WorldWideScience

Sample records for subaerial debris flows

  1. Managing Debris Flow Risks

    OpenAIRE

    Zimmermann, Markus N.

    2004-01-01

    Debris flows represent a widespread threat to villages and small towns in the Swiss Alps. For many centuries people “managed” such risks by trying to avoid hazardous areas. However, major debris flow and flood events in the last 25 years have revealed that the degree of freedom to engage in this type of risk management has substantially decreased. This became especially evident during the 1999 disasters in a number of places in Switzerland. The winter of that year was unusually wet. In Februa...

  2. Tsunami Generated by a Two-Phase Submarine Debris Flow

    Science.gov (United States)

    Pudasaini, S. P.

    2012-04-01

    The general two-phase debris flow model proposed by Pudasaini (2011) is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model includes several essential physical aspects, including Mohr-Coulomb plasticity for the solid stress, while the fluid stress is modelled as a solid volume fraction gradient enhanced non-Newtonian viscous stress. The generalized interfacial momentum transfer includes the viscous drag, buoyancy, and the virtual mass. The generalized drag covers both the solid-like and fluid-like contributions, and can be applied to linear to quadratic drags. Strong couplings exist between the solid and the fluid momentum transfer. The advantage of the real two-phase debris flow model over classical single-phase or quasi-two-phase models is that by considering the solid (and/or the fluid) volume fraction appropriately, the initial mass can be divided into several (even mutually disjoint) parts; a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This offers a unique and innovative opportunity within a single framework to simultaneously simulate (a) the sliding debris (or landslide), (b) the water lake or ocean, (c) the debris impact at the lake or ocean, (d) tsunami generation and propagation, (e) mixing and separation between the solid and the fluid phases, and (f) sediment transport and deposition process in the bathymetric surface. The new model is applied to two-phase subaerial and submarine debris flows. Benchmark numerical simulations reveal that the dynamics of the debris impact induced tsunamis are fundamentally different than the tsunami generated by pure rock avalanche and landslides. Special attention is paid to study the basic features of the debris impact to the mountain lakes or oceans. This includes the generation, amplification and propagation of the multiple

  3. The physics of debris flows

    Science.gov (United States)

    Iverson, R.M.

    1997-01-01

    Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ???10 m3 of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate

  4. Surface chemistry associated with the cooling and subaerial weathering of recent basalt flows

    Science.gov (United States)

    White, A.F.; Hochella, M.F.

    1992-01-01

    The surface chemistry of fresh and weathered historical basalt flows was characterized using surface-sensitive X-ray photoelectron spectroscopy (XPS). Surfaces of unweathered 1987-1990 flows from the Kilauea Volcano, Hawaii, exhibited variable enrichment in Al, Mg, Ca, and F due to the formation of refractory fluoride compounds and pronounced depletion in Si and Fe from the volatilization of SiF4 and FeF3 during cooling. These reactions, as predicted from shifts in thermodynamic equilibrium with temperature, are induced by diffusion of HF from the flow interiors to the cooling surface. The lack of Si loss and solid fluoride formation for recent basalts from the Krafla Volcano, Iceland, suggest HF degassing at higher temperatures. Subsequent short-term subaerial weathering reactions are strongly influenced by the initial surface composition of the flow and therefore its cooling history. Successive samples collected from the 1987 Kilauea flow demonstrated that the fluoridated flow surfaces leached to a predominantly SiO2 composition by natural weathering within one year. These chemically depleted surfaces were also observed on Hawaiian basalt flows dating back to 1801 AD. Solubility and kinetic models, based on thermodynamic and kinetic data for crystalline AlF3, MgF2, and CaF2, support observed elemental depletion rates due to chemical weathering. Additional loss of alkalis from the Hawaiian basalt occurs from incongruent dissolution of the basalt glass substrate during weathering. ?? 1992.

  5. Autogenic dynamics of debris-flow fans

    Science.gov (United States)

    van den Berg, Wilco; de Haas, Tjalling; Braat, Lisanne; Kleinhans, Maarten

    2015-04-01

    Alluvial fans develop their semi-conical shape by cyclic avulsion of their geomorphologically active sector from a fixed fan apex. These cyclic avulsions have been attributed to both allogenic and autogenic forcings and processes. Autogenic dynamics have been extensively studied on fluvial fans through physical scale experiments, and are governed by cyclic alternations of aggradation by unconfined sheet flow, fanhead incision leading to channelized flow, channel backfilling and avulsion. On debris-flow fans, however, autogenic dynamics have not yet been directly observed. We experimentally created debris-flow fans under constant extrinsic forcings, and show that autogenic dynamics are a fundamental intrinsic process on debris-flow fans. We found that autogenic cycles on debris-flow fans are driven by sequences of backfilling, avulsion and channelization, similar to the cycles on fluvial fans. However, the processes that govern these sequences are unique for debris-flow fans, and differ fundamentally from the processes that govern autogenic dynamics on fluvial fans. We experimentally observed that backfilling commenced after the debris flows reached their maximum possible extent. The next debris flows then progressively became shorter, driven by feedbacks on fan morphology and flow-dynamics. The progressively decreasing debris-flow length caused in-channel sedimentation, which led to increasing channel overflow and wider debris flows. This reduced the impulse of the liquefied flow body to the flow front, which then further reduced flow velocity and runout length, and induced further in-channel sedimentation. This commenced a positive feedback wherein debris flows became increasingly short and wide, until the channel was completely filled and the apex cross-profile was plano-convex. At this point, there was no preferential transport direction by channelization, and the debris flows progressively avulsed towards the steepest, preferential, flow path. Simultaneously

  6. Entrainment of Bed Sediments by Debris Flow

    OpenAIRE

    Sherchan, Bigyan

    2016-01-01

    Debris flows have proved to be a major worldwide hazard for more than 100 years owing to the destruction of lives, property and infrastructures. This occurrence of debris flows is likely to increase in the future due to the impending climate change. The large runout distance of the debris flow due to its ability to entrain materials along its way is one of the main causes for destruction. The objective of this study was to research the mechanism of entrainment in debris flows and to inves...

  7. Analysis of the Mobilization of Debris Flows

    Science.gov (United States)

    1974-10-01

    for the debris flows was determined by walking upstream from the deposits, following lateral ridges of debris and debris plastered along the creek...central Peru (Blackwelder, 1928, p. 482). The flows oc- cured during a period when thundershowers were raging on the high mountain slopes and are...Andes of central Peru (Singewald, In Blackwelder, 1928), Nelson County, Virginia (Williams and Guy, 1971, 1973), Ulvldal, Norway (Rapp, 1963), Mgeta

  8. Debris flows: behavior and hazard assessment

    Science.gov (United States)

    Iverson, Richard M.

    2014-01-01

    Debris flows are water-laden masses of soil and fragmented rock that rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form lobate deposits when they spill onto valley floors. Because they have volumetric sediment concentrations that exceed 40 percent, maximum speeds that surpass 10 m/s, and sizes that can range up to ~109 m3, debris flows can denude slopes, bury floodplains, and devastate people and property. Computational models can accurately represent the physics of debris-flow initiation, motion and deposition by simulating evolution of flow mass and momentum while accounting for interactions of debris' solid and fluid constituents. The use of physically based models for hazard forecasting can be limited by imprecise knowledge of initial and boundary conditions and material properties, however. Therefore, empirical methods continue to play an important role in debris-flow hazard assessment.

  9. The debris-flow rheology myth

    Science.gov (United States)

    Iverson, R.M.; ,

    2003-01-01

    Models that employ a fixed rheology cannot yield accurate interpretations or predictions of debris-flow motion, because the evolving behavior of debris flows is too complex to be represented by any rheological equation that uniquely relates stress and strain rate. Field observations and experimental data indicate that debris behavior can vary from nearly rigid to highly fluid as a consequence of temporal and spatial variations in pore-fluid pressure and mixture agitation. Moreover, behavior can vary if debris composition changes as a result of grain-size segregation and gain or loss of solid and fluid constituents in transit. An alternative to fixed-rheology models is provided by a Coulomb mixture theory model, which can represent variable interactions of solid and fluid constituents in heterogeneous debris-flow surges with high-friction, coarse-grained heads and low-friction, liquefied tails. ?? 2003 Millpress.

  10. Estimating the topographic predictability of debris flows

    Science.gov (United States)

    Meyer, Nele Kristin; Schwanghart, Wolfgang; Korup, Oliver; Romstad, Bård; Etzelmüller, Bernd

    2014-02-01

    The Norwegian traffic network is impacted by about 2000 landslides, avalanches, and debris flows each year that incur high economic losses. Despite the urgent need to mitigate future losses, efforts to locate potential debris flow source areas have been rare at the regional scale. We tackle this research gap by exploring a minimal set of possible topographic predictors of debris flow initiation that we input to a Weights-of-Evidence (WofE) model for mapping the regional susceptibility to debris flows in western Norway. We use an inventory of 429 debris flows that were recorded between 1979 and 2008, and use the terrain variables of slope, total curvature, and contributing area (flow accumulation) to compute the posterior probabilities of local debris flow occurrence. The novelty of our approach is that we quantify the uncertainties in the WofE approach arising from different predictor classification schemes and data input, while estimating model accuracy and predictive performance from independent test data. Our results show that a percentile-based classification scheme excels over a manual classification of the predictor variables because differing abundances in manually defined bins reduce the reliability of the conditional independence tests, a key, and often neglected, prerequisite for the WofE method. The conditional dependence between total curvature and flow accumulation precludes their joint use in the model. Slope gradient has the highest true positive rate (88%), although the fraction of area classified as susceptible is very large (37%). The predictive performance, i.e. the reduction of false positives, is improved when combined with either total curvature or flow accumulation. Bootstrapping shows that the combination of slope and flow accumulation provides more reliable predictions than the combination of slope and total curvature, and helps refining the use of slope-area plots for identifying morphometric fingerprints of debris flow source areas, an

  11. Woody debris flow behavior from experimental analysis

    Science.gov (United States)

    Bateman, Allen; Medina, Vicente; Morloti, Emanuele; Renaud, Alexis

    2010-05-01

    A consequence of debris flow in streams are well known, the collapse of the stream flooding all over the land. The high momentum flux of those flows can devastate houses, drag and crushes cars, etc. The presence of woody debris into the flow rise the flow depth and increment the collapse of the streams, bridges and structures. The present preliminary study offer a qualitative comparison between a debris flow and a woody debris flow with similar flow characteristics. To obtain this a series of experiments were performed in the Morph-dynamic Laboratory of the Hydraulic, Marine and Environmental Department. A high slope flume of 9 meters length, 40 cm width and 60 cm high was used. Up to 5 experiments were running in the flume. Initially the material was placed dry in the bed conforming a 20 cm depth of granular material changing the way of water wave entrance. Always water wave was introduced as a step function with different step size and different flow duration in order to introduce the same volume of water, just enough to saturate all the material in the channel. The flow was filmed with a handycam in order to see the general flow characteristics and with a high speed camera, just in a section, to visualize the flow velocities. Several woody pieces were placed along the channel to simulate the presence of wood and tress in the stream. Each tree was constructed in such a way that each one have a root made by rocks simulating a real root and different mass distribution. The comparison with experiments without wood was clever to understand the influence of woods in the debris flow. The woody debris flow alone creates natural dams along the stream without presence of inciters obstacles along the reach.

  12. Amplification of postwildfire peak flow by debris

    Science.gov (United States)

    Kean, Jason W.; McGuire, Luke; Rengers, Francis; Smith, Joel B.; Staley, Dennis M.

    2016-01-01

    In burned steeplands, the peak depth and discharge of postwildfire runoff can substantially increase from the addition of debris. Yet methods to estimate the increase over water flow are lacking. We quantified the potential amplification of peak stage and discharge using video observations of postwildfire runoff, compiled data on postwildfire peak flow (Qp), and a physically based model. Comparison of flood and debris flow data with similar distributions in drainage area (A) and rainfall intensity (I) showed that the median runoff coefficient (C = Qp/AI) of debris flows is 50 times greater than that of floods. The striking increase in Qp can be explained using a fully predictive model that describes the additional flow resistance caused by the emergence of coarse-grained surge fronts. The model provides estimates of the amplification of peak depth, discharge, and shear stress needed for assessing postwildfire hazards and constraining models of bedrock incision.

  13. Density Estimations in Laboratory Debris Flow Experiments

    Science.gov (United States)

    Queiroz de Oliveira, Gustavo; Kulisch, Helmut; Malcherek, Andreas; Fischer, Jan-Thomas; Pudasaini, Shiva P.

    2016-04-01

    Bulk density and its variation is an important physical quantity to estimate the solid-liquid fractions in two-phase debris flows. Here we present mass and flow depth measurements for experiments performed in a large-scale laboratory set up. Once the mixture is released and it moves down the inclined channel, measurements allow us to determine the bulk density evolution throughout the debris flow. Flow depths are determined by ultrasonic pulse reflection, and the mass is measured with a total normal force sensor. The data were obtained at 50 Hz. The initial two phase material was composed of 350 kg debris with water content of 40%. A very fine pebble with mean particle diameter of 3 mm, particle density of 2760 kg/m³ and bulk density of 1400 kg/m³ in dry condition was chosen as the solid material. Measurements reveal that the debris bulk density remains high from the head to the middle of the debris body whereas it drops substantially at the tail. This indicates lower water content at the tail, compared to the head and the middle portion of the debris body. This means that the solid and fluid fractions are varying strongly in a non-linear manner along the flow path, and from the head to the tail of the debris mass. Importantly, this spatial-temporal density variation plays a crucial role in determining the impact forces associated with the dynamics of the flow. Our setup allows for investigating different two phase material compositions, including large fluid fractions, with high resolutions. The considered experimental set up may enable us to transfer the observed phenomena to natural large-scale events. Furthermore, the measurement data allows evaluating results of numerical two-phase mass flow simulations. These experiments are parts of the project avaflow.org that intends to develop a GIS-based open source computational tool to describe wide spectrum of rapid geophysical mass flows, including avalanches and real two-phase debris flows down complex natural

  14. Numerical modeling of the debris flows runout

    Directory of Open Access Journals (Sweden)

    Federico Francesco

    2017-01-01

    Full Text Available Rapid debris flows are identified among the most dangerous of all landslides. Due to their destructive potential, the runout length has to be predicted to define the hazardous areas and design safeguarding measures. To this purpose, a continuum model to predict the debris flows mobility is developed. It is based on the well known depth-integrated avalanche model proposed by Savage and Hutter (S&H model to simulate the dry granular materials flows. Conservation of mass and momentum equations, describing the evolving geometry and the depth averaged velocity distribution, are re-written taking into account the effects of the interstitial pressures and the possible variation of mass along the motion due to erosion/deposition processes. Furthermore, the mechanical behaviour of the debris flow is described by a recently developed rheological law, which allows to take into account the dissipative effects of the grain inelastic collisions and friction, simultaneously acting within a ‘shear layer’, typically at the base of the debris flows. The governing PDEs are solved by applying the finite difference method. The analysis of a documented case is finally carried out.

  15. Numerical modeling of the debris flows runout

    Science.gov (United States)

    Federico, Francesco; Cesali, Chiara

    2017-06-01

    Rapid debris flows are identified among the most dangerous of all landslides. Due to their destructive potential, the runout length has to be predicted to define the hazardous areas and design safeguarding measures. To this purpose, a continuum model to predict the debris flows mobility is developed. It is based on the well known depth-integrated avalanche model proposed by Savage and Hutter (S&H model) to simulate the dry granular materials flows. Conservation of mass and momentum equations, describing the evolving geometry and the depth averaged velocity distribution, are re-written taking into account the effects of the interstitial pressures and the possible variation of mass along the motion due to erosion/deposition processes. Furthermore, the mechanical behaviour of the debris flow is described by a recently developed rheological law, which allows to take into account the dissipative effects of the grain inelastic collisions and friction, simultaneously acting within a `shear layer', typically at the base of the debris flows. The governing PDEs are solved by applying the finite difference method. The analysis of a documented case is finally carried out.

  16. Debris flow relationships in the Central Spanish Pyrenees

    OpenAIRE

    Beguería, S.; A. Lorente; Garcia-Ruiz, J. M.

    2001-01-01

    Debris flows represent the most active geomorphic risk in mountainous areas, affecting infrastructures, human settlements and touristic resorts (Takahashi et al., 1981). For this reason, much effort has been put in assessing where debris flows occur and ranking the factors that trigger them, but also in defining two essential parameters in establishing debris flow hazards: what is the distance travelled by debris flows (especially the runout distance), and what is the volume of material carri...

  17. Evaluating intensity parameters for debris flow vulnerability

    Science.gov (United States)

    Keiler, Margreth

    2014-05-01

    In mountain regions natural hazard processes such as debris flows or hyper-concentrated flows repeatedly lead to high damages. After an event, detailed documentation of the meteorological, hydrological and geomorphological indicators are standardized, and additional data on debris covering run out areas, indicators for processes velocity and transported volumes are gathered. Information on deposition height of debris is an important parameter to estimate the intensity of the process impacting the buildings and infrastructure and hence to establish vulnerability curves. However, the deposition height of mobilized material in settlements and on infrastructure is mostly not directly evaluated because recovery work starts immediately or even during the event leading to a removal of accumulated material. Different approaches exist to reconstruct deposition heights after torrent events, such as mind mapping, comparison of LIDAR-based DEM before and after the event as well as the reconstruction by using photo documentation and the estimation of deposition heights according to standardised elements at buildings and infrastructure. In our study, these different approaches to estimate deposition height and the spatial distribution of the accumulated material are applied and compared against each other by using the case study of the debris flow event in Brienz (Switzerland) which occurred during the serve flood events of August 2005 in the Alps. Within the analysis, different factors including overall costs and time consumption (manpower, equipment), accuracy and preciseness are compared and evaluated to establish optimal maps of the extent and deposition depth after torrent events and to integrate this information in the vulnerability analysis.

  18. Assessment of Debris Flow Hazards, North Mountain, Phoenix, AZ

    Science.gov (United States)

    Reavis, K. J.; Wasklewicz, T. A.

    2014-12-01

    Urban sprawl in many western U.S. cities has expanded development onto alluvial fans. In the case of metropolitan Phoenix, AZ (MPA), urban sprawl has led to an exponential outward growth into surrounding mountainous areas and onto alluvial fans. Building on alluvial fans places humans at greater risk to flooding and debris flow hazards. Recent research has shown debris flows often supply large quantities of material to many alluvial fans in MPA. However, the risk of debris flows to built environments is relatively unknown. We use a 2D debris flow modeling approach, aided by high-resolution airborne LiDAR and terrestrial laser scanning (TLS) topographic data, to examine debris flow behavior in a densely populated portion of the MPA to assess the risk and vulnerability of debris flow damage to the built infrastructure. A calibrated 2D debris flow model is developed for a "known" recent debris flow at an undeveloped site in MPA. The calibrated model and two other model scenarios are applied to a populated area with historical evidence of debris flow activity. Results from the modeled scenarios show evidence of debris flow damage to houses built on the alluvial fan. Debris flow inundation is also evident on streets on the fan. We use housing values and building damage to estimate the costs assocaited with various modeled debris flow scenarios.

  19. Uncertainties in Predicting Debris Flow Hazards Following Wildfire

    NARCIS (Netherlands)

    Hyde, K.D.; Riley, Karin; Stoof, C.R.

    2016-01-01

    Wildfire increases the probability of debris flows posing hazardous conditions where values-at-risk exist downstream of burned areas. Conditions and processes leading to postfire debris flows usually follow a general sequence defined here as the postfire debris flow hazard cascade: biophysical

  20. Debris flow-induced topographic changes: effects of recurrent debris flow initiation.

    Science.gov (United States)

    Chen, Chien-Yuan; Wang, Qun

    2017-08-12

    Chushui Creek in Shengmu Village, Nantou County, Taiwan, was analyzed for recurrent debris flow using numerical modeling and geographic information system (GIS) spatial analysis. The two-dimensional water flood and mudflow simulation program FLO-2D were used to simulate debris flow induced by rainfall during typhoon Herb in 1996 and Mindulle in 2004. Changes in topographic characteristics after the debris flows were simulated for the initiation of hydrological characteristics, magnitude, and affected area. Changes in topographic characteristics included those in elevation, slope, aspect, stream power index (SPI), topographic wetness index (TWI), and hypsometric curve integral (HI), all of which were analyzed using GIS spatial analysis. The results show that the SPI and peak discharge in the basin increased after a recurrence of debris flow. The TWI was higher in 2003 than in 2004 and indicated higher potential of landslide initiation when the slope of the basin was steeper. The HI revealed that the basin was in its mature stage and was shifting toward the old stage. Numerical simulation demonstrated that the parameters' mean depth, maximum depth, affected area, mean flow rate, maximum flow rate, and peak flow discharge were increased after recurrent debris flow, and peak discharge occurred quickly.

  1. Superelevation Calculation of Debris Flow Climbing Ascending Slopes

    Directory of Open Access Journals (Sweden)

    HaiXin Zhao

    2017-01-01

    Full Text Available We present a new method for calculating the superelevation of debris flow when it encounters obstacles in the process of flowing. Our calculation method is based on the Bingham Model for debris flow determination and considers the vertical difference of debris flow velocity and characteristic parameters of debris flow on a hypothetical basis. Moreover, we conducted an indoor flume experiment to verify the accuracy and reasonability of our calculation method. The experimental results showed that our method is able to accurately calculate the superelevation of debris flow with a root-mean-square error (16%. Furthermore, we provide an in-depth example of how our calculation method can be employed. Ultimately, we conclusively prove that our calculation method can be used for the superelevation calculation of debris flow climbing ascending slopes. Finally, we provide more exact parameters for debris flow protection engineering.

  2. GENERALIZED VISCOPLASTIC MODELING OF DEBRIS FLOW.

    Science.gov (United States)

    Chen, Cheng-lung

    1988-01-01

    The earliest model developed by R. A. Bagnold was based on the concept of the 'dispersive' pressure generated by grain collisions. Some efforts have recently been made by theoreticians in non-Newtonian fluid mechanics to modify or improve Bagnold's concept or model. A viable rheological model should consist both of a rate-independent part and a rate-dependent part. A generalized viscoplastic fluid (GVF) model that has both parts as well as two major rheological properties (i. e. , the normal stress effect and soil yield criterion) is shown to be sufficiently accurate, yet practical for general use in debris-flow modeling. In fact, Bagnold's model is found to be only a particular case of the GVF model. analytical solutions for (steady) uniform debris flows in wide channels are obtained from the GVF model based on Bagnold's simplified assumption of constant grain concentration.

  3. Proportional loss functions for debris flow events

    Directory of Open Access Journals (Sweden)

    C. M. Rheinberger

    2013-08-01

    Full Text Available Quantitative risk assessments of debris flows and other hydrogeological hazards require the analyst to predict damage potentials. A common way to do so is by use of proportional loss functions. In this paper, we analyze a uniquely rich dataset of 132 buildings that were damaged in one of five large debris flow events in Switzerland. Using the double generalized linear model, we estimate proportional loss functions that may be used for various prediction purposes including hazard mapping, landscape planning, and insurance pricing. Unlike earlier analyses, we control for confounding effects of building characteristics, site specifics, and process intensities as well as for overdispersion in the data. Our results suggest that process intensity parameters are the most meaningful predictors of proportional loss sizes. Cross-validation tests suggest that the mean absolute prediction errors of our models are in the range of 11%, underpinning the accurateness of the approach.

  4. [Research progress in post-fire debris flow].

    Science.gov (United States)

    Di, Xue-ying; Tao, Yu-zhu

    2013-08-01

    The occurrence of the secondary disasters of forest fire has significant impacts on the environment quality and human health and safety. Post-fire debris flow is one of the most hazardous secondary disasters of forest fire. To understand the occurrence conditions of post-fire debris flow and to master its occurrence situation are the critical elements in post-fire hazard assessment. From the viewpoints of vegetation, precipitation threshold and debris flow material sources, this paper elaborated the impacts of forest fire on the debris flow, analyzed the geologic and geomorphic conditions, precipitation and slope condition that caused the post-fire debris flow as well as the primary mechanisms of debris-flow initiation caused by shallow landslide or surface runoff, and reviewed the research progress in the prediction and forecast of post-fire debris flow and the related control measures. In the future research, four aspects to be focused on were proposed, i. e., the quantification of the relationships between the fire behaviors and environmental factors and the post-fire debris flow, the quantitative research on the post-fire debris flow initiation and movement processes, the mechanistic model of post-fire debris flow, and the rapid and efficient control countermeasures of post-fire debris flow.

  5. Self-organization criticality of debris flow rheology

    Institute of Scientific and Technical Information of China (English)

    WANG Yuyi; JAN Chyandeng; CHEN Xiaoqing; HAN Wenliang

    2003-01-01

    Based on the viewpoint of stress and strain self-organization criticality of debris flow mass, this paper probes into inter-nonlinear action between different factors in the thixotropic liquefaction system of loose clastic soil onslope to make clastic soil in slope develop naturally towards critical stress status, and slope debris flow finally occurs under trigging by rainstorm. Also according to observation and analysis of self-organization criticality of sedimentrunoff system of viscous debris flow surges in ravines and power relation between magnitude and frequency of debris flows, this paper expounds similarity of the self-organized structure of debris flow mass. The self-organized critical system is a weak chaotic system. Debris flow occurrences can be predicted accordingly by means of observation at certain time scale and analysis of self-organization criticality of magnitude, frequency and time interval of debris flows.

  6. Prevention of debris flow disasters on Chengdu-Kunming Railway.

    Science.gov (United States)

    Wang, W; Xu, W L; Liu, S J

    2001-07-01

    Chengdu-Kunming Railway is an important transport line on southwestern China. However, this railway's safety is often threatened by debris flows. How to effectively forecast and alarm the debris flow disasters and reduce the losses is the aim to study the prevention system in this paper. The factors to cause or influence debris flow are divided into four parts--the basin environmental factors, the basin meteoric factors, the prevention work's elements and the flood-relief work's elements, and the prevention system is made up of three models--a judgment model to assess the debris flow gully's seriousness, a forecast model to predict the debris flow's occurrence and an alarm model to evaluate the debris flow's disaster. Afterwards, a concise structure chart is worked out and verified by the field data from Chengdu-Kunming Railway. This prevention system will provide beneficial reference for the debris flow's monitoring network to be executed on Chengdu-Kunming Railway.

  7. Modelling debris flows down general channels

    Directory of Open Access Journals (Sweden)

    S. P. Pudasaini

    2005-01-01

    Full Text Available This paper is an extension of the single-phase cohesionless dry granular avalanche model over curved and twisted channels proposed by Pudasaini and Hutter (2003. It is a generalisation of the Savage and Hutter (1989, 1991 equations based on simple channel topography to a two-phase fluid-solid mixture of debris material. Important terms emerging from the correct treatment of the kinematic and dynamic boundary condition, and the variable basal topography are systematically taken into account. For vanishing fluid contribution and torsion-free channel topography our new model equations exactly degenerate to the previous Savage-Hutter model equations while such a degeneration was not possible by the Iverson and Denlinger (2001 model, which, in fact, also aimed to extend the Savage and Hutter model. The model equations of this paper have been rigorously derived; they include the effects of the curvature and torsion of the topography, generally for arbitrarily curved and twisted channels of variable channel width. The equations are put into a standard conservative form of partial differential equations. From these one can easily infer the importance and influence of the pore-fluid-pressure distribution in debris flow dynamics. The solid-phase is modelled by applying a Coulomb dry friction law whereas the fluid phase is assumed to be an incompressible Newtonian fluid. Input parameters of the equations are the internal and bed friction angles of the solid particles, the viscosity and volume fraction of the fluid, the total mixture density and the pore pressure distribution of the fluid at the bed. Given the bed topography and initial geometry and the initial velocity profile of the debris mixture, the model equations are able to describe the dynamics of the depth profile and bed parallel depth-averaged velocity distribution from the initial position to the final deposit. A shock capturing, total variation diminishing numerical scheme is implemented to

  8. Effects of basal debris on glacier flow.

    Science.gov (United States)

    Iverson, Neal R; Cohen, Denis; Hooyer, Thomas S; Fischer, Urs H; Jackson, Miriam; Moore, Peter L; Lappegard, Gaute; Kohler, Jack

    2003-07-04

    Glacier movement is resisted partially by debris, either within glaciers or under glaciers in water-saturated layers. In experiments beneath a thick, sliding glacier, ice containing 2 to 11% debris exerted shear traction of 60 to 200 kilopascals on a smooth rock bed, comparable to the total shear traction beneath glaciers and contrary to the usual assumption that debris-bed friction is negligible. Imposed pore-water pressure that was 60 to 100% of the normal stress in a subglacial debris layer reduced shear traction on the debris sufficiently to halt its deformation and cause slip of ice over the debris. Slip resistance was thus less than debris shearing resistance.

  9. Geotechnical properties of debris-flow sediments and slurries

    Science.gov (United States)

    Major, J.J.; Iverson, R.M.; McTigue, D.F.; Macias, S.; Fiedorowicz, B.K.

    1997-01-01

    Measurements of geotechnical properties of various poorly sorted debris-flow sediments and slurries (??? 32 mm diameter) emphasize their granular nature, and reveal that properties of slurries can differ significantly from those of compacted sediments. Measurements show that: (1) cohesion probably offers little resistance to shear in most debris flows under low confining stresses normally found in nature; (2) intrinsic hydraulic permeabilities of compacted debris-flow sediments vary from about 10-14-10-9 m2; permeabilities of 'typical' debris-flow slurries fall toward the low end of the range; (3) debris-flow slurries are characterized by very large values of 'elastic' compressibility (C approx. 10-2 kPa-1); and (4) hydraulic diffusivities of quasistatically consolidating slurries are approx. 10-4-10-7 m2/s. Low hydraulic diffusivity of debris slurries permits excess fluid pressure and low effective strength to persist during sediment transport and deposition.

  10. Mapping debris flow susceptibility using analytical network process ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 126; Issue 8. Mapping debris flow ... Rapid debris flows, a mixture of unconsolidated sediments and water travelling at speeds >10 m/s are the most destructive water related mass movements that affect hill and mountain regions. The predisposing factors setting the ...

  11. Frequency and initiation of debris flows in Grand Canyon, Arizona

    Science.gov (United States)

    Griffiths, Peter G.; Webb, Robert H.; Melis, Theodore S.

    2004-12-01

    Debris flows from 740 tributaries transport sediment into the Colorado River in Grand Canyon, Arizona, creating rapids that control its longitudinal profile. Debris flows mostly occur when runoff triggers failures in colluvium by a process termed "the fire hose effect." Debris flows originate from a limited number of geologic strata, almost exclusively shales or other clay-rich, fine-grained formations. Observations from 1984 through 2003 provide a 20 year record of all debris flows that reached the Colorado River in Grand Canyon, and repeat photography provides a 100 year record of debris flows from 147 tributaries. Observed frequencies are 5.1 events/year from 1984 to 2003, and historic frequencies are 5.0 events/year from 1890 to 1983. Logistic regression is used to model historic frequencies based on drainage basin parameters observed to control debris flow initiation and transport. From 5 to 7 of the 16 parameters evaluated are statistically significant, including drainage area, basin relief, and the height of and gradient below debris flow source areas, variables which reflect transport distance and potential energy. The aspect of the river channel, which at least partially reflects storm movement within the canyon, is also significant. Model results are used to calculate the probability of debris flow occurrence at the river over a century for all 740 tributaries. Owing to the variability of underlying geomorphic controls, the distribution of this probability is not uniform among tributaries of the Colorado River in Grand Canyon.

  12. Acoustic module of the Acquabona (Italy debris flow monitoring system

    Directory of Open Access Journals (Sweden)

    A. Galgaro

    2005-01-01

    Full Text Available Monitoring of debris flows aimed to the assessment of their physical parameters is very important both for theoretical and practical purposes. Peak discharge and total volume of debris flows are crucial for designing effective countermeasures in many populated mountain areas where losses of lives and property damage could be avoided. This study quantifies the relationship between flow depth, acoustic amplitude of debris flow induced ground vibrations and front velocity in the experimental catchment of Acquabona, Eastern Dolomites, Italy. The analysis of data brought about the results described in the following. Debris flow depth and amplitude of the flow-induced ground vibrations show a good positive correlation. Estimation of both mean front velocity and peak discharge can be simply obtained monitoring the ground vibrations, through geophones installed close to the flow channel; the total volume of debris flow can be so directly estimated from the integral of the ground vibrations using a regression line. The application of acoustic technique to debris flow monitoring seems to be of the outmost relevance in risk reduction policies and in the correct management of the territory. Moreover this estimation is possible in other catchments producing debris flows of similar characteristics by means of their acoustic characterisation through quick and simple field tests (Standard Penetration Tests and seismic refraction surveys.

  13. Enhancing debris flow modeling parameters integrating Bayesian networks

    Science.gov (United States)

    Graf, C.; Stoffel, M.; Grêt-Regamey, A.

    2009-04-01

    Applied debris-flow modeling requires suitably constraint input parameter sets. Depending on the used model, there is a series of parameters to define before running the model. Normally, the data base describing the event, the initiation conditions, the flow behavior, the deposition process and mainly the potential range of possible debris flow events in a certain torrent is limited. There are only some scarce places in the world, where we fortunately can find valuable data sets describing event history of debris flow channels delivering information on spatial and temporal distribution of former flow paths and deposition zones. Tree-ring records in combination with detailed geomorphic mapping for instance provide such data sets over a long time span. Considering the significant loss potential associated with debris-flow disasters, it is crucial that decisions made in regard to hazard mitigation are based on a consistent assessment of the risks. This in turn necessitates a proper assessment of the uncertainties involved in the modeling of the debris-flow frequencies and intensities, the possible run out extent, as well as the estimations of the damage potential. In this study, we link a Bayesian network to a Geographic Information System in order to assess debris-flow risk. We identify the major sources of uncertainty and show the potential of Bayesian inference techniques to improve the debris-flow model. We model the flow paths and deposition zones of a highly active debris-flow channel in the Swiss Alps using the numerical 2-D model RAMMS. Because uncertainties in run-out areas cause large changes in risk estimations, we use the data of flow path and deposition zone information of reconstructed debris-flow events derived from dendrogeomorphological analysis covering more than 400 years to update the input parameters of the RAMMS model. The probabilistic model, which consistently incorporates this available information, can serve as a basis for spatial risk

  14. Systems and Sensors for Debris-flow Monitoring and Warning

    Directory of Open Access Journals (Sweden)

    Lorenzo Marchi

    2008-04-01

    Full Text Available Debris flows are a type of mass movement that occurs in mountain torrents. They consist of a high concentration of solid material in water that flows as a wave with a steep front. Debris flows can be considered a phenomenon intermediate between landslides and water floods. They are amongst the most hazardous natural processes in mountainous regions and may occur under different climatic conditions. Their destructiveness is due to different factors: their capability of transporting and depositing huge amounts of solid materials, which may also reach large sizes (boulders of several cubic meters are commonly transported by debris flows, their steep fronts, which may reach several meters of height and also their high velocities. The implementation of both structural and nonstructural control measures is often required when debris flows endanger routes, urban areas and other infrastructures. Sensor networks for debris-flow monitoring and warning play an important role amongst non-structural measures intended to reduce debris-flow risk. In particular, debris flow warning systems can be subdivided into two main classes: advance warning and event warning systems. These two classes employ different types of sensors. Advance warning systems are based on monitoring causative hydrometeorological processes (typically rainfall and aim to issue a warning before a possible debris flow is triggered. Event warning systems are based on detecting debris flows when these processes are in progress. They have a much smaller lead time than advance warning ones but are also less prone to false alarms. Advance warning for debris flows employs sensors and techniques typical of meteorology and hydrology, including measuring rainfall by means of rain gauges and weather radar and monitoring water discharge in headwater streams. Event warning systems use different types of sensors, encompassing ultrasonic or radar gauges, ground vibration sensors, videocameras, avalanche

  15. Systems and Sensors for Debris-flow Monitoring and Warning.

    Science.gov (United States)

    Arattano, Massimo; Marchi, Lorenzo

    2008-04-04

    Debris flows are a type of mass movement that occurs in mountain torrents. They consist of a high concentration of solid material in water that flows as a wave with a steep front. Debris flows can be considered a phenomenon intermediate between landslides and water floods. They are amongst the most hazardous natural processes in mountainous regions and may occur under different climatic conditions. Their destructiveness is due to different factors: their capability of transporting and depositing huge amounts of solid materials, which may also reach large sizes (boulders of several cubic meters are commonly transported by debris flows), their steep fronts, which may reach several meters of height and also their high velocities. The implementation of both structural and nonstructural control measures is often required when debris flows endanger routes, urban areas and other infrastructures. Sensor networks for debris-flow monitoring and warning play an important role amongst non-structural measures intended to reduce debris-flow risk. In particular, debris flow warning systems can be subdivided into two main classes: advance warning and event warning systems. These two classes employ different types of sensors. Advance warning systems are based on monitoring causative hydrometeorological processes (typically rainfall) and aim to issue a warning before a possible debris flow is triggered. Event warning systems are based on detecting debris flows when these processes are in progress. They have a much smaller lead time than advance warning ones but are also less prone to false alarms. Advance warning for debris flows employs sensors and techniques typical of meteorology and hydrology, including measuring rainfall by means of rain gauges and weather radar and monitoring water discharge in headwater streams. Event warning systems use different types of sensors, encompassing ultrasonic or radar gauges, ground vibration sensors, videocameras, avalanche pendulums, photocells

  16. Particle size and concentration effects in laboratory debris flow mixtures

    Science.gov (United States)

    Queiroz de Oliveira, Gustavo; Baselt, Ivo; Fischer, Jan-Thomas; Pudasaini, Shiva P.

    2017-04-01

    Large scale chute experiments, as considered here, are essential for the proper understanding of the complex dynamic behavior of debris flow mixtures consisting of solid particles and viscous fluid. Main flow features that are measured on a laboratory scale are the debris flow front velocity, flow depth and mass evolution. We estimate the debris front position by image analysis technique, which in turn allows to evaluate the respective front velocity. Flow depths are determined by ultrasonic pulse reflections, and the masses are estimated with sensors measuring the normal forces. We investigate the influence of the two phase mixture material composition, including different fluid fractions. The laboratory set up consists of a large rectangular channel, 1.3 m wide and 7 m long. These dimensions allow also a lateral expansion of the debris flow when it moves down the inclined channel. Experiments on debris mixtures with different particle sizes and solid concentrations but same total mass are performed to evaluate the difference in spatial evolution of the debris flow dynamics with the same initial potential energy. The experiments reveal that the debris front with large particle size is faster than with the small ones for all solid volume concentrations. The increase of solid volume fraction shows a decrease of flow velocity, which was observed only in the experiments with the small particle. The flow depth and mass measurements at multiple locations along the downslope direction of the chute indicate different dynamical behavior for different particles sizes. The debris flow depth and mass showed no significant differences for large particles with varying initial solid volume concentrations. In contrast, low solid volume concentration resulted in low debris flow depth and mass in the experiments with small particles. This indicates that the particle size plays an important role in the debris flow transport in different solid volume concentration. So, the initial

  17. 40Ar/39Ar geochronology of subaerial lava flows of Barren Island volcano and the deep crust beneath the Andaman Island Arc, Burma Microplate

    Science.gov (United States)

    Ray, Jyotiranjan S.; Pande, Kanchan; Bhutani, Rajneesh

    2015-06-01

    Little was known about the nature and origin of the deep crust beneath the Andaman Island Arc in spite of the fact that it formed part of the highly active Indonesian volcanic arc system, one of the important continental crust forming regions in Southeast Asia. This arc, formed as a result of subduction of the Indian Plate beneath the Burma Microplate (a sliver of the Eurasian Plate), contains only one active subaerial magmatic center, Barren Island volcano, whose evolutional timeline had remained uncertain. In this work, we present results of the first successful attempt to date crustal xenoliths and their host lava flows from the island, by incremental heating 40Ar/39Ar method, in an attempt to understand the evolutionary histories of the volcano and its basement. Based on concordant plateau and isochron ages, we establish that the oldest subaerial lava flows of the volcano are 1.58 ± 0.04 (2σ) Ma, and some of the plagioclase xenocrysts have been derived from crustal rocks of 106 ± 3 (2σ) Ma. Mineralogy (anorthite + Cr-rich diopside + minor olivine) and isotopic compositions (87Sr/86Sr 7.0) of xenoliths not only indicate their derivation from a lower (oceanic) crustal olivine gabbro but also suggest a genetic relationship between the arc crust and the ophiolitic basement of the Andaman accretionary prism. We speculate that the basements of the forearc and volcanic arc of the Andaman subduction zone belong to a single continuous unit that was once attached to the western margin of the Eurasian Plate.

  18. Volcanic debris flows in developing countries - The extreme need for public education and awareness of debris-flow hazards

    Science.gov (United States)

    Major, J.J.; Schilling, S.P.; Pullinger, C.R.; ,

    2003-01-01

    In many developing countries, volcanic debris flows pose a significant societal risk owing to the distribution of dense populations that commonly live on or near a volcano. At many volcanoes, modest volume (up to 500,000 m 3) debris flows are relatively common (multiple times per century) and typically flow at least 5 km along established drainages. Owing to typical debris-flow velocities there is little time for authorities to provide effective warning of the occurrence of a debris flow to populations within 10 km of a source area. Therefore, people living, working, or recreating along channels that drain volcanoes must learn to recognize potentially hazardous conditions, be aware of the extent of debris-flow hazard zones, and be prepared to evacuate to safer ground when hazardous conditions develop rather than await official warnings or intervention. Debris-flow-modeling and hazard-assessment studies must be augmented with public education programs that emphasize recognizing conditions favorable for triggering landslides and debris flows if effective hazard mitigation is to succeed. ?? 2003 Millpress,.

  19. Anthropogenic effect on avalanche and debris flow activity

    Directory of Open Access Journals (Sweden)

    S. A. Sokratov

    2013-01-01

    Full Text Available The paper presents examples of the change in snow avalanches and debris flows activity due to the anthropogenic pressure on vegetation and relief. The changes in dynamical characteristics of selected snow avalanches and debris flows due to the anthropogenic activity are quantified. The conclusion is made that the anthropogenic effects on the snow avalanches and debris flows activity are more pronounced than the possible effects of the climate change. The necessity is expressed on the unavoidable changes of the natural environment as the result of a construction and of use of the constructed infrastructure to be account for in corresponding planning of the protection measures.

  20. Forecasting Inundation from Debris Flows That Grow By Entraining Sediment

    Science.gov (United States)

    Reid, M. E.; Coe, J. A.; Brien, D. L.

    2014-12-01

    Destructive debris flows often grow, and extend their runouts, by entraining sediment as they travel. However, incorporating varied entrainment processes into physics-based flow routing models is challenging. As an alternative, we developed a relatively simple, automated method for forecasting the inundation hazards posed by debris flows that entrain sediment and coalesce from multiple flows. Within a drainage network, we amalgamate the effects of many possible debris flows with each flow volume proportional to an entrainment rate scaled by the upslope contributing area, and then use these volumes in the USGS GIS-based inundation model LAHARZ. Our approach only requires estimates of two parameters: spatial entrainment rate & maximum entrainment area or maximum volume. Our procedure readily integrates various sediment sources and it can portray different inundation hazard levels on a GIS-based map by varying our two parameters. We applied this approach to part of the Coast Range, southern Oregon, USA. Using aerial photography, we mapped debris flows triggered by a large 1996 rain event on a LiDAR-derived topographic base, and identified initiation locations, travel paths, and areas of channel erosion and deposition. Many catchments experienced multiple debris flows that coalesced downstream and about 95% of the debris flows entrained sediment as they traveled. Flows typically stopped entraining sediment before the upslope contributing area reached ~500,000 m2. We used pre- and post-debris-flow stereo photos to estimate spatial entrainment rates in four clear-cut catchments having both channel erosion and coalescence of flows; these rates varied from 0.12 to 0.2 m3/m2. GIS-based inundation maps, using our automated methods, are quite similar to the mapped flow paths and deposits. Given appropriate parameters, our approach could be applied to a variety of steep, channelized environments where entrainment is important, such as alpine and post-wildfire slopes.

  1. Evidence of debris flow occurrence after wildfire in southeast Australia

    Science.gov (United States)

    Nyman, Petter; Sheridan, Gary; Smith, Hugh; Lane, Patrick

    2010-05-01

    With the recent increase in wildfire activity in the southeast Australia, an apparent gap has emerged in relation to our understanding of how the landscape responds to fire and the role of extreme erosion events in the region. Numerous reports of ‘flash floods", "mud torrents' and "landslides" in fire affected areas have only recently been recognised as significant events that warrant more detailed investigation. The aims of this study were to i) collect and show evidence of debris flow occurrence following recent wildfires in Victoria; ii) identify thresholds and key hydrological properties; and iii) present preliminary data on erosion rates from selected debris flows. The result showed that twelve out of fifteen recorded extreme erosion events originated from runoff generated debris flows. These occurred in Dry Eucalypt forests in steep and severely burnt headwater catchments throughout mountainous regions of north-, central- and eastern Victoria. The debris flows were triggered by intense, short duration rainfall events with annual exceedance probability in the order of 20%. This is the first study that documents the occurrence of runoff generated debris flows in Australia, so the observations and data are compared with the existing knowledge from similar post-fire responses in the western USA. Typical features common to both systems include low infiltration capacity of burnt catchments, widespread sheet erosion and levee lined rills on steep upper hillslopes and severe channel erosion initiated in response to convergent flow in previously un-scoured drainage lines. Runoff generated debris flow were not recorded in wet or damp forest types suggesting that this process is less likely to operate in these forest environments. One isolated case of mass failure generated debris flow was recorded in wet forest. The outcome of the study indicates that runoff generated debris flows are an important process to be considered during post-fire risk assessment of

  2. Analysis of debris-flow velocities due to superelevation

    Science.gov (United States)

    Scheidl, C.; Rickenmann, D.; McArdell, B. W.

    2012-12-01

    For debris flows the estimation of the maximum flow-velocity is considered to be essential. Often the runout or the degree of exposure of a debris-flow event can only be predicted, based on the assessment of the maximum velocity. In practice, geomorphologic traces like flood marks on banks provide important information about the flowing process of a debris flow. A possible approach to estimate maximum flow velocities is based on the vortex equation by using superelevation marks. Superelevation can be observed in bending channels, where the flow-height of the inner-curvature is lower than the flow-height of the outer-curvature, caused by the centrifugal acceleration of the flow. For the estimation of debris-flow velocities with the vortex equation, a correction factor (>1) is often introduced, accounting for the viscosity and vertical sorting of the bulk mixture. Several studies show that the correction factor may be as high as 10 and may depend on bend geometry and debris flow material properties. The objective of this work is therefore to analyze the influence of channel geometry and material properties on the vortex equation when applying to debris flows. In particular, the project aims to compare observed flow velocities from physical modeling in flume experiments with observations from debris-flow field sites. In a first step experimental investigations are done at the laboratory of the Swiss Federal Institute WSL, Birmensdorf. The flume consists of a flexible plastic half-pipe and is mounted on a wooden plane construction. At the moment two different bend radii (1.0 m and 3.0 m) with a bend angle of 60° are implemented. The total length of the flume is further covered with 40 grit silicon carbide sandpaper reflecting a constant basal friction layer. To apply for the complexity of a debris-flow process, three different material mixtures based on three different grain size distributions, were defined. Superelevation is measured by using high speed cameras

  3. Classification of debris flow phenomena in the Faroe Islands

    DEFF Research Database (Denmark)

    Dahl, Mads-Peter Jakob; E. Mortensen, Lis; Jensen, Niels H.

    2012-01-01

    a multidisciplinary study involving geomorphological fieldwork and qualitative collection of indigenous landslide knowledge, presents physical characteristics to classify debris flow phenomena into groups named with Faroese terms. The following landslide definitions are proposed. Brekku-skriðulop (English translation...

  4. Recent advances in modeling landslides and debris flows

    CERN Document Server

    2015-01-01

    Landslides and debris flows belong to the most dangerous natural hazards in many parts of the world. Despite intensive research, these events continue to result in human suffering, property losses, and environmental degradation every year. Better understanding of the mechanisms and processes of landslides and debris flows will help make reliable predictions, develop mitigation strategies and reduce vulnerability of infrastructure. This book presents contributions to the workshop on Recent Developments in the Analysis, Monitoring and Forecast of Landslides and Debris Flow, in Vienna, Austria, September 9, 2013. The contributions cover a broad spectrum of topics from material behavior, physical modelling over numerical simulation to applications and case studies. The workshop is a joint event of three research projects funded by the European Commission within the 7th Framework Program: MUMOLADE (Multiscale modelling of landslides and debris flows, www.mumolade.com), REVENUES (Numerical Analysis of Slopes with V...

  5. Predicting sediment delivery from debris flows after wildfire

    Science.gov (United States)

    Nyman, Petter; Smith, Hugh G.; Sherwin, Christopher B.; Langhans, Christoph; Lane, Patrick N. J.; Sheridan, Gary J.

    2015-12-01

    Debris flows are an important erosion process in wildfire-prone landscapes. Predicting their frequency and magnitude can therefore be critical for quantifying risk to infrastructure, people and water resources. However, the factors contributing to the frequency and magnitude of events remain poorly understood, particularly in regions outside western USA. Against this background, the objectives of this study were to i) quantify sediment yields from post-fire debris flows in southeast Australian highlands and ii) model the effects of landscape attributes on debris flow susceptibility. Sediment yields from post-fire debris flows (113-294 t ha- 1) are 2-3 orders of magnitude higher than annual background erosion rates from undisturbed forests. Debris flow volumes ranged from 539 to 33,040 m3 with hillslope contributions of 18-62%. The distribution of erosion and deposition above the fan were related to a stream power index, which could be used to model changes in yield along the drainage network. Debris flow susceptibility was quantified with a logistic regression and an inventory of 315 debris flow fans deposited in the first year after two large wildfires (total burned area = 2919 km2). The differenced normalised burn ratio (dNBR or burn severity), local slope, radiative index of dryness (AI) and rainfall intensity (from rainfall radar) were significant predictors in a susceptibility model, which produced excellent results in terms identifying channels that were eroded by debris flows (Area Under Curve, AUC = 0.91). Burn severity was the strongest predictor in the model (AUC = 0.87 when dNBR is used as single predictor) suggesting that fire regimes are an important control on sediment delivery from these forests. The analysis showed a positive effect of AI on debris flow probability in landscapes where differences in moisture regimes due to climate are associated with large variation in soil hydraulic properties. Overall, the results from this study based in the

  6. Estimating critical water supply for debris flow initiation in Norway

    Science.gov (United States)

    Meyer, N. K.; Dyrrdal, A. V.; Frauenfelder, R.; Etzelmüller, B.; Nadim, F.

    2012-04-01

    Debris flows frequently affect the Norwegian road and railway infrastructure, especially during spring and autumn. While the debris flow activity in autumn is mainly due to the occurrence of extreme rainfall events, debris flows in spring often occur during periods of rapid snow melt. Existing rainfall threshold values that indicate critical conditions for debris-flow initiation are largely based on precipitation data recorded by meteorological stations. However, during winter the measured amount of precipitation (accumulated as snow) can differ significantly from the actual amount of water that is released to the ground, which is in turn the more critical factor for debris flow initiation. In this study, the data on the actual water supply by the Norwegian Water and Energy Directorate (NVE), and the Norwegian Meteorological Institute (met.no) were used to assess the threshold values. Compared to rainfall data, these data define the hydro-meteorological threshold conditions more accurately throughout the year - i.e. the debris flow triggering conditions due to snow accumulation in autumn and winter and snow melt in spring and summer. Three intensity-duration threshold curves were derived by analyzing the data on 502 past debris flows for water supply durations of 1 to 7 days. Normalization of the data was accomplished using the local "precipitation day normal" to account for regional differences in climate. The minimum threshold indicates the lower boundary above which debris-flow occurrence has been recorded and ranges between 6 and 63 mm/day for different locations and durations. The medium threshold (ranging between 7 and 131 mm/day) characterizes the conditions that are likely to initiate debris flows. Water supply rates exceeding the maximum threshold are regarded as a certain trigger and lie between 12 and 250 mm/day. Based on the obtained threshold curves a frequency analysis over durations of 1, 3 and 7 days for the period 1981-2010 was conducted

  7. An assessment of prediction tools to Norwegian debris flows

    OpenAIRE

    Frekhaug, Martine Holm

    2015-01-01

    The occurrence of debris flows in Norway is a challenge to settlement and infrastructure. Due to a high mobility, that causes long run-outs, they can lead to severe damages. This constitute a large cost to the Norwegian Water and Energy Directorate (NWED), the Norwegian Public Roads Administration (NPRA) and the Norwegian National Rail Administration (NNRA). A predicted increase in precipitation during this century will most likely increase the frequency of debris flows. Thus, the need for ac...

  8. Scaling and design of landslide and debris-flow experiments

    Science.gov (United States)

    Iverson, Richard M.

    2015-01-01

    Scaling plays a crucial role in designing experiments aimed at understanding the behavior of landslides, debris flows, and other geomorphic phenomena involving grain-fluid mixtures. Scaling can be addressed by using dimensional analysis or – more rigorously – by normalizing differential equations that describe the evolving dynamics of the system. Both of these approaches show that, relative to full-scale natural events, miniaturized landslides and debris flows exhibit disproportionately large effects of viscous shear resistance and cohesion as well as disproportionately small effects of excess pore-fluid pressure that is generated by debris dilation or contraction. This behavioral divergence grows in proportion to H3, where H is the thickness of a moving mass. Therefore, to maximize geomorphological relevance, experiments with wet landslides and debris flows must be conducted at the largest feasible scales. Another important consideration is that, unlike stream flows, landslides and debris flows accelerate from statically balanced initial states. Thus, no characteristic macroscopic velocity exists to guide experiment scaling and design. On the other hand, macroscopic gravity-driven motion of landslides and debris flows evolves over a characteristic time scale (L/g)1/2, where g is the magnitude of gravitational acceleration and L is the characteristic length of the moving mass. Grain-scale stress generation within the mass occurs on a shorter time scale, H/(gL)1/2, which is inversely proportional to the depth-averaged material shear rate. A separation of these two time scales exists if the criterion H/L debris-flow behavior but cannot be used to study macroscopic landslide or debris-flow dynamics.

  9. Debris flow characteristics and relationships in the Central Spanish Pyrenees

    Directory of Open Access Journals (Sweden)

    A. Lorente

    2003-01-01

    Full Text Available Unconfined debris flows (i.e. not in incised channels are one of the most active geomorphic processes in mountainous areas. Since they can threaten settlements and infrastructure, statistical and physically based procedures have been developed to assess the potential for landslide erosion. In this study, information on debris flow characteristics was obtained in the field to define the debris flow runout distance and to establish relationships between debris flow parameters. Such relationships are needed for building models which allow us to improve the spatial prediction of debris flow hazards. In general, unconfined debris flows triggered in the Flysch Sector of the Central Spanish Pyrenees are of the same order of magnitude as others reported in the literature. The deposition of sediment started at 17.8°, and the runout distance represented 60% of the difference in height between the head of the landslide and the point at which deposition started. The runout distance was relatively well correlated with the volume of sediment.

  10. Debris flow susceptibility assessment after the 2008 Wenchuan earthquake

    Science.gov (United States)

    Fan, Xuanmei; van Westen, Cees; Tang, Chenxiao; Tang, Chuan

    2014-05-01

    Due to a tremendous amount of loose material from landslides that occurred during the Wenchuan earthquake, the frequency and magnitude of debris flows have been immensely increased, causing many casualties and economic losses. This study attempts to assess the post-earthquake debris flow susceptibility based on catchment units in the Wenchuan county, one of the most severely damaged county by the earthquake. The post earthquake debris flow inventory was created by RS image interpretation and field survey. According to our knowledge to the field, several relevant factors were determined as indicators for post-earthquake debris flow occurrence, including the distance to fault surface rupture, peak ground acceleration (PGA), coseismic landslide density, rainfall data, internal relief, slope, drainage density, stream steepness index, existing mitigation works etc. These indicators were then used as inputs in a heuristic model that was developed by adapting the Spatial Multi Criteria Evaluation (SMCE) method. The relative importance of the indicators was evaluated according to their contributions to the debris flow events that have occurred after the earthquake. The ultimate goal of this study is to estimate the relative likelihood of debris flow occurrence in each catchment, and use this result together with elements at risk and vulnerability information to assess the changing risk of the most susceptible catchment.

  11. [Relations of landslide and debris flow hazards to environmental factors].

    Science.gov (United States)

    Zhang, Guo-ping; Xu, Jing; Bi, Bao-gui

    2009-03-01

    To clarify the relations of landslide and debris flow hazards to environmental factors is of significance to the prediction and evaluation of landslide and debris flow hazards. Base on the latitudinal and longitudinal information of 18431 landslide and debris flow hazards in China, and the 1 km x 1 km grid data of elevation, elevation difference, slope, slope aspect, vegetation type, and vegetation coverage, this paper analyzed the relations of landslide and debris flow hazards in this country to above-mentioned environmental factors by the analysis method of frequency ratio. The results showed that the landslide and debris flow hazards in China more occurred in lower elevation areas of the first and second transitional zones. When the elevation difference within a 1 km x 1 km grid cell was about 300 m and the slope was around 30 degree, there was the greatest possibility of the occurrence of landslide and debris hazards. Mountain forest land and slope cropland were the two land types the hazards most easily occurred. The occurrence frequency of the hazards was the highest when the vegetation coverage was about 80%-90%.

  12. What is the velocity profile of debris flows?

    Science.gov (United States)

    Walter, Fabian; McArdell, Brian

    2015-04-01

    The distribution of flow velocity within a debris flow is difficult to determine at full scale in the field due to the large forces and inherently destructive nature of the flow. However, knowledge of the distribution of velocity within a flow would be helpful to constrain rheological models and to better understand the internal dynamics of such flows. Here we describe recent efforts to determine the velocity of debris flows as a function of distance from the channel bed. Measurements were made at the Illgraben, Switzerland, which exhibits a wide variety of flows, ranging from turbulent debris floods to flows which resemble laminar mud flows to more classical debris flows with a clear granular front. The Illgraben observation station is therefore an ideal location to investigate debris flow dynamics. Our measurements were made using sensors embedded on a 14 m long, 2.5 m tall steel-reinforced concrete wall constructed flush with the torrent channel walls. The main instrumentation consists of 18 geophones (10 Hz natural frequency) installed on square steel plates with a side length of 0.3 m. Each steel plate is acoustically isolated from the wall and the other plates through the use of elastomer elements. The geophone plates are arranged in six rows of three sensors with a dimension of 1.8 m in the vertical direction and 1.5 m in the horizontal direction (i.e. parallel to the flow direction). A sensorless plate separates each plate in the horizontal direction. The data are collected at 2 kHz using a high-speed (synchronous) capture card in a pc. The elevation of the flow surface is determined at a cross-stream distance 1 m away from the wall, using a laser sensor installed on a bridge above the wall. We present a processing approach for the geophone data with the goal to track particle sliding across the sensor plates. For signals near or above the sensors' natural frequency (10 Hz), the measured time series are poorly correlated between sensors. Therefore, we use a

  13. Debris-flow observations in the Zermatt Valley

    Science.gov (United States)

    Graf, Christoph

    2015-04-01

    In the Alps, a multitude of unstable slopes is located at altitudes of ~2700 m asl, where sediment transfers typically happen outside the range of humans or their infrastructure. The situation is slightly different in the Zermatt Valley, a high-elevation, north-south oriented glacial valley in the Swiss Alps, where the detachment of melting permafrost results in rock falls on steep slopes and debris flows in high-gradient gullies through which till is transferred directly to the inhabited valley floor at elevations between 1100 (N) and 1600 m asl (S). As a result of the excellent database on past disasters in the valley, recent developments and measurements in the local rock glacier bodies and current torrential events, I show data from some debris-flow torrents to document impacts of past, ongoing and possible future changes of debris flows originating from periglacial environments. Debris flows are typically initiated by the abrupt input of considerable quantities of water. The water-saturated masses of fragmented rock and soil slump down mountainsides into gullies which in turn mobilize stored sediment in the channels. In addition to triggering by extreme rainstorms, debris flows have also been reported to be released by rapid snowmelt, rain-on-snow storms, or the sudden emptying of glacier water bodies or through the rupture of landslide dams. More frequently, debris flows occur as a result of high-intensity, convective rainstorms of short duration or low-intensity advective precipitation events over several days. Displacement rates and instability of rock glaciers have increased further recently to show movement rates without historical precedents. At Grabengufer (Dorfbach) e.g., increasing air and ice temperatures have favoured the development of annual displacement rates from just a few decimetres in the past decades to 80 m in 2010. Similar behaviour was observed in catchments nearby. As a consequence of the enhanced movement of these permafrost bodies and

  14. Debris-flow runout susceptibility mapping for the French Alps.

    Science.gov (United States)

    Mathieu, Alexandre; Malet, Jean-Philippe; Remaître, Alexandre

    2014-05-01

    Debris-flows are one of the most important gravity-driven hazards in mountainous areas mainly due to their high velocity and long travel distance. Estimation of potential initiation areas and delineation of the down-slope endangered zones possibly affected by debris-flow deposits are crucial. The objective of this work is to propose a first delineation of debris flow susceptibility for the French Alps by combining information from a debris flow catalogue and runout analyses with a large scale debris flow model. The landslide source areas are estimated from statistics of recorded events in catchments and the dominant lithology, landcover and slope conditions observed in the catchments. The runout areas are estimated from a probabilistic approach using multiple flow routing algorithms and the angle of reach concept. Since the reliability of such an approach is closely linked to the accuracy of the topography, a digital elevation model at 25m resolution is used. The susceptibility analysis is carried out for each catchment and the reliability of the results (i.e. number of pixels as sources, etc.) is assessed by comparison with the landslide catalogues. Results indicate the most susceptible catchments where further detailed assessments are needed at smaller spatial scales.

  15. An example of debris-flows hazard modeling using GIS

    Directory of Open Access Journals (Sweden)

    L. Melelli

    2004-01-01

    Full Text Available We present a GIS-based model for predicting debris-flows occurrence. The availability of two different digital datasets and the use of a Digital Elevation Model (at a given scale have greatly enhanced our ability to quantify and to analyse the topography in relation to debris-flows. In particular, analysing the relationship between debris-flows and the various causative factors provides new understanding of the mechanisms. We studied the contact zone between the calcareous basement and the fluvial-lacustrine infill adjacent northern area of the Terni basin (Umbria, Italy, and identified eleven basins and corresponding alluvial fans. We suggest that accumulations of colluvium in topographic hollows, whatever the sources might be, should be considered potential debris-flow source areas. In order to develop a susceptibility map for the entire area, an index was calculated from the number of initiation locations in each causative factor unit divided by the areal extent of that unit within the study area. This index identifies those units that produce the most debris-flows in each Representative Elementary Area (REA. Finally, the results are presented with the advantages and the disadvantages of the approach, and the need for further research.

  16. Mechanics of debris flows and rock avalanches: Chapter 43

    Science.gov (United States)

    Iverson, Richard M.; Fernando, Harindra Joseph

    2012-01-01

    Debris flows are geophysical phenomena intermediate in character between rock avalanches and flash floods. They commonly originate as water-laden landslides on steep slopes and transform into liquefied masses of fragmented rock, muddy water, and entrained organic matter that disgorge from canyons onto valley floors. Typically including 50%–70% solid grains by volume, attaining speeds >10 m/s, and ranging in size up to ∼109 m3, debris flows can denude mountainsides, inundate floodplains, and devastate people and property (Figure 43.1). Notable recent debris-flow disasters resulted in more than 20,000 fatalities in Armero, Colombia, in 1985 and in Vargas state, Venezuela, in 1999.

  17. Dynamic modelling of debris flow erosion and deposition with application to the USGS debris flow flume experiments

    Science.gov (United States)

    Deubelbeiss, Y.; McArdell, B. W.

    2012-04-01

    The dynamics of a debris flow can be significantly influenced by erosion and deposition processes during an event because volume changes have a strong influence on flow properties such as flow velocity, flow height and runout distance. It is therefore worth exploring how to include these processes in numerical models which are used for hazard assessment and mitigation measure planning. However, the mechanism that drives the erosion of material at the base of a debris flow, is still under debate. There are different processes attributed to erosion: it has been proposed that erosion is caused by stresses due to granular interactions at the front, which strongly depend on particle size, transmission of mean basal shear stresses to the bed or excess pore fluid pressure. Because there is no definitive solution for a general erosion model, we implement different erosion relationships accounting for different entrainment types in a numerical model and test its influence on the flow behavior. We use a 2D numerical model (RAMMS), based on the shallow water equations, employing the Voellmy friction relationship. Snow avalanche data indicate a simple velocity-driven erosion rate. Ice-avalanche simulations, on the other hand, showed that a correlation of erosion with velocity does not lead to satisfying results (too high entrainment in the tail) and a correlation with flow height combined with velocity (momentum) is preferably applied. The momentum-driven relationship enhances the entrainment at the flow front. However, these laws do not consider processes on smaller scales, such as particle fluctuations within the flowing mass. Therefore, we consider an erosion relationship based on an extended Voellmy friction model, which employs an additional equation for the energy conservation. The energy equation is a measure for the random kinetic energy (RKE, equivalent to granular temperature) produced by the random movement of particles in a debris flow. In this model friction is

  18. A new debris flow monitoring barrier to measure debris flow impact/structure/ground interaction in the Gadria torrent

    Science.gov (United States)

    Nagl, Georg; Hübl, Johannes

    2017-04-01

    Debris flow monitoring is a keystone in debris flow research. Based on the lack of investigations of the interaction of rapid mass movement and structural mitigation measures, a new monitoring system has been installed in the well monitored Gadria torrent in South Tyrol. For design of active structural measures, like check dams, the engineering task is to come to an amicable solution of all necessary subjects. Starting with the estimation of parameters of the rapid mass movement itself to the design load and finally to the foundation of the structure. At all stages big uncertainties are given. The basis for accurate design is a comprehensive approach. For this reason, a new monitoring station was built in autumn 2016, to investigate the interaction of a debris flow with the structures and the ground. Two structures unify the new monitoring system. The first, a transversal check dam, flush to channel bed, contain two weighing devices each equipped with a pore pressure sensor. One device is also able to measure the shear force additional in two directions. The second barrier similar to a debris flow breaker but only with one singe wall centered on a foundation plate, is located downstream to the first one. 14 load cells are installed on the upward front of the structure to analyze the spatial force distribution of debris flow impact pressure. Nine earth pressure sensors under the foundation of the structure deliver the earth pressure distribution. The acceleration of the construction can be measured by a 3D accelerometer installed on the top. In case of a movement, two extensometers detect any displacement. Mounted strain gauges give insights of stresses in concrete and reinforcement. Each sensor has a sampling frequency of 2400 Hz. Furthermore it is planned to measure the flow velocity distribution over flow depth too. The new monitoring station should help to acquire data for understanding the debris flow/structure/ground interaction to facilitate the improvement

  19. Hydrometeorological threshold conditions for debris flow initiation in Norway

    Directory of Open Access Journals (Sweden)

    N. K. Meyer

    2012-10-01

    Full Text Available Debris flows, triggered by extreme precipitation events and rapid snow melt, cause considerable damage to the Norwegian infrastructure every year. To define intensity-duration (ID thresholds for debris flow initiation critical water supply conditions arising from intensive rainfall or snow melt were assessed on the basis of daily hydro-meteorological information for 502 documented debris flow events. Two threshold types were computed: one based on absolute ID relationships and one using ID relationships normalized by the local precipitation day normal (PDN. For each threshold type, minimum, medium and maximum threshold values were defined by fitting power law curves along the 10th, 50th and 90th percentiles of the data population. Depending on the duration of the event, the absolute threshold intensities needed for debris flow initiation vary between 15 and 107 mm day−1. Since the PDN changes locally, the normalized thresholds show spatial variations. Depending on location, duration and threshold level, the normalized threshold intensities vary between 6 and 250 mm day−1. The thresholds obtained were used for a frequency analysis of over-threshold events giving an estimation of the exceedance probability and thus potential for debris flow events in different parts of Norway. The absolute thresholds are most often exceeded along the west coast, while the normalized thresholds are most frequently exceeded on the west-facing slopes of the Norwegian mountain ranges. The minimum thresholds derived in this study are in the range of other thresholds obtained for regions with a climate comparable to Norway. Statistics reveal that the normalized threshold is more reliable than the absolute threshold as the former shows no spatial clustering of debris flows related to water supply events captured by the threshold.

