
"Construction of another part of the Large Hadron Collider (LHC), the worl's largest particle accelerator at CERN in Switzerland, is nearing completion. The Compact Muon Solenoid (CMS) is oner of the LHC project's four large particle detectors. (1/2 page)
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Response of the chitinolytic microbial community to chitin amendments of dune soils
De Boer, W.; Gerards, S.; Klein Gunnewiek, P.J.A.; Modderman, R.
1999-01-01
The dynamics of culturable chitin-degrading microorganisms were studied during a 16-week incubation of chitin-amended coastal dune soils that differed in acidity. Soil samples were incubated at normal (5% Why) and high (15% w/w) moisture levels. More than half of the added chitin was decomposed
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Le Mauff, Baptiste; Juigner, Martin; Ba, Antoine; Robin, Marc; Launeau, Patrick; Fattal, Paul
2018-03-01
Three beach and dune systems located in the northeastern part of the Bay of Biscay in France were monitored over 5 years with a time series of three airborne LiDAR datasets. The three study sites illustrate a variety of morphological beach types found in this region. Reproducible monitoring solutions adapted to basic and complex beach and dune morphologies using LiDAR time series were investigated over two periods bounded by the three surveys. The first period (between May 2008 and August 2010) is characterized by a higher prevalence of storm events, and thus has a greater potential for eroding the coast, than the second period (between August 2010 and September 2013). During the first period, the central and northeastern part of the Bay of Biscay was notably impacted by Storm Xynthia, with water levels and wave heights exceeding the 10-year return period and 1-year return period, respectively. Despite differences in dune morphology between the sites, the dune crest (Dhigh) and the dune base (Dlow) are efficiently extracted from each DEM. Based on the extracted dune base, an original shoreline mobility indicator is built displaying a combination of the horizontal and vertical migrations of this geomorphic indicator between two LiDAR datasets. A 'Geomorphic Change Detection' is also completed by computing DEMs of Difference (DoD) resulting in segregated maps of erosion and deposition and sediment budgets. Accounting for the accuracy of LiDAR datasets, a probabilistic approach at a 95% confidence interval is used as a threshold for the Geomorphic Change Detection showing more reliable results. However, caution should be taken when interpreting thresholded maps of changes and sediment budgets because some beach processes may be masked, especially on wide tidal beaches, by only keeping the most significant changes. The results of the shoreline mobility and Geomorphic Change Detection show a high variability in the beach responses between and within the three study
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Advanced GPR imaging of sedimentary features: integrated attribute analysis applied to sand dunes
Zhao, Wenke; Forte, Emanuele; Fontolan, Giorgio; Pipan, Michele
2018-04-01
We evaluate the applicability and the effectiveness of integrated GPR attribute analysis to image the internal sedimentary features of the Piscinas Dunes, SW Sardinia, Italy. The main objective is to explore the limits of GPR techniques to study sediment-bodies geometry and to provide a non-invasive high-resolution characterization of the different subsurface domains of dune architecture. On such purpose, we exploit the high-quality Piscinas data-set to extract and test different attributes of the GPR trace. Composite displays of multi-attributes related to amplitude, frequency, similarity and textural features are displayed with overlays and RGB mixed models. A multi-attribute comparative analysis is used to characterize different radar facies to better understand the characteristics of internal reflection patterns. The results demonstrate that the proposed integrated GPR attribute analysis can provide enhanced information about the spatial distribution of sediment bodies, allowing an enhanced and more constrained data interpretation.
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White Sands, New Mexico as seen from STS-60
1994-01-01
White Sands National Monument (Park) is easily recognized in the center of this near-vertical color photograph. White Sands is the world's largest gypsum dune field. It represents an alabaster sea that covers nearly 300 square miles. At the southwest corner of the White Sands is dry lake, Lucero. In terms of cultural features the city of Alamogordo and Holloman Air Force Base can be seen with great clarity on this photograph.
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Liu, Ruyin; Li, Ke; Zhang, Hongxun; Zhu, Junge; Joshi, DevRaj
2014-11-01
The microbial community compositions and potential ammonia oxidation in the topsoil at different positions of sand dune (stoss slope, crest, lee slope, and interdune) from the Gurbantunggut Desert, the largest semi-fixed desert in China, were investigated using several molecular methods. Actinobacteria and Proteobacteria (especially Alphaproteobacteria) were commonly the dominant taxa across all soil samples. Bacterial communities were similar in soils collected from the stoss slopes and interdunes (HC-BSCs, biological soil crusts with a high abundance of cyanobacteria), containing more abundant cyanobacterial populations (16.9-24.5%) than those (0.2-0.7% of Cyanobacteria) in the crests and lee slopes (LC-BSCs, biological soil crusts with a low abundance of cyanobacteria). The Cyanobacteria were mainly composed of Microcoleus spp., and quantitative PCR analysis revealed that 16S rRNA gene copy numbers of Cyanobacteria (especially genus Microcoleus) were at least two orders of magnitude higher in HC-BSCs than in LC-BSCs. Heterotrophic Geodermatophilus spp. frequently occurred in HC-BSCs (2.5-8.0%), whereas genera Arthrobacter, Bacillus, and Segetibacter were significantly abundant in LC-BSC communities. By comparison, the desert archaeal communities were less complex, and were dominated by Nitrososphaera spp. The amoA gene abundance of ammonia-oxidizing archaea (AOA) was higher than that of ammonia-oxidizing bacteria (AOB) in all soil samples, particularly in the interdunal soils (10(6)-10(8) archaeal amoA gene copies per gram dry soil), indicating that AOA possibly dominate the ammonia oxidation at the interdunes.
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Modelling Scour in Front of Dune Revetments in a Surf-beat Model
Van Geer, P.F.C.; Van Thiel de Vries, J.S.M.; Boers, M.; Den Bieman, J.P.; McCall, R.T.
2014-01-01
This paper presents adaptations to the XBeach model aimed at including the relevant processes for the generation of scour holes at the toe of a revetment. Dutch assessment rules for the safety of sea defenses need to be adjusted to cope with a combination of sandy dunes and hard elements. To that
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International Nuclear Information System (INIS)
Al-Sagaby, A.; Moallim, A.
2001-01-01
The investigation of recharge in the sand dune, Qasim, Saudi Arabia, with the help of chloride concentration and isotope content has revealed inconsistent pattern and less homogeneity. Monotonic chloride concentration and isotope content was the result of seasonal recharge occurrence in the study area. In addition, applying chloride mass-balance method, recharge rate calculation in the sand dune site, Qasim, Saudi Arabia, was made. The results (1.80 and 1.84mmy -1 - dune site) estimated during this project using this method was a long way below the recharge rates (30mmy -1 , 13.4mmy -1 in the dune site and 5mmy -1 in the swale site) obtained with the application of tritium method in the previous years (1994 and 1996). 1.80 and 1.84mmy -1 was for CRP-Saud-9405 project and was calculated 1997 and 1998 respectively. The reason for the lower recharge rate with the application of chloride mass-balance method could be the source of chloride input and high evaporation, which causes accumulation of chloride salts in the area. (author)
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Cause rare d'une perforation de la cloison nasale
Jahidi, Ali; Hemmaoui, Bouchaïb; Itoua, Wulfran Rosaire; Errami, Noureddine; Benariba, Fouad
2014-01-01
Les perforations de la cloison nasale constituent une pathologie fréquente en ORL. Leurs causes sont multiples et restent dominées par les traumatismes chirurgicaux. Les étiologies infectieuses et notamment la tuberculose sont rares. Nous présentons le cas d'une patiente ayant bénéficié d'une méatotomie bilatérale et chez laquelle une perforation de la cloison nasale a été découverte lors d'un examen systématique à un an de son intervention. D'abord considérée comme une complication de la chirurgie, la biopsie des berges de la perforation a permis de déterminer son origine tuberculeuse. La présentation clinique des perforations de la cloison nasale n'est pas spécifique. Elles sont souvent asymptomatiques et de découverte fortuite. Les traumatismes notamment chirurgicaux sont le plus siuvent en cause. L′orogine tuberculeuse resta très rare. Le diagnostic de certitude de tuberculose repose sur la biopsie des berges de cette perforation. Le but de ce travail est de mettre en avant l'intérêt de la biopsie dans le diagnostic de la tuberculose de la cloison nasale. Cette biopsie doit être systématique même en cas d'antécédents de chirurgie endonasale qui est le plus souvent en cause dans les perforations de la cloison nasale. PMID:24932334
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Energy Technology Data Exchange (ETDEWEB)
Faugeras, P E [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires. Groupe de recherches sur la fusion controlee
1967-07-01
The problem of the scattering of plane electromagnetic waves from a non-uniform, cylindrically symmetrical plasma is solved analytically, by a self-consistent field method, for a wave with the electric field parallel to the cylinder axis. Numerical results for the diffracted field are plotted for interesting ranges of the parameters involved: diameter, density on the axis, radial profile of the density, and collision frequencies. The case where the incident field is cylindric (waves surfaces parallel to the cylinder axis) is examined - this permits to connect theoretical calculations and experimental diffraction patterns, and also to explain the diffraction effects observed in a classical microwave interferometry experiment. These results, and the possibility of measuring exactly the diffracted field (showed by experiments with dielectric and metallic rods) lead to a new plasma diagnostic method, based on the diffraction, which has no theoretical limitations and it usable when the classical free-space wave methods are not (plasma diameter lower than 10 wave lengths). The feasibility of this method is tested with a plasma at atmospheric pressure and a 2 mm incident wavelength. The plasma is obtained by the laminar flow of a plasma torch, with a working gas (He or Ar) seeded by potassium (density continuously variable between 10{sup 11} and 10{sup 15} e/cm{sup 3}. Some diffraction patterns by this plasma and for various incident waves, are also given and explained with theoretical calculations. (author) [French] On etudie la diffusion coherente d'une onde electromagnetique par un cylindre de plasma inhomogene par une methode de champ self-consistant, et pour une onde de vecteur electrique parallele a l'axe du cylindre. On a calcule le champ diffracte en faisant varier le diametre du cylindre, la densite sur l'axe, le profil de densite et les frequences de collisions, et on donne ici les principaux resultats. On examine ensuite le cas d'une onde incidente cylindrique
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State-space modeling indicates rapid invasion of an alien shrub in coastal dunes
DEFF Research Database (Denmark)
Damgaard, Christian Frølund; Nygaard, Bettina; Ejrnæs, Rasmus
2011-01-01
allows separation of process and sampling variance, thus enabling ecological predictions with a known degree of uncertainty. The method is applied for the invasive shrub Rosa rugosa (Japanese rose) in Danish fixed dunes. The probability of observing R. rugosa increased significantly from 0.18 to 0...