  20. On predicting debris flows in arid mountain belts

    Science.gov (United States)

    Stolle, Amelie; Langer, Maria; Blöthe, Jan Henrik; Korup, Oliver

    2015-03-01

    The use of topographic metrics for estimating the susceptibility to, and reconstructing the characteristics of, debris flows has a long research tradition, although largely devoted to humid mountainous terrain. The exceptional 2010 monsoonal rainstorms in the high-altitude mountain desert of Ladakh and Zanskar, NW India, were a painful reminder of how susceptible arid regions are to rainfall-triggered flash floods, landslides, and debris flows. The rainstorms of August 4-6 triggered numerous debris flows, killing 182 people, devastating 607 houses, and more than 10 bridges around Ladakh's capital of Leh. The lessons from this disaster motivated us to revisit methods of predicting (a) flow parameters such as peak discharge and maximum velocity from field and remote sensing data, and (b) the susceptibility to debris flows from catchment morphometry. We focus on quantifying uncertainties tied to these approaches. Comparison of high-resolution satellite images pre- and post-dating the 2010 rainstorm reveals the extent of damage and catastrophic channel widening. Computations based on these geomorphic markers indicate maximum flow velocities of 1.6-6.7 m s- 1 with runout of up to ~ 10 km on several alluvial fans that sustain most of the region's settlements. We estimate median peak discharges of 310-610 m3 s- 1, which are largely consistent with previous estimates. Monte Carlo-based error propagation for a single given flow-reconstruction method returns a variance in discharge similar to one derived from juxtaposing several different flow reconstruction methods. We further compare discriminant analysis, classification tree modelling, and Bayesian logistic regression to predict debris-flow susceptibility from morphometric variables of 171 catchments in the Ladakh Range. These methods distinguish between fluvial and debris flow-prone catchments at similar success rates, but Bayesian logistic regression allows quantifying uncertainties and relationships between potential

  1. Mount Baker lahars and debris flows, ancient, modern, and future

    Science.gov (United States)

    Tucker, David S; Scott, Kevin M.; Grossman, Eric E.; Linneman, Scott

    2014-01-01

    The Middle Fork Nooksack River drains the southwestern slopes of the active Mount Baker stratovolcano in northwest Washington State. The river enters Bellingham Bay at a growing delta 98 km to the west. Various types of debris flows have descended the river, generated by volcano collapse or eruption (lahars), glacial outburst floods, and moraine landslides. Initial deposition of sediment during debris flows occurs on the order of minutes to a few hours. Long-lasting, down-valley transport of sediment, all the way to the delta, occurs over a period of decades, and affects fish habitat, flood risk, gravel mining, and drinking water.

  2. Secondary crater-initiated debris flow on the Moon

    Science.gov (United States)

    Martin-Wells, K. S.; Campbell, D. B.; Campbell, B. A.; Carter, L. M.; Fox, Q.

    2017-07-01

    In recent work, radar circular polarization echo properties have been used to identify secondary craters without distinctive ;secondary; morphologies. Because of the potential for this method to improve our knowledge of secondary crater populations-in particular the effect of secondary populations on crater-derived ages based on small craters-it is important to understand the origin of radar polarization signatures associated with secondary impacts. In this paper, we utilize Lunar Reconnaissance Orbiter Camera photographs to examine the geomorphology of secondary craters with radar circular polarization ratio enhancements. Our investigation reveals evidence of dry debris flow with an impact melt component at such secondary craters. We hypothesize that these debris flows were initiated by the secondary impacts themselves, and that they have entrained blocky material ejected from the secondaries. By transporting this blocky material downrange, we propose that these debris flows (rather than solely ballistic emplacement) are responsible for the tail-like geometries of enhanced radar circular polarization ratio associated with the secondary craters investigated in this work. Evidence of debris flow was observed at both clustered and isolated secondary craters, suggesting that such flow may be a widespread occurrence, with important implications for the mixing of primary and local material in crater rays.

  3. Pebble orientation on large, experimental debris-flow deposits

    Science.gov (United States)

    Major, J.J.

    1998-01-01

    Replicable, pronounced orientation of discoid pebbles (??? 8 mm) embedded on surfaces of large (??? 10 m3) experimental debris-flow deposits reveals that strongly aligned, imbricate fabric can develop rapidly over short distances in mass flows. Pebble long axes aligned subparallel to deposit margins as well as subparallel to margins of surge waves arrested within the deposits. Pebble alignment exhibited modes both parallel to (a(p)), and normal to (a(t)), the primary flow direction; intermediate axes dipped preferentially inward from surge-wave margins (b(i) orientation). Repetitive development of margin-parallel, imbricate fabric distributed across deposit surfaces provides compelling evidence that deposits formed dominantly through progressive incremental accretion rather than through simple en masse emplacement. Pronounced fabric along deposit and arrested surge-wave margins reflects significant grain interaction along flow margins. This sedimentological evidence for significant marginal grain interaction complements theoretical analyses (Iverson, 1997) and other experimental data (Major, 1996: Iverson, 1997) that indicate that resistance along flow margins is an important factor affecting debris-flow deposition. The fabric on the experimental deposits demonstrates that debris flows can develop strongly imbricate particle orientation that mimics fabric developed during fluvial deposition. Particle shape and local stress fields appear to have more control over fabric development than does general depositional process. Other criteria in addition to particle orientation are needed to discriminate mass flow from fluvial gravel deposits and to unravel depositional history. ?? 1998 Elsevier Science B.V. All rights reserved.

  4. Small scale modelling of dynamic impact of debris flows

    Science.gov (United States)

    Sanvitale, Nicoletta; Bowman, Elisabeth

    2017-04-01

    Fast landslides, such as debris flows, involve high speed downslope motion of rocks, soil and water. Engineering attempts to reduce the risk posed by these natural hazards often involve the placement of barriers or obstacles to inhibit movement. The impact pressures exert by debris flows are difficult to estimate because they not only depend on the geometry and size of the flow and the obstacle but also on the characteristics of the flow mixture. The presence of a solid phase can increase local impact pressure due to hard contact often caused by single boulder. This can lead to higher impact forces compared to the estimates of the peak pressure value obtained from hydraulic based models commonly adopted in such analyses. The proposed study aims at bringing new insight to the impact loading of structures generated by segregating granular debris flow. A small-scale flume, designed to enable plane laser induced fluorescence (PLIF) and digital image correlation (DIC) to be applied internally will be used for 2D analyses. The flow will incorporate glass particles suitable for refractive index matching (RIM) with a matched fluid to gain optical access to the internal behaviour of the flow, via a laser sheet applied away from sidewall boundaries. For these tests, the focus will be on assessing 2D particle interactions in unsteady flow. The paper will present in details the methodology and the set-up of the experiments together with some preliminary results

  5. Debris flow relationships in the Central Spanish Pyrenees

    NARCIS (Netherlands)

    Beguería, S.; Lorente, A.; Garcia-Ruiz, J.M.

    2002-01-01

    It is commonly accepted that, in terms of volume moved in a short space of time, debris flows are one of the most powerful mechanisms for transporting material downslope (Johnson & Rodine, 1984; Takahashi, 1991; Bathurst et al., 1997). They occur if i) sediment availability, ii) water input, and

  6. Soil slips and debris flows on terraced slopes

    Directory of Open Access Journals (Sweden)

    G. B. Crosta

    2003-01-01

    Full Text Available Terraces cover large areas along the flanks of many alpine and prealpine valleys. Soil slips and soil slips-debris flows are recurrent phenomena along terraced slopes. These landslides cause damages to people, settlements and cultivations. This study investigates the processes related to the triggering of soil slip-debris flows in these settings, analysing those occurred in Valtellina (Central Alps, Italy on November 2000 after heavy prolonged rainfalls. 260 landslides have been recognised, mostly along the northern valley flank. About 200 soil slips and slumps occurred in terraced areas and a third of them evolved into debris flows. Field work allowed to recognise the settings at soil slip-debris flow source areas. Landslides affected up to 2.5 m of glacial, fluvioglacial and anthropically reworked deposits overlying metamorphic basement. Laboratory and in situ tests allowed to characterise the geotechnical and hydraulic properties of the terrains involved in the initial failure. Several stratigraphic and hydrogeologic factors have been individuated as significant in determining instabilities on terraced slopes. They are the vertical changes of physical soil properties, the presence of buried hollows where groundwater convergence occurs, the rising up of perched groundwater tables, the overflow and lateral infiltration from superficial drainage network, the runoff concentration by means of pathways and the insufficient drainage of retaining walls.

  7. Mapping debris flow susceptibility using analytical network process ...

    Indian Academy of Sciences (India)

    Evangelin Ramani Sujatha

    2017-11-23

    Nov 23, 2017 ... roads, power transmission lines, plantations, settle- ments and at rare events disrupts road connectivity between the hill town and the plains. No major injuries or loss of life was reported due to debris flow in this region, but there was considerable disruption to local and tourist traffic as well as cargo carriers.

  8. Debris flow characteristics and relationships in the Central Spanish Pyrenees

    NARCIS (Netherlands)

    Lorente, A.; Beguería, S.; Bathurst, J.C.; García-Ruiz, J.M.

    2003-01-01

    Unconfined debris flows (i.e., not in incised channels) are one of the most active geomorphic processes in mountainous areas. Since they can threaten settlements and infrastructure, statistical and physically based procedures have been developed to assess the potential for landslide erosion. In

  9. Assessing debris flow activity in a changing climate : open access

    NARCIS (Netherlands)

    Turkington, T.; Remaitre, A.; Ettema, J.; Hussin, H.Y.; van Westen, C.J.

    2016-01-01

    Future trends in debris flow activity are constructed based on bias-corrected climate change projections using two meteorological proxies: daily precipitation and Convective Available Potential Energy (CAPE) combined with specific humidity for two Alpine areas. Along with a comparison between

  10. Assessing debris flow activity in a changing climate

    NARCIS (Netherlands)

    Turkington, T.; Remaitre, A.; Ettema, J.; Hussin, H.Y.; van Westen, C.J.

    2016-01-01

    Future trends in debris flow activity are constructed based on bias-corrected climate change projections using two meteorological proxies: daily precipitation and Convective Available Potential Energy (CAPE) combined with specific humidity for two Alpine areas. Along with a comparison between

  11. Debris flow early warning systems in Norway: organization and tools

    Science.gov (United States)

    Kleivane, I.; Colleuille, H.; Haugen, L. E.; Alve Glad, P.; Devoli, G.

    2012-04-01

    In Norway, shallow slides and debris flows occur as a combination of high-intensity precipitation, snowmelt, high groundwater level and saturated soil. Many events have occurred in the last decades and are often associated with (or related to) floods events, especially in the Southern of Norway, causing significant damages to roads, railway lines, buildings, and other infrastructures (i.e November 2000; August 2003; September 2005; November 2005; Mai 2008; June and Desember 2011). Since 1989 the Norwegian Water Resources and Energy Directorate (NVE) has had an operational 24 hour flood forecasting system for the entire country. From 2009 NVE is also responsible to assist regions and municipalities in the prevention of disasters posed by landslides and snow avalanches. Besides assisting the municipalities through implementation of digital landslides inventories, susceptibility and hazard mapping, areal planning, preparation of guidelines, realization of mitigation measures and helping during emergencies, NVE is developing a regional scale debris flow warning system that use hydrological models that are already available in the flood warning systems. It is well known that the application of rainfall thresholds is not sufficient to evaluate the hazard for debris flows and shallow slides, and soil moisture conditions play a crucial role in the triggering conditions. The information on simulated soil and groundwater conditions and water supply (rain and snowmelt) based on weather forecast, have proved to be useful variables that indicate the potential occurrence of debris flows and shallow slides. Forecasts of runoff and freezing-thawing are also valuable information. The early warning system is using real-time measurements (Discharge; Groundwater level; Soil water content and soil temperature; Snow water equivalent; Meteorological data) and model simulations (a spatially distributed version of the HBV-model and an adapted version of 1-D soil water and energy balance

  12. The Influence of an EPS Concrete Buffer Layer Thickness on Debris Dams Impacted by Massive Stones in the Debris Flow

    Directory of Open Access Journals (Sweden)

    Xianbin Yu

    2015-01-01

    Full Text Available The failure of debris dams impacted by the massive stones in a debris flow represents a difficult design problem. Reasonable materials selection and structural design can effectively improve the resistance impact performance of debris dams. Based on the cushioning properties of expanded polystyrene (EPS concrete, EPS concrete as a buffer layer poured on the surface of a rigid debris dam was proposed. A three-dimensional numerical calculation model of an EPS concrete buffer layer/rigid debris dam was established. The single-factor theory revealed change rules for the thickness of the buffer layer concerning the maximal impact force of the rigid debris dam surface through numerical simulation. Moreover, the impact force-time/history curves under different calculation conditions for the rigid debris dam surface were compared. Simulation results showed that the EPS concrete buffer layer can not only effectively extend the impact time of massive stones affecting the debris dam but also reduce the impact force of the rigid debris dam caused by massive stones in the debris flow. The research results provide theoretical guidance for transferring the energy of the massive stone impact, creating a structural design and optimizing debris dams.

  13. A study of methods to estimate debris flow velocity

    Science.gov (United States)

    Prochaska, A.B.; Santi, P.M.; Higgins, J.D.; Cannon, S.H.

    2008-01-01

    Debris flow velocities are commonly back-calculated from superelevation events which require subjective estimates of radii of curvature of bends in the debris flow channel or predicted using flow equations that require the selection of appropriate rheological models and material property inputs. This research investigated difficulties associated with the use of these conventional velocity estimation methods. Radii of curvature estimates were found to vary with the extent of the channel investigated and with the scale of the media used, and back-calculated velocities varied among different investigated locations along a channel. Distinct populations of Bingham properties were found to exist between those measured by laboratory tests and those back-calculated from field data; thus, laboratory-obtained values would not be representative of field-scale debris flow behavior. To avoid these difficulties with conventional methods, a new preliminary velocity estimation method is presented that statistically relates flow velocity to the channel slope and the flow depth. This method presents ranges of reasonable velocity predictions based on 30 previously measured velocities. ?? 2008 Springer-Verlag.

  14. Avulsions and the spatio-temporal evolution of debris-flow fans

    NARCIS (Netherlands)

    De Haas, T.|info:eu-repo/dai/nl/374023190; Densmore, A. L.; Stoffel, M.H.; Suwa, H.; Imaizumi, F.; Ballesteros-Cánovas, J. A.; Wasklewicz, T.

    Debris flows are water-laden masses of sediment that move rapidly through channel networks and over alluvial fans, where they can devastate people and property. Episodic shifts in the position of a debris-flow channel, termed avulsions, are critical for debris-flow fan evolution and for

  15. Response of steelhead/rainbow trout (Oncorhynchus mykiss) populations to debris flows

    Science.gov (United States)

    Jason L. White; Bret C. Harvey

    2017-01-01

    To better understand the effects of debris flows on salmonid populations, we studied juvenile steelhead/rainbow trout (Oncorhynchus mykiss) populations in six streams in the Klamath Mountains of northern California: three affected by debris flows on 01 January 1997 and three that experienced elevated streamflows but no debris flows. We surveyed...

  16. Debris flows through different forest age classes in the central Oregon Coast Range

    Science.gov (United States)

    C. L. May

    2002-01-01

    Abstract - Debris flows in the Pacific Northwest can play a major role in routing sediment and wood stored on hillslopes and in first- through third-order channels and delivering it to higher-order channels. Field surveys following a large regional storm event investigated 53 debris flows in the central Oregon Coast Range to determine relationships among debris flow...

  17. Effects of debris flow composition on runout, depositional mechanisms, and deposit morphology in laboratory experiments

    NARCIS (Netherlands)

    de Haas, Tjalling; Braat, Lisanne; Leuven, Jasper R F W; Lokhorst, Ivar R.; Kleinhans, Maarten G.

    Predicting debris flow runout is of major importance for hazard mitigation. Apart from topography and volume, runout distance and area depends on debris flow composition and rheology, but how is poorly understood. We experimentally investigated effects of composition on debris flow runout,

  18. Experimental study on the rheological behaviour of debris flow

    Directory of Open Access Journals (Sweden)

    A. Scotto di Santolo

    2010-12-01

    Full Text Available A model able to describe all the processes involved in a debris flow can be very complex owing to the sudden changing of the material that turns from solid into liquid state. The two phases of the phenomenon are analysed separately referring to soil mechanics procedures with regard to the trigger phase, and to an equivalent fluid for the post-failure phase. The present paper is devoted to show the experimental results carried out to evaluate the behaviour assumed by a pyroclastic-derived soil during the flow. A traditional fluid tool has been utilized: a standard rotational rheometer equipped with two different geometries. The soils tested belong to deposits that cover the slopes of the Campania region, Italy, often affected by debris flows. The influence of solid concentration Cv and grain size distribution was tested: the soils were destructurated, sieved and mixed with water starting from the in situ porosity. All material mixtures showed a non-Newtonian fluid behaviour with a yield stress τy that increases with a solid volumetric concentration and decreases for an increase of sand fraction. The experimental data were fitted with standard model for fluids. A simple relation between Cv and τy was obtained. The yield stress seems to be a key parameter for describing and predicting the post-failure behaviour of debris flows. These results suggest that in the field a small change in solid fraction, due to rainfall, will cause a slight decrease of the static yield stress, readily inducing a rapid flow which will stop only when the dynamic yield stress is reached, namely on a much smoother slope. This can explain the in situ observed post-failure behaviour of debris flows, which are able to flow over very long distances even on smooth slopes.

  19. Debris flow runup on vertical barriers and adverse slopes

    Science.gov (United States)

    Iverson, Richard M.; George, David L.; Logan, Matthew

    2016-01-01

    Runup of debris flows against obstacles in their paths is a complex process that involves profound flow deceleration and redirection. We investigate the dynamics and predictability of runup by comparing results from large-scale laboratory experiments, four simple analytical models, and a depth-integrated numerical model (D-Claw). The experiments and numerical simulations reveal the important influence of unsteady, multidimensional flow on runup, and the analytical models highlight key aspects of the underlying physics. Runup against a vertical barrier normal to the flow path is dominated by rapid development of a shock, or jump in flow height, associated with abrupt deceleration of the flow front. By contrast, runup on sloping obstacles is initially dominated by a smooth flux of mass and momentum from the flow body to the flow front, which precedes shock development and commonly increases the runup height. D-Claw simulations that account for the emergence of shocks show that predicted runup heights vary systematically with the adverse slope angle and also with the Froude number and degree of liquefaction (or effective basal friction) of incoming flows. They additionally clarify the strengths and limitations of simplified analytical models. Numerical simulations based on a priori knowledge of the evolving dynamics of incoming flows yield quite accurate runup predictions. Less predictive accuracy is attained in ab initio simulations that compute runup based solely on knowledge of static debris properties in a distant debris flow source area. Nevertheless, the paucity of inputs required in ab initio simulations enhances their prospective value in runup forecasting.

  20. Evaluating Voellmy resistance parameters for debris-flow simulation models

    Science.gov (United States)

    Schraml, Klaus; McArdell, Brian; Graf, Christoph; Thomschitz, Barbara; Kaitna, Roland

    2014-05-01

    Gravitationally-driven processes such as debris flows constitute a major risk in alpine regions. In order to avoid damages on infrastructure and settlements, the delineation of hazardous areas is required. For this, numerical simulation tools are often applied for use in engineering hazard assessment. For model calibration, information on past events provides a basis to estimate or constrain the essential input parameters. In this study we used two numerical simulation models for evaluating model friction parameters to best-fit runout lengths and deposition patterns of observed past debris-flow events on two alpine fans in Austria with flow deposit volumes of 10,000 m³ and 25,000 m³, respectively. The RAMMS-DF (RApid Mass MovementS - Debris Flow) runout model is based on a Voellmy-type relation to describe the flow friction, and the software DAN3D (Dynamic Analysis of Landslides) allows selecting different rheologies, including a Voellmy-type friction relation. All calculations were based on the same digital elevation model with a 1 m resolution and the same initial conditions. Our results show that both models are able to satisfactorily replicate observed deposition patterns. The best-fit parameter sets of the Voellmy-Coulomb friction coefficient and turbulent coefficient for both study sites and both simulation models were in the range of 0.07-0.11 and 200-400, respectively. In case the deposition area is forested, the Coulomb friction parameter was considerably increased by a factor of around 3 to account for additional surface roughness. A sensitivity analysis shows a slightly higher sensitivity of model parameters for the DAN3D model than for the RAMMS-DF model. This study contributes to the evaluation of realistic model parameters for the simulation of small alpine debris flows on forested and non-forested fans.

  1. Internal characteristics of refractive-index matched debris flows

    Science.gov (United States)

    Gollin, Devis; Bowman, Elisabeth; Sanvitale, Nicoletta

    2016-04-01

    Debris flows are channelized masses of granular material saturated with water that travel at high speeds downslope. Their destructive character represents a hazard to lives and properties, especially in regions of high relief and runoff. The characteristics that distinguish their heterogeneous, multi-phase, nature are numerous: non-uniform surge formation, particle size ranging from clay to boulders, flow segregation with larger particles concentrating at the flow front and fluid at the tail making the composition and volume of the bulk varying with time and space. These aspects render these events very difficult to characterise and predict, in particular in the area of the deposit spread or runout - zones which are generally of most interest in terms of human risk. At present, considerable gaps exist in our understanding of the flow dynamics of debris flows, which originates from their complex motion and relatively poor observations available. Flume studies offer the potential to examine in detail the behaviour of model debris flows, however, the opaque nature of these flows is a major obstacle in gaining insight of their internal behaviour. Measurements taken at the sidewalls may be poorly representative leading to incomplete or misleading results. To probe internally to the bulk of the flow, alternative, nonintrusive techniques can be used, enabling, for instance, velocities and solid concentrations within the flowing material to be determined. We present experimental investigations into polydisperse granular flows of spherical immersed particles down an inclined flume, with specific attention directed to their internal behavior. To this end, the refractive indices of solids and liquid are closely matched allowing the two phases to be distinguished. Measurements are then made internally at a point in the channel via Plane Laser Induced Fluorescence, Particle Tracking Velocimetry, PTV and Particle Image Velocimetry, PIV. The objective is to to increase our

  2. On debris flows, river networks, and the spatial structure of channel morphology.

    Science.gov (United States)

    P.E. Bigelow; L.E. Benda; D.J. Miller; K.M. Burnett

    2007-01-01

    In this paper, we examine the influence of debris-flow deposits and fans on channels and habitat characteristics in small to intermediate-size watersheds in the Oregon Coast Range. We evaluate: (1) the proportion of stream length bordered by debris fans and the spacing between fans, (2) the recurrence interval of debris flows in unmanaged watersheds, (3) the proportion...

  3. Unravelling the evolution and avulsion mechanisms of debris-flow fans

    Science.gov (United States)

    de Haas, Tjalling; Densmore, Alex; Stoffel, Markus; Ballesteros-Cánovas, Juan; Suwa, Hiroshi; Imaizumi, Fumitoshi; Wasklewicz, Thad

    2017-04-01

    Debris flows are water-laden masses of soil and fragmented rock that rush down mountainsides and spill out onto valley floors and alluvial fans, where they can devastate people and property. Expansion of human population into mountainous regions and the effects of global warming have increased the hazardous effects of debris flows over the last decades. Debris-flow channel avulsions (channel shifts) are critical to debris-flow fan evolution and hazard mitigation, because avulsions distribute debris flows and associated hazards through space and time. However, both the long-term evolution of debris-flow fans and their avulsion process are poorly understood. We aim to unravel the spatio-temporal patterns of debris-flow fan evolution and their avulsion mechanisms and tendency. Here we present a combined analysis of laboratory experiments; field data (repeat topographic analyses and dendrogeomorphological and lichenometrical reconstructions from debris-flow fans in Japan, USA, Switserland and France) and numerical modelling, identifying the main drivers of avulsion on debris-flow fans and their associated spatio-temporal evolution. We show that there are two main processes driving avulsions on debris-flow fans operating at two distinct timescales. (1) Channel plugs locally block channels forcing subsequent flows to avulse and follow alternative flow paths. The frequent but stochastic nature of channel-plug formation leads to a partly unpredictable avulsion and spatial depositional patterns on timescales of a few events. (2) Nevertheless, over timescales of tens of events the average locus of debris-flow deposition is observed to gradually shift towards the topographically lower parts of a fan, highlighting the importance of topographic compensation in the avulsion process on debris-flow fans. We further show that the magnitude-frequency distribution of the debris flows feeding a fan strongly affects the spatio-temporal patterns of deposition. Our results have strong

  4. A comparative assessment of two different debris flow propagation approaches - blind simulations on a real debris flow event

    Science.gov (United States)

    Stancanelli, L. M.; Foti, E.

    2015-04-01

    A detailed comparison between the performances of two different approaches to debris flow modelling was carried out. In particular, the results of a mono-phase Bingham model (FLO-2D) and that of a two-phase model (TRENT-2D) obtained from a blind test were compared. As a benchmark test the catastrophic event of 1 October 2009 which struck Sicily causing several fatalities and damage was chosen. The predicted temporal evolution of several parameters of the debris flow (such as flow depth and propagation velocity) was analysed in order to investigate the advantages and disadvantages of the two models in reproducing the global dynamics of the event. An analysis between the models' results with survey data have been carried out, not only for the determination of statistical indicators of prediction accuracy, but also for the application of the Receiver Operator Characteristic (ROC) approach. Provided that the proper rheological parameters and boundary conditions are assigned, both models seem capable of reproducing the inundation areas in a reasonably accurate way. However, the main differences in the application rely on the choice of such rheological parameters. Indeed, within the more user-friendly FLO-2D model the tuning of the parameters must be done empirically, with no evidence of the physics of the phenomena. On the other hand, for the TRENT-2D the parameters are physically based and can be estimated from the properties of the solid material, thus reproducing more reliable results. A second important difference between the two models is that in the first method the debris flow is treated as a homogeneous flow, in which the total mass is kept constant from its initiation in the upper part of the basin to the deposition in a debris fan. In contrast, the second approach is suited to reproduce the erosion and deposition processes and the displaced mass can be directly related to the rainfall event. Application of both models in a highly urbanized area reveals the

  5. Numerical Simulation of Real Debris-Flow Events

    Science.gov (United States)

    Fraccarollo, L.; Papa, M.

    2000-09-01

    A one-dimensional model is presented to predict debris-flow runouts. The model is based on shallow water type assumptions. The fluid is assumed to be homogeneous and the original bed of the flow domain to be unerodible. The fluid is characterized by a rheology of Bingham type. A numerical tool able to cope with the nature of debris flows has been worked out. It represents an extension of a second order accurate and conservative method of Godunov type. Special care has been devoted to the influence of the source terms and of the geometrical representation of the natural cross sections, which play a fundamental role. The application concerns a monitored event in the Dolomites in Italy, where field analyses allowed a characterization of the behavior of solid-liquid mixture as a yield stress material. The comparison between numerical simulations and field observations highlights the impossibility of representing all phases of the flow with constant values of the rheological parameters. Nevertheless the results show that it is possible to separately represent the phase of the flow in the upstream reach and the phase of the deposition in the alluvial fan, with a good agreement with field observations.

  6. Debris flow occurrence and sediment persistence, Upper Colorado River Valley, CO

    Science.gov (United States)

    Grimsley, Kyle J; Rathburn, Sara L.; Friedman, Jonathan M.; Mangano, Joseph F.

    2016-01-01

    Debris flow magnitudes and frequencies are compared across the Upper Colorado River valley to assess influences on debris flow occurrence and to evaluate valley geometry effects on sediment persistence. Dendrochronology, field mapping, and aerial photographic analysis are used to evaluate whether a 19th century earthen, water-conveyance ditch has altered the regime of debris flow occurrence in the Colorado River headwaters. Identifying any shifts in disturbance processes or changes in magnitudes and frequencies of occurrence is fundamental to establishing the historical range of variability (HRV) at the site. We found no substantial difference in frequency of debris flows cataloged at eleven sites of deposition between the east (8) and west (11) sides of the Colorado River valley over the last century, but four of the five largest debris flows originated on the west side of the valley in association with the earthen ditch, while the fifth is on a steep hillslope of hydrothermally altered rock on the east side. These results suggest that the ditch has altered the regime of debris flow activity in the Colorado River headwaters as compared to HRV by increasing the frequency of debris flows large enough to reach the Colorado River valley. Valley confinement is a dominant control on response to debris flows, influencing volumes of aggradation and persistence of debris flow deposits. Large, frequent debris flows, exceeding HRV, create persistent effects due to valley geometry and geomorphic setting conducive to sediment storage that are easily delineated by valley confinement ratios which are useful to land managers.

  7. Debris Flow Occurrence and Sediment Persistence, Upper Colorado River Valley, CO.

    Science.gov (United States)

    Grimsley, K J; Rathburn, S L; Friedman, J M; Mangano, J F

    2016-07-01

    Debris flow magnitudes and frequencies are compared across the Upper Colorado River valley to assess influences on debris flow occurrence and to evaluate valley geometry effects on sediment persistence. Dendrochronology, field mapping, and aerial photographic analysis are used to evaluate whether a 19th century earthen, water-conveyance ditch has altered the regime of debris flow occurrence in the Colorado River headwaters. Identifying any shifts in disturbance processes or changes in magnitudes and frequencies of occurrence is fundamental to establishing the historical range of variability (HRV) at the site. We found no substantial difference in frequency of debris flows cataloged at eleven sites of deposition between the east (8) and west (11) sides of the Colorado River valley over the last century, but four of the five largest debris flows originated on the west side of the valley in association with the earthen ditch, while the fifth is on a steep hillslope of hydrothermally altered rock on the east side. These results suggest that the ditch has altered the regime of debris flow activity in the Colorado River headwaters as compared to HRV by increasing the frequency of debris flows large enough to reach the Colorado River valley. Valley confinement is a dominant control on response to debris flows, influencing volumes of aggradation and persistence of debris flow deposits. Large, frequent debris flows, exceeding HRV, create persistent effects due to valley geometry and geomorphic setting conducive to sediment storage that are easily delineated by valley confinement ratios which are useful to land managers.

  8. The importance of entrainment and bulking on debris flow runout modeling: examples from the Swiss Alps

    OpenAIRE

    Frank, F.; McArdell, B. W.; Huggel, C.; A. Vieli

    2015-01-01

    This study describes an investigation of channel-bed entrainment of sediment by debris flows. An entrainment model, developed using field data from debris flows at the Illgraben catchment, Switzerland, was incorporated into the existing RAMMS debris-flow model, which solves the 2-D shallow-water equations for granular flows. In the entrainment model, an empirical relationship between maximum shear stress and measured erosion is used to determine the maximum potential erosion depth. Additional...

  9. Modeling of debris flow depositional patterns according to the catchment and sediment source area characteristics

    OpenAIRE

    Tiranti, Davide; Deangeli, Chiara

    2015-01-01

    A method to predict the most probable flow rheology in Alpine debris flows is presented. The methods classifies outcropping rock masses in catchments on the basis of the type of resulting unconsolidated deposits. The grain size distribution of the debris material and the depositional style of past debris flow events are related to the dominant flow processes: viscoplastic and frictional/collisional. Three catchments in the upper Susa Valley (Western Alps), characterized by different lithologi...

  10. The importance of erosion for debris flow runout modelling from applications to the Swiss Alps

    OpenAIRE

    Frank, F.; McArdell, B. W.; Huggel, C.; A. Vieli

    2015-01-01

    This study describes an investigation of channel-bed erosion of sediment by debris flows. An erosion model, developed using field data from debris flows at the Illgraben catchment, Switzerland, was incorporated into the existing RAMMS debris-flow model, which solves the 2-D shallow-water equations for granular flows. In the erosion model, the relationship between maximum shear stress and measured erosion is used to determine the maximum potential erosion depth. Additionally,...

  11. Critical Rainfall Conditions Triggering Shallow Landslides or Debris Flows in Torrents - Analysis of Debris Flow events 2012, 2013 and 2014 in Austria

    Science.gov (United States)

    Moser, Markus; Mehlhorn, Susanne; Janu, Stefan

    2015-04-01

    Generally, debris flows are caused by both small-scale intensive precipitation and long lasting rainfalls with lower intensity but high pre-wetting or both combined. The triggering mechanism of the debris flow events in Austria 2012, 2013 and 2014 were mass movements (rapid shallow landslides) on steep slopes in the upper catchments. Those masses slide with very high velocity into the torrent beds provoking hyperconcentrated flows or debris flows. In areas of the geologically unstable Greywacke zone, the torrents were cleared up onto the bedrock and the debris was deposited in the storage areas of existing debris flow breakers or in torrents without technical protection measures the debris caused catastrophic damage to residential buildings and other infrastructural facilities on the alluvial fan. Following the events, comprehensive documentation work was undertaken comprising precipitation analysis (rainfall data, weather radar data), identification and quantification of the landslide masses, cross profiles along the channel and of deposition in the storage areas or on the fan. The documentation and analysis of torrential events is an essential part of an integrated risk management. It supports the understanding of the occurred processes to mitigate future hazards. Unfortunately, the small-scale heavy rain events are not detected by the precipitation stations. Therefore, weather radar data (INCA-Data) analysis was used to determine the - usually very local - intensities which caused those catastrophic landslides and debris flows. Analysis results showed an agreement with the range of the previously known precipitation thresholds for debris flow triggering in the Alps.

  12. Effects of wood on debris flow runout in small mountain watersheds.

    Science.gov (United States)

    Stephen T. Lancaster; Shannon K. Hayes

    2003-01-01

    Debris flows have typically been viewed as two-phase mixtures of sediment and water, but in forested mountain landscapes, wood can represent a sizable fraction of total flow volume. The effects of this third phase on flow behavior are poorly understood. To evaluate whether wood can have a significant effect on debris flow runout in small mountainous watersheds, we used...

  13. Scaling up debris-flow experiments on a centrifuge

    Science.gov (United States)

    Hung, C.; Capart, H.; Crone, T. J.; Grinspum, E.; Hsu, L.; Kaufman, D.; Li, L.; Ling, H.; Reitz, M. D.; Smith, B.; Stark, C. P.

    2013-12-01

    Boundary forces generated by debris flows can be powerful enough to erode bedrock and cause considerable damage to infrastructure during runout. Formulation of an erosion-rate law for debris flows is therefore a high priority, and it makes sense to build such a law around laboratory experiments. However, running experiments big enough to generate realistic boundary forces is a logistical challenge to say the least [1]. One alternative is to run table-top simulations with unnaturally weak but fast-eroding pseudo-bedrock, another is to extrapolate from micro-erosion of natural substrates driven by unnaturally weak impacts; hybrid-scale experiments have also been conducted [2]. Here we take a different approach in which we scale up granular impact forces by running our experiments under enhanced gravity in a geotechnical centrifuge [3]. Using a 40cm-diameter rotating drum [2] spun at up to 100g, we generate debris flows with an effective depth of over several meters. By varying effective gravity from 1g to 100g we explore the scaling of granular flow forces and the consequent bed and wall erosion rates. The velocity and density structure of these granular flows is monitored using laser sheets, high-speed video, and particle tracking [4], and the progressive erosion of the boundary surfaces is measured by laser scanning. The force structures and their fluctuations within the granular mass and at the boundaries are explored with contact dynamics numerical simulations that mimic the lab experimental conditions [5]. In this presentation we summarize these results and discuss how they can contribute to the formulation of debris-flow erosion law. [1] Major, J. J. (1997), Journal of Geology 105: 345-366, doi:10.1086/515930 [2] Hsu, L. (2010), Ph.D. thesis, University of California, Berkeley [3] Brucks, A., et al (2007), Physical Review E 75, 032301, doi:10.1103/PhysRevE.75.032301 [4] Spinewine, B., et al (2011), Experiments in Fluids 50: 1507-1525, doi: 10.1007/s00348

  14. Dynamic Modelling of Erosion and Deposition Processes in Debris Flows With Application to Real Debris Flow Events in Switzerland

    Science.gov (United States)

    Deubelbeiss, Y.; McArdell, B. W.; Graf, C.

    2011-12-01

    The dynamics of a debris flow can be significantly influenced by erosion and deposition processes during an event because volume changes have a strong influence on flow properties such as flow velocity, flow heights and runout distances. It is therefore worth exploring how to include these processes in numerical models, which are used for hazard assessment and mitigation measure planning. However, it is still under debate, what mechanism drives the erosion of material at the base of a debris flow. There are different processes attributed to erosion: it has been proposed that erosion correlates with the stresses due to granular interactions at the front, which in turn strongly depend on particle size or it may be related to basal shear forces. Because it is expected that larger flow heights result in larger stresses one can additionally hypothesize that there is a correlation between erosion rate and flow height. To test different erosion laws in a numerical model and its influence on the flow behavior we implement different relationships and compare simulation results with field data. Herefore, we use the numerical model, RAMMS (Christen et al., 2010), employing the Voellmy-fluid friction law. While it has already been shown that a correlation of erosion with velocity does not lead to a satisfying result (too high entrainment in the tail) a correlation with flow height combined with velocity (momentum) has been successfully applied to ice-avalanches. Currently, we are testing the momentum-driven and for comparison we reconsider the simple velocity-driven erosion rate. However, these laws do not consider processes on a smaller scale such as particle fluctuations resulting in energy production, which might play an important role. Therefore, we additionally consider an erosion model that has potential to draw new insights on the erosion process in debris flows. The model is based on an extended Voellmy model, which additionally employs an equation, which is a measure

  15. Study of pore fluid effect on the mobility of granular debris flows

    Science.gov (United States)

    Zhou, Gordon G. D.; Sun, Q. C.

    2017-06-01

    Granular debris flows in nature are composed of a wide range of solids and viscous pore fluids, moving at high velocities down sloping channels. The pore fluids in a granular debris flow affect the interactions between the solid and fluid phases and thus govern the debris-flow mobility. Study of the pore fluid effect (i.e., excess pore water pressures correlated to solid structures, and the viscous shearing and dragging) is essential for understanding the high flow mobility of granular debris flows. This study critically reviews two dimensionless numbers with clear physical meanings, then demonstrates a new application of field monitoring data for identifying natural debris flows on large scales (i.e., surge and continuous debris-flows, respectively). This study illustrates that, the pore fluid viscous shearing stress dominates solid inertial stress due to solids collision. It is also found that different to continuous debris-flows, the high pore fluid pressures generated in surge debris-flow body dissipate quite slowly and mostly influence particle contact behaviour significantly. A new scientific criterion for identification of continuous and surge debris flow in nature can be given by this study.

  16. Field measurement of basal forces generated by erosive debris flows

    Science.gov (United States)

    McCoy, S.W.; Tucker, G.E.; Kean, J.W.; Coe, J.A.

    2013-01-01

    It has been proposed that debris flows cut bedrock valleys in steeplands worldwide, but field measurements needed to constrain mechanistic models of this process remain sparse due to the difficulty of instrumenting natural flows. Here we present and analyze measurements made using an automated sensor network, erosion bolts, and a 15.24 cm by 15.24 cm force plate installed in the bedrock channel floor of a steep catchment. These measurements allow us to quantify the distribution of basal forces from natural debris‒flow events that incised bedrock. Over the 4 year monitoring period, 11 debris‒flow events scoured the bedrock channel floor. No clear water flows were observed. Measurements of erosion bolts at the beginning and end of the study indicated that the bedrock channel floor was lowered by 36 to 64 mm. The basal force during these erosive debris‒flow events had a large‒magnitude (up to 21 kN, which was approximately 50 times larger than the concurrent time‒averaged mean force), high‒frequency (greater than 1 Hz) fluctuating component. We interpret these fluctuations as flow particles impacting the bed. The resulting variability in force magnitude increased linearly with the time‒averaged mean basal force. Probability density functions of basal normal forces were consistent with a generalized Pareto distribution, rather than the exponential distribution that is commonly found in experimental and simulated monodispersed granular flows and which has a lower probability of large forces. When the bed sediment thickness covering the force plate was greater than ~ 20 times the median bed sediment grain size, no significant fluctuations about the time‒averaged mean force were measured, indicating that a thin layer of sediment (~ 5 cm in the monitored cases) can effectively shield the subjacent bed from erosive impacts. Coarse‒grained granular surges and water‒rich, intersurge flow had very similar basal force distributions despite

  17. Hazard Assessment of Debris Flows in the Reservoir Region of Wudongde Hydropower Station in China

    OpenAIRE

    Cencen Niu; Qing Wang; Jianping Chen; Wen Zhang; Liming Xu; Ke Wang

    2015-01-01

    The outbreak of debris flows in a reservoir region can affect the stability of hydropower stations and threaten the lives of the people living downstream of dams. Therefore, determining the hazard degree of debris flows in a reservoir region is of great importance. SPOT5 remote sensing images and digital elevation models are introduced to determine the characteristics of debris-flow catchments. The information is acquired through comprehensive manual investigation and satellite image interpre...

  18. Debris flows in the eastern Italian Alps: seasonality and atmospheric circulation patterns

    OpenAIRE

    E. I. Nikolopoulos; M. Borga; Marra, F.; Crema, S.; Marchi, L.

    2015-01-01

    The work examines the seasonality and large-scale atmospheric circulation patterns associated with debris-flow occurrence in the Trentino–Alto Adige region (eastern Italian Alps). Analysis is based on classification algorithms applied to a uniquely dense archive of debris flows and hourly rain gauge precipitation series covering the period 2000–2009. Results highlight the seasonal and synoptic forcing patterns linked to debris flows in the study area. Summer and fall season ...

  19. Debris flow hazard modelling on medium scale: Valtellina di Tirano, Italy

    OpenAIRE

    Blahut, J.; P. Horton; Sterlacchini, S.; Jaboyedoff, M.

    2010-01-01

    Debris flow hazard modelling at medium (regional) scale has been subject of various studies in recent years. In this study, hazard zonation was carried out, incorporating information about debris flow initiation probability (spatial and temporal), and the delimitation of the potential runout areas. Debris flow hazard zonation was carried out in the area of the Consortium of Mountain Municipalities of Valtellina di Tirano (Central Alps, Italy). The complexity of the phenomenon, the scale of th...

  20. Instrumental record of debris flow initiation during natural rainfall: Implications for modeling slope stability

    Science.gov (United States)

    David R. Montgomery; Kevin M. Schmidt; William E. Dietrich; Jim. McKean

    2009-01-01

    The middle of a hillslope hollow in the Oregon Coast Range failed and mobilized as a debris flow during heavy rainfall in November 1996. Automated pressure transducers recorded high spatial variability of pore water pressure within the area that mobilized as a debris flow, which initiated where local upward flow from bedrock developed into overlying colluvium....

  1. Influence of rheology on debris-flow simulation

    Directory of Open Access Journals (Sweden)

    M. Arattano

    2006-01-01

    Full Text Available Systems of partial differential equations that include the momentum and the mass conservation equations are commonly used for the simulation of debris flow initiation, propagation and deposition both in field and in laboratory research. The numerical solution of the partial differential equations can be very complicated and consequently many approximations that neglect some of their terms have been proposed in literature. Many numerical methods have been also developed to solve the equations. However we show in this paper that the choice of a reliable rheological model can be more important than the choice of the best approximation or the best numerical method to employ. A simulation of a debris flow event that occurred in 2004 in an experimental basin on the Italian Alps has been carried out to investigate this issue. The simulated results have been compared with the hydrographs recorded during the event. The rheological parameters that have been obtained through the calibration of the mathematical model have been also compared with the rheological parameters obtained through the calibration of previous events, occurred in the same basin. The simulation results show that the influence of the inertial terms of the Saint-Venant equation is much more negligible than the influence of the rheological parameters and the geometry. A methodology to quantify this influence has been proposed.

  2. Headwater sediment dynamics in a debris flow catchment constrained by high-resolution topographic surveys

    Science.gov (United States)

    Loye, Alexandre; Jaboyedoff, Michel; Theule, Joshua Isaac; Liébault, Frédéric

    2016-06-01

    Debris flows have been recognized to be linked to the amounts of material temporarily stored in torrent channels. Hence, sediment supply and storage changes from low-order channels of the Manival catchment, a small tributary valley with an active torrent system located exclusively in sedimentary rocks of the Chartreuse Massif (French Alps), were surveyed periodically for 16 months using terrestrial laser scanning (TLS) to study the coupling between sediment dynamics and torrent responses in terms of debris flow events, which occurred twice during the monitoring period. Sediment transfer in the main torrent was monitored with cross-section surveys. Sediment budgets were generated seasonally using sequential TLS data differencing and morphological extrapolations. Debris production depends strongly on rockfall occurring during the winter-early spring season, following a power law distribution for volumes of rockfall events above 0.1 m3, while hillslope sediment reworking dominates debris recharge in spring and autumn, which shows effective hillslope-channel coupling. The occurrence of both debris flow events that occurred during the monitoring was linked to recharge from previous debris pulses coming from the hillside and from bedload transfer. Headwater debris sources display an ambiguous behaviour in sediment transfer: low geomorphic activity occurred in the production zone, despite rainstorms inducing debris flows in the torrent; still, a general reactivation of sediment transport in headwater channels was observed in autumn without new debris supply, suggesting that the stored debris was not exhausted. The seasonal cycle of sediment yield seems to depend not only on debris supply and runoff (flow capacity) but also on geomorphic conditions that destabilize remnant debris stocks. This study shows that monitoring the changes within a torrent's in-channel storage and its debris supply can improve knowledge on recharge thresholds leading to debris flow.

  3. The origins of Late Quaternary debris avalanche and debris flow deposits from Cofre de Perote volcano, México

    Science.gov (United States)

    Diaz-Castellon, Rodolfo; Hubbard, Bernard E.; Carrasco-Nunez, Gerardo; Rodríguez-Vargas, José Luis

    2012-01-01

    Cofre de Perote volcano is a compound, shield-like volcano located in the northeastern Trans-Mexican volcanic belt. Large debris avalanche and lahar deposits are associated with the evolution of Cofre. The two best preserved of these debris-avalanche and debris-flow deposits are the ∼42 ka “Los Pescados debris flow” deposit and the ∼11–13 ka “Xico avalanche” deposit, both of which display contrasting morphological and textural characteristics, source materials, origins and emplacement environments. Laboratory X-ray diffraction and visible-infrared reflectance spectroscopy were used to identify the most abundant clay, sulfate, ferric-iron, and silica minerals in the deposits, which were either related to hydrothermal alteration or chemical weathering processes. Cloud-free Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing imagery, supporting EO-1 Hyperion image spectra, and field ground truth samples were used to map the mineralogy and distribution of hydrothermally altered rocks on the modern summit of Cofre de Perote. The results were then compared to minerals identified in the two debris-avalanche and debris-flow deposits in order to assess possible source materials and origins for the two deposits.The older Los Pescados debris-flow deposit contains mostly halloysite and hydrous silica minerals, which match the dominant mineralogy of soils and weathered volcanic deposit in the surrounding flanks of Cofre de Perote. Its source materials were most likely derived from initially noncohesive or clay-poor flows, which subsequently bulked with clay-rich valley soils and alluvium in a manner similar to lahars from Nevado del Ruiz in 1985, but on a larger scale. The younger Xico avalanche deposit contains abundant smectite, jarosite, kaolinite, gypsum, and mixed-layered illite/smectite, which are either definitely or most likely of hydrothermal alteration origin. Smectite in particular appears to be the most abundant and

  4. A combined triggering-propagation modeling approach for the assessment of rainfall induced debris flow susceptibility

    Science.gov (United States)

    Stancanelli, Laura Maria; Peres, David Johnny; Cancelliere, Antonino; Foti, Enrico

    2017-07-01

    Rainfall-induced shallow slides can evolve into debris flows that move rapidly downstream with devastating consequences. Mapping the susceptibility to debris flow is an important aid for risk mitigation. We propose a novel practical approach to derive debris flow inundation maps useful for susceptibility assessment, that is based on the integrated use of DEM-based spatially-distributed hydrological and slope stability models with debris flow propagation models. More specifically, the TRIGRS infiltration and infinite slope stability model and the FLO-2D model for the simulation of the related debris flow propagation and deposition are combined. An empirical instability-to-debris flow triggering threshold calibrated on the basis of observed events, is applied to link the two models and to accomplish the task of determining the amount of unstable mass that develops as a debris flow. Calibration of the proposed methodology is carried out based on real data of the debris flow event occurred on 1 October 2009, in the Peloritani mountains area (Italy). Model performance, assessed by receiver-operating-characteristics (ROC) indexes, evidences fairly good reproduction of the observed event. Comparison with the performance of the traditional debris flow modeling procedure, in which sediment and water hydrographs are inputed as lumped at selected points on top of the streams, is also performed, in order to assess quantitatively the limitations of such commonly applied approach. Results show that the proposed method, besides of being more process-consistent than the traditional hydrograph-based approach, can potentially provide a more accurate simulation of debris-flow phenomena, in terms of spatial patterns of erosion and deposition as well on the quantification of mobilized volumes and depths, avoiding overestimation of debris flow triggering volume and, thus, of maximum inundation flow depths.

  5. Timing of susceptibility to post-fire debris flows in the western USA

    Science.gov (United States)

    DeGraff, Jerome V.; Cannon, Susan H.; Gartner, Joseph E.

    2015-01-01

    Watersheds recently burned by wildfires can have an increased susceptibility to debris flow, although little is known about how long this susceptibility persists, and how it changes over time. We here use a compilation of 75 debris-flow response and fire-ignition dates, vegetation and bedrock class, rainfall regime, and initiation process from throughout the western U.S. to address these issues. The great majority (85 percent) of debris flows occurred within the first 12 months following wildfire, with 71 percent within the first six months. Seven percent of the debris flows occurred between 1 and 1.5 years after a fire, or during the second rainy season to impact an area. Within the first 1.5 years following fires, all but one of the debris flows initiated through runoff-dominated processes, and debris flows occurred in similar proportions in forested and non-forested landscapes. Geologic materials affected how long debris-flow activity persisted, and the timing of debris flows varied within different rainfall regimes. A second, later period of increased debris flow susceptibility between 2.2 and 10 years after fires is indicated by the remaining 8 percent of events, which occurred primarily in forested terrains and initiated largely through landslide processes. The short time period between fire and debris-flow response within the first 1.5 years after ignition, and the longer-term response between 2.2 and 10 years after fire, demonstrate the necessity of both rapid and long-term reactions by land managers and emergency-response agencies to mitigate hazards from debris flows from recently burned areas in the western U.S.

  6. Development and maintenance of a telescoping debris flow fan in response to human-induced fan surface channelization, Chalk Creek Valley Natural Debris Flow Laboratory, Colorado, USA

    Science.gov (United States)

    Wasklewicz, T.; Scheinert, C.

    2016-01-01

    Channel change has been a constant theme throughout William L. Graf's research career. Graf's work has examined channel changes in the context of natural environmental fluctuations, but more often has focused on quantifying channel change in the context of anthropogenic modifications. Here, we consider how channelization of a debris flows along a bajada has perpetuated and sustained the development of 'telescoping' alluvial fan. Two-dimensional debris-flow modeling shows the importance of the deeply entrenched channelized flow in the development of a telescoping alluvial fan. GIS analyses of repeat (five different debris flows), high-resolution (5 cm) digital elevation models (DEMs) generated from repeat terrestrial laser scanning (TLS) data elucidate sediment and topographic dynamics of the new telescoping portion of the alluvial fan (the embryonic fan). Flow constriction from channelization helps to perpetuate debris-flow runout and to maintain the embryonic fan and telescoping nature of the alluvial fan complex. Embryonic fan development, in response to five debris flows, proceeds with a major portion of the flows depositing on the southern portion of the embryonic fan. The third through the fifth debris flows also begin to shift some deposition to the northern portion of the embryonic. The transfer of sediment from a higher portion of the embryonic fan to a lower portion continues currently on the embryonic fan. While channelized flow has been shown to be critical to the maintenance of the telescoping fan, the flow constriction has led to higher than background levels of sediment deposition in Chalk Creek, a tributary of the Arkansas River. A majority of the sediment from each debris flow is incorporated into Chalk Creek as opposed to being stored on the embryonic fan.

  7. Study on the Formation and Initial Transport for Non-Homogeneous Debris Flow

    Directory of Open Access Journals (Sweden)

    An Ping Shu

    2017-04-01

    Full Text Available Non-homogeneous debris flows generally occur during the rainy seasons in Southwest China, and have received considerable attention in the literature. Regarding the complexity in debris flow dynamics, experimental approaches have proven to be effective in revealing the formative mechanism for debris flow, and quantifying the relations between the various influencing factors with debris-flow formation and subsequent transport processes. Therefore, a flume-based and experimental study was performed at the Debris Flow Observation and Research Station of Jiangjia Gully in Yunnan Province, to theoretically analyze favorable conditions for debris-flow formation and initial transport by selecting the median particle size d50, flow rate Q, vertical grading coefficient ψ, slopes S, and the initial soil water contents W as the five variables for investigation. To achieve this, an optimal combination of these variables was made through an orthogonal experimental design to determine their relative importance upon the occurrence and initial mobilization behavior of a debris flow and to further enhance our insight into debris-flow triggering and transport mechanisms.

  8. Control works in debris-flow channels: influence on morphology and sediment transfer

    Science.gov (United States)

    Marchi, L.

    2012-04-01

    Extensive torrent control works, such as grade-control dams, debris basins, deflecting walls, etc. have been implemented in the European Alps since the last decades of 19th century. These structural measures, aimed at stabilizing channels and to control sediment transport, are also widespread in Japan and are increasingly present in other mountain regions. As debris flows are one of the most destructive processes in steep mountain channels, hydraulic works are often intended to attenuate debris-flow hazard. Multi-temporal aerial photos and historic records permit evaluating the long term effects of torrent control works on the morphological settings of the channels and the delivery of sediment. The experience arising from over one century of torrent control works in debris-flow channels of the Alps permits also to improve the management of steep headwater catchments. A basic issue in the management of debris-flow channels is the recognition of success versus failure of engineering control works. Successful debris-flow control works provide benchmarks for further implementations, whereas the failure in reducing debris-flow hazard may lead to refinements in planning and design of control works or to the choice of preferring non-structural measures for coping with debris flows. Data from historical archives on debris-flow occurrence and on the performance of control works are the basic sources of information for these analyses. Moreover, when dealing with hydraulic structures for debris-flow control, it should be reminded that the artificial morphology resulting from the construction of check dams provides only a temporary stability to the channel and adjacent banks. This stresses the importance of evaluating the state of conservation and the effectiveness of control works and implies the need for their careful and continuous maintenance. Inventories of hydraulic structures, coupled with detailed data on catchment and channel topography, sediment sources and supply

  9. Runoff-generated debris flows: observations and modeling of surge initiation, magnitude, and frequency

    Science.gov (United States)

    Kean, Jason W.; McCoy, Scott W.; Tucker, Gregory E.; Staley, Dennis M.; Coe, Jeffrey A.

    2013-01-01

    Runoff during intense rainstorms plays a major role in generating debris flows in many alpine areas and burned steeplands. Yet compared to debris flow initiation from shallow landslides, the mechanics by which runoff generates a debris flow are less understood. To better understand debris flow initiation by surface water runoff, we monitored flow stage and rainfall associated with debris flows in the headwaters of two small catchments: a bedrock-dominated alpine basin in central Colorado (0.06 km2) and a recently burned area in southern California (0.01 km2). We also obtained video footage of debris flow initiation and flow dynamics from three cameras at the Colorado site. Stage observations at both sites display distinct patterns in debris flow surge characteristics relative to rainfall intensity (I). We observe small, quasiperiodic surges at low I; large, quasiperiodic surges at intermediate I; and a single large surge followed by small-amplitude fluctuations about a more steady high flow at high I. Video observations of surge formation lead us to the hypothesis that these flow patterns are controlled by upstream variations in channel slope, in which low-gradient sections act as “sediment capacitors,” temporarily storing incoming bed load transported by water flow and periodically releasing the accumulated sediment as a debris flow surge. To explore this hypothesis, we develop a simple one-dimensional morphodynamic model of a sediment capacitor that consists of a system of coupled equations for water flow, bed load transport, slope stability, and mass flow. This model reproduces the essential patterns in surge magnitude and frequency with rainfall intensity observed at the two field sites and provides a new framework for predicting the runoff threshold for debris flow initiation in a burned or alpine setting.

  10. Catastrophic debris-flows: geological hazard and human influence

    Science.gov (United States)

    Del Ventisette, Chiara; Garfagnoli, Francesca; Ciampalini, Andrea; Battistini, Alessandro; Gigli, Giovanni; Moretti, Sandro; Casagli, Nicola

    2013-04-01

    Rainfall-induced landslides are widespread phenomena often affecting urbanized areas and causing intense damages and casualties. The management of the post-event phase requires a fast evaluation of the involved areas and triggering factors. The latter are fundamental to evaluate the stability of the area affected by landslides, in order to facilitate quick and safe activities of the Civil Protection Authorities during the emergency. On October 1st 2009, a prolonged and intense rainstorm triggered hundreds of landslides (predominantly debris flows) in an area of about 50 km2 in the north-eastern sector of Sicily (Italy). Debris flows swept the highest parts of many villages and passed over the SS114 state highway and the Messina-Catania railway, causing more than 30 fatalities. This work deals with the geological and hydro-geomorphological studies performed as a part of the post-disaster activities operated in collaboration with Civil Protection Authority, with the aim of examining landslides effects and mechanisms. The data were elaborated into a GIS platform, to evaluate the influence of urbanization on the drainage pattern and were correlated with the lithological and structural framework of the area. The case study of Giampilieri focuses the attention on the necessity of sustainable land use and reasonable urban management in areas characterized by a high hydrogeological hazard and on the tremendous destructive power of these phenomena, which are capable of causing a large number of victims in such small villages. Field surveys and stereo-photo geomorphological analysis revealed a significant human influence on determining landslide triggering causes, as well as the final amount of damage. In particular, destruction and injuries in the built-up area of Giampilieri were made even more severe by the main water flow lines made narrower due to building activity and enlargement of the urban area. The area maintains a high degree of hazard: deposits of poorly

  11. Influence of check dams on debris-flow run-out intensity

    Directory of Open Access Journals (Sweden)

    A. Remaître

    2008-12-01

    Full Text Available Debris flows are very dangerous phenomena claiming thousands of lives and millions of Euros each year over the world. Disaster mitigation includes non-structural (hazard mapping, insurance policies, active structural (drainage systems and passive structural (check dams, stilling basins countermeasures. Since over twenty years, many efforts are devoted by the scientific and engineering communities to the design of proper devices able to capture the debris-flow volume and/or break down the energy. If considerable theoretical and numerical work has been performed on the size, the shape and structure of check dams, allowing the definition of general design criteria, it is worth noting that less research has focused on the optimal location of these dams along the debris-flow pathway.

    In this paper, a methodological framework is proposed to evaluate the influence of the number and the location of the check dams on the reduction of the debris-flow intensity (in term of flow thickness, flow velocity and volume. A debris-flow model is used to simulate the run-out of the debris flow. The model uses the Janbu force diagram to resolve the force equilibrium equations; a bingham fluid rheology is introduced and represents the resistance term. The model has been calibrated on two muddy debris-flow events that occurred in 1996 and 2003 at the Faucon watershed (South French Alps.

    Influence of the check dams on the debris-flow intensity is quantified taking into account several check dams configurations (number and location as input geometrical parameters. Results indicate that debris-flow intensity is decreasing with the distance between the source area and the first check dams. The study demonstrates that a small number of check dams located near the source area may decrease substantially the debris-flow intensity on the alluvial fans.

  12. Linking rainfall-induced landslides with debris flows runout patterns towards catchment scale hazard assessment

    Science.gov (United States)

    Fan, Linfeng; Lehmann, Peter; McArdell, Brian; Or, Dani

    2017-03-01

    Debris flows and landslides induced by heavy rainfall represent an ubiquitous and destructive natural hazard in steep mountainous regions. For debris flows initiated by shallow landslides, the prediction of the resulting pathways and associated hazard is often hindered by uncertainty in determining initiation locations, volumes and mechanical state of the mobilized debris (and by model parameterization). We propose a framework for linking a simplified physically-based debris flow runout model with a novel Landslide Hydro-mechanical Triggering (LHT) model to obtain a coupled landslide-debris flow susceptibility and hazard assessment. We first compared the simplified debris flow model of Perla (1980) with a state-of-the art continuum-based model (RAMMS) and with an empirical model of Rickenmann (1999) at the catchment scale. The results indicate that predicted runout distances by the Perla model are in reasonable agreement with inventory measurements and with the other models. Predictions of localized shallow landslides by LHT model provides information on water content of released mass. To incorporate effects of water content and flow viscosity as provided by LHT on debris flow runout, we adapted the Perla model. The proposed integral link between landslide triggering susceptibility quantified by LHT and subsequent debris flow runout hazard calculation using the adapted Perla model provides a spatially and temporally resolved framework for real-time hazard assessment at the catchment scale or along critical infrastructure (roads, railroad lines).

  13. Differentiation of debris-flow and flash-flood deposits: implications for paleoflood investigations

    Science.gov (United States)

    Waythomas, Christopher F.; Jarrett, Robert D.; ,

    1993-01-01

    Debris flows and flash floods are common geomorphic processes in the Colorado Rocky Mountain Front Range and foothills. Usually, debris flows and flash floods are associated with excess summer rainfall or snowmelt, in areas were unconsolidated surficial deposits are relatively thick and slopes are steep. In the Front Range and foothills, flash flooding is limited to areas below about 2300m whereas, debris flow activity is common throughout the foothill and alpine zones and is not necessarily elevation limited. Because flash floods and debris flows transport large quantities of bouldery sediment, the resulting deposits appear somewhat similar even though such deposits were produced by different processes. Discharge estimates based on debris-flow deposits interpreted as flash-flood deposits have large errors because techniques for discharge retrodiction were developed for water floods with negligible sediment concentrations. Criteria for differentiating between debris-flow and flash-flood deposits are most useful for deposits that are fresh and well-exposed. However, with the passage of time, both debris-flow and flash-flood deposits become modified by the combined effects of weathering, colluviation, changes in surface morphology, and in some instances removal of interstitial sediment. As a result, some of the physical characteristics of the deposits become more alike. Criteria especially applicable to older deposits are needed. We differentiate flash-flood from debris-flow and other deposits using clast fabric measurements and other morphologic and sedimentologic techniques (e.g., deposit morphology, clast lithology, particle size and shape, geomorphic setting).

  14. Grain-Size Analysis of Debris Flow Alluvial Fans in Panxi Area along Jinsha River, China

    Directory of Open Access Journals (Sweden)

    Wen Zhang

    2015-11-01

    Full Text Available The basic geometric parameters of 236 debris flow catchments were determined by interpreting SPOT5 remote sensing images with a resolution of 2.5 m in a 209 km section along the Jinsha River in the Panxi area, China. A total of 27 large-scale debris flow catchments were selected for detailed in situ investigation. Samples were taken from two profiles in the deposition zone for each debris flow catchment. The φ value gradation method of the grain size was used to obtain 54 histograms with abscissa in a logarithmic scale. Five types of debris flows were summarized from the outline of the histogram. Four grain size parameters were calculated: mean grain size, standard deviation, coefficient of skewness, and coefficient of kurtosis. These four values were used to evaluate the features of the histogram. The grain index that reflects the transport (kinetic energy information of debris flows was defined to describe the characteristics of the debris-flow materials. Furthermore, a normalized grain index based on the catchment area was proposed to allow evaluation of the debris flow mobility. The characteristics of the debris-flow materials were well-described by the histogram of grain-size distribution and the normalized grain index.

  15. Alpine debris flows triggered by a 28 July 1999 thunderstorm in the central Front Range, Colorado

    Science.gov (United States)

    Godt, Jonathan W.; Coe, Jeffrey A.

    2007-02-01

    On 28 July 1999, about 480 alpine debris flows were triggered by an afternoon thunderstorm along the Continental Divide in Clear Creek and Summit counties in the central Front Range of Colorado. The thunderstorm produced about 43 mm of rain in 4 h, 35 mm of which fell in the first 2 h. Several debris flows triggered by the storm impacted Interstate Highway 70, U.S. Highway 6, and the Arapahoe Basin ski area. We mapped the debris flows from color aerial photography and inspected many of them in the field. Three processes initiated debris flows. The first process initiated 11% of the debris flows and involved the mobilization of shallow landslides in thick, often well vegetated, colluvium. The second process, which was responsible for 79% of the flows, was the transport of material eroded from steep unvegetated hillslopes via a system of coalescing rills. The third, which has been termed the "firehose effect," initiated 10% of the debris flows and occurred where overland flow became concentrated in steep bedrock channels and scoured debris from talus deposits and the heads of debris fans. These three processes initiated high on steep hillsides (> 30°) in catchments with small contributing areas (material along their paths.

  16. Comparing debris flow relationships in the Alps and in the Pyrenees

    NARCIS (Netherlands)

    Beguería, S.; García-Ruiz, J.M.; Lorente, A.; Martí, C.

    2002-01-01

    Debris flows are a well known geomorphic process all over the World, as can be seen in the map presented by Innes (1983). In fact, many authors consider that debris flows are the most active geomorphic hazard in mountain areas, affecting human settlements, infrastructures and touristic resorts

  17. Hydrologic system state at debris flow initiation in the Pitztal catchment, Austria

    Science.gov (United States)

    Mostbauer, Karin; Hrachowitz, Markus; Prenner, David; Kaitna, Roland

    2017-04-01

    Debris flows represent a severe hazard in mountain regions. Though significant effort has been made to forecast such events, the trigger conditions as well as the hydrologic disposition of a watershed at the time of debris flow occurrence are not well understood. To improve our knowledge on the connection between debris flow initiation and the hydrologic system, this study applies a semi-distributed conceptual rainfall-runoff model, linking different system state variables such as soil moisture, snowmelt, or runoff with documented debris flow events in the Pitztal watershed, western Austria. The hydrologic modelling was performed on a daily basis between 1953 and 2012. High-intensity rainfall could be identified as the dominant trigger (31 out of 43 debris flows), while triggering exclusively by low-intensity, long-lasting rainfall was only observed in one single case. The remaining events were related to snowmelt; whether all of these events where triggered by rain-on-snow, or whether some of these events were actually triggered by snowmelt only, remains unclear since the occurrence of un- resp. underrecorded rainfall was detected frequently. The usage of a conceptual hydrological model for investigating debris flow initiation constitutes a novel approach in debris flow research and was assessed as very valuable. For future studies, it is recommended to evaluate also sub-daily information. As antecedent snowmelt was found to be much more important to debris flow initiation than antecedent rainfall, it might prove beneficial to include snowmelt in the commonly used rainfall intensity-duration thresholds.

  18. Sensitivity of the initiation of debris flow to initial soil moisture

    NARCIS (Netherlands)

    Hu, W.; Xu, Q.; Wang, G. H.; van Asch, T. W J; Hicher, P. Y.

    2015-01-01

    The initiation of debris flows is commonly attributed either to fluidization as a result of rainfall-induced landslides or to gully erosion induced by concentrated runoffs. A series of flume tests have been performed to show how the initial soil moisture influences the initiation of debris flows. At

  19. Modelling of Source Areas and Runout for Debris Flow Susceptibility Assessment at Regional Scale (Norway)

    Science.gov (United States)

    Melchiorre, Caterina; Stalsberg, Knut; Horton, Pascal

    2010-05-01

    This contribution focuses on combined methods to map debris flow susceptibility at regional scale. Classification of watersheds and an index approach framework, based on topographic/hydrological characteristics, was used to discriminate debris flow source areas, whereas runout areas were assessed by means of an energy-limited model coupled with a routing algorithm based on the random walk concept. Those methods were tested at basin scale in the Balsfjord municipality in northern Norway, where debris flows frequently affect road transportation. For this area a DEM at 5 m, a quaternary map at 5:000, and a map of debris flow tracks and source areas at 5:000 are available. The classification of watersheds was performed first by extracting attributes related to sediment production and internal relief, and then by means of multivariate analysis. The selection of source area cells was done only on debris flow watersheds by following an index approach framework. The runout model was then executed on those cells. The model uses hydrological routines to calculate the runout path and empirical relationship of debris flow trajectories to assess the runout distance. A preliminary analysis of the results shows that circa 90% or the debris flow watersheds were correctly classified. A good correlation between mapped and modelled source and runout areas was found. Future work will consist of evaluating different strategies to quantitatively assess the quality of the obtained susceptibility map. A complete validation of the model is difficult due to the sparse information on debris flows in the area.

  20. Sedimentology, Behavior, and Hazards of Debris Flows at Mount Rainier, Washington

    Science.gov (United States)

    Scott, K.M.; Vallance, J.W.; Pringle, P.T.

    1995-01-01

    Mount Rainier is potentially the most dangerous volcano in the Cascade Range because of its great height, frequent earthquakes, active hydrothermal system, and extensive glacier mantle. Many debris flows and their distal phases have inundated areas far from the volcano during postglacial time. Two types of debris flows, cohesive and noncohesive, have radically different origins and behavior that relate empirically to clay content. The two types are the major subpopulations of debris flows at Mount Rainier. The behavior of cohesive flows is affected by the cohesion and adhesion of particles; noncohesive flows are dominated by particle collisions to the extent that particle cataclasis becomes common during near-boundary shear. Cohesive debris flows contain more than 3 to 5 percent of clay-size sediment. The composition of these flows changed little as they traveled more than 100 kilometers from Mount Rainier to inundate parts of the now-populated Puget Sound lowland. They originate as deep-seated failures of sectors of the volcanic edifice, and such failures are sufficiently frequent that they are the major destructional process of Mount Rainier's morphologic evolution. In several deposits of large cohesive flows, a lateral, megaclast-bearing facies (with a mounded or hummocky surface) contrasts with a more clay-rich facies in the center of valleys and downstream. Cohesive flows at Mount Rainier do not correlate strongly with volcanic activity and thus can recur without warning, possibly triggered by non-magmatic earthquakes or by changes in the hydrothermal system. Noncohesive debris flows contain less than 3 to 5 percent clay-size sediment. They form most commonly by bulking of sediment in water surges, but some originate directly or indirectly from shallow slope failures that do not penetrate the hydrothermally altered core of the volcano. In contrast with cohesive flows, most noncohesive flows transform both from and to other flow types and are, therefore, the

  1. Quantifying sources of fine sediment supplied to post-fire debris flows using fallout radionuclide tracers

    Science.gov (United States)

    Smith, Hugh; Sheridan, Gary; Nyman, Petter; Child, David; Lane, Patrick; Hotchkis, Michael

    2013-04-01

    The supply of fine sediment and ash has been identified as an important factor contributing to the initiation of runoff-generated debris flows after fire. However, despite the significance of fines for post-fire debris flow generation, no investigations have sought to quantify sources of this material in debris flow affected catchments. In this study, we employ fallout radionuclides (Cs-137, excess Pb-210 and Pu-239,240) as tracers to measure proportional contributions of fine sediment (<10 μm) from hillslope surface and channel bank sources to levee and terminal fan deposits formed by post-fire debris flows in two forest catchments in southeastern Australia. While Cs-137 and excess Pb-210 have been widely used in sediment tracing studies, application of Pu as a tracer represents a recent development and was limited to only one catchment. The estimated range in hillslope surface contributions of fine sediment to individual debris flow deposits in each catchment was 22-69% and 32-74%, respectively. No systematic change in the source contributions to debris flow deposits was observed with distance downstream from channel initiation points. Instead, spatial variability in source contributions was largely influenced by the pattern of debris flow surges forming the deposits. Linking the sediment tracing with interpretation of depositional evidence allowed reconstruction of temporal sequences in sediment source contributions to debris flow surges. Hillslope source inputs dominated most elevated channel deposits such as marginal levees that were formed under peak flow conditions. This indicated the importance of hillslope runoff and sediment supply for debris flow generation in both catchments. In contrast, material stored within channels that was deposited during subsequent surges was predominantly channel-derived. The results demonstrate that fallout radionuclide tracers may provide unique information on the changing source contributions of fine sediment during debris

  2. Debris flow cartography using differential GNSS and Theodolite measurements

    Science.gov (United States)

    Khazaradze, Giorgi; Guinau, Marta; Calvet, Jaume; Furdada, Gloria; Victoriano, Ane; Génova, Mar; Suriñach, Emma

    2016-04-01

    The presented results form part of a CHARMA project, which pursues a broad objective of reducing damage caused by uncontrolled mass movements, such as rockfalls, snow avalanches and debris flows. Ultimate goal of the project is to contribute towards the establishment of new scientific knowledge and tools that can help in the design and creation of early warning systems. Here we present the specific results that deal with the application of differential GNSS and classical geodetic (e.g. theodolite) methods for mapping debris and torrential flows. Specifically, we investigate the Portainé stream located in the Pallars Sobirà region of Catalonia (Spain), in the eastern Pyrenees. In the last decade more than ten debris-flow type phenomena have affected the region, causing considerable economic losses. Since early 2014, we have conducted several field campaigns within the study area, where we have employed a multi-disciplinary approach, consisting of geomorphological, dendro-chronological and geodetic methods, in order to map the river bed and reconstruct the history of the extreme flooding and debris flow events. Geodetic studies included several approaches, using the classical and satellite based methods. The former consisted of angle and distance measurements between the Geodolite 502 total station and the reflecting prisms placed on top of the control points located within the riverbed. These type of measurements are precise, although present several disadvantages such as the lack of absolute coordinates that makes the geo-referencing difficult, as well as a relatively time-consuming process that involves two persons. For this reason, we have also measured the same control points using the differential GNSS system, in order to evaluate the feasibility of replacing the total station measurements with the GNSS. The latter measuring method is fast and can be conducted by one person. However, the fact that the study area is within the riverbed, often below the trees

  3. ANALYSIS OF DEBRIS FLOW BEHAVIOR USING AIRBORNE LIDAR AND IMAGE DATA

    Directory of Open Access Journals (Sweden)

    G. Kim

    2016-06-01

    Full Text Available The frequency of debris flow events caused by severe rainstorms has increased in Korea. LiDAR provides high-resolution topographical data that can represent the land surface more effectively than other methods. This study describes the analysis of geomorphologic changes using digital surface models derived from airborne LiDAR and aerial image data acquired before and after a debris flow event in the southern part of Seoul, South Korea in July 2011. During this event, 30 houses were buried, 116 houses were damaged, and 22 human casualties were reported. Longitudinal and cross-sectional profiles of the debris flow path reconstructed from digital surface models were used to analyze debris flow behaviors such as landslide initiation, transport, erosion, and deposition. LiDAR technology integrated with GIS is a very useful tool for understanding debris flow behavior.

  4. Debris flows from small catchments of the Ma Ha Tuak Range, metropolitan Phoenix, Arizona

    Science.gov (United States)

    Dorn, Ronald I.

    2010-08-01

    Debris flows debauch from tiny but steep mountain catchments throughout metropolitan Phoenix, Arizona, USA. Urban growth in the past half-decade has led to home construction directly underneath hundreds of debris-flow channels, but debris flows are not recognized as a potential hazard at present. One of the first steps in a hazard assessment is to determine occurrence rates. The north flank of the Ma Ha Tuak Range, just 10 km from downtown Phoenix, was selected to determine the feasibility of using the varnish microlaminations (VML) method to date every debris-flow levee from 127 catchment areas. Only 152 of the 780 debris-flow levees yielded VML ages in a first round of sampling; this high failure rate is due to erosion of VML by microcolonial fungi. The temporal pattern of preserved debris-flow levees indicates anomalously high production of debris flows at about 8.1 ka and about 2.8 ka, corresponding to Northern Hemisphere climatic anomalies. Because many prior debris flows are obliterated by newer events, the minimum overall occurrence rates of 1.3 debris flows per century for the last 60 ka, 2.2 flows/century for the latest Pleistocene, and 5 flows/century for the last 8.1 ka has little meaning in assessment of a contemporary hazard. This is because newer debris flows have obliterated an unknown number of past deposits. More meaningful to a hazards analysis is the estimate that 56 flows have occurred in the last 100 years on the north side of the range, an estimate that is consistent with direct observations of three small debris flows resulting events from a January 18-22, 2010 storm producing 70 mm of precipitation in the Ma Ha Tuak Range, and a 500 m long debris flow in a northern metropolitan Phoenix location that received over 150 mm of precipitation in this same storm. These findings support the need for a more extensive hazard assessment of debris flows in metropolitan Phoenix.

  5. Debris flow hazard modelling on medium scale: Valtellina di Tirano, Italy

    Directory of Open Access Journals (Sweden)

    J. Blahut

    2010-11-01

    Full Text Available Debris flow hazard modelling at medium (regional scale has been subject of various studies in recent years. In this study, hazard zonation was carried out, incorporating information about debris flow initiation probability (spatial and temporal, and the delimitation of the potential runout areas. Debris flow hazard zonation was carried out in the area of the Consortium of Mountain Municipalities of Valtellina di Tirano (Central Alps, Italy. The complexity of the phenomenon, the scale of the study, the variability of local conditioning factors, and the lacking data limited the use of process-based models for the runout zone delimitation. Firstly, a map of hazard initiation probabilities was prepared for the study area, based on the available susceptibility zoning information, and the analysis of two sets of aerial photographs for the temporal probability estimation. Afterwards, the hazard initiation map was used as one of the inputs for an empirical GIS-based model (Flow-R, developed at the University of Lausanne (Switzerland. An estimation of the debris flow magnitude was neglected as the main aim of the analysis was to prepare a debris flow hazard map at medium scale. A digital elevation model, with a 10 m resolution, was used together with landuse, geology and debris flow hazard initiation maps as inputs of the Flow-R model to restrict potential areas within each hazard initiation probability class to locations where debris flows are most likely to initiate. Afterwards, runout areas were calculated using multiple flow direction and energy based algorithms. Maximum probable runout zones were calibrated using documented past events and aerial photographs. Finally, two debris flow hazard maps were prepared. The first simply delimits five hazard zones, while the second incorporates the information about debris flow spreading direction probabilities, showing areas more likely to be affected by future debris flows. Limitations of the modelling arise

  6. Elements of an improved model of debris-flow motion

    Science.gov (United States)

    Iverson, R.M.

    2009-01-01

    A new depth-averaged model of debris-flow motion describes simultaneous evolution of flow velocity and depth, solid and fluid volume fractions, and pore-fluid pressure. Non-hydrostatic pore-fluid pressure is produced by dilatancy, a state-dependent property that links the depth-averaged shear rate and volumetric strain rate of the granular phase. Pore-pressure changes caused by shearing allow the model to exhibit rate-dependent flow resistance, despite the fact that the basal shear traction involves only rate-independent Coulomb friction. An analytical solution of simplified model equations shows that the onset of downslope motion can be accelerated or retarded by pore-pressure change, contingent on whether dilatancy is positive or negative. A different analytical solution shows that such effects will likely be muted if downslope motion continues long enough, because dilatancy then evolves toward zero, and volume fractions and pore pressure concurrently evolve toward steady states. ?? 2009 American Institute of Physics.

  7. Spatial estimation of debris flows-triggering rainfall and its dependence on rainfall severity

    Science.gov (United States)

    Destro, Elisa; Marra, Francesco; Nikolopoulos, Efthymios; Zoccatelli, Davide; Creutin, Jean-Dominique; Borga, Marco

    2016-04-01

    Forecasting the occurrence of landslides and debris flows (collectively termed 'debris flows' hereinafter) is fundamental for issuing hazard warnings, and focuses largely on rainfall as a triggering agent. Debris flow forecasting relies very often on the identification of combinations of depth and duration of rainfall - rainfall thresholds - that trigger widespread debris flows. Rainfall estimation errors related to the sparse nature of raingauge data are enhanced in case of convective rainfall events characterized by limited spatial extent. Such errors have been shown to cause underestimation of the rainfall thresholds and, thus, less efficient forecasts of debris flows occurrence. This work examines the spatial organization of debris flows-triggering rainfall around the debris flow initiation points using high-resolution, carefully corrected radar data for a set of short duration (Alps. The set includes eleven debris-flow triggering rainfall events that occurred in the study area between 2005 and 2014. The selected events are among the most severe in the region during this period and triggered a total of 99 debris flows that caused significant damage to people and infrastructures. We show that the spatial rainfall organisation depends on the severity (measured via the estimated return time-RT) of the debris flow-triggering rainfall. For more frequent events (RTdebris flow location coincides with a local minimum, whereas for less frequent events (RT>20 yrs) the triggering rainfall presents a local peak corresponding to the debris flow initiation point. Dependence of these features on rainfall duration is quite limited. The characteristics of the spatial rainfall organisation are exploited to understand the performances and results of three different rainfall interpolation techniques: nearest neighbour (NN), inverse distance weighting (IDW) and ordinary kriging (OK). We show that the features of the spatial organization of the debris flow triggering rainfall

  8. Slit-check dams for the control of debris flow

    Science.gov (United States)

    Armanini, Aronne; Larcher, Michele

    2017-04-01

    Debris flows are paroxysmal events that mobilize, alongside water, huge quantities of sediment in a very short time, then with both solid and liquid huge discharges, possibly exceeding the capacity of the current torrent restoration works. In this respect, the climate change forcing cannot be ignored. In the majority of urbanized areas, that are generally the most vulnerable, there is often not enough space to create channelling works able to let the volumes pass through without overflowing. The simplest, less expensive and most sustainable solution consists in reducing the peak solid discharge by creating storage areas upstream of the settlements, typically upstream of the alluvial fans, allowing for reduced works of canalization, that are compatible with the constraints imposed by the urbanization. The general idea consists in storing a part of the flowing solids during the peak of the hydrograph and releasing it in a successive phase or during minor floods. For this purpose, and in order to optimize the solid peak discharge reduction, it is necessary that properly designed open-check dams, capable of inducing a significative sedimentation of the solid discharge only when this exceeds a design-threshold value, control the deposition basins. A correct design of the check dam is crucial in order to induce the sedimentation in the right amount and at the right moment: a too early sedimentation might fill the volume before the peak, like in the case of close-check dams, while a too weak sedimentation might not use the whole available volume. In both cases, the channelling works might not be sufficient to let all the flow pass through, compromising the safety of the settlement. To avoid this inconvenience, we propose the use of slit-check dams, whose efficiency has already been proved for bed load. Check dams are often designed only on the base of the designer's experience. Besides, even today it is often believed that the filtering effect of open check dams is

  9. Estimation of the surface velocity of debris flow with computer-based spatial filtering.

    Science.gov (United States)

    Uddin, M S; Inaba, H; Itakura, Y; Kasahara, M

    1998-09-10

    A computer-based spatial-filtering velocimeter to measure the surface velocity of natural debris flow is described. This is a simple and interesting technique implemented with a spatial filter constructed as a software program that processes the video image of debris flow instead of a hardware implementation. The surface velocity of the debris flow at the Mt. Yakedake Volcano, Japan, was estimated by this computer-based spatial-filtering method, and the results were compared with those obtained by a hardware-based spatial-filtering method. Computer-based spatial filtering has the important advantage of a capability for tuning the spatial-filter parameters to the target flow.

  10. Basal interstitial water pressure in laboratory debris flows over a rigid bed in an open channel

    Directory of Open Access Journals (Sweden)

    N. Hotta

    2012-08-01

    Full Text Available Measuring the interstitial water pressure of debris flows under various conditions gives essential information on the flow stress structure. This study measured the basal interstitial water pressure during debris flow routing experiments in a laboratory flume. Because a sensitive pressure gauge is required to measure the interstitial water pressure in shallow laboratory debris flows, a differential gas pressure gauge with an attached diaphragm was used. Although this system required calibration before and after each experiment, it showed a linear behavior and a sufficiently high temporal resolution for measuring the interstitial water pressure of debris flows. The values of the interstitial water pressure were low. However, an excess of pressure beyond the hydrostatic pressure was observed with increasing sediment particle size. The measured excess pressure corresponded to the theoretical excess interstitial water pressure, derived as a Reynolds stress in the interstitial water of boulder debris flows. Turbulence was thought to induce a strong shear in the interstitial space of sediment particles. The interstitial water pressure in boulder debris flows should be affected by the fine sediment concentration and the phase transition from laminar to turbulent debris flow; this should be the subject of future studies.

  11. Procedures for the documentation of historical debris flows: application to the Chieppena Torrent (Italian alps).

    Science.gov (United States)

    Marchi, Lorenzo; Cavalli, Marco

    2007-09-01

    The reconstruction of triggering conditions, geomorphic effects, and damage produced by historical floods and debris flows significantly contributes to hazard assessment, allowing improved risk mitigation measures to be defined. Methods for the analysis of historical floods and debris flows vary greatly according to the type and quality of available data, which in turn are influenced by the time the events occurred. For floods and debris flows occurring in the Alps a few decades ago (between about 1950 and 1980), the documentation is usually better than for previous periods but, unlike events of most recent years, quantitative data are usually scanty and the description of the events does not aim to identify processes according to current terminology and classifications. The potential, and also the limitations of historical information available for the reconstruction of historical debris flows in the Alps have been explored by analyzing a high-magnitude debris flow that occurred on November 4, 1966 in the Chieppena Torrent (northeastern Italy). Reconstruction of the event was based on the use of written documentation, terrestrial and aerial photographs, and geomorphological maps. The analysis aimed to define the temporal development of phenomena, recognizing the type of flow processes and assessing some basic flow variables, such as volume, channel-debris yield rate, erosion depth, total distance traveled, and runout distance on the alluvial fan. The historical development of torrent hydraulic works, both before and after the debris flow of November 1966, was also analyzed with regard to the technical solutions adopted and their performance.

  12. Debris flow hazard assessment in the Langtauferer valley, South Tyrol, Northern Italy.

    Science.gov (United States)

    Reichegger, Martina; Busetto, Daniela; Glade, Thomas; Zischg, Andreas

    2013-04-01

    Debris flows pose a significant threat to the environment and society in numerous alpine valleys. Various approaches exist to assess the respective hazards in order to delineate regions, which are prone to a given magnitude and frequency of debris flows. This research aims to couple the hydraulic FLO-2D model with a sediment assessment model in order to identify endangered settlement areas situated on the torrential fans. A hazard assessment for debris flows was conducted on seven torrential fans in the Langtauferer valley, South Tyrol, northern Italy. The debris flow process was simulated by the hydraulic FLO-2D computer model for return periods 30, 100 and 300 years. The main input parameters had to be determined previously: water runoff was calculated by a rainfall-runoff model and the amount of sediment entrainable by debris flows was estimated in the field. For validation the results were compared with historical debris flow data. A classification in high and very high debris flow hazard based on maximum flow depths showed that none of the settlement areas are affected by the highest hazard class. Comparing the results with historic events, the chosen model inputs water runoff and amount of sediment appear plausible and therefore applicable in planning strategies.

  13. Debris flow impact on mitigation barriers: a new method for particle-fluid-structure interactions

    Science.gov (United States)

    Marchelli, Maddalena; Pirulli, Marina; Pudasaini, Shiva P.

    2016-04-01

    Channelized debris-flows are a type of mass movements that involve water-charged, predominantly coarse-grained inorganic and organic material flowing rapidly down steep confined pre-existing channels (Van Dine, 1985). Due to their rapid movements and destructive power, structural mitigation measures have become an integral part of counter measures against these phenomena, to mitigate and prevent damages resulting from debris-flow impact on urbanized areas. In particular, debris barriers and storage basins, with some form of debris-straining structures incorporated into the barrier constructed across the path of a debris-flow, have a dual role to play: (1) to stimulate deposition by presenting a physical obstruction against flow, and (2) to guarantee that during normal conditions stream water and bedload can pass through the structure; while, during and after an extreme event, the water that is in the flow and some of the fine-grained sediment can escape. A new method to investigate the dynamic interactions between the flowing mass and the debris barrier is presented, with particular emphasis on the effect of the barrier in controlling the water and sediment content of the escaping mass. This aspect is achieved by implementing a new mechanical model into an enhanced two-phase dynamical mass flow model (Pudasaini, 2012), in which solid particles mixture and viscous fluid are taken into account. The complex mechanical model is defined as a function of the energy lost during impact, the physical and geometrical properties of the debris barrier, separate but strongly interacting dynamics of boulder and fluid flows during the impact, particle concentration distribution, and the slope characteristics. The particle-filtering-process results in a large variation in the rheological properties of the fluid-dominated escaping mass, including the substantial reduction in the bulk density, and the inertial forces of the debris-flows. Consequently, the destructive power and run

  14. Disaster Characteristics and Mitigation Measures of Huge Glacial Debris Flows along the Sichuan-Tibet Railway

    Science.gov (United States)

    Liu, Jinfeng; You, Yong; Zhang, Guangze; Wang, Dong; Chen, Jiangang; Chen, Huayong

    2017-04-01

    The Ranwu-Tongmai section of the Sichuan-Tibet Railway passes through the Palongzangbu River basin which locates in the southeast Qinghai-Tibetan Plateau. Due to widely distributed maritime glacier in this area, the huge glacier debris flows are very developed. Consequently, the disastrous glacier debris flows with huge scale (106-108 m3 for one debris flow event) and damage become one of the key influencing factors for the route alignment of the Sichuan-Tibet Railway. The research on disaster characteristics and mitigation measures of huge glacial debris flows in the study area were conducted by the remote sensing interpretation, field investigation, parameter calculation and numerical simulation. Firstly, the distribution of the glaciers, glacier lakes and glacier debris flows were identified and classified; and the disaster characteristics for the huge glacier debris flow were analyzed and summarized. Secondly, the dynamic parameters including the flood peak discharge, debris flow peak discharge, velocity, total volume of a single debris flow event were calculated. Based on the disaster characteristics and the spatial relation with the railway, some mitigation principles and measures were proposed. Finally, the Guxiang Gully, where a huge glacier debris flow with 2*108m3 in volume occurred in 1953, was selected as a typical case to analyze its disaster characteristics and mitigation measures. The interpretation results show that the glacier area is about 970 km2 which accounts for 19% of the total study area. 130 glacier lakes and 102 glacier debris flows were identified and classified. The Sichuan-Tibet Railway passes through 43 glacier debris flows in the study area. The specific disaster characteristics were analyzed and corresponding mitigation measures were proposed for the route selection of the railway. For the Guxiang Gully, a numerical simulation to simulate the deposition condition at the alluvial fan was conducted. the simulation results show that the

  15. Relations between rainfall and triggering of debris-flow: case study of Cancia (Dolomites, Northeastern Italy

    Directory of Open Access Journals (Sweden)

    M. Bacchini

    2003-01-01

    Full Text Available Debris-flows occurring in the area of Cancia (Dolomites, Northeastern Italy in recent years have exposed the population to serious risk. In response to the recurring hazard, an alarm and monitoring system was installed to provide a sufficient level of safeguard for inhabitants and infrastructures. The data recorded at three rain gauges during debris-flow events has been analysed, taking into consideration the different elevation of the gauges to delineate the storm rainfall distributions. Rainfall data is compared with the occurrence of debris-flows to examine relations between debris-flow initiation and rainfall. In addition, the data is compared with that recorded during debris-flows which occurred under similar or different geological settings in the Eastern Italian Alps, in order to define triggering thresholds. A threshold for debris-flow activity in terms of mean intensity, duration and mean annual precipitation (M.A.P. is defined for the study area The normalised rainfall and the normalised intensity are expressed as a per cent with respect to M.A.P. This threshold is compared with thresholds proposed by other authors, and the comparison shows that a lower value is obtained, indicating the debris-flow susceptibility of the area. The threshold equations are:  R/M.A.P. = - 1.36 · ln(I + 3.93  where I > 2 mm/h  I /M.A.P. = 0.74 · D-0.56.  The determination of a debris-flow threshold is linked to the necessity of a fast decisional phase in a warning system for debris-flow protection. This threshold cannot be used as a predictive tool, but rather as a warning signal for technicians who manage the monitoring/warning system.

  16. Assessment of the frictional effect of forests on debris flow runout in numerical models

    Science.gov (United States)

    Schraml, Klaus; McArdell, Brian W.; Graf, Christoph; Stoffel, Markus; Kaitna, Roland

    2013-04-01

    Geomorphic processes like debris flows constitute a major risk in alpine regions. It is therefore of prime importance to delineate areas of high hazard potential to reduce the loss of life and severe damages to settlements and infrastructure. The two dimensional dynamic model RAMMS DF (RApid Mass MovementS Debris Flow) is an engineering prediction tool designed for predicting the flow intensity and runout behavior of debris flows. It is based on a numerical solution to the shallow water equations for granular flow including the well known Voellmy friction relation. In this contribution we use RAMMS to simulate recent debris flow deposition on forested fans reconstructed by dendrogeomorphic analyses for two study sites located in the Austrian Alps. Trees obviously influenced by past debris flow activity were sampled and further used to determine the spatial extent of past depositions on the fan. An average deposition height assessed from field investigations was used to derive an estimate of past event volumes as input for RAMMS. Simulation results were improved using separate friction parameter sets for forested areas and as a consequence the replications of the mapped deposition pattern were derived. Our goal is to derive a physically based algorithm which depends partially on the properties of the trees (e.g. spacing and diameter) and on the granulometry of the flow. This study contributes to the evaluation of realistic model parameters for simulation of debris flow deposition outside of the channel on alpine fans.

  17. Hazard assessment of debris flows for Leung King Estateof Hong Kong by incorporating GIS with numericalsimulations

    Directory of Open Access Journals (Sweden)

    K. T. Chau

    2004-01-01

    Full Text Available As over seventy percent of the land of Hong Kong is mountainous, rainfall-induced debris flows are not uncommon in Hong Kong. The objective of this study is to incorporate numerical simulations of debris flows with GIS to identify potential debris flow hazard areas. To illustrate this approach, the proposed methodology is applied to Leung King Estate in Tuen Mun. A Digital Elevation Model (DEM of the terrain and the potential debris-flow sources were generated by using GIS to provide the required terrain and flow source data for the numerical simulations. A theoretical model by Takahashi et al. (1992 improved by incorporating a new erosion initiation criterion was used for simulating the runout distances of debris flows. The well-documented 1990 Tsing Shan debris flow, which occurred not too far from Leung King Estate, was used to calibrate most of the flow parameters needed for computer simulations. Based on the simulation results, a potential hazard zone was identified and presented by using GIS. Our proposed hazard map was thus determined by flow dynamics and a deposition mechanism through computer simulations without using any so- called expert opinions, which are bounded to be subjective and biased.

  18. Regional danger assessment of Debris flow and its engineering mitigation practice in Sichuan-Tibet highway

    Science.gov (United States)

    Su, Pengcheng; Sun, Zhengchao; li, Yong

    2017-04-01

    Luding-Kangding highway cross the eastern edge of Qinghai-Tibet Plateau where belong to the most deep canyon area of plateau and mountains in western Sichuan with high mountain and steep slope. This area belongs to the intersection among Xianshuihe, Longmenshan and Anninghe fault zones which are best known in Sichuan province. In the region, seismic intensity is with high frequency and strength, new tectonic movement is strong, rock is cracked, there are much loose solid materials. Debris flow disaster is well developed under the multiple effects of the earthquake, strong rainfall and human activity which poses a great threat to the local people's life and property security. So this paper chooses Kangding and LuDing as the study area to do the debris flow hazard assessment through the in-depth analysis of development characteristics and formation mechanism of debris flow. Which can provide important evidence for local disaster assessment and early warning forecast. It also has the important scientific significance and practical value to safeguard the people's life and property safety and the security implementation of the national major project. In this article, occurrence mechanism of debris flow disasters in the study area is explored, factor of evaluation with high impact to debris flow hazards is identified, the database of initial evaluation factors is made by the evaluation unit of basin. The factors with high impact to hazards occurrence are selected by using the stepwise regression method of logistic regression model, at the same time the factors with low impact are eliminated, then the hazard evaluation factor system of debris flow is determined in the study area. Then every factors of evaluation factor system are quantified, and the weights of all evaluation factors are determined by using the analysis of stepwise regression. The debris flows hazard assessment and regionalization of all the whole study area are achieved eventually after establishing the

  19. On the evaluation of debris flows dynamics by means of mathematical models

    Directory of Open Access Journals (Sweden)

    M. Arattano

    2003-01-01

    Full Text Available The prediction of debris flow dynamic characteristics in a debris flow prone torrent is generally made through the investigation of past events. This investigation can be carried out through a survey of the marks left by past debris flows along the channel and through a detailed analysis of the type and shape of the deposits found on the debris fan. The rheological behaviour of future debris flows can then be inferred from the results of these surveys and their dynamic characteristics can be estimated applying well known formulas proposed in literature. These latter will make use of the assumptions on the rheological behaviour previously made. This type of estimation has been performed for a debris flow occurred in an instrumented basin, on the North-Eastern Italian Alps, in 1996 and the results have been compared to those obtained by means of a mathematical simulation. For the calibration of the mathematical model the limnographs recorded by three different ultrasonic gauges installed along a torrent reach on the fan were used. The comparison evidenced the importance of time data recordings for a correct prediction of the debris flows dynamics. Without the availability of data recordings, the application of formulas based only on assumptions derived from field analysis could be misleading.

  20. Debris Flows in a Changing Climate: Experimental and Field Investigations of the Influence of Changes in Moisture on Matrix Properties, Interparticle Interactions, and Subsequent Debris Flow Behaviors

    Science.gov (United States)

    Hill, K. M.; Densmore, A.; Longjas, A.; Mullenbach, J.; Fouty, T.; Fei, M.; Zhou, G.; Sun, Q.

    2016-12-01

    Debris flows, rapid gravity-driven mixtures of sediment (boulders, gravels, sands, and mud) and water, are important geomorphological agents of landscape change and common natural hazards in mountainous regions. Worldwide, there is evidence that the frequency and magnitude of debris flows are increasing under recent changes in macro and micro climate. We investigate the influence of moisture differences associated with climate change on debris flow behaviors at the field and laboratory scales. Field measurements of debris flow fan deposits in Owens Valley during glacial and interglacial periods - likely corresponding to periods of higher and lower levels of water content in the soil and flows - show marked differences in avulsion frequencies, channel aspect ratios, sorting in the deposits and depositional geometries. These measurements suggest that differing moisture levels change the density and rheology of the matrix - the watery / muddy interstitial fluid - which, in turn, can significantly alter the dynamic behavior of the debris flow itself. This supports recent experimental results (Kaitna et al., 2014 & 2015) that changing the properties of the matrix of experimental flows appears to change the nature and relative importance of interparticle interactions compared to those associated with the fluid and subsequently influence the flow dynamics. We test these hypotheses using controlled laboratory experiments in flumes of two different sizes and where we systematically vary interstitial fluid properties and scale of the experiments. In both flumes we present high speed particle tracking and measurements of pore pressure and stress at the bed to show how the flow and entrainment behavior varies as the flow transitions from inertial to viscous, that is, as pore pressures and other fluid effects become increasingly dominant over inter-particle interactions, reflected in the Bagnold (1954) number. We also demonstrate that some effects, like bed fabric and fragility

  1. Modeling of debris flow depositional patterns according to the catchments and sediment source areas characteristics

    Directory of Open Access Journals (Sweden)

    Davide eTiranti

    2015-03-01

    Full Text Available A method to predict the most probable flow rheology in Alpine debris flows is presented. The methods classifies outcropping rock masses in catchments on the basis of the type of resulting unconsolidated deposits. The grain size distribution of the debris material and the depositional style of past debris flow events are related to the dominant flow processes: viscoplastic and frictional/collisional. Three catchments in the upper Susa Valley (Western Alps, characterized by different lithologies, were selected for numerical analysis carried out with a Cellular Automata code with viscoplastic and frictional/collisional rheologies. The obtained numerical results are in good agreement with in site evidences in terms of depositional patterns, confirming the possibility of choosing the rheology of the debris flow based on the source material within the catchment.

  2. Predicting spatial distribution of postfire debris flows and potential consequences for native trout in headwater streams

    Science.gov (United States)

    Sedell, Edwin R; Gresswell, Bob; McMahon, Thomas E.

    2015-01-01

    Habitat fragmentation and degradation and invasion of nonnative species have restricted the distribution of native trout. Many trout populations are limited to headwater streams where negative effects of predicted climate change, including reduced stream flow and increased risk of catastrophic fires, may further jeopardize their persistence. Headwater streams in steep terrain are especially susceptible to disturbance associated with postfire debris flows, which have led to local extirpation of trout populations in some systems. We conducted a reach-scale spatial analysis of debris-flow risk among 11 high-elevation watersheds of the Colorado Rocky Mountains occupied by isolated populations of Colorado River Cutthroat Trout (Oncorhynchus clarkii pleuriticus). Stream reaches at high risk of disturbance by postfire debris flow were identified with the aid of a qualitative model based on 4 primary initiating and transport factors (hillslope gradient, flow accumulation pathways, channel gradient, and valley confinement). This model was coupled with a spatially continuous survey of trout distributions in these stream networks to assess the predicted extent of trout population disturbances related to debris flows. In the study systems, debris-flow potential was highest in the lower and middle reaches of most watersheds. Colorado River Cutthroat Trout occurred in areas of high postfire debris-flow risk, but they were never restricted to those areas. Postfire debris flows could extirpate trout from local reaches in these watersheds, but trout populations occupy refugia that should allow recolonization of interconnected, downstream reaches. Specific results of our study may not be universally applicable, but our risk assessment approach can be applied to assess postfire debris-flow risk for stream reaches in other watersheds.

  3. Discharge of landslide-induced debris flows: case studies of Typhoon Morakot in southern Taiwan

    Science.gov (United States)

    Chen, J.-C.; Chuang, M.-R.

    2014-07-01

    Three debris-flow gullies, the Hong-Shui-Xian (HSX), Sha-Xin-Kai (SXK), and Xin-Kai-Dafo (XKD) gullies, located in the Shinfa area of southern Taiwan, were selected as case studies on the discharge of landslide-induced debris flows caused by Typhoon Morakot in 2009. The inundation characteristics of the three debris flows, such as the debris-flow volume V, deposition area Ad, and maximum flow depth, were collected by field investigations and simulated using the numerical modeling software FLO-2D. The discharge coefficient cb, defined as the ratio of the debris-flow discharge Qdp to the water-flow discharge Qwp, was proposed to determine Qdp, and Qwp was estimated by a rational equation. Then, cb was calibrated by a comparison between the field investigation and the numerical simulation of the inundation characteristics of debris flows. Our results showed that the values of cb range from 6 to 18, and their values are affected by the landslide ratio RL. Empirical relationships for cb versus RL, Qdp versus Qwp, Qdp versus V, and Ad versus V are also presented.

  4. Field investigations of the interaction between debris flows and forest vegetation in two Alpine fans

    Science.gov (United States)

    Michelini, Tamara; Bettella, Francesco; D'Agostino, Vincenzo

    2017-02-01

    A key objective in debris-flow hazard mitigation is the reduction of the potential depositional area in the fan. From this point of view, forested areas are able to provide a protective function hindering the flow motion and promoting the surge deposition. Despite extensive research on Alpine forests and their protective functions, relatively few studies in the literature have quantitatively focused on the relationship between debris-flow depositional features and vegetation. In light of the above, our research investigates how vegetation characteristics in the fan area interact with debris-flow deposition. Field investigations were carried out in two Alpine fans where debris-flow events occurred in the summer of 2012. By recording the characteristics of 1567 involved trees and the associated deposit thicknesses, this paper provides a data set that contributes to the improvement of the knowledge of these interaction processes. The integration of literature findings and the analysis of the collected dataset adds insights into the relationships between tree characteristics and the dynamics of debris flow during the runout path. The main results prove the capacity of the forest of uniformly promoting flow-energy dissipation, presence of high species diversity in debris-flow deposits when comparing disturbed and undisturbed forest stands, tree mortality largely affecting small diameters management of protection forests in alluvial fans are suggested.

  5. Sediment budget monitoring of debris-flow and bedload transport in the Manival Torrent, SE France

    Directory of Open Access Journals (Sweden)

    J. I. Theule

    2012-03-01

    Full Text Available Steep mountain catchments typically experience large sediment pulses from hillslopes which are stored in headwater channels and remobilized by debris-flows or bedload transport. Event-based sediment budget monitoring in the active Manival debris-flow torrent in the French Alps during a two-year period gave insights into the catchment-scale sediment routing during moderate rainfall intensities which occur several times each year. The monitoring was based on intensive topographic resurveys of low- and high-order channels using different techniques (cross-section surveys with total station and high-resolution channel surveys with terrestrial and airborne laser scanning. Data on sediment output volumes from the main channel were obtained by a sediment trap. Two debris-flows were observed, as well as several bedload transport flow events. Sediment budget analysis of the two debris-flows revealed that most of the debris-flow volumes were supplied by channel scouring (more than 92%. Bedload transport during autumn contributed to the sediment recharge of high-order channels by the deposition of large gravel wedges. This process is recognized as being fundamental for debris-flow occurrence during the subsequent spring and summer. A time shift of scour-and-fill sequences was observed between low- and high-order channels, revealing the discontinuous sediment transfer in the catchment during common flow events. A conceptual model of sediment routing for different event magnitude is proposed.

  6. Analysis of debris-flow recordings in an instrumented basin: confirmations and new findings

    Directory of Open Access Journals (Sweden)

    M. Arattano

    2012-03-01

    Full Text Available On 24 August 2006, a debris flow took place in the Moscardo Torrent, a basin of the Eastern Italian Alps instrumented for debris-flow monitoring. The debris flow was recorded by two seismic networks located in the lower part of the basin and on the alluvial fan, respectively. The event was also recorded by a pair of ultrasonic sensors installed on the fan, close to the lower seismic network. The comparison between the different recordings outlines particular features of the August 2006 debris flow, different from that of events recorded in previous years. A typical debris-flow wave was observed at the upper seismic network, with a main front abruptly appearing in the torrent, followed by a gradual decrease of flow height. On the contrary, on the alluvial fan the wave displayed an irregular pattern, with low flow depth and the main peak occurring in the central part of the surge both in the seismic recording and in the hydrographs. Recorded data and field evidences indicate that the surge observed on the alluvial fan was not a debris flow, and probably consisted in a water surge laden with fine to medium-sized sediment. The change in shape and characteristics of the wave can be ascribed to the attenuation of the surge caused by the torrent control works implemented in the lower basin during the last years.

  7. Wildfire impacts on the processes that generate debris flows in burned watersheds

    Science.gov (United States)

    Parise, M.; Cannon, S.H.

    2012-01-01

    Every year, and in many countries worldwide, wildfires cause significant damage and economic losses due to both the direct effects of the fires and the subsequent accelerated runoff, erosion, and debris flow. Wildfires can have profound effects on the hydrologic response of watersheds by changing the infiltration characteristics and erodibility of the soil, which leads to decreased rainfall infiltration, significantly increased overland flow and runoff in channels, and movement of soil. Debris-flow activity is among the most destructive consequences of these changes, often causing extensive damage to human infrastructure. Data from the Mediterranean area and Western United States of America help identify the primary processes that result in debris flows in recently burned areas. Two primary processes for the initiation of fire-related debris flows have been so far identified: (1) runoff-dominated erosion by surface overland flow; and (2) infiltration-triggered failure and mobilization of a discrete landslide mass. The first process is frequently documented immediately post-fire and leads to the generation of debris flows through progressive bulking of storm runoff with sediment eroded from the hillslopes and channels. As sediment is incorporated into water, runoff can convert to debris flow. The conversion to debris flow may be observed at a position within a drainage network that appears to be controlled by threshold values of upslope contributing area and its gradient. At these locations, sufficient eroded material has been incorporated, relative to the volume of contributing surface runoff, to generate debris flows. Debris flows have also been generated from burned basins in response to increased runoff by water cascading over a steep, bedrock cliff, and incorporating material from readily erodible colluvium or channel bed. Post-fire debris flows have also been generated by infiltration-triggered landslide failures which then mobilize into debris flows. However

  8. GIS-based modeling of debris flow processes in an Alpine catchment, Antholz valley, Italy

    Science.gov (United States)

    Sandmeier, Christine; Damm, Bodo; Terhorst, Birgit

    2010-05-01

    Debris flows are frequent natural hazards in mountain regions, which seriously can threat human lives and economic values. In the European Alps the occurrence of debris flows might even increase with respect to climate change, including permafrost degradation, glacier retreat and variable precipitation patterns. Thus, detailed understanding of process parameters and spatial distribution of debris flows is necessary to take appropriate protection measures for risk assessment. In this context, numerical models have been developed and applied successfully for simulation and prediction of debris-flow hazards and related process areas. In our study a GIS-based model is applied in an alpine catchment to address the following questions: Where are potential initiating areas of debris flows? How much material can be mobilized? What is the influence of topography and precipitation? The study area is located in the Antholz valley in the eastern Alps of Northern Italy. The investigated catchment of the Klammbach creek comprises 6.5 km² and is divided into two sub-catchments. Geologically it is dominated by metamorphic rock and altitudes range between 1310 and 3270 m. In summer 2005 a debris flow of more than 100000 m³ took place, originating from a steep, sparsely vegetated debris cone in the western part of the catchment. According to a regional study, the lower permafrost boundary in this area has risen by 250 m. In a first step, during a field survey, geomorphological mapping was performed, several channel cross-sections were measured and sediment samples were taken. Using mapping results and aerial images, a geomorphological map was created. In further steps, results from the field work, the geomorphological map and existing digital data sets, including a digital elevation model with 2.5 m resolution, are used to derive input data for the modeling of debris flow processes. The model framework ‘r.debrisflow' based on GRASS GIS is applied (Mergili, 2008*), as it is

  9. Contrasting origin of two clay-rich debris flows at Cayambe Volcanic Complex, Ecuador

    Science.gov (United States)

    Detienne, M.; Delmelle, P.; Guevara, A.; Samaniego, P.; Opfergelt, S.; Mothes, P. A.

    2017-04-01

    We investigate the sedimentological and mineralogical properties of a debris flow deposit west of Cayambe Volcanic Complex, an ice-clad edifice in Ecuador. The deposit exhibits a matrix facies containing up to 16 wt% of clays. However, the stratigraphic relationship of the deposit with respect to the Canguahua Formation, a widespread indurated volcaniclastic material in the Ecuadorian inter-Andean Valley, and the deposit alteration mineralogy differ depending on location. Thus, two different deposits are identified. The Río Granobles debris flow deposit ( 1 km3) is characterised by the alteration mineral assemblage smectite + jarosite, and sulphur isotopic analyses point to a supergene hydrothermal alteration environment. This deposit probably derives from a debris avalanche initiated before 14-21 ka by collapse of a hydrothermally altered rock mass from the volcano summit. In contrast, the alteration mineralogy of the second debris flow deposit, which may itself comprise more than one unit, is dominated by halloysite + smectite and relates to a shallower and more recent (3200 m) volcanic soils. Our study reinforces the significance of hydrothermal alteration in weakening volcano flanks and in favouring rapid transformation of a volcanic debris avalanche into a clay-rich debris flow. It also demonstrates that mineralogical analysis provides crucial information for resolving the origin of a debris flow deposit in volcanic terrains. Finally, we posit that slope instability, promoted by ongoing subglacial hydrothermal alteration, remains a significant hazard at Cayambe Volcanic Complex.

  10. Reduction Effect Analysis of Erosion Control Facilities Using Debris Flow Numerical Model

    Science.gov (United States)

    Jun, Kyewon; Kim, Younghwan; Oh, Chaeyeon; Lee, Hojin; Kim, SoungDoug

    2017-04-01

    With the increase in frequency of typhoons and heavy rains following the climate change, the scale of damage from the calamities in the mountainous areas has been growing larger and larger, which is different from the past. For the case of Korea where 64% of land is consisted of the mountainous areas, establishment of the check dams has been drastically increased after 2000 in order to reduce the damages from the debris flow. However, due to the lack of data on scale, location and kind of check dams established for reducing the damages in debris flow, the measures to prevent damages based on experience and subjective basis have to be relied on. This study, the high-precision DEM data was structured by using the terrestrial LiDAR in the Jecheon area where the debris flow damage occurred in July 2009. And, from the numerical models of the debris flow, Kanako-2D that is available to reflect the erosion and deposition action was applied to install the erosion control facilities (water channel, check dam) and analyzed the effect of reducing the debris flow shown in the downstream. After installing the erosion control facilities, most of debris flow moves along the water channel to reduce the area to expand the debris flow, and after installing the check dam, the flow depth and flux of the debris flow were reduced along with the erosion. However, even after constructing the erosion control facilities, damages were still inflicted on private residences or agricultural sites located on the upper regions where the deposition was made. Acknowledgments This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(NRF-2016R1D1A3B03933362)

  11. A probabilistic model of debris-flow delivery to stream channels, demonstrated for the Coast Range of Oregon, USA

    Science.gov (United States)

    Daniel J. Miller; Kelly M. Burnett

    2008-01-01

    Debris flows are important geomorphic agents in mountainous terrains that shape channel environments and add a dynamic element to sediment supply and channel disturbance. Identification of channels susceptible to debris-flow inputs of sediment and organic debris, and quantification of the likelihood and magnitude of those inputs, are key tasks for characterizing...

  12. The perfect debris flow? Aggregated results from 28 large-scale experiments

    Science.gov (United States)

    Iverson, Richard M.; Logan, Matthew; LaHusen, Richard G.; Berti, Matteo

    2010-01-01

    Aggregation of data collected in 28 controlled experiments reveals reproducible debris-flow behavior that provides a clear target for model tests. In each experiment ∼10 m3 of unsorted, water-saturated sediment composed mostly of sand and gravel discharged from behind a gate, descended a steep, 95-m flume, and formed a deposit on a nearly horizontal runout surface. Experiment subsets were distinguished by differing basal boundary conditions (1 versus 16 mm roughness heights) and sediment mud contents (1 versus 7 percent dry weight). Sensor measurements of evolving flow thicknesses, basal normal stresses, and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated, coarse-grained, high-friction snouts, followed by bodies of nearly liquefied, finer-grained debris. Mud enhanced flow mobility by maintaining high pore pressures in flow bodies, and bed roughness reduced flow speeds but not distances of flow runout. Roughness had these effects because it promoted debris agitation and grain-size segregation, and thereby aided growth of lateral levees that channelized flow. Grain-size segregation also contributed to development of ubiquitous roll waves, which had diverse amplitudes exhibiting fractal number-size distributions. Despite the influence of these waves and other sources of dispersion, the aggregated data have well-defined patterns that help constrain individual terms in a depth-averaged debris-flow model. The patterns imply that local flow resistance evolved together with global flow dynamics, contradicting the hypothesis that any consistent rheology applied. We infer that new evolution equations, not new rheologies, are needed to explain how characteristic debris-flow behavior emerges from the interactions of debris constituents.

  13. Experimental Study on the Performance of Polyurethane-Steel Sandwich Structure under Debris Flow

    National Research Council Canada - National Science Library

    Peizhen Li; Shutong Liu; Zheng Lu

    2017-01-01

    Polyurethane-steel sandwich structure, which creatively uses the polyurethane-steel sandwich composite as a structural material, is proposed to strengthen the impact resistance of buildings under debris flow...

  14. A Virtual Geographic Environment for Debris Flow Risk Analysis in Residential Areas

    National Research Council Canada - National Science Library

    Lingzhi Yin; Jun Zhu; Yi Li; Chao Zeng; Qing Zhu; Hua Qi; Mingwei Liu; Weilian Li; Zhenyu Cao; Weijun Yang; Pengcheng Zhang

    2017-01-01

    Emergency risk assessment of debris flows in residential areas is of great significance for disaster prevention and reduction, but the assessment has disadvantages, such as a low numerical simulation...

  15. Hazard Assessment of Debris Flows in the Reservoir Region of Wudongde Hydropower Station in China

    Directory of Open Access Journals (Sweden)

    Cencen Niu

    2015-11-01

    Full Text Available The outbreak of debris flows in a reservoir region can affect the stability of hydropower stations and threaten the lives of the people living downstream of dams. Therefore, determining the hazard degree of debris flows in a reservoir region is of great importance. SPOT5 remote sensing images and digital elevation models are introduced to determine the characteristics of debris-flow catchments. The information is acquired through comprehensive manual investigation and satellite image interpretation. Ten factors that influence debris flow are extracted for the hazard assessment. The weight of these factors is determined using the analytic hierarchy process method. As a multi-criterion decision analysis method, fuzzy synthetic evaluation is applied for hazard assessment.

  16. Capturing spatiotemporal variation in wildfires for improving postwildfire debris-flow hazard assessments: Chapter 20

    Science.gov (United States)

    Haas, Jessica R.; Thompson, Matthew P.; Tillery, Anne C.; Scott, Joe H.

    2017-01-01

    Wildfires can increase the frequency and magnitude of catastrophic debris flows. Integrated, proactive natural hazard assessment would therefore characterize landscapes based on the potential for the occurrence and interactions of wildfires and postwildfire debris flows. This chapter presents a new modeling effort that can quantify the variability surrounding a key input to postwildfire debris-flow modeling, the amount of watershed burned at moderate to high severity, in a prewildfire context. The use of stochastic wildfire simulation captures variability surrounding the timing and location of ignitions, fire weather patterns, and ultimately the spatial patterns of watershed area burned. Model results provide for enhanced estimates of postwildfire debris-flow hazard in a prewildfire context, and multiple hazard metrics are generated to characterize and contrast hazards across watersheds. Results can guide mitigation efforts by allowing planners to identify which factors may be contributing the most to the hazard rankings of watersheds.

  17. Debris flows in the eastern Italian Alps: seasonality and atmospheric circulation patterns

    National Research Council Canada - National Science Library

    Nikolopoulos, E. I; Borga, M; Marra, F; Crema, S; Marchi, L

    2015-01-01

    ... (eastern Italian Alps). Analysis is based on classification algorithms applied to a uniquely dense archive of debris flows and hourly rain gauge precipitation series covering the period 2000–2009...

  18. Debris flow hazard modelling on medium scale: Valtellina di Tirano, Italy

    National Research Council Canada - National Science Library

    Blahut, J; Horton, P; Sterlacchini, S; Jaboyedoff, M

    2010-01-01

    ... (spatial and temporal), and the delimitation of the potential runout areas. Debris flow hazard zonation was carried out in the area of the Consortium of Mountain Municipalities of Valtellina di Tirano (Central Alps, Italy...

  19. Implementation of the RAMMS DEBRIS FLOW to Italian case studies

    Science.gov (United States)

    Vennari, Carmela; Mc Ardell, Brian; Parise, Mario; Santangelo, Nicoletta; Santo, Antonio

    2016-04-01

    RAMMS (RApid Mass MovementS) Debris Flow runout model solves 2D shallow-water equation using the Voellmy friction law. The model has been developed by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), and the Swiss Federal Institute for Snow and Avalanche Research (SLF). It requires as input the following data: topography, release area or hydrograph, and the friction parameters μ and ξ. Deposition height, velocity, pressure and momentum are the most important outcomes, also in terms of Max values. The model was applied primarily in Alpine catchments to simulate debris flow runout. Beside the Alps, alluvial events are very common even in torrential catchments of the Southern Apennines of Italy, and contribute to build alluvial fans mainly located at the foothill of carbonate and volcanic mountains. During the last decades several events occurred in these areas, often highly populated, and caused serious damage to society and to people. Several case studies have been selected from a database on alluvial events in torrential catchments of Campania region, aimed at applying the RAMMS model to back-analyze the documented events, and to simulate future similar scenarios in different triggering conditions. In order to better understand the obtained data and choose the best results, field data are mandatories. For this reason we focused our attention on torrential events for which field data concerning deposition area and deposition height were available. We simulated different scenarios, with variable peak discharge and friction parameters, reproducing also the influence of anthropogenic structures. To choose the best results, observed data and predicted data were compared in an objective way, by means of a quantitative analysis. Predicted and observed deposition areas were compared in a GIS environment, and the best test was evaluated by computing several statistics accuracy derived from the confusion matrix, including the sensitivity, that

  20. Radar rainfall estimation for the identification of debris-flow precipitation thresholds

    Science.gov (United States)

    Marra, Francesco; Nikolopoulos, Efthymios I.; Creutin, Jean-Dominique; Borga, Marco

    2014-05-01

    Identification of rainfall thresholds for the prediction of debris-flow occurrence is a common approach for warning procedures. Traditionally the debris-flow triggering rainfall is derived from the closest available raingauge. However, the spatial and temporal variability of intense rainfall on mountainous areas, where debris flows take place, may lead to large uncertainty in point-based estimates. Nikolopoulos et al. (2014) have shown that this uncertainty translates into a systematic underestimation of the rainfall thresholds, leading to a step degradation of the performances of the rainfall threshold for identification of debris flows occurrence under operational conditions. A potential solution to this limitation lies on use of rainfall estimates from weather radar. Thanks to their high spatial and temporal resolutions, these estimates offer the advantage of providing rainfall information over the actual debris flow location. The aim of this study is to analyze the value of radar precipitation estimations for the identification of debris flow precipitation thresholds. Seven rainfall events that triggered debris flows in the Adige river basin (Eastern Italian Alps) are analyzed using data from a dense raingauge network and a C-Band weather radar. Radar data are elaborated by using a set of correction algorithms specifically developed for weather radar rainfall application in mountainous areas. Rainfall thresholds for the triggering of debris flows are identified in the form of average intensity-duration power law curves using a frequentist approach by using both radar rainfall estimates and raingauge data. Sampling uncertainty associated to the derivation of the thresholds is assessed by using a bootstrap technique (Peruccacci et al. 2012). Results show that radar-based rainfall thresholds are largely exceeding those obtained by using raingauge data. Moreover, the differences between the two thresholds may be related to the spatial characteristics (i.e., spatial

  1. Can we reduce debris flow to an equivalent one-phase flow?

    Science.gov (United States)

    Chareyre, B.; Marzougui, D.; Chauchat, J.

    2015-09-01

    A recent extension of the discrete element method is reported for the simulation of dense mixtures of non-colloidal particles and viscous fluids in the non-inertial regime. As an application, we examine the interplay between rate dependent dilatancy and hydro-mechanical coupling which can be expected in debris flow. The numerical model includes sphere-sphere contacts using a soft contact approach [2], short range hydrodynamic interactions defined by frame-invariant expressions of forces and torques in the lubrication approximation, and drag forces resulting from the poromechanical coupling computed with the DEM-PFV technique [3]. The bulk shear stress is decomposed into contact stress and hydrodynamic stress. Both contributions are shown to be increasing functions of a dimensionless shear rate Iv, in agreement with experimental results [4]. Statistics of microstructural variables highlight a complex interplay between solid contacts and hydrodynamic interactions. In contrast with a popular idea, the results suggest that lubrication may not necessarily reduce the contribution of contact forces to the bulk shear stress. The proposed model is general and applies directly to sheared satured granular media in which pore pressure feedback plays a key role. We argue that it can be the case for debris fow, especially during the triggering phase, when run-out include transitional phases, and when the flow is stopped. It is then concluded that debris cannot be computed by assuming solely the rheological properties of an equivalent mixture.

  2. Catastrophic debris flows transformed from landslides in volcanic terrains : mobility, hazard assessment and mitigation strategies

    Science.gov (United States)

    Scott, Kevin M.; Macias, Jose Luis; Naranjo, Jose Antonio; Rodriguez, Sergio; McGeehin, John P.

    2001-01-01

    Communities in lowlands near volcanoes are vulnerable to significant volcanic flow hazards in addition to those associated directly with eruptions. The largest such risk is from debris flows beginning as volcanic landslides, with the potential to travel over 100 kilometers. Stratovolcanic edifices commonly are hydrothermal aquifers composed of unstable, altered rock forming steep slopes at high altitudes, and the terrain surrounding them is commonly mantled by readily mobilized, weathered airfall and ashflow deposits. We propose that volcano hazard assessments integrate the potential for unanticipated debris flows with, at active volcanoes, the greater but more predictable potential of magmatically triggered flows. This proposal reinforces the already powerful arguments for minimizing populations in potential flow pathways below both active and selected inactive volcanoes. It also addresses the potential for volcano flank collapse to occur with instability early in a magmatic episode, as well as the 'false-alarm problem'-the difficulty in evacuating the potential paths of these large mobile flows. Debris flows that transform from volcanic landslides, characterized by cohesive (muddy) deposits, create risk comparable to that of their syneruptive counterparts of snow and ice-melt origin, which yield noncohesive (granular) deposits, because: (1) Volcano collapses and the failures of airfall- and ashflow-mantled slopes commonly yield highly mobile debris flows as well as debris avalanches with limited runout potential. Runout potential of debris flows may increase several fold as their volumes enlarge beyond volcanoes through bulking (entrainment) of sediment. Through this mechanism, the runouts of even relatively small collapses at Cascade Range volcanoes, in the range of 0.1 to 0.2 cubic kilometers, can extend to populated lowlands. (2) Collapse is caused by a variety of triggers: tectonic and volcanic earthquakes, gravitational failure, hydrovolcanism, and

  3. Modeling debris-flow runout patterns on two alpine fans with different dynamic simulation models

    OpenAIRE

    Schraml, K.; B. Thomschitz; McArdell, B. W.; Graf, C.; R. Kaitna

    2015-01-01

    Predicting potential deposition areas of future debris-flow events is important for engineering hazard assessment in alpine regions. To this end, numerical simulation models are commonly used tools. However, knowledge of appropriate model parameters is essential but often not available. In this study we use two numerical simulation models, RAMMS–DF (rapid mass movement system–debris-flow) and DAN3D (dynamic analysis of landslides in three dimensions), to back-calculate two w...

  4. Numerical Modeling of Debris Flow Force Caused by Climate Change and Its application to Check Dam

    Science.gov (United States)

    KIM, S. D.; Jun, K.; JUN, B. H.; Lee, H. J.; TAK, W. J.

    2016-12-01

    Due to global warming, climate change cause a super hurricane and heavy rainfall frequently. Heavy rainfall cause by debris flow in mountainous terrains, and disasters by debris flow force have continuously increased. The purpose of this study is to analyze the characteristics of debris flow force acting on the check dam. The numerical approach to the debris flow force was performed by the Finite Difference Method (FDM) based on the erosion-deposition combination model including the equation of continuity, mass conservation, and momentum conservation. In order to investigate behavior of the debris flow force according to the variance of supplying water discharge and channel slope angle, a rectangular straight channel and one closed type check dam was set up for conducting numerical simulations. As the supply water discharges increase, the curve of the impact force by debris flow becomes unstable and fluctuation with high impact force occurred as time passes. And the peak impact force showed a steeper slope and appeared more quickly, the high impact force undergoes a fluctuation with high speed, and acting on the check dam. At the mountainous upstream, strong rainfall energy provoke a repeat erosion and deposition which results in debris flow force causing much damage along the check dam at the mountainous place. The analyses of the present study help provide information to predict future debris flow force and how to design for the check dam. This research was supported by a grant [MPSS-NH-2014-74] through the Disaster and Safety Management Institute funded by Ministry of Public Safety and Security of Korean government

  5. Development of the Assessment Items of Debris Flow Using the Delphi Method

    Science.gov (United States)

    Byun, Yosep; Seong, Joohyun; Kim, Mingi; Park, Kyunghan; Yoon, Hyungkoo

    2016-04-01

    In recent years in Korea, Typhoon and the localized extreme rainfall caused by the abnormal climate has increased. Accordingly, debris flow is becoming one of the most dangerous natural disaster. This study aimed to develop the assessment items which can be used for conducting damage investigation of debris flow. Delphi method was applied to classify the realms of assessment items. As a result, 29 assessment items which can be classified into 6 groups were determined.

  6. Application of the Empirical Thresholds of Precipitation to the Debris Flows in Mexico

    Science.gov (United States)

    Cardoso-Landa, G.

    2013-05-01

    The debris flows are particularly dangerous for the life and the properties due to its high speeds and great destructive force, destroying houses, ways, bridges, trees and cultures, currents and ecosystems throughout its trajectory. The extraordinary precipitation events are one of the predominant physical processes that produce the genesis of the debris flows. The empirical thresholds of precipitation are based on the historical analyses of the occurrence relation precipitation/debris flow, for example statistical analyses. At the present time a limited number of this type of empirical thresholds exists and have been used different diagrams to represent them, depending on the combinations of precipitation parameters more commonly used: antecedent precipitation, duration, accumulated intensity and rain, and the most commons are that obtained by Caine and Aleotti. An analytical presentation of the concept of threshold of precipitation of a debris flow was recently introduced by Iritanno et al. (1998), who introduced the called function of mobilization Y(t), indirectly describing all the factors that contribute to trigger a process of landslides and that is dependent, in every moment of time t, the amount of water infiltrate on the ground before the time t. In the full article was applied the Iritanno's function of mobilization to the records of precipitation that produced the debris flows in the north of Puebla State, in the country of México, obtaining relationships intensity of rain-duration for these debris flows are greater from 3.43 to 2.1 times over empirical thresholds of precipitation generators of debris flows proposed by Caine and Aleotti in other regions of the world. .Intensity of precipitation for the debris flows in Mexicot;

  7. Probabilistic rainfall thresholds for triggering debris flows in a human-modified landscape

    Science.gov (United States)

    Giannecchini, Roberto; Galanti, Yuri; D'Amato Avanzi, Giacomo; Barsanti, Michele

    2016-03-01

    In the Carrara Marble Basin (CMB; Apuan Alps, Italy) quarrying has accumulated widespread and thick quarry waste, lying on steep slopes and invading valley bottoms. The Apuan Alps are one of the rainiest areas in Italy and rainstorms often cause landslides and debris flows. The stability conditions of quarry waste are difficult to assess, owing to its textural, geotechnical and hydrogeological variability. Therefore, empirical rainfall thresholds may be effective in forecasting the possible occurrence of debris flows in the CMB. Three types of thresholds were defined for three rain gauges of the CMB and for the whole area: rainfall intensity-rainfall duration (ID), cumulated event rainfall-rainfall duration (ED), and cumulated event rainfall normalized by the mean annual precipitation-rainfall intensity (EMAPI). The rainfall events recorded from 1950 to 2005 was analyzed and compared with the occurrence of debris flows involving the quarry waste. They were classified in events that triggered one or more debris flows and events that did not trigger debris flows. This dataset was fitted using the logistic regression method that allows us to define a set of thresholds, corresponding to different probabilities of failure (from 10% to 90%) and therefore to different warning levels. The performance of the logistic regression in defining probabilistic thresholds was evaluated by means of contingency tables, skill scores and receiver operating characteristic (ROC) analysis. These analyses indicate that the predictive capability of the three types of threshold is acceptable for each rain gauge and for the whole CMB. The best compromise between the number of correct debris flow predictions and the number of wrong predictions is obtained for the 40% probability thresholds. The results obtained can be tested in an experimental debris flows forecasting system based on rainfall thresholds, and could have implications for the debris flow hazard and risk assessment in the CMB.

  8. Modeling four occurred debris flow events in the Dolomites area (North-Eastern Italian Alps)

    Science.gov (United States)

    Boreggio, Mauro; Gregoretti, Carlo; Degetto, Massimo; Bernard, Martino

    2016-04-01

    Four occurred debris flows in the Dolomites area (North-Eastern Italian Alps) are modeled by back-analysis. The four debris flows events are those occurred at Rio Lazer (Trento) on the 4th of November 1966, at Fiames (Belluno) on the 5th of July 2006, at Rovina di Cancia (Belluno) on the 18th of July 2009 and at Rio Val Molinara (Trento) on the 15th of August 2010. In all the events, runoff entrained sediments present on natural channels and formed a solid-liquid wave that routed downstream. The first event concerns the routing of debris flow on an inhabited fan. The second event the deviation of debris flow from the usual path due to an obstruction with the excavation of a channel in the scree and the downstream spreading in a wood. The third event concerns the routing of debris flow in a channel with an ending the reservoir, its overtopping and final spreading in the inhabited area. The fourth event concerns the routing of debris flow along the main channel downstream the initiation area until spreading just upstream a village. All the four occurred debris flows are simulated by modeling runoff that entrained debris flow for determining the solid-liquid hydrograph. The routing of the solid-liquid hydrograph is simulated by a bi-phase cell model based on the kinematic approach. The comparison between simulated and measured erosion and deposition depths is satisfactory. Nearly the same parameters for computing erosion and deposition were used for all the four occurred events. The maps of erosion and deposition depths are obtained by comparing the results of post-event surveys with the pre-event DEM. The post-event surveys were conducted by using different instruments (LiDAR and GPS) or the combination photos-single points depth measurements (in this last case it is possible obtaining the deposition/erosion depths by means of stereoscopy techniques).

  9. Comparing debris flow relationships in the Alps and in the Pyrenees

    OpenAIRE

    Beguería, S.; J. M. García-Ruiz; A. Lorente; Martí, C.

    2002-01-01

    Debris flows are a well known geomorphic process all over the World, as can be seen in the map presented by Innes (1983). In fact, many authors consider that debris flows are the most active geomorphic hazard in mountain areas, affecting human settlements, infrastructures and touristic resorts (Takahashi et al., 1981). Many papers even report the loss of lives, both in developed and in developing countries. This is the reason why many studies have been devoted to identify the factors that tri...

  10. Influence of check dams on debris-flow run-out intensity

    OpenAIRE

    Remaître, A.; Asch, Th.W.J. van; Malet, J.-P.; Maquaire, O.

    2008-01-01

    Debris flows are very dangerous phenomena claiming thousands of lives and millions of Euros each year over the world. Disaster mitigation includes non-structural (hazard mapping, insurance policies), active structural (drainage systems) and passive structural (check dams, stilling basins) countermeasures. Since over twenty years, many efforts are devoted by the scientific and engineering communities to the design of proper devices able to capture the debris-flow volume and/or break down the e...

  11. Response of a Brook Trout Population and Instream Habitat to a Catastrophic Flood and Debris Flow

    Science.gov (United States)

    Criag N. Roghair; C. Andrew Dolloff; Martin K. Underwood

    2002-01-01

    In June 1995, a massive flood and debris flow impacted fish and habitat along the lower 1.9 km of the Staunton River, a headwater stream located in Shenandoah National Park, Virginia. In the area affected by debris flow, the stream bed was scoured and new substrate materials were deposited, trees were removed from a 30-m-wide band in the riparian area, and all fish...

  12. Experimental Study on Impact Load on a Dam Due to Debris Flow

    Science.gov (United States)

    lwao Miyoshi

    1991-01-01

    When a dam is struck by mud or debris flow, it is put under a great impact load and sometimes is destroyed. To prevent such destruction, it is important to perform basic research about the impact load on a dam due to debris flow. Thus, we have made an experimental study and tried to establish a method to estimate such a impact load on the dam. The experiment was...

  13. [Three cases of nasal sinus foreign body caused by debris flow].

    Science.gov (United States)

    Li, Yimei; Shi, Zhu; Wang, Juxin

    2013-05-01

    A retrospective analysis of 3 patients with nasal sinus foreign body caused by debris flow admitted to our department. All of the three patients showed foreign odor and mucopurulent discharge in nasal cavity after the debris flow blast injury. CT examination found high density soft tissue shadow or calcification in the nasal sinus. All the diagnoses were nasal sinus foreign body in three patients. The nasal sinus foreign bodies was dislodged through endoscopic sinus surgery. Three patients are all well-healed.