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Observations and analytical modeling of freshwater and rainwater lenses in coastal dune systems
Stuijfzand, Pieter
2016-01-01
Observations are reported on (i) groundwater recharge rates under various types of vegetation as measured with megalysimeters in the dunes, (ii) freshwater lenses along the Dutch North Sea coast in the early 1900s, and (iii) rainwater lenses that develop on top of laterally migrating,
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La recherche écosanté en pratique : Applications novatrices d'une ...
International Development Research Centre (IDRC) Digital Library (Canada)
22 juil. 2014 ... ... de l'écosanté forment un tout qui prouve à quel point il s'agit d'un domaine dynamique et en évolution constante doté d'une mission claire et animé par une communauté de praticiens scientifique toujours plus large. Mario Henry Rodríguez, Directeur général, Instituto Nacional de Salud Pública, Mexique.
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2012-09-13
... writing or picked up in person at Indiana Dunes National Lakeshore, 1100 N. Mineral Springs Road, Porter... for public inspection in their entirety. Dated: July 27, 2012. Michael T. Reynolds, Regional Director...
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Lisimenka, Aliaksandr; Kubicki, Adam
2017-02-01
A new spectral analysis technique is proposed for rhythmic bedform quantification, based on the 2D Fourier transform involving the calculation of a set of low-order spectral moments. The approach provides a tool for efficient quantification of bedform length and height as well as spatial crest-line alignment. Contrary to the conventional method, it not only describes the most energetic component of an undulating seabed surface but also retrieves information on its secondary structure without application of any band-pass filter of which the upper and lower cut-off frequencies are a priori unknown. Validation is based on bathymetric data collected in the main Vistula River mouth area (Przekop Wisły), Poland. This revealed two generations (distinct groups) of dunes which are migrating seawards along distinct paths, probably related to the hydrological regime of the river. The data enable the identification of dune divergence and convergence zones. The approach proved successful in the parameterisation of topographic roughness, an essential aspect in numerical modelling studies.
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Mobile dune fixation by a fast-growing clonal plant : a full life-cycle analysis
Li, Shou-Li; Yu, Fei-Hai; Werger, Marinus J A; Dong, Ming; During, Heinjo J; Zuidema, Pieter A
2015-01-01
Desertification is a global environmental problem, and arid dunes with sparse vegetation are especially vulnerable to desertification. One way to combat desertification is to increase vegetation cover by planting plant species that can realize fast population expansion, even in harsh environments.
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Mobile dune fixation by a fast-growing clonal plant: a full life-cycle analysis
Werger, M.J.A.; During, H.J.; Zuidema, P.A.
2015-01-01
Desertification is a global environmental problem, and arid dunes with sparse vegetation are especially vulnerable to desertification. One way to combat desertification is to increase vegetation cover by planting plant species that can realize fast population expansion, even in harsh environments.
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Mughal, Iqra; Jadoon, Khan; Mai, Paul Martin; Al-Mashharawi, Samir; Missimer, Thomas
2015-01-01
A component of designing a managed aquifer recharge system in a dune aquifer is the control of diffusive evaporative loss of water which is governed by the physical properties of the sediments and the position of the water table. A critical water table position is the “extinction depth”, below which no further loss of water occurs via diffusion. Field experiments were conducted to measure the extinction depth of sediments taken from a typical dune field in the region. The soil grain size characteristics, laboratory porosity, and saturated hydraulic conductivity were measured. The sand is classified as well-sorted, very fine sand with a mean grain diameter of 0.15 mm. Soil moisture gradients and diffusion loss rates were measured using sensors in a non-weighing lysimeter that was placed below land surface. The sand was saturated carefully with water from the bottom to the top and was exposed to the natural climate for a period of about two months. The moisture gradient showed a gradual decline during measurement until extinction depth was reached at about 100 cm below surface after 56 days. Diurnal temperature changes were observed in the upper 75 cm of the column and were negligible at greater depth.
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Mughal, Iqra
2015-12-10
A component of designing a managed aquifer recharge system in a dune aquifer is the control of diffusive evaporative loss of water which is governed by the physical properties of the sediments and the position of the water table. A critical water table position is the “extinction depth”, below which no further loss of water occurs via diffusion. Field experiments were conducted to measure the extinction depth of sediments taken from a typical dune field in the region. The soil grain size characteristics, laboratory porosity, and saturated hydraulic conductivity were measured. The sand is classified as well-sorted, very fine sand with a mean grain diameter of 0.15 mm. Soil moisture gradients and diffusion loss rates were measured using sensors in a non-weighing lysimeter that was placed below land surface. The sand was saturated carefully with water from the bottom to the top and was exposed to the natural climate for a period of about two months. The moisture gradient showed a gradual decline during measurement until extinction depth was reached at about 100 cm below surface after 56 days. Diurnal temperature changes were observed in the upper 75 cm of the column and were negligible at greater depth.
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Directory of Open Access Journals (Sweden)
Iqra Mughal
2015-12-01
Full Text Available A component of designing a managed aquifer recharge system in a dune aquifer is the control of diffusive evaporative loss of water which is governed by the physical properties of the sediments and the position of the water table. A critical water table position is the “extinction depth”, below which no further loss of water occurs via diffusion. Field experiments were conducted to measure the extinction depth of sediments taken from a typical dune field in the region. The soil grain size characteristics, laboratory porosity, and saturated hydraulic conductivity were measured. The sand is classified as well-sorted, very fine sand with a mean grain diameter of 0.15 mm. Soil moisture gradients and diffusion loss rates were measured using sensors in a non-weighing lysimeter that was placed below land surface. The sand was saturated carefully with water from the bottom to the top and was exposed to the natural climate for a period of about two months. The moisture gradient showed a gradual decline during measurement until extinction depth was reached at about 100 cm below surface after 56 days. Diurnal temperature changes were observed in the upper 75 cm of the column and were negligible at greater depth.
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Modelling dune erosion, overwash and breaching at Fire Island (NY) during hurricane Sandy
De Vet, P.L.M.; McCall, R.T.; Den Bieman, J.P.; Stive, M.J.F.; Van Ormondt, M.
2015-01-01
In 2012, Hurricane Sandy caused a breach at Fire Island (NY, USA), near Pelican Island. This paper aims at modelling dune erosion, overwash and breaching processes that occured during the hurricane event at this stretch of coast with the numerical model XBeach. By using the default settings, the
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Annexe 3. Constitution d'une exploitation à Homs
2015-01-01
‘Abd al-Laṭīf, né en 1925, est jardinier à Horns. Il exploite avec son fils aîné et l'aide de deux de ses petits-fils un jardin de quelques 35 dunum (3,5 hectares) situé dans le zūr al-Ǧdīdeh, secteur central de la zone agricole. Cette grande exploitation, constituée de plusieurs parcelles ayant différents statuts, est en partie le produit d'une histoire familiale dont je voudrais présenter ici brièvement les principaux aspects. Figure 50 – Alliances matrimoniales entre la lignée de ‘Abbās e...
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Harris, Peter T.
1991-07-01
Large subtidal sand dunes (sandwaves) located in Adolphus Channel, Torres Strait, have been observed to reverse their asymmetric orientation between September-February. This has been attributed to a reversal in wind-driven currents, which flow westward during the SE trade season (April-November) and eastwards during the NW monsoon season [December-March: HARRIS (1989) Continental Shelf Research, 9, 981-1002]. Observations in September 1988 and February 1989 from another area of dunes in Torres Strait corroborate this asymmetry reversal pattern. The results indicate that such reversals may be common in Torres Strait and in other areas where subtidal bedforms are subject to modification by superimposed, seasonally reversing, wind-driven currents.
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Díaz Rizo, Oscar; Buzón González, Fran; Arado López, Juana O; Denis Alpízar, Otoniel
2015-12-30
Concentrations of chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn) and lead (Pb) in dune sands from six urban and suburban Matanzas (Cuba) resorts and Varadero beach were estimated by X-ray fluorescence analysis. Ranges of metal contents in dune sands show a strong variation across the studied locations (in mg/kg(-1)): 20-2964 for Cr, 17-183 for Ni, 17-51 for Cu, 18-88 for Zn and 5-29 for Pb. The values of contamination factors and contamination degrees how that two of the studied Matanzas's resorts (Judio and Chirry) are strongly polluted. The comparison with Sediment Quality Guidelines shows that dune sands from Judio resort represent a serious risk for humans, due to polluted Cr and Ni levels, while sands from the rest of the studied resorts, including Varadero beach, do not represent any risk for public use. Copyright © 2015 Elsevier Ltd. All rights reserved.
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Kochemasov, G. G.
2008-09-01
Widely circulating opinion that titanian methane lowlands in a broad equatorial region are covered with eolian formations needs to be carefully checked. Of coarse, all three solid bodies with atmospheres in the inner solar system have dunes. Why do not have them on Titan? Most probably they do exist but discovered by radar up to now cross-cutting rippling features cannot be taken for them. For this there are several reasons. How it can be that prevailing "dune" strike coincides with prevailing wind direction? Normally (with some African exceptions) one sees real terrestrial dunes stretching across winds. And this is understandable from a point of view eolian dunes formation. This formation gives particular cross profile to dunes. Asymmetric profile - one slope is long and gentle and another one short and abrupt. But titanian "dunes" are mostly uniform and symmetric. And this characteristic is preserved for many hundreds of kilometers of very straight features. Then, the finest solid particles precipitation from the thick atmosphere of Titan should be distributed on the satellite surface more uniformly and cover dark lowlands and light icy highlands of the wide equatorial belt more or less evenly. But "dunes" are strictly associated with dark lowlands and tend to turn round light icy obstacles. Cindering smoggy particles to produce sands for making dunes is a pure imagination. Then, radar preferably sees one direction but nevertheless one or more crossing directions of rippling are distinguished (Fig.3, 4) They mean two wind directions at the same time or another wind direction at another time? If so, the earlier "dunes" should be more or less obliterated by the later ones. Nothing of the kind! Both crossing ripples directions are fresh. Then, eolian action is not seen at the higher latitudes (Fig. 5). There are no winds there? Probably it is not so. Only a liquid state of methane can help (but liquid should be disturbed by winds). Solid methane there is also
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Lang, Jörg; Winsemann, Jutta
2013-10-01
The preservation of bedforms related to supercritical flows and hydraulic jumps is commonly considered to be rare in the geologic record, although these bedforms are known from a variety of depositional environments. This field-based study presents a detailed analysis of the sedimentary facies and stacking pattern of deposits of cyclic steps, chutes-and-pools, antidunes and humpback dunes from three-dimensional outcrops. The well exposed Middle Pleistocene successions from northern Germany comprise glacilacustrine ice-contact subaqueous fan and glacial lake-outburst flood deposits. The studied successions give new insights into the depositional architecture of bedforms related to supercritical flows and may serve as an analogue for other high-energy depositional environments such as fluvial settings, coarse-grained deltas or turbidite systems. Deposits of cyclic steps occur within the glacial lake-outburst flood succession and are characterised by lenticular scours infilled by gently to steeply dipping backsets. Cyclic steps formed due to acceleration and flow thinning when the glacial lake-outburst flood spilled over a push-moraine ridge. These bedforms are commonly laterally and vertically truncated and alternate with deposits of chutes-and-pools and antidunes. The subaqueous fan successions are dominated by laterally extensive sinusoidal waveforms, which are interpreted as deposits of aggrading stationary antidunes, which require quasi-steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation. Humpback dunes are characterised by downflow divergent cross-stratification, displaying differentiation into topsets, foresets and bottomsets, and are interpreted as deposited at the transition from subcritical to supercritical flow conditions or vice versa. Gradual lateral and vertical transitions between humpback dunes and antidune deposits are very common. The absence of planar-parallel stratification in all studied successions
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Les SIG-P au service d'une gestion durable des ressources ...