  14. Modelling debris transport within glaciers by advection in a full-Stokes ice flow model

    Science.gov (United States)

    Wirbel, Anna; Jarosch, Alexander H.; Nicholson, Lindsey

    2017-04-01

    As mountain glaciers recede worldwide, an increasing proportion of the remaining glacierized area is expected to become debris covered. The spatio-temporal development of a surface debris cover has profound effects on the glacier behaviour and meltwater generation, yet little is known about how glacier dynamics influence the spatial distribution of an emerging debris cover. Motivated by this lack of understanding, we present a coupled model to simulate advection and resulting deformation of debris features within glaciers. The finite element model developed in python consists of an advection scheme coupled to a full-Stokes ice flow model, using FEniCS as the numerical framework. We show results from numerical tests that demonstrate its suitability to model advection-dominated transport of concentration in a divergence-free velocity field. The capabilities of the coupled model are demonstrated by simulating transport of debris features of different initial size, shape and location through modelled velocity fields of representative mountain glaciers. The results indicate that deformation of initial debris inputs, as a consequence of being transported through the glacier, plays an important role in determining the location and rate of debris emergence at the glacier surface. The presented work lays the foundation for comprehensive simulations of realistic patterns of debris cover, their spatial and temporal variability and the timescales over which debris covers can form.

  15. Coupling of rainfall-induced landslide triggering model with predictions of debris flow runout distances

    Science.gov (United States)

    Lehmann, Peter; von Ruette, Jonas; Fan, Linfeng; Or, Dani

    2014-05-01

    Rapid debris flows initiated by rainfall induced shallow landslides present a highly destructive natural hazard in steep terrain. The impact and run-out paths of debris flows depend on the volume, composition and initiation zone of released material and are requirements to make accurate debris flow predictions and hazard maps. For that purpose we couple the mechanistic 'Catchment-scale Hydro-mechanical Landslide Triggering (CHLT)' model to compute timing, location, and landslide volume with simple approaches to estimate debris flow runout distances. The runout models were tested using two landslide inventories obtained in the Swiss Alps following prolonged rainfall events. The predicted runout distances were in good agreement with observations, confirming the utility of such simple models for landscape scale estimates. In a next step debris flow paths were computed for landslides predicted with the CHLT model for a certain range of soil properties to explore its effect on runout distances. This combined approach offers a more complete spatial picture of shallow landslide and subsequent debris flow hazards. The additional information provided by CHLT model concerning location, shape, soil type and water content of the released mass may also be incorporated into more advanced models of runout to improve predictability and impact of such abruptly-released mass.

  16. Characteristics of rainfall triggering of debris flows in the Chenyulan watershed, Taiwan

    Directory of Open Access Journals (Sweden)

    J. C. Chen

    2013-04-01

    Full Text Available This paper reports the variation in rainfall characteristics associated with debris flows in the Chenyulan watershed, central Taiwan, between 1963 and 2009. The maximum hourly rainfall Im, the maximum 24 h rainfall Rd, and the rainfall index RI (defined as the product RdIm were analysed for each rainfall event that triggered a debris flow within the watershed. The corresponding number of debris flows initiated by each rainfall event (N was also investigated via image analysis and/or field investigation. The relationship between N and RI was analysed. Higher RI of a rainfall event would trigger a larger number of debris flows. This paper also discusses the effects of the Chi-Chi earthquake (CCE on this relationship and on debris flow initiation. The results showed that the critical RI for debris flow initiation had significant variations and was significantly lower in the years immediately following the CCE of 1999, but appeared to revert to the pre-earthquake condition about five years later. Under the same extreme rainfall event of RI = 365 cm2 h−1, the value of N in the CCE-affected period could be six times larger than that in the non-CCE-affected periods.

  17. Exploiting LSPIV to assess debris-flow velocities in the field

    Directory of Open Access Journals (Sweden)

    J. I. Theule

    2018-01-01

    Full Text Available The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek. Free software has been employed for preliminary treatment (orthorectification and format conversion of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.

  18. Exploiting LSPIV to assess debris-flow velocities in the field

    Science.gov (United States)

    Theule, Joshua I.; Crema, Stefano; Marchi, Lorenzo; Cavalli, Marco; Comiti, Francesco

    2018-01-01

    The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV) can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface) are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek). Free software has been employed for preliminary treatment (orthorectification and format conversion) of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.

  19. Model simulations of flood and debris flow timing in steep catchments after wildfire

    Science.gov (United States)

    Rengers, Francis; McGuire, Luke; Kean, Jason W.; Staley, Dennis M.; Hobley, D.E.J

    2016-01-01

    Debris flows are a typical hazard on steep slopes after wildfire, but unlike debris flows that mobilize from landslides, most post-wildfire debris flows are generated from water runoff. The majority of existing debris-flow modeling has focused on landslide-triggered debris flows. In this study we explore the potential for using process-based rainfall-runoff models to simulate the timing of water flow and runoff-generated debris flows in recently burned areas. Two different spatially distributed hydrologic models with differing levels of complexity were used: the full shallow water equations and the kinematic wave approximation. Model parameter values were calibrated in two different watersheds, spanning two orders of magnitude in drainage area. These watersheds were affected by the 2009 Station Fire in the San Gabriel Mountains, CA, USA. Input data for the numerical models were constrained by time series of soil moisture, flow stage, and rainfall collected at field sites, as well as high-resolution lidar-derived digital elevation models. The calibrated parameters were used to model a third watershed in the burn area, and the results show a good match with observed timing of flow peaks. The calibrated roughness parameter (Manning's $n$) was generally higher when using the kinematic wave approximation relative to the shallow water equations, and decreased with increasing spatial scale. The calibrated effective watershed hydraulic conductivity was low for both models, even for storms occurring several months after the fire, suggesting that wildfire-induced changes to soil-water infiltration were retained throughout that time. Overall the two model simulations were quite similar suggesting that a kinematic wave model, which is simpler and more computationally efficient, is a suitable approach for predicting flood and debris flow timing in steep, burned watersheds.

  20. On the efficiency of an open retention check dam against a debris flow

    Science.gov (United States)

    D'Agostino, Vincenzo; Bertoldi, Gabriele; Bettella, Francesco

    2017-04-01

    The high-intensity rainfalls occurred on the 4th of August 2015 triggered different debris flows in the torrent Boite valley (Belluno, Italy). Three people died and considerable damages to villages and infrastructures were caused. The research investigates on the debris-flow event occurred in the rio Rudan catchment (south facing slope of the Antelao peak, Dolomites; tributary of the Boite torrent) and particularly on the interaction of the debris-flow front with a retention open check dam placed at the fan apex. The rainfall intensity of the rainstorm reached a value of 38 mm in 0.5 h (precipitation measured by the raingauge installed on the Antelao massif by the Regional Agency for Environmental Prevention and Protection of Veneto Region, ARPAV). This rainfall triggered a debris flow, which deposited 25000 cubic meters of solid material in the terminal reach of the channel and in the storage basin of the retention check dam. The research is voted to: i) conduct the back analysis of the debris-flow event estimating the peak discharge upstream and downstream of the check dam; ii) evaluate the influence of the structure on the reduction of the maximum debris-flow surge; iii) estimate the impact force of the flow on the structure. The back analysis was carried out through the application of different methodologies supported by field surveys (significant cross sections in different channel reaches, Close Range Photogrammetry of the fan area, measurement of the sizes of the biggest boulders entrained by the flow). The different methods used for the reconstruction of the maximum discharge of the debris flow provided converging values, allowing to conclude that the structure was capable to halve the peak discharge and to efficiently protect the neighboring village. Finally, the back calculation of the impact force of the flow against the check dam was conducted through the analysis of structure damages and indicated some design criteria for the most exposed parts of the

  1. Investigating the self-organization of debris flows: theory, modelling, and empirical work

    Science.gov (United States)

    von Elverfeldt, Kirsten; Keiler, Margreth; Elmenreich, Wilfried; Fehárvári, István; Zhevzhyk, Sergii

    2014-05-01

    Here we present the conceptual framework of an interdisciplinary project on the theory, empirics, and modelling of the self-organisation mechanisms within debris flows. Despite the fact that debris flows are causing severe damages in mountainous regions such as the Alps, the process behaviour of debris flows is still not well understood. This is mainly due to the process dynamics of debris flows: Erosion and material entrainment are essential for their destructive power, and because of this destructiveness it is nearly impossible to measure and observe these mechanisms in action. Hence, the interactions between channel bed and debris flow remain largely unknown whilst this knowledge is crucial for the understanding of debris flow behaviour. Furthermore, while these internal parameter interactions are changing during an event, they are at the same time governing the temporal and spatial evolution of a given event. This project aims at answering some of these unknowns by means of bringing theory, empirical work, and modelling of debris flows together. It especially aims at explaining why process types are switching along the flow path during an event, e.g. the change from a debris flow to a hyperconcentrated flow and back. A second focus is the question of why debris flows sometimes exhibit strong erosion and sediment mobilisation during an event and at other times they do not. A promising theoretical framework for the analysis of these observations is that of self-organizing systems, and especially Haken's theory of synergetics. Synergetics is an interdisciplinary theory of open systems that are characterized by many individual, yet interacting parts, resulting in spatio-temporal structures. We hypothesize that debris flows can successfully be analysed within this theoretical framework. In order to test this hypothesis, an innovative modelling approach is chosen in combination with detailed field work. In self-organising systems the interactions of the system

  2. Effects of Debris Flows on Stream Ecosystems of the Klamath Mountains, Northern California

    Science.gov (United States)

    Cover, M. R.; Delafuente, J. A.; Resh, V. H.

    2006-12-01

    We examined the long-term effects of debris flows on channel characteristics and aquatic food webs in steep (0.04-0.06 slope), small (4-6 m wide) streams. A large rain-on-snow storm event in January 1997 resulted in numerous landslides and debris flows throughout many basins in the Klamath Mountains of northern California. Debris floods resulted in extensive impacts throughout entire drainage networks, including mobilization of valley floor deposits and removal of vegetation. Comparing 5 streams scoured by debris flows in 1997 and 5 streams that had not been scoured as recently, we determined that debris-flows decreased channel complexity by reducing alluvial step frequency and large woody debris volumes. Unscoured streams had more diverse riparian vegetation, whereas scoured streams were dominated by dense, even-aged stands of white alder (Alnus rhombiflia). Benthic invertebrate shredders, especially nemourid and peltoperlid stoneflies, were more abundant and diverse in unscoured streams, reflecting the more diverse allochthonous resources. Debris flows resulted in increased variability in canopy cover, depending on degree of alder recolonization. Periphyton biomass was higher in unscoured streams, but primary production was greater in the recently scoured streams, suggesting that invertebrate grazers kept algal assemblages in an early successional state. Glossosomatid caddisflies were predominant scrapers in scoured streams; heptageniid mayflies were abundant in unscoured streams. Rainbow trout (Oncorhynchus mykiss) were of similar abundance in scoured and unscoured streams, but scoured streams were dominated by young-of-the-year fish while older juveniles were more abundant in unscoured streams. Differences in the presence of cold-water (Doroneuria) versus warm-water (Calineuria) perlid stoneflies suggest that debris flows have altered stream temperatures. Debris flows have long-lasting impacts on stream communities, primarily through the cascading effects of

  3. Probabilistic forecasts of debris-flow hazard at the regional scale with a combination of models.

    Science.gov (United States)

    Malet, Jean-Philippe; Remaître, Alexandre

    2015-04-01

    Debris flows are one of the many active slope-forming processes in the French Alps, where rugged and steep slopes mantled by various slope deposits offer a great potential for triggering hazardous events. A quantitative assessment of debris-flow hazard requires the estimation, in a probabilistic framework, of the spatial probability of occurrence of source areas, the spatial probability of runout areas, the temporal frequency of events, and their intensity. The main objective of this research is to propose a pipeline for the estimation of these quantities at the region scale using a chain of debris-flow models. The work uses the experimental site of the Barcelonnette Basin (South French Alps), where 26 active torrents have produced more than 150 debris-flow events since 1850 to develop and validate the methodology. First, a susceptibility assessment is performed to identify the debris-flow prone source areas. The most frequently used approach is the combination of environmental factors with GIS procedures and statistical techniques, integrating or not, detailed event inventories. Based on a 5m-DEM and derivatives, and information on slope lithology, engineering soils and landcover, the possible source areas are identified with a statistical logistic regression model. The performance of the statistical model is evaluated with the observed distribution of debris-flow events recorded after 1850 in the study area. The source areas in the three most active torrents (Riou-Bourdoux, Faucon, Sanières) are well identified by the model. Results are less convincing for three other active torrents (Bourget, La Valette and Riou-Chanal); this could be related to the type of debris-flow triggering mechanism as the model seems to better spot the open slope debris-flow source areas (e.g. scree slopes), but appears to be less efficient for the identification of landslide-induced debris flows. Second, a susceptibility assessment is performed to estimate the possible runout distance

  4. Evidence for debris flow gully formation initiated by shallow subsurface water on Mars

    Science.gov (United States)

    Lanza, N.L.; Meyer, G.A.; Okubo, C.H.; Newsom, Horton E.; Wiens, R.C.

    2010-01-01

    The morphologies of some martian gullies appear similar to terrestrial features associated with debris flow initiation, erosion, and deposition. On Earth, debris flows are often triggered by shallow subsurface throughflow of liquid water in slope-mantling colluvium. This flow causes increased levels of pore pressure and thus decreased shear strength, which can lead to slide failure of slope materials and subsequent debris flow. The threshold for pore pressure-induced failure creates a distinct relationship between the contributing area supplying the subsurface flow and the slope gradient. To provide initial tests of a similar debris flow initiation hypothesis for martian gullies, measurements of the contributing areas and slope gradients were made at the channel heads of martian gullies seen in three HiRISE stereo pairs. These gullies exhibit morphologies suggestive of debris flows such as leveed channels and lobate debris fans, and have well-defined channel heads and limited evidence for multiple flows. Our results show an area-slope relationship for these martian gullies that is consistent with that observed for terrestrial gullies formed by debris flow, supporting the hypothesis that these gullies formed as the result of saturation of near-surface regolith by a liquid. This model favors a source of liquid that is broadly distributed within the source area and shallow; we suggest that such liquid could be generated by melting of broadly distributed icy materials such as snow or permafrost. This interpretation is strengthened by observations of polygonal and mantled terrain in the study areas, which are both suggestive of near-surface ice. ?? 2009 Elsevier Inc.

  5. A comparative 2D modeling of debris-flow propagation and outcomes for end-users

    Science.gov (United States)

    Bettella, F.; Bertoldi, G.; Pozza, E.; McArdell, B. W.; D'Agostino, V.

    2012-04-01

    In Alpine regions gravity-driven natural hazards, in particular debris flows, endanger settlements and human life. Mitigation strategies based on hazard maps are necessary tools for land planning. These maps can be made more precise by using numerical models to forecasting the inundated areas after a careful setting of those 'key parameters' (K-P) which directly affect the flow motion and its interaction with the ground surface. Several physically based 2D models are available for practitioners and governmental agencies, but the selection criteria of model type and of the related K-P remain flexible and partly subjective. This remark has driven us to investigate how different models simulate different types of debris flows (from granular to muddy debris flows, going through intermediate types), in particular when the flow is influenced by the presence of deposition basins. Two commercial 2D physical models (RAMMS and FLO-2D) have been tested for five well-documented debris flows events from five Italian catchments were different geology and flow dynamics are observed: 1) a viscous debris flow occurred in 2009 in a catchment with a metamorphic geology (Gadria torrent, Bolzano Province); 2) the 2009 granular debris flow in an granitic geological setting (Rio Dosson, Trento Province); 3-4) two events occurred in the 'rio Val del Lago' and 'rio Molinara' (Trento Province) in 2010 where porphyritic lithology prevails (intermediate granular debris flow); 5) the Rotolon torrent (Vicenza Province) 2009 debris flow containing sedimentary rocks enclosed in an abundant clay-rich matrix (intermediate viscous case). Event volumes range from 5.000 to 50.000 cubic meters. The Gadria, Rotolon and Val del Lago events are also influenced by artificial retention basins. Case study simulations allowed delineation of some practical end-user suggestions and good practices in order to guide the model choice and the K-P setting, particularly related to different flow dynamics. The

  6. Evidence of debris flow occurrence after wildfire in upland catchments of south-east Australia

    Science.gov (United States)

    Nyman, Petter; Sheridan, Gary J.; Smith, Hugh G.; Lane, Patrick N. J.

    2011-02-01

    Numerous reports of "flash floods", "mud torrents" and "landslides" in burnt landscapes of south-east Australia were only recently linked to debris flows and recognised as a significant process that warrant more detailed investigation. This paper provides a systematic documentation of high-magnitude erosion events after wildfire in south-east Australia, focusing on small (fire runoff generated debris flows in Australia, so the discussion draws on literature from the western USA, where a large body of research has been dedicated to evaluating the risk posed by post-fire debris flows and their role in landscape processes. Typical features common to both systems include low infiltration capacity of burnt catchments; widespread sheet erosion and levee lined rills on steep upper hillslopes; and severe channel erosion initiated in response to convergent flow in previously un-scoured drainage lines. The depth of sheet erosion on surveyed slopes in the upper catchments (4.6 ± 0.96 mm to 18.4 ± 2.7 mm) indicates that hillslope material provides an important source of sediment. The average channel entrainment rate of three debris flows ranged from 0.6 to 1.4 m 3 m -1. Runoff generated debris flows were not recorded in wet or damp forest types suggesting that this process is unlikely to operate in these forest environments. One isolated case of mass failure generated debris flow was recorded in wet forest. The outcome of the study indicates that runoff generated debris flows in dry eucalypt forest are an important process to be considered during post-fire risk assessment of hydrological hazards.

  7. Quantitative reconstruction of late Holocene surface evolution on an alpine debris-flow fan

    Science.gov (United States)

    Schürch, Peter; Densmore, Alexander L.; Ivy-Ochs, Susan; Rosser, Nick J.; Kober, Florian; Schlunegger, Fritz; McArdell, Brian; Alfimov, Vasili

    2016-12-01

    Debris-flow fans form a ubiquitous record of past debris-flow activity in mountainous areas, and may be useful for inferring past flow characteristics and consequent future hazard. Extracting information on past debris flows from fan records, however, requires an understanding of debris-flow deposition and fan surface evolution; field-scale studies of these processes have been very limited. In this paper, we document the patterns and timing of debris-flow deposition on the surface of the large and exceptionally active Illgraben fan in southwestern Switzerland. We use terrain analysis, radiocarbon dating of sediment fill in the Illgraben catchment, and cosmogenic 10Be and 36Cl exposure dating of debris-flow deposits on the fan to constrain the temporal evolution of the sediment routing system in the catchment and on the fan during the past 3200 years. We show that the fan surface preserves a set of debris-flow lobes that were predominantly deposited after the occurrence of a large rock avalanche near the fan apex at about 3200 years ago. This rock avalanche shifted the apex of the fan and impounded sediment within the Illgraben catchment. Subsequent evolution of the fan surface has been governed by both lateral and radial shifts in the active depositional lobe, revealed by the cosmogenic radionuclide dates and by cross-cutting geometrical relationships on the fan surface. This pattern of frequent avulsion and fan surface occupation provides field-scale evidence of the type of large-scale compensatory behavior observed in experimental sediment routing systems.

  8. Evolution of a natural debris flow: In situ measurements of flow dynamics, video imagery, and terrestrial laser scanning

    Science.gov (United States)

    McCoy, S.W.; Kean, J.W.; Coe, J.A.; Staley, D.M.; Wasklewicz, T.A.; Tucker, G.E.

    2010-01-01

    Many theoretical and laboratory studies have been undertaken to understand debris-flow processes and their associated hazards. However, complete and quantitative data sets from natural debris flows needed for confirmation of these results are limited. We used a novel combination of in situ measurements of debris-flow dynamics, video imagery, and pre- and postflow 2-cm-resolution digital terrain models to study a natural debris-flow event. Our field data constrain the initial and final reach morphology and key flow dynamics. The observed event consisted of multiple surges, each with clear variation of flow properties along the length of the surge. Steep, highly resistant, surge fronts of coarse-grained material without measurable pore-fluid pressure were pushed along by relatively fine-grained and water-rich tails that had a wide range of pore-fluid pressures (some two times greater than hydrostatic). Surges with larger nonequilibrium pore-fluid pressures had longer travel distances. A wide range of travel distances from different surges of similar size indicates that dynamic flow properties are of equal or greater importance than channel properties in determining where a particular surge will stop. Progressive vertical accretion of multiple surges generated the total thickness of mapped debris-flow deposits; nevertheless, deposits had massive, vertically unstratified sedimentological textures. ?? 2010 Geological Society of America.

  9. LATE PLIOCENE-HOLOCENE DEBRIS FLOW DEPOSITS IN THE IONIAN SEA (EASTERN MEDITERRANEAN

    Directory of Open Access Journals (Sweden)

    GIOVANNI ALOISI DE LARDEREL

    1997-11-01

    Full Text Available Widespread coring of the Eastern Mediterranean Basin has outlined the existence of a systematic relation between lithology of debris flow deposits and physiographic setting. Whilst the topographic highs are characterized by pelagic sedimentation, the basin floors are alternatively subject to pelagic sedimentation and re-sedimentation pro cesses. Amongst the latters, turbidity flows and debris flows are the most common transport mechanisms.In this paper we present the study of the debris flow pro cess in the Ionian Sea using visual description of cores, grain size, carbonate content and smear slide analysis carried out on gravity and piston cores recovered over the past 20 years. A distinction has been made between debris flow deposits originating from the continental margins (North Africa and Malta Escarpment and those emplaced in the small basins amidst the Calabrian and Mediterranean ridges "Cobblestone Topography". As a result of the difference in setting, the former debris flow deposits include a great variety of lithologies and ages whilst the latter involve the pelagic sediments forming the typical Eastern Mediterranean Plio-Quaternary succession. A detailed study of clast and matrix structures makes it possible to describe the flows in terms of existing classifications of sediment gravity flows and to assume a clast support mechanism. Finally, biostratigraphy coupled with the presence of widespread marker beds enabled us to estimate the age of emplacement of the deposits and to hypothesize a triggering mechanism for flow initiation. Three flows are strictly related to the pelagic turbidite named homogenite, triggered by the explosive eruption of the Santorini volcano (Minoan eruption and therefore have an estimated age of 3,500 BP. The other deposits have ages ranging from 9,000 BP to about 70,000 BP and were originated by debris flows triggered by events such as earthquakes and glacial low sea level stands.    

  10. Debris flow monitoring in the Acquabona watershed on the Dolomites (Italian Alps)

    Science.gov (United States)

    Berti, M.; Genevois, R.; LaHusen, R.; Simoni, A.; Tecca, P.R.

    2000-01-01

    In 1997 a field monitoring system was installed in Acquabona Creek in the Dolomites (Eastern Italian Alps) to observe the hydrologic conditions for debris flow occurrence and some dynamic properties of debris flow. The monitoring system consists of three remote stations: an upper one located at the head of a deeply-incised channel and two others located downstream. The system is equipped with sensors for measuring rainfall, pore pressures in the mobile channel bottom, ground vibrations, debris flow depth, total normal stress and fluid pore-pressure at the base of the flow. Two video cameras record events at the upper channel station and one video is installed at the lowermost station. During summer 1998, three debris flows (volumes from less than 1000 m3 up to 9000 m3) occurred at Acquabona. The following results were obtained from a preliminary analysis of the data: 1) All of the flows were triggered by rainfalls of less than 1 hour duration, with peak rainfall intensities ranging from 4.8 to 14.7 mm / 10 minute. 2) Debris flows initiated in several reaches of the channel, including the head of the talus slope. 3) The initial surges of the mature flows had a higher solid concentration and a lower velocity (up to 4 m/s) than succeeding, more dilute surges (more than 7 m/s). 4) Total normal stress and pore fluid pressures measured at the base of the flow (mean depth about 1.1 m) were similar (about 15 kPa), indicating a completely liquefied flow. 5) Peak flows entrained debris at a rate of about 6 m3/m of channel length and channel bed scouring was proportional to the local slope gradient and was still evident in the lower channel where the slope was 7??. ?? 2000 Elsevier Science Ltd. All rights reserved.

  11. The importance of erosion for debris flow runout modelling from applications to the Swiss Alps

    Science.gov (United States)

    Frank, F.; McArdell, B. W.; Huggel, C.; Vieli, A.

    2015-04-01

    This study describes an investigation of channel-bed erosion of sediment by debris flows. An erosion model, developed using field data from debris flows at the Illgraben catchment, Switzerland, was incorporated into the existing RAMMS debris-flow model, which solves the 2-D shallow-water equations for granular flows. In the erosion model, the relationship between maximum shear stress and measured erosion is used to determine the maximum potential erosion depth. Additionally, the maximum rate of erosion, measured at the same field site, is used to constrain the erosion rate. The model predicts plausible erosion values in comparison with field data from highly erosive debris flow events at the Spreitgraben torrent channel, Switzerland in 2010, without any adjustment to the coefficients in the erosion model. We find that by including channel erosion in runout models a more realistic flow pattern is produced than in simulations where entrainment is not included. In detail, simulations without channel bed erosion show more lateral outflow from the channel where it has not been observed in the field. Therefore the erosion model may be especially useful for practical applications such as hazard analysis and mapping, as well as scientific case studies of erosive debris flows.

  12. The importance of entrainment and bulking on debris flow runout modeling: examples from the Swiss Alps

    Science.gov (United States)

    Frank, F.; McArdell, B. W.; Huggel, C.; Vieli, A.

    2015-11-01

    This study describes an investigation of channel-bed entrainment of sediment by debris flows. An entrainment model, developed using field data from debris flows at the Illgraben catchment, Switzerland, was incorporated into the existing RAMMS debris-flow model, which solves the 2-D shallow-water equations for granular flows. In the entrainment model, an empirical relationship between maximum shear stress and measured erosion is used to determine the maximum potential erosion depth. Additionally, the average rate of erosion, measured at the same field site, is used to constrain the erosion rate. The model predicts plausible erosion values in comparison with field data from highly erosive debris flow events at the Spreitgraben torrent channel, Switzerland in 2010, without any adjustment to the coefficients in the entrainment model. We find that by including bulking due to entrainment (e.g., by channel erosion) in runout models a more realistic flow pattern is produced than in simulations where entrainment is not included. In detail, simulations without entrainment show more lateral outflow from the channel where it has not been observed in the field. Therefore the entrainment model may be especially useful for practical applications such as hazard analysis and mapping, as well as scientific case studies of erosive debris flows.

  13. Predicting debris flow occurrence in Eastern Italian Alps based on hydrological and geomorphological modelling

    Science.gov (United States)

    Nikolopoulos, Efthymios I.; Borga, Marco; Destro, Elisa; Marchi, Lorenzo

    2015-04-01

    Most of the work so far on the prediction of debris flow occurrence is focused on the identification of critical rainfall conditions. However, findings in the literature have shown that critical rainfall thresholds cannot always accurately identify debris flow occurrence, leading to false detections (positive or negative). One of the main reasons for this limitation is attributed to the fact that critical rainfall thresholds do not account for the characteristics of underlying land surface (e.g. geomorphology, moisture conditions, sediment availability, etc), which are strongly related to debris flow triggering. In addition, in areas where debris flows occur predominantly as a result of channel bed failure (as in many Alpine basins), the triggering factor is runoff, which suggests that identification of critical runoff conditions for debris flow prediction is more pertinent than critical rainfall. The primary objective of this study is to investigate the potential of a triggering index (TI), which combines variables related to runoff generation and channel morphology, for predicting debris flows occurrence. TI is based on a threshold criterion developed on past works (Tognacca et al., 2000; Berti and Simoni, 2005; Gregoretti and Dalla Fontana, 2008) and combines information on unit width peak flow, local channel slope and mean grain size. Estimation of peak discharge is based on the application of a distributed hydrologic model, while local channel slope is derived from a high-resolution (5m) DEM. Scaling functions of peak flows and channel width with drainage area are adopted since it is not possible to measure channel width or simulate peak flow at all channel nodes. TI values are mapped over the channel network thus allowing spatially distributed prediction but instead of identifying debris flow occurrence on single points, we identify their occurrence with reference to the tributary catchment involved. Evaluation of TI is carried out for five different basins

  14. An Analysis of Post-Fire Debris Flow Occurrence at Two Temporal Scales

    Science.gov (United States)

    Staley, D. M.; Kean, J. W.; Gartner, J. E.

    2011-12-01

    The seasonal climate, rugged topography and high relief of the Peninsular and Transverse Ranges of southern California contribute to a particularly high susceptibility to wildfire during the dry season and debris flows during the wet season. Debris flows generated in recently burned areas have repeatedly caused casualties and damaged infrastructure. With a goal of reducing the hazard to local populations, the U.S. Geological Survey has been intensively monitoring the meteorological conditions that contribute to the initiation of post-fire debris flows since 2003. Data collected in these monitoring efforts have been used to derive rainfall intensity-duration thresholds to predict the timing of debris flows. A perceived limitation of the existing thresholds is that they are temporally static, because they do not account for the influence of within-storm dynamics, seasonal rainfall, and changes in soil moisture content. Here, we attempt to develop relations between meteorological, climatic and hydrologic variables and the occurrence of debris flows with the long-term goal of developing a temporally dynamic rainfall intensity-duration threshold. We investigate the variability of debris-flow occurrence on two temporal scales. First, we compare the within-storm variability of recorded debris flow times with measures of cumulative rainfall, rainfall intensity and soil moisture content. Short-duration (≤ 30-minutes), high-intensity bursts of rainfall are tightly correlated with the recorded times of debris flows, regardless of soil moisture content or cumulative storm rainfall. Preliminary evidence suggests that debris-flow magnitude may correlate with temporally coincident local peaks of both short duration (≤ 30-minute) and longer duration (≥ 360-minute) peaks of rainfall intensity. Second, we investigate the influence of total rainfall accumulation, changes in soil moisture content, and number and average intensity of rainstorms on debris-flow occurrence during

  15. Simulating debris flows through a hexagonal cellular automata model: SCIDDICA S3–hex

    Directory of Open Access Journals (Sweden)

    D. D’Ambrosio

    2003-01-01

    Full Text Available Cellular Automata (CA represent a formal frame for dynamical systems, which evolve on the base of local interactions. Some types of landslide, such as debris flows, match well this requirement. The latest hexagonal release (S3–hex of the deterministic model SCIDDICA, specifically developed for simulating debris flows, is described. For CA simulation purposes, landslides can be viewed as a dynamical system, subdivided into elementary parts, whose state evolves exclusively as a consequence of local interactions within a spatial and temporal discretum. Space is the world of the CA, here constituted by hexagonal cells. The attributes of each cell ("substates" describe physical characteristics. For computational reasons, the natural phenomenon is "decomposed" into a number of elementary processes, whose proper composition makes up the "transition function" of the CA. By simultaneously applying this function to all the cells, the evolution of the phenomenon can be simulated in terms of modifications of the substates. SCIDDICA S3–hex exhibits a great flexibility in modelling debris flows. With respect to the previous releases of the model, the mechanism of progressive erosion of the soil cover has been added to the transition function. Considered substates are: altitude; thickness and energy of landslide debris; depth of erodable soil cover; debris outflows. Considered elementary processes are: mobilisation triggering and effect (T1, debris outflows (I1, update of landslide debris thickness and energy (I2, and energy loss (T2.  Simulations of real debris flows, occurred in Campania (Southern Italy in May 1998 (Sarno and December 1999 (San Martino V.C. and Cervinara, have been performed for model calibration purposes; some examples of analysis are briefly described. Possible applications of the method are: risk mapping, also based on a statistical approach; evaluating the effects of mitigation actions (e.g. stream deviations, topographic

  16. Study on the evaluation method of debris flow and the hillside landslide scale of debris flow in nazardous torrent; Dosekiryu kiken keiryu ni okeru hokai kibo no hyoka ni kansuru kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, S. [National Defense Academy, Kanagawa (Japan); Ishikawa, Y. [Public Works Research Inst., Tsukuba (Japan); Mizuyama, T. [Kyoto Univ., Kyoto (Japan). Faculty of Agriculture; Furukawa, K. [Yamaguchi Univ., Yamaguchi (Japan). Faculty of Engineering; Araki, Y. [Chuden Engineering Consultants Co. Ltd., Hiroshima (Japan)

    1995-09-20

    Among natural disasters, earth and sand disaster, such as landslide, landslip, and so forth, including debris flow occurs all over the country every year. Among the earth and sand disasters, debris flow disaster presents the most large destructive power phenomenon, producting the most mass of earth and sand. The debris flow has a following characteristics, translation distance of earth and sand is long and the mass of earth and sand is carried away owing to take in unstable earth and sand deposited on torrent floor with flowing, therefore, the damage is very wide rangs to downstream area. An investigation of debris flow in hazardous torrent was conducted all over the country which estimated the degree of risk in debris flow. From the investigation, debris flow was evident in a lot of mountain torrents. In this study, the present evaluation on the degree of risk in debris flow was examined and the evaluation method of debris flow and hillside landslide scale which was used land map as the only factor, for example, the east area of Nagasaki City that was mostly damaged by debris flow in July, 1982, were proposed. 13 refs., 13 figs., 7 tabs.

  17. Onset of submarine debris flow deposition far from original giant landslide.

    Science.gov (United States)

    Talling, P J; Wynn, R B; Masson, D G; Frenz, M; Cronin, B T; Schiebel, R; Akhmetzhanov, A M; Dallmeier-Tiessen, S; Benetti, S; Weaver, P P E; Georgiopoulou, A; Zühlsdorff, C; Amy, L A

    2007-11-22

    Submarine landslides can generate sediment-laden flows whose scale is impressive. Individual flow deposits have been mapped that extend for 1,500 km offshore from northwest Africa. These are the longest run-out sediment density flow deposits yet documented on Earth. This contribution analyses one of these deposits, which contains ten times the mass of sediment transported annually by all of the world's rivers. Understanding how this type of submarine flow evolves is a significant problem, because they are extremely difficult to monitor directly. Previous work has shown how progressive disintegration of landslide blocks can generate debris flow, the deposit of which extends downslope from the original landslide. We provide evidence that submarine flows can produce giant debris flow deposits that start several hundred kilometres from the original landslide, encased within deposits of a more dilute flow type called turbidity current. Very little sediment was deposited across the intervening large expanse of sea floor, where the flow was locally very erosive. Sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea-floor gradient from 0.05 degrees to 0.01 degrees. This debris flow was probably generated by flow transformation from the decelerating turbidity current. The alternative is that non-channelized debris flow left almost no trace of its passage across one hundred kilometres of flat (0.2 degrees to 0.05 degrees) sea floor. Our work shows that initially well-mixed and highly erosive submarine flows can produce extensive debris flow deposits beyond subtle slope breaks located far out in the deep ocean.

  18. Experiment study of mud to the moving process influent about viscous debris flow along slope

    Science.gov (United States)

    Jun, JiXian; Ying, Liang; Li, Pan Hua; Qiang, OuGuo

    2018-01-01

    Mud is the main component of viscous debris flow. The physical model experiments of viscous debris flow were carried out through the mixing mud with different density and fixed components of coarse particles. The width, longitudinal movement distance and motion velocity were recorded by video cameras during experiment. Through viscous debris flow physical model experiments, the influence of mud to transverse width, longitudinal movement distance and motion velocity was discussed. The physical model experiment results show that the motion forms change from inviscid particle flow to viscous debris flow and to the whole mass sliding with the increase of mud density; the width and the length along the slope decrease with mud density increasing; the movement process has classified phenomena about viscous debris flow composed by different mud densities: the velocity increases rapidly with time and the change gradient is steady when the density of mud is lower than 1.413g/cm3; the movement process can be divided into two stages when the density of mud is higher than 1.413g/cm3: the movement velocity is lower and the gradient change is small in the initial stage; but in the second stage, the movement velocity increases quickly, and the gradient is higher than the first stage, and with steady value.

  19. Numerical simulation of failure behavior of granular debris flows based on flume model tests.

    Science.gov (United States)

    Zhou, Jian; Li, Ye-xun; Jia, Min-cai; Li, Cui-na

    2013-01-01

    In this study, the failure behaviors of debris flows were studied by flume model tests with artificial rainfall and numerical simulations (PFC(3D)). Model tests revealed that grain sizes distribution had profound effects on failure mode, and the failure in slope of medium sand started with cracks at crest and took the form of retrogressive toe sliding failure. With the increase of fine particles in soil, the failure mode of the slopes changed to fluidized flow. The discrete element method PFC(3D) can overcome the hypothesis of the traditional continuous medium mechanic and consider the simple characteristics of particle. Thus, a numerical simulations model considering liquid-solid coupled method has been developed to simulate the debris flow. Comparing the experimental results, the numerical simulation result indicated that the failure mode of the failure of medium sand slope was retrogressive toe sliding, and the failure of fine sand slope was fluidized sliding. The simulation result is consistent with the model test and theoretical analysis, and grain sizes distribution caused different failure behavior of granular debris flows. This research should be a guide to explore the theory of debris flow and to improve the prevention and reduction of debris flow.

  20. Positive feedback and momentum growth during debris-flow entrainment of wet bed sediment

    Science.gov (United States)

    Iverson, R.M.; Reid, M.E.; Logan, M.; LaHusen, R.G.; Godt, J.W.; Griswold, J.P.

    2011-01-01

    Debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep, debris-mantled slopes. The flows can then grow dramatically in size and speed as they entrain material from their beds and banks, but the mechanism of this growth is unclear. Indeed, momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged. Here we use data from large-scale experiments to assess the entrainment of bed material by debris flows. We find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows. The increased pore pressure facilitates progressive scour of the bed, reduces basal friction and instigates positive feedback that causes flow speed, mass and momentum to increase. If dryer bed sediment is entrained, however, the feedback becomes negative and flow momentum declines. We infer that analogous feedbacks could operate in other types of gravity-driven mass flow that interact with erodible beds. ?? 2011 Macmillan Publishers Limited. All rights reserved.

  1. Field Reconnaissance of Debris Flows Triggered by a July 21, 2007, Thunderstorm in Alpine, Colorado, and Vicinity

    Science.gov (United States)

    Coe, Jeffrey A.; Godt, Jonathan W.; Wait, T.C.; Kean, Jason W.

    2007-01-01

    On the evening of July 21, 2007, a slow-moving thunderstorm triggered about 45 debris flows on steep mountainsides near the community of Alpine, Colorado. Most of the debris flows were initiated by surface-water runoff that eroded and entrained loose sediment in previously existing channels. About 12 of the debris-flow channels were located in the lower half of Weldon Gulch upslope from Alpine, which is on a debris fan at the mouth of the Gulch. Most of these channels were deeply incised by the flows, and many of the resulting oversteepened channel banks are now failing and beginning to refill the channels with sediment. Debris flows that emerged from the mouth of Weldon Gulch primarily flowed onto the eastern half of the debris fan and closed roads and damaged vehicles and structures. Debris-flow deposits on the fan generally become finer grained and thinner with distance from the head of the fan. Given the existing conditions in Weldon Gulch, it is estimated that the debris-flow hazard on the fan has neither decreased nor increased as a result of the July 21 debris flows. Preventive measures that need to be considered by Alpine residents and government officials concerned with safety on the fan include: (1) establishing a channel and(or) catchment/diversion structure on the fan that routes future water and debris flows in a manner that protects existing roads and structures, and (2) maintaining vigilance during rainstorms by watching and listening for unusual flows of water or debris that may indicate debris-flow activity upstream, particularly during the summer months when thunderstorms are common in the area.

  2. Evaluation of a debris-flow entrainment model on field cases from the Swiss Alps

    Science.gov (United States)

    Frank, Florian; McArdell, Brian; Huggel, Christian; Vieli, Andreas

    2015-04-01

    Debris-flow erosion is an important process for shaping the landscape and highly relevant in terms of hazard due to the potential of substantially increasing the flow magnitude. Here we describe the development and testing of a model for the erosion of sediment deposits by entrainment. The model is based on a generalization of field data from the Illgraben torrent channel in Switzerland, where the slope of the channel on the fan varies between 8% and 10%. The entrainment model predicts the maximum depth of erosion as a function of basal shear stress (Schürch et al., 2011), and limits the rate of erosion to be less than the maximum erosion rate observed at the Illgraben by Berger et al. (2010, 2011). The entrainment model is a module implemented in the RAMMS debris-flow runout model which solves the 2D shallow water equations of motion for granular flows and includes the Voellmy friction relation (Christen et al., 2012). The intention of the model is to provide a tool to researchers and practitioners to estimate and investigate the influence of debris-flow erosion on the runout of debris flows, at least until new physically-based models are available. After calibration of the friction coefficients without considering entrainment, the model was systematically tested at two field sites where both the sequence of debris flows is known and where differential terrain elevation models have been used to identify the spatial pattern of erosion. Tests at the field site Spreitgraben (Canton Berne), where the channel slope on the fan is approximately 30%, indicate that the new model is better at predicting the flow pattern in comparison with model results without entrainment. Additionally, when sediment erosion is included in model, the shape of the debris-flow wave (flow depth as a function of time) has a generally steep debris-flow front, which is typical of field observations of debris flows. The model as also evaluated at the field site Meretschibach catchment (Canton

  3. Description and analysis of the debris flows occurred during 2008 in the Eastern Pyrenees

    Directory of Open Access Journals (Sweden)

    M. Portilla

    2010-07-01

    Full Text Available Rainfall-triggered landslides taking place in the Spanish Eastern Pyrenees have usually been analysed on a regional scale. Most research focussed either on terrain susceptibility or on the characteristics of the critical rainfall, neglecting a detailed analysis of individual events. In contrast to other mountainous regions, research on debris flow has only been performed marginally and associated hazard has mostly been neglected.

    In this study, five debris flows, which occurred in 2008, are selected; and site specific descriptions and analysis regarding geology, morphology, rainfall data and runout were performed. The results are compared with worldwide data and some conclusions on hazard assessment are presented.

    The five events can be divided into two in-channel debris flows and three landslide-triggered debris flows. The in-channel generated debris flows exceeded 10 000 m3, which are unusually large mass movements compared to historic events which occurred in the Eastern Pyrenees. In contrast, the other events mobilised total volumes less than 2000 m3. The geomorphologic analysis showed that the studied events emphasize similar patterns when compared to published data focussing on slope angle in the initiation zone or catchment area.

    Rainfall data revealed that all debris flows were triggered by high intensity-short duration rainstorms during the summer season. Unfortunately, existing rainfall thresholds in the Eastern Pyrenees consider long-lasting rainfall, usually occurring in autumn/winter. Therefore, new thresholds should be established taking into account the rainfall peak intensity in mm/h, which seems to be a much more relevant factor for summer than the event's total precipitation.

    The runout analysis of the 2008 debris flows confirms the trend that larger volumes generally induce higher mobility. The numerical simulation of the Riu Runer event shows that its dynamic behaviour

  4. A new hierarchical Bayesian approach to analyse environmental and climatic influences on debris flow occurrence

    Science.gov (United States)

    Jomelli, Vincent; Pavlova, Irina; Eckert, Nicolas; Grancher, Delphine; Brunstein, Daniel

    2015-12-01

    How can debris flow occurrences be modelled at regional scale and take both environmental and climatic conditions into account? And, of the two, which has the most influence on debris flow activity? In this paper, we try to answer these questions with an innovative Bayesian hierarchical probabilistic model that simultaneously accounts for how debris flows respond to environmental and climatic variables. In it, full decomposition of space and time effects in occurrence probabilities is assumed, revealing an environmental and a climatic trend shared by all years/catchments, respectively, clearly distinguished from residual "random" effects. The resulting regional and annual occurrence probabilities evaluated as functions of the covariates make it possible to weight the respective contribution of the different terms and, more generally, to check the model performances at different spatio-temporal scales. After suitable validation, the model can be used to make predictions at undocumented sites and could be used in further studies for predictions under future climate conditions. Also, the Bayesian paradigm easily copes with missing data, thus making it possible to account for events that may have been missed during surveys. As a case study, we extract 124 debris flow event triggered between 1970 and 2005 in 27 catchments located in the French Alps from the French national natural hazard survey and model their variability of occurrence considering environmental and climatic predictors at the same time. We document the environmental characteristics of each debris flow catchment (morphometry, lithology, land cover, and the presence of permafrost). We also compute 15 climate variables including mean temperature and precipitation between May and October and the number of rainy days with daily cumulative rainfall greater than 10/15/20/25/30/40 mm day- 1. Application of our model shows that the combination of environmental and climatic predictors explained 77% of the overall

  5. Testing seismic amplitude source location for fast debris-flow detection at Illgraben, Switzerland

    Directory of Open Access Journals (Sweden)

    F. Walter

    2017-06-01

    Full Text Available Heavy precipitation can mobilize tens to hundreds of thousands of cubic meters of sediment in steep Alpine torrents in a short time. The resulting debris flows (mixtures of water, sediment and boulders move downstream with velocities of several meters per second and have a high destruction potential. Warning protocols for affected communities rely on raising awareness about the debris-flow threat, precipitation monitoring and rapid detection methods. The latter, in particular, is a challenge because debris-flow-prone torrents have their catchments in steep and inaccessible terrain, where instrumentation is difficult to install and maintain. Here we test amplitude source location (ASL as a processing scheme for seismic network data for early warning purposes. We use debris-flow and noise seismograms from the Illgraben catchment, Switzerland, a torrent system which produces several debris-flow events per year. Automatic in situ detection is currently based on geophones mounted on concrete check dams and radar stage sensors suspended above the channel. The ASL approach has the advantage that it uses seismometers, which can be installed at more accessible locations where a stable connection to mobile phone networks is available for data communication. Our ASL processing uses time-averaged ground vibration amplitudes to estimate the location of the debris-flow front. Applied to continuous data streams, inversion of the seismic amplitude decay throughout the network is robust and efficient, requires no manual identification of seismic phase arrivals and eliminates the need for a local seismic velocity model. We apply the ASL technique to a small debris-flow event on 19 July 2011, which was captured with a temporary seismic monitoring network. The processing rapidly detects the debris-flow event half an hour before arrival at the outlet of the torrent and several minutes before detection by the in situ alarm system. An analysis of continuous seismic

  6. Testing seismic amplitude source location for fast debris-flow detection at Illgraben, Switzerland

    Science.gov (United States)

    Walter, Fabian; Burtin, Arnaud; McArdell, Brian W.; Hovius, Niels; Weder, Bianca; Turowski, Jens M.

    2017-06-01

    Heavy precipitation can mobilize tens to hundreds of thousands of cubic meters of sediment in steep Alpine torrents in a short time. The resulting debris flows (mixtures of water, sediment and boulders) move downstream with velocities of several meters per second and have a high destruction potential. Warning protocols for affected communities rely on raising awareness about the debris-flow threat, precipitation monitoring and rapid detection methods. The latter, in particular, is a challenge because debris-flow-prone torrents have their catchments in steep and inaccessible terrain, where instrumentation is difficult to install and maintain. Here we test amplitude source location (ASL) as a processing scheme for seismic network data for early warning purposes. We use debris-flow and noise seismograms from the Illgraben catchment, Switzerland, a torrent system which produces several debris-flow events per year. Automatic in situ detection is currently based on geophones mounted on concrete check dams and radar stage sensors suspended above the channel. The ASL approach has the advantage that it uses seismometers, which can be installed at more accessible locations where a stable connection to mobile phone networks is available for data communication. Our ASL processing uses time-averaged ground vibration amplitudes to estimate the location of the debris-flow front. Applied to continuous data streams, inversion of the seismic amplitude decay throughout the network is robust and efficient, requires no manual identification of seismic phase arrivals and eliminates the need for a local seismic velocity model. We apply the ASL technique to a small debris-flow event on 19 July 2011, which was captured with a temporary seismic monitoring network. The processing rapidly detects the debris-flow event half an hour before arrival at the outlet of the torrent and several minutes before detection by the in situ alarm system. An analysis of continuous seismic records furthermore

  7. Preliminary Study on the Damping Effect of a Lateral Damping Buffer under a Debris Flow Load

    Directory of Open Access Journals (Sweden)

    Zheng Lu

    2017-02-01

    Full Text Available Simulating the impact of debris flows on structures and exploring the feasibility of applying energy dissipation devices or shock isolators to reduce the damage caused by debris flows can make great contribution to the design of disaster prevention structures. In this paper, we propose a new type of device, a lateral damping buffer, to reduce the vulnerability of building structures to debris flows. This lateral damping buffer has two mechanisms of damage mitigation: when debris flows impact on a building, it acts as a buffer, and when the structure vibrates due to the impact, it acts as a shock absorber, which can reduce the maximum acceleration response and subsequent vibration respectively. To study the effectiveness of such a lateral damping buffer, an impact test is conducted, which mainly involves a lateral damping buffer attached to a two-degree-of-freedom structure under a simulated debris flow load. To enable the numerical study, the equation of motion of the structure along with the lateral damping buffer is derived. A subsequent parametric study is performed to optimize the lateral damping buffer. Finally, a practical design procedure is also provided.

  8. Empirical atmospheric thresholds for debris flows and flash floods in the southern French Alps

    Science.gov (United States)

    Turkington, T.; Ettema, J.; van Westen, C. J.; Breinl, K.

    2014-06-01

    Debris flows and flash floods are often preceded by intense, convective rainfall. The establishment of reliable rainfall thresholds is an important component for quantitative hazard and risk assessment, and for the development of an early warning system. Traditional empirical thresholds based on peak intensity, duration and antecedent rainfall can be difficult to verify due to the localized character of the rainfall and the absence of weather radar or sufficiently dense rain gauge networks in mountainous regions. However, convective rainfall can be strongly linked to regional atmospheric patterns and profiles. There is potential to employ this in empirical threshold analysis. This work develops a methodology to determine robust thresholds for flash floods and debris flows utilizing regional atmospheric conditions derived from ECMWF ERA-Interim reanalysis data, comparing the results with rain-gauge-derived thresholds. The method includes selecting the appropriate atmospheric indicators, categorizing the potential thresholds, determining and testing the thresholds. The method is tested in the Ubaye Valley in the southern French Alps (548 km2), which is known to have localized convection triggered debris flows and flash floods. This paper shows that instability of the atmosphere and specific humidity at 700 hPa are the most important atmospheric indicators for debris flows and flash floods in the study area. Furthermore, this paper demonstrates that atmospheric reanalysis data are an important asset, and could replace rainfall measurements in empirical exceedance thresholds for debris flows and flash floods.

  9. Hazard Assessment of Debris-Flow along the Baicha River in Heshigten Banner, Inner Mongolia, China.

    Science.gov (United States)

    Cao, Chen; Xu, Peihua; Chen, Jianping; Zheng, Lianjing; Niu, Cencen

    2016-12-29

    This study focused on a cloud model approach for considering debris-flow hazard assessment, in which the cloud model provided a model for transforming the qualitative and quantitative expressions. Additionally, the entropy method and analytical hierarchy process were united for calculating the parameters weights. The weighting method avoids the disadvantages inherent in using subjective or objective methods alone. Based on the cloud model and component weighting method, a model was established for the analysis of debris-flow hazard assessment. There are 29 debris-flow catchments around the pumped storage power station in the study area located near Zhirui (Inner Mongolia, China). Field survey data and 3S technologies were used for data collection. The results of the cloud model calculation process showed that of the 29 catchments, 25 had low debris-flow hazard assessment, three had moderate hazard assessment, and one had high hazard assessment. The widely used extenics method and field geological surveys were used to validate the proposed approach. This approach shows high potential as a useful tool for debris-flow hazard assessment analysis. Compared with other prediction methods, it avoids the randomness and fuzziness in uncertainty problems, and its prediction results are considered reasonable.

  10. New insights into debris-flow hazards from an extraordinary event in the Colorado Front Range

    Science.gov (United States)

    Coe, Jeffrey A.; Kean, Jason W.; Godt, Jonathan W.; Baum, Rex L.; Jones, Eric S.; Gochis, David; Anderson, Gregory S

    2016-01-01

    Rainfall on 9–13 September 2013 triggered at least 1,138 debris flows in a 3430 km2 area of the Colorado Front Range. The historical record reveals that the occurrence of these flows over such a large area in the interior of North America is highly unusual. Rainfall that triggered the debris flows began after ~75 mm of antecedent rain had fallen, a relatively low amount compared to other parts of the United States. Most flows were triggered in response to two intense rainfall periods, one 12.5-hour-long period on 11–12 September, and one 8-hour-long period on 12 September. The maximum 10 min. intensities during these periods were 67 and 39 mm/hr. Ninety-five percent of flows initiated in canyons and on hogbacks at elevations lower than a widespread erosion surface of low slope and relief (25°), predominantly south- and east-facing slopes with upslope contributing areas 3300 m2. Areal concentrations of debris flows revealed that colluvial soils formed on sedimentary rocks were more susceptible to flows than soils on crystalline rocks. This event should serve as an alert to government authorities, emergency responders, and residents in the Front Range and other interior continental areas with steep slopes. Widespread debris flows in these areas occur infrequently but may pose a greater risk than in areas with shorter return periods, because the public is typically unprepared for them.

  11. Debris Flows Associated With Lava Extrusion at Three Stratocones; Cleveland, Pavlof (Alaska) and Stromboli (Italy)

    Science.gov (United States)

    van Manen, S.; Dehn, J.

    2008-12-01

    Debris flows that occur contemporaneously with lava flow extrusion have been observed visually, with handheld thermal infrared cameras and in Advanced Very High Resolution Radiometer (AVHRR) satellite data at Stromboli, Cleveland and Pavlof. At Pavlof these debris flows can also be identified in the seismic record. These basaltic equivalents of block and ash flows are low energy, low velocity, low temperature (200- 300° C) with varying grain sizes. Deposits of these flows show little or no sorting. They originate from the 'A'a× flow front but form a cohesive flow with minor elutriation of ash. Further downslope they precede and underly lava flows, partly guiding the path of later flows. At Pavlof and Cleveland they lie on top of layers of snow and ice. At Pavlof this has resulted in these flows feeding lahars, at Cleveland they form an insulating layer between the snow and the active lava flow. Field evidence has shown that the snow layer can even be present years after the emplacement of the lava flow on top of the debris flow. This suggests that this layering is an integral part of the structure of the volcanic cone, providing preferred failure planes and resulting in instability. In the future this could result in either failure of large parts of the volcanic edifice of these volcanoes or large scale phreato-magmatic explosions. The handheld thermal imagery of these debris flows obtained on Stromboli will provide a clearer insight into their thermal regime, and when combined with satellite and seismic data, a hazard assessment of these flows can be made.

  12. Estimation of the annual flow and stock of marine debris in South Korea for management purposes.

    Science.gov (United States)

    Jang, Yong Chang; Lee, Jongmyoung; Hong, Sunwook; Mok, Jin Yong; Kim, Kyoung Shin; Lee, Yun Jeong; Choi, Hyun-Woo; Kang, Hongmook; Lee, Sukhui

    2014-09-15

    The annual flow and stock of marine debris in the Sea of Korea was estimated by summarizing previous survey results and integrating them with other relevant information to underpin the national marine debris management plan. The annual inflow of marine debris was estimated to be 91,195 tons [32,825 tons (36% of the total) from sources on land and 58,370 tons (64%) from ocean sources]. As of the end of 2012, the total stock of marine debris on all South Korean coasts (12,029 tons), the seabed (137,761 tons), and in the water column (2451 tons) was estimated to be 152,241 tons. In 2012, 42,595 tons of marine debris was collected from coasts, seabeds, and the water column. This is a very rare case study that estimated the amount of marine debris at a national level, the results of which provide essential information for the development of efficient marine debris management policies. Copyright © 2014 Elsevier Ltd. All rights reserved.

  13. A novel mechanical model for phase-separation in debris flows

    Science.gov (United States)

    Pudasaini, Shiva P.

    2015-04-01

    Understanding the physics of phase-separation between solid and fluid phases as a two-phase mass moves down slope is a long-standing challenge. Here, I propose a fundamentally new mechanism, called 'separation-flux', that leads to strong phase-separation in avalanche and debris flows. This new model extends the general two-phase debris flow model (Pudasaini, 2012) to include a separation-flux mechanism. The new flux separation mechanism is capable of describing and controlling the dynamically evolving phase-separation, segregation, and/or levee formation in a real two-phase, geometrically three-dimensional debris flow motion and deposition. These are often observed phenomena in natural debris flows and industrial processes that involve the transportation of particulate solid-fluid mixture material. The novel separation-flux model includes several dominant physical and mechanical aspects that result in strong phase-separation (segregation). These include pressure gradients, volume fractions of solid and fluid phases and their gradients, shear-rates, flow depth, material friction, viscosity, material densities, boundary structures, gravity and topographic constraints, grain shape, size, etc. Due to the inherent separation mechanism, as the mass moves down slope, more and more solid particles are brought to the front, resulting in a solid-rich and mechanically strong frontal surge head followed by a weak tail largely consisting of the viscous fluid. The primary frontal surge head followed by secondary surge is the consequence of the phase-separation. Such typical and dominant phase-separation phenomena are revealed here for the first time in real two-phase debris flow modeling and simulations. However, these phenomena may depend on the bulk material composition and the applied forces. Reference: Pudasaini, Shiva P. (2012): A general two-phase debris flow model. J. Geophys. Res., 117, F03010, doi: 10.1029/2011JF002186.

  14. The application of numerical debris flow modelling for the generation of physical vulnerability curves

    Science.gov (United States)

    Luna, B. Quan; Blahut, J.; van Westen, C. J.; Sterlacchini, S.; van Asch, T. W. J.; Akbas, S. O.

    2011-07-01

    For a quantitative assessment of debris flow risk, it is essential to consider not only the hazardous process itself but also to perform an analysis of its consequences. This should include the estimation of the expected monetary losses as the product of the hazard with a given magnitude and the vulnerability of the elements exposed. A quantifiable integrated approach of both hazard and vulnerability is becoming a required practice in risk reduction management. This study aims at developing physical vulnerability curves for debris flows through the use of a dynamic run-out model. Dynamic run-out models for debris flows are able to calculate physical outputs (extension, depths, velocities, impact pressures) and to determine the zones where the elements at risk could suffer an impact. These results can then be applied to consequence analyses and risk calculations. On 13 July 2008, after more than two days of intense rainfall, several debris and mud flows were released in the central part of the Valtellina Valley (Lombardy Region, Northern Italy). One of the largest debris flows events occurred in a village called Selvetta. The debris flow event was reconstructed after extensive field work and interviews with local inhabitants and civil protection teams. The Selvetta event was modelled with the FLO-2D program, an Eulerian formulation with a finite differences numerical scheme that requires the specification of an input hydrograph. The internal stresses are isotropic and the basal shear stresses are calculated using a quadratic model. The behaviour and run-out of the flow was reconstructed. The significance of calculated values of the flow depth, velocity, and pressure were investigated in terms of the resulting damage to the affected buildings. The physical damage was quantified for each affected structure within the context of physical vulnerability, which was calculated as the ratio between the monetary loss and the reconstruction value. Three different empirical

  15. A comparison of laboratory and field observations of superelevation in debris flows

    Science.gov (United States)

    McArdell, Brian W.; Scheidl, Christian; Graf, Christoph; Rickenmann, Dieter

    2017-04-01

    Post-event estimation of debris-flow velocity is a central part of hazard analysis. Estimates of debris-flow velocity are useful for e.g. dimensioning mitigation measures, calibrating or testing debris-flow runout models, constructing intensity-based hazard maps, and designing warning systems. However independent field observations of velocity are rare and it is often necessary to indirectly estimate flow velocity. The difference in mud elevation on either side of a channel through a bend of a constant radius can be used to estimate the flow velocity using a vortex method developed for a Newtonian fluid. In 2015 we reported on the application of the vortex method to calculate the front velocity of debris flows in the laboratory (Scheidl et al., 2015). In the laboratory experiments, we found a statistically significant correction factor k for the application of the vortex equation to debris flows under supercritical flow conditions, with somewhat more scatter for subcritical flows. Nevertheless, it was possible to derive a forced-vortex equation, without a correction factor, after considering active and passive earth pressures within the flow. Herein, we compare the laboratory results with field data from the Illgraben and Schipfenbach torrents in Switzerland. Using video recordings and flow trajectory data for 17 debris flows at the Illgraben debris-flow observation station in Switzerland, we were able to independently test the application of the new forced vortex equation against field data. The general trend observed in the laboratory are confirmed using the field data: the correction factor k decreases with increasing Froude number of the flow. However the field data show a much larger degree of scatter in the vortex-equation correction factor in comparison with the laboratory data. The debris flows in the field differ from the laboratory channel in many ways. Although the observation section at the Illgraben was fairly uniform in terms of the surface width of

  16. Automated, reproducible delineation of zones at risk from inundation by large volcanic debris flows

    Science.gov (United States)

    Schilling, Steve P.; Iverson, Richard M.

    1997-01-01

    Large debris flows can pose hazards to people and property downstream from volcanoes. We have developed a rapid, reproducible, objective, and inexpensive method to delineate distal debris-flow hazard zones. Our method employs the results of scaling and statistical analyses of the geometry of volcanic debris flows (lahars) to predict inundated valley cross-sectional areas (A) and planimetric areas (B) as functions of lahar volume. We use a range of specified lahar volumes to evaluate A and B. In a Geographic Information System (GIS) we employ the resulting range of predicted A and B to delineate gradations in inundation hazard, which is highest near the volcano and along valley thalwegs and diminishes as distances from the volcano and elevations above valley floors increase. Comparison of our computer-generated hazard maps with those constructed using traditional, field-based methods indicates that our method can provide an accurate means of delineating lahar hazard zones.

  17. DEBRIS FLOW AND LANDSLIDE HAZARDS UNDER CERTAIN TYPES OF ATMOSPHERIC CIRCULATION

    Directory of Open Access Journals (Sweden)

    Nina Kononova

    2012-01-01

    Full Text Available Conditions of formation and development of landslides and debris flows in the Black Sea coast of the Caucasus and on Sakhalin Island were considered. They are formed under the influence of heavy rainfall under the influence of the Mediterranean cyclones outlet in the Black Sea coast of the Caucasus and of the Pacific cyclones outlet on Sakhalin Island in the same macro-circulation processes. Activity of landslides and debris flows in these regions has been shown to be connected with certain types of atmospheric circulation during the XX—the beginning of the XXI century. Based on these results, possible increase in the activity of landslides and debris flows, in the Black Sea coast of the Caucasus and Sakhalin Island, is suggested.

  18. Empirical assessment of debris flow risk on a regional scale in Yunnan province, southwestern China.

    Science.gov (United States)

    Liu, Xilin; Yue, Zhong Qi; Tham, Lesliw George; Lee, Chack Fan

    2002-08-01

    Adopting the definition suggested by the United Nations, a risk model for regional debris flow assessment is presented. Risk is defined as the product of hazard and vulnerability, both of which are necessary for evaluation. A Multiple-Factor Composite Assessment Model is developed for quantifying regional debris flow hazard by taking into account eight variables that contribute to debris flow magnitude and its frequency of occurrence. Vulnerability is a measure of the potential total losses. On a regional scale, it can be measured by the fixed asset, gross domestic product, land resources, population density, as well as the age, education, and wealth of the inhabitants. A nonlinear power-function assessment model that accounts for these indexes is developed. As a case study, the model is applied to compute the hazard, vulnerability and risk for each prefecture of the Yunnan province in southwestern China.

  19. Report on the 4th International Conference on monitoring, simulation, prevention and remediation of dense and debris flows - Debris Flow 2012

    Directory of Open Access Journals (Sweden)

    Daniele de Wrachien

    2012-09-01

    Full Text Available Debris and hyper-concentrated flows are amongst the most destructive of all water-related disasters. These hazards are likely to become more frequent and more important in the future due to the effects of the increase in population, urbanization, land subsidence and the impact of climate change. They affect both rural and urban environments, particularly in river basins and in mountain areas. In recent years, they have attracted more and more attention from the scientific and professional communities due to the number of lives lost, and there is growing public concern for the future. New methods and measures are required to cope with debris flow changes and to achieve a harmonious balance between the environment and economic forces.

  20. Combining Spatial Models for Shallow Landslides and Debris-Flows Prediction

    Directory of Open Access Journals (Sweden)

    Eurípedes Vargas do Amaral

    2013-05-01

    Full Text Available Mass movements in Brazil are common phenomena, especially during strong rainfall events that occur frequently in the summer season. These phenomena cause losses of lives and serious damage to roads, bridges, and properties. Moreover, the illegal occupation by slums on the slopes around the cities intensifies the effect of the mass movement. This study aimed to develop a methodology that combines models of shallow landslides and debris-flows in order to create a map with landslides initiation and debris-flows volume and runout distance. The study area comprised of two catchments in Rio de Janeiro city: Quitite and Papagaio that drained side by side the west flank of the Maciço da Tijuca, with an area of 5 km2. The method included the following steps: (a location of the susceptible areas to landslides using SHALSTAB model; (b determination of rheological parameters of debris-flow from the back-analysis technique; and (c combination of SHALSTAB and FLO-2D models to delineate the areas more susceptible to mass movements. These scenarios were compared with the landslide and debris-flow event of February 1996. Many FLO-2D simulations were exhaustively made to estimate the rheological parameters from the back-analysis technique. Those rheological coefficients of single simulation were back-calculated by adjusting with area and depth of the debris-flow obtained from field data. The initial material volume in the FLO-2D simulations was estimated from SHALSTAB model. The combination of these two mathematical models, SHALSTAB and FLO-2D, was able to predict both landslides and debris-flow events. Such procedures can reduce the casualties and property damage, delineating hazard areas, to estimate hazard intensities for input into risk studies providing information for public policy and planning.

  1. Predicting the probability and volume of postwildfire debris flows in the intermountain western United States

    Science.gov (United States)

    Cannon, S.H.; Gartner, J.E.; Rupert, M.G.; Michael, J.A.; Rea, A.H.; Parrett, C.

    2010-01-01

    Empirical models to estimate the probability of occurrence and volume of postwildfire debris flows can be quickly implemented in a geographic information system (GIS) to generate debris-flow hazard maps either before or immediately following wildfires. Models that can be used to calculate the probability of debris-flow production from individual drainage basins in response to a given storm were developed using logistic regression analyses of a database from 388 basins located in 15 burned areas located throughout the U.S. Intermountain West. The models describe debris-flow probability as a function of readily obtained measures of areal burned extent, soil properties, basin morphology, and rainfall from short-duration and low-recurrence-interval convective rainstorms. A model for estimating the volume of material that may issue from a basin mouth in response to a given storm was developed using multiple linear regression analysis of a database from 56 basins burned by eight fires. This model describes debris-flow volume as a function of the basin gradient, aerial burned extent, and storm rainfall. Applications of a probability model and the volume model for hazard assessments are illustrated using information from the 2003 Hot Creek fire in central Idaho. The predictive strength of the approach in this setting is evaluated using information on the response of this fire to a localized thunderstorm in August 2003. The mapping approach presented here identifies those basins that are most prone to the largest debris-flow events and thus provides information necessary to prioritize areas for postfire erosion mitigation, warnings, and prefire management efforts throughout the Intermountain West.

  2. Propagation of a channelized debris-flow: experimental investigation and parameters identification for numerical modelling

    Science.gov (United States)

    Termini, Donatella

    2013-04-01

    Recent catastrophic events due to intense rainfalls have mobilized large amount of sediments causing extensive damages in vast areas. These events have highlighted how debris-flows runout estimations are of crucial importance to delineate the potentially hazardous areas and to make reliable assessment of the level of risk of the territory. Especially in recent years, several researches have been conducted in order to define predicitive models. But, existing runout estimation methods need input parameters that can be difficult to estimate. Recent experimental researches have also allowed the assessment of the physics of the debris flows. But, the major part of the experimental studies analyze the basic kinematic conditions which determine the phenomenon evolution. Experimental program has been recently conducted at the Hydraulic laboratory of the Department of Civil, Environmental, Aerospatial and of Materials (DICAM) - University of Palermo (Italy). The experiments, carried out in a laboratory flume appositely constructed, were planned in order to evaluate the influence of different geometrical parameters (such as the slope and the geometrical characteristics of the confluences to the main channel) on the propagation phenomenon of the debris flow and its deposition. Thus, the aim of the present work is to give a contribution to defining input parameters in runout estimation by numerical modeling. The propagation phenomenon is analyzed for different concentrations of solid materials. Particular attention is devoted to the identification of the stopping distance of the debris flow and of the involved parameters (volume, angle of depositions, type of material) in the empirical predictive equations available in literature (Rickenmanm, 1999; Bethurst et al. 1997). Bethurst J.C., Burton A., Ward T.J. 1997. Debris flow run-out and landslide sediment delivery model tests. Journal of hydraulic Engineering, ASCE, 123(5), 419-429 Rickenmann D. 1999. Empirical relationships

  3. Debris-flow runout predictions based on the average channel slope (ACS)

    Science.gov (United States)

    Prochaska, A.B.; Santi, P.M.; Higgins, J.D.; Cannon, S.H.

    2008-01-01

    Prediction of the runout distance of a debris flow is an important element in the delineation of potentially hazardous areas on alluvial fans and for the siting of mitigation structures. Existing runout estimation methods rely on input parameters that are often difficult to estimate, including volume, velocity, and frictional factors. In order to provide a simple method for preliminary estimates of debris-flow runout distances, we developed a model that provides runout predictions based on the average channel slope (ACS model) for non-volcanic debris flows that emanate from confined channels and deposit on well-defined alluvial fans. This model was developed from 20 debris-flow events in the western United States and British Columbia. Based on a runout estimation method developed for snow avalanches, this model predicts debris-flow runout as an angle of reach from a fixed point in the drainage channel to the end of the runout zone. The best fixed point was found to be the mid-point elevation of the drainage channel, measured from the apex of the alluvial fan to the top of the drainage basin. Predicted runout lengths were more consistent than those obtained from existing angle-of-reach estimation methods. Results of the model compared well with those of laboratory flume tests performed using the same range of channel slopes. The robustness of this model was tested by applying it to three debris-flow events not used in its development: predicted runout ranged from 82 to 131% of the actual runout for these three events. Prediction interval multipliers were also developed so that the user may calculate predicted runout within specified confidence limits. ?? 2008 Elsevier B.V. All rights reserved.

  4. GIS-based cell model for simulating debris flow runout on a fan

    Science.gov (United States)

    Gregoretti, Carlo; Degetto, Massimo; Boreggio, Mauro

    2016-03-01

    A GIS-based cell model, based on a kinematic approach is proposed to simulate debris flow routing on a fan. The sediment-water mixture is modeled as a monophasic continuum, and the flow pattern is discretized by square cells, 1 m in size, that coincide with the DEM cells. Flow occurs from cells with a higher mixture free surface to those with a lower mixture free surface. A uniform-flow law is used if the elevation of the former cell is higher than that of the latter; otherwise, the flow is simulated using the broad-crested weir law. Erosion and deposition are simulated using an empirical law that is adjusted for a monophasic continuum. The sediment concentration in the routing volume is computed at each time step and controls both erosion and deposition. The cell model is used to simulate a debris flow that occurred on the Rio Lazer (Dolomites, North-Eastern Italian Alps) on November 4th, 1966. Furthermore, the hydrologic and the hydraulic conditions for the initiation of debris flow are simulated, providing the solid-liquid hydrograph of the resulting debris flow. A number of simulations has been carried out with physically reasonable parameters. The results are compared with the extension of the debris-flow deposition area and the map of observed depths of deposited sediments. This comparison shows that the proposed model provides good performance. The analysis of sensitivity carried out by systematically varying the model parameters shows that lower performances are associated with parameter values that are not physically reasonable. The same event is also simulated using a cellular automata model and a finite volume two-dimensional model. The results show that the two models provide a sediment deposition pattern less accurate than that provided by the present cell model.

  5. Evaluation of different methods for discharge measurement for debris flows at the Lattenbach creek

    Science.gov (United States)

    Huebl, Johannes; Schimmel, Andreas; Koschuch, Richard

    2017-04-01

    The Lattenbach creek, District of Landeck, Tyrol is a very active torrent located in a geologic fault zone in the western part of Austria with a catchment area of 5.3 km2. The channel separates the Northern Limestone Alps in the North from the Crystalline Alps in the South. The highest elevation in the watershed is around 2900 m above sea level (asl), the confluence with the river Sanna at 840 m asl. Aside from the regular flood events with bedload transport, the torrent produced five debris flows and three debris floods within recent years. Due to the frequent debris flows and debris floods events the torrent is monitored by the Institute of Mountain Risk Engineering since several years. The parameters that are currently measured during an event include meteorological data (rainfall, temperature, etc.) in the upper part of the catchment (station Dawinalpe) and run-off data from the middle and lower reach of the torrent at the villages Grins and Pians. In the last years the monitoring equipment has been constantly improved. Additional to the standard sensors like several radar gauges for water level measurements, a first version of a detection system based on a combination of infrasound and seismic sensors is installed at the monitoring station closed to Grins. This system is build up on a minimum of one seismic and one infrasound sensor which are co-located and a microcontroller which runs a detection algorithm to detect debris flows and debris floods with high accuracy in real time directly on-site. Two of this system are installed in a distance of 90 m and can therefore be used to measure the surge velocity. Further a high frequency Pulse Doppler Radar has been installed, which provides the opportunity to measure the surface velocity of a debris flow in different range gates. Together with a recently installed 2D-Laser scanner this setup provides the possibility to determine a very precise approximation of the discharge with a high temporal resolution by

  6. Exploiting Maximum Entropy method and ASTER data for assessing debris flow and debris slide susceptibility for the Giampilieri catchment (north-eastern Sicily, Italy).

    KAUST Repository

    Lombardo, Luigi

    2016-07-18

    This study aims at evaluating the performance of the Maximum Entropy method in assessing landslide susceptibility, exploiting topographic and multispectral remote sensing predictors. We selected the catchment of the Giampilieri stream, which is located in the north-eastern sector of Sicily (southern Italy), as test site. On 1/10/2009, a storm rainfall triggered in this area hundreds of debris flow/avalanche phenomena causing extensive economical damage and loss of life. Within this area a presence-only-based statistical method was applied to obtain susceptibility models capable of distinguish future activation sites of debris flow and debris slide, which where the main source failure mechanisms for flow or avalanche type propagation. The set of predictors used in this experiment comprised primary and secondary topographic attributes, derived by processing a high resolution digital elevation model, CORINE land cover data and a set of vegetation and mineral indices obtained by processing multispectral ASTER images. All the selected data sources are dated before the disaster. A spatially random partition technique was adopted for validation, generating fifty replicates for each of the two considered movement typologies in order to assess accuracy, precision and reliability of the models. The debris slide and debris flow susceptibility models produced high performances with the first type being the best fitted. The evaluation of the probability estimates around the mean value for each mapped pixel shows an inverted relation, with the most robust models corresponding to the debris flows. With respect to the role of each predictor within the modelling phase, debris flows appeared to be primarily controlled by topographic attributes whilst the debris slides were better explained by remotely sensed derived indices, particularly by the occurrence of previous wildfires across the slope. The overall excellent performances of the two models suggest promising perspectives for

  7. Hazard assessment of landslide and debris flow in the Rjeina river valley, Croatia

    Science.gov (United States)

    Wang, Chunxiang; Watanabe, Naoki; Marui, Hideaki

    2013-04-01

    The Rječina River extends approximately 18.7km long and flows into the Adriatic Sea at the center of Rijeka City, Croatia. Landslide, debris flow and rockfall are main geohazards in the middle part of the Rječina river basin. The zone between the Valići reservoir dam and the Pasac Bridge is particularly the most unstable and hazardous area in the river basin. The Grohovo landslide in the middle part of the river basin is located on the valley's slope facing southwest and situated at just downstream of the Valići dam. This landslide is the largest active landslide along the Adriatic Sea coast in Croatia. Assuming that serious heavy rainfall or earthquake occurs, it is most likely to occur two types of geohazard event. One scenario is that the debris deposited on the Grohovo landslide will move down to the channel of the Rječina River and dam up the river course. Another scenario is that the slope deposits on the landslide will be mixed with water and subsequently turn into a debris flow reaching to Rijeka City. We simulate both two cases of the formation of landslide-dam and the occurrence of debris-flow by two integrated models using GIS to represent the dynamic process across 3D terrains. In the case of the formation of landslide-dam, it is assumed that slope deposits will move downhill after failing along a shear zone. GIS-based revised Hovland's 3D limit equilibrium model is used to simulate the movement and stoppage of the slope deposits to form landslide-dam. The 3D factor of safety will be calculated step by step during the sliding process simulation. Stoppage is defined by the factor of safety much greater than one and the velocity equal to zero. The simulation result shows that the height of the landslide-dam will be nine meters. In case of debris flow, the mixture of slope deposits and water will be differentiated from landslide by fluid-like deformation of the mobilized material. GIS-based depth-averaged 2D numerical model is used to predict the

  8. Debris flow monitoring experience in the Cancia basin (Dolomites, Northeast Italian Alps).

    Science.gov (United States)

    Stancanelli, Laura; Bernard, Martino; Gregoretti, Carlo; Berti, Matteo; Simoni, Alessandro; Lanzoni, Stefano

    2016-04-01

    The monitoring campaign presented here aims to understand the dynamics of sediment transport processes in small head-water catchments of the Italian Alps and to evaluate the rainfall thresholds for debris flow triggering. The monitored basin of Cancia is located on the Eastern Italian Dolomites, in the Belluno Province. In particular, it is situated on the left side on the Boite river valley, next to the Borca di Cadore village, and is delimited by the western slope of the Mt. Antelao. The drainage area is 1.8 km2 while the elevation ranges from 2451 m a.s.l. to 880 m a.s.l., with a slope varying from 30-40° in the upper part to 10-15° in the lower part (fan area). The basin is characterized by a lithology very common in the Italian Alps, which consist of high permeability, poorly sorted rock debris, containing boulders up to 3-4 m in diameter, and include heterogeneous scree, alluvium and old debris flow deposits. The spatial distribution of sediment is characterized by: an upper part where prevails the presence of rocks, a medium part characterized by poorly sorted rock debris and fine sediment material, and a downstream part plenty of sediment material The Cancia basin is prone to stony debris flows, owing to the plenty availability of loose and coarse sediments and frequent convective events. In particular, the smaller grain sized material is provided by the erosion of lateral slope, while gravel, pebbles and cobbles are provided by the upper part of the basin, characterized by rocky material. The precipitation regime is marked by rainfalls of short duration and high intensity, usually occurring in the summer period. The debris flow channel has began to be surveyed in August 2009 to identify the debris flow generation area. At the beginning of July 2013 topographical surveys of the channel downstream the triggering area began in order to investigate the morphological evolution of the debris flow channel from 2013 until 2015. Moreover, at the beginning of

  9. Description and analysis of major debris flows occurred during 2008 in the Eastern Pyrenees

    Science.gov (United States)

    Chevalier, G.; Postilla, M.; Hürlimann, M.

    2009-04-01

    In the Eastern Pyrenees, debris flows are not as frequent as in other mountainous areas such as the Alps. Nevertheless, several important events have occurred in 2008 provoking damages to essential infrastructures and causing large economic loss. A rainstorm at the beginning of June 2008 generated various surficial slides and debris flows in the area of Berga, located in the Pre-Pyrenees. A major flow obstructed the tunnel entrance of a national road during several days. Another rainstorm on August 1 caused several debris flows and debris floods in the Southern sector of Andorra, situated in the Axial Pyrenees. The most important event occurred in the Riu Runer torrent and destroyed the main building at the Andorran border. Finally, a large debris flow was triggered by a thunderstorm on September 11 near Rialp, Axial Pyrenees. Some installations of Port-Ainé's ski-resort were damaged and its access road was destroyed at several points. Preliminary results of these three events are presented focussing on the initiation, flow behaviour and deposition processes. Moreover, the influence of human activity on the initiation was analysed. Field surveys and interpretation of aerial photographs are carried out in order to obtain geomorphologic information as well as data on the hydraulic characteristics. Additionally, rainfall as triggering is studied using records from nearby observation stations and data from weather radars. Finally, the dynamic behaviour is simulated at one site applying numerical modelling. Volume estimates of the two events occurred in the Axial Pyrenees range from 5000 up to 10000 m3. These are rather large magnitudes compared to historic debris flows in the same area. The initiation process of both events can be defined as in-channel formation. Field observations indicated important erosion rates of up to 10 m3/m characteristic of the high flow velocities estimated along the flow trajectory. In contrast, the Berga event was caused by a surficial

  10. Sediment tracing, mixing and budgets in debris flow catchments: a cosmogenic nuclide perspective

    Science.gov (United States)

    Kober, Florian; Hippe, Kristina; Salcher, Bernhard; Grischott, Reto; Christl, Markus; Hählen, Nils

    2013-04-01

    Mountain catchments are at the start of the source-to-sink cycle in erosional and sedimentary environments. These catchments are sensitive to climate, geomorphic inheritance and human perturbation and are commonly dominated by episodic mass-wasting processes (landslides, debris flows). Quantifying the production and evacuation of sediment from such catchments (i.e. their erosion rates) is difficult and highly dependent on the spatial and temporal scales investigated and the methods/techniques applied. Crucial questions are where and when the sediment is mobilized and discharged, and where and how the quantitative erosion measurement is taken in time and space. We have investigated such issues in the Haslital Aare of Central Switzerland, from a sediment yield and a cosmogenic nuclide perspective. Localized mobilization of sediment as debris flows due to rockfall, heavy rainfall and permafrost thawing has been quantified volumetrically and in terms of cosmogenic nuclide (10Be) concentrations. Sediment sources and reservoirs (talus slope deposits, glacial debris, hillslopes, debris flow fans) are investigated at the source site, at the tributary - trunk stream junction (debris-flow subcatchment scale, ~4 km2) and at the outlet of the catchment (~70 km2). These measurements indicate that the sediment is not as thoroughly mixed at subcatchment and catchment scale as required by the concept of cosmogenic nuclide. However, a balancing effect (potentially back to natural background levels) of localized signals is observed at variable temporal and spatial distances of the episodic event. Detected sediment volumes mobilized during debris-flow events are larger than those calculated from cosmogenic nuclide derived denudation rates. This is largely due to lateral and vertical sediment entrainment in debris flow channels for which the cosmogenic nuclide method is little sensitive. The incorporation of non-steady produced sediment (residing in shielded fan deposits) can yield

  11. Modeling debris-flow runout patterns on two alpine fans with different dynamic simulation models

    Science.gov (United States)

    Schraml, K.; Thomschitz, B.; McArdell, B. W.; Graf, C.; Kaitna, R.

    2015-07-01

    Predicting potential deposition areas of future debris-flow events is important for engineering hazard assessment in alpine regions. To this end, numerical simulation models are commonly used tools. However, knowledge of appropriate model parameters is essential but often not available. In this study we use two numerical simulation models, RAMMS-DF (rapid mass movement system-debris-flow) and DAN3D (dynamic analysis of landslides in three dimensions), to back-calculate two well-documented debris-flow events in Austria and to compare the range and sensitivity of input parameters for the Voellmy flow model. All simulations are based on the same digital elevation models and similar boundary conditions. Our results show that observed deposition patterns are best matched with a parameter set of μ [-] and ξ [m s-2], ranging between 0.07 to 0.11 and 200 to 300 m s-2, respectively, for RAMMS-DF, and between 0.07 to 0.08 and 300 to 400 m s-2, respectively, for DAN3D. Sensitivity analysis shows a higher sensitivity of model parameters for the DAN3D model than for the RAMMS-DF model. This contributes to the evaluation of realistic model parameters for simulation of debris-flows in steep mountain catchments and highlights the sensitivity of the models.

  12. Modeling debris-flow runout patterns on two alpine fans with different dynamic simulation models

    Science.gov (United States)

    Schraml, K.; Thomschitz, B.; McArdell, B. W.; Graf, C.; Kaitna, R.

    2015-02-01

    Predicting potential deposition areas of future debris-flow events is important for engineering hazard assessment in alpine regions. For this, numerical simulation models are commonly used tools. However, knowledge of appropriate model parameters is essential but often not available. In this study we use two numerical simulation models, RAMMS-DF (Rapid Mass Movement System - Debris Flow) and DAN3D (Dynamic Analysis of Landslides in Three Dimensions), to back-calculate two well-documented debris-flow events in Austria and to compare the range and sensitivity of input parameters for the Voellmy flow model. All simulations are based on the same digital elevation model with a 1 m resolution and similar initial conditions. Our results show that both simulation tools are capable of matching observed deposition patterns. The best fit parameter set of μ [-] and ξ [m s-2] range between 0.07-0.11 and 200-300 m s-2, respectively, for RAMMS-DF, and 0.07-0.08 and 300-400 m s-2, respectively, for DAN3D. Sensitivity analyses show a higher sensitivity of model parameters for the DAN3D model than for the RAMMS-DF model. This study shall contribute to the evaluation of realistic model parameters for simulation of debris-flows in steep mountain catchments and highlights the sensitivity of the models.

  13. Topographic susceptibility for debris flow initiation along transport routes in NW-Norway

    Science.gov (United States)

    Meyer, Nele K.; Schwanghart, Wolfgang; Korup, Oliver; Romstad, Bård; Etzelmüller, Bernd

    2013-04-01

    The Norwegian transport infrastructure is frequently affected by rapid mass movements. Aside from snow avalanches and rock falls, debris flows account for high economical costs related to road and railway damages each year. However, studies investigating debris flow initiation conditions at a regional scale are rarely available for Norway. Thus, our objectives are to identify a set of terrain attributes as predictor variables for critical topographic conditions of debris flow initiation and to develop a statistical model to obtain a regional susceptibility map for NW-Norway. A debris flow inventory and the terrain variables slope, curvature and flow accumulation derived from a DEM with a resolution of 20 m x 20 m serve as input to a Weights-of-Evidence (WofE) model that we use to estimate posterior probabilities of debris flow occurrence on a pixel basis. The inventory is a point dataset of initiation locations of 429 debris flow events documented between 1979 and 2008. We divide the dataset into a training dataset consisting of debris flow events prior to 2005 and a test dataset with the events in the ongoing years. We address three topics related to model quality: model adequacy, model robustness and model accuracy. The model adequacy is tested by applying two different classification schemes (fixed intervals, percentile intervals) to the three variables slope, curvature and flow accumulation independently, and in combination. The model robustness is addressed by running the model several times with small variations in the input data set, i.e. using a random selection of 2/3 of the training dataset. The model accuracy is determined by applying the best model to the test data set and by estimating its predictive performance. Beside the susceptibility map itself, WofE offers the possibility to conduct an uncertainty map related to the posterior probabilities. This map is used for spatial error quantification. First results show that curvature is the strongest

  14. Estimating construction and demolition debris generation using a materials flow analysis approach.

    Science.gov (United States)

    Cochran, K M; Townsend, T G

    2010-11-01

    The magnitude and composition of a region's construction and demolition (C&D) debris should be understood when developing rules, policies and strategies for managing this segment of the solid waste stream. In the US, several national estimates have been conducted using a weight-per-construction-area approximation; national estimates using alternative procedures such as those used for other segments of the solid waste stream have not been reported for C&D debris. This paper presents an evaluation of a materials flow analysis (MFA) approach for estimating C&D debris generation and composition for a large region (the US). The consumption of construction materials in the US and typical waste factors used for construction materials purchasing were used to estimate the mass of solid waste generated as a result of construction activities. Debris from demolition activities was predicted from various historical construction materials consumption data and estimates of average service lives of the materials. The MFA approach estimated that approximately 610-78 × 10(6)Mg of C&D debris was generated in 2002. This predicted mass exceeds previous estimates using other C&D debris predictive methodologies and reflects the large waste stream that exists. Copyright © 2010 Elsevier Ltd. All rights reserved.

  15. Distribution of Amphipods (Gammarus nipponensis Ueno) Among Mountain Headwater Streams with Different Legacies of Debris Flow Occurrence

    Science.gov (United States)

    To understand the impacts of debris flows on the distribution of an amphipod with limited dispersal ability in the context of stream networks, we surveyed the presence of Gammarus nipponensis in 87 headwater streams with different legacies of debris flow occurrence within an 8.5-...

  16. Potential postwildfire debris-flow hazards - A prewildfire evaluation for the Jemez Mountains, north-central New Mexico

    Science.gov (United States)

    Anne C. Tillery; Jessica Haas

    2016-01-01

    Wildfire can substantially increase the probability of debris flows, a potentially hazardous and destructive form of mass wasting, in landscapes that have otherwise been stable throughout recent history. Although the exact location, extent, and severity of wildfire or subsequent rainfall intensity and duration cannot be known, probabilities of fire and debris‑flow...

  17. Triggering conditions and depositional characteristics of a disastrous debris flow event in Zhouqu city, Gansu Province, northwestern China

    NARCIS (Netherlands)

    Tang, C.; Rengers, N.; Asch, Th.W.J. van; Yang, Y.H.; Wang, G.F.

    2011-01-01

    On 7 August 2010, catastrophic debris flows were triggered by a rainstorm in the catchments of the Sanyanyu and Luojiayu torrents, Zhouqu County, Gansu Province northwestern China. These two debris flows originated shortly after a rainstorm with an intensity of 77.3 mm h−1 and transported a total

  18. Evaluation of debris-flow mitigation structures on runout using a computational model and field-monitoring data

    Science.gov (United States)

    Graf, Christoph; McArdell, Brian W.

    2010-05-01

    Recent channel changes caused by rock avalanches in the source area of a catchment near Preonzo, Switzerland, resulted in the unexpected bypass of existing mitigation structures. Two debris flow deflection dams were built in the source area to re-direct debris flows back into the old channel which connects to an existing debris flow retention basin. The torrent is monitored by an automated debris-flow observation station which provides information on front velocities and flow depths of torrential events such as debris flows and flash floods. Following construction of the deflection dams, the station was moved to the new channel and successfully recorded several debris-flow events. Numerical simulation was used to evaluate the effectiveness of such mitigation measures. Using the RAMMS (Rapid Mass Movements) simulation software, which describes the flow of debris using the 2D shallow water equations for granular flows and a Voellmy relationship for the friction, we describe simulations where we evaluate the effectiveness of the new deflection dams. First the model was calibrated using data from an event in 2004, then the dams were incorporated into the topography using the RAMMS model, and finally the model was run over the new topography using data from an event that occurred in 2007. Results indicate that the new deflection dams should function as intended for debris flows of about the same size as the event in 2004, however larger flows are expected to overtop the deflection dams. In general, the ability to incorporate mitigation structures into the topography has proven to be a useful tool for the rapid evaluation of protection measures, also for other Alpine debris flow problems. However several complicating issues arise, such as local flow deposition causing channel blockage. A modified version of the Voellmy friction relation, where the friction is a function of the internal random kinetic energy of the flow, provides a more realistic description of in

  19. Updated logistic regression equations for the calculation of post-fire debris-flow likelihood in the western United States

    Science.gov (United States)

    Staley, Dennis M.; Negri, Jacquelyn A.; Kean, Jason W.; Laber, Jayme L.; Tillery, Anne C.; Youberg, Ann M.

    2016-06-30

    Wildfire can significantly alter the hydrologic response of a watershed to the extent that even modest rainstorms can generate dangerous flash floods and debris flows. To reduce public exposure to hazard, the U.S. Geological Survey produces post-fire debris-flow hazard assessments for select fires in the western United States. We use publicly available geospatial data describing basin morphology, burn severity, soil properties, and rainfall characteristics to estimate the statistical likelihood that debris flows will occur in response to a storm of a given rainfall intensity. Using an empirical database and refined geospatial analysis methods, we defined new equations for the prediction of debris-flow likelihood using logistic regression methods. We showed that the new logistic regression model outperformed previous models used to predict debris-flow likelihood.

  20. A comparison between Bayes discriminant analysis and logistic regression for prediction of debris flow in southwest Sichuan, China

    Science.gov (United States)

    Xu, Wenbo; Jing, Shaocai; Yu, Wenjuan; Wang, Zhaoxian; Zhang, Guoping; Huang, Jianxi

    2013-11-01

    In this study, the high risk areas of Sichuan Province with debris flow, Panzhihua and Liangshan Yi Autonomous Prefecture, were taken as the studied areas. By using rainfall and environmental factors as the predictors and based on the different prior probability combinations of debris flows, the prediction of debris flows was compared in the areas with statistical methods: logistic regression (LR) and Bayes discriminant analysis (BDA). The results through the comprehensive analysis show that (a) with the mid-range scale prior probability, the overall predicting accuracy of BDA is higher than those of LR; (b) with equal and extreme prior probabilities, the overall predicting accuracy of LR is higher than those of BDA; (c) the regional predicting models of debris flows with rainfall factors only have worse performance than those introduced environmental factors, and the predicting accuracies of occurrence and nonoccurrence of debris flows have been changed in the opposite direction as the supplemented information.

  1. Assessing The Hazard of Sediment Yield From Debris Flows. A Case Study In The Central Spanish Pyrenees

    Science.gov (United States)

    Lorente, Adrián; Beguería, Santiago; García-Ruiz, José M.

    A total of 961 debris flows have been identified and mapped in the Upper Aragon and Gallego Valleys, Central Spanish Pyrenees. Information on lithology, plant cover, land uses as well as different maps derived from the Digital Terrain Model has been implemented into a Geographic Information System in order to apply a Discriminant Analysis. A logistic regression was used to produce a debris flow susceptibility map focused in the Flysch Sect or, where most of debris flows occurred. Information on different debris flow parameters have been taken in the field in order to forecast the runout distance according to the characteristics of these parameters. This procedure allow us to produce a model that forecast the probabilities of each debris flow to arrive to a fluvial channel and to become a sediment source.

  2. Mapping debris flow susceptibility using analytical network process in Kodaikkanal Hills, Tamil Nadu (India)

    Science.gov (United States)

    Sujatha, Evangelin Ramani; Sridhar, Venkataramana

    2017-12-01

    Rapid debris flows, a mixture of unconsolidated sediments and water travelling at speeds > 10 m/s are the most destructive water related mass movements that affect hill and mountain regions. The predisposing factors setting the stage for the event are the availability of materials, type of materials, stream power, slope gradient, aspect and curvature, lithology, land use and land cover, lineament density, and drainage. Rainfall is the most common triggering factor that causes debris flow in the Palar subwatershed and seismicity is not considered as it is a stable continental region and moderate seismic zone. Also, there are no records of major seismic activities in the past. In this study, one of the less explored heuristic methods known as the analytical network process (ANP) is used to map the spatial propensity of debris flow. This method is based on top-down decision model and is a multi-criteria, decision-making tool that translates subjective assessment of relative importance to weights or scores and is implemented in the Palar subwatershed which is part of the Western Ghats in southern India. The results suggest that the factors influencing debris flow susceptibility in this region are the availability of material on the slope, peak flow, gradient of the slope, land use and land cover, and proximity to streams. Among all, peak discharge is identified as the chief factor causing debris flow. The use of micro-scale watersheds demonstrated in this study to develop the susceptibility map can be very effective for local level planning and land management.

  3. Measurements of debris flow velocity through cross-correlation of instrumentation data

    Directory of Open Access Journals (Sweden)

    M. Arattano

    2005-01-01

    Full Text Available Detection of debris flow occurrence can be efficiently obtained through different types of sensors. A pair of ultrasonic sensors placed at a known distance from each other along a torrent have been used as a method to obtain mean front velocity of debris-flows, in addition to their use as detectors of debris flow occurrence. Also seismic and acoustic sensors have been employed to measure debris-flow front velocity and discharge in the same manner. In order to obtain velocity measurements, however, these methods require the presence of a well identifiable and defined main front in the debris flow wave. The time lag between the recordings of the front of the wave at two consecutive stations allows an estimation of its mean velocity. When a well-defined front is not present and no recurrent feature can be found along the wave, the measurement of velocity may prove difficult. The cross-correlation technique may help identifying the mean velocity of the flow in such cases. In fact, cross correlation allows to determine the mean time lag elapsed between the recording of two sets of data of the same event at different positions. This technique may be also used to measure velocity using signals coming from different types of sensors, for instance where a ground vibration detector has been placed along a torrent where an ultrasonic sensor was already present or viceversa. An application has been made using field data recorded through seismic and ultrasonic sensors in a small instrumented catchment in the Italian Alps (Moscardo Torrent.

  4. Glacial-interglacial climate changes recorded by debris flow fan deposits, Owens Valley, California

    Science.gov (United States)

    D'Arcy, Mitch; Roda-Boluda, Duna C.; Whittaker, Alexander C.

    2017-08-01

    It is hotly debated whether and how climate changes are recorded by terrestrial stratigraphy. Basin sediments produced by catchment-alluvial fan systems may record past climate over a variety of timescales, and could offer unique information about how climate controls sedimentation. Unfortunately, there are fundamental uncertainties about how climatic variables such as rainfall and temperature translate into sedimentological signals. Here, we examine 35 debris flow fan surfaces in Owens Valley, California, that record deposition throughout the past 125,000 years, during which climate has varied significantly. We show that the last full glacial-interglacial cycle is recorded with high fidelity by the grain size distributions of the debris flow deposits. These flows transported finer sediment during the cooler glacial climate, and became systematically coarser-grained as the climate warmed and dried. We explore the physical mechanisms that might explain this signal, and rule out changes in sediment supply through time. Instead, we propose that grain size records past changes in storm intensity, which is responsible for debris flow initiation in this area and is decoupled from average rainfall rates. This is supported by an exponential Clausius-Clapeyron-style scaling between grain size and temperature, and also reconciles with climate dynamics and the initiation of debris flows. The fact that these alluvial fans exhibit a strong, sustained sensitivity to orbital climate changes sheds new light on how eroding landscapes and their sedimentary products respond to climatic forcing. Finally, our findings highlight the importance of threshold-controlled events, such as storms and debris flows, in driving erosion and sedimentation at the Earth's surface in response to climate change.

  5. Coupled prediction of flash flood response and debris flow occurrence in an alpine basin

    Science.gov (United States)

    Amponsah, William

    2015-04-01

    Coupled prediction of flash flood response and debris flow occurrence in an alpine basin Author(s): William Amponsah1, E.I. Nikolopoulos2, Lorenzo Marchi1, Roberto Dinale4, Francesco Marra3,Davide Zoccatelli2 , Marco Borga2 Affiliation(s): 1CNR - IRPI, Corso Stati Uniti 4, 35127, Padova, ITALY, 2Department of Land, Environment, Agriculture and Forestry, University of Padova,VialeDell'Università 16, 35020, Legnaro PD, ITALY 3Department of Geography, Hebrew University of Jerusalem, ISRAEL 4Ufficio Idrografico, Provincia Autonoma di Bolzano, Bolzano, Italy This contribution examines the main hydrologic and morphologic metrics responsible for widespread triggering of debris-flows associated with flash flood occurrences in headwater alpine catchments.To achieve this objective, we investigate the precipitation forcing, hydrologic responses and landslides and debris-flow occurrences that prevailed during the August 4-5, 2012 extreme flash flood on the 140 km2 Vizze basin in the Eastern Alps of Italy. An intensive post-event survey was carried out a few days after the flood. This included the surveys of cross-sectional geometry and flood marks for the estimation of the peak discharges at multiple river sections and of the initiation and deposition areas of several debris flows. Rainfall estimates are based on careful analysis of weather radar observations and raingauge data. These data and observations permitted the implementation and calibration of a spatially distributed hydrological model, which was used to derive simulated flood hydrographs in 58 tributaries of the Vizze basin. Of these, 33 generated debris-flows, with area ranging from 0.02 km2 to 10 km2, with an average of 1.5 km2. With 130 mm peak event rainfall and a duration of 4 hours (with a max intensity of 90 mm h-1 for 10 min), model-simulated unit peak discharges range from 4 m3 s-1 km-2for elementary catchments up to 10 km2 to 2 m3 s-1 km-2 for catchments in the range of 50 - 100 km2. These are very high

  6. Forecasting inundation from debris flows that grow during travel, with application to the Oregon Coast Range, USA

    Science.gov (United States)

    Reid, Mark E.; Coe, Jeffrey A.; Brien, Dianne

    2016-01-01

    Many debris flows increase in volume as they travel downstream, enhancing their mobility and hazard. Volumetric growth can result from diverse physical processes, such as channel sediment entrainment, stream bank collapse, adjacent landsliding, hillslope erosion and rilling, and coalescence of multiple debris flows; incorporating these varied phenomena into physics-based debris-flow models is challenging. As an alternative, we embedded effects of debris-flow growth into an empirical/statistical approach to forecast potential inundation areas within digital landscapes in a GIS framework. Our approach used an empirical debris-growth function to account for the effects of growth phenomena. We applied this methodology to a debris-flow-prone area in the Oregon Coast Range, USA, where detailed mapping revealed areas of erosion and deposition along paths of debris flows that occurred during a large storm in 1996. Erosion was predominant in stream channels with slopes > 5°. Using pre- and post-event aerial photography, we derived upslope contributing area and channel-length growth factors. Our method reproduced the observed inundation patterns produced by individual debris flows; it also generated reproducible, objective potential inundation maps for entire drainage networks. These maps better matched observations than those using previous methods that focus on proximal or distal regions of a drainage network.

  7. Debris flows risk analysis and direct loss estimation: the case study of Valtellina di Tirano, Italy

    Czech Academy of Sciences Publication Activity Database

    Blahůt, Jan; Glade, T.; Sterlacchini, S.

    2014-01-01

    Roč. 11, č. 2 (2014), s. 288-307 ISSN 1672-6316 Institutional support: RVO:67985891 Keywords : Debris flows * Risk analysis * Economic losses * Central Alps * Italy Subject RIV: DE - Earth Magnetism, Geodesy, Geography OBOR OECD: Physical geography Impact factor: 0.963, year: 2014

  8. Delay in the flow of plant debris on floodplains overgrown with shrub vegetation

    Directory of Open Access Journals (Sweden)

    Mateusz Hämmerling

    2014-12-01

    Full Text Available The study aims to analyze the statistical probability of the slowing down of the plant debris flow through an area rich in shrub vegetation during floods. The shrub density has a direct influence on water velocity. The study was conducted in a 2-meter section of an artificial hydraulic flume. 15 tests were made for each of the different-shaped elements. The artificial elements used were either rectangular or elliptical in shape. Tests were conducted for three different spacings of cylindrical elements imitating the shrub vegetation and for three different depths of the hydraulic flume. Analysis of the test results leads to the conclusion that an increase in the density of cylindrical elements does not always cause an increase in the flow time of plant debris. The study also shows that an increase in the water depth causes an increase in the flow time of elements imitating the thick debris, which is due to a decrease in the water flow velocity. The study also presents an analysis of the probability of plant debris being detained by the cylindrical elements imitating the shrubs. This probability was observed to be higher for rectangular than elliptical elements. It was also observed to be inversely proportional to the water depth. The obtained results indicate that the subject matter of the current study is very interesting and complex and merits further investigation.

  9. The application of numerical debris flow modelling for the generation of physical vulnerability curves

    Czech Academy of Sciences Publication Activity Database

    Quan Luna, B.; Blahůt, Jan; van Westen, C.J.; Sterlacchini, S.; van Asch, T.W.J.; Akbas, S.O.

    2011-01-01

    Roč. 11, č. 7 (2011), s. 2047-2060 ISSN 1561-8633 Institutional research plan: CEZ:AV0Z30460519 Keywords : debris flow modelling * hazard * vulnerability curves Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.983, year: 2011 http://www.nat-hazards-earth-syst-sci.net/11/2047/2011/

  10. Transformation of ground vibration signal for debris-flow monitoring and detection in alarm systems.

    Science.gov (United States)

    Abancó, Clàudia; Hürlimann, Marcel; Fritschi, Bruno; Graf, Christoph; Moya, José

    2012-01-01

    Debris flows are fast mass movements formed by a mix of water and solid materials, which occur in steep torrents, and are a source of high risks for human settlements. Geophones are widely used to detect the ground vibration induced by passing debris flows. However, the recording of geophone signals usually requires storing a huge amount of data, which leads to problems in storage capacity and power consumption. This paper presents a method to transform and simplify the signals measured by geophones. The key input parameter is the ground velocity threshold, which removes the seismic noise that is not related to debris flows. A signal conditioner was developed to implement the transformation and the ground velocity threshold was set by electrical resistors. The signal conditioner was installed at various European monitoring sites to test the method. Results show that data amount and power consumption can be greatly reduced without losing much information on the main features of the debris flows. However, the outcome stresses the importance of choosing a ground vibration threshold, which must be accurately calibrated. The transformation is also suitable to detect other rapid mass movements and to distinguish among different processes, which points to a possible implementation in alarm systems.

  11. Recognizing the importance of tropical forests in limiting rainfall-induced debris flows

    Science.gov (United States)

    Worldwide concern for continuing loss of montane forest cover in the tropics usually focuses on adverse ecological consequences. Less recognized, but equally important to inhabitants of these affected regions, is an increasing susceptibility to rainfall-induced debris flows and t...

  12. Impact of rainfall spatial aggregation on the identification of debris flow occurrence thresholds

    Directory of Open Access Journals (Sweden)

    F. Marra

    2017-09-01

    Full Text Available The systematic underestimation observed in debris flow early warning thresholds has been associated with the use of sparse rain gauge networks to represent highly non-stationary rainfall fields. Remote sensing products permit concurrent estimates of debris-flow-triggering rainfall for areas poorly covered by rain gauges, but the impact of using coarse spatial resolutions to represent such rainfall fields is still to be assessed. This study uses fine-resolution radar data for ∼  100 debris flows in the eastern Italian Alps to (i quantify the effect of spatial aggregation (1–20 km grid size on the estimation of debris-flow-triggering rainfall and on the identification of early warning thresholds and (ii compare thresholds derived from aggregated estimates and rain gauge networks of different densities. The impact of spatial aggregation is influenced by the spatial organization of rainfall and by its dependence on the severity of the triggering rainfall. Thresholds from aggregated estimates show 8–21 % variation in the parameters whereas 10–25 % systematic variation results from the use of rain gauge networks, even for densities as high as 1∕10 km−2.

  13. Streamside policies for headwater channels: an example considering debris flows in the Oregon coastal province.

    Science.gov (United States)

    K.M. Burnett; D.J. Miller

    2007-01-01

    Headwater streams differ in susceptibility to debris flows and thus in importance as wood and sediment sources for larger rivers. Identifying and appropriately managing the most susceptible headwater streams is of interest. We developed and illustrated a method to delineate alternative aquatic conservation emphasis zones (ACEZs) considering probabilities for traversal...

  14. Impact of rainfall spatial aggregation on the identification of debris flow occurrence thresholds

    Science.gov (United States)

    Marra, Francesco; Destro, Elisa; Nikolopoulos, Efthymios I.; Zoccatelli, Davide; Creutin, Jean Dominique; Guzzetti, Fausto; Borga, Marco

    2017-09-01

    The systematic underestimation observed in debris flow early warning thresholds has been associated with the use of sparse rain gauge networks to represent highly non-stationary rainfall fields. Remote sensing products permit concurrent estimates of debris-flow-triggering rainfall for areas poorly covered by rain gauges, but the impact of using coarse spatial resolutions to represent such rainfall fields is still to be assessed. This study uses fine-resolution radar data for ˜  100 debris flows in the eastern Italian Alps to (i) quantify the effect of spatial aggregation (1-20 km grid size) on the estimation of debris-flow-triggering rainfall and on the identification of early warning thresholds and (ii) compare thresholds derived from aggregated estimates and rain gauge networks of different densities. The impact of spatial aggregation is influenced by the spatial organization of rainfall and by its dependence on the severity of the triggering rainfall. Thresholds from aggregated estimates show 8-21 % variation in the parameters whereas 10-25 % systematic variation results from the use of rain gauge networks, even for densities as high as 1/10 km-2.

  15. Objective definition of rainfall intensity-duration thresholds for the initiation of post-fire debris flows in southern California

    Science.gov (United States)

    Staley, Dennis; Kean, Jason W.; Cannon, Susan H.; Schmidt, Kevin M.; Laber, Jayme L.

    2012-01-01

    Rainfall intensity–duration (ID) thresholds are commonly used to predict the temporal occurrence of debris flows and shallow landslides. Typically, thresholds are subjectively defined as the upper limit of peak rainstorm intensities that do not produce debris flows and landslides, or as the lower limit of peak rainstorm intensities that initiate debris flows and landslides. In addition, peak rainstorm intensities are often used to define thresholds, as data regarding the precise timing of debris flows and associated rainfall intensities are usually not available, and rainfall characteristics are often estimated from distant gauging locations. Here, we attempt to improve the performance of existing threshold-based predictions of post-fire debris-flow occurrence by utilizing data on the precise timing of debris flows relative to rainfall intensity, and develop an objective method to define the threshold intensities. We objectively defined the thresholds by maximizing the number of correct predictions of debris flow occurrence while minimizing the rate of both Type I (false positive) and Type II (false negative) errors. We identified that (1) there were statistically significant differences between peak storm and triggering intensities, (2) the objectively defined threshold model presents a better balance between predictive success, false alarms and failed alarms than previous subjectively defined thresholds, (3) thresholds based on measurements of rainfall intensity over shorter duration (≤60 min) are better predictors of post-fire debris-flow initiation than longer duration thresholds, and (4) the objectively defined thresholds were exceeded prior to the recorded time of debris flow at frequencies similar to or better than subjective thresholds. Our findings highlight the need to better constrain the timing and processes of initiation of landslides and debris flows for future threshold studies. In addition, the methods used to define rainfall thresholds in this

  16. Modelling the runout of a debris flow of the Western Ghats, Kerala, India

    Science.gov (United States)

    Lukose Kuriakose, S.; Luna, B. Quan; Begueria Portugues, S.; van Westen, C. J.

    2009-04-01

    Debris flows as a result of shallow landslides are increasingly a concern in Kerala, the south western state of India. The plateau margins of highland Kerala (The Western Ghats) have all prerequisites of an active erosion zone where the natural terrain setup is conducive to slope failure/mass movements. Rainfall during two monsoons (South West and North East) that are effective in the state is identified as the primary trigger of debris flows. The flows are confined to the existing drainage lines and widen the streambeds that they follow, causing significant crop destruction (and occasionally loss of lives) along the path. Most often the amount of material that initiates the flows is less than a 1000 m3. Scouring is seen along the runout zone adding often an additional 30 to 80% more material. One such debris flow event of 2001 which occurred in the Kottayam district of Kerala was modelled with a Coulomb frictional and a Voellmy model in the DAN3D software. DAN3D is based on a Lagrangian formulation that discretises the flow in a number of particles representing bed-normal columns of flow. The values of the field variables for each particle are calculated at each time step using an interpolation technique based on Smoothed Particle Hydrodynamics (SPH). Bed entrainment was simulated after defining an entrainment zone, a maximum depth of supply material and the average growth or erosion rate. Result of the modeling shows that shallow failures using frictional material overestimates the runout zone and velocities. The Voellmy model underestimate deposit thickness where spreading is dominant but the velocity is better fitted during the course of the flow. Entrainment of material from the path and the ability to change rheology depending on the path material can be important. The reasonable results of the modeling show its flexibility which can be used to predict a simplified behaviour of debris flows.

  17. Quantitative risk assessment using empirical vulnerability functions from debris flow event reconstruction

    Science.gov (United States)

    Luna, Byron Quan; Blahut, Jan; Camera, Corrado; van Westen, Cees; Sterlacchini, Simone; Apuani, Tiziana; Akbas, Sami

    2010-05-01

    For a quantitative risk assessment framework it is essential to assess not only the hazardous process itself but to perform an analysis of their consequences. This quantitative assessment should include the expected monetary losses as the product of the probability of occurrence of a hazard with a given magnitude and its vulnerability. A quantifiable integrated approach of both hazard and risk is becoming a required practice in risk reduction management. Dynamic run-out models for debris flows are able to calculate physical outputs (extension, depths, velocities, impact pressures) and to determine the zones where the elements at risk could suffer an impact. These results are then applied for vulnerability and risk calculations. The risk assessment has been conducted in the Valtellina Valley, a typical Italian alpine valley lying in northern Italy (Lombardy Region). On 13th July 2008, after more than two days of intense rainfall, several debris and mud flows were released in the central part of valley between Morbegno and Berbenno. One of the largest debris flows occurred in Selvetta. The debris flow event was reconstructed after extensive field work and interviews with local inhabitants and civil protection teams. Also inside the Valtellina valley, between the 22nd and the 23rd of May 1983, two debris flows happened in Tresenda (Teglio municipality), causing casualties and considerable economic damages. On the same location, during the 26th of November 2002, another debris flow occurred that caused significant damage. For the quantification of a new scenario, the outcome results obtained from the event of Selvetta were applied in Tresenda. The Selvetta and Tresenda event were modelled with the FLO2D program. FLO2D is an Eulerian formulation with a finite differences numerical scheme that requires the specification of an input hydrograph. The internal stresses are isotropic and the basal shear stresses are calculated using a quadratic model. The significance of

  18. Sediment delivery in debris-flow torrents: two case studies in the Italian Alps

    Science.gov (United States)

    Bertoldi, Gabriele; Vincenzo, D'Agostino

    2013-04-01

    Flood-risk mitigation strategy is moving from fixed, structural and costly mitigation measures to more effective proactive solutions. This change is driven both by Flood Directive 2007/60/EC and limitations of financial resources and it requires a deep knowledge of the involved processes. In mountain catchments debris flow and debris floods are the most important sources of hazard and their impact on the fan areas is heavily conditioned by the sediment dynamics along the 'transport' reaches of the torrents. Last advances show how many cases of erosion and deposition within the transport reach greatly affect the total volume that is delivered to the fan as well the overall dynamics of the debris flow/flood event. Due to logistic and practical constraints this intermediate phase of the process has been scarcely investigated and the complex behavior of the sediment budgeting in torrent-streams is emerging. The objective of this work consists of collecting information on the evolution of the debris-flow sediment budget along Alpine torrents in order to provide novel data about erosive, depositional and recharging processes under different geological conditions. Two high frequency debris-flow catchments have been selected: the Rio Rudan basin in the geological setting of the Dolomites (near Cortina d'Ampezzo, Veneto Region, Italy) and the metamorphic dominated catchment of the Rio Gadria (near Lasa, Trentino Alto Adige, Italy), which has been recently instrumented (EU project Monitor II). Periodical field monitoring has been carried out since summer 2011. 25 cross sections have been observed in the Rio Rudan catchment along a 480 m torrent reach (slope of 36%) where additional sediment entrainment after debris-flow initiation takes place. 20 cross sections have been selected in the upper Rio Gadria basin and more precisely in two reaches close to debris-flow triggerring areas. Other 31 cross sections have been also monitored of the Rio Gadria main channel covering a

  19. Large woody debris and flow resistance in step-pool channels, Cascade Range, Washington

    Science.gov (United States)

    Curran, Janet H.; Wohl, Ellen E.

    2003-01-01

    Total flow resistance, measured as Darcy-Weisbach f, in 20 step-pool channels with large woody debris (LWD) in Washington, ranged from 5 to 380 during summer low flows. Step risers in the study streams consist of either (1) large and relatively immobile woody debris, bedrock, or roots that form fixed, or “forced,” steps, or (2) smaller and relatively mobile wood or clasts, or a mixture of both, arranged across the channel by the stream. Flow resistance in step-pool channels may be partitioned into grain, form, and spill resistance. Grain resistance is calculated as a function of particle size, and form resistance is calculated as large woody debris drag. Combined, grain and form resistance account for less than 10% of the total flow resistance. We initially assumed that the substantial remaining portion is spill resistance attributable to steps. However, measured step characteristics could not explain between-reach variations in flow resistance. This suggests that other factors may be significant; the coefficient of variation of the hydraulic radius explained 43% of the variation in friction factors between streams, for example. Large woody debris generates form resistance on step treads and spill resistance at step risers. Because the form resistance of step-pool channels is relatively minor compared to spill resistance and because wood in steps accentuates spill resistance by increasing step height, we suggest that wood in step risers influences channel hydraulics more than wood elsewhere in the channel. Hence, the distribution and function, not just abundance, of large woody debris is critical in steep, step-pool channels.

  20. Assessing the debris flow run-out frequency of a catchment in the French Alps using a parameterization analysis with the RAMMS numerical run-out model

    OpenAIRE

    Y. A. Hussin; Quan Luna, B.; C. J. Van Westen; M. Christen; Malet, J.P.; Asch, Th.W.J. van

    2012-01-01

    Debris flows occurring in the European Alps frequently cause significant damage to settlements, power-lines and transportation infrastructure which has led to traffic disruptions, economic loss and even death. Estimating the debris flow run-out extent and the parameter uncertainty related to run-out modeling are some of the difficulties found in the Quantitative Risk Assessment (QRA) of debris flows. Also, the process of the entrainment of material into a debris flow is until now not complete...

  1. Predicting the delivery of sediment and associated nutrients from post-fire debris flows in small upland catchments

    Science.gov (United States)

    Nyman, Petter; Sheridan, Gary; Smith, Hugh; Lane, Patrick

    2014-05-01

    Post-fire debris flows are extreme erosion events that can dominate the long term supply of sediment from headwaters to streams in upland catchments. Predicting the location, frequency and magnitude of debris flows is therefore important for understanding sediment dynamics in upland catchments and providing a basis on which to manage hydro-geomorphic risk in burned areas. In this study we survey 10 post-fire debris flow events in southeast Australia with aims to i) identify rainfall conditions underlying the debris flow response, ii) quantify erosion rates in hillslope and channel source areas, and iii) estimate the delivery of sediment and water quality constituents to receiving waterways. Rainfall events that triggered debris flows had an annual exceedance probability ranging from 0.1 to 0.6, and 30-minute intensities, I30, ranging from 17-60 mm h-1. Sediment delivery by debris flows (100-200 t ha-1) is similar to that which has been reported for similar events in the western US and Spain. In terms of eroded volume, there was on average an equal contribution from hillslopes and channels to debris flows, which is in agreement with the calculations of surface and subsurface source contributions obtained from radionuclide concentrations. In terms of the potential water quality impacts from post-fire debris flows, the hillslopes had much higher concentration of constituents such as fine clay and silt, plant available phosphorous and total carbon. The data on debris flow magnitude was used to evaluate two different approaches for predicting sediment delivery from debris flows. A statistical debris flow model developed by the US Geological Surveys and parameterized for catchments in western US performed well (R2 = 0.92) in terms of predicting the overall volume of material delivered at the catchment outlet. An alternative modeling approach, using local slope and contributing area as predictors of erosion, also produced good results, and could be used to obtain more

  2. Evidence for enhanced debris-flow activity in the Northern Calcareous Alps since the 1980s (Plansee, Austria)

    Science.gov (United States)

    Dietrich, A.; Krautblatter, M.

    2017-06-01

    Debris flows are among the most important natural hazards. The Northern Calcareous Alps with their susceptible lithology are especially affected by a double digit number of major hazard events per year. It is hypothesised that debris-flow intensity has increased significantly in the last decades in the Northern Calcareous Alps coincident to increased rainstorm frequencies, but yet there is only limited evidence. The Plansee catchment exposes extreme debris-flow activity due to the intensely jointed Upper Triassic Hauptdolomit lithology, being responsible for most of the debris-flow activity in the Northern Calcareous Alps. The debris flows feed into a closed sediment system, the Plansee Lake, where Holocene/Lateglacial sedimentation rates, rates since the late 1940s and recent rates can be inferred accurately. Using aerial photos and field mapping, the temporal and spatial development of eight active debris-flow fans is reconstructed in six time intervals from 1947, 1952, 1971, 1979, 1987, 2000 and 2010 and mean annual debris-flow volumes are calculated. These are compared with mean Holocene/Lateglacial debris-flow volumes derived from the most prominent cone whose contact with the underlying till is revealed by electrical resistivity tomography (ERT). Debris-flow activity there increased by a factor of 10 from 1947-1952 (0.23 ± 0.07 · 103 m3/yr) to 1987-2000 (2.41 ± 0.66 · 103 m3/yr). Mean post-1980 rates from all eight fans exceed pre-1980 rates by a factor of more than three coinciding with enhanced rainstorm activity recorded at meteorological stations in the Northern Calcareous Alps. The frequency of rain storms (def. 35 mm/d) has increased in the study area on average by 10% per decade and has nearly doubled since 1921. Recent debris-flow activity is also 2-3 times higher than mean Holocene/Lateglacial rates. The strong correlation between the non-vegetated catchment area and the annual debris-flow volume might indicate a decadal positive feedback between

  3. Sporadic, rainfall triggered landslides and debris flows in the monsoon, Nepal Himalaya

    Science.gov (United States)

    Fort, Monique; Etienne, Cossart; Alexis, Conte; Natacha, Gribenski; Gilles, Arnaud-Fassetta

    2010-05-01

    Small river catchments play a major role in the overall denudation of the Himalayas, because they may generate extreme, geomorphic events. We characterize their potential impacts on the morphology and functioning of trunk rivers, and indirectly on infrastructure and settlements located along the valley floor. Our study case, the Ghatte Khola, is an intermittent tributary of the Kali Gandaki (Western Nepal) affected by occasional debris flow events. The cause of the debris flows is a persistent planar slide zone (dip slope) that is reactivated by pre- or monsoon heavy rainfall on the upper, forested catchment. As a result, the narrow valley of the upstream part of the tributary is temporary clogged by slide masses, until sudden, landslide outburst floods occur. Downstream, where the channel is entrenched across a 5-8 m thick debris fan, the functioning of successive debris flows cause bank erosion and stream channel widening. At the junction with the Kali Gandaki, the flows may aggrade debris volumes large enough to dam the Kali Gandaki for a few hours and cause the level of this major river to rise more than 5 m upstream. During the last 40 years, pulsed aggradations transferred erosion point to the opposite (left bank) side of the Kali Gandaki. This ephemeral, yet threatening behaviour of the stream, occurs every two or three years, according to field investigations (geomorphic mapping, sediment analysis) and interviews of villagers. We present various scenarios simulated using the SAGA-GIS cellular automata combined with a Digital Elevation Model. We discuss the available rainfall intensity-duration thresholds susceptible to trigger Himalayan landslides. Our study suggests that such high-magnitude/low-frequency events are very efficient to foster sediment fluxes and create temporary sediment storages in Himalayan valleys, a fact that is to be considered prior to any new settlement and road design in a country where infrastructures are rapidly developing.

  4. Effective mitigation of debris flows at Lemon Dam, La Plata County, Colorado

    Science.gov (United States)

    deWolfe, V.G.; Santi, P.M.; Ey, J.; Gartner, J.E.

    2008-01-01

    To reduce the hazards from debris flows in drainage basins burned by wildfire, erosion control measures such as construction of check dams, installation of log erosion barriers (LEBs), and spreading of straw mulch and seed are common practice. After the 2002 Missionary Ridge Fire in southwest Colorado, these measures were implemented at Knight Canyon above Lemon Dam to protect the intake structures of the dam from being filled with sediment. Hillslope erosion protection measures included LEBs at concentrations of 220-620/ha (200-600% of typical densities), straw mulch was hand spread at concentrations up to 5.6??metric tons/hectare (125% of typical densities), and seeds were hand spread at 67-84??kg/ha (150% of typical values). The mulch was carefully crimped into the soil to keep it in place. In addition, 13 check dams and 3 debris racks were installed in the main drainage channel of the basin. The technical literature shows that each mitigation method working alone, or improperly constructed or applied, was inconsistent in its ability to reduce erosion and sedimentation. At Lemon Dam, however, these methods were effective in virtually eliminating sedimentation into the reservoir, which can be attributed to a number of factors: the density of application of each mitigation method, the enhancement of methods working in concert, the quality of installation, and rehabilitation of mitigation features to extend their useful life. The check dams effectively trapped the sediment mobilized during rainstorms, and only a few cubic meters of debris traveled downchannel, where it was intercepted by debris racks. Using a debris volume-prediction model developed for use in burned basins in the Western U.S., recorded rainfall events following the Missionary Ridge Fire should have produced a debris flow of approximately 10,000??m3 at Knight Canyon. The mitigation measures, therefore, reduced the debris volume by several orders of magnitude. For comparison, rainstorm

  5. Comparison of flow resistance relations for debris flows using a one-dimensional finite element simulation model

    Directory of Open Access Journals (Sweden)

    D. Naef

    2006-01-01

    Full Text Available This paper describes a one-dimensional finite element code for debris flows developed to model the flow within a steep channel and the stopping conditions on the fan. The code allows the systematic comparison of a wide variety of previously proposed one-phase flow resistance laws using the same finite element solution method. The one-dimensional depth-averaged equations of motion and the numerical model are explained. The model and implementation of the flow resistance relations was validated using published analytical results for the dam break case. Reasonable agreement for the front velocities and stopping location for a debris-flow event in the Kamikamihori torrent in Japan can be achieved with turbulent flow resistance relations including 'stop' terms which allow the flow to come to rest on a gently sloping surface. While it is possible to match the overall bulk flow behavior using relatively simple flow resistance relations, they must be calibrated. A sensitivity analysis showed that the shape of the upstream input hydrograph does not much affect the flow conditions in the lower part of the flow path, whereas the event volume is much more important.

  6. Debris flow run off simulation and verification ‒ case study of Chen-You-Lan Watershed, Taiwan

    Directory of Open Access Journals (Sweden)

    M.-L. Lin

    2005-01-01

    Full Text Available In 1996 typhoon Herb struck the central Taiwan area, causing severe debris flow in many subwatersheds of the Chen-You-Lan river watershed. More severe cases of debris flow occurred following Chi-Chi earthquake, 1999. In order to identify the potentially affected area and its severity, the ability to simulate the flow route of debris is desirable. In this research numerical simulation of debris flow deposition process had been carried out using FLO-2D adopting Chui-Sue river watershed as the study area. Sensitivity study of parameters used in the numerical model was conducted and adjustments were made empirically. The micro-geomorphic database of Chui-Sue river watershed was generated and analyzed to understand the terrain variations caused by the debris flow. Based on the micro-geomorphic analysis, the debris deposition in the Chui-Sue river watershed in the downstream area, and the position and volume of debris deposition were determined. The simulated results appeared to agree fairly well with the results of micro-geomorphic study of the area when not affected by other inflow rivers, and the trends of debris distribution in the study area appeared to be fairly consistent.

  7. Influence of topography on debris flow development in Ichino-sawa subwatershed of Ohya-kuzure landslide, Japan

    Science.gov (United States)

    Tsunetaka, H.; Hotta, N.; Imaizumi, F.; Hayakawa, Y. S.

    2015-12-01

    Large sediment movements, such as deep-seated landslides, produce unstable sediment over the long term. Most of the unstable sediment in a mountain torrent is discharged via the development of debris flows through entrainment. Consequently, after a large sediment movement, debris flows have long-term effects on the watershed regime. However, the development of debris flows in mountain torrents is poorly understood, since the topography is more complicated than downstream. We compared temporal changes in topography to examine how topography affects the development of flows. The study site was the Ichino-sawa subwatershed in the Ohya-kuzure landslide, Japan. Unstable sediment has been produced continuously since the landslide occurred in 1707. Several topographic surveys using a terrestrial laser scanner (TLS) and aerial shoots by an unmanned aerial vehicle (UAV) were performed between November 2011 (TLS) or November 2014 (UAV) and August 2015. High-resolution digital elevation models were created from the TLS and UAV results to detect temporal topographic changes. Debris flow occurrences and rainfall were also monitored using interval cameras and rain gauges. Downstream, the deposit depth decreased after the debris flows. Upstream, more complex changes were detected due to surges in the debris flows, which not only induced entrainment, but were also deposited in the valley floor. Furthermore, sediment was supplied from the stream bank during the debris flows. Consequently, several debris flows of different magnitudes were observed, although the rainfall conditions did not differ significantly. The results imply that the magnitude of the debris flows was affected by successive sediment movement resulting from the changing of the topographic conditions.

  8. Coupled DEM-CFD analyses of landslide-induced debris flows

    CERN Document Server

    Zhao, Tao

    2017-01-01

    This book reflects the latest research results in computer modelling of landslide-induced debris flows. The book establishes an understanding of the initiation and propagation mechanisms of landslides by means of numerical simulations, so that mitigation strategies to reduce the long-term losses from landslide hazards can be devised. In this context, the book employs the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) to investigate the mechanical and hydraulic behaviour of granular materials involved in landslides – an approach that yields meaningful insights into the flow mechanisms, concerning e.g. the mobilization of sediments, the generation and dissipation of excess pore water pressures, and the evolution of effective stresses. As such, the book provides valuable information, useful methods and robust numerical tools that can be successfully applied in the field of debris flow research.

  9. Andic soil features and debris flows in Italy. New perspective towards prediction

    Science.gov (United States)

    Scognamiglio, Solange; Calcaterra, Domenico; Iamarino, Michela; Langella, Giuliano; Orefice, Nadia; Vingiani, Simona; Terribile, Fabio

    2016-04-01

    Debris flows are dangerous hazards causing fatalities and damage. Previous works have demonstrated that the materials involved by debris flows in Campania (southern Italy) are soils classified as Andosols. These soils have peculiar chemical and physical properties which make them fertile but also vulnerable to landslide. In Italy, andic soil properties are found both in volcanic and non-volcanic mountain ecosystems (VME and NVME). Here, we focused on the assessment of the main chemical and physical properties of the soils in the detachment areas of eight debris flows occurred in NVME of Italy in the last 70 years. Such landslides were selected by consulting the official Italian geodatabase (IFFI Project). Andic properties (by means of ammonium oxalate extractable Fe, Si and Al forms for the calculation of Alo+1/2Feo) were also evaluated and a comparison with soils of VME was performed to assess possible common features. Landslide source areas were characterised by slope gradient ranging from 25° to 50° and lithological heterogeneity of the bedrock. The soils showed similar, i.e. all were very deep, had a moderately thick topsoil with a high organic carbon (OC) content decreasing regularly with depth. The cation exchange capacity trend was generally consistent with the OC and the pH varied from extremely to slightly acid, but increased with depth. Furthermore, the soils had high water retention values both at saturation (0.63 to 0.78 cm3 cm-3) and in the dryer part of the water retention curve, and displayed a prevalent loamy texture. Such properties denote the chemical and physical fertility of the investigated ecosystems. The values of Alo+1/2Feoindicated that the soils had vitric or andic features and can be classified as Andosols. The comparison between NVME soils and those of VME showed similar depth, thickness of soil horizons, and family texture, whereas soil pH, degree of development of andic properties and allophane content were higher for VME soils. Such

  10. The influence of vegetation cover on debris-flow density during an extreme rainfall in the northern Colorado Front Range

    Science.gov (United States)

    Rengers, Francis; McGuire, Luke; Coe, Jeffrey A.; Kean, Jason W.; Baum, Rex L.; Staley, Dennis M.; Godt, Jonathan W.

    2016-01-01

    We explored regional influences on debris-flow initiation throughout the Colorado Front Range (Colorado, USA) by exploiting a unique data set of more than 1100 debris flows that initiated during a 5 day rainstorm in 2013. Using geospatial data, we examined the influence of rain, hillslope angle, hillslope aspect, and vegetation density on debris-flow initiation. In particular we used a greenness index to differentiate areas of high tree density from grass and bare soil. The data demonstrated an overwhelming propensity for debris-flow initiation on south-facing hillslopes. However, when the debris-flow density was analyzed with respect to total rainfall and greenness we found that most debris flows occurred in areas of high rainfall and low tree density, regardless of hillslope aspect. These results indicate that present-day tree density exerts a stronger influence on debris-flow initiation locations than aspect-driven variations in soil and bedrock properties that developed over longer time scales.

  11. Instrumental record of debris flow initiation during natural rainfall: Implications for modeling slope stability

    Science.gov (United States)

    Montgomery, D.R.; Schmidt, K.M.; Dietrich, W.E.; McKean, J.

    2009-01-01

    The middle of a hillslope hollow in the Oregon Coast Range failed and mobilized as a debris flow during heavy rainfall in November 1996. Automated pressure transducers recorded high spatial variability of pore water pressure within the area that mobilized as a debris flow, which initiated where local upward flow from bedrock developed into overlying colluvium. Postfailure observations of the bedrock surface exposed in the debris flow scar reveal a strong spatial correspondence between elevated piezometric response and water discharging from bedrock fractures. Measurements of apparent root cohesion on the basal (Cb) and lateral (Cl) scarp demonstrate substantial local variability, with areally weighted values of Cb = 0.1 and Cl = 4.6 kPa. Using measured soil properties and basal root strength, the widely used infinite slope model, employed assuming slope parallel groundwater flow, provides a poor prediction of hydrologie conditions at failure. In contrast, a model including lateral root strength (but neglecting lateral frictional strength) gave a predicted critical value of relative soil saturation that fell within the range defined by the arithmetic and geometric mean values at the time of failure. The 3-D slope stability model CLARA-W, used with locally observed pore water pressure, predicted small areas with lower factors of safety within the overall slide mass at sites consistent with field observations of where the failure initiated. This highly variable and localized nature of small areas of high pore pressure that can trigger slope failure means, however, that substantial uncertainty appears inevitable for estimating hydrologie conditions within incipient debris flows under natural conditions. Copyright 2009 by the American Geophysical Union.

  12. Laboratory experiments investigating entrainment by debris flows and associated increased mobility

    Science.gov (United States)

    Moberly, D.; Maki, L.; Hill, K. M.

    2014-12-01

    As debris flows course down a steep hillside they entrain bed materials such as loose sediments. The entrainment of materials not only increases the size of the debris flows but the mobility as well. The mechanics underlying the particle entrainment and the associated increased mobility are not well-understood. Existing models for the entrainment process include those that explicitly consider stress ratios, the angle of inclination, and the particle fluxes relative to those achieved under steady conditions. Others include an explicit consideration of the physics of the granular state: the visco-elastic nature of particle flows and, alternatively, the role of macroscopic force chains. Understanding how well these different approaches account for entrainment and deposition rates is important for accurate debris flow modeling, both in terms of the rate of growth and also in terms of the increased mobility associated with the entrainment. We investigate how total and instantaneous entrainment and deposition vary with macroscopic stresses and particle-scale interactions for different particle sizes and different fluid contents using laboratory experiments in an instrumented experimental laboratory debris flow flume. The flume has separate, independent water supplies for the bed and "supply" (parent debris flow), and the bed is instrumented with pore pressure sensors and a basal stress transducer. We monitor flow velocities, local structure, and instantaneous entrainment and deposition rates using a high speed camera. We have found that systems with a mixture of particle sizes are less erosive and more depositional than systems of one particle size under otherwise the same conditions. For both mixtures and single-sized particle systems, we have observed a relatively linear relationship between total erosion and the slope angle for dry flows. Increasing fluid content typically increases entrainment. Measurements of instantaneous entrainment indicate similar dependencies

  13. Debris flow initiation by runoff in a recently burned basin: Is grain-by-grain sediment bulking or en masse failure to blame?

    Science.gov (United States)

    McGuire, Luke; Rengers, Francis; Kean, Jason W.; Staley, Dennis M.

    2017-01-01

    Postwildfire debris flows are frequently triggered by runoff following high-intensity rainfall, but the physical mechanisms by which water-dominated flows transition to debris flows are poorly understood relative to debris flow initiation from shallow landslides. In this study, we combined a numerical model with high-resolution hydrologic and geomorphic data sets to test two different hypotheses for debris flow initiation during a rainfall event that produced numerous debris flows within a recently burned drainage basin. Based on simulations, large volumes of sediment eroded from the hillslopes were redeposited within the channel network throughout the storm, leading to the initiation of numerous debris flows as a result of the mass failure of sediment dams that built up within the channel. More generally, results provide a quantitative framework for assessing the potential of runoff-generated debris flows based on sediment supply and hydrologic conditions.