International Development Research Centre (IDRC) Digital Library (Canada)
Les SIG-P au service d'une gestion durable des ressources naturelles et de la sécurité alimentaire en Afrique. Les pays africains ont besoin de données convenables aux fins de la formulation et de la mise en oeuvre de politiques et de stratégies de sécurité alimentaire systématiques et cohérentes. Ces pays disposent de ...
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Loope, Walter L.; Loope, Henry M.; Goble, Ronald J.; Fisher, Timothy G.; Lytle, David E.; Legg, Robert J.; Wysocki, Douglas A.; Hanson, Paul R.; Young, Aaron R.
2012-01-01
Current models of landscape response to Holocene climate change in midcontinent North America largely reconcile Earth orbital and atmospheric climate forcing with pollen-based forest histories on the east and eolian chronologies in Great Plains grasslands on the west. However, thousands of sand dunes spread across 12,000 km2 in eastern upper Michigan (EUM), more than 500 km east of the present forest-prairie ecotone, present a challenge to such models. We use 65 optically stimulated luminescence (OSL) ages on quartz sand deposited in silt caps (n = 8) and dunes (n = 57) to document eolian activity in EUM. Dune building was widespread ca. 10–8 ka, indicating a sharp, sustained decline in forest cover during that period. This decline was roughly coincident with hydrologic closure of the upper Great Lakes, but temporally inconsistent with most pollen-based models that imply canopy closure throughout the Holocene. Early Holocene forest openings are rarely recognized in pollen sums from EUM because faint signatures of non-arboreal pollen are largely obscured by abundant and highly mobile pine pollen. Early Holocene spikes in nonarboreal pollen are recorded in cores from small ponds, but suggest only a modest extent of forest openings. OSL dating of dune emplacement provides a direct, spatially explicit archive of greatly diminished forest cover during a very dry climate in eastern midcontinent North America ca. 10–8 ka.
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View of sand dunes in the San Juan Province of Western Argentina
1975-01-01
A near vertical view of sand dunes in the San Juan Province of Western Argentina, as photographed from the Apollo spacecraft in Earth orbit during the joint U.S.-USSR Apollo Soyuz Test Project (ASTP) mission. The picture was taken at an altitude of 220 kilometers (136 statute miles). The photograph was taken at an altitude of 228 kilometers (141 statute miles).
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Alternative Fuels Data Center: America's Largest Home Runs on Biodiesel in
North Carolina America's Largest Home Runs on Biodiesel in North Carolina to someone by E-mail Share Alternative Fuels Data Center: America's Largest Home Runs on Biodiesel in North Carolina on Facebook Tweet about Alternative Fuels Data Center: America's Largest Home Runs on Biodiesel in North
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Caracterisation sociodemographique, clinique et criminologique d?une population de 210 meurtriers
2009-01-01
Resume Cet article, de nature essentiellement descriptive, interroge les caracteristiques sociodemographiques, cliniques et criminologiques d?une population de 210 meurtriers examines par deux experts psychiatres angevins pendant une periode de 30 ans. Les meurtriers de notre serie sont majoritairement des hommes (73 %) d?age jeune, 33 ans en moyenne, sans emploi (51 %), vivant seuls au moment des faits (49 %). Ils ont des antecedents psychiatriques dans deux tiers des cas et des a...
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Energy Technology Data Exchange (ETDEWEB)
Warburton, Thomas Karl [Sheffield U.
2017-01-01
The Deep Underground Neutrino Experiment (DUNE) is a next-generation neutrino experiment which will be built at the Sanford Underground Research Facility (SURF), and will receive a wide-band neutrino beam from Fermilab, 1300~km away. At this baseline DUNE will be able to study many of the properties of neutrino mixing, including the neutrino mass hierarchy and the value of the CP-violating complex phase ($\\delta_{CP}$). DUNE will utilise Liquid Argon (LAr) Time Projection Chamber (TPC) (LArTPC) technology, and the Far Detector (FD) will consist of four modules, each containing 17.1~kt of LAr with a fiducial mass of around 10~kt. Each of these FD modules represents around an order of magnitude increase in size, when compared to existing LArTPC experiments. \\\\ The 35 ton detector is the first DUNE prototype for the single (LAr) phase design of the FD. There were two running periods, one from November 2013 to February 2014, and a second from November 2015 to March 2016. During t he second running period, a system of TPCs was installed, and cosmic-ray data were collected. A method of particle identification was developed using simulations, though this was not applied to the data due to the higher than expected noise level. A new method of determining the interaction time of a track, using the effects of longitudinal diffusion, was developed using the cosmic-ray data. A camera system was also installed in the detector for monitoring purposes, and to look for high voltage breakdowns. \\\\ Simulations concerning the muon-induced background rate to nucleon decay are performed, following the incorporation of the MUon Simulations UNderground (MUSUN) generator into the DUNE software framework. A series of cuts which are based on Monte Carlo truth information is developed, designed to reject simulated background events, whilst preserving simulated signal events in the $n \\rightarrow K^{+} + e^{-}$ decay channel. No background events are seen to survive the app lication of
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Identifying the node spreading influence with largest k-core values
International Nuclear Information System (INIS)
Lin, Jian-Hong; Guo, Qiang; Dong, Wen-Zhao; Tang, Li-Ying; Liu, Jian-Guo
2014-01-01
Identifying the nodes with largest spreading influence of complex networks is one of the most promising domains. By taking into account the neighbors' k-core values, we present an improved neighbors' k-core (INK) method which is the sum of the neighbors' k-core values with a tunable parameter α to evaluate the node spreading influence with largest k-core values. Comparing with the Susceptible–Infected–Recovered (SIR) results for four real networks, the INK method could identify the node spreading influence with largest k-core values more accurately than the ones generated by the degree k, closeness C, betweenness B and coreness centrality method. - Highlights: • We present an improved neighbors' k-core (INK) method to evaluate the node spreading influence with largest k-core values. • The INK method could identify the node spreading influence with largest k-core values more accurately. • Kendall's tau τ of INK method with α=1 are highly identical to rank the node influence
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Energy Technology Data Exchange (ETDEWEB)
Galgaro, A.; Finzi, E. [Padua Univ., Padua (Italy). Dipt. di Geologia, Paleontologia e Geofisica; Tosi, L. [Consiglio Nazionale delle Ricerche, Venice (Italy). Ist. per l Studio della Dinamica delle Grandi Masse
2000-04-01
The internal structures of some surviving sand dunes and the ancient shore-lines along the coast south of Venice (Italy) have been investigated integrating ground probing radar (GPR) profiles, vertical electrical soundings (VES) and water conductivity measurements in some boreholes. The GPR penetration depth has been limited (4-5 m, using a 400 MHz antenna) by the high conductivity of salt water saturating pores of the shallow sediments. On the other hand, the excellent spatial resolution of the radar survey provided an estimate of internal dune bedding features, such as cross lamination and forwarding ancient covered coast-lines dated in the Thirties. The interpretation of the data, in particular along one line 360 m long intercepting a sizeable sand-dune bank, seems to offer clues to the evolutional history of the coast line and the depth of transition from fresh-water to brackish-salt water. The water table was detected with electrical measurements and direct observations in boreholes, whereas the transition between fresh and salt water was pointed out indirectly by the high energy absorption and total back-reflection of the electromagnetic waves, encountered at this boundary, and directly by the strong decrease in VES resistivity values.
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Directory of Open Access Journals (Sweden)
Nina Rosa Zanin Zanella
2010-01-01
Full Text Available The vegetation cover of a sand dune was surveyed ten years after the improvement of a restoration project that utilized seed sowing, seedling planting and seedling transplantation from an adjacent area with watering in the first months. On the upper part of the restored dune, the vegetation was sparse (53% but more developed than that of the adjacent control area (34%, both presenting herbaceous/subshrub physiognomy with predominance of Panicum racemosum. On the slope of the restored dune, a shrub vegetation developed, presenting a percentage cover (90% similar to that of the control area (100%. Dodonaea viscosa was the dominant species on this restored face. The establishment of arboreal and shrub species seedlings on the upper dune was good. In part, this improved the species richness, but contributed to dissimilarity between this area and the control site. A lower species richness was presented on the slope and the similarity to the control area was even lower. Plants introduced by sowing and seedling transplantation showed success and contributed to the similarity with the adjacent vegetation. Seedlings of arboreal and shrub plants survived on the upper dune. These species are represented in a more developed stage of succession, differing from the adjacent control area.
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Dune Ecosystem Management of the Razim-Sinoie Littoral Bar (Romania
Directory of Open Access Journals (Sweden)
Gheorghe ROMANESCU
2010-12-01
Full Text Available The Razim-Sinoie lagoon complex is located in the south-eastern part of Romania. It is bordered by the Dobrudja region to the west and north, the Danube Delta to the north-east and the Black Sea to the east. An assessment of the quality of dunes was made in that area and several conservation measures were proposed. The age of the Razim-Sinoie littoral bar cannot be older than 1500 - 2000 years, according to to the total closure of the Halmyris bay and the end of the harbour activities in Histria and, subsequently, in Enisala. Transversally, the littoral bar is quite symmetrical, with few differences between the part towards the sea, which is more abrupt, and the less abrupt part towards the lagoon. Most of the sediments that make up the littoral bar are of Danubian origin and the rest are of marine origin (bio-constructional, caused by the smashing of the empty shells. The materials get transported by the littoral stream and deposited by waves and wind. The average increase of the marine level is between 1 and 2 cm/year. Even if the transgressive phenomenon occurs along the entire bar, several sectors are slightly eroded (as in Portita, others are slightly progradated (as in Chituc-Capul Midia and the rest have a precarious relative equilibrium (Periboina, Periteasca. The reduced water transparency facilitates a good development of the shell population, and causes the terrigenic material/organogenic material ratio (T/O to be 50/50. As a result of the reduction of the Danube solid discharge which supplied the littoral bar, the whole alignment was affected, and, consequently, a generalized retreat of the shore line occurred. Under such circumstances, a supplementary sediment discharge was necessary, but without affecting the nearby ecosystems. Supplementary material can be brought from offshore, from the - 20m deep isobath or by building canals between the Sfantu Gheorghe arm of the Danube (the southernmost arm and the littoral nearby. In that
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44 CFR 65.11 - Evaluation of sand dunes in mapping coastal flood hazard areas.