  14. Debris flow initiation by runoff in a recently burned basin: Is grain-by-grain sediment bulking or en masse failure to blame?

    Science.gov (United States)

    McGuire, Luke A.; Rengers, Francis K.; Kean, Jason W.; Staley, Dennis M.

    2017-07-01

    Postwildfire debris flows are frequently triggered by runoff following high-intensity rainfall, but the physical mechanisms by which water-dominated flows transition to debris flows are poorly understood relative to debris flow initiation from shallow landslides. In this study, we combined a numerical model with high-resolution hydrologic and geomorphic data sets to test two different hypotheses for debris flow initiation during a rainfall event that produced numerous debris flows within a recently burned drainage basin. Based on simulations, large volumes of sediment eroded from the hillslopes were redeposited within the channel network throughout the storm, leading to the initiation of numerous debris flows as a result of the mass failure of sediment dams that built up within the channel. More generally, results provide a quantitative framework for assessing the potential of runoff-generated debris flows based on sediment supply and hydrologic conditions.

  15. Triggering conditions and depositional characteristics of a disastrous debris flow event in Zhouqu city, Gansu Province, northwestern China

    Directory of Open Access Journals (Sweden)

    C. Tang

    2011-11-01

    Full Text Available On 7 August 2010, catastrophic debris flows were triggered by a rainstorm in the catchments of the Sanyanyu and Luojiayu torrents, Zhouqu County, Gansu Province northwestern China. These two debris flows originated shortly after a rainstorm with an intensity of 77.3 mm h−1 and transported a total volume of about 2.2 million m3, which was deposited on an existing debris fan and into a river. This catastrophic event killed 1765 people living on this densely urbanised fan. The poorly sorted sediment contains boulders up to 3–4 m in diameter. In this study, the geomorphological features of both debris flow catchment areas are analyzed based on the interpretation of high-resolution remote sensing imagery combined with field investigation. The characteristics of the triggering rainfall and the initiation of the debris flow occurrence are discussed. Using empirical equations, the peak velocities and discharges of the debris flows were estimated to be around 9.7 m s−1 and 1358 m3 s−1 for the Sanyanyu torrent and 11 m s−1 and 572 m3 s−1 for the Luojiayu torrent. The results of this study contribute to a better understanding of the conditions leading to catastrophic debris flow events.

  16. Trigger Analysis and Modelling of Very Large Debris Flows in Santa Teresa, Cusco, Southern Peru

    Science.gov (United States)

    Buis, Daniel; Huggel, Christian; Frey, Holger; Giráldez, Claudia; Rohrer, Mario; Christen, Marc; Portocarrero, César

    2014-05-01

    The Peruvian Andes have repeatedly been affected by large mass movements such as landslides, avalanches and debris flows. In 1998, two very large debris flows in the region of Machu Picchu (Sacsara and Ahobamba), southern Peru, destroyed the town of Santa Teresa, an important hydropower scheme and further infrastructure. The debris flows on the order of 5 to 25 million m3 volume rank among the largest recently observed events of this type worldwide. Despite their extreme dimensions, these events have not been studied in detail. An important limitation for more insight studies is the remote location of the mass flows and the very sparse information and data available for the study region. Neither triggering processes nor mass flow process characteristics have been understood to date. This study tries to fill some of these gaps in understanding that are critical to improved assessment of hazards and eventual risk reduction measures. For the trigger analysis we used data and information from field work, a limited number of ground based meteorological data, and complementary satellite derived data. Results indicate that in the case of the Sacsara event, heavy rainfall likely was a main trigger. For Ahobamba, antecedent rainfall as well as snow and ice melt leading to saturation of glacial sediments must have played an important role. Simulations with a dynamic debris flow model (RAMMS) allowed us to constrain a number of flow parameters such as flow height and velocity, runout distance and flow and deposition volumes. Strong surging flow behavior was detected, resulting in very large runout distance (exceeding 20 km); which rather depends on the largest single surge volume, not the total event volume. Based on the identification of potential mass flow sources we modeled a number of scenarios. The assessment of related hazards, including a preliminary hazard map, showed that several communities in catchments draining towards Santa Teresa are endangered by mass movements

  17. Navier-Stokes Equation and Computational Scheme for Non-Newtonian Debris Flow

    Directory of Open Access Journals (Sweden)

    Ignazio Licata

    2014-01-01

    Full Text Available This paper proposes a computational approach to debris flow model. In recent years, the theoretical activity on the classical Herschel-Bulkley model (1926 has been very intense, but it was in the early 80s that the opportunity to explore the computational model has enabled considerable progress in identifying the subclasses of applicability of different sets of boundary conditions and their approximations. Here we investigate analytically the problem of the simulation of uniform motion for heterogeneous debris flow laterally confined taking into account mainly the geological data and methodological suggestions derived from simulation with cellular automata and grid systems, in order to propose a computational scheme able to operate a compromise between “global” predictive capacities and computing effort.

  18. Brief Communication: A new testing field for debris flow warning systems and algorithms

    Science.gov (United States)

    Arattano, M.; Coviello, V.; Cavalli, M.; Comiti, F.; Macconi, P.; Marchi, L.; Theule, J.; Crema, S.

    2015-03-01

    Early warning systems (EWSs) are among the measures adopted for the mitigation of debris flow hazards. EWSs often employ algorithms that require careful and long testing to grant their effectiveness. A permanent installation has been so equipped in the Gadria basin (Eastern Italian Alps) for the systematic test of event-EWSs. The installation is conceived to produce didactic videos and host informative visits. The populace involvement and education is in fact an essential step in any hazard mitigation activity and it should envisaged in planning any research activity. The occurrence of a debris flow in the Gadria creek, in the summer of 2014, allowed a first test of the installation and the recording of an informative video on EWSs.

  19. Brief Communication: A new testing field for debris flow warning systems

    Science.gov (United States)

    Arattano, M.; Coviello, V.; Cavalli, M.; Comiti, F.; Macconi, P.; Theule, J.; Crema, S.

    2015-07-01

    A permanent field installation for the systematic test of debris flow warning systems and algorithms has been equipped on the eastern Italian Alps. The installation was also designed to produce didactic videos and it may host informative visits. The populace education is essential and should be envisaged in planning any research on hazard mitigation interventions: this new installation responds to this requirement and offers an example of integration between technical and informative needs. The occurrence of a debris flow in 2014 allowed the first tests of a new warning system under development and to record an informative video on its performances. This paper will provide a description of the installation and an account of the first technical and informative results obtained.

  20. Back calculation of Debris flow Run-Out & Entrainment Using the Voellmy Rheology

    OpenAIRE

    Bayissa, Lemessa Fille

    2017-01-01

    Debris flow is one of the many geo-hazards that cause a major damage worldwide. It can cause loss of human lives especially to those living in mountainous regions. Besides, it cause economic damage by destroying properties and infrastructure. Forecasting and controlling the hazard associated to this type of mass movements is still a difficult task that requires qualitative and quantitative analyses. However, the development of numerical dynamic run out models has a major advantage in the stud...

  1. Setup of an experimental device for high-speed debris flows generating 2D impulse waves

    OpenAIRE

    Bateman Pinzón, Allen; Bregoli, Francesco; Medina Iglesias, Vicente César de; Rast, Manuel; Bentz, Clara

    2011-01-01

    Landslides and debris flows falling into reservoirs, natural lakes, fjords or seas can generate impulse waves, which can be assimilated to tsunami-water waves. Such wave’s behavior can be highly destructive regarding dams and other structures and infrastructures as well as people living along shorelines. Destructive observed past events, such Vajont Dam in Italy (1963) or Lituya Bay in Alaska (1958), are not enough to describe and finally properly prevent the phenomenon. Experimental studies ...

  2. Roads at risk: traffic detours from debris flows in southern Norway

    Science.gov (United States)

    Meyer, N. K.; Schwanghart, W.; Korup, O.; Nadim, F.

    2015-05-01

    Globalisation and interregional exchange of people, goods, and services has boosted the importance of and reliance on all kinds of transport networks. The linear structure of road networks is especially sensitive to natural hazards. In southern Norway, steep topography and extreme weather events promote frequent traffic disruption caused by debris flows. Topographic susceptibility and trigger frequency maps serve as input into a hazard appraisal at the scale of first-order catchments to quantify the impact of debris flows on the road network in terms of a failure likelihood of each link connecting two network vertices, e.g. road junctions. We compute total additional traffic loads as a function of traffic volume and excess distance, i.e. the extra length of an alternative path connecting two previously disrupted network vertices using a shortest-path algorithm. Our risk metric of link failure is the total additional annual traffic load, expressed as vehicle kilometres, because of debris-flow-related road closures. We present two scenarios demonstrating the impact of debris flows on the road network and quantify the associated path-failure likelihood between major cities in southern Norway. The scenarios indicate that major routes crossing the central and north-western part of the study area are associated with high link-failure risk. Yet options for detours on major routes are manifold and incur only little additional costs provided that drivers are sufficiently well informed about road closures. Our risk estimates may be of importance to road network managers and transport companies relying on speedy delivery of services and goods.

  3. Roads at risk - traffic detours from debris flows in southern Norway

    Science.gov (United States)

    Meyer, N. K.; Schwanghart, W.; Korup, O.; Nadim, F.

    2014-10-01

    Globalization and interregional exchange of people, goods, and services has boosted the importance of and reliance on all kinds of transport networks. The linear structure of road networks is especially sensitive to natural hazards. In southern Norway, steep topography and extreme weather events promote frequent traffic disruption caused by debris flows. Topographic susceptibility and trigger frequency maps serve as input into a hazard appraisal at the scale of first-order catchments to quantify the impact of debris flows on the road network in terms of a failure likelihood of each link connecting two network vertices, e.g., road junctions. We compute total additional traffic loads as a function of traffic volume and excess distance, i.e. the extra length of an alternative path connecting two previously disrupted network vertices using a shortest-path algorithm. Our risk metric of link failure is the total additional annual traffic load expressed as vehicle kilometers because of debris-flow related road closures. We present two scenarios demonstrating the impact of debris flows on the road network, and quantify the associated path failure likelihood between major cities in southern Norway. The scenarios indicate that major routes crossing the central and northwestern part of the study area are associated with high link failure risk. Yet options for detours on major routes are manifold, and incur only little additional costs provided that drivers are sufficiently well informed about road closures. Our risk estimates may be of importance to road network managers and transport companies relying of speedy delivery of services and goods.

  4. A Debris Backwards Flow Simulation System for Malaysia Airlines Flight 370

    OpenAIRE

    Eichhorn, Mike; Haertel, Alexander

    2017-01-01

    This paper presents a system based on a Two-Way Particle-Tracking Model to analyze possible crash positions of flight MH370. The particle simulator includes a simple flow simulation of the debris based on a Lagrangian approach and a module to extract appropriated ocean current data from netCDF files. The influence of wind, waves, immersion depth and hydrodynamic behavior are not considered in the simulation.

  5. Brief Communication: A new testing field for debris flow warning systems

    OpenAIRE

    Arattano, M.; Coviello, V; M. Cavalli; Comiti, F.; P. Macconi; J. Theule; Crema, S.

    2015-01-01

    A permanent field installation for the systematic test of debris flow warning systems and algorithms has been equipped on the eastern Italian Alps. The installation was also designed to produce didactic videos and it may host informative visits. The populace education is essential and should be envisaged in planning any research on hazard mitigation interventions: this new installation responds to this requirement and offers an example of integration between technical and in...

  6. Post-fire hillslope debris flows: Evidence of a distinct erosion process

    Science.gov (United States)

    Langhans, Christoph; Nyman, Petter; Noske, Philip J.; Van der Sant, Rene E.; Lane, Patrick N. J.; Sheridan, Gary J.

    2017-10-01

    After wildfire a hitherto unexplained erosion process that some authors have called 'miniature debris flows on hillslopes' and that leave behind levee-lined rills has been observed in some regions of the world. Despite the unusual proposition of debris flow on planar hillslopes, the process has not received much attention. The objectives of this study were to (1) accumulate observational evidence of Hillslope Debris Flows (HDF) as we have defined the process, to (2) understand their initiation process by conducting runoff experiments on hillslopes, to (3) propose a conceptual model of HDF, and to (4) contrast and classify HDF relative to other erosion and transport processes in the post-wildfire hillslope domain. HDF have been observed at relatively steep slope gradients (0.4-0.8), on a variety of geologies, and after fire of at least moderate severity and consist of a lobe of gravel- to cobble-sized material 0.2-1 m wide that is pushed by runoff damming up behind it. During initiation, runoff moved individual particles that accumulated a small distance downslope until the accumulation of grains failed and formed the granular lobe of the HDF. HDF are a threshold process, and runoff rates of 0.5 L s- 1 2 L s- 1 were required for their initiation during the experiments. The conceptual model highlights HDF as a geomorphic process distinct from channel debris flows, because they occur on planar, unconfined hillslopes rather than confined channels. HDF can erode very coarse non-cohesive surface soil, which distinguishes them from rill erosion that have suspended and bedload transport. On a matrix of slope and grain size, HDF are enveloped between purely gravity-driven dry ravel, and mostly runoff driven bedload transport in rills.

  7. Large scale debris-flow hazard assessment: a geotechnical approach and GIS modelling

    Directory of Open Access Journals (Sweden)

    G. Delmonaco

    2003-01-01

    Full Text Available A deterministic distributed model has been developed for large-scale debris-flow hazard analysis in the basin of River Vezza (Tuscany Region – Italy. This area (51.6 km 2 was affected by over 250 landslides. These were classified as debris/earth flow mainly involving the metamorphic geological formations outcropping in the area, triggered by the pluviometric event of 19 June 1996. In the last decades landslide hazard and risk analysis have been favoured by the development of GIS techniques permitting the generalisation, synthesis and modelling of stability conditions on a large scale investigation (>1:10 000. In this work, the main results derived by the application of a geotechnical model coupled with a hydrological model for the assessment of debris flows hazard analysis, are reported. This analysis has been developed starting by the following steps: landslide inventory map derived by aerial photo interpretation, direct field survey, generation of a database and digital maps, elaboration of a DTM and derived themes (i.e. slope angle map, definition of a superficial soil thickness map, geotechnical soil characterisation through implementation of a backanalysis on test slopes, laboratory test analysis, inference of the influence of precipitation, for distinct return times, on ponding time and pore pressure generation, implementation of a slope stability model (infinite slope model and generalisation of the safety factor for estimated rainfall events with different return times. Such an approach has allowed the identification of potential source areas of debris flow triggering. This is used to detected precipitation events with estimated return time of 10, 50, 75 and 100 years. The model shows a dramatic decrease of safety conditions for the simulation when is related to a 75 years return time rainfall event. It corresponds to an estimated cumulated daily intensity of 280–330 mm. This value can be considered the hydrological triggering

  8. Sediment entrainment by debris flows: In situ measurements from the headwaters of a steep catchment

    Science.gov (United States)

    McCoy, S.W.; Kean, Jason W.; Coe, Jeffrey A.; Tucker, G.E.; Staley, Dennis M.; Wasklewicz, T.A.

    2012-01-01

    Debris flows can dramatically increase their volume, and hence their destructive potential, by entraining sediment. Yet quantitative constraints on rates and mechanics of sediment entrainment by debris flows are limited. Using an in situ sensor network in the headwaters of a natural catchment we measured flow and bed properties during six erosive debris-flow events. Despite similar flow properties and thicknesses of bed sediment entrained across all events, time-averaged entrainment rates were significantly faster for bed sediment that was saturated prior to flow arrival compared with rates for sediment that was dry. Bed sediment was entrained from the sediment-surface downward in a progressive fashion and occurred during passage of dense granular fronts as well as water-rich, inter-surge flow.En massefailure of bed sediment along the sediment-bedrock interface was never observed. Large-magnitude, high-frequency fluctuations in total normal basal stress were dissipated within the upper 5 cm of bed sediment. Within this near surface layer, concomitant fluctuations in Coulomb frictional resistance are expected, irrespective of the influence of pore fluid pressure or fluctuations in shear stress. If the near-surface sediment was wet as it was overridden by a flow, additional large-magnitude, high-frequency pore pressure fluctuations were measured in the near-surface bed sediment. These pore pressure fluctuations propagated to depth at subsonic rates and in a diffusive manner. The depth to which large excess pore pressures propagated was typically less than 10 cm, but scaled as (D/fi)0.5, in which D is the hydraulic diffusivity and fi is the frequency of a particular pore pressure fluctuation. Shallow penetration depths of granular-normal-stress fluctuations and excess pore pressures demonstrate that only near-surface bed sediment experiences the full dynamic range of effective-stress fluctuations, and as a result, can be more easily entrained than deeper sediment

  9. Rainfall control of debris-flow triggering in the Réal Torrent, Southern French Prealps

    Science.gov (United States)

    Bel, Coraline; Liébault, Frédéric; Navratil, Oldrich; Eckert, Nicolas; Bellot, Hervé; Fontaine, Firmin; Laigle, Dominique

    2017-08-01

    This paper investigates the occurrence of debris flow due to rainfall forcing in the Réal Torrent, a very active debris flow-prone catchment in the Southern French Prealps. The study is supported by a 4-year record of flow responses and rainfall events, from three high-frequency monitoring stations equipped with geophones, flow stage sensors, digital cameras, and rain gauges measuring rainfall at 5-min intervals. The classic method of rainfall intensity-duration (ID) threshold was used, and a specific emphasis was placed on the objective identification of rainfall events, as well as on the discrimination of flow responses observed above the ID threshold. The results show that parameters used to identify rainfall events significantly affect the ID threshold and are likely to explain part of the threshold variability reported in the literature. This is especially the case regarding the minimum duration of rain interruption (MDRI) between two distinct rainfall events. In the Réal Torrent, a 3-h MDRI appears to be representative of the local rainfall regime. A systematic increase in the ID threshold with drainage area was also observed from the comparison of the three stations, as well as from the compilation of data from experimental debris-flow catchments. A logistic regression used to separate flow responses above the ID threshold, revealed that the best predictors are the 5-min maximum rainfall intensity, the 48-h antecedent rainfall, the rainfall amount and the number of days elapsed since the end of winter (used as a proxy of sediment supply). This emphasizes the critical role played by short intense rainfall sequences that are only detectable using high time-resolution rainfall records. It also highlights the significant influence of antecedent conditions and the seasonal fluctuations of sediment supply.

  10. Risk Evaluation of Debris Flow Hazard Based on Asymmetric Connection Cloud Model

    Directory of Open Access Journals (Sweden)

    Xinyu Xu

    2017-01-01

    Full Text Available Risk assessment of debris flow is a complex problem involving various uncertainty factors. Herein, a novel asymmetric cloud model coupled with connection number was described here to take into account the fuzziness and conversion situation of classification boundary and interval nature of evaluation indicators for risk assessment of debris flow hazard. In the model, according to the classification standard, the interval lengths of each indicator were first specified to determine the digital characteristic of connection cloud at different levels. Then the asymmetric connection clouds in finite intervals were simulated to analyze the certainty degree of measured indicator to each evaluation standard. Next, the integrated certainty degree to each grade was calculated with corresponding indicator weight, and the risk grade of debris flow was determined by the maximum integrated certainty degree. Finally, a case study and comparison with other methods were conducted to confirm the reliability and validity of the proposed model. The result shows that this model overcomes the defect of the conventional cloud model and also converts the infinite interval of indicators distribution into finite interval, which makes the evaluation result more reasonable.

  11. HIGH-RESOLUTION DEBRIS FLOW VOLUME MAPPING WITH UNMANNED AERIAL SYSTEMS (UAS AND PHOTOGRAMMETRIC TECHNIQUES

    Directory of Open Access Journals (Sweden)

    M. S. Adams

    2016-06-01

    Full Text Available Debris flows cause an average € 30 million damages and 1-2 fatalities every year in Austria. Detailed documentation of their extent and magnitude is essential for understanding, preventing and mitigating these natural hazard events. The recent development of unmanned aerial systems (UAS has provided a new possibility for on-demand high-resolution monitoring and mapping. Here, we present a study, where the spatial extent and volume of a large debris flow event were mapped with different UAS, fitted with commercial off-the-shelf sensors. Orthophotos and digital terrain models (DTM were calculated using structure-from-motion photogrammetry software. Terrain height differences caused by the debris flow in the catchment and valley floor were derived by subtracting the pre-event airborne laser scanning (ALS DTM from a post-event UAS-DTM. The analysis of the volumetric sediment budget showed, that approximately 265,000 m³ material was mobilised in the catchment, of which 45,000 m³ settled there; of the material, which reached the valley floor, 120,000 m³ was deposited, while another 10,000 m³ was eroded from there. The UAS-results were validated against ALS data and imagery from a traditional manned-aircraft photogrammetry campaign. In conclusion, the UAS-data can reach an accuracy and precision comparable to manned aircraft data, but with the added benefits of higher flexibility, easier repeatability, less operational constraints and higher spatial resolution.

  12. Submarine debris flows and continental slople evolution in front of Quaternary ice sheets, Baffin Bay, Canadian Arctic

    Energy Technology Data Exchange (ETDEWEB)

    Hiscott, R.N.; Aksu, A.E. (Memorial Univ. of Newfoundland, St. John' s (Canada))

    1994-03-01

    Baffin Bay is a semi-enclosed extension of the Labrador Sea in the Canadian Arctic. The upper Pliocene and Quaternary successions beneath the continental slope contain important slumps and debris-flow deposits. New high-resolution single-channel seismic data have been acquired from a 500 to 600-m-deep transverse trough that indents that shelf in an area where glacial outflow was focused during the Pliocene and Pleistocene. Major shelf-edge progradation occurred both inside and on the flanks of the transverse trough. In the lower slope, several large debris flows carried proglacial deposits into the deep basin. The largest of these debris flows dramatically reshaped the sea floor by reducing bottom slopes both by proximal erosion and distal thickening of the debris-flow deposit. Subsequently, the lower slope was starved of terrigenous input, and the upper slope was steepened by accumulation of basinward thinning wedges of mass flow deposits. The processes of emplacement of large debris flows, slope reshaping, and out-of-phase accumulation identified in upper and lower slope areas of Baffin Bay are relevant to the interpretation of other line-source margins affected by major sea level falls or changes in sediment influx, including siliciclastic slope aprons and carbonate platform margins. On fans, muddy debris flows provide both a potential seal for hydrocarbons generated after burial and a potentially important mass of organic-rich mudstones that may act as source rocks in the subsurface. 32 refs., 14 figs., 1 tab.

  13. Effects of ground freezing and snow avalanche deposits on debris flows in alpine environments

    Directory of Open Access Journals (Sweden)

    E. Bardou

    2004-01-01

    Full Text Available Debris flows consist of a mixture of water and sediments of various sizes. Apart from few exceptions, the water is usually contributed directly from precipitation. In a high mountain environment like the Alps, it appears necessary to consider infiltration of water into the ground during rainfall events, the runoff characteristics and the potential supply of sediment as a function of a multitude of climatic and hydrogeological factors. This paper outlines several new processes - either linked to ice formation in the ground before an event, or to the presence of snow avalanche deposits - that change the probability of observing an event. These processes were identified during field observations connected with extreme weather events that occurred recently in the Valais Alps (south-western Switzerland: they can be seen as factors either amplifying or reducing the potential of slope instability caused by the precipitation event. An intense freezing of the ground during the week preceding the exceptional rainfall event in mid-October 2000 amplified the probability of triggering debris flows between roughly 1800 and 2300m asl. Both growth of ice needles and superficial ground freezing destroyed soil aggregates (increasing the availability of sediments and/or, a deeper ground freezing resulted in decreased infiltration rate (increased runoff during the first hours of heavy rainfall. The presence of snow avalanche deposits in a gully could be simultaneously an amplifying factor (the snow deposits increase the base flow and create a sliding plane for the sediments, mainly at the time of summer storms or a reducing factor (reduction in the impact energy of the raindrops, mainly at the time of winter storms of the risk of triggering debris flows. If it is not currently possible to establish rainfall threshold values for debris flow triggering, the knowledge and the implementation of these processes in the analysis of the potential triggering (for example by

  14. Debris flow runout simulation at the basin scale: Zêzere valley (Estrela Mountain, Portugal)

    Science.gov (United States)

    Melo, Raquel; van Asch, Theo; Luís Zêzere, José

    2017-04-01

    Following the wildfires occurred in 2005 in the upper part of the Zêzere valley (Estrela Mountain, Central Portugal), several debris flows were triggered under intense rainfall. The event caused infrastructural and economical damage, although no life was lost. The present research aims to simulate the runout of two debris flows occurred during the event as well as back-calculate the rheological parameters and the excess rainfall involved. To achieve these purposes a numerical model was used, which integrates surface runoff, concentrated erosion along the channels, propagation and deposition of flow material. Frequently, due the lack of information about the soil thickness in catchment areas, the models assume a homogeneous value for the entire area. In this study, the map of the soil thickness - interpreted as the depth to bedrock - was based on the simplified geomorphologically indexed soil thickness (sGIST) model. The rheological parameters were tested and calibrated using 3 different types of rheology: Bingham, Coulomb-viscous and Voellmy. Moreover, the amount of excess rainfall and the erosion factor were also considered for calibration purposes. Since there is no reliable information about the total volume of material deposited after the event, the validation of the runout models was performed by comparing the results with the spatial pattern of the debris flows occurred in the study area in 2005. The rheological and entrainment parameters obtained for the most accurate simulation were then used to perform four scenarios of debris flows runout at the basin scale (i.e., the Zêzere valley). For each scenario, the excess rainfall simulated varied. Since there is a lack of quantitative information to validate these models, the results were compared with historical references of events in the study area. Regarding the results obtained in the scenarios, we identified at least 6 gullies where debris flows occurred in the past and caused material damage and loss of

  15. Probability and volume of potential postwildfire debris flows in the 2010 Fourmile burn area, Boulder County, Colorado

    Science.gov (United States)

    Ruddy, Barbara C.; Stevens, Michael R.; Verdin, Kristine

    2010-01-01

    This report presents a preliminary emergency assessment of the debris-flow hazards from drainage basins burned by the Fourmile Creek fire in Boulder County, Colorado, in 2010. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence and volumes of debris flows for selected drainage basins. Data for the models include burn severity, rainfall total and intensity for a 25-year-recurrence, 1-hour-duration rainstorm, and topographic and soil property characteristics. Several of the selected drainage basins in Fourmile Creek and Gold Run were identified as having probabilities of debris-flow occurrence greater than 60 percent, and many more with probabilities greater than 45 percent, in response to the 25-year recurrence, 1-hour rainfall. None of the Fourmile Canyon Creek drainage basins selected had probabilities greater than 45 percent. Throughout the Gold Run area and the Fourmile Creek area upstream from Gold Run, the higher probabilities tend to be in the basins with southerly aspects (southeast, south, and southwest slopes). Many basins along the perimeter of the fire area were identified as having low probability of occurrence of debris flow. Volume of debris flows predicted from drainage basins with probabilities of occurrence greater than 60 percent ranged from 1,200 to 9,400 m3. The predicted moderately high probabilities and some of the larger volumes responses predicted for the modeled storm indicate a potential for substantial debris-flow effects to buildings, roads, bridges, culverts, and reservoirs located both within these drainages and immediately downstream from the burned area. However, even small debris flows that affect structures at the basin outlets could cause considerable damage.

  16. Modelling potential debris flows on soil covered catchment areas along the Upper Chama River Basin, Northwestern Venezuela

    OpenAIRE

    Mora, Rengifo Zenon Ortega

    2007-01-01

    Debris flows in the Venezuelan Andes are common geomorphologic processes that reflect the sediment supply capacity of this regional mountain system. In this study a regional model for potential debris flows on soil and vegetation-covered hillslopes, in watershed domains is presented. The method used in this investigation is a combination of remote sensing techniques, morphometric and hydrologic parameters. The study area is the Upper Chama River Watershed,North-western Venezuela. The input da...

  17. Tree-Ring Reconstruction of Debris-Flow Events Leading to Overbank Sedimentation on the Illgraben Cone (Valais Alps, Switzerland)

    OpenAIRE

    Stoffel, Markus; Bollschweiler, Michelle; Leutwiler, Astrid; Aeby, Patrick

    2008-01-01

    Dendrogeomorphological analyses of trees affected by debris flows have regularly been used to date past events. However, while previous studies in the Swiss Alps have focused primarily on granitic and gneissic debris-flow material and on Larix decidua Mill. and Picea abies (L.) Karst. trees, they have – at the same time – widely disregarded torrents dominated by finely fractured calcareous and dolomitic lithologies and forests populated with Pinus sylvestris L. In this paper, we report on res...

  18. Using patterns of debris flow erosion and deposition in the Icelandic Westfjords to delineate hazard zones.

    Science.gov (United States)

    Conway, S. J.; Decaulne, A.; Balme, M. R.; Murray, J. B.; Towner, M. C.

    2009-04-01

    Debris flows pose a significant risk to infrastructure and people; hence the aim of this study is to better understand the behaviour of debris flows by studying examples from above the town of Ísafjörður in north-western Iceland. Debris flow is a recognised hazard in the region [1], but above Ísafjörður occurs with particularly high regularity [2] and can involve large volumes of debris. We have used airborne laser altimeter (LiDAR) and differential GPS data to produce isopach maps of flows that occurred in 1999, 2007 and 2008 above Ísafjörður and in adjacent valleys. Compared to observations from the literature, e.g. [3-5], these flows start depositing at unusually high slope gradients (up to 45°). However the larger flows are also unusually mobile compared to typical hill-slope debris flows [4], but they are not as mobile as channelized flows [6]. This means that for a given volume their run-out distance is much greater than expected and hence more likely to reach the town. The volumes for the flows were calculated in two ways: firstly we were able to take the difference between the surfaces before (LiDAR) and after (dGPS) three small flows that occurred in 2008. Secondly, for flows prior to our 2008 LiDAR survey, we interpolated the pre-flow surface based on surrounding topography and measured differences from our post-flow surveys. The second method therefore has a tendency to over-estimate the flow volumes. The scheme for dGPS surveying involved obtaining numerous cross sections and taking long profiles along the channel and adjacent levees. Based on the volumes that we have calculated using these more accurate methods, we have increased the value of volume estimates for recorded historic debris flows reported by [2] and have revised the local denudation rate to 45 mm per 100 yr. Using the isopach maps and associated field observations we have found a relationship between slope and deposition volume, where the runout and pattern of deposition is a

  19. Identification of debris flows occurrence thresholds: rainfall spatial aggregation outperforms raingauge sampling

    Science.gov (United States)

    Destro, Elisa; Marra, Francesco; Efthymios, Nikolopoulos; Davide, Zoccatelli; Borga, Marco

    2017-04-01

    Regional early-warning systems for debris flows are often based on rainfall thresholds: empirical relationships between the depth (or intensity) and duration of the triggering rainfall identified from past events. Rain gauge based thresholds have been used in different regions worldwide but their implementation is conditional to the existence of in-situ observations and their accuracy is thus limited. Satellite precipitation products provide global debris flow-concurrent estimates over areas poorly covered by rain gauge networks or radar systems. Deriving local, regional or global thresholds from such datasets promises to increase the size of the training datasets and to allow consistently comparing thresholds for different regions and/or periods. However, satellite estimation of debris flow triggering rainfall is hampered by two issues: (a) the coarse resolution of satellite products and (b) the uncertainty related to precipitation retrieval algorithms. This study aims at isolating the contribution of the coarse resolution of satellite precipitation products in the derivation of debris flows occurrence thresholds. The work builds upon high-resolution (1 km, 5 min), adjusted weather radar estimates for 11 storms, which collectively triggered 99 debris flows in the eastern Italian alps. First, we analyze the impact of spatial aggregation on the identification of triggering rainfall characterized by different return periods and we show how these observations influence the derivation of depth-duration thresholds. Second, we compare the thresholds derived aggregated estimates to the ones obtained from rain gauge networks of different densities. Results from this study are summarised as follows. (a) The impact of spatial aggregation depends on the return period of the triggering rainfall: aggregated estimates for long return periods (> 10 years) are consistently underestimated while aggregated estimates for short return periods (< 10 years) are more variable and

  20. An Early Warning System from debris flows based on ground vibration monitoring data

    Science.gov (United States)

    Arattano, Massimo; Coviello, Velio

    2015-04-01

    Among the different countermeasures that can be adopted for the mitigation of landslide hazard, Early Warning Systems (EWSs) are receiving an increasing attention. EWSs are the set of capacities needed to generate and disseminate timely and meaningful warning information to enable individuals and communities threatened by a hazard to appropriately act, in sufficient time, to reduce the possibility of harm or loss (UNEP, 2012). An EWS from debris flows can be classified into two main categories: advance and event EWSs. Advance EWSs predict the occurrence of a debris flow by monitoring hydro-meteorological conditions that may lead to its initiation. Despite their widespread adoption, these latter systems are prone to false alarms because they are heavily affected by bias between regional rainfall threshold and local conditions. Event EWSs, on the contrary, detect the occurrence of a debris flow when the process is already in progress. They usually rely on the use of algorithms for processing in real time the monitoring data. Their effectiveness depends on the reliability of those algorithms, which require long development and testing phases. A specific testing field for event EWSs has been equipped in the Gadria instrumented basin, located in the Eastern Italian Alps. A specifically designed monitoring unit capable to record data from different type of sensors and to implement aboard warning algorithms has been installed along a straight reach of the torrent. A flashing light, installed on the bank of the torrent, has been wired to this unit. The flashing light is framed by a fixed video camera that also shoots the passage of debris flows in the torrent. This provides a visual verification of the efficacy of the algorithm under test, particularly useful to show to practitioners and administrators a clear demonstration of the warning outcome. In this work, we present the performance of a warning algorithm that has been experimented in the Gadria testing field in 2013

  1. The altitude effect on the climatic factors controlling debris flows activation: the Marderello Torrent case study

    Science.gov (United States)

    Palladino, Michela; Turconi, Laura; Savio, Gabriele; Tropeano, Domenico

    2015-04-01

    The left Cenischia valley includes some of the best known alpine basins prone to debris flow in Northwestern Italian Alps. In particular, in the Marderello catchment (6,6 km²), a left tributary of the Cenischia river, 31 important debris flood/flow events occurred during the last one hundred years. According to the chronicles of the last three centuries, events with significant volumes are on the average liable to take place every 3-4 years, whereas minor events may occur even twice per year. Due to the high frequency of activations, the site is of relevant interest for monitoring purposes. Since the early nineties, the CNR IRPI equipped the Marderello basin with meteorological monitoring devices. The rainfall monitoring network consists of four rain gauges, placed at different elevations, between 800 m a.s.l. and 2854 m a.s.l. Other meteorological data (air moisture and temperature, atmospheric pressure, wind speed and direction) are provided by three stations located at 3150, 2150 and 830 m a.s.l. The main objective of the monitoring is the investigation of the triggering conditions for debris flows initiation. In the scientific literature the prediction of debris flows is often tackled by the use of empirical methods, based on the analysis of past activation and related rainfall triggering conditions. The effectiveness of these methods strictly depends on the representativeness of the meteorological monitoring stations used to collect the data. In complex orography sites, as the Alpine catchments are, the remarkable elevation gaps between the source areas of debris flows and the rain gauges position make it difficult to identify the triggering rainfall. To attain more reliable results, the elevation effect must be considered. In fact, elevation influences the precipitation in terms of cumulative values and, as a result of the temperature gradient, it controls the nature of the precipitation (rain/snow). In the present study we use the rainfall and temperature

  2. Hydrological disposition of flash flood and debris flows events in an Alpine watershed in Austria

    Science.gov (United States)

    Prenner, David; Kaitna, Roland; Mostbauer, Karin; Hrachowitz, Markus

    2017-04-01

    Debris flows and flash floods including intensive bedload transport represent severe hazards in the Alpine environment of Austria. For neither of these processes, explicit rainfall thresholds - even for specific regions - are available. This may be due to insufficient data on the temporal and spatial variation of precipitation, but probably also due to variations of the geomorphic and hydrological disposition of a watershed to produce such processes in the course of a rainfall event. In this contribution we investigate the importance of the hydrological system state for triggering debris flows and flash floods in the Ill/Suggadin watershed (500 km2), Austria, by analyzing the effects of dynamics in system state variables such as soil moisture, snow pack, or ground water level. The analysis is based on a semi-distributed conceptual rainfall-runoff model, spatially discretizing the watershed according to the available precipitation observations, elevation, topographic considerations and land cover. Input data are available from six weather stations on a daily basis ranging back to 1947. A Thiessen polygon decomposition results in six individual precipitation zones with a maximum area of about 130 km2. Elevation specific behavior of the quantities temperature and precipitation is covered through an elevation-resolved computation every 200 m. Spatial heterogeneity is considered by distinct hydrological response units for bare rock, forest, grassland, and riparian zone. To reduce numerical smearing on the hydrological results, the Implicit Euler scheme was used to discretize the balance equations. For model calibration we utilized runoff hydrographs, snow cover data as well as prior parameter and process constraints. The obtained hydrological output variables are linked to documented observed flash flood and debris flow events by means of a multivariate logistic regression. We present a summary about the daily hydrological disposition of experiencing a flash flood or

  3. Probability and volume of potential postwildfire debris flows in the 2011 Indian Gulch burn area, near Golden, Colorado

    Science.gov (United States)

    Ruddy, Barbara C.

    2011-01-01

    This report presents an assessment of the debris-flow hazards from drainage basins burned in 2011 by the Indian Gulch wildfire near Golden, Colorado. Empirical models derived from statistical evaluation of data collected from recently burned drainage basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence and debris-flow volumes for selected drainage basins. Input for the models include measures of burn severity, topographic characteristics, soil properties, and rainfall total and intensity for a (1) 2-year-recurrence, 1-hour-duration rainfall, (2) 10-year-recurrence, 1-hour-duration rainfall, and (3) 25-year-recurrence, 1-hour-duration rainfall. Estimated debris-flow probabilities in the drainage basins of interest ranged from 2 percent in response to the 2-year-recurrence, 1-hour-duration rainfall to a high of 76 percent in response to the 25-year-recurrence, 1-hour-duration rainfall. Estimated debris-flow volumes ranged from a low of 840 cubic meters to a high of 26,000 cubic meters, indicating a considerable hazard should debris flows occur.

  4. A database on post-fire erosion rates and debris flows in Mediterranean-Basin watersheds

    Science.gov (United States)

    Parise, M.; Cannon, S. H.

    2009-04-01

    Wildfires can affect many Mediterranean countries on a yearly bases, producing damage and economic losses, both as direct effect of the fires and as consequent events, including erosion and sedimentation in the recently burned areas. Even though most of the wildfires occur in Spain, Portugal, southern France, Italy and Greece, it can be stated that no one of the Mediterranean countries is completely immune by such hazards. In addition to destruction of the vegetation, and in addition to direct losses to the built-up environment, further effects may also be registered as a consequence of the fire, even weeks or months after its occurrence. Wildfire can have, in fact, profound effects on the hydrologic response of watersheds, and debris-flow activity is among the most destructive consequences of these effects, often causing extensive damage to human infrastructure. Wildfires are today continuously monitored by several European institutions, and forecasting of the conditions (weather, temperature, wind, etc.) more likely conducive to their occurrence is often available in real time. On the other hand, not much is known about the processes that occur as a consequence of the fire, including erosion and debris flows. These are often underestimated, and become object of study only after some catastrophic event has occurred. This is in strong contrast with all the established techniques of risk mitigation; as a result, no prevention action is generally considered, and the society relies only on the emergency phase following a disaster. Aimed at contributing to gather information about the occurrence of erosional and debris-flow activity in recently burned Mediterranean areas, and at making available these information to land planners and scientists, a specific database has been compiled and presented in this contribution. To date, scientific literature on the topic in Europe has never been catalogued, and was dispersed in a number of different journals and in conference

  5. Debris flow evolution and the activation of an explosive hydrothermal system; Te Maari, Tongariro, New Zealand

    Science.gov (United States)

    Procter, J. N.; Cronin, S. J.; Zernack, A. V.; Lube, G.; Stewart, R. B.; Nemeth, K.; Keys, H.

    2014-10-01

    Analysis of the pre- and post-eruption topography, together with observations of the avalanche deposition sequence, yields a triggering mechanism for the 6 August 2012 eruption of Upper Te Maari. The avalanche was composed of a wedge of c. 683 000-774 000 m3 of coarse breccia, spatter and clay-rich tuffs and diamictons which slid from the western flanks of the Upper Te Maari Crater, the failure plane is considered to be a hydrothermally altered clay layer. This landslide led to a pressure drop of up to 0.5 MPa, enough to generate an explosive eruption from the hydrothermal system below, which had been activated over the months earlier by additional heat and gas from a shallow intrusion. The landslide transformed after c. 700 m into a clay-rich cohesive debris flow, eroding soils from steep, narrow stretches of channel, before depositing on intermediate broad flatter reaches. After each erosive reach, the debris flow contained greater clay and mud contents and became more mobile. At c. 2 km flow distance, however, the unsaturated flow stopped, due to a lack of excess pore pressure. This volume controlled flow deposited thick, steep sided lobes behind an outer levee, accreting inward and upward to form a series of curved surface ridges.

  6. Application of different techniques to obtain spatial estimates of debris flows erosion and deposition depths

    Science.gov (United States)

    Boreggio, Mauro; Gregoretti, Carlo; Degetto, Massimo; Bernard, Martino

    2016-04-01

    In Alpine regions, debris flows endanger settlements and human life. Danger mitigation strategies based on the preparation of hazard maps are necessary tools for the current land planning. To date, hazard maps are obtained by using one- or two-dimensional numerical models that are able to forecast the potential inundated areas, after careful calibration of those input parameters that directly affect the flow motion and its interaction with the ground surface (sediments entrainment or deposition). In principle, the reliability of these numerical models can be tested by flume experiments in laboratory using, for example, particles and water mixtures. However, for more realistic materials including coarse particles, the scaling effects are still difficult to account for. In some cases, where there are enough data (for example, point measures of flow depths and velocities or spatial estimation of erosion and deposition depths), these models can be tested against field observations. As it regards the spatial estimates of debris flows erosion and deposition depths, different approaches can be followed to obtain them, mainly depending on both the type and accuracy of the available initial data. In this work, we explain the methods that have been employed to obtain the maps of erosion and deposition depths for three occurred debris flows in the Dolomites area (North-Eastern Italian Alps). The three events are those occurred at Rio Lazer (Trento) on the 4th of November 1966, at Fiames (Belluno) on the 5th of July 2006 and at Rio Val Molinara (Trento) on the 15th of August 2010. For each case study, we present the available initial data and the related problems, the techniques that have been used to overcome them and finally the results obtained.

  7. Resolved granular debris-flow simulations with a coupled SPH-DCDEM model

    Science.gov (United States)

    Birjukovs Canelas, Ricardo; Domínguez, José M.; Crespo, Alejandro J. C.; Gómez-Gesteira, Moncho; Ferreira, Rui M. L.

    2016-04-01

    Debris flows represent some of the most relevant phenomena in geomorphological events. Due to the potential destructiveness of such flows, they are the target of a vast amount of research (Takahashi, 2007 and references therein). A complete description of the internal processes of a debris-flow is however still an elusive achievement, explained by the difficulty of accurately measuring important quantities in these flows and developing a comprehensive, generalized theoretical framework capable of describing them. This work addresses the need for a numerical model applicable to granular-fluid mixtures featuring high spatial and temporal resolution, thus capable of resolving the motion of individual particles, including all interparticle contacts. This corresponds to a brute-force approach: by applying simple interaction laws at local scales the macro-scale properties of the flow should be recovered by upscaling. This methodology effectively bypasses the complexity of modelling the intermediate scales by resolving them directly. The only caveat is the need of high performance computing, a demanding but engaging research challenge. The DualSPHysics meshless numerical implementation, based on Smoothed Particle Hydrodynamics (SPH), is expanded with a Distributed Contact Discrete Element Method (DCDEM) in order to explicitly solve the fluid and the solid phase. The model numerically solves the Navier-Stokes and continuity equations for the liquid phase and Newton's motion equations for solid bodies. The interactions between solids are modelled with classical DEM approaches (Kruggel-Emden et al, 2007). Among other validation tests, an experimental set-up for stony debris flows in a slit check dam is reproduced numerically, where solid material is introduced trough a hopper assuring a constant solid discharge for the considered time interval. With each sediment particle undergoing tens of possible contacts, several thousand time-evolving contacts are efficiently treated

  8. Evidence for enhanced debris flow activity in the Northern Calcareous Alps since the 1980s (Plansee, Austria)

    Science.gov (United States)

    Dietrich, Andreas; Krautblatter, Michael

    2016-04-01

    From 1950 to 2011 almost 80.000 people lost their lives through the occurrence of debris flow events (Dowling and Santi, 2014). Debris flows occur in all alpine regions due to intensive rainstorms and mobilisable loose debris. Due to their susceptible lithology, the Northern Calcareous Alps are affected by a double digit number of major hazard events per year. Some authors hypothesised a relation between an increasing frequency of heavy rainstorms and an increasing occurrence of landslides in general (Beniston and Douglas, 1996) and debris flows in special (Pelfini and Santilli, 2008), but yet there is only limited evidence. The Plansee catchment in the Ammergauer Alps consists of intensely jointed Upper Triassic Hauptdolomit lithology and therefore shows extreme debris flow activity. To investigate this activity in the last decades, the temporal and spatial development of eight active debris flow fans is examined with GIS and field mapping. The annual rates since the late 1940s are inferred accurately by using aerial photos from 1947, 1952, 1971, 1979, 1987, 2000 and 2010. These rates are compared to the mean Holocene/Lateglacial debris flow volume derived from the most prominent cone. The contact with the underlying till is revealed by electrical resistivity tomography (ERT). It shows that the mean annual debris flow volume has increased there by a factor of 10 from 1947-1952 (0.23 ± 0.07 10³m³/yr) to 1987-2000 (2.41 ± 0.66 10³m³/yr). A similar trend can be seen on all eight fans: mean post-1980 rates exceed pre-1980 rates by a factor of more than three. This increasing debris flow activity coincides with an enhanced rainstorm (def. 35 mm/d) frequency recorded at the nearest meteorological station. Since 1921 the frequency of heavy rainstorms has increased there on average by 10% per decade. Recent debris flow rates are also 2-3 times higher compared to mean Holocene/Lateglacial rates. Furthermore, we state a strong correlation between the non

  9. Effects of vegetation on debris flow mitigation: A case study from Gansu province, China

    Science.gov (United States)

    Wang, Siyuan; Meng, Xingmin; Chen, Guan; Guo, Peng; Xiong, Muqi; Zeng, Runqiang

    2017-04-01

    Debris flows are traditionally controlled using civil engineering structures such as check dams. However, the misuse of such strategies may sometimes trigger environmental hazards such as the catastrophic landslide in 2010 in Zouqu county, China, and therefore other methods such as the use of vegetation as an eco-engineering tool are increasingly being adopted. The aim of the present research was to investigate the bioengineering effects of vegetation over time in an area prone to debris flows in Gansu province, China. We collected detailed data from 2012 to 2014 on vegetation type, density, and root system morphology, and measured profiles across the valley. In addition, we assessed the increased soil cohesion provided by the root development of three monospecific stands of Robinia pseudoacacia of different ages growing within the debris valley, and on a larger scale, their effects on channel morphology. These data were incorporated into a modified form of BSTEM (Bank Stability and Toe Erosion Model) and a cellular braided-stream model. The results indicate that with increasing age, the FOS (factor of safety) of the bank would be significantly increased, and that the flooded area in the valley caused by simulated flood events would be decreased by 18-24%, on average. Subsequently, field data were incorporated into a cellular model to simulate sediment movement and the effects of vegetation on the channel dynamics. The results demonstrate that the stability provided by vegetation could result in a less active valley system and that overall the development of debris-controlling vegetation could make a major contribution to ecosystem restoration. However, careful management is essential for making optimum use of the vegetation.

  10. Detailed study of a catchment prone to debris flows along the International Road n° 7, Mendoza Province, Argentina

    Science.gov (United States)

    Wick, E.; Baumann, V.; Favre-Bulle, G.; Jaboyedoff, M.; Loye, A.; Marengo, H.; Rosas, M.

    2009-04-01

    The International Road 7 crosses Argentina from East to West, linking Buenos Aires to the Chile border. Crossing the Andes Cordillera, it is exposed to numerous natural hazards, such as avalanches, rockfalls and debris flows. This study focuses on a catchment prone to debris flows above the International Road n° 7 between Potrerillos and Uspallata (Mendoza Province, Argentina) and is part of a regional study that assesses the hazard along the mountainous section of this road. The catchment measures 4.7 km2 and is constituted of three main torrents that unite a few meters above the International Road. Heavy rainfalls triggered debris flows in each of these torrents during the evening of 11 January 2005, reaching the road apparently at a very short interval of time. A car was hit by one of these debris flows and two people were injured. The study has been realized from Quickbird satellite imagery and field data principally. The conditions that triggered the debris flows in this catchment were established from meteorological data, as well as particle size and mineralogy of the material. Satellite imagery and a digital elevation model showed that the debris flows initiated mainly at the top of the catchment. Erosion of a highly altered granite produced abundant sandy material. The debris flows were classified as granular matrix with a collisional-frictional behavior. Various calculations of volumes, peak discharges and velocities (~ 7 m/s) were realized using different approaches. It appears that important volumes could be mobilized, especially in the longest torrent. A new event could imply more than 65'000 m3 of material. A detailed geomorphologic study shows the effect of mitigation works on the debris flows hazard. Indeed, the torrents were deviated towards a more adequate place for the construction of a road bridge. Three propagation scenarios show the limited efficiency of these works. The road bridge is under-dimensioned and deposits of the 2005 event have not

  11. Numerical simulation of the debris flow dynamics with an upwind scheme and specific friction treatment

    Science.gov (United States)

    Sánchez Burillo, Guillermo; Beguería, Santiago; Latorre, Borja; Burguete, Javier

    2014-05-01

    Debris flows, snow and rock avalanches, mud and earth flows are often modeled by means of a particular realization of the so called shallow water equations (SWE). Indeed, a number of simulation models have been already developed [1], [2], [3], [4], [5], [6], [7]. Debris flow equations differ from shallow water equations in two main aspects. These are (a) strong bed gradient and (b) rheology friction terms that differ from the traditional SWE. A systematic analysis of the numerical solution of the hyperbolic system of equations rising from the shallow water equations with different rheological laws has not been done. Despite great efforts have been done to deal with friction expressions common in hydraulics (such as Manning friction), landslide rheologies are characterized by more complicated expressions that may deal to unphysical solutions if not treated carefully. In this work, a software that solves the time evolution of sliding masses over complex bed configurations is presented. The set of non- linear equations is treated by means of a first order upwind explicit scheme, and the friction contribution to the dynamics is treated with a suited numerical scheme [8]. In addition, the software incorporates various rheological models to accommodate for different flow types, such as the Voellmy frictional model [9] for rock and debris avalanches, or the Herschley-Bulkley model for debris and mud flows. The aim of this contribution is to release this code as a free, open source tool for the simulation of mass movements, and to encourage the scientific community to make use of it. The code uses as input data the friction coefficients and two input files: the topography of the bed and the initial (pre-failure) position of the sliding mass. In addition, another file with the final (post-event) position of the sliding mass, if desired, can be introduced to be compared with the simulation obtained result. If the deposited mass is given, an error estimation is computed by

  12. Development of Inspection and Investigation Techniques to Prepare Debris Flow in Urban Areas

    Science.gov (United States)

    Seong, Joo-Hyun; Jung, Min-Hyeong; Park, Kyung-Han; An, Jai-Wook; Kim, Jiseong

    2017-04-01

    Due to the urban development, various facilities are located in mountainous areas near the city, and the damage to the occurrence of the debris flow is increasing in the urban area. However, quantitative inspection and investigation techniques are not sufficient for preparing debris flow in the urban area around the world. Therefore, in this study, we developed the debris flow inspection and investigation techniques, which are suitable for urban characteristics, regarding the soil hazard prevention and restoration in urban area. First, the inspection and investigation system is divided into the daily occurrence and the occurrence of the soil hazard event, and the inspection / investigation flow chart were developed based on the kind of inspection and correspondence required for each situation. The types of inspections applied in this study were determined as daily inspection, regular inspections, special emergency inspection, damage emergency inspection and In-depth safety inspection. The management agency, term of inspection, objects to be inspected, and contents of inspection work were presented according to type of each inspection. The daily inspection routinely checks for signs of collapse and conditions of facilities in urban areas which show vulnerability for soil hazard and that are conducted from the management agency. In the case of regular inspection, an expert for soil hazards regularly conducts detailed visual surveys on mountainous areas, steep slopes, prevention facilities and adjacent facilities in vulnerable areas. On the other hand, it was decided that the emergency inspection is carried out in the event of the occurrence of vulnerable element or soil hazards. Acknowledgement This study was conducted with the research iund support by the constructiontechnology research project of the Ministry of Land, Infrastructure and Transport (project number 16SCIP-B069989-04)

  13. Postwildfire debris-flow hazard assessment of the area burned by the 2013 West Fork Fire Complex, southwestern Colorado

    Science.gov (United States)

    Verdin, Kristine L.; Dupree, Jean A.; Stevens, Michael R.

    2013-01-01

    This report presents a preliminary emergency assessment of the debris-flow hazards from drainage basins burned by the 2013 West Fork Fire Complex near South Fork in southwestern Colorado. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence, potential volume of debris flows, and the combined debris-flow hazard ranking along the drainage network within and just downstream from the burned area, and to estimate the same for 54 drainage basins of interest within the perimeter of the burned area. Input data for the debris-flow models included topographic variables, soil characteristics, burn severity, and rainfall totals and intensities for a (1) 2-year-recurrence, 1-hour-duration rainfall, referred to as a 2-year storm; (2) 10-year-recurrence, 1-hour-duration rainfall, referred to as a 10-year storm; and (3) 25-year-recurrence, 1-hour-duration rainfall, referred to as a 25-year storm. Estimated debris-flow probabilities at the pour points of the 54 drainage basins of interest ranged from less than 1 to 65 percent in response to the 2-year storm; from 1 to 77 percent in response to the 10-year storm; and from 1 to 83 percent in response to the 25-year storm. Twelve of the 54 drainage basins of interest have a 30-percent probability or greater of producing a debris flow in response to the 25-year storm. Estimated debris-flow volumes for all rainfalls modeled range from a low of 2,400 cubic meters to a high of greater than 100,000 cubic meters. Estimated debris-flow volumes increase with basin size and distance along the drainage network, but some smaller drainages also were predicted to produce substantial debris flows. One of the 54 drainage basins of interest had the highest combined hazard ranking, while 9 other basins had the second highest combined hazard ranking. Of these 10 basins with the 2 highest

  14. Magnitude-Based Postfire Debris Flow Rainfall Accumulation-Duration Thresholds for Emergency-Response Planning

    Science.gov (United States)

    Cannon, S. H.; Boldt, E. M.; Laber, J. L.; Kean, J. W.; Staley, D. M.

    2011-12-01

    Following wildfires, emergency-response and public-safety agencies can be faced with evacuation and resource-deployment decisions well in advance of coming winter storms and during storms themselves. Information critical to these decisions is needed for recently burned areas in the San Gabriel Mountains of southern California. A compilation of information on the hydrologic response to winter storms from recently burned areas in southern California steeplands is used to develop a system for classifying magnitudes of hydrologic response in this setting. The four-class system describes combinations of reported volumes of individual debris flows, consequences of debris flows and floods in an urban setting, and spatial extents of the hydrologic response. Magnitude 0 events show a negligible response, while Magnitude I events are characterized by small (storm drains may be blocked, a few streets may be partially flooded or blocked by water and debris, and a few buildings near the mountain front may be damaged. Magnitude II events are characterized by two to five moderately-sized (1,000 to 10,000 m3) debris flows or one large (>10,000 m3) event. Several culverts or storm drains may be blocked or fail, several streets may be flooded or completely blocked by water and debris, and buildings, streets, and bridges may be damaged or destroyed. Magnitude III events consist of widespread and abundant debris flows of volumes >10,000 m3 and high discharge flooding causing significant impact to the built environment. Many streets, storm drains, and streets may be completely blocked by debris, making many streets unsafe for travel. Several large buildings, sections of infrastructure corridors and bridges may be damaged or destroyed. The range of rainfall conditions associated with different magnitude classes are defined by correlating local rainfall data with the response magnitude information. Magnitude 0 events can be expected when within-storm rainfall accumulations (A) of given

  15. Relationship Analysis of Debris Flow-inducing Factors in Typhoon Morakot Affected Area By Using Data Mining Techniques

    Science.gov (United States)

    Shen, Che-Wei; Hsiao, Cheng-Yang; Ku, Bing-Huan; Tsao, Ting-Chi; Cheng, Chin-Tung; Lo, Wen-Chun; Chen, Chen-Yu

    2013-04-01

    Typhoon Morakot lashed Taiwan during Aug. 7 to 9, 2009. It dumped heavy rainfall in southern Taiwan, especially around the Central Mountain Range in Pingtung, Chia-Yi, and Kaohsiung County. In view of this, Comprehensive field investigation was carried out by government and private organizations after Typhoon Morakot, useful information of debris flow was gathered. Besides, after Typhoon Morakot, the debris flow-inducing factors become more challenging in Taiwan, many aspects had to be considered. The scope of this study was mainly discussed in debris flow-inducing factors in serious damaged areas which including Nantou, Chia-Yi, Tainan, Kaohsiung, Pingtung, Taitung County. Totally 218 torrents were included. Field investigation data and disaster records of Typhoon Morakot were utilized to analyze debris flow-inducing factors in three aspects: terrain, rainfall and sediment source. First, by using Principle Component Analysis(PCA) and Pearson Product Moment Correlation Analysis(CA) to select significant factors, 101 factors were reduced to the most important 18. Then through descriptive statistics and scatter diagram were selected to discuss the correlation among "Average slope gradient of watershed", "Landslide rate along the stream within 50m buffer zone" as well as the "rainfall intensity during Typhoon Morakot". The above charts were used to summarize the range of factor value which tend to occur phenomenon of debris flow in Typhoon Morakot. Besides, Random Forest Algorithm (RF) was utilized to research the relationship toward multi-variables. The significant factors which tend to affect the debris flow-inducing factor were "effective accumulated rainfall", "hourly rainfall", "landslide rate along the stream within 50m buffer zone", "average elevation value of effective watershed area higher than 10 degree", sequentially. By the results, the most significant factor is the rainfall factor during Typhoon Morakot. The results can be utilized in improving debris

  16. Debris flows on forested cones – reconstruction and comparison of frequencies in two catchments in Val Ferret, Switzerland

    Directory of Open Access Journals (Sweden)

    M. Bollschweiler

    2007-01-01

    Full Text Available Debris flows represent a major threat to infrastructure in many regions of the Alps. Since systematic acquisition of data on debris-flow events in Switzerland only started after the events of 1987, there is a lack of historical knowledge on earlier debris-flow events for most torrents. It is therefore the aim of this study to reconstruct the debris-flow activity for the Reuse de Saleinaz and the La Fouly torrents in Val Ferret (Valais, Switzerland. In total, 556 increment cores from 278 heavily affected Larix decidua Mill., Picea abies (L. Karst. and Pinus sylvestris L. trees were sampled. Trees on the cone of Reuse de Saleinaz show an average age of 123 years at sampling height, with the oldest tree aged 325 years. Two periods of intense colonization (the 1850s–1880s and the 1930s–1950s are observed, probably following high-magnitude events that would have eliminated the former forest stand. Trees on the cone of Torrent de la Fouly indicate an average age of 119 years. As a whole, tree-ring analyses allowed assessment of 333 growth disturbances belonging to 69 debris-flow events. While the frequency for the Reuse de Saleinaz study site comprises 39 events between AD 1743 and 2003, 30 events could be reconstructed at the Torrent de la Fouly for the period 1862–2003. Even though the two study sites evince considerably different characteristics in geology, debris-flow material and catchment morphology, they apparently produce debris flows at similar recurrence intervals. We suppose that, in the study region, the triggering and occurrence of events is transport-limited rather than weathering-limited.

  17. Comparing thixotropic and Herschel–Bulkley parameterizations for continuum models of avalanches and subaqueous debris flows

    Directory of Open Access Journals (Sweden)

    C.-H. Jeon

    2018-01-01

    Full Text Available Avalanches and subaqueous debris flows are two cases of a wide range of natural hazards that have been previously modeled with non-Newtonian fluid mechanics approximating the interplay of forces associated with gravity flows of granular and solid–liquid mixtures. The complex behaviors of such flows at unsteady flow initiation (i.e., destruction of structural jamming and flow stalling (restructuralization imply that the representative viscosity–stress relationships should include hysteresis: there is no reason to expect the timescale of microstructure destruction is the same as the timescale of restructuralization. The non-Newtonian Herschel–Bulkley relationship that has been previously used in such models implies complete reversibility of the stress–strain relationship and thus cannot correctly represent unsteady phases. In contrast, a thixotropic non-Newtonian model allows representation of initial structural jamming and aging effects that provide hysteresis in the stress–strain relationship. In this study, a thixotropic model and a Herschel–Bulkley model are compared to each other and to prior laboratory experiments that are representative of an avalanche and a subaqueous debris flow. A numerical solver using a multi-material level-set method is applied to track multiple interfaces simultaneously in the simulations. The numerical results are validated with analytical solutions and available experimental data using parameters selected based on the experimental setup and without post hoc calibration. The thixotropic (time-dependent fluid model shows reasonable agreement with all the experimental data. For most of the experimental conditions, the Herschel–Bulkley (time-independent model results were similar to the thixotropic model, a critical exception being conditions with a high yield stress where the Herschel–Bulkley model did not initiate flow. These results indicate that the thixotropic relationship is promising for

  18. Video-Seismic coupling for debris flow study at Merapi Volcano, Indonesia

    Science.gov (United States)

    Budi Wibowo, Sandy; Lavigne, Franck; Mourot, Philippe; Sukatja, Bambang

    2016-04-01

    Previous lahar disasters caused at least 44.252 death toll worldwide from 1600 to 2010 of which 52 % was due to a single event in the late 20th century. The need of a better understanding of lahar flow behavior makes general public and stakeholders much more curious than before. However, the dynamics of lahar in motion is still poorly understood because data acquisition of active flows is difficult. This research presents debris-flow-type lahar on February 28, 2014 at Merapi volcano in Indonesia. The lahar dynamics was studied in the frame of the SEDIMER Project (Sediment-related Disasters following the 2010 centennial eruption of Merapi Volcano, Java, Indonesia) based on coupling between video and seismic data analysis. We installed a seismic station at Gendol river (1090 meters asl, 4.6 km south from the summit) consisting of two geophones placed 76 meters apart parallel to the river, a high definition camera on the edge of the river and two raingauges at east and west side of the river. The results showed that the behavior of this lahar changed continuously during the event. The lahar front moved at an average speed of 4.1 m/s at the observation site. Its maximum velocity reached 14.5 m/s with a peak discharge of 473 m3/s. The maximum depth of the flow reached 7 m. Almost 600 blocks of more than 1 m main axis were identified on the surface of the lahar during 36 minutes, which represents an average block discharge of 17 blocks per minute. Seismic frequency ranged from 10 to 150 Hz. However, there was a clear difference between upstream and downstream seismic characteristics. The interpretation related to this difference could be improved by the results of analysis of video recordings, especially to differentiate the debris flow and hyperconcentrated flow phase. The lahar video is accessible online to the broader community (https://www.youtube.com/watch?v=wlVssRoaPbw). Keywords: lahar, video, seismic signal, debris flow, hyperconcentrated flow, Merapi, Indonesia.

  19. Novel method for cell debris removal in the flow cytometric cell cycle analysis using carboxy-fluorescein diacetate succinimidyl ester.

    Science.gov (United States)

    Terho, Perttu; Lassila, Olli

    2006-06-01

    Cell cycle analysis with flow cytometry using propidium iodide (PI) can be difficult in some cases because of the cell debris. Here, we introduce debris removal using intranuclear protein staining (DRIPS), a novel method for separating intact nuclei and cell debris to different populations using carboxy-fluorescein diacetate succinimidyl ester (CFSE). To study the apoptosis-sensitivity, chicken DT40 B cell lymphoma cell line was gamma irradiated. After the irradiation, the cells were incubated up to 8 h and the stages of the cell cycle were followed with flow cytometry. CFSE staining, done simultaneously with PI, stained the cell debris brighter than intact nuclei and could be excluded from the histogram with a simple gating procedure. The method is reliable and reproducible and can be executed within 15 min. DRIPS-method greatly enhances the analysis of difficult cell cycle samples. Copyright 2006 International Society for Analytical Cytology.

  20. Characterization, critical rainfall, and 2D-numerical modeling of Philippine non-volcanic debris flows from the December 2015 Typhoon Melor event

    Science.gov (United States)

    Llanes, F.

    2016-12-01

    On 15 December 2015, Typhoon Melor made landfall in Oriental Mindoro, Philippines, the eastern province of an island more than 120 km south of Manila. The typhoon brought heavy rains that generated debris flows in multiple watersheds in the municipality of Baco while subsequently triggering debris flows on the watersheds that lined the Digdig segment of the Philippine Fault in the provinces of Aurora and Nueva Ecija, more than 300 km north of Mindoro island. In this study, ground mapping and interviews were conducted in the affected watersheds of Baco, Dingalan in Aurora, as well as Bongabon, Gabaldon, and Laur in Nueva Ecija to determine the extent, lithology, and grain size distribution of the debris-flow deposits. IfSAR images acquired in 2013 and Landsat 8 satellite images were then utilized to determine the watershed characteristics of these areas and to identify the factors that triggered debris flows in each one. Global Satellite Mapping of Precipitation (GSMaP) data was then used to generate intensity-duration plots of the typhoon rainfall for each of the watersheds. Known global thresholds of debris flows and the time of debris-flow occurrence derived from interviews were graphed on the plots to determine the best fit to characterize the debris-flow events. IfSAR images used in characterizing the deposits were utilized to run Flow-R, a Matlab-compiled numerical model for regional scale debris-flow assessments. The same images were used to run FLO-2D, a flood-routing software that has been extensively used for mudflow simulations. Lastly, the IfSAR images were utilized to simulate Debris-2D, another debris flow simulation program. Results show that whereas Flow-R is better suited to assess the probability of debris flows on a larger area prior to an event, Debris-2D and FLO-2D can both generate a more detailed hazard map of an area. Between the two latter programs, Debris-2D can be better simulated even without prior knowledge of debris flows occurring in

  1. A morphologic proxy for debris flow erosion with application to the earthquake deformation cycle and beyond

    Science.gov (United States)

    Roering, J. J.; Penserini, B.; Streig, A. R.

    2016-12-01

    In unglaciated steeplands, valley reaches dominated by debris flow scour and incision set landscape form as they often account for >80% of valley network length and relief. While hillslope and fluvial process models have frequently been combined with digital topography to develop morphologic proxies for erosion rate and drainage divide migration, debris flow-dominated networks, despite their ubiquity, have not been exploited for this purpose. Here, we applied a published empirical function (Stock and Dietrich, 2003) that describes how slope-area data systematically deviate from so-called fluvial power-law behavior at small drainage areas. Using airborne lidar data for 83 small ( 1 km2) catchments in the western Oregon Coast Range, we quantified variation in model parameters and observed that the curvature of the power-law scaling deviation varies with catchment-averaged erosion rate estimated from cosmogenic nuclides in stream sediments. Given consistent climate and lithology across our study area and assuming steady erosion, we used this calibrated denudation-morphology relationship to map spatial patterns of long-term uplift for dozens of small catchments. By combining our predicted spatial pattern of long-term uplift rate with paleoseismic and geodetic (tide gauge, GPS, and leveling) data, we estimated the spatial distribution of coseismic subsidence experienced during megathrust earthquakes along the Cascadia subduction zone. Our estimates of coseismic subsidence near the coast (0.4 to 0.7 m for earthquake recurrence intervals of 300 to 500 years) agree with field measurements from stratigraphic studies. Our results also demonstrate that coseismic subsidence decreases inland to negligible values >25 km from the coast, reflecting the diminishing influence of the earthquake deformation cycle in the uplift of the interior coastal ranges. More generally, our results demonstrate that debris flow valley networks serve as highly localized, yet broadly distributed

  2. Wood anatomical analysis of Alnus incana and Betula pendula injured by a debris-flow event.

    Science.gov (United States)

    Arbellay, Estelle; Stoffel, Markus; Bollschweiler, Michelle

    2010-10-01

    Vessel chronologies in ring-porous species have been successfully employed in the past to extract the climate signal from tree rings. Environmental signals recorded in vessels of ring-porous species have also been used in previous studies to reconstruct discrete events of drought, flooding and insect defoliation. However, very little is known about the ability of diffuse-porous species to record environmental signals in their xylem cells. Moreover, time series of wood anatomical features have only rarely been used to reconstruct former geomorphic events. This study was therefore undertaken to characterize the wood anatomical response of diffuse-porous Alnus incana (L.) Moench and Betula pendula Roth to debris-flow-induced wounding. Tree microscopic response to wounding was assessed through the analysis of wood anatomical differences between injured rings formed in the debris-flow event year and uninjured rings formed in the previous year. The two ring types were examined close and opposite to the injury in order to determine whether wound effects on xylem cells decrease with increasing tangential distance from the injury. Image analysis was used to measure vessel parameters as well as fiber and parenchyma cell (FPC) parameters. The results of this study indicate that injured rings are characterized by smaller vessels as compared with uninjured rings. By contrast, FPC parameters were not found to significantly differ between injured and uninjured rings. Vessel and FPC parameters mainly remained constant with increasing tangential distance from the injury, except for a higher proportion of vessel lumen area opposite to the injury within A. incana. This study highlights the existence of anatomical tree-ring signatures-in the form of smaller vessels-related to past debris-flow activity and addresses a new methodological approach to date injuries inflicted on trees by geomorphic processes.

  3. Susceptibility Evaluation of Debris Flow Based on Experience Weight Method Combined with “3S” Technology: A Case Study from Dongchuan in Yunnan Province, China

    Science.gov (United States)

    Xu, Jun; Cheng, Xianfeng; Huang, Qianrui; Chen, Yu; Qi, Wufu; Yuan, Jia; Yang, Jiaqing

    2017-12-01

    Dongchuan, located in Yunnan Province, China, is well known as “debris flow museum” in the world because of its special geological background and intensive mining activities. There are more than 100 ravines of debris flow in the area of 1859 km2, which have caused disastrous damages. Regional gullies for debris flow susceptibility evaluation can play an important role in reducing damage of debris flows in Dongchuan. In this paper, we selected Dongchuan as a case study to research the susceptibility evaluation of debris flow based on experience weight method combined with “3s” technology. The result shows that most of debris flow gullies in Dongchuan face high risk, while few face moderate risk or very high risk.

  4. Assessing the effects of check dams on sediment dynamics in a debris-flow catchment through SfM technique

    Science.gov (United States)

    Cucchiaro, Sara; Beinat, Alberto; Calsamiglia, Aleix; Cavalli, Marco; Cazorzi, Federico; Crema, Stefano; Marchi, Lorenzo

    2017-04-01

    The Moscardo Torrent (eastern Italian Alps) is a small rugged catchment (drainage area 4.1 km2, range in elevation between 890 and 2043 m) frequently affected by debris flows that deliver large amounts of sediment to the receiving stream, and cause concerns for infrastructures located on the alluvial fan and near the confluence. Over the last decades, hydraulic control works were implemented in the main channel to limit bed erosion and to stabilize channel banks. Although the objectives of training works have been only partly achieved, check dams and hillslope stabilization works have affected the sediment transfer from hillslopes to the channels and along the main channel. The effects of hydraulic control works were investigated by means of multi-temporal Structure from Motion (SfM) surveys based on images taken from the ground and UAV. The ground and air based surveys were carried out over a channel reach in which two check dams have recently been built. SfM surveys were taken before and after three debris-flow events (occurred between June and July 2016), allowing the generation of four high-resolution Digital Elevation Models (DEMs). Geomorphic changes caused by the debris-flow events have been assessed in order to produce the DEM of Differences (DoDs with a 0.2 m spatial resolution) that allowed estimating erosion and deposition volumes in the study area. Furthermore a debris-flow monitoring system has been in operation in the Moscardo Torrent; the analysis of the videos and of the hydrographs recorded by ultrasonic sensors permitted to assess the debris-flow volumes. These estimates were used to characterize the magnitude of events in support of the topographic analysis. By examining the changing pattern of erosion and deposition over time it was possible to understand the check dams' effects on sediment dynamics. The results show that the new check dams effectively stored sediment transported by the three debris flows. However, once the check dams have been

  5. Community Based Warning and Evacuation System against Debris Flow in the Upper Jeneberang River, Gowa, South Sulawesi

    Directory of Open Access Journals (Sweden)

    Sutikno Hardjosuwarno

    2008-07-01

    Full Text Available Gigantic collapse of the Caldera wall of Mt. Bawakaraeng (2,830 m in March 2004 had supplied the sediment volume of 230 million to the most upper stream of Jeneberang River, which flowed down to the lower reach in the form of debris flow which is triggered by rainfall. The purpose of the research is to provide a system which is able to forecast the occurrence of debris flow, to identify the weak points along the river course, to identify the hazard areas and how to inform effectively and efficiently the warning messages to the inhabitants in the dangerous area by using the existing modern equipment combined with the traditional one. The standard rainfall which is used to judge the occurrence of debris flow was established by Yano method. It is based on the historical data of rainfall that trigger and not trigger to the occurrence of debris flow which is widely used in Japan so far. The hazard area was estimated by Two-Dimensional Simulation Model for debris flow, the debris flow arrival time at each point in the river were estimated by dividing their distance from reference point by debris flow velocity, where the check dam no. 7-1 in Manimbahoi was designated as reference point. The existing evacuation routes were checked by field survey, the strength and coverage of sound for kentongan and manual siren were examined using sound pressure level at the location of the existing monitoring post and the effectiveness of warning and evacuation were evaluated by comparing the warning and evacuation time against the debris flow arrival time. It was resulted that debris flow occurrence was triggered by short duration of high rainfall intensity, long duration of low rainfall intensity and the outbreak of natural dam which is formed by land slide or bank collapses. The hazard area of upper Jeneberang River are mostly located on the river terraces where the local inhabitants earn their living through cultivating the river terraces as paddy fields, dry

  6. Idealized debris flow in flume with bed driven by a conveyor belt

    Science.gov (United States)

    Ling, Chi-Hai; Chen, Cheng-lung

    1989-01-01

    The generalized viscoplastic fluid (GVF) model is used to derive the theoretical expressions of two-dimensional velocities and surface profile for debris flow established in a flume with bed driven by a conveyor belt. The rheological parameters of the GVF model are evaluated through the comparison of theoretical results with measured data. A slip velocity of the established (steady) nonuniform flow on the moving bed (i.e., the conveyor belt) is observed, and a relation between the slip velocity and the velocity gradient at the bed is derived. Two belts, one rough and the other smooth, were tested. The flow profile in the flume is found to be linear and dependent on the roughness of the belt, but not much on its speed.

  7. Debris-flow modeling at Meretschibach and Bondasca catchments, Switzerland: sensitivity testing of field-data-based entrainment model

    Science.gov (United States)

    Frank, Florian; McArdell, Brian W.; Oggier, Nicole; Baer, Patrick; Christen, Marc; Vieli, Andreas

    2017-06-01

    Debris-flow volumes can increase due to the incorporation of sediment into the flow as a consequence of channel-bed erosion along the flow path. This study describes a sensitivity analysis of the recently introduced RAMMS (Rapid Mass Movements) debris-flow entrainment model, which is intended to help solve problems related to predicting the runout of debris flows. The entrainment algorithm predicts the depth and rate of erosion as a function of basal shear stress based on an analysis of erosion measurements at the Illgraben catchment, Switzerland (Frank et al., 2015). Starting with a landslide-type initiation in the RAMMS model, the volume of entrained sediment was calculated for recent well-documented debris-flow events at the Bondasca and the Meretschibach catchments, Switzerland. The sensitivity to the initial landslide volume was investigated by systematically varying the initial landslide volume and comparing the resulting debris-flow volume with estimates from the field sites. In both cases, the friction coefficients in the RAMMS runout model were calibrated using the model, whereby the entrainment module was (1) inactivated to find plausible values for general flow properties by adjusting both coefficients (ξ and μ) and then (2) activated to further refine coefficient μ, which controls erosion (patterns). The results indicate that the model predicts plausible erosion volumes in comparison with field data. By including bulking due to entrainment in runout models, more realistic runout patterns are predicted in comparison to starting the model with the entire debris-flow volume (initial landslide plus entrained sediment). In particular, lateral bank overflow - not observed during these events - is prevented when using the sediment entrainment model, even in very steep (≈ 60-65 %) and narrow (4-6 m) torrent channels. Predicted sediment entrainment volumes are sensitive to the initial landslide volume, suggesting that the model may be useful for both

  8. r.avaflow, the GIS simulation model for avalanche and debris flows: new developments and challenges

    Science.gov (United States)

    Mergili, Martin; Queiroz de Oliveira, Gustavo; Fischer, Jan-Thomas; Krenn, Julia; Kulisch, Helmut; Malcherek, Andreas; Pudasaini, Shiva P.

    2016-04-01

    We present the latest developments and discuss some of the key challenges with regard to the novel and unified computational tool r.avaflow, representing an advanced, comprehensive, GIS-based open source simulation environment for two-phase geophysical mass flows such as avalanches of snow or rock, flows of debris or mud, and related process chains. r.avaflow is freely available and adoptable as a raster module of the GRASS GIS software (http://www.avaflow.org). We focus on the following issues: (1) We back-calculate a laboratory-scale debris flow experiment with r.avaflow and thereby show that different types of drag may govern the evolving flow dynamics, depending on the initial flow configuratiuon. In particular, it appears necessary to consider viscous ambient drag in order to achieve simulation results in line with experimentally measurements. (2) We employ a set of well-documented rock avalanche events to illustrate the use of a built-in functionality for parameter sensitivity analysis and optimization. To do so, we demonstrate possible strategies going beyond the deficient one-at-a-time simulation approach. They allow us to test three or more parameters at once with a limited number of model runs. Computational times are kept at an acceptable level by multi-core processing strategies and use of the Vienna Scientific Cluster. We further discuss a number of key issues with regard to (i) arbitrary mountain topography; and (ii) entrainment and deposition of material. Most tests indicate a good model performance when the affected areas predicted for a late stage of the flow simulation are compared with observed affected areas. However, we note that such a validation is not fully justified without the implementation of a physically correct model for the deposition process. Acknowledgement: The work was conducted as part of the international cooperation project "A GIS simulation model for avalanche and debris flows (avaflow)" supported by the Austrian Science Fund

  9. Assessing the debris flow run-out frequency of a catchment in the French Alps using a parameterization analysis with the RAMMS numerical run-out model

    Science.gov (United States)

    Hussin, H. Y.; Luna, B. Quan; van Westen, C. J.; Christen, M.; Malet, J.-P.; van Asch, Th. W. J.

    2012-04-01

    Debris flows occurring in the European Alps frequently cause significant damage to settlements, power-lines and transportation infrastructure which has led to traffic disruptions, economic loss and even death. Estimating the debris flow run-out extent and the parameter uncertainty related to run-out modeling are some of the difficulties found in the Quantitative Risk Assessment (QRA) of debris flows. Also, the process of the entrainment of material into a debris flow is until now not completely understood. Debris flows observed in the French Alps entrain 5 - 50 times the amount of volume compared to the initially mobilized source volume. In this study we analyze a debris flow that occurred in 2003 at the Faucon catchment in the Barcelonnette Basin (Southern French Alps). The analysis was carried out using the Voellmy rheology and an entrainment model imbedded in the RAMMS 2D numerical modeling software. The historic event was back calibrated based on source, entrainment and deposit volumes, including the run-out distance, velocities and deposit heights of the debris flow. This was then followed by a sensitivity analysis of the rheological and entrainment parameters to produce 120 debris flow scenarios leading to a frequency assessment of the run-out distance and deposit height at the debris fan. The study shows that the Voellmy frictional parameters mainly influence the run-out distance and velocity of the flow, while the entrainment parameter has a major impact on the debris flow height. The frequency assessment of the 120 simulated scenarios further gives an indication on the most likely debris flow run-out extents and heights for this catchment. Such an assessment can be an important link between the rheological model parameters and the spatial probability of the run-out for the Quantitative Risk Assessment (QRA) of debris flows.

  10. Parameterization of a numerical 2-D debris flow model with entrainment: a case study of the Faucon catchment, Southern French Alps

    OpenAIRE

    Hussin, H. Y.; Quan Luna, B.; C. J. Van Westen; M. Christen; Malet, J.-P.; Asch, Th.W.J. van

    2012-01-01

    - The occurrence of debris flows has been recorded for more than a century in the European Alps, accounting for the risk to settlements and other human infrastructure that have led to death, building damage and traffic disruptions. One of the difficulties in the quantitative hazard assessment of debris flows is estimating the run-out behavior, which includes the run-out distance and the related hazard intensities like the height and velocity of a debris flow. In addition, as observed in th...

  11. Adaptive computer-based spatial-filtering method for more accurate estimation of the surface velocity of debris flow.

    Science.gov (United States)

    Uddin, M S; Inaba, H; Itakura, Y; Yoshida, Y; Kasahara, M

    1999-11-10

    An adaptive computer-based spatial-filtering velocimeter to measure the surface velocity of a natural debris flow with high accuracy is described that can adjust the filter parameters, specifically, the slit width of the filter, based on the surface-pattern characteristics of the flow. A computer simulation confirms the effectiveness of this technique. The surface velocity of a natural debris flow at the Mt. Yakedake Volcano, Japan, was estimated by this adaptive method, and the results were compared with those obtained by two other methods: hardware-based spatial filtering and normal computer-based spatial filtering.

  12. Probability and volume of potential postwildfire debris flows in the 2012 Waldo Canyon Burn Area near Colorado Springs, Colorado

    Science.gov (United States)

    Verdin, Kristine L.; Dupree, Jean A.; Elliott, John G.

    2012-01-01

    This report presents a preliminary emergency assessment of the debris-flow hazards from drainage basins burned by the 2012 Waldo Canyon fire near Colorado Springs in El Paso County, Colorado. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence and potential volume of debris flows along the drainage network of the burned area and to estimate the same for 22 selected drainage basins along U.S. Highway 24 and the perimeter of the burned area. Input data for the models included topographic parameters, soil characteristics, burn severity, and rainfall totals and intensities for a (1) 2-year-recurrence, 1-hour-duration rainfall, referred to as a 2-year storm (29 millimeters); (2) 10-year-recurrence, 1-hour-duration rainfall, referred to as a 10-year storm (42 millimeters); and (3) 25-year-recurrence, 1-hour-duration rainfall, referred to as a 25-year storm (48 millimeters). Estimated debris-flow probabilities at the pour points of the the drainage basins of interest ranged from less than 1 to 54 percent in response to the 2-year storm; from less than 1 to 74 percent in response to the 10-year storm; and from less than 1 to 82 percent in response to the 25-year storm. Basins and drainage networks with the highest probabilities tended to be those on the southern and southeastern edge of the burn area where soils have relatively high clay contents and gradients are steep. Nine of the 22 drainage basins of interest have greater than a 40-percent probability of producing a debris flow in response to the 10-year storm. Estimated debris-flow volumes for all rainfalls modeled range from a low of 1,500 cubic meters to a high of greater than 100,000 cubic meters. Estimated debris-flow volumes increase with basin size and distance along the drainage network, but some smaller drainages were also predicted to produce

  13. Debris flow analysis with a one-dimensional dynamic run-out model that incorporates entrained material

    NARCIS (Netherlands)

    Quan Luna, B.; Remaître, A.; Asch, Th.W.J. van; Malet, J.P.; Westen, C.J. van

    2010-01-01

    Estimating the magnitude and the intensity of rapid landslides like debris flows is fundamental to evaluate quantitatively the hazard in a specific location. Intensity varies through the travelled course of the flow and can be described by physical features such as deposited volume, velocities,

  14. A hacker's guide to catching a debris flow: Lessons learned from four years of chasing mud in Colorado and southern California

    Science.gov (United States)

    Kean, J. W.; McCoy, S. W.; Staley, D. M.; Coe, J.; Leeper, R.; Tucker, G. E.

    2012-12-01

    Direct measurements of natural debris flows provide valuable insights into debris-flow processes and hazards. Yet debris flows are difficult to "catch" because they live in rugged terrain, appear infrequently, and have an appetite for destroying monitoring equipment. We present an overview of some successful (and failed) techniques we have used over the past four years to obtain direct measurements of 40+ debris flows in Colorado and southern California. Following the "MacGyver" theme of the session, we focus on the improvised equipment and methods we use in our hunt for quality data. These include an inexpensive erosion sensor to measure rates of debris-flow entrainment, a custom load cell enclosure for measuring debris-flow normal force, tracer rocks implanted with passive integrated transponders, basic pressure transducers to measure debris-flow timing, and standard digital cameras adapted to obtain high-resolution (1936 x 1288 pixels) video footage of debris flows. These techniques are also suitable for catching data on elusive flash floods. In addition, we also share some practical solutions to the logistical problems associated with installing monitoring equipment in rugged debris-flow terrain, such as suspension of non-contact stage gages high above channels.

  15. Applications of simulation technique on debris-flow hazard zone delineation: a case study in Hualien County, Taiwan

    Directory of Open Access Journals (Sweden)

    S. M. Hsu

    2010-03-01

    Full Text Available Debris flows pose severe hazards to communities in mountainous areas, often resulting in the loss of life and property. Helping debris-flow-prone communities delineate potential hazard zones provides local authorities with useful information for developing emergency plans and disaster management policies. In 2003, the Soil and Water Conservation Bureau of Taiwan proposed an empirical model to delineate hazard zones for all creeks (1420 in total with potential of debris flows and utilized the model to help establish a hazard prevention system. However, the model does not fully consider hydrologic and physiographical conditions for a given creek in simulation. The objective of this study is to propose new approaches that can improve hazard zone delineation accuracy and simulate hazard zones in response to different rainfall intensity. In this study, a two-dimensional commercial model FLO-2D, physically based and taking into account the momentum and energy conservation of flow, was used to simulate debris-flow inundated areas.

    Sensitivity analysis with the model was conducted to determine the main influence parameters which affect debris flow simulation. Results indicate that the roughness coefficient, yield stress and volumetric sediment concentration dominate the computed results. To improve accuracy of the model, the study examined the performance of the rainfall-runoff model of FLO-2D as compared with that of the HSPF (Hydrological Simulation Program Fortran model, and then the proper values of the significant parameters were evaluated through the calibration process. Results reveal that the HSPF model has a better performance than the FLO-2D model at peak flow and flow recession period, and the volumetric sediment concentration and yield stress can be estimated by the channel slope. The validation of the model for simulating debris-flow hazard zones has been confirmed by a comparison of field evidence from historical debris-flow

  16. The 1980 Polallie Creek debris flow and subsequent dam-break flood, East Fork Hood River basin, Oregon

    Science.gov (United States)

    Gallino, Gary L.; Pierson, Thomas C.

    1984-01-01

    At approximately 9 p.m. on December 25, 1980, intense rainfall and extremely wet antecedent conditions combined to trigger a landslide of approximately 5,000 cubic yards at the head of Polallie Creek Canyon on the northeast flank of Mount Hood. The landslide was transformed rapidly into a debris flow, which surged down the channel at velocities between about 40 and 50 ft/s, eroding and incorporating large volumes of channel fill and uprooted vegetation. When it reached the debris fan at the confluence with the East Fork Hood River, the debris flow deposited approximately 100,000 cubic yards of saturated, poorly sorted debris to a maximum thickness of 35 ft, forming a 750-ft-long temporary dam across the channel. Within approximately 12 minutes, a lake of 85 acre-feet formed behind the blockage, breached the dam, and sent a flood wave down the East Fork Hood River. The combined debris flow and flood resulted in one fatality and over $13 million in damage to a highway, bridges, parks, and a water-supply pipeline. Application of simple momentum- and energy-balance equations, and uniform flow equations resulted in debris flow peak discharges ranging from 50,000 ft3/s to 300,000 ft3/s at different locations in the Polallie Creek Canyon. This wide range is attributed to temporary damming at the boulder- and log-rich flow front in narrow, curving reaches of the channel. When the volume of the solid debris was subtracted out, assuming a minimum peak debris-flow discharge of 100,000 ft3/s at the canyon mouth, a minimum peak-water discharge of 40,000 ft3/s was obtained. A computer dam-break model simulated peak flow for the outbreak flood on the East Fork Hood River in the range of 20,000 to 30,000 ft3/s using various breach shapes and durations of breach between 5 and 15 minutes. A slope conveyance computation 0.25 mi downstream from the dam gave a peak water discharge (solids subtracted out) for the debris-laden flood of 12,000 to 20,000 ft3/s, depending on the channel

  17. Elementary theory of bed-sediment entrainment by debris flows and avalanches

    Science.gov (United States)

    Iverson, Richard M.

    2012-01-01

    Analyses of mass and momentum exchange between a debris flow or avalanche and an underlying sediment layer aid interpretations and predictions of bed-sediment entrainment rates. A preliminary analysis assesses the behavior of a Coulomb slide block that entrains bed material as it descends a uniform slope. The analysis demonstrates that the block's momentum can grow unstably, even in the presence of limited entrainment efficiency. A more-detailed, depth-integrated continuum analysis of interacting, deformable bodies identifies mechanical controls on entrainment efficiency, and shows that entrainment rates satisfy a jump condition that involves shear-traction and velocity discontinuities at the flow-bed boundary. Explicit predictions of the entrainment rateEresult from making reasonable assumptions about flow velocity profiles and boundary shear tractions. For Coulomb-friction tractions, predicted entrainment rates are sensitive to pore fluid pressures that develop in bed sediment as it is overridden. In the simplest scenario the bed sediment liquefies completely, and the entrainment-rate equation reduces toE = 2μ1gh1 cos θ(1 − λ1)/ , where θ is the slope angle, μ1 is the flow's Coulomb friction coefficient, h1 is its thickness, λ1 is its degree of liquefaction, and is its depth-averaged velocity. For values ofλ1ranging from 0.5 to 0.8, this equation predicts entrainment rates consistent with rates of 0.05 to 0.1 m/s measured in large-scale debris-flow experiments in which wet sediment beds liquefied almost completely. The propensity for bed liquefaction depends on several factors, including sediment porosity, permeability, and thickness, and rates of compression and shear deformation that occur when beds are overridden.

  18. Calibration and deployment of a fiber-optic sensing system for monitoring debris flows.

    Science.gov (United States)

    Huang, Ching-Jer; Chu, Chung-Ray; Tien, Tsung-Mo; Yin, Hsiao-Yuen; Chen, Ping-Sen

    2012-01-01

    This work presents a novel fiber-optic sensing system, capable of monitoring debris flows or other natural hazards that produce ground vibrations. The proposed sensing system comprises a demodulator (BraggSCOPE, FS5500), which includes a broadband light source and a data logger, a four-port coupler and four Fiber Bragg Grating (FBG) accelerometers. Based on field tests, the performance of the proposed fiber-optic sensing system is compared with that of a conventional sensing system that includes a geophone or a microphone. Following confirmation of the reliability of the proposed sensing system, the fiber-optic sensing systems are deployed along the Ai-Yu-Zi and Chu-Shui Creeks in Nautou County of central Taiwan for monitoring debris flows. Sensitivity test of the deployed fiber-optic sensing system along the creek banks is also performed. Analysis results of the seismic data recorded by the systems reveal in detail the frequency characteristics of the artificially generated ground vibrations. Results of this study demonstrate that the proposed fiber-optic sensing system is highly promising for use in monitoring natural disasters that generate ground vibrations.

  19. Postwildfire debris flows hazard assessment for the area burned by the 2011 Track Fire, northeastern New Mexico and southeastern Colorado

    Science.gov (United States)

    Tillery, Anne C.; Darr, Michael J.; Cannon, Susan H.; Michael, John A.

    2011-01-01

    In June 2011, the Track Fire burned 113 square kilometers in Colfax County, northeastern New Mexico, and Las Animas County, southeastern Colorado, including the upper watersheds of Chicorica and Raton Creeks. The burned landscape is now at risk of damage from postwildfire erosion, such as that caused by debris flows and flash floods. This report presents a preliminary hazard assessment of the debris-flow potential from basins burned by the Track Fire. A pair of empirical hazard-assessment models developed using data from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence and volume of debris flows at the outlets of selected drainage basins within the burned area. The models incorporate measures of burn severity, topography, soils, and storm rainfall to estimate the probability and volume of post-fire debris flows following the fire. In response to a design storm of 38 millimeters of rain in 30 minutes (10-year recurrence-interval), the probability of debris flow estimated for basins burned by the Track fire ranged between 2 and 97 percent, with probabilities greater than 80 percent identified for the majority of the tributary basins to Raton Creek in Railroad Canyon; six basins that flow into Lake Maloya, including the Segerstrom Creek and Swachheim Creek basins; two tributary basins to Sugarite Canyon, and an unnamed basin on the eastern flank of the burned area. Estimated debris-flow volumes ranged from 30 cubic meters to greater than 100,000 cubic meters. The largest volumes (greater than 100,000 cubic meters) were estimated for Segerstrom Creek and Swachheim Creek basins, which drain into Lake Maloya. The Combined Relative Debris-Flow Hazard Ranking identifies the Segerstrom Creek and Swachheim Creek basins as having the highest probability of producing the largest debris flows. This finding indicates the greatest post-fire debris-flow impacts may be expected to Lake Maloya

  20. Estimated probabilities, volumes, and inundation areas depths of potential postwildfire debris flows from Carbonate, Slate, Raspberry, and Milton Creeks, near Marble, Gunnison County, Colorado

    Science.gov (United States)

    Stevens, Michael R.; Flynn, Jennifer L.; Stephens, Verlin C.; Verdin, Kristine L.

    2011-01-01

    During 2009, the U.S. Geological Survey, in cooperation with Gunnison County, initiated a study to estimate the potential for postwildfire debris flows to occur in the drainage basins occupied by Carbonate, Slate, Raspberry, and Milton Creeks near Marble, Colorado. Currently (2010), these drainage basins are unburned but could be burned by a future wildfire. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of postwildfire debris-flow occurrence and debris-flow volumes for drainage basins occupied by Carbonate, Slate, Raspberry, and Milton Creeks near Marble. Data for the postwildfire debris-flow models included drainage basin area; area burned and burn severity; percentage of burned area; soil properties; rainfall total and intensity for the 5- and 25-year-recurrence, 1-hour-duration-rainfall; and topographic and soil property characteristics of the drainage basins occupied by the four creeks. A quasi-two-dimensional floodplain computer model (FLO-2D) was used to estimate the spatial distribution and the maximum instantaneous depth of the postwildfire debris-flow material during debris flow on the existing debris-flow fans that issue from the outlets of the four major drainage basins. The postwildfire debris-flow probabilities at the outlet of each drainage basin range from 1 to 19 percent for the 5-year-recurrence, 1-hour-duration rainfall, and from 3 to 35 percent for 25-year-recurrence, 1-hour-duration rainfall. The largest probabilities for postwildfire debris flow are estimated for Raspberry Creek (19 and 35 percent), whereas estimated debris-flow probabilities for the three other creeks range from 1 to 6 percent. The estimated postwildfire debris-flow volumes at the outlet of each creek range from 7,500 to 101,000 cubic meters for the 5-year-recurrence, 1-hour-duration rainfall, and from 9,400 to 126,000 cubic meters for

  1. Estimated probability of postwildfire debris flows in the 2012 Whitewater-Baldy Fire burn area, southwestern New Mexico

    Science.gov (United States)

    Tillery, Anne C.; Matherne, Anne Marie; Verdin, Kristine L.

    2012-01-01

    In May and June 2012, the Whitewater-Baldy Fire burned approximately 1,200 square kilometers (300,000 acres) of the Gila National Forest, in southwestern New Mexico. The burned landscape is now at risk of damage from postwildfire erosion, such as that caused by debris flows and flash floods. This report presents a preliminary hazard assessment of the debris-flow potential from 128 basins burned by the Whitewater-Baldy Fire. A pair of empirical hazard-assessment models developed by using data from recently burned basins throughout the intermountain Western United States was used to estimate the probability of debris-flow occurrence and volume of debris flows along the burned area drainage network and for selected drainage basins within the burned area. The models incorporate measures of areal burned extent and severity, topography, soils, and storm rainfall intensity to estimate the probability and volume of debris flows following the fire. In response to the 2-year-recurrence, 30-minute-duration rainfall, modeling indicated that four basins have high probabilities of debris-flow occurrence (greater than or equal to 80 percent). For the 10-year-recurrence, 30-minute-duration rainfall, an additional 14 basins are included, and for the 25-year-recurrence, 30-minute-duration rainfall, an additional eight basins, 20 percent of the total, have high probabilities of debris-flow occurrence. In addition, probability analysis along the stream segments can identify specific reaches of greatest concern for debris flows within a basin. Basins with a high probability of debris-flow occurrence were concentrated in the west and central parts of the burned area, including tributaries to Whitewater Creek, Mineral Creek, and Willow Creek. Estimated debris-flow volumes ranged from about 3,000-4,000 cubic meters (m3) to greater than 500,000 m3 for all design storms modeled. Drainage basins with estimated volumes greater than 500,000 m3 included tributaries to Whitewater Creek, Willow

  2. Identification of debris-flow hazards in warm deserts through analyzing past occurrences: Case study in South Mountain, Sonoran Desert, USA

    Science.gov (United States)

    Dorn, Ronald I.

    2016-11-01

    After recognition that debris flows co-occur with human activities, the next step in a hazards analysis involves estimating debris-flow probability. Prior research published in this journal in 2010 used varnish microlamination (VML) dating to determine a minimum occurrence of 5 flows per century over the last 8100 years in a small mountain range of South Mountain adjacent to neighborhoods of Phoenix, Arizona. This analysis led to the conclusion that debris flows originating in small mountain ranges in arid regions like the Sonoran Desert could pose a hazard. Two major precipitation events in the summer of 2014 generated 35 debris flows in the same study area of South Mountain-providing support for the importance of probability analysis as a key step in a hazards analysis in warm desert settings. Two distinct mechanisms generated the 2014 debris flows: intense precipitation on steep slopes in the first storm; and a firehose effect whereby runoff from the second storm was funneled rapidly by cleaned-out debris-flow chutes to remobilize Pleistocene debris-flow deposits. When compared to a global database on debris flows, the 2014 storms were among the most intense to generate desert debris flows - indicating that storms of lesser intensity are capable of generating debris flows in warm desert settings. The 87Sr/86Sr analyses of fines and clasts in South Mountain debris flows of different ages reveal that desert dust supplies the fines. Thus, wetter climatic periods of intense rock decay are not needed to resupply desert slopes with fines; instead, a combination of dust deposition supplying fines and dirt cracking generating coarse clasts can re-arm chutes in a warm desert setting with abundant dust.

  3. Prediction of the run out extents of the Slano Blato landslide for future debris flow events

    Science.gov (United States)

    Askarinejad, Amin; Leu, Pascal; Macek, Matej; Petkovsek, Ana; Springman, Sarah

    2013-04-01

    The Slano Blato landslide has a volume of about 1 mio m3 and is located in the western part of Slovenia. It has been considered to be a potential natural hazard for the village of Lokavec for more than 200 years. Several mud flows, exhibiting a range of volumes and velocities, have originated from the landslide body since the year 2000, when the landslide was reactivated due to an intense rainfall event. A series of obstacles, including safety dams and deposition ponds, have been constructed for the remediation of the landslide. These obstacles are designed to absorb and contain future debris flow hazard. A prerequisite to any risk analysis is to establish the vulnerability to the hazard event. The aim of this work is to simulate possible future debris flow scenarios in order to predict the run out distances, flow heights, impact pressures and potential effects on the downstream village buildings and infrastructure. The simulations were carried out using the RAMMS program (RApid Mass MovementS, www.ramms.slf.ch). A three dimensional terrain model of the landslide area and the downstream zones, with or without the inclusion of the obstacles, was made for the simulations and different scenarios concerning the released volume, the internal friction and viscosity of the sliding mass were studied. The results indicate that low viscosity mudflows with a volume of 5,000 m3 endanger some parts of Lokavec village. However, the simulations with volumes of 15,000 and 50,000 m3 predict catastrophic effects in terms of either impact pressures or deposition heights for the majority of houses. Moreover, the simulations confirmed that the choice of the material properties (internal friction and viscosity), the characteristics of the release hydrograph, event location, and natural or man-made obstacles play major roles in the run out distances and impact pressures.

  4. Using Logistic Regression to Predict the Probability of Debris Flows in Areas Burned by Wildfires, Southern California, 2003-2006

    Science.gov (United States)

    Rupert, Michael G.; Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Helsel, Dennis R.

    2008-01-01

    Logistic regression was used to develop statistical models that can be used to predict the probability of debris flows in areas recently burned by wildfires by using data from 14 wildfires that burned in southern California during 2003-2006. Twenty-eight independent variables describing the basin morphology, burn severity, rainfall, and soil properties of 306 drainage basins located within those burned areas were evaluated. The models were developed as follows: (1) Basins that did and did not produce debris flows soon after the 2003 to 2006 fires were delineated from data in the National Elevation Dataset using a geographic information system; (2) Data describing the basin morphology, burn severity, rainfall, and soil properties were compiled for each basin. These data were then input to a statistics software package for analysis using logistic regression; and (3) Relations between the occurrence or absence of debris flows and the basin morphology, burn severity, rainfall, and soil properties were evaluated, and five multivariate logistic regression models were constructed. All possible combinations of independent variables were evaluated to determine which combinations produced the most effective models, and the multivariate models that best predicted the occurrence of debris flows were identified. Percentage of high burn severity and 3-hour peak rainfall intensity were significant variables in all models. Soil organic matter content and soil clay content were significant variables in all models except Model 5. Soil slope was a significant variable in all models except Model 4. The most suitable model can be selected from these five models on the basis of the availability of independent variables in the particular area of interest and field checking of probability maps. The multivariate logistic regression models can be entered into a geographic information system, and maps showing the probability of debris flows can be constructed in recently burned areas of

  5. Biographical sketch of a giant: Deciphering recent debris-flow dynamics from the Ohya landslide body (Japanese Alps)

    Science.gov (United States)

    Imaizumi, Fumitoshi; Trappmann, Daniel; Matsuoka, Norikazu; Tsuchiya, Satoshi; Ohsaka, Okihiro; Stoffel, Markus

    2016-11-01

    Debris-flow frequency, discharge, and travel distance are highly catchment dependent and typically controlled by topography, hydrological conditions, and sediment supply. As a consequence, detailed and case-specific investigations are needed to decipher debris-flow histories in order to improve hazard mitigation. This study documents past (ca. 10 years) debris-flow occurrences originating from the Ohya landslide, central Japan, by using a large set of methods including field monitoring, repeat airborne LiDAR, orthophoto interpretation, and tree-ring reconstructions. We demonstrate that the different approaches generally agree on the occurrence of debris flows but that mismatches may exist when it comes to the assessment of areas affected by individual events. These differences may even exceed the usual errors in precision inherent to each of the methods used. In the present case, high-resolution orthophoto interpretation tends to underestimate areas affected by debris flows, especially in the vertical direction, in the absence of lateral movement of the channel bed and as a result of shade and areas under trees. On the other hand, we realize that LiDAR data cannot necessarily be used to distinguish local changes in topography from noise. Tree-ring analyses can help to improve the temporal resolution of the analysis, but may have limitations when it comes to the definition of areas affected by an event because of the point-type nature of data. We conclude that the best and most complete results are obtained by combining multiple methods to improve the spatial and temporal resolution of past debris flows and to delimit areas affected by individual events.

  6. Debris-flow dominance of alluvial fans masked by runoff reworking and weathering

    Science.gov (United States)

    de Haas, Tjalling; Ventra, Dario; Carbonneau, Patrice E.; Kleinhans, Maarten G.

    2014-07-01

    Arid alluvial fan aggradation is highly episodic and fans often comprise active and inactive sectors. Hence the morphology and texture of fan surfaces are partly determined by secondary processes of weathering and erosion in addition to primary processes of aggradation. This introduces considerable uncertainty in the identification of formative processes of terrestrial and Martian fans from aerial and satellite imagery. The objectives of this study are (i) to develop a model to describe the sedimentological and morphological evolution of inactive fan surfaces in arid settings, and (ii) to assess the relative importance of primary processes of aggradation and secondary processes of weathering and reworking for surface morphology and sedimentology and for the stratigraphic record. We studied an alluvial fan characterized by a recently active sector and a long-abandoned, inactive sector along the coast of the hyperarid Atacama Desert. Here, rates of primary geomorphic activity are exceptionally low because of extreme aridity, while weathering rates are relatively high because of the effects of coastal fogs. Long-term processes of fan aggradation and reworking were determined through sedimentological facies analysis of stratigraphic sections. Ground surveys for textural and morphological patterns at the fan surface were integrated with remote-sensing by an Unmanned Airborne Vehicle (UAV). Discharges and sediment-transport capacities were calculated to estimate the efficiency of secondary runoff in reshaping the inactive fan sector. Stratigraphic sections reveal that the fan was dominantly aggraded by debris flows, whereas surface morphology is dominated by debris-flow signatures in the active sector and by weathering and runoff on the inactive sector. On the latter, rapid particle breakdown prevents the formation of a coarse desert pavement. Furthermore, relatively frequent local runoff events erode proximal debris-flow channels on the inactive sector to form local lag

  7. Landscape aridity, fire severity and rainfall intensity as controls on debris flow frequency after the 2009 Black Saturday Wildfires in Victoria

    Science.gov (United States)

    Nyman, Petter; Sherwin, Christopher; Sheridan, Gary; Lane, Patrick

    2015-04-01

    This study uses aerial imagery and field surveys to develop a statistical model for determining debris flow susceptibility in a landscape with variable terrain, soil and vegetation properties. A measure of landscape scale debris flow response was obtained by recording all debris flow affected drainage lines in the first year after fire in a ~258 000 ha forested area that was burned by the 2009 Black Saturday Wildfire in Victoria. A total of 12 500 points along the drainage network were sampled from catchments ranging in size from 0.0001 km2to 75 km2. Local slope and the attributes of the drainage areas (including the spatially averaged peak intensity) were extracted for each sample point. A logistic regression was used to model how debris flow susceptibility varies with the normalised burn ratio (dNBR, from Landsat imagery), rainfall intensity (from rainfall radar), slope (from DEM) and aridity (from long-term radiation, temperature and rainfall data).The model of debris flow susceptibility produced a good fit with the observed debris flow response of drainage networks within the burned area and was reliable in distinguishing between drainage lines which produced debris flows and those which didn't. The performance of the models was tested through multiple iterations of fitting and testing using unseen data. The local channel slope captured the effect of scale on debris flow susceptibility with debris flow probability approaching zero as the channel slope decreased with increasing drainage area. Aridity emerged as an important predictor of debris flow susceptibility, with increased likelihood of debris flows in drier parts of the landscape, thus reinforcing previous research in the region showing that post-fire surface runoff from wet Eucalypt forests is insufficient for initiating debris flows. Fire severity, measured as dNBR, was also a very important predictor. The inclusion of local channel slope as a predictor of debris flow susceptibility proved to be an

  8. Integrating X-MP radar data to estimate rainfall induced debris flow in the Merapi volcanic area

    Science.gov (United States)

    Syarifuddin, Magfira; Oishi, Satoru; Legono, Djoko; Hapsari, Ratih Indri; Iguchi, Masato

    2017-12-01

    After the 2010 eruption, more than 50 volcanic debris flow (lahar) events occurred during the rainy season of 2010-2011 at Mount Merapi, Indonesia. The lahars occurred following rainfall of severe intensity in the upstream area, where remaining volcanic material was deposited. Estimation of rainfall-induced lahars at Mt. Merapi is difficult and uncertain because the upstream area is dangerous and inaccessible. On 17 February 2016, a lahar occurred in the upstream region of the Gendol River on the southeastern flank of Mt. Merapi after a maximum rainfall intensity of 69 mm/h was monitored on the peak of Mt. Merapi by X-band multi-parameter (X-MP) radar. In this study, rainfall intensity estimates from X-MP radar were applied to generate boundary discharge of a numerical model of debris flow at the catchment scale. The numerical simulation was able to estimate volcanic debris flow occurrence and magnitude. The reliability of radar-rainfall data and the effects of the sabo dam on reducing the impacts of lahar disaster were also examined. The numerical lahar simulation showed relevant results that were comparable to the real condition. The closed type sabo dam caused more than 50% lahar sediment decrement and a flow delay time of 40 min. However, the sediment accumulation has caused increasing flow velocity and higher erosion rate in the 2D area. This study demonstrated the effectiveness of remote monitoring of rainfall combined with numerical debris flow modeling for applied practical use in disaster management.

  9. Probability and volume of potential postwildfire debris flows in the 2012 High Park Burn Area near Fort Collins, Colorado

    Science.gov (United States)

    Verdin, Kristine L.; Dupree, Jean A.; Elliott, John G.

    2012-01-01

    This report presents a preliminary emergency assessment of the debris-flow hazards from drainage basins burned by the 2012 High Park fire near Fort Collins in Larimer County, Colorado. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence and volume of debris flows along the burned area drainage network and to estimate the same for 44 selected drainage basins along State Highway 14 and the perimeter of the burned area. Input data for the models included topographic parameters, soil characteristics, burn severity, and rainfall totals and intensities for a (1) 2-year-recurrence, 1-hour-duration rainfall (25 millimeters); (2) 10-year-recurrence, 1-hour-duration rainfall (43 millimeters); and (3) 25-year-recurrence, 1-hour-duration rainfall (51 millimeters). Estimated debris-flow probabilities along the drainage network and throughout the drainage basins of interest ranged from 1 to 84 percent in response to the 2-year-recurrence, 1-hour-duration rainfall; from 2 to 95 percent in response to the 10-year-recurrence, 1-hour-duration rainfall; and from 3 to 97 in response to the 25-year-recurrence, 1-hour-duration rainfall. Basins and drainage networks with the highest probabilities tended to be those on the eastern edge of the burn area where soils have relatively high clay contents and gradients are steep. Estimated debris-flow volumes range from a low of 1,600 cubic meters to a high of greater than 100,000 cubic meters. Estimated debris-flow volumes increase with basin size and distance along the drainage network, but some smaller drainages were also predicted to produce substantial volumes of material. The predicted probabilities and some of the volumes predicted for the modeled storms indicate a potential for substantial debris-flow impacts on structures, roads, bridges, and culverts located both within and

  10. Single-grain quartz OSL dating of debris flow deposits from Men Tou Gou, south west Beijing, China

    DEFF Research Database (Denmark)

    Zhao, Qiuyue; Thomsen, Kristina Jørkov; Murray, A. S.

    2017-01-01

    of the return frequency of these debris flows, risk assessment and climate change research. In this project, we use quartz single-grain optically stimulated luminescence (OSL) methods to determine the burial ages of five debris flow samples from the Zhai Tang region -60 km west of Beijing. OSL characteristics...... were found to be acceptable despite the low inherent brightness of quartz extracted from these samples. Single-grain thermal transfer was determined to be negligible and beta dose recovery experiments were satisfactory. The quartz single-grain dose distributions strongly indicate that the samples were...

  11. Life, death and revival of debris-flow fans on Earth and Mars : fan dynamics and climatic inferences

    OpenAIRE

    de Haas, T.

    2016-01-01

    Alluvial fans are ubiquitous landforms in high-relief regions on Earth and Mars. They have a semi-conical shape and are located at the transition between highlands and adjacent basins. Alluvial fans can form by a range of processes including debris flows, which are water-laden masses of soil and rock with volumetric sediment concentrations exceeding 40%. In this thesis, I aim to (1) unravel the formative dynamics of debris-flow fans and, building on these insights, to (2) reconstruct hydrolog...

  12. Post-Fire Debris-Flow Hazard Assessments at the U.S. Geological Survey - Recent Advances and Future Directions

    Science.gov (United States)

    Staley, D. M.; Kean, J. W.; Smoczyk, G. M.; Negri, J. A.

    2014-12-01

    Wildfire can have profound effects on the hydrologic response of a watershed, and debris-flow activity is among the most destructive consequences of these effects. The continued high likelihood of catastrophic wildfires in the western U. S. and the encroachment of development into fire-prone areas have created the need to develop tools to identify and quantify the potential hazards posed by debris flows generated from burned watersheds. These tools are critically needed by Federal, State, and local agencies to mitigate the impacts of debris flows on people, their property, infrastructure and natural resources. Applied research at the U.S. Geological Survey (USGS) Landslide Hazards Program is focused on providing timely, science-based assessments of post-fire debris-flow hazard. Formerly, post-fire debris-flow hazard assessments were disseminated by means of the USGS Open-File Report publication series, which included poster-sized maps that predicted the probability, volume, and combined hazard for given watersheds. Feedback from collaborators suggested that 1) the reports were not sufficiently timely for immediate post-fire use, 2) the static maps were difficult to use for site-specific assessments, and 3) individual assessments were often cost-prohibitive. Beginning in January 2014, the USGS has transitioned to a web-based method for disseminating post-fire debris-flow hazard assessments. This new platform addresses the primary concerns of our stakeholders in three ways. First, the turnaround time has been reduced from 1-2 months for a map and written report, to 3-4 days for a web-based map assessment. This allows response teams to incorporate the assessment results into their reports, which are urgently needed immediately after fires. Second, the new website is interactive and accompanied by downloadable geospatial data of predictions for several storm scenarios. These features permit casual (local residents) and power-users (GIS experts) to evaluate site

  13. TITAN2F: a pseudo-3-D model of 2-phase debris flows

    Science.gov (United States)

    Córdoba, G.; Sheridan, M. F.; Pitman, E. B.

    2015-06-01

    Debris flows, avalanches, landslides, and other geophysical mass flows can contain O(106-1010) m3 or more of material. These flows commonly consist of mixture of soil and rocks with a significant quantity of interstitial fluid. They can be tens of meters deep, and their runouts can extend many kilometers. The complicated rheology of such a mixture challenges every constitutive model that can reasonably be applied; the range of length and timescales involved in such mass flows challenges the computational capabilities of existing systems.This paper extends recent efforts to develop a depth averaged "thin layer" model for geophysical mass flows that contain a mixture of solid material and fluid. Concepts from the engineering community are integrated with phenomenological findings in geo-science, resulting in a theory that accounts for the principal solid and fluid forces as well as interactions between the phases, across a wide range of solid volume fraction. A principal contribution here is to present drag and phase interaction terms that comport with the literature in geo-sciences. The program predicts the evolution of the concentration and dynamic pressure. The theory is validated with with data from one dimensional dam break solutions and it is verified with data from artificial channel experiments.

  14. Post-failure characteristics of weathered soils in Korea: determination of rheological thresholds and debris flow mobility

    Science.gov (United States)

    Jeong, Sueng-Won; Fukuoka, Hiroshi; Im, Sang-June

    2013-04-01

    Landslides in Korea are mainly triggered by localized summer heavy rainfall. The water infiltration, wetting and fluidization process are the key roles in slope instability. Mechanically, a loss in soil strength of the soil at weakend layer takes place as a result of water infiltration. The transition from slides to flows can be defined by the variation in strength parameters. In the flowing stage with large volume of sediments, debris flow impact may be governed by the rheology of the failed mass. We performed the rheological tests using the ball-measuring and vane-inserted rheometer and examined a possible threshold of landslides on mudstone, weathered granitic and gneissic soils in the mountainous region of Korea. The materials examined exhibited the shear-thinning behavior, which is the viscosity decreases with increasing shear rates. There are positive relationships between liquidity index and rheological values (i.e., yield stress and viscosities). However, the difference in rheological properties is of significance for given shear rates. The effect of wall-slip in different geometries is emphasized. This work is also concerned with post-failure characteristics of rainfall-induced landslides that occur in Chuncheon, Miryang and Seoul debris flow occurrence in 2011. They are mainly composed of gneissic, sedimentary and gneissic weathered soils. The rheological properties is helpful to predict the mobilization of fine-laden debris flows. In the relationship between shear stress and shear rate, one of simplest rheological models, i.e., the ideal Bingham fluid model, is selected to examine the flow pattern and depositional features of debris flows. A comparison will be made for the debris flow occurence on weahtered soils in Korea.

  15. "State of the Art" of technical protection measures in Austria and the effectiveness documented during bedload and debris flow events

    Science.gov (United States)

    Moser, Markus; Mehlhorn, Susanne; Rudolf-Miklau, Florian; Suda, Jürgen

    2017-04-01

    Since the beginning of systematic torrent control in Austria 130 years ago, barriers are constructed for protection purposes. Until the end of the 1960s, solid barriers were built at the exits of depositional areas to prevent dangerous debris flows from reaching high consequence areas. The development of solid barriers with large slots or slits to regulate sediment transport began with the use of reinforced concrete during the 1970s (Rudolf-Miklau, Suda 2011). In order to dissipate the energy of debris flows debris flow breakers have been designed since the 1980s. By slowing and depositing the surge front of the debris flow, downstream reaches of the stream channel and settlement areas should be exposed to considerably lower dynamic impact. In the past, the technological development of these constructions was only steered by the experiences of the engineering practice while an institutionalized process of standardization comparable to other engineering branches was not existent. In future all structures have to be designed and dimensioned according to the EUROCODE standards. This was the reason to establish an interdisciplinary working group (ON-K 256) at the Austrian Standards Institute (ASI), which has managed to developed comprehensive new technical standards for torrent control engineering, including load models, design, dimensioning and life cycle assessment of torrent control works (technical standard ONR 24800 - series). Extreme torrential events comprise four definable displacement processes floods; fluvial solid transport; hyper-concentrated solid transport (debris floods) and debris flow (stony debris flow or mud-earth flow). As a rule, the design of the torrential barriers has to follow its function (Kettl, 1984). Modern protection concepts in torrent control are scenario-oriented and try to optimize different functions in a chain of protections structures (function chain). More or less the first step for the designing the optimal construction type is

  16. Swarm slide - debris flow disaster induced by extreme rainfall in Hiroshima, August 2014 and lessons learnt in urban designing

    Science.gov (United States)

    Fukuoka, H.; Wang, C.

    2015-12-01

    Hiroshima city was hit by swarm debris flows along a narrow, and linear-shaped rain band of 2 km x 10 km which appeared in the early morning of August 20, 2014. Most of the flows were induced by shallow slide in the upstream. This disaster claimed 74 death, although this city experienced very similar disaster in 1999, claiming more than 30 residents lives. In the most severely affected debris flow torrent, more than 50 residents were killed. Most of the casualties arose in the wooden, vulnerable houses constructed in front of the exit of torrents. Points and lessons learnt from the disaster are as follows:1. Authors collected two types of sands from the source scar of the initial debris slides which induced debris flows. Tested by the ring shear apparatus under pore-pressure control condition, clear "Sliding surface liquefaction" was confirmed for both samples even under small normal stress, representing the small thickness of the slides. These results shows even instant excess pore pressure could initiate the slides and trigger slide-induced debris flow byundrained loading onto the torrent deposits.2. Apparently long-term land-use change since 1945 affected and raised the vulnerability of the community. Residential area had expanded into hill-slope (mountainous / semi-mountainous area) especially along the torrents. Those communities were developed on the past debris flow fan.3. As the devastated area is very close to downtown of Hiroshima city, it gave large societal impact to the Japanese citizens. After 1999 Hiroshima debris flow disaster, the Landslide disaster reduction law which intends to promote designation of landslide potential risk zones, was adopted in 2000. Immediately after 2014 disaster, national diet approved revision of the bill to promote rapid completion of the designation over the national territory. MLIT (Ministry of Land, Infrastructure, Tranportation and Tourism) decided to install X-band rain radars at more sites to cover whole city zones

  17. Investigation of flow regime in debris bed formation behavior with nonspherical particles

    Directory of Open Access Journals (Sweden)

    Songbai Cheng

    2018-02-01

    Full Text Available It is important to clarify the characteristics of flow regimes underlying the debris bed formation behavior that might be encountered in core disruptive accidents of sodium-cooled fast reactors. Although in our previous publications, by applying dimensional analysis technique, an empirical model, with its reasonability confirmed over a variety of parametric conditions, has been successfully developed to predict the regime transition and final bed geometry formed, so far this model is restricted to predictions of debris mixtures composed of spherical particles. Focusing on this aspect, in this study a new series of experiments using nonspherical particles have been conducted. Based on the knowledge and data obtained, an extension scheme is suggested with the purpose of extending the base model to cover the particle-shape influence. Through detailed analyses and given our current range of experimental conditions, it is found that, by coupling the base model with this scheme, respectable agreement between experiments and model predictions for the regime transition can be achieved for both spherical and nonspherical particles. Knowledge and evidence from our work might be utilized for the future improvement of design of an in-vessel core catcher as well as the development and verification of sodium-cooled fast reactor severe accident analysis codes in China.

  18. Examples of Models Fit to Magnetic Anomalies Observed Over Subaerial, Submarine, and Subglacial Volcanoes in the West Antarctic Rift System

    Science.gov (United States)

    Behrendt, J. C.; Finn, C. A.; Blankenship, D. D.

    2006-12-01

    Aeromagnetic and marine magnetic surveys over the volcanically active West Antarctic rift system, constrained by seismic reflection profiles over the Ross Sea continual shelf, and radar ice sounding surveys over the West Antarctic Ice Sheet (WAIS) allowed calculation of models fit to very high-amplitude anomalies. We present several examples: exposed 2700-m high, subaerial erupted volcano Mt Melbourne; the 750-m high source of anomaly D (Hamilton submarine volcano) in the Ross sea; and the 600-m high edifice of Mt. CASERTZ beneath the WAIS. The character of these anomalies and their sources varies greatly, and is inferred to be the result of subaerial, submarine and subglacial emplacement respectively. Mt. Melbourne erupted through the WAIS at a time when it was grounded over the Ross Sea continental shelf. Highly magnetic volcanic flows inferred to have high remanent (normal) magnetization in the present field direction produce the 600-nT positive anomaly. The flows protected the edifice above the ice from erosion. Negligible amounts of probably subglacially erupted, apparently non-magnetic hyaloclastite exist in association with Mt. Melbourne. Mt. CASERTZ is nonmagnetic and the edifice is interpreted as consisting of a transient mound of unconsolidated hyaloclastite injected into the WAIS. However Mt. CASERTZ, about 8-km diameter, overlies a 200-m high, 40-km wide highly magnetic residual edifice modeled as the top of the source (an active subglacial volcano) of a 400-nT high positive anomaly. Any former edifices comprising hyaloclastite, pillow breccia or other volcanic debris injected into the moving WAIS apparently have been removed. About 400 other high- amplitude anomalies associated with low relief (80 percent less than 200 m) edifices at the base of the ice (the tops of the sources of these steep gradient anomalies) beneath the WAIS defined by radar ice sounding have been interpreted as having former hyaloclastite edifices, which were removed by the moving

  19. Assessing the debris flow run-out frequency of a catchment in the French Alps using a parameterization analysis with the RAMMS numerical run-out model

    NARCIS (Netherlands)

    Hussin, Y.A.; Quan Luna, B.; Van Westen, C.J.; Christen, M.; Malet, J.P.; Asch, Th.W.J. van

    2012-01-01

    Debris flows occurring in the European Alps frequently cause significant damage to settlements, power-lines and transportation infrastructure which has led to traffic disruptions, economic loss and even death. Estimating the debris flow run-out extent and the parameter uncertainty related to

  20. An instrumented flume to investigate the initiation mechanism of the post-earthquake huge debris flow in the southwest of China

    NARCIS (Netherlands)

    Hu, W.; Xu, Q.; Rui, C.; Huang, R. Q.; van Asch, T. W J; Zhu, X.; Xu, Q. Q.

    2015-01-01

    The 2008 Wenchuan Earthquake in SW China in the Sichuan Province generated many co-seismic landslides, which delivered a huge amount of loose co-seismic landslide deposits. It caused a dramatic increase in debris flow occurrence in the subsequent years. The mechanism of these runoff debris flows has

  1. Large Scale Debris-flow Hazard Assessment : A Geotechnical Approach and Gis Modelling

    Science.gov (United States)

    Delmonaco, G.; Leoni, G.; Margottini, C.; Puglisi, C.; Spizzichino, D.

    A deterministic approach has been developed for large-scale landslide hazard analysis carried out by ENEA, the Italian Agency for New Technologies, Energy and Environ- ment, in the framework of TEMRAP- The European Multi-Hazard Risk Assessment Project, finalised to the application of methodologies to incorporate the reduction of natural disasters. The territory of Versilia, and in particular the basin of Vezza river (60 Km2), has been chosen as test area of the project. The Vezza river basin, was affected by over 250 shallow landslides (debris/earth flow) mainly involving the metamorphic geological formations outcropping in the area triggered by the hydro-meteorological event of 19th June 1996. Many approaches and methodologies have been proposed in the scientific literature aimed at assessing landslide hazard and risk, depending es- sentially on scope of work, availability of data and scale of representation. In the last decades landslide hazard and risk analyses have been favoured by the development of GIS techniques that have permitted to generalise, synthesise and model the stability conditions at large scale (>1:10.000) investigation. In this work, the main results de- rived by the application of a geotechnical model coupled with a hydrological model for the assessment of debris flows hazard analysis, are reported. The deterministic analysis has been developed through the following steps: 1) elaboration of a landslide inventory map through aerial photo interpretation and direct field survey; 2) genera- tion of a data-base and digital maps; 3) elaboration of a DTM and slope angle map; 4) definition of a superficial soil thickness map; 5) litho-technical soil characterisation, through implementation of a back-analysis on test slopes and laboratory test analy- sis; 6) inference of the influence of precipitation, for distinct return times, on ponding time and pore pressure generation; 7) implementation of a slope stability model (in- finite slope model) and

  2. THRESH—Software for tracking rainfall thresholds for landslide and debris-flow occurrence, user manual

    Science.gov (United States)

    Baum, Rex L.; Fischer, Sarah J.; Vigil, Jacob C.

    2018-02-28

    Precipitation thresholds are used in many areas to provide early warning of precipitation-induced landslides and debris flows, and the software distribution THRESH is designed for automated tracking of precipitation, including precipitation forecasts, relative to thresholds for landslide occurrence. This software is also useful for analyzing multiyear precipitation records to compare timing of threshold exceedance with dates and times of historical landslides. This distribution includes the main program THRESH for comparing precipitation to several kinds of thresholds, two utility programs, and a small collection of Python and shell scripts to aid the automated collection and formatting of input data and the graphing and further analysis of output results. The software programs can be deployed on computing platforms that support Fortran 95, Python 2, and certain Unix commands. The software handles rainfall intensity-duration thresholds, cumulative recent-antecedent precipitation thresholds, and peak intensity thresholds as well as various measures of antecedent precipitation. Users should have predefined rainfall thresholds before running THRESH.

  3. Towards an empirical vulnerability function for use in debris flow risk assessment

    Directory of Open Access Journals (Sweden)

    S. Fuchs

    2007-08-01

    Full Text Available In quantitative risk assessment, risk is expressed as a function of the hazard, the elements at risk and the vulnerability. From a natural sciences perspective, vulnerability is defined as the expected degree of loss for an element at risk as a consequence of a certain event. The resulting value is dependent on the impacting process intensity and the susceptibility of the elements at risk, and ranges from 0 (no damage to 1 (complete destruction. With respect to debris flows, the concept of vulnerability – though widely acknowledged – did not result in any sound quantitative relationship between process intensities and vulnerability values so far, even if considerable loss occurred during recent years.

    To close this gap and establish this relationship, data from a well-documented debris flow event in the Austrian Alps was used to derive a quantitative vulnerability function applicable to buildings located on the fan of the torrent. The results suggest a second order polynomial function to fit best to the observed damage pattern. Vulnerability is highly dependent on the construction material used for exposed elements at risk. The buildings studied within the test site were constructed by using brick masonry and concrete, a typical design in post-1950s building craft in alpine countries. Consequently, the presented intensity-vulnerability relationship is applicable to this construction type within European mountains. However, a wider application of the presented method to additional test sites would allow for further improvement of the results and would support an enhanced standardisation of the vulnerability function.

  4. Rehabilitation of a debris-flow prone mountain stream in southwestern China - Strategies, effects and implications

    Science.gov (United States)

    Yu, Guo-an; Huang, He Qing; Wang, Zhaoyin; Brierley, Gary; Zhang, Kang

    2012-01-01

    SummaryRehabilitation of Shengou Creek, a small, steep mountain stream in southwestern China that is prone to debris flows, started more than 30 years ago through an integrated program of engineering applications (check dams and guiding dikes), biological measures (reforestation), and social measures (reducing human disturbance). Small and medium-sized check dams and guiding dikes were constructed on key upper and middle sections of the creek to stabilize hillslopes and channel bed. Meanwhile, Leucaena leucocephala, a drought-tolerant, fast-growing, and highly adaptive plant species, was introduced to promote vegetation recovery in the watershed. The collective community structure of tree, shrub, and herb assemblages in the artificial L. leucocephala forest, which developed after 7 years, enhanced soil structure and drastically reduced soil erosion on hillslopes. Cultivation of steep land was strictly controlled in the basin, and some inhabitants were encouraged to move from upstream areas to downstream towns to reduce disturbance. These integrated measures reduced sediment supply from both hillslopes and upstream channels, preventing sediment-related hazards. The development of natural streambed resistance structures (mainly step-pool systems) and luxuriant riparian vegetation aided channel stability, diversity of stream habitat, and ecological maintenance in the creek. These findings are compared with Jiangjia and Xiaobaini Ravines, two adjacent non-rehabilitated debris-flow streams which have climate and geomorphologic conditions similar to Shengou Creek. Habitat diversity indices, taxa richness, biodiversity, and bio-community indices are much higher in Shengou Creek relative to Jiangjia and Xiaobaini Ravines, attesting to the effectiveness of rehabilitation measures.

  5. A two-phase debris-flow model that includes coupled evolution of volume fractions, granular dilatancy, and pore-fluid pressure

    Science.gov (United States)

    George, David L.; Iverson, Richard M.

    2011-01-01

    Pore-fluid pressure plays a crucial role in debris flows because it counteracts normal stresses at grain contacts and thereby reduces intergranular friction. Pore-pressure feedback accompanying debris deformation is particularly important during the onset of debrisflow motion, when it can dramatically influence the balance of forces governing downslope acceleration. We consider further effects of this feedback by formulating a new, depth-averaged mathematical model that simulates coupled evolution of granular dilatancy, solid and fluid volume fractions, pore-fluid pressure, and flow depth and velocity during all stages of debris-flow motion. To illustrate implications of the model, we use a finite-volume method to compute one-dimensional motion of a debris flow descending a rigid, uniformly inclined slope, and we compare model predictions with data obtained in large-scale experiments at the USGS debris-flow flume. Predictions for the first 1 s of motion show that increasing pore pressures (due to debris contraction) cause liquefaction that enhances flow acceleration. As acceleration continues, however, debris dilation causes dissipation of pore pressures, and this dissipation helps stabilize debris-flow motion. Our numerical predictions of this process match experimental data reasonably well, but predictions might be improved by accounting for the effects of grain-size segregation.

  6. Change in snow avalanche and debris flow hazards in the region of Krasnaya Polyana as the result of anthropogenic activity

    Science.gov (United States)

    Shnyparkov, A. L.; Seliverstov, Y. G.; Sokratov, S. A.; Koltermann, K. P.

    2012-04-01

    The first evaluations of the snow avalanches and debris flow danger in the region of Krasnaya Polyana (Winter Olympic Games 2014 site) were made by the staff of LSADF in 1960s. In those times the danger was estimated as medium and low. Active development of the region started in 2000, when the ski (mountain climatic health) resort Alpika Service was constructed at the north slope of Aibga mountain range. Then the Alpine resorts Rosa Khutor and Gornaya Karusel [Mountain Carousel] were put into operation on the same slope. OAO Gazprom was also developing its own ski resort at the neighbouring Psekhako ridge. As the result of deforestation the quantity of small snow avalanches increased on the Aibga slopes. Skiers were caught several times by avalanches initiated by them in the reported avalanche events. The construction of ski runs, motorways, roads, as well as building of other related infrastructure has resulted in considerable change in relief. The sediment capping was dumped into stream canals, which resulted in the formation of debris flows, threatening the infrastructure of the ski resorts. The relief change related to the on going Olympic constructions is especially pronounced, when newly formed landfilling on some slopes becomes the material for landslides and debris flows and beds for avalanches. Thus, the degree of snow avalanche and debris flows danger increased considerably in the recent years, requiring originally unplanned mitigation measures.

  7. Life, death and revival of debris-flow fans on Earth and Mars : fan dynamics and climatic inferences

    NARCIS (Netherlands)

    de Haas, T.|info:eu-repo/dai/nl/374023190

    2016-01-01

    Alluvial fans are ubiquitous landforms in high-relief regions on Earth and Mars. They have a semi-conical shape and are located at the transition between highlands and adjacent basins. Alluvial fans can form by a range of processes including debris flows, which are water-laden masses of soil and

  8. Persistent effects of wildfire and debris flows on the invertebrate prey base of rainbow trout in Idaho streams

    Science.gov (United States)

    Amanda E. Rosenberger; Jason B. Dunham; John M. Buffington; Mark S. Wipfli

    2011-01-01

    Wildfire and debris flows are important physical and ecological drivers in headwater streams of western North America. Past research has primarily examined short-term effects of these disturbances; less is known about longer-term impacts. We investigated wildfire effects on the invertebrate prey base for drift-feeding rainbow trout (Oncorhynchus mykiss, Walbaum) in...

  9. Physically based dynamic run-out modelling for quantitative debris flow risk assessment: a case study in Tresenda, northern Italy

    Czech Academy of Sciences Publication Activity Database

    Quan Luna, B.; Blahůt, Jan; Camera, C.; Van Westen, C.; Apuani, T.; Jetten, V.; Sterlacchini, S.

    2014-01-01

    Roč. 72, č. 3 (2014), s. 645-661 ISSN 1866-6280 Institutional support: RVO:67985891 Keywords : debris flow * FLO-2D * run-out * quantitative hazard and risk assessment * vulnerability * numerical modelling Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.765, year: 2014

  10. Improving transferability strategies for debris flow susceptibility assessment: Application to the Saponara and Itala catchments (Messina, Italy)

    KAUST Repository

    Cama, M.

    2017-03-30

    Debris flows can be described as rapid gravity-induced mass movements controlled by topography that are usually triggered as a consequence of storm rainfalls. One of the problems when dealing with debris flow recognition is that the eroded surface is usually very shallow and it can be masked by vegetation or fast weathering as early as one-two years after a landslide has occurred. For this reason, even areas that are highly susceptible to debris flow might suffer of a lack of reliable landslide inventories. However, these inventories are necessary for susceptibility assessment. Model transferability, which is based on calibrating a susceptibility model in a training area in order to predict the distribution of debris flows in a target area, might provide an efficient solution to dealing with this limit. However, when applying a transferability procedure, a key point is the optimal selection of the predictors to be included for calibrating the model in the source area. In this paper, the issue of optimal factor selection is analysed by comparing the predictive performances obtained following three different factor selection criteria. The study includes: i) a test of the similarity between the source and the target areas; ii) the calibration of the susceptibility model in the (training) source area, using different criteria for the selection of the predictors; iii) the validation of the models, both at the source (self-validation, through random partition) and at the target (transferring, through spatial partition) areas. The debris flow susceptibility is evaluated here using binary logistic regression through a R-scripted based procedure.Two separate study areas were selected in the Messina province (southern Italy) in its Ionian (Itala catchment) and Tyrrhenian sides (Saponara catchment), each hit by a severe debris flow event (in 2009 and 2011, respectively).The investigation attested that the best fitting model in the calibration areas resulted poorly performing

  11. Improving transferability strategies for debris flow susceptibility assessment: Application to the Saponara and Itala catchments (Messina, Italy)

    Science.gov (United States)

    Cama, M.; Lombardo, L.; Conoscenti, C.; Rotigliano, E.