2010-10-01
... mapping coastal flood hazard areas. 65.11 Section 65.11 Emergency Management and Assistance FEDERAL... Insurance Program IDENTIFICATION AND MAPPING OF SPECIAL HAZARD AREAS § 65.11 Evaluation of sand dunes in mapping coastal flood hazard areas. (a) General conditions. For purposes of the NFIP, FEMA will consider...
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Manuel et site Web de ressources sur l'élaboration d'une constitution
International Development Research Centre (IDRC) Digital Library (Canada)
élaboration d'une constitution est devenue un élément essentiel dans le cheminement vers la paix et la démocratie, en période de conflit, après un conflit et dans un contexte de transition. Les constitutions servent à régir les relations entre un État et ...
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Naqshband, Suleyman; Ribberink, Jan S.; Hulscher, Suzanne J.M.H.
2014-01-01
Dunes are common bed forms in sand bed rivers and are of central interest in water management purposes. Due to flow separation and associated energy dissipation, dunes form the main source of hydraulic roughness. A large number of dune dimension data sets was compiled and analyzed in this study—414
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Li, Xinrong
2016-04-01
Biological soil crust (BSC) is a vital component in the stabilized sand dunes with a living cover up to more than 70% of the total, which has been considered as a bio-mediator that directly influences and regulates the sand dune ecosystem processes. However, its influences on soil hydrological processes have been long neglected in Chinese deserts. In this study, BSCs of different successional stages were chose to test their influence on the hydrological processes of stabilized dune, where the groundwater deep exceeds 30m, further to explore why occur the sand-binding vegetation replacement between shrubs and herbs. Our long-term observation (60 years) shows that cyanobacteria crust has been colonized and developed after 3 years since the sand-binding vegetation has been established and dune fixation using planted xerophytic shrubs and made sand barrier (straw-checkerboard) on shifting dune surface, lichen and moss crust occurred after 20 years, and the cover of moss dominated crust could reach 70 % after 50 years. The colonization and development of BSC altered the initial soil water balance of revegetated areas by influencing rainfall infiltration, soil evaporation and dew water entrapment. The results show that BSC obviously reduced the infiltration that occurred during most rainfall events (80%), when rainfall was greater than 5 mm or less than 20 mm. The presence of BSC reduced evaporation of topsoil after small rainfall (<5 mm) because its high proportion of finer particles slowed the evaporation rate, thus keeping the water in the soil surface longer, and crust facilitated topsoil evaporation when rainfall reached 10 mm. The amount of dew entrapment increases with the succession of BSC. Moreover, the effect of the later successional BSC to dew entrapment, rainfall infiltration and evaporation was more obvious than the early successional BSC on stabilized dunes. In general, BSC reduced the amount of rainfall water that reached deeper soil (0.4-3m), which is
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Pye, K.; Blott, S. J.
2008-12-01
Monitoring of frontal dune erosion and accretion on the Sefton coast in northwest England over the past 50 years has revealed significant spatial and temporal variations. Previous work has shown that the spatial variations primarily reflect longshore differences in beach and nearshore morphology, energy regime and sediment budget, but the causes of temporal variations have not previously been studied in detail. This paper presents the results of work carried out to test the hypothesis that a major cause of temporal variation is changes in the frequency and magnitude of storms, surges and resulting high tides. Dune toe erosion/accretion records dating from 1958 have been compared with tide gauge records at Liverpool and Heysham. Relatively high dune erosion rates at Formby Point 1958-1968 were associated with a relatively large number of storm tides. Slower erosion at Formby, and relatively rapid accretion in areas to the north and south, occurred during the 1970's and 1980's when there were relatively few major storm tides. After 1990 rates of dune erosion at Formby increased again, and dunes to the north and south experienced slower accretion. During this period high storm tides have been more frequent, and the annual number of hours with water levels above the critical level for dune erosion has increased significantly. An increase in the rate of mean sea-level rise at both Liverpool and Heysham is evident since 1990, but we conclude that this factor is of less importance than the occurrence of extreme high tides and wave action associated with storms. The incidence of extreme high tides shows an identifiable relationship with the lunar nodal tidal cycle, but the evidence indicates that meteorological forcing has also had a significant effect. Storms and surges in the eastern Irish Sea are associated with Atlantic depressions whose direction and rate of movement have a strong influence on wind speeds, wave energy and the height of surge tides. However
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Analysis of Human Standing Balance by Largest Lyapunov Exponent
Directory of Open Access Journals (Sweden)
Kun Liu
2015-01-01
Full Text Available The purpose of this research is to analyse the relationship between nonlinear dynamic character and individuals’ standing balance by the largest Lyapunov exponent, which is regarded as a metric for assessing standing balance. According to previous study, the largest Lyapunov exponent from centre of pressure time series could not well quantify the human balance ability. In this research, two improvements were made. Firstly, an external stimulus was applied to feet in the form of continuous horizontal sinusoidal motion by a moving platform. Secondly, a multiaccelerometer subsystem was adopted. Twenty healthy volunteers participated in this experiment. A new metric, coordinated largest Lyapunov exponent was proposed, which reflected the relationship of body segments by integrating multidimensional largest Lyapunov exponent values. By using this metric in actual standing performance under sinusoidal stimulus, an obvious relationship between the new metric and the actual balance ability was found in the majority of the subjects. These results show that the sinusoidal stimulus can make human balance characteristics more obvious, which is beneficial to assess balance, and balance is determined by the ability of coordinating all body segments.
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Liu, Qiang; Van Mieghem, Piet
2018-02-01
Since a real epidemic process is not necessarily Markovian, the epidemic threshold obtained under the Markovian assumption may be not realistic. To understand general non-Markovian epidemic processes on networks, we study the Weibullian susceptible-infected-susceptible (SIS) process in which the infection process is a renewal process with a Weibull time distribution. We find that, if the infection rate exceeds 1 /ln(λ1+1 ) , where λ1 is the largest eigenvalue of the network's adjacency matrix, then the infection will persist on the network under the mean-field approximation. Thus, 1 /ln(λ1+1 ) is possibly the largest epidemic threshold for a general non-Markovian SIS process with a Poisson curing process under the mean-field approximation. Furthermore, non-Markovian SIS processes may result in a multimodal prevalence. As a byproduct, we show that a limiting Weibullian SIS process has the potential to model bursts of a synchronized infection.
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Réjouissons-nous d'une initiative visant à introduire un système ...
International Development Research Centre (IDRC) Digital Library (Canada)
4 déc. 2017 ... Heartfile a assumé le coût d'une intervention chirurgicale pour une malformation cardiaque, et il peut de nouveau pratiquer son sport préféré, le cricket. Photo: CRDI / Tom Pilston. Onze hôpitaux sont inscrits au programme de Heartfile dans trois des quatre provinces pakistanaises, et les opérations ...
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Sand fences: An environment-friendly technique to restore degraded coastal dunes
Digital Repository Service at National Institute of Oceanography (India)
Mascarenhas, A.
of prevailing winds (Matias et al. 2005). Our observations show that sand gets deposited 2 to 6 m downwind behind artificial barriers lying on the beach. A series of fences can therefore intercept wind-blown sand over a considerable area along the frontal beach..., but fashioned artificially; (e) Restoration of coastal dunes can be adopted wherever these features are damaged due to natural processes or human interference. Acknowledgements: The author is grateful to the Director, NIO, Goa, for permission to publish...
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Directory of Open Access Journals (Sweden)
L. Tosi
2000-06-01
Full Text Available The internal structures of some surviving sand dunes and the ancient shore-lines along the coast south of Venice have been investigated integrating Ground Probing Radar (GPR profiles, Vertical Electrical Soundings (VES and water conductivity measurements in some boreholes. The GPR penetration depth has been limited (4-5 m,using a 400 MHz antenna by the high conductivity of salt water saturating pores of the shallow sediments. On the other hand, the excellent spatial resolution of the radar survey provided an estimate of internal dune bedding features, such as cross lamination and forwarding ancient covered coast-lines dated in the Thirties. The interpretation of the data, in particular along one line 360 m long intercepting a sizable sand-dune bank, seems to offer clues to the evolutional history of the coast line and the depth of transition from fresh-water to brackish-salt water. The water table was detected with electrical measurements and direct observations in boreholes, whereas the transition between fresh and salt water (brackish water was pointed out indirectly by the high energy absorption and total back-reflection of the EM waves, encountered at this boundary, and directly by the strong decrease in VES resistivity values.
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Nonstandard neutrino interactions at DUNE, T2HK and T2HKK
International Nuclear Information System (INIS)
Liao, Jiajun; Marfatia, Danny; Whisnant, Kerry
2017-01-01
Here, we study the matter effect caused by nonstandard neutrino interactions (NSI) in the next generation long-baseline neutrino experiments, DUNE, T2HK and T2HKK. If multiple NSI parameters are nonzero, the potential of these experiments to detect CP violation, determine the mass hierarchy and constrain NSI is severely impaired by degeneracies between the NSI parameters and by the generalized mass hierarchy degeneracy. In particular, a cancellation between leading order terms in the appearance channels when ϵ_e_τ= cot θ _2_3ϵ_e_μ, strongly affects the sensitivities to these two NSI parameters at T2HK and T2HKK. We also study the dependence of the sensitivities on the true CP phase and the true mass hierarchy, and find that overall DUNE has the best sensitivity to the magnitude of the NSI parameters, while T2HKK has the best sensitivity to CP violation whether or not there are NSI. Furthermore, for T2HKK a smaller off-axis angle for the Korean detector is better overall. We find that due to the structure of the leading order terms in the appearance channel probabilities, the NSI sensitivities in a given experiment are similar for both mass hierarchies, modulo the phase change δ→δ + 180°.