    2017-07-01

    Debris flows can be described as rapid gravity-induced mass movements controlled by topography that are usually triggered as a consequence of storm rainfalls. One of the problems when dealing with debris flow recognition is that the eroded surface is usually very shallow and it can be masked by vegetation or fast weathering as early as one-two years after a landslide has occurred. For this reason, even areas that are highly susceptible to debris flow might suffer of a lack of reliable landslide inventories. However, these inventories are necessary for susceptibility assessment. Model transferability, which is based on calibrating a susceptibility model in a training area in order to predict the distribution of debris flows in a target area, might provide an efficient solution to dealing with this limit. However, when applying a transferability procedure, a key point is the optimal selection of the predictors to be included for calibrating the model in the source area. In this paper, the issue of optimal factor selection is analysed by comparing the predictive performances obtained following three different factor selection criteria. The study includes: i) a test of the similarity between the source and the target areas; ii) the calibration of the susceptibility model in the (training) source area, using different criteria for the selection of the predictors; iii) the validation of the models, both at the source (self-validation, through random partition) and at the target (transferring, through spatial partition) areas. The debris flow susceptibility is evaluated here using binary logistic regression through a R-scripted based procedure. Two separate study areas were selected in the Messina province (southern Italy) in its Ionian (Itala catchment) and Tyrrhenian sides (Saponara catchment), each hit by a severe debris flow event (in 2009 and 2011, respectively). The investigation attested that the best fitting model in the calibration areas resulted poorly

  12. A depth-averaged debris-flow model that includes the effects of evolving dilatancy. I. physical basis

    Science.gov (United States)

    Iverson, Richard M.; George, David L.

    2014-01-01

    To simulate debris-flow behaviour from initiation to deposition, we derive a depth-averaged, two-phase model that combines concepts of critical-state soil mechanics, grain-flow mechanics and fluid mechanics. The model's balance equations describe coupled evolution of the solid volume fraction, m, basal pore-fluid pressure, flow thickness and two components of flow velocity. Basal friction is evaluated using a generalized Coulomb rule, and fluid motion is evaluated in a frame of reference that translates with the velocity of the granular phase, vs. Source terms in each of the depth-averaged balance equations account for the influence of the granular dilation rate, defined as the depth integral of ∇⋅vs. Calculation of the dilation rate involves the effects of an elastic compressibility and an inelastic dilatancy angle proportional to m−meq, where meq is the value of m in equilibrium with the ambient stress state and flow rate. Normalization of the model equations shows that predicted debris-flow behaviour depends principally on the initial value of m−meq and on the ratio of two fundamental timescales. One of these timescales governs downslope debris-flow motion, and the other governs pore-pressure relaxation that modifies Coulomb friction and regulates evolution of m. A companion paper presents a suite of model predictions and tests.

  13. Debris Flows and Floods in Southeastern Arizona from Extreme Precipitation in July 2006 - Magnitude, Frequency, and Sediment Delivery

    Science.gov (United States)

    Webb, Robert H.; Magirl, Christopher S.; Griffiths, Peter G.; Boyer, Diane E.

    2008-01-01

    From July 31 to August 1, 2006, an unusual set of atmospheric conditions aligned to produce record floods and an unprecedented number of slope failures and debris flows in southeastern Arizona. During the week leading up to the event, an upper-level low-pressure system centered over New Mexico generated widespread and locally heavy rainfall in southeastern Arizona, culminating in a series of strong, mesoscale convective systems that affected the region in the early morning hours of July 31 and August 1. Rainfall from July 27 through 30 provided sufficient antecedent moisture that the storms of July 31 through August 1 resulted in record streamflow flooding in northeastern Pima County and eastern Pinal County. The rainfall caused at least 623 slope failures in four mountain ranges, including more than 30 near Bowie Mountain in the northern Chiracahua Mountains, and 113 at the southern end of the Huachuca Mountains within and adjacent to Coronado National Memorial. In the Santa Catalina Mountains north of Tucson, 435 slope failures spawned debris flows on July 31 that, together with flood runoff, damaged structures and roads, affecting infrastructure within Tucson's urban boundary. Heavy, localized rainfall in the Galiuro Mountains on August 1, 2006, resulted in at least 45 slope failures and an unknown number of debris flows in Aravaipa Canyon. In the southern Santa Catalina Mountains, the maximum 3-day precipitation measured at a climate station for July 29-31 was 12.04 in., which has a 1,200-year recurrence interval. Other rainfall totals from late July to August 1 in southeastern Arizona also exceeded 1,000-year recurrence intervals. The storms produced floods of record along six watercourses, and these floods had recurrence intervals of 100-500 years. Repeat photography suggests that the spate of slope failures was historically unprecedented, and geologic mapping and cosmogenic dating of ancient debris-flow deposits indicate that debris flows reaching alluvial

  14. Evaluation on the Implementation of Early Warning System for Debris Flow in Merapi Area (Case Study at Boyong River

    Directory of Open Access Journals (Sweden)

    Ali Cahyadi Achmad

    2015-09-01

    Full Text Available One of disasters caused by volcanic activity of Mount Merapi is secondary disaster. The disaster usually occurs after eruption and this volcanic activity produces volcanic and pyroclastic material deposit around the top of the mountain as a result of previous eruption. This material might collapse downward in the form of debris flow as it is affected by natural event such as high intensity rainfall. Therefore, a research is needed to analyze whether existing forecasting and early warning system are capable to provide information for the people living in hazardous area before the debris flood occur. This research was carried out using field survey, observation and interview method. Data analysis used qualitative descriptive method by making description of actual condition of the researched location general condition and qualitative analysis of telemetry system installed on Mount Merapi. The qualitative analysis of telemetry system covers network, hardware, software, power supply, security system, operation and maintenance, also human resources. Research analysis used primary and secondary data. Research results revealed that mean rainfall intensity above of 60 mm/hour might trigger debris flood. Early warning should be given at the rainfall intensity level of 50-55 mm/hour, and debris flood time travel from the upstream to the observed location in Pulowatu Village is 45 minute. Based on the analysis of the present forecasting and early warning system, it is known that some of the equipment is not well functioned, so that debris flow cannot be predicted and detected. This is caused by the lack of human resource quality of the officers in operating and maintaining the equipment. Concerning that matter, it is necessary to conduct some improvement to achieve better forecasting and early warning system in order to give information regarding occurrence of debris flow.

  15. A stochastic germ-grain model to estimate wildfire induced debris flow risks in a changing climate

    Science.gov (United States)

    Sheridan, G. J.; Jones, O. D.; Nyman, P.; Lane, P. N.

    2011-12-01

    Debris flows following wildfire can wash sediment and ash into streams and reservoirs, contaminating water supplies for cities and towns. The fire behavior and erosion processes preceding these contamination events are frequently modeled separately. However climate change may alter both the size and frequency of fires, as well as the intensity and frequency of post-fire erosive storm events. What are the water quality risks associated with these possible simultaneous changes to both the fire and erosive rainfall regimes? When assessing changes in risk due to climate change we argue that the most important property of the system is the "volume" of the intersection in space and time of burnt areas and debris-flow generating storms. The modeling focus should therefore be directed at quantifying changes in the overlap (in space and time) between fire and debris-flow generating storm events, rather than at the geophysical processes that drive them individually. In this presentation we propose the use of a germ-grain based coverage process model to quantify the size of this intersection as a function of the regional fire regime and the local rainfall properties. In this new model we consider fires and debris-flow generating storms as independent stochastic processes with properties of spatial extent, temporal duration, and frequency of occurrence. The approach is illustrated in Figure 1, where we have superimposed random realizations of fires (large discs) and erosive storm processes (small discs) in space (horizontal axis) and time (vertical axis). The volume of intersection of the two processes, shown by the overlap of the large and small discs, gives a measure of hazard of debris flows, and we can quantify how the magnitude of this hazard changes in response to changing fire and rainfall regimes. We use fire history and climatology data to parameterize the germ-grain model for historic conditions in the South East of Australia to illustrate how the model parameters

  16. Derivation of critical rainfall thresholds for shallow landslides as a tool for debris flow early warning systems

    Directory of Open Access Journals (Sweden)

    M. N. Papa

    2013-10-01

    Full Text Available Real-time assessment of debris-flow hazard is fundamental for developing warning systems that can mitigate risk. A convenient method to assess the possible occurrence of a debris flow is to compare measured and forecasted rainfalls to critical rainfall threshold (CRT curves. Empirical derivation of the CRT from the analysis of past events' rainfall characteristics is not possible when the database of observed debris flows is poor or when the environment changes with time. For debris flows and mud flows triggered by shallow landslides or debris avalanches, the above limitations may be overcome through the methodology presented. In this work the CRT curves are derived from mathematical and numerical simulations, based on the infinite-slope stability model in which slope instability is governed by the increase in groundwater pressure due to rainfall. The effect of rainfall infiltration on landside occurrence is modelled through a reduced form of the Richards equation. The range of rainfall durations for which the method can be correctly employed is investigated and an equation is derived for the lower limit of the range. A large number of calculations are performed combining different values of rainfall characteristics (intensity and duration of event rainfall and intensity of antecedent rainfall. For each combination of rainfall characteristics, the percentage of the basin that is unstable is computed. The obtained database is opportunely elaborated to derive CRT curves. The methodology is implemented and tested in a small basin of the Amalfi Coast (South Italy. The comparison among the obtained CRT curves and the observed rainfall amounts, in a playback period, gives a good agreement. Simulations are performed with different degree of detail in the soil parameters characterization. The comparison shows that the lack of knowledge about the spatial variability of the parameters may greatly affect the results. This problem is partially mitigated by

  17. Debris-flow risk analysis in a managed torrent based on a stochastic life-cycle performance.

    Science.gov (United States)

    Ballesteros Cánovas, J A; Stoffel, M; Corona, C; Schraml, K; Gobiet, A; Tani, S; Sinabell, F; Fuchs, S; Kaitna, R

    2016-07-01

    Two key factors can affect the functional ability of protection structures in mountains torrents, namely (i) infrastructure maintenance of existing infrastructures (as a majority of existing works is in the second half of their life cycle), and (ii) changes in debris-flow activity as a result of ongoing and expected future climatic changes. Here, we explore the applicability of a stochastic life-cycle performance to assess debris-flow risk in the heavily managed Wartschenbach torrent (Lienz region, Austria) and to quantify associated, expected economic losses. We do so by considering maintenance costs to restore infrastructure in the aftermath of debris-flow events as well as by assessing the probability of check dam failure (e.g., as a result of overload). Our analysis comprises two different management strategies as well as three scenarios defining future changes in debris-flow activity resulting from climatic changes. At the study site, an average debris-flow frequency of 21 events per decade was observed for the period 1950-2000; activity at the site is projected to change by +38% to -33%, according to the climate scenario used. Comparison of the different management alternatives suggests that the current mitigation strategy will allow to reduce expected damage to infrastructure and population almost fully (89%). However, to guarantee a comparable level of safety, maintenance costs is expected to increase by 57-63%, with an increase of maintenance costs by ca. 50% for each intervention. Our analysis therefore also highlights the importance of taking maintenance costs into account for risk assessments realized in managed torrent systems, as they result both from progressive and event-related deteriorations. We conclude that the stochastic life-cycle performance adopted in this study represents indeed an integrated approach to assess the long-term effects and costs of prevention structures in managed torrents. Copyright © 2016 Elsevier B.V. All rights reserved.

  18. Potential postwildfire debris-flow hazards—A prewildfire evaluation for the Jemez Mountains, north-central New Mexico

    Science.gov (United States)

    Tillery, Anne C.; Haas, Jessica R.

    2016-08-11

    Wildfire can substantially increase the probability of debris flows, a potentially hazardous and destructive form of mass wasting, in landscapes that have otherwise been stable throughout recent history. Although the exact location, extent, and severity of wildfire or subsequent rainfall intensity and duration cannot be known, probabilities of fire and debris‑flow occurrence for given locations can be estimated with geospatial analysis and modeling. The purpose of this report is to provide information on which watersheds might constitute the most serious potential debris-flow hazards in the event of a large-scale wildfire and subsequent rainfall in the Jemez Mountains. Potential probabilities and estimated volumes of postwildfire debris flows in both the unburned and previously burned areas of the Jemez Mountains and surrounding areas were estimated using empirical debris-flow models developed by the U.S. Geological Survey in combination with fire behavior and burn probability models developed by the U.S. Forest Service.Of the 4,998 subbasins modeled for this study, computed debris-flow probabilities in 671 subbasins were greater than 80 percent in response to the 100-year recurrence interval, 30-minute duration rainfall event. These subbasins ranged in size from 0.01 to 6.57 square kilometers (km2), with an average area of 0.29 km2, and were mostly steep, upstream tributaries to larger channels in the area. Modeled debris-flow volumes in 465 subbasins were greater than 10,000 cubic meters (m3), and 14 of those subbasins had modeled debris‑flow volumes greater than 100,000 m3.The rankings of integrated relative debris-flow hazard indexes for each subbasin were generated by multiplying the individual subbasin values for debris-flow volume, debris‑flow probability, and average burn probability. The subbasins with integrated hazard index values in the top 2 percent typically are large, upland tributaries to canyons and channels primarily in the Upper Rio Grande

  19. Rock-glacier dynamics and magnitude-frequency relations of debris flows in a high-elevation watershed: Ritigraben, Swiss Alps

    Science.gov (United States)

    Lugon, Ralph; Stoffel, Markus

    2010-09-01

    A widespread risk in high mountains is related to the accumulation of loose sediments on steep slopes, which represent potential sources of different types of geomorphic processes including debris flows. This paper combines data on 50 yr of permafrost creep at the Ritigraben rock glacier (Valais, Swiss Alps) with magnitude-frequency (M-F) relationships of debris flows recorded in the Ritigraben torrent originating at the rock-glacier front. Debris production and volumetric changes at the rock-glacier front are compared with debris-flow activity recorded on the cone and potential couplings and feedbacks between debris sources, channel processes and debris sinks. The dataset existing for the Ritigraben rock glacier and its debris-flow system is unique and allows prime insights into controls and dynamics of permafrost processes and related debris-flow activity in a constantly changing and warming high-altitude environment. Acceleration in rock-glacier movement rates is observed in the (1950s and) 1960s, followed by a decrease in flow rates by the 1970s, before movements increase again after the early 1990s. At a decadal scale, measured changes in rock-glacier movements at Ritigraben are in concert with changes in atmospheric temperatures in the Alps. Geodetic data indicates displacement rates in the frontal part of the rock glacier of up to 0.6-0.9 m yr -1 since the beginning of systematic measurements in 1995. While the Ritigraben rock glacier has always formed a sediment reservoir for the associated debris-flow system, annual horizontal displacement rates of the rock-glacier body have remained quite small and are in the order of decimeters under current climatic conditions. Sediment delivery from the rock-glacier front alone could not therefore be sufficient to support the 16 debris flows reconstructed on the cone since 1958. On the contrary, debris accumulated at the foot of the rock glacier, landslide and rockfall activity as well as the partial collapse of

  20. Modelling shallow debris flows of the Coulomb-mixture type over temporally varying topography

    Directory of Open Access Journals (Sweden)

    Y. C. Tai

    2012-02-01

    Full Text Available We propose a saturated binary mixture model for debris flows of the Coulomb-mixture type over temporally varying topography, where the effects of erosion and deposition are considered. Due to the deposition or erosion processes, the interface between the moving material and the stagnant base is a non-material singular surface. The motion of this singular surface is determined by the mass exchange between the flowing layer and the ground. The ratio of the relative velocity between the two constituents to the velocity of the solid phase is assumed to be small, so that the governing equations can be reduced to a system of the quasi-single-phase type. A shock-capturing numerical scheme is implemented to solve the derived equation system. The deposition shapes of a finite mass sliding down an inclined planary chute are investigated for a range of mixture ratios. The geometric evolution of the deposition is presented, which allows the possibility of mimicking the development of levee deposition.

  1. Set-up of debris-flow monitoring stations in the Eastern Pyrenees. Preliminary results and first experiences.

    Science.gov (United States)

    Hürlimann, Marcel; Abancó, Claudia; Moya, Jose; Chevalier, Guillaume; Raïmat, Carles; Luis-Fonseca, Roberto

    2010-05-01

    Direct observations of debris flows in the field by monitoring stations are of great importance to improve understandings of triggering, flow behaviour and accumulation of debris flows. Upon the knowledge of the authors, in Europe debris-flow monitoring stations are only situated in the Alps (Italy and Switzerland), while no test site is located in a catchment affected by Mediterranean climate. In 2005, the first monitoring system was set up by GEOBRUGG IBERICA SA in the Erill catchment, situated in the Axial Pyrenees. A flexible ring net VX160-H4 with load-cells was installed together with a video camera and four geophones. In addition, a meteorological station completed the instrumentation. During 2009, the monitoring of two additional catchments has been set up; Senet in the Axial Pyrenees and Ensija in the Pre-Pyrenees. Four geophones and one ultrasonic device are installed along the torrent in order to determine the flow velocity and flow depth/discharge of the events. As in Erill, a meteorological station completes the devices and measures rainfall and temperature. The main objective of the three monitoring stations is to get some insights on how the Mediterranean climate influences the critical rainfall for debris-flow initiation. The flow behaviour of debris flows is another major goal, while the Erill test site focuses basically on the effectiveness of flexible ring nets. In addition, the Erill installation also acts as protection for the village located on the fan. The calibration, installation and analysis during the testing phase showed that a correct implementation of the different sensors is not an easy task and needs knowledge in geophysics, electronics, telecommunications etc. Especially geophones and ultrasonic devices need special attentions. Geophone outputs are strongly affected by the type of underground and the distance to the torrent, while the measures of the ultrasonic sensor clearly depend on the temperature. To simplify the data storage

  2. Debris flow risk mitigation by the means of rigid and flexible barriers – experimental tests and impact analysis

    Directory of Open Access Journals (Sweden)

    L. Canelli

    2012-05-01

    Full Text Available The impact of a debris flow on a structure can have disastrous effects because of the enormous destructive potential of this type of phenomenon. Although the introduction of risk mitigation structures such as the Sabo Dam, the filter dam and more recently flexible barriers is usual, there are very few methods that are universally recognized for the safe design of such structures. This study presents the results of experimental tests, conducted with the use of a specifically created flume, in order to obtain detailed knowledge of the mechanical aspects, and to analyze the dynamics of the impact of a debris flow on different types of structures. The analyses of the tests, together with the calculation of the thrust caused by the flow, have made it possible to analyze the dynamics of the impact, which has shown differing effects, on the basis of the type of barrier that has been installed.

  3. Geomorphic change caused by outburst floods and debris flows at Mount Rainier, Washington, with emphasis on Tahoma Creek valley

    Science.gov (United States)

    Walder, J.S.; Driedger, C.L.

    1994-01-01

    Debris flows have caused rapid geomorphic change in several glacierized drainages on Mount Rainier, Washington. Nearly all of these flows began as glacial outburst floods, then transformed to debris flows by incorporating large masses of sediment in channel reaches where streams have incised proglacial sediments and stagnant glacier ice. This stagnant ice is a relic of advanced glacier positions achieved during the mid-nineteenth century Little Ice Age maximum and the readvance of the 1960's and 1970's. Debris flows have been especially important agents of geomorphic change along Tahoma Creek, which drains South Tahoma Glacier. Debris flows in Tahoma Creek valley have transported downstream about 107 m3 Of sediment since 1967, causing substantial aggradation and damage to roads and facilities in Mount Rainier National Park. The average denudation rate in the upper part of the Tahoma Creek drainage basin in the same period has been extraordinarily high: more than 20 millimeters per year, a value exceeded only rarely in basins affected by debris flows. However, little or none of this sediment has yet passed out of the Tahoma Creek drainage basin. Outburst floods from South Tahoma Glacier form by release of subglacially stored water. The volume of stored water discharged during a typical outburst flood would form a layer several tens of millimeters thick over the bed of the entire glacier, though it is more likely that large linked cavities account for most of the storage. Statistical analysis shows that outburst floods usually occur during periods of atypically hot or rainy weather in summer or early autumn, and that the probability of an outburst increases with temperature (a proxy measure of ablation rate) or rainfall rate. On the basis of these results, we suggest that outburst floods are triggered when rapid input of water to the glacier bed causes transient increase in water pressure, thereby destabilizing the linked-cavity system. The probabilistic nature of

  4. Map of debris flows caused by rainfall during 1996 in parts of the Reedsport and Deer Head Point quadrangles, Douglas County, southern Coast Range, Oregon

    Science.gov (United States)

    Coe, Jeffrey A.; Michael, John A.; Burgos, Marianela Mercado

    2011-01-01

    This 1:12,000-scale map shows an inventory of debris flows caused by rainfall during 1996 in a 94.4 km2 area in the southern Coast Range of Oregon. This map and associated digital data are part of a larger U.S. Geological Survey study of debris flows in the southern Coast Range. Available evidence indicates that the flows were triggered by a rain storm that occurred between November 17 and 19. The closest rain gage in the Coast Range (Goodwin Peak) recorded 245 mm during the storm. Maximum rainfall intensity during the storm was 13.2 mm/hr on November 18. Debris flows were photogrammetrically mapped from 1:12,000-scale aerial photographs flown in May, 1997. The inventory is presented on imagery derived from LiDAR data acquired in 2008. We classified mapped debris flows into four categories based on the type of debris-flow activity: (1) discrete slide source areas, (2) predominantly erosion, (3) predominantly transport or mixed erosion and deposition, and (4) predominantly deposition. Locations of woody-debris jams are also shown on the map. The area encompassed by debris flows is 2.1 percent of the 94.4 km2 map area.

  5. Space-time organization of debris flows-triggering rainfall and its effect on the identification of the rainfall threshold relationship

    Science.gov (United States)

    Marra, F.; Nikolopoulos, E. I.; Creutin, J. D.; Borga, M.

    2016-10-01

    Debris flow occurrence is generally forecasted by means of empirical rainfall depth-duration thresholds based on raingauge observations. Rainfall estimation errors related to the sparse nature of raingauge data are enhanced in case of convective rainfall events characterized by limited spatial extent. Such errors have been shown to cause underestimation of the rainfall thresholds and, thus, less efficient forecasts of debris flows occurrence. This work examines the spatial organization of debris flows-triggering rainfall around the debris flow initiation points using high-resolution, carefully corrected radar data for a set of short duration (Alps. On average, triggering rainfall presents a local peak corresponding to the debris flow initiation point, with rain depth at 5 km (10 km) distance being on average around 70% (40%) of rain depth observed at the debris flow initiation points. The peak is consistently enhanced for events characterized by short durations and causes a systematic underestimation of the rainfall depth-duration thresholds when rainfall is measured away from the debris flow initiation points. We develop an analytical framework that exploits the general characteristics of the spatial rainfall organization to predict the systematic underestimation of the depth-duration thresholds when rainfall is sampled away from the initiation points. Predictions obtained based on this analytical framework are assessed using a Monte Carlo sampling technique.

  6. A low-cost method to measure the timing of post-fire flash floods and debris flows relative to rainfall

    Science.gov (United States)

    Kean, Jason W.; Staley, Dennis M.; Leeper, Robert J.; Schmidt, Kevin Michael; Gartner, Joseph E.

    2012-01-01

    Data on the specific timing of post-fire flash floods and debris flows are very limited. We describe a method to measure the response times of small burned watersheds to rainfall using a low-cost pressure transducer, which can be installed quickly after a fire. Although the pressure transducer is not designed for sustained sampling at the fast rates ({less than or equal to}2 sec) used at more advanced debris-flow monitoring sites, comparisons with high-data rate stage data show that measured spikes in pressure sampled at 1-min intervals are sufficient to detect the passage of most debris flows and floods. Post-event site visits are used to measure the peak stage and identify flow type based on deposit characteristics. The basin response timescale (tb) to generate flow at each site was determined from an analysis of the cross correlation between time series of flow pressure and 5-min rainfall intensity. This timescale was found to be less than 30 minutes for 40 post-fire floods and 11 post-fire debris flows recorded in 15 southern California watersheds ({less than or equal to} 1.4 km2). Including data from 24 other debris flows recorded at 5 more instrumentally advanced monitoring stations, we find there is not a substantial difference in the median tb for floods and debris flows (11 and 9 minutes, respectively); however, there are slight, statistically significant differences in the trends of flood and debris-flow tb with basin area, which are presumably related to differences in flow speed between floods and debris flows.

  7. Flow-R, a model for susceptibility mapping of debris flows and other gravitational hazards at a regional scale

    Directory of Open Access Journals (Sweden)

    P. Horton

    2013-04-01

    Full Text Available The development of susceptibility maps for debris flows is of primary importance due to population pressure in hazardous zones. However, hazard assessment by process-based modelling at a regional scale is difficult due to the complex nature of the phenomenon, the variability of local controlling factors, and the uncertainty in modelling parameters. A regional assessment must consider a simplified approach that is not highly parameter dependant and that can provide zonation with minimum data requirements. A distributed empirical model has thus been developed for regional susceptibility assessments using essentially a digital elevation model (DEM. The model is called Flow-R for Flow path assessment of gravitational hazards at a Regional scale (available free of charge under http://www.flow-r.org and has been successfully applied to different case studies in various countries with variable data quality. It provides a substantial basis for a preliminary susceptibility assessment at a regional scale. The model was also found relevant to assess other natural hazards such as rockfall, snow avalanches and floods. The model allows for automatic source area delineation, given user criteria, and for the assessment of the propagation extent based on various spreading algorithms and simple frictional laws. We developed a new spreading algorithm, an improved version of Holmgren's direction algorithm, that is less sensitive to small variations of the DEM and that is avoiding over-channelization, and so produces more realistic extents. The choices of the datasets and the algorithms are open to the user, which makes it compliant for various applications and dataset availability. Amongst the possible datasets, the DEM is the only one that is really needed for both the source area delineation and the propagation assessment; its quality is of major importance for the results accuracy. We consider a 10 m DEM resolution as a good compromise between processing time

  8. Debris Flow Susceptibility Assessment in the Wudongde Dam Area, China Based on Rock Engineering System and Fuzzy C-Means Algorithm

    Directory of Open Access Journals (Sweden)

    Yanyan Li

    2017-09-01

    Full Text Available Debris flows in the Wudongde dam area, China could pose a huge threat to the running of the power station. Therefore, it is of great significance to carry out a susceptibility analysis for this area. This paper presents an application of the rock engineering system and fuzzy C-means algorithm (RES_FCM for debris flow susceptibility assessment. The watershed of the Jinsha River close to the Wudongde dam site in southwest China was taken as the study area, where a total of 22 channelized debris flow gullies were mapped by field investigations. Eight environmental parameters were selected for debris flow susceptibility assessment, namely, lithology, watershed area, slope angle, stream density, length of the main stream, curvature of the main stream, distance from fault and vegetation cover ratio. The interactions among these parameters and their weightings were determined using the RES method. A debris flow susceptibility map was produced by dividing the gullies into three categories of debris flow susceptibility based on the susceptibility index (SI using the FCM algorithm. The results show that the susceptibility levels for nine of the debris flow gullies are high, nine are moderate and four are low, respectively. The RES based K-means algorithm (RES_KM was used for comparison. The results suggest that the RES_FCM method and the RES_KM method provide very close evaluation results for most of the debris flow gullies, which also agree well with field investigations. The prediction accuracy of the new method is 90.9%, larger than that obtained by the RES_KM method (86.4%. Therefore, the RES_FCM method performs better than the RES_KM method for assessing the susceptibility of debris flows.

  9. Debris-flow risk analysis in a managed torrent based on a stochastic life-cycle performance

    Energy Technology Data Exchange (ETDEWEB)

    Ballesteros Cánovas, J.A., E-mail: juan.ballesteros@dendrolab.ch [Dendrolab.ch. Institute for Geological Sciences, University of Bern, Baltzerstrasse 1 + 3, CH-3012 Bern (Switzerland); Climate Change an Climate Impacts (C3i) Institute for Environmental Sciences, University of Geneva, 66 Boulevard Carl-Vogt, CH-1205 Geneva (Switzerland); Stoffel, M. [Dendrolab.ch. Institute for Geological Sciences, University of Bern, Baltzerstrasse 1 + 3, CH-3012 Bern (Switzerland); Climate Change an Climate Impacts (C3i) Institute for Environmental Sciences, University of Geneva, 66 Boulevard Carl-Vogt, CH-1205 Geneva (Switzerland); Department of Earth Sciences, University of Geneva, 13 rue des Maraîchers, CH-1205 Geneva (Switzerland); Corona, C. [Centre National de la Recherche Scientifique (CNRS) UMR6042 Geolab, 4 rue Ledru, F-63057 Clermont-Ferrand Cedex (France); Schraml, K. [Institute for Alpine Hazards, University of Natural Resources and Life Sciences, Vienna (BOKU), A-1190 Vienna (Austria); Gobiet, A. [University of Graz, Wegener Center for Climate and Global Change (WegCenter), A-8010 Graz (Austria); Central Office for Meteorology and Geodynamics (ZAMG), A-1190 Vienna (Austria); Tani, S. [University of Graz, Wegener Center for Climate and Global Change (WegCenter), A-8010 Graz (Austria); Sinabell, F. [Austrian Institute of Economic Research, A-1030 Vienna (Austria); Fuchs, S.; Kaitna, R. [Institute for Alpine Hazards, University of Natural Resources and Life Sciences, Vienna (BOKU), A-1190 Vienna (Austria)

    2016-07-01

    Two key factors can affect the functional ability of protection structures in mountains torrents, namely (i) infrastructure maintenance of existing infrastructures (as a majority of existing works is in the second half of their life cycle), and (ii) changes in debris-flow activity as a result of ongoing and expected future climatic changes. Here, we explore the applicability of a stochastic life-cycle performance to assess debris-flow risk in the heavily managed Wartschenbach torrent (Lienz region, Austria) and to quantify associated, expected economic losses. We do so by considering maintenance costs to restore infrastructure in the aftermath of debris-flow events as well as by assessing the probability of check dam failure (e.g., as a result of overload). Our analysis comprises two different management strategies as well as three scenarios defining future changes in debris-flow activity resulting from climatic changes. At the study site, an average debris-flow frequency of 21 events per decade was observed for the period 1950–2000; activity at the site is projected to change by + 38% to − 33%, according to the climate scenario used. Comparison of the different management alternatives suggests that the current mitigation strategy will allow to reduce expected damage to infrastructure and population almost fully (89%). However, to guarantee a comparable level of safety, maintenance costs is expected to increase by 57–63%, with an increase of maintenance costs by ca. 50% for each intervention. Our analysis therefore also highlights the importance of taking maintenance costs into account for risk assessments realized in managed torrent systems, as they result both from progressive and event-related deteriorations. We conclude that the stochastic life-cycle performance adopted in this study represents indeed an integrated approach to assess the long-term effects and costs of prevention structures in managed torrents. - Highlights: • Debris flows are considered

  10. Debris flow hazards in plantation forests in New Zealand: what we know and need to know

    Science.gov (United States)

    Phillips, Chris; Basher, Les; Marden, Michael; Harrison, Duncan; Heaphy, Marie

    2015-04-01

    In recent years, extensive storm-induced landsliding has mobilised woody residue during or after plantation forest harvesting and caused debris flows that have affected houses, roads and bridges downstream of forests in several parts of New Zealand. In part, this relates to increasing levels of harvesting activity as many plantations originally planted for soil conservation purposes have reached merchantable size but could also be in response to an increasing incidence of high intensity storms affecting parts of New Zealand. In several cases these incidents have featured on national television and in newspaper headlines with members of the public complaining about the consequences of forestry operations on steep erodible hill country. Forestry companies have responded by developing more detailed environmental impact assessment and erosion and sediment control planning approaches, and by assisting with clean-up operations. Similarly regional councils (the regulatory bodies) have looked more closely at the environmental impacts of forest harvesting and some have modified erosion and sediment control guidelines, previously largely applied to urban earthworks, for forestry application. As part of a wider research programme that aims to raise the profitability and improve the sustainability of New Zealand's forestry sector, we collected information from both forestry companies and regional and unitary councils via survey and interviews to determine the size and scope of the issue, how individual forest companies were identifying and managing the risk, and to determine if national threshold conditions or standards could be established. Even with risk management and good management practices in place, it will not be possible to entirely avoid slope failures and debris flows following harvesting in the future. Thus the need to determine a national level of understanding of what can and can't be managed for is important to allow the development of risk management approaches

  11. Catastrophic debris flows on 13 August 2010 in the Qingping area, southwestern China: The combined effects of a strong earthquake and subsequent rainstorms

    NARCIS (Netherlands)

    Tang, C.; Asch, Th.W.J. van; Chang, M.; Chen, G.Q.; Zhao, X.H.; Huang, X.C.

    In the Wenchuan area in SW China, an abundance of loose co-seismic landslide debris was present on the slopes after the Wenchuan earthquake, which in later years served as source material for rainfall-induced debris flows or shallow landslides. Slopes composed of Cambrian sandstones and siltstones

  12. Influential factors on debris flow events and hillslope-channel connectivity in Alpine regions: case studies from two Alpine regions in Styria, Austria

    Science.gov (United States)

    Traper, Sandra; Pöppl, Ronald; Rascher, Eric; Sass, Oliver

    2016-04-01

    In recent times different types of natural disasters like debris flow events have attracted increasing attention worldwide, since they can cause great damage and loss of infrastructure or even lives is not unusual when it comes to such an event. The engagement with debris flows is especially important in mountainous areas like Austria, since Alpine regions have proved to be particularly prone to the often harmful consequences of such events because of increasing settlement of previously uninhabited regions. Due to those frequently damaging effects of debris flows, research on this kind of natural disaster often focuses on mitigation and recovery measures after an event and on how to restore the initial situation. However, a view on the situation of an area, where severe debris flows recently occurred and are well documented, before the actual event can aid in discovering important preparatory factors that contribute to initiating debris flows and hillslope-channel connectivity in the first place. Valuable insights into the functioning and preconditions of debris flows and their potential connectivity to the main channel can be gained. The study focuses on two geologically different areas in the Austrian Alps, which are both prone to debris flows and have experienced rather severe events recently. Based on data from debris flow events in two regions in Styria (Austria), the Kleinsölk and the Johnsbach valleys, the aim of the study is to identify factors which influence the development of debris flows and the potential of such debris flows to reach the main channel potentially clogging up the river (hillslope-channel connectivity). The degree of hillslope-channel coupling was verified in extensive TLS and ALS surveys, resulting in DEMs of different resolution and spatial extension. Those factors are obtained, analyzed and evaluated with DEM-based GIS- and statistical analyses. These include factors that are attributed to catchment topography, such as slope angle

  13. A GIS-based numerical model for simulating the kinematics of mud and debris flows over complex terrain

    Directory of Open Access Journals (Sweden)

    S. Beguería

    2009-11-01

    Full Text Available This article presents MassMov2D, a two-dimensional model of mud and debris flow dynamics over complex topography, based on a numerical integration of the depth-averaged motion equations using a shallow water approximation. The core part of the model was implemented using the GIS scripting language PCRaster. This environment provides visualization of the results through map animations and time series, and a user-friendly interface. The constitutive equations and the numerical solution adopted in MassMov2D are presented in this article. The model was applied to two field case studies of mud flows on torrential alluvial fans, one in the Austrian Tyrol (Wartschenbach torrent and the other in the French Alps (Faucon torrent. Existing data on the debris flow volume, input discharge and deposits were used to back-analyze those events and estimate the values of the leading parameters. The results were compared with modeling codes used by other authors for the same case studies. The results obtained with MassMov2D matched well with the observed debris flow deposits, and are in agreement with those obtained using alternative codes.

  14. Debris flow recurrence periods and multi-temporal observations of colluvial fan evolution in central Spitsbergen (Svalbard)

    Science.gov (United States)

    Bernhardt, H.; Reiss, D.; Hiesinger, H.; Hauber, E.; Johnsson, A.

    2017-11-01

    Fan-shaped accumulations of debris flow deposits are common landforms in polar regions such as Svalbard. Although depositional processes in these environments are of high interest to climate as well as Mars-analog research, several parameters, e.g., debris flow recurrence periods, remain poorly constrained. Here, we present an investigation based on remote sensing as well as in situ data of a 0.4 km2 large colluvial fan in Hanaskogdalen, central Spitsbergen. We analyzed high resolution satellite and aerial images covering five decades from 1961 to 2014 and correlated them with lichenometric dating as well as meteorological data. Image analyses and lichenometry deliver consistent results and show that the recurrence period of large debris flows (≥ 400 m3) is about 5 to 10 years, with smaller flows averaging at two per year in the period from 2008 to 2013. While this is up to two orders of magnitude shorter than previous estimates for Svalbard (80 to 500 years), we found the average volume of 220 m3 per individual flow to be similar to previous estimates for the region. Image data also reveal that an avulsion took place between 1961 and 1976, when the active part of the fan moved from its eastern to its western portion. A case study of the effects of a light rain event ( 5 mm/day) in the rainy summer of 2013, which triggered a large debris flow, further shows that even light precipitation can trigger major flows. This is made possible by multiple light rain events or gradual snow melt pre-saturating the permafrost ground and has to be taken into account when predicting the likelihood of potentially hazardous mass wasting in polar regions. Furthermore, our findings imply a current net deposition rate on the colluvial fan of 480 m3/year, which is slightly less than the integrated net deposition rate of 576 to 720 m3/year resulting from the current fan volume divided by the 12,500 to 10,000 years since the onset of fan build-up after the area's deglaciation. However

  15. Experimental investigation on single-phase pressure losses in nuclear debris beds: Identification of flow regimes and effective diameter

    Energy Technology Data Exchange (ETDEWEB)

    Clavier, R., E-mail: remi.clavier@irsn.fr [Institut de Radioprotection et de Sûreté Nucléaire (IRSN) – PSN-RES/SEREX/LE2M, Cadarache bât. 327, 13115 St Paul-lez-Durance (France); Chikhi, N., E-mail: nourdine.chikhi@irsn.fr [Institut de Radioprotection et de Sûreté Nucléaire (IRSN) – PSN-RES/SEREX/LE2M, Cadarache bât. 327, 13115 St Paul-lez-Durance (France); Fichot, F. [Institut de Radioprotection et de Sûreté Nucléaire (IRSN) – PSN-RES/SAG/LEPC, Cadarache bât. 700, 13115 St Paul-lez-Durance (France); Quintard, M. [Université de Toulouse – INPT – UPS – Institut de Mécanique des Fluides de Toulouse (IMFT), Allée Camille Soula, F-31400 Toulouse (France); CNRS – IMFT, F-31400 Toulouse (France)

    2015-10-15

    Highlights: • Single-phase pressure drops versus flow rates in particle beds are measured. • Conditions are representative of the reflooding of a nuclear fuel debris bed. • Darcy, weak inertial, strong inertial and weak turbulent regimes are observed. • A Darcy–Forchheimer law is found to be a good approximation in this domain. • A predictive correlation is derived from new experimental data. - Abstract: During a severe nuclear power plant accident, the degradation of the reactor core can lead to the formation of debris beds. The main accident management procedure consists in injecting water inside the reactor vessel. Nevertheless, large uncertainties remain regarding the coolability of such debris beds. Motivated by the reduction of these uncertainties, experiments have been conducted on the CALIDE facility in order to investigate single-phase pressure losses in representative debris beds. In this paper, these results are presented and analyzed in order to identify a simple single-phase flow pressure loss correlation for debris-bed-like particle beds in reflooding conditions, which cover Darcean to Weakly Turbulent flow regimes. The first part of this work is dedicated to study macro-scale pressure losses generated by debris-bed-like particle beds, i.e., high sphericity (>80%) particle beds with relatively small size dispersion (from 1 mm to 10 mm). A Darcy–Forchheimer law, involving the sum of a linear term and a quadratic deviation, with respect to filtration velocity, has been found to be relevant to describe this behavior in Darcy, Strong Inertial and Weak Turbulent regimes. It has also been observed that, in a restricted domain (Re = 15 to Re = 30) between Darcy and Weak Inertial regimes, deviation is better described by a cubic term, which corresponds to the so-called Weak Inertial regime. The second part of this work aims at identifying expressions for coefficients of linear and quadratic terms in Darcy–Forchheimer law, in order to obtain a

  16. ANALYSIS OF DEBRIS FLOW DISASTER DUE TO HEAVY RAIN BY X-BAND MP RADAR DATA

    Directory of Open Access Journals (Sweden)

    M. Nishio

    2016-06-01

    Full Text Available On August 20 of 2014, Hiroshima City (Japan was struck by local heavy rain from an autumnal rain front. The resultant debris flow disaster claimed 75 victims and destroyed many buildings. From 1:30 am to 4:30 am on August 20, the accumulated rainfall in Hiroshima City exceeded 200 mm. Serious damage occurred in the Asakita and Asaminami wards of Hiroshima City. As a disaster prevention measure, local heavy rain (localized torrential rains is usually observed by the Automated Meteorological Data Acquisition System (AMeDAS operated by the Japan Meteorological Agency (JMA and by the C-band radar operated by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT of Japan, with spatial resolutions of 2.5 km and 1 km, respectively. The new X-band MP radar system enables more detailed rainfall observations than the C-band radar. In fact, this radar can observe local rainfall throughout Japan in near-real time over a minimum mesh size of 250 m. A fine-scale accumulated rainfall monitoring system is crucial for disaster prevention, and potential disasters can be alerted by the hazard levels of the accumulated rainfall.

  17. Traumatic resin ducts in Larix decidua stems impacted by debris flows.

    Science.gov (United States)

    Bollschweiler, Michelle; Stoffel, Markus; Schneuwly, Dominique M; Bourqui, Karin

    2008-02-01

    Following mechanical injury, stems of many conifers produce tangential rows of traumatic resin ducts (TRDs), the distribution of which has been used to date geomorphic events. However, little is known about how far TRD formation extends tangentially and axially from the point of injury or what the time course of TRD appearance is. We analyzed 28 injuries in eight Larix decidua Mill. tree stems resulting from debris flows in October 2000 and November 2004. Injuries occurred outside the period of cambial activity, and TRD formation occurred in the first layers of the growth ring formed in the year following that of injury. The axial extent of TRD formation averaged 74 cm and was greater above the injury than below it. At the height of the wound center, TRDs extended horizontally to a mean of 18% of the stem circumference excluding that portion where the cambium had been destroyed. In subsequent growth rings, TRDs, if present, were confined mainly to the height of the center of injury. Both the vertical and horizontal extent of TRD formation was related to the injury size. Within growth rings, the position of TRD formation changed with increasing distance from the wound progressing from early earlywood to later portions of the growth ring.

  18. Rockfall and debris flow mitigation : Innovative systems for a new efficient and integrated approach

    Science.gov (United States)

    Villard, Nicolas; Robit, Philippe

    2014-05-01

    In the French Alps the latest generation of high performance systems against rockfall and debris flow has been developed by the contractor GTS taking a relatively lightweight approach, developed from decades of experience working with the more traditional catch fence systems. It allows to adapt the solution to the field rather than the opposite. Moreover it offers relevant alternates economically, in a global context of budget restrictions, and environmentally, with lower carbon emissions and impacts. The new barriers and patented systems have minimal anchoring requirements and are effective in difficult ground conditions. They are designed to be as simple, safe and rapid as possible to install in any location, including high on the slope by rope access workers. Barriers can now cost effectively be installed near the failure source, where energies are lower and where shorter fences can mitigate the hazard. System components have been kept as simple as possible to ensure maximum lifetime, minimise maintenance requirements and to facilitate repairs in the field at low cost. GTS has carried out extensive multi-scale analyses of their new systems including full scale testing to meet evolving guidelines.

  19. Modelling the Timing and Location of Shallow Landslides and Debris Flows Using the SHETRAN Model

    Science.gov (United States)

    Bovolo, C. I.; Bathurst, J. C.

    2006-12-01

    Research on landslide incidence has tended to focus on threshold relationships and has only recently started to look into predicting the location, timing and magnitude of landslide events as a function of climate and geomorphology. In addition, only a few studies consider the post landslide effects of erosion or downstream sediment transport in rivers and most models are limited to areas of a few square kilometres or less. The SHETRAN landslide model is a physically based system which can predictively examine shallow landslide and debris flow incidence on a spatially distributed basis, at the scale of a catchment (New Zealand. A high intensity, single peak rainfall event produced similar number of landslides as a constant low intensity rainfall event of the same duration. Where rainfall increased to a peak at the end of the event, fewer landslides were produced, whilst the least number of landslides were produced where rainfall decreased from a peak at the start of the event. In general, landslides occur at the peak of the rainfall event or at the time of maximum soil saturation but vary according to rainfall distribution and magnitude patterns. Graphs of the number of landslides as a function of rainfall event intensity and duration are given as a series of curves which can be compared with existing thresholds and show the severity of the event in terms of the number of landslides for a given rainfall condition.

  20. Assessment of debris-flow susceptibility at medium-scale in the Barcelonnette Basin, France

    Directory of Open Access Journals (Sweden)

    M. S. Kappes

    2011-02-01

    Full Text Available Debris flows are among the most dangerous processes in mountainous areas due to their rapid rate of movement and long runout zone. Sudden and rather unexpected impacts produce not only damages to buildings and infrastructure but also threaten human lives. Medium- to regional-scale susceptibility analyses allow the identification of the most endangered areas and suggest where further detailed studies have to be carried out. Since data availability for larger regions is mostly the key limiting factor, empirical models with low data requirements are suitable for first overviews. In this study a susceptibility analysis was carried out for the Barcelonnette Basin, situated in the southern French Alps. By means of a methodology based on empirical rules for source identification and the empirical angle of reach concept for the 2-D runout computation, a worst-case scenario was first modelled. In a second step, scenarios for high, medium and low frequency events were developed. A comparison with the footprints of a few mapped events indicates reasonable results but suggests a high dependency on the quality of the digital elevation model. This fact emphasises the need for a careful interpretation of the results while remaining conscious of the inherent assumptions of the model used and quality of the input data.

  1. The use of airborne LiDAR data for the analysis of debris flow events in Switzerland

    Directory of Open Access Journals (Sweden)

    C. Scheidl

    2008-10-01

    Full Text Available A methodology of magnitude estimates for debris flow events is described using airborne LiDAR data. Light Detection And Ranging (LiDAR is a widely used technology to generate digital elevation information. LiDAR data in alpine regions can be obtained by several commercial companies where the automated filtering process is proprietary and varies from companies to companies. This study describes the analysis of geomorphologic changes using digital terrain models derived from commercial LiDAR data. The estimation of the deposition volumes is based on two digital terrain models covering the same area but differing in their time of survey. In this study two surveyed deposition areas of debris flows, located in the canton of Berne, Switzerland, were chosen as test cases. We discuss different grid interpolating techniques, other preliminary work and the accuracy of the used LiDAR data and volume estimates.

  2. Earth-like aqueous debris-flow activity on Mars at high orbital obliquity in the last million years.

    Science.gov (United States)

    de Haas, T; Hauber, E; Conway, S J; van Steijn, H; Johnsson, A; Kleinhans, M G

    2015-06-23

    Liquid water is currently extremely rare on Mars, but was more abundant during periods of high obliquity in the last few millions of years. This is testified by the widespread occurrence of mid-latitude gullies: small catchment-fan systems. However, there are no direct estimates of the amount and frequency of liquid water generation during these periods. Here we determine debris-flow size, frequency and associated water volumes in Istok crater, and show that debris flows occurred at Earth-like frequencies during high-obliquity periods in the last million years on Mars. Results further imply that local accumulations of snow/ice within gullies were much more voluminous than currently predicted; melting must have yielded centimetres of liquid water in catchments; and recent aqueous activity in some mid-latitude craters was much more frequent than previously anticipated.

  3. Geologic, geomorphic, and meteorological aspects of debris flows triggered by Hurricanes Frances and Ivan during September 2004 in the Southern Appalachian Mountains of Macon County, North Carolina (southeastern USA)

    Science.gov (United States)

    R. M. Wooten; K. A. Gillon; A. C. Witt; R. S. Latham; T. J. Douglas; J. B. Bauer; S. J. Fuemmeler; L. G. Lee

    2008-01-01

    In September 2004, rain from the remnants of Hurricanes Frances and Ivan triggered at least 155 landslides in the Blue Ridge Mountains of North Carolina. At least 33 debris flows occurred in Macon County, causing 5 deaths, destroying 16 homes, and damaging infrastructure. We mapped debris flows and debris deposits using a light-detecting and ranging digital elevation...

  4. Video monitoring in the Gadria debris flow catchment: preliminary results of large scale particle image velocimetry (LSPIV)

    Science.gov (United States)

    Theule, Joshua; Crema, Stefano; Comiti, Francesco; Cavalli, Marco; Marchi, Lorenzo

    2015-04-01

    Large scale particle image velocimetry (LSPIV) is a technique mostly used in rivers to measure two dimensional velocities from high resolution images at high frame rates. This technique still needs to be thoroughly explored in the field of debris flow studies. The Gadria debris flow monitoring catchment in Val Venosta (Italian Alps) has been equipped with four MOBOTIX M12 video cameras. Two cameras are located in a sediment trap located close to the alluvial fan apex, one looking upstream and the other looking down and more perpendicular to the flow. The third camera is in the next reach upstream from the sediment trap at a closer proximity to the flow. These three cameras are connected to a field shelter equipped with power supply and a server collecting all the monitoring data. The fourth camera is located in an active gully, the camera is activated by a rain gauge when there is one minute of rainfall. Before LSPIV can be used, the highly distorted images need to be corrected and accurate reference points need to be made. We decided to use IMGRAFT (an opensource image georectification toolbox) which can correct distorted images using reference points and camera location, and then finally rectifies the batch of images onto a DEM grid (or the DEM grid onto the image coordinates). With the orthorectified images, we used the freeware Fudaa-LSPIV (developed by EDF, IRSTEA, and DeltaCAD Company) to generate the LSPIV calculations of the flow events. Calculated velocities can easily be checked manually because of the already orthorectified images. During the monitoring program (since 2011) we recorded three debris flow events at the sediment trap area (each with very different surge dynamics). The camera in the gully was in operation in 2014 which managed to record granular flows and rockfalls, which particle tracking may be more appropriate for velocity measurements. The four cameras allows us to explore the limitations of camera distance, angle, frame rate, and image

  5. Parameterization of a numerical 2-D debris flow model with entrainment: a case study of the Faucon catchment, Southern French Alps

    National Research Council Canada - National Science Library

    Hussin, H.Y; Quan Luna, B; van Westen, C.J; Christen, M; Malet, J.P; van Asch, Th.W.J

    2012-01-01

      The occurrence of debris flows has been recorded for more than a century in the European Alps, accounting for the risk to settlements and other human infrastructure that have led to death, building...

  6. Subaerial salt extrusions in Iran as analogues of ice sheets, streams and glaciers

    Science.gov (United States)

    Talbot, Christopher J.; Pohjola, Veijo

    2009-12-01

    Ice (H 20) and salt (halite, NaCl) share many physical properties and resemble each other in hand specimens and subaerial gravity-driven flows. However, while most significant bodies of ice accumulate in cold highlands and gravity-spread where and soon after they form, most significant bodies of salt accumulate in tropical marine basins and have to be buried by > 1 km of other rocks before they flow. Buried salt is driven by differential loading into various categories of piercing structures known as diapirs. Many diapirs extrude onto the surface as sheets of allochthonous (out of place) salt. Thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years, mainly in the toes of passive continental margins and in orogenic belts where some are > 10 3 km 2 in area. Most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in Iran. These were compared to ice glaciers soon after they were introduced to western science, a comparison that has been neglected since. Here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists. The profiles, internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss. However, whereas snow merely compacts where it accumulates, salt sheets are fed from below by already deformed salt. When salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier-like flows known as namakiers. After locally exhausting their deep source layers, salt fountains spread to the profiles of viscous droplets normal for ice caps. Ice typically deforms at > 80% (usually > 90%) of its absolute melting temperature while most salt deforms at memories than in ice

  7. Parameterization of a numerical 2-D debris flow model with entrainment: a case study of the Faucon catchment, Southern French Alps

    Science.gov (United States)

    Hussin, H. Y.; Luna, B. Quan; van Westen, C. J.; Christen, M.; Malet, J.-P.; van Asch, Th. W. J.

    2012-10-01

    The occurrence of debris flows has been recorded for more than a century in the European Alps, accounting for the risk to settlements and other human infrastructure that have led to death, building damage and traffic disruptions. One of the difficulties in the quantitative hazard assessment of debris flows is estimating the run-out behavior, which includes the run-out distance and the related hazard intensities like the height and velocity of a debris flow. In addition, as observed in the French Alps, the process of entrainment of material during the run-out can be 10-50 times in volume with respect to the initially mobilized mass triggered at the source area. The entrainment process is evidently an important factor that can further determine the magnitude and intensity of debris flows. Research on numerical modeling of debris flow entrainment is still ongoing and involves some difficulties. This is partly due to our lack of knowledge of the actual process of the uptake and incorporation of material and due the effect of entrainment on the final behavior of a debris flow. Therefore, it is important to model the effects of this key erosional process on the formation of run-outs and related intensities. In this study we analyzed a debris flow with high entrainment rates that occurred in 2003 at the Faucon catchment in the Barcelonnette Basin (Southern French Alps). The historic event was back-analyzed using the Voellmy rheology and an entrainment model imbedded in the RAMMS 2-D numerical modeling software. A sensitivity analysis of the rheological and entrainment parameters was carried out and the effects of modeling with entrainment on the debris flow run-out, height and velocity were assessed.

  8. Parameterization of a numerical 2-D debris flow model with entrainment: a case study of the Faucon catchment, Southern French Alps

    Directory of Open Access Journals (Sweden)

    H. Y. Hussin

    2012-10-01

    Full Text Available The occurrence of debris flows has been recorded for more than a century in the European Alps, accounting for the risk to settlements and other human infrastructure that have led to death, building damage and traffic disruptions. One of the difficulties in the quantitative hazard assessment of debris flows is estimating the run-out behavior, which includes the run-out distance and the related hazard intensities like the height and velocity of a debris flow. In addition, as observed in the French Alps, the process of entrainment of material during the run-out can be 10–50 times in volume with respect to the initially mobilized mass triggered at the source area. The entrainment process is evidently an important factor that can further determine the magnitude and intensity of debris flows. Research on numerical modeling of debris flow entrainment is still ongoing and involves some difficulties. This is partly due to our lack of knowledge of the actual process of the uptake and incorporation of material and due the effect of entrainment on the final behavior of a debris flow. Therefore, it is important to model the effects of this key erosional process on the formation of run-outs and related intensities. In this study we analyzed a debris flow with high entrainment rates that occurred in 2003 at the Faucon catchment in the Barcelonnette Basin (Southern French Alps. The historic event was back-analyzed using the Voellmy rheology and an entrainment model imbedded in the RAMMS 2-D numerical modeling software. A sensitivity analysis of the rheological and entrainment parameters was carried out and the effects of modeling with entrainment on the debris flow run-out, height and velocity were assessed.

  9. A 2D-3D strategy for resolving tsunami-generated debris flow in urban environments

    Science.gov (United States)

    Birjukovs Canelas, Ricardo; Conde, Daniel; Garcia-Feal, Orlando; João Telhado, Maria; Ferreira, Rui M. L.

    2017-04-01

    The incorporation of solids, either sediment from the natural environment or remains from buildings or infrastructures is a relevant feature of tsunami run-up in urban environments, greatly increasing the destructive potential of tsunami propagation. Two-dimensional (2D) models have been used to assess the propagation of the bore, even in dense urban fronts. Computational advances are introduced in this work, namely a fully lagrangian, 3D description of the fluid-solid flow, coupled with a high performance meshless implementation capable of dealing with large domains and fine discretizations. A Smoothed Particle Hydrodynamics (SPH) Navier-Stokes discretization and a Distributed Contact Discrete Element Method (DCDEM) description of solid-solid interactions provide a state-of the-art fluid-solid flow description. Together with support for arbitrary geometries, centimetre scale resolution simulations of a city section in Lisbon downtown are presented. 2D results are used as boundary conditions for the 3D model, characterizing the incoming wave as it approaches the coast. It is shown that the incoming bore is able to mobilize and incorporate standing vehicles and other urban hardware. Such fully featured simulation provides explicit description of the interactions among fluid, floating debris (vehicles and urban furniture), the buildings and the pavement. The proposed model presents both an innovative research tool for the study of these flows and a powerful and robust approach to study, design and test mitigation solutions at the local scale. At the same time, due to the high time and space resolution of these methodologies, new questions are raised: scenario-building and initial configurations play a crucial role but they do not univocally determine the final configuration of the simulation, as the solution of the Navier-Stokes equations for high Reynolds numbers possesses a high number of degrees of freedom. This calls for conducting the simulations in a

  10. What does control debris-flow channel-bed erosion? A LiDAR-based change detection compared to velocity, momentum and pressure derived from a calibrated model.

    Science.gov (United States)

    Dietrich, Andreas; Krautblatter, Michael

    2017-04-01

    Erosion capacity and bedrock incision of debris flows are poorly understood. Here we present a unique study of a recent debris-flow event (06/2015) in the Allgaeu Alps (Germany). More than 50 terrestrial laser scan positions (TLS) of a mountain torrent (1.2 km) have been used to detect geomorphic change by comparing the new elevation model to an airborne laser scan (ALS) performed in 2007. It shows that the debris flow incised up to 4 m into the channel-bed, resulting in an erosion volume of 9.700 ± 1.600 m3 and a deposition volume of 1.200 ± 300 m3 in the channel. Errors were considered by a spatial variable threshold based on the point density of the ALS and TLS as well as the slopes of the DEMs. A numerical single-phase model (RAMMS Debris Flow) was carefully calibrated with detailed field data. The derived velocity, pressure and momentum of the model were compared to the geomorphic change. It shows that all three parameters explain erosion by more than 50 %. The results contribute to better define the possibilities and limitations of a combined TLS and ALS analysis for geomorphic change detection in complex terrain. The explanation of the erosion capacity with simulated parameters of a debris flow might be revolutionary for upcoming predictions of potential future debris-flow volumes.

  11. Testing the use of OSL from quartz grains for dating debris flows in Miyun, northeast Beijing, China

    DEFF Research Database (Denmark)

    Zhao, Qiuyue; Thomsen, Kristina Jørkov; Murray, Andrew

    2015-01-01

    Extreme seasonal summer rain storms are common in the mountains to the north east of Beijing and these often result in mass movement of sediment slurries transported for up to a few km. These debris flows can be deadly and are very destructive to infrastructure and agriculture. This project tests...... the application of luminescence dating to determining the return frequency of such extreme events. The high sediment concentration and the very short flow duration gives very little opportunity for daylight resetting during transport and only a small fraction of the total mass is likely to be reset before...

  12. Four-way coupling of a three-dimensional debris flow solver to a Lagrangian Particle Simulation: method and first results

    Science.gov (United States)

    von Boetticher, Albrecht; Rickenmann, Dieter; McArdell, Brian; Kirchner, James W.

    2017-04-01

    Debris flows are dense flowing mixtures of water, clay, silt, sand and coarser particles. They are a common natural hazard in mountain regions and frequently cause severe damage. Modeling debris flows to design protection measures is still challenging due to the complex interactions within the inhomogeneous material mixture, and the sensitivity of the flow process to the channel geometry. The open-source, OpenFOAM-based finite-volume debris flow model debrisInterMixing (von Boetticher et al, 2016) defines rheology parameters based on the material properties of the debris flow mixture to reduce the number of free model parameters. As a simplification in this first model version, gravel was treated as a Coulomb-viscoplastic fluid, neglecting grain-to-grain collisions and the coupling between the coarser gravel grains and the interstitial fluid. Here we present an extension of that solver, accounting for the particle-to-particle and particle-to-boundary contacts with a Lagrangian Particle Simulation composed of spherical grains and a user-defined grain size distribution. The grain collisions of the Lagrangian particles add granular flow behavior to the finite-volume simulation of the continuous phases. The two-way coupling exchanges momentum between the phase-averaged flow in a finite volume cell, and among all individual particles contained in that cell, allowing the user to choose from a number of different drag models. The momentum exchange is implemented in the momentum equation and in the pressure equation (ensuring continuity) of the so-called PISO-loop, resulting in a stable 4-way coupling (particle-to-particle, particle-to-boundary, particle-to-fluid and fluid-to-particle) that represents the granular and viscous flow behavior of debris flow material. We will present simulations that illustrate the relative benefits and drawbacks of explicitly representing grain collisions, compared to the original debrisInterMixing solver.

  13. Evolution of a giant debris flow in the transitional mountainous region between the Tibetan Plateau and the Qinling Mountain range, Western China: Constraints from broadband seismic records

    Science.gov (United States)

    Huang, Xinghui; Li, Zhengyuan; Yu, Dan; Xu, Qiang; Fan, Junyi; Hao, Zhen; Niu, Yanping

    2017-10-01

    The catastrophic Sanyanyu and Luojiayu debris flows, which were induced by heavy rainfall, occurred at approximately midnight, August 7th, 2010 (Beijing time, UTC + 8) and claimed 1,765 lives. Most seismic stations located within 150 km did not detect the debris flows except for the closest seismic station, ZHQ, indicating that the seismic signals generated by the debris flows decayed rapidly. We analyzed broadband seismic signals from the ZHQ seismic station, beginning approximately 20 min before the outbreak of the Sanyanyu debris flow, to rebuild its evolution processes. Seismic signals can detect development of the Sanyanyu debris flow approximately 20 min after a heavy rain started falling in its initiation area; this time was characterized by a gradual increase in seismic amplitude accompanied by a series of spike signals that were probably generated by rock collapses within the catchment. The frequency contents and the characteristics of seismic signals before and after 23:33:15 (T1) are distinctively different, which we interpret as being generated by a large quantity of flowing material entering the main channel, marking the formation of the Sanyanyu debris flow. We attribute seismic amplitude increases between 23:33:15 (T1) and 23:34:26 (T2) and between 23:35:40 (T3) and 23:36:49 (T4) to entrainment of the deposit material after initiation of the debris flow and to its flow through a colluvial deposit area, respectively. The main frequency band broadening of seismic signals after 23:37:30 (T5) is believed to have been induced by impacts between the flowing material and check dams.

  14. Sample size matters: Investigating the optimal sample size for a logistic regression debris flow susceptibility model

    Science.gov (United States)

    Heckmann, Tobias; Gegg, Katharina; Becht, Michael

    2013-04-01

    Statistical approaches to landslide susceptibility modelling on the catchment and regional scale are used very frequently compared to heuristic and physically based approaches. In the present study, we deal with the problem of the optimal sample size for a logistic regression model. More specifically, a stepwise approach has been chosen in order to select those independent variables (from a number of derivatives of a digital elevation model and landcover data) that explain best the spatial distribution of debris flow initiation zones in two neighbouring central alpine catchments in Austria (used mutually for model calculation and validation). In order to minimise problems arising from spatial autocorrelation, we sample a single raster cell from each debris flow initiation zone within an inventory. In addition, as suggested by previous work using the "rare events logistic regression" approach, we take a sample of the remaining "non-event" raster cells. The recommendations given in the literature on the size of this sample appear to be motivated by practical considerations, e.g. the time and cost of acquiring data for non-event cases, which do not apply to the case of spatial data. In our study, we aim at finding empirically an "optimal" sample size in order to avoid two problems: First, a sample too large will violate the independent sample assumption as the independent variables are spatially autocorrelated; hence, a variogram analysis leads to a sample size threshold above which the average distance between sampled cells falls below the autocorrelation range of the independent variables. Second, if the sample is too small, repeated sampling will lead to very different results, i.e. the independent variables and hence the result of a single model calculation will be extremely dependent on the choice of non-event cells. Using a Monte-Carlo analysis with stepwise logistic regression, 1000 models are calculated for a wide range of sample sizes. For each sample size

  15. Potential postwildfire debris-flow hazards: a prewildfire evaluation for the Sandia and Manzano Mountains and surrounding areas, central New Mexico

    Science.gov (United States)

    Tillery, Anne C.; Haas, Jessica R.; Miller, Lara W.; Scott, Joe H.; Thompson, Matthew P.

    2014-01-01

    Wildfire can drastically increase the probability of debris flows, a potentially hazardous and destructive form of mass wasting, in landscapes that have otherwise been stable throughout recent history. Although there is no way to know the exact location, extent, and severity of wildfire, or the subsequent rainfall intensity and duration before it happens, probabilities of fire and debris-flow occurrence for different locations can be estimated with geospatial analysis and modeling efforts. The purpose of this report is to provide information on which watersheds might constitute the most serious, potential, debris-flow hazards in the event of a large-scale wildfire and subsequent rainfall in the Sandia and Manzano Mountains. Potential probabilities and estimated volumes of postwildfire debris flows in the unburned Sandia and Manzano Mountains and surrounding areas were estimated using empirical debris-flow models developed by the U.S. Geological Survey in combination with fire behavior and burn probability models developed by the U.S. Department of Agriculture Forest Service. The locations of the greatest debris-flow hazards correlate with the areas of steepest slopes and simulated crown-fire behavior. The four subbasins with the highest computed debris-flow probabilities (greater than 98 percent) were all in the Manzano Mountains, two flowing east and two flowing west. Volumes in sixteen subbasins were greater than 50,000 square meters and most of these were in the central Manzanos and the western facing slopes of the Sandias. Five subbasins on the west-facing slopes of the Sandia Mountains, four of which have downstream reaches that lead into the outskirts of the City of Albuquerque, are among subbasins in the 98th percentile of integrated relative debris-flow hazard rankings. The bulk of the remaining subbasins in the 98th percentile of integrated relative debris-flow hazard rankings are located along the highest and steepest slopes of the Manzano Mountains. One

  16. Atmospheric circulation patterns, cloud-to-ground lightning, and locally intense convective rainfall associated with debris flow initiation in the Dolomite Alps of northeastern Italy

    Science.gov (United States)

    Underwood, S. Jeffrey; Schultz, Michael D.; Berti, Metteo; Gregoretti, Carlo; Simoni, Alessandro; Mote, Thomas L.; Saylor, Anthony M.

    2016-02-01

    The Dolomite Alps of northeastern Italy experience debris flows with great frequency during the summer months. An ample supply of unconsolidated material on steep slopes and a summer season climate regime characterized by recurrent thunderstorms combine to produce an abundance of these destructive hydro-geologic events. In the past, debris flow events have been studied primarily in the context of their geologic and geomorphic characteristics. The atmospheric contribution to these mass-wasting events has been limited to recording rainfall and developing intensity thresholds for debris mobilization. This study aims to expand the examination of atmospheric processes that preceded both locally intense convective rainfall (LICR) and debris flows in the Dolomite region. 500 hPa pressure level plots of geopotential heights were constructed for a period of 3 days prior to debris flow events to gain insight into the synoptic-scale processes which provide an environment conducive to LICR in the Dolomites. Cloud-to-ground (CG) lightning flash data recorded at the meso-scale were incorporated to assess the convective environment proximal to debris flow source regions. Twelve events were analyzed and from this analysis three common synoptic-scale circulation patterns were identified. Evaluation of CG flashes at smaller spatial and temporal scales illustrated that convective processes vary in their production of CF flashes (total number) and the spatial distribution of flashes can also be