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Pneumonie organisée révélatrice d'une polymyosite
Ben Saad, Ahmed; Joobeur, Samah; Rouetbi, Naceur; Mhamed, Saousen Cheikh; Skhiri, Néji; Mribah, Hathami; El Kamel, Ali
2014-01-01
Les polymyosites (PM) sont des connectivites très rares, d’étiologie inconnue, dotées d'un grand polymorphisme clinique et évolutif. Elles peuvent être associées à d'autres manifestations viscérales notamment pulmonaires telles que la pneumopathie interstitielle. Ces complications respiratoires sont souvent associées à un taux de mortalité élevé. Les cas de pneumonie organisée révélatrice de polymyosite sont rarement rapportés dans la littérature et de description récente. Nous rapportons l'observation d'une patiente âgée de 53 ans qui a présenté, 14 mois après avoir porter le diagnostic d'une pneumonie organisée, des myalgies diffuses, un ‘dème des membres inférieurs et une élévation des enzymes musculaires. La biopsie musculaire a confirmé le diagnostic de la myosite. L’évolution était favorable sous corticothérapie. Le traitement de la PO associée au PM n'est pas clairement établi. La corticothérapie constitue le traitement de première intention. PMID:25722789
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Shang, Wen; Li, Yu-qiang; Wang, Shao-kun; Feng, Jing; Su, Na
2011-08-01
This paper studied the dynamic changes of surface (0-15 cm) soil organic carbon (SOC) and light-fraction organic carbon (LFOC) in 25- and 35-year-old sand-fixing Mongolian pine (Pinus sylvestris var. mongolica) plantations in Horqin Sandy Land, with a mobile dune as a comparison site. After the afforestation on mobile dune, the content of coarse sand in soil decreased, while that of fine sand and clay-silt increased significantly. The SOC and LFOC contents also increased significantly, but tended to decrease with increasing soil depth. Afforestation increased the storages of SOC and LFOC in surface soil, and the increment increased with plantation age. In the two plantations, the increment of surface soil LFOC storage was much higher than that of SOC storage, suggesting that mobile dune afforestation had a larger effect on surface soil LFOC than on SOC.
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2013-02-21
... Lakeshore (SLBE or Lakeshore) was established in 1970 ``for the benefit, inspiration, education, recreation... home destination. SLBE offers visitors recreational activities such as hiking, backpacking, kayaking...-Benefit and Regulatory Flexibility Analyses Leelanau Scenic Heritage Route Trailway, Sleeping Bear Dunes...
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James, Noel P.; Bone, Yvonne
2017-07-01
Much of western Eyre Peninsula adjacent to the Great Australian Bight is veneered with siliceous and calcareous Quaternary aeolian dunes. The lengthy coastline adjacent to this cool-water carbonate factory is a series of Precambrian crystalline bedrock-Pleistocene aeolianite headlands that separate many long, sweeping, Holocene carbonate sand beaches and their backbeach dunes. Incessant SW waves, rolling swells, and onshore winds have resulted in > 350 km of semi-continuous calcareous strandline aeolian sands. The sediment is composed of quartz grains, Cenozoic limestone clasts, and relict particles (extraclasts) but the deposits are overwhelmingly dominated by contemporaneous biofragments from offshore. These skeletal grains are, in order of relative abundance, molluscs > benthic foraminifers > coralline algae > bryozoans, and echinoids. Benthic foraminifers are mostly small (especially rotaliids and miliolids) but the large relict symbiont-bearing protistMarginopora vertebralis, which grew in the latter stages of MIS 2, is present locally. There are no significant onshore-offshore trends within individual beach-dune complexes. There is, however, a prominent spatial partitioning, with extraclast-rich sediments in the north and biofragment-rich deposits in the south. This areal trend is interpreted to result from more active seafloor carbonate production in the south, an area of conspicuous seasonal nutrient upwelling and profound nektic and benthic biological productivity. The overall system is strikingly similar to Holocene and Pleistocene aeolianites along the inboard margin of the Lacepede Shelf and Bonney Coast some 500 km to the southeast, implying a potential universality to the nature of cool-water carbonate aeolianite deposition. The composition of these cool-water aeolianites is more multifaceted than those formed on warm-water, shallow flat-topped platforms, largely because of the comparatively deep, temperate shelf, the high-energy wave and swell
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Li, Stephanie
2009-01-01
Leslie Marmon Silko began her most recent work, "Gardens in the Dunes" (1999), intending to write a novel that would not be political. Following the publication of "Almanac of the Dead" (1992), which was simultaneously hailed as one of the most important books of the twentieth century and condemned for its angry self-righteousness, Silko…
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Mughal, Iqra
2013-01-01
In arid lands, a major contribution to water loss is by soil water evaporation. Desert sand dunes in arid regions are devoid of runoff and have high rates of infiltration. Rainwater is commonly stored within them because of the low permeability
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Directory of Open Access Journals (Sweden)
Eduardo Resende Secchi
2012-12-01
Full Text Available This paper presents data on species composition and use of habitat of medium and large sized mammal assemblages in a coastal dunes segment and adjacent marshes at Rio Grande municipality, southern Rio Grande do Sul State, Brazil. Records were obtained through visualization of living animals and identification of footprints, feces and remains. From November 2007 to September 2008, nine 600 m long and 5 m wide linear transects were settled on coastal dunes segment (frontal and intermediate dunes and adjacent marshes, parallel to ocean shore on a 23 km section at Cassino Beach. Transects were settled in areas under high, medium and low levels of anthropic occupancy (A1, A2 and A3, respectively, being three transects on each area. Fourteen species were recorded, distributed in five orders and 10 families. Lepus europaeus was the most frequent species (81.9% of the transect walks, present in all areas and seasons, followed by Lycalopex gimnocercus (23.5% and Conepatus chinga (10.3%. Five species were present on A1, seven on A2 and fourteen on A3. Seven species were recorded on frontal dunes, nine on intermediate dunes and 13 on adjacent marshes.
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Pye, Kenneth; Blott, Simon J.
2016-08-01
An important question for coastal management concerns the importance of individual storms and clusters of storms on longer term beach sediment budgets, beach and dune erosion, and coastal flood risk. Between October 2013 and March 2014 a series of deep Atlantic low pressure systems crossed the Northeast Atlantic, and strong winds, high waves and high water levels affected many coastal areas in the UK and other parts of western Europe. Net dune recession of up to 12.1 m occurred around Formby Point. On 5 December 2013 the highest water level ever recorded at Liverpool (6.22 m ODN) coincided with waves of Hs of 4.55 m and Tp of 9.3 s in Liverpool Bay. Wave trimming of the dune toe occurred along the entire length of the Sefton coast, but significant dune erosion occurred only where the upper beach (between the mean high water spring tide level and the dune toe) was dune system, mostly at Formby Point. However, some parts of the beach to the south of Formby Point gained sediment, indicating net north to south transport over the winter. When considered in a longer term context, the 2013-14 winter represents only a small perturbation on the longer-term coast trend of erosion at Formby Point and progradation to the north and south. Analysis of LiDAR data over a longer time period 1999-2014 indicated upper beach and dune sediment loss of 780 × 103 m3 from the north-central part of Formby Point, with net gains of 806 × 103 m3 and 2116 × 103 m3 in areas to the north and south, respectively. This indicates a net onshore transport of 2142 × 103 m3 from Liverpool Bay towards the coast between Birkdale and Altcar, with a further net total of 210 × 103 m3 transported towards the shore between Altcar and Crosby. In view of the demonstrated value of airborne LiDAR surveys for the quantification of storm impacts and longer term coastal changes, it is recommended that such surveys should be undertaken before and after each winter storm period, covering the area between mean low
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Sand erosion at the toe of a gabion-protected dune face
Chapman, A.
1992-01-01
The purpose of this research project was to study the manner in which erosion takes place the the toe of a dune slope protected by gabions, and to examine the response of the gabions to this erosion. A sand slope overlaid by model gabions was subjected to wave attack in a hydraulic flume, and periodic measurements of the bottom profile were taken. The results showed that the gabions performed well, and continued to provide protection to the slope even after a considerable amount of erosion an...
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Boterenbrood, A.J.; Donsellaar-Ten Bokkel Huinink, van W.A.E.; Donselaar, van J.
1956-01-01
Une évaluation des plantes d’après leur pouvoir édificateur de dunes doit être précédée d’une description de leur structure a côté de l’étendue et de la densité des organes aériens il faut considérer d’importance capitale et décisive la structure des organes souterrains, tel que KÜHNHOLTZLORDAT
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Effective arithmetic in finite fields based on Chudnovsky's multiplication algorithm
Atighehchi , Kévin; Ballet , Stéphane; Bonnecaze , Alexis; Rolland , Robert
2016-01-01
International audience; Thanks to a new construction of the Chudnovsky and Chudnovsky multiplication algorithm, we design efficient algorithms for both the exponentiation and the multiplication in finite fields. They are tailored to hardware implementation and they allow computations to be parallelized, while maintaining a low number of bilinear multiplications.À partir d'une nouvelle construction de l'algorithme de multiplication de Chudnovsky et Chudnovsky, nous concevons des algorithmes ef...
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2010-12-14
... public lands in Texas. It is evident that the dunes sagebrush lizard is still present at the park, but... expected to contribute to habitat loss, modification, or fragmentation in the future include wind and solar... and Solar Energy Development Eastern New Mexico and western Texas are highly suitable areas for wind...
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Case Report - Le syndrome de Cri du Chat : A propos d'une ...
African Journals Online (AJOL)
Le syndrome du Cri du Chat (Cri du Chat syndrome, CdCS) est une anomalie chromosomique résultant d'une délétion de taille variable de l'extrémité du bras court du chromosome 5 (5p), incluant une région critique située en p15.2. Il représente une des délétions chromosomiques les plus fréquentes, son incidence dans ...
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broken magnet highlights largest collider's engineering challenges
Inman, Mason
2007-01-01
"Even at the world's soon-to-be largest particle accelerator - a device that promises to push the boundaries of physics - scientists need to be mindful of one of the most fundamental laws in the universe: Murphy's Law. (2 pages)
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Nucléation, ascension et éclatement d'une bulle de champagne
Liger-Belair, G.
2006-03-01
People have long been fascinated by bubbles and foams dynamics, and since the pioneering work of Leonardo da Vinci in the early 16th century, this subject has generated a huge bibliography. However, only quite recently, much interest was devoted to bubbles in Champagne wines and carbonated beverages. Since the time of the benedictine monk dom Pierre Perignon (1638-1715), champagne is the wine of celebration. This fame is largely linked to the elegance of its effervescence and foaming properties. In this book, the latest results about the chemical physics behind the bubbling properties of Champagne and sparkling wines are collected and fully illustrated. The first chapter is devoted to the history of champagne and to a presentation of the tools of the physical chemistry of interfaces needed for a whole comprehension of the book. Then, the three main steps of a fleeting champagne bubble's life are presented in chronological order, that is, the bubble nucleation on the glass wall (Chap.2), the bubble ascent and growth through the liquid matrix (Chap.3), and the bursting of bubbles at the liquid surface (Chap.4), which constitutes the most intriguing, functional, and visually appealing step. L'objectif général de ce travail consacré à l'étude des processus physicochimiques liés à l'effervescence des vins de Champagne était de décortiquer les différentes étapes de la vie d'une bulle de champagne en conditions réelles de consommation, dans une flûte. Nous résumons ci-après les principaux résultats obtenus pour chacune des étapes de la vie de la bulle, depuis sa naissance sur les parois d'une flûte, jusqu'à son éclatement en surface. Nucléation À l'aide d'une caméra rapide munie d'un objectif de microscope, nous avons pu mettre à mal une idée largement répandue. Ce ne sont pas les anfractuosités de la surface du verre ou de la flûte qui sont responsable de la nucléation hétérogène des bulles, mais des particules adsorbées sur les parois du
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Directory of Open Access Journals (Sweden)
Anne-Laure Markovina
2010-03-01
Full Text Available Mimicking natural processes lead to progressive colonization and stabilization of the reconstructed beach dune ecosystem, as part of the ecologically sustainable development of Magenta Shores, on the central coast of New South Wales, Australia. The retained and enhanced incipient dune formed the first line of storm defence. Placement of fibrous Leptospermum windrows allowed wind blown sand to form crests and swales parallel to the beach. Burial of Spinifex seed head in the moist sand layer achieved primary colonization of the reconstructed dune and development of a soil fungal hyphae network prior to introduction of secondary colonizing species. Monitoring stakes were used as roosts by birds, promoting re-introduction of native plant species requiring germination by digestive tract stimulation. Bush regeneration reduced competition from weeds, allowing native vegetation cover to succeed. On-going weeding and monitoring are essential at Magenta Shores until bitou bush is controlled for the entire length of beach. The reconstructed dunes provide enhanced protection from sand movement and storm bite, for built assets, remnant significant vegetation and sensitive estuarine ecosystems.
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Kok, Jasper F
2010-02-19
Much of the surface of Mars is covered by dunes, ripples, and other features formed by the blowing of sand by wind, known as saltation. In addition, saltation loads the atmosphere with dust aerosols, which dominate the Martian climate. We show here that saltation can be maintained on Mars by wind speeds an order of magnitude less than required to initiate it. We further show that this hysteresis effect causes saltation to occur for much lower wind speeds than previously thought. These findings have important implications for the formation of dust storms, sand dunes, and ripples on Mars.
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Mise en place d'une base de données pour une modélisation ...
African Journals Online (AJOL)
Mise en place d'une base de données pour une modélisation hydrologique distribuée du bassin versant du Bandama (Côte d'Ivoire) : apport d'un modèle numérique d'altitude, de la télédétection et du SIG Physitel.
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DEFF Research Database (Denmark)
Marchante, Elizabete; Kjøller, Annelise; Struwe, Sten
2008-01-01
to new areas, displacing the native vegetation. These invaded ecosystems contrast with the native dune ecosystems that are typically dominated by herb and shrub communities. This study characterizes belowground changes to the native environment as a result of recent (20 y...
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The Dunes and Rivers of Titan and Earth : An overview of comparative landscapes and processes
Lorenz, R. D.
2006-12-01
Cassini has shown Titan to have a strikingly varied and Earth-like landscape with extensive regions modified by aeolian and fluvial sediment transport. The formation of large linear sand dunes, apparently occupying most of the low-latitude low-albedo regions such as Shangri-La and Belet, is something of a surprise, given how weak thermally-driven winds were expected to be. The explanation appears to be the gravitational tide due to Saturn, which may be the dominant driver of near-surface winds. The linear dunes observed with the Cassini RADAR are strikingly similar to such dunes seen in areas with seasonally-changing winds on Earth, such as Namibia and Arabia. Instructive comparisons may be made as excellent spaceborne radar images and in-situ studies exist of these features, giving us a window into how Titan works. The weak solar flux implies average rainfall on Titan is low, perhaps only 1cm per year. Yet like many terrestrial arid regions, the landscape is nonetheless significantly altered (at least in some places) by pluvial and fluvial processes, because when it does rain, it does so violently. Models of thunderstorms, and of sediment transport, integrate neatly with Cassini observations of fluvial networks. A recent development is the detection of probable lakes : these demand an understanding of littoral processes and, in turn, wind-wave generation. Titan is an energy-poor environment, but one in which it is easier to transport materials. Many of the factors in sediment generation and transport appear to cancel out. It remains to be seen whether Titan, as an exotic laboratory, will teach us more about Earth, or whether our home planet, as an accessible analog, will teach us more about Titan. The comparisons only make both worlds seem all the more intriguing.
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Holocene coastal dune development and environmental changes in Helis area (NW Peloponnese, Greece
Directory of Open Access Journals (Sweden)
L. STAMATOPOULOS
2017-12-01
Full Text Available The coastal area of western Peloponnese is characterized by Pleistocene and Holocene marine deposits. The study area shows the effects of different phases of coastal morphology evolution and is located along a wave-dominated and microtidal coast in the northwestern Peloponnese, 40 km southwest of Patras city. Three significant morphogenetic phases occurred during the Holocene. The first was radiometrically aged from 7000 to 3810 years BP, marking the end of the rapid postglacial transgression. The second, between 3810 and 1400 years BP, was characterized by high rates of sedimentation, possibly because of the proximity of the mouth of the Peneus River, and resulted in the accumulation of predominantly fluvial sediments. During the third and younger phase, from 1400 years BP to the present, landward migration of the coast and deposition of aeolian sands occurred. Archaeological and morphological evidences suggest that this last phase should be related to a low sea-level stand followed by a slow sea-level rise, up to the present-day position and by humid-temperate climate. The collected data concerning the Holocene coastal dune belts, suggest that main phases of dune development could be related to the effects of sea-level changes, climatic conditions, and in a subordinate way, to human activity.
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Eon, Rehman S.; Gerace, Aaron D.; Montanaro, Matthew; Ambeau, Brittany L.; McCorkel, Joel T.
2018-01-01
The ability of sensors to detect changes in the Earth's environment is dependent on retrieving radiometrically consistent and calibrated measurements from its surface. Intercalibration provides consistency among satellite instruments and ensures fidelity of scientific information. Intercalibration is especially important for spaceborne satellites without any on-board calibration, as accuracy of instruments is significantly affected by changes that occur postlaunch. To better understand the key parameters that impact the intercalibration process, this paper describes a simulation environment that was developed to support the primary mission of the Algodones Dunes campaign. Specifically, measurements obtained from the campaign were utilized to create a synthetic landscape to assess the feasibility of using the Algodones Dunes system as an intercalibration site for spaceborne instruments. The impact of two key parameters (differing view-angles and temporal offsets between instruments) on the intercalibration process was assessed. Results of these studies indicate that although the accuracy of intercalibration is sensitive to these parameters, proper knowledge of their impact leads to situations that minimize their effect. This paper concludes with a case study that addresses the feasibility of performing intercalibration on the International Space Station's platform to support NASA's CLARREO, the climate absolute radiance and refractivity observatory, mission.
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Joint Asymptotic Distributions of Smallest and Largest Insurance Claims
Directory of Open Access Journals (Sweden)
Hansjörg Albrecher
2014-07-01
Full Text Available Assume that claims in a portfolio of insurance contracts are described by independent and identically distributed random variables with regularly varying tails and occur according to a near mixed Poisson process. We provide a collection of results pertaining to the joint asymptotic Laplace transforms of the normalised sums of the smallest and largest claims, when the length of the considered time interval tends to infinity. The results crucially depend on the value of the tail index of the claim distribution, as well as on the number of largest claims under consideration.
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Leach, C. K.; And Others
1997-01-01
Describes the Distance Educational Network of Europe (DUNE) project that aims at enhancing the development of distance education in an international context. Highlights issues relating to the delivery of distance-learning courses in a transnational forum. Describes the genetic engineering course that aims at explaining the core techniques of…
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Ciccarelli, Daniela
2015-11-01
Plant communities of coastal dunes are distributed along a characteristic sea-inland gradient. Generally, there is a shift from annual and short height species with small leaves in the initial successional stages to perennial tall shrubs with tough leaves in later phases. Assessing the community-weighted mean (CWM) trait values is used in plant ecology to describe ecosystem properties especially during succession. In particular, CSR (Competitive, Stress-tolerant, and Ruderal strategy) classification allows us to explore community functional shifts in terms of disturbance, stress and competition selective forces. The functional basis of the psammophilous succession was studied based on the following questions: (1) Can we circumscribe different functional types among plant species of Mediterranean coastal dunes? (2) How do CWM trait values vary along the environmental sea-inland gradient? (3) What is the relative importance of competition, stress and disturbance in the processes of plant community assembling? (4) Can we postulate that along primary successions there is generally a shift from ruderality to stress-tolerance? An explorative analysis of functional groups was performed by Non-Metric Multidimensional Scaling (NMDS) analysing nine morpho-functional traits measured for 45 taxa from 880 dune plots localised in Tuscany (central Italy, Europe). NMDS ordination showed a scattered distribution of psammophytes that could not be delimited in precise plant functional types. The first NMDS axis has been interpreted as a leaf economics axis because it was correlated to leaf area (LA) and leaf dry matter content (LDMC), while the second one was a plant size axis because of its correlation with canopy height. Along the sea-inland gradient, pioneer plant communities of upper beach were dominated by ruderals (with the lowest values of LDMC and specific leaf area - SLA), well-adapted to the harsh environmental conditions of coastal dunes. More distant from the sea, where
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International Nuclear Information System (INIS)
Thoma, G.; Esser, N.; Sonntag, C.; Weiss, W.; Rudolph, J.; Leveque, P.
1978-01-01
A new soil-air suction method with soil water vapor adsorption by 4 A-molecular sieve provides soil moisture samples from various depths for environmental isotope analysis and yields soil temperature profiles. A field tritium tracer experiment shows that this insitu sampling method has an isotope profile resolution of about 5-10 cm only. Application of this method in the Pilat sand dune (Bordeaux/France) yielded deuterium and tritium profiles down to 25 meters depth. Bomb tritium measurements of monthly lysimeter percolate samples available since 1961 show that the tritium response has a mean delay of 5 months in case of a sand lysimeter and of 2.5 years for a loess loam lysimeter. A simple HETP model simulates the layered downward movement of soil water and the longitudinal dispersion in the lysimeters. Field capacity and evapotranspiration taken as open parameters yield tritium concentration values of the lysimeters' percolate which are in close agreement with the experimental results. Based on local meteorological data the HETP model applied to tritium tracer experiments in the unsaturated zone further yiels an individual prediction of the momentary tracer position and of the soil moisture distribution. This prediction can be checked experimentally at selected intervals by coring. (orig.) [de
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Kamola, Diane L.; Chan, Marjorie A.
1988-04-01
The Permian Cutler Formation (White Rim Sandstone) in the Capitol Reef National Park area in southern Utah is an excellent example of a coastal dune complex subjected to periodic flooding by marine waters. Wind-ripple, grainfall and grainflow laminae compose the cross-sets deposited by eolian dunes. However, wave-reworked structures such as oscillation ripples, the occurrence of the characteristically marine trace fossils Thalassinoides and Chondrites, and interfingering marine carbonate beds of the Kaibab Formation collectively indicate marine interaction with the eolian environment. Four facies are distinguished: cross-stratified sandstone, burrowed to bioturbated sandstone, brecciated and deformed sandstone, and ripple-laminated sandstone and thin carbonate beds. One unusual aspect of the cross-stratified sandstone facies is the abundance of coarse-grained sand. Coarse-grained sand is atypical in many ancient eolian slipface deposits, but occurs here in large slipface foresets as both grainflow and wind-ripple deposits. No water-laid structures are found in these slipface deposits. Coarse-grained sand was probably transported to the Cutler shoreline by fluvial systems draining the Uncompahgre Uplift to the east, and then concentrated as coarse-grained ripples in interdune areas. Some of these coarse-grained ripples migrated up the stoss side of the dunes and accumulations of coarse-grained sand avalanched down the crest to form grainflow deposits. An extensive amount of soft-sediment deformation is indicated by the presence of convolute bedding and brecciation. These features occur near the zone of interfingering with marine carbonate beds of the Kaibab Formation. The water-saturated and moist conditions required for extensive deformation may have been controlled by the proximity of these sandstones to the shoreline, and fluctuations in the associated groundwater table.
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Interfacial liquid water on Mars and its potential role in formation of hill and dune gullies
Kossacki, Konrad J.; Markiewicz, Wojciech J.
2010-11-01
Gullies are among the most intriguing structures identified on the surface of Mars. Most common are gullies located on the slopes of craters which are probably formed by liquid water transported by shallow aquifers (Heldmann, J.L., Carlsson, E., Johansson, H., Mellon, M.T., Toon, O.B. [2007]. Icarus 188, 324-344). Two particular types of gullies are found on slopes of isolated hills and dunes. The hill-slope gullies are located mostly at 50°S, which is at the high end of latitudes of bulk of the gullies found so far. The dune gullies are found in several locations up to 65°S (Reiss, D., Jaumann, R., Kereszturi, A., Sik, A., Neukum, G. [2007]. Lunar Planet. Sci. XXXVIII. Abstract 1993), but the best known are those in Russel crater at 54°S. The hill and dune gullies are longer than others making the aquifers explanation for their formation unlikely (Balme, M., Mangold, N., Baratoux, D., Costard, F., Gosselin, M., Masson, P., Pnet, P., Neukum, G. [2006]. J. Geophys. Res. 111. doi:10.1029/2005JE002607). Recently it has been noted that thin liquid films of interfacial water can play a role in rheological processes on the surface of Mars (Moehlmann, D. [2008]. Icarus 195, 131-139. Kereszturi, A., Moehlmann, D., Berczi, Sz., Ganti, T., Kuti, A., Sik, A., Horvath, A. [2009]. Icarus 201, 492-503.). Here we try to answer the question whether interfacial liquid water may occur on Mars in quantities large enough to play a role in formation of gullies. To verify this hypothesis we have calculated thermal models for hills and dunes of various steepness, orientation and physical properties. We find that within a range of average expected values of parameters it is not possible to have more than a few monolayers of liquid water at depths greater than a centimeter. To create subsurface interfacial water film significantly thicker and hence to produce conditions for the slope instability, parameters have to be chosen to have their extreme realistic values or an additional source
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Energy Technology Data Exchange (ETDEWEB)
Engelmann, J J [Commissariat a l' Energie Atomique, Saclay (France).Centre d' Etudes Nucleaires
1960-07-01
Description of a well-type {gamma} chamber for routine measurements of sources between 1 {mu}curie and 1 curie. Approximate calculation of some geometrical parameters by which the zone of constant sensitivity may be increased. Calculation of the sensitivity of such a chamber and comparison with the experimental results. (author) [French] Description d'une chambre a puits {gamma}, destinee aux mesures de routine de sources entre 1 {mu}curie et 1 curie. Calcul approche de quelques parametres geometriques permettant d'accroitre la zone d'egale sensibilite. Calcul de la sensibilite d'une telle chambre et confrontation avec les resultats experimentaux. (auteur)
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Localisation d'une source sonore par un réseau de microphones
Thaljaoui , Adel; Brulin , Damien; Val , Thierry; Nasri , Nejah
2014-01-01
National audience; L'assistance à domicile d'une personne âgée, notamment la connaissance de sa position géographique en tout instant, est devenue actuellement l'une des problématiques les plus urgentes. L'exploitation de l'information audio captée par un réseau de capteurs munis de microphones constitue un axe de recherche prometteur qui pourrait contribuer à une meilleure localisation dans le cadre des maisons intelligentes. Nous introduisons, dans cet article, nos premiers travaux sur la l...
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Almalki, H.; Alkhalifah, Tariq Ali
2012-01-01
The complex near-surface structure is a major problem in land seismic data. This is more critical when data acquisition takes place over sand dune surfaces, where the base of the sand acts as a trap for energy and, depending on its shape, can
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2012-09-07
... Availability of the Proposed Imperial Sand Dunes Recreation Area Management Plan and California Desert... California Desert Conservation Area (CDCA) Plan Amendment/Final Environmental Impact Statement (EIS), for the.... District Court in September 2006. Portions of the biological opinion for the Peirson's milkvetch were also...
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Hubbard, Bernard E.; Hooper, Donald M.; Solano, Federico; Mars, John C.
2018-01-01
We apply linear deconvolution methods to derive mineral and glass proportions for eight field sample training sites at seven dune fields: (1) Algodones, California; (2) Big Dune, Nevada; (3) Bruneau, Idaho; (4) Great Kobuk Sand Dunes, Alaska; (5) Great Sand Dunes National Park and Preserve, Colorado; (6) Sunset Crater, Arizona; and (7) White Sands National Monument, New Mexico. These dune fields were chosen because they represent a wide range of mineral grain mixtures and allow us to gauge a better understanding of both compositional and sorting effects within terrestrial and extraterrestrial dune systems. We also use actual ASTER TIR emissivity imagery to map the spatial distribution of these minerals throughout the seven dune fields and evaluate the effects of degraded spectral resolution on the accuracy of mineral abundances retrieved. Our results show that hyperspectral data convolutions of our laboratory emissivity spectra outperformed multispectral data convolutions of the same data with respect to the mineral, glass and lithic abundances derived. Both the number and wavelength position of spectral bands greatly impacts the accuracy of linear deconvolution retrieval of feldspar proportions (e.g. K-feldspar vs. plagioclase) especially, as well as the detection of certain mafic and carbonate minerals. In particular, ASTER mapping results show that several of the dune sites display patterns such that less dense minerals typically have higher abundances near the center of the active and most evolved dunes in the field, while more dense minerals and glasses appear to be more abundant along the margins of the active dune fields.
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Hubbard, Bernard E.; Hooper, Donald M.; Solano, Federico; Mars, John C.
2018-02-01
We apply linear deconvolution methods to derive mineral and glass proportions for eight field sample training sites at seven dune fields: (1) Algodones, California; (2) Big Dune, Nevada; (3) Bruneau, Idaho; (4) Great Kobuk Sand Dunes, Alaska; (5) Great Sand Dunes National Park and Preserve, Colorado; (6) Sunset Crater, Arizona; and (7) White Sands National Monument, New Mexico. These dune fields were chosen because they represent a wide range of mineral grain mixtures and allow us to gauge a better understanding of both compositional and sorting effects within terrestrial and extraterrestrial dune systems. We also use actual ASTER TIR emissivity imagery to map the spatial distribution of these minerals throughout the seven dune fields and evaluate the effects of degraded spectral resolution on the accuracy of mineral abundances retrieved. Our results show that hyperspectral data convolutions of our laboratory emissivity spectra outperformed multispectral data convolutions of the same data with respect to the mineral, glass and lithic abundances derived. Both the number and wavelength position of spectral bands greatly impacts the accuracy of linear deconvolution retrieval of feldspar proportions (e.g. K-feldspar vs. plagioclase) especially, as well as the detection of certain mafic and carbonate minerals. In particular, ASTER mapping results show that several of the dune sites display patterns such that less dense minerals typically have higher abundances near the center of the active and most evolved dunes in the field, while more dense minerals and glasses appear to be more abundant along the margins of the active dune fields.
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Dissolved Oxygen Dynamics in Backwaters of North America's Largest River Swamp
Bueche, S. M.; Xu, Y. J.; Reiman, J. H.
2017-12-01
The Atchafalaya River (AR) is the largest distributary of the Mississippi River flowing through south-central Louisiana, creating North America's largest river swamp basin - the Atchafalaya River Basin (ARB). Prior to human settlement, the AR's main channel was highly connected to this large wetland ecosystem. However, due to constructed levee systems and other human modifications, much of the ARB is now hydrologically disconnected from the AR's main channel except during high flow events. This lack of regular inputs of fresh, oxygenated water to these wetlands, paired with high levels of organic matter decomposition in wetlands, has caused low oxygen-deprived hypoxic conditions in the ARB's back waters. In addition, due to the incredibly nutrient-rich and warm nature of the ARB, microbial decomposition in backwater areas with limited flow often results in potentially stressful, if not lethal, levels of DO for organisms during and after flood pulses. This study aims to investigate dynamics of dissolved oxygen in backwaters of the Atchafalaya River Basin, intending to answer a crucial question about hydrological and water quality connectivity between the river's mainstem and its floodplain. Specifically, the study will 1) conduct field water quality measurements, 2) collect composite water samples for chemical analysis of nutrients and carbon, 3) investigate DO dynamics over different seasons for one year, and 4) determine the major factors that affect DO dynamics in this unique swamp ecosystem. The study is currently underway; therefore, in this presentation we will share the major findings gained in the past several months and discuss backwater effects on river chemistry.
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Guaranteeing uptime at worl's largest particle physics lab
Brodkin, Jon
2007-01-01
"As the European agency CERN was gearing up to build the world's largest particle accelerator, officials there knew they could not afford to have problems in their technical infrastructure cause any downtime." (1 page)
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DEFF Research Database (Denmark)
Johnsen, Ib
2014-01-01
Rhynchostegium megapolitanum was observed during a study of the effects of the invasive non-native Rosa rugosa in a sand dune. The vascular as well as the epiphytic and epigeic cryptogam vegetation was recorded., and soil properties were measured. Epihytic lichens were abundant on dead or dying b...... branches of Rosa rugosa scrubs, under which the stable substrate and high light exposure provided growth conditions for an epigeic community dominated by lichens and bryophytes. The occurrence of the rare bryophyte Rhynchostegium megapolitanum is discussed......Rhynchostegium megapolitanum was observed during a study of the effects of the invasive non-native Rosa rugosa in a sand dune. The vascular as well as the epiphytic and epigeic cryptogam vegetation was recorded., and soil properties were measured. Epihytic lichens were abundant on dead or dying...
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Rosenthal, D.M.; Ludwig, F.; Donovan, L.A.
2005-01-01
In arid ecosystems, variation in precipitation causes broad-scale spatial heterogeneity in soil moisture, but differences in soil texture, development, and plant cover can also create substantial local soil moisture heterogeneity. The boundary between inland desert sand dunes and adjacent desert
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2013-08-01
The goal of this study was to evaluate the effectiveness of sand dunes along New Jerseys Coast in reducing damage during Sandy. The study area included eight selected zones with different damage levels from Ocean County. A model to independently p...
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Migration d'une broche dans le canal médullaire cervical après une ...
African Journals Online (AJOL)
Migration d'une broche dans le canal médullaire cervical après une ostéosynthèse de l'articulation acromio-claviculaire. Bah Aliou, El Alaoui Adil. Abstract. We report the case of a 49 year-old right-handed chef with left shoulder trauma occurred during a football game. The diagnosis was fracture of the distal quarter of ...
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Futur d'une infrastructure de correction automatisée : CodeGradX
Queinnec , Christian; Pons , Olivier
2016-01-01
Cet article évoque quelques expériences et nouvelles idées au-tour d'une infrastructure de correction automatisée de programmes. CodeGradX est une infrastructure de correction automatisée de programmes. Elle est en service depuis 2008 (initialement sous le nom de FW4EX) et a depuis corrigé plus de 150 000 soumissions d'étudiants à des exercices principalement en Scheme, utilitaires d'Unix, JavaScript mais aussi en C, Octave, O'Caml, Python sans oublier les compétitions annuelles des Journées ...
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The world's largest LNG producer's next market
International Nuclear Information System (INIS)
Fuller, R.; Isworo Suharno; Simandjuntak, W.M.P.
1996-01-01
The development of the domestic gas market in Indonesia, the world's largest liquefied natural gas producing country, is described as part of the overall impact of the country's oil and gas production. The first large scale use of natural gas in Indonesia was established in 1968 when a fertiliser plant using gas as the feedstock was built. Ultimately, through increased yields, this has enabled Indonesia to be self-sufficient in rice and an exporter of fertiliser. Problems which stand in the way of further developments include: capital, though Pertamina and PGN are perceived as attractive for foreign investment; the lack of a regulatory framework for gas; geographical constraints, among them the fact that the gas deposits are remote from the largest population concentrations; lack of infrastructure. There are nevertheless plans for expansion and the provision of an integrated gas pipeline system. Pertamina, which has responsibility for all oil and gas developments, and PGN, whose primary role has been as a manufacturer and distributor of gas, are now working together in the coordination of all gas activities. (10 figures). (UK)
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Questioning the environmental stress hypothesis for gall diversity of restinga vegetation on dunes
Arriola, Ígor A.; F. MeloJr., JoãoCarlos; S. Isaias, RosyMary
2015-01-01
AbstractThe Atlantic Coast Restinga is a mosaic of plant communities with a distinct floristic and phytophysiognomy, exposed to luminous, thermal, and saline stresses. Plants of the restinga must have special features commonly associated to xeric environments, and are expected to host a high diversity of galling herbivores. We studied gall morphotypes, and recorded the diversity of galls on plants growing in sand dunes in a remnant area of restinga (Acaraí State Park) in São Francisco do Sul,...
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Worlds Largest Wave Energy Project 2007 in Wales
DEFF Research Database (Denmark)
Christensen, Lars; Friis-Madsen, Erik; Kofoed, Jens Peter
2006-01-01
This paper introduces world largest wave energy project being developed in Wales and based on one of the leading wave energy technologies. The background for the development of wave energy, the total resource ands its distribution around the world is described. In contrast to wind energy turbines...... Dragon has to be scaled in accordance with the wave climate at the deployment site, which makes the Welch demonstrator device the worlds largest WEC so far with a total width of 300 meters. The project budget, the construction methods and the deployment site are also given....... a large number of fundamentally different technologies are utilised to harvest wave energy. The Wave Dragon belongs to the wave overtopping class of converters and the paper describes the fundamentals and the technical solutions used in this wave energy converter. An offshore floating WEC like the Wave...
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2012-10-02
... FURTHER INFORMATION CONTACT: Larry Crist, Field Supervisor, U.S. Fish and Wildlife Service, Utah Field... burrows, dune migration characteristics that permit vegetation to develop and persist within dune swales... sediment characteristics not conducive for vegetation nor suitable for larval burrows, dune migration...
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First Experience from the World Largest fully commercial Solar Heating Plant
DEFF Research Database (Denmark)
Heller, Alfred; Furbo, Simon
1997-01-01
The first experience from the largest solar heating plant in the world is given. The plant is situated in Marstal and is has a total area of 8000 square m.......The first experience from the largest solar heating plant in the world is given. The plant is situated in Marstal and is has a total area of 8000 square m....
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Kaneko, Korehisa; Matsushima, Hajime
2017-12-01
Chiba Prefecture, Japan, lies very near Tokyo, the capital city of Japan. It borders the sea on three sides and is banded by coastal dunes. Several sake breweries are located near these dunes. Although there are records of sake brewing along the coast of Tokyo Bay since 1925, sake breweries have completely disappeared in several areas. We believe that sake brewing in these areas benefited from the ecosystem services afforded them by their proximity to the coastal ecosystem. We investigated potential environmental factors (e.g., landscape, soil, and groundwater), as well as conditions that could have driven sake brewers away from the coastal area. Many of the sake breweries that no longer exist were located on coastal dunes (i.e., sand, sandbanks, and natural levees) and obtained their water from a freshwater layer located 3-10 m below the surface. We speculate that these sake breweries benefited from using natural ingredients found in the coastal zone. We also investigated the following factors that may have negatively impacted the breweries, driving them out of business: (1) bankruptcies and reconstruction difficulties that followed the destructive 1923 Great Kanto earthquake, (2) industrial wartime adjustments during World War II (1939-1945), (3) development of coastal industries during the period from 1960 to 1975, and (4) increasing choices for other alcoholic drinks (e.g., beer, wine, and whiskey) from the 1960s to the present.[Figure not available: see fulltext.
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Challenges with the largest commercial hydrogen station in the world
Energy Technology Data Exchange (ETDEWEB)
Charbonneau, Thomas; Gauthier, Pierre [Air Liquide Canada (Canada)
2010-07-01
This abstract's objective is to share with the participants the story of the largest hydrogen fueling station made to this date and to kick-start the story, we will cover the challenges; first the technical ones; the operational ones; the distribution ones and; the financial ones. We will then move on to review the logistic (geographic) issues raised by the project and conclude our presentation by sharing the output values of the largest fueling station built so far in the world. (orig.)
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van Breukelen, B.M.; Appelo, C.A.J.; Olsthoorn, T.N.
1998-01-01
Water quality changes were modelled along a flowpath in a plume of artificially recharged, pretreated Rhine water in the dunes of the Amsterdam Water Supply, after 24 years of infiltration. The hydrogeochemical transport model PHREEQC was extended with dispersion/diffusion and kinetics for selected
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Johnson, C.; Chen, Q. J.
2017-12-01
Coastal barrier landforms serve as the first line of defense against oceanic and meteorological forcing. Widespread recognition of this function has prompted coastal managers to adopt systematic restoration programs. The state of Louisiana has, in response to its critically eroding shorelines (Byrnes et al., 2017), implemented 30 barrier island and headland restoration projects over the past three decades. The Caminada Headlands Beach and Dune Restoration Project, completed in 2016, restored 22.5 kilometers of Louisiana's coastline by elevating the cross-shore profile and placing approximately 250,000 m3 of sediment within the back- and foreshore. Interventions of this magnitude are significant perturbations to the local sediment budget and geomorphodynamic equilibrium. In Louisiana, an important question is the immediate fate of placed sediment transported during the passage of a hurricane, as the potential to ultimately retain this sediment is influenced by the location of its deposition. The direction of net sediment transport (on- or offshore) depends mainly on the elevation of the storm surge relative to the dune crest, but also on the evolution of the cross-shore water surface gradient and the spatial configuration of biogeophysical properties and hard-structures (Sherwood et al., 2014; Smallegan et al., 2016) . Prior to its restoration, the Caminada headlands were generally of low elevation with the majority of dune crest extending less than 50 cm above MHW and several active breaches. Hurricanes Gustav (2008) and Isaac (2012) made landfall directly on the headlands with inundating storm surges that resulted in observed overwash deposition (Doran et al, 2009; Guy et al, 2013), i.e. landward directed sediment transport and deposition. An open-source process-based morphological model (XBeach) is used to study hurricane induced sediment transport for both pre- and post-restoration of the Caminada headlands. Hindcast pre-restoration simulations of Gustav's and
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El Mazouz, S.; Hafidi, J.; Fejjal, N.; Mejjati, H.; Cherkab, L.; Gharib, N.; Abbassi, A.
2010-01-01
Summary Les séquelles esthétiques des alopécies cicatricielles sur séquelles de brûlures sont responsables de préjudices empêchant parfois la réinsertion sociale du patient, surtout chez les sujets de sexe féminin. Le cuir chevelu permet la réalisation de lambeaux permettant de couvrir ces alopécies. Les Auteurs décrivent le cas d'une jeune patiente victime d'une alopécie cicatricielle sur séquelles de brûlures chez qui ils ont réalisé un lambeau expansé du cuir chevelu et mettent le point sur la prise en charge de ces lésions à travers ce cas clinique et une revue de littérature. PMID:21991195
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International Nuclear Information System (INIS)
Robelius, Fredrik
2007-01-01
Since the 1950s, oil has been the dominant source of energy in the world. The cheap supply of oil has been the engine for economic growth in the western world. Since future oil demand is expected to increase, the question to what extent future production will be available is important. The belief in a soon peak production of oil is fueled by increasing oil prices. However, the reliability of the oil price as a single parameter can be questioned, as earlier times of high prices have occurred without having anything to do with a lack of oil. Instead, giant oil fields, the largest oil fields in the world, can be used as a parameter. A giant oil field contains at least 500 million barrels of recoverable oil. Only 507, or 1 % of the total number of fields, are giants. Their contribution is striking: over 60 % of the 2005 production and about 65 % of the global ultimate recoverable reserve (URR). However, giant fields are something of the past since a majority of the largest giant fields are over 50 years old and the discovery trend of less giant fields with smaller volumes is clear. A large number of the largest giant fields are found in the countries surrounding the Persian Gulf. The domination of giant fields in global oil production confirms a concept where they govern future production. A model, based on past annual production and URR, has been developed to forecast future production from giant fields. The results, in combination with forecasts on new field developments, heavy oil and oil sand, are used to predict future oil production. In all scenarios, peak oil occurs at about the same time as the giant fields peak. The worst-case scenario sees a peak in 2008 and the best-case scenario, following a 1.4 % demand growth, peaks in 2018