Debris Flow Behavior Research Articles

Flume model test on the behavior of debris flows into the reservoir and the impact pressure acting on the dam embankment

Flume model test on the behavior of debris flows into the reservoir and the impact pressure acting on the dam embankment

Exploring debris flow deposit morphology in river valleys: Insights from physical modeling experiments

A comprehensive understanding of the deposit morphodynamics of debris flows in river valleys is crucial for disaster prevention and mitigation in mountainous areas. However, debris flows in river valleys are complex and variable, and the influence of the composition and terrain on deposit mechanisms and morphology remains unclear. In this study, a series of laboratory experiments were conducted to investigate the impact of the water content, slope, and grain size distribution on the deposit morphology of debris flows in river valleys. In the experiments, debris flows form narrow and elongated shuttle-shaped deposits upon entering river valleys. Increased water content and slope enhance the mobility of debris flows, resulting in wider deposit widths, gentler deposit slopes, and larger deposit areas. An increase in the gravel fraction partially facilitates the movement and deposition of debris flows. However, a large number of coarse particles may increase internal friction within the debris flow, hindering the spread of deposits and resulting in a relatively concentrated deposit with a steeper morphology. Furthermore, the debris flow regime shifts from friction to collision as the water content, slope, and gravel fraction increase. Debris flows dominated by collision forces exhibit higher mobility and a wider impact area, potentially leading to more severe disaster consequences. Compared with unconfined debris flows, the deposit area of debris flows in the river valley is smaller, and the deposit width to height ratio is larger. There is a power function relationship between deposition area and Savage number in river valleys. Additionally, particle sorting and flow regime transformation during the movement and deposition of debris flows can significantly impact the morphology and internal structure of the deposits in river valleys and then affect the development of debris flow dam breaching. In summary, this study utilized experiments to simulate natural debris flows, offering fresh insights into the depositional behavior of debris flows in river valleys.

Impact Behavior of Dense Debris Flows Regulated by Pore‐Pressure Feedback

AbstractThe impact dynamics of dilute debris flows (typically volumetric solid fractions<50%) have been extensively investigated within the framework of hydraulics. For dense debris flows, the impact mechanisms have been poorly studied. From a geotechnical viewpoint, the feedback between granular dilatancy and pore‐pressure response may play an important role in the dense debris‐flow regime. In this study, the impact behavior of dense and dilute debris flows in an instrumented flume is analyzed. The basal stresses (normal/shear stresses, pore‐fluid pressure) and impact pressure on a rigid barrier are measured. A time‐dependent creeping mode is observed for the impact process of slow‐moving dense debris flows, which cannot be accurately estimated using current debris‐flow load models. At the grain scale, this macroscopic creeping mode is a result of the feedback between granular dilatancy and pore‐pressure response. This feedback can be further characterized by examining the timescales associated with pore‐pressure generation and dissipation. The regulation of pore‐pressure feedback on basal shear stress, impact load, and state of static deposit is revealed. Finally, a tentative phase diagram is proposed for dense and dilute debris‐flow impact. The proposed framework complements the theory for debris‐flow impact loads.

Debris-flow activity in the Japanese Alps is controlled by extreme precipitation and ENSO – Evidence from multi-centennial tree-ring records

Japanese mountains are recurrently affected by mass movements and sediment-related disasters. Large efforts have therefore been undertaken to enhance understanding of the impacts and triggering of recent disasters, but ancient and continuous records to put recent events into perspective are still lacking. Here, we present a multi-centennial tree-ring-based debris-flow reconstruction in two size-contrasting torrential catchments of the Japanese Alps. We analyzed 197 affected trees growing on debris-flow fans and along torrential channels, which allowed us to identify 62 past events (38 and 24 in each catchment) from the late 19th century to today. The new chronology shows a non-stationary behavior of debris flows in the long-term, and an upward trend in debris flow activity over the last decades. Analysis of the 3-day rainfall legacy explains the occurrence of debris flows best, whereas rainfall thresholds show a positive trend linked to an increase in the occurrence of extreme precipitation over the last decades. Our results clearly support a link between debris flows with the passage of typhoons as well as La Niña events. The unprecedented length of the debris-flow record provided here opens new avenues for climate change and sediment-disaster research in Japan. Thus, our findings have important implications for the understanding of past, recent, and near-future debris-flow trajectories under climate change scenarios.

A new coupled depth-integrated model incorporating 3D DDA on debris flow with large boulders

Debris flow frequently occurs in mountainous regions and can cause serious damages to residents and structures in susceptible areas. Conventional debris flow simulation (DFS) with a depth-integrated model has been widely used to study debris flow behavior. In DFS, two-phase fluid of water and solid is considered. However, large boulders are often entrained in debris flows in practice. Obviously, the behaviors of debris flow with large boulders cannot be correctly described by DFS with two-phase fluid model. Therefore, a new coupling method for simulating debris flow with large boulders is developed by combining three-dimensional discontinuous deformation analysis (3D DDA) with conventional DFS. The dynamic behavior of those entrained boulders in debris flow can be solved by 3D DDA while the kinematic and mechanic behaviors of two-phase fluid are predicted by conventional DFS. An interactive module is introduced to address the interaction between solid motion in 3D DDA module and fluid field in DFS module. The imposed interaction forces from fluid on solid block include buoyancy, drag force and static pressure. Drag effect between adjacent blocks in debris flow is evaluated empirically to make the calculated drag force more realistic. For the block resistance to the debris flow, an equivalent solution is proposed by time-varying elevation of terrain node. Subsequently, the developed 3D DDA-DFS method is validated by several simple examples. Further, a case study is carried out to discuss the kinematic and mechanic behaviors of debris flow with large boulders based on a real catchment. The dam safety under different dam material properties is investigated when debris flow with large boulders happens. The simulation results suggest debris flow with large boulders can be more destructive than a pure debris flow. The developed 3D DDA-DFS method is a promising approach to study debris flow with large boulders.

Debris Flow Behaviors During the 2018 West Japan Rainstorm Disaster

Debris Flow Behaviors During the 2018 West Japan Rainstorm Disaster

Three-dimensional modeling of the impact behavior of debris flows in areas affected by earthquakes

Three-dimensional modeling of the impact behavior of debris flows in areas affected by earthquakes

Control mechanisms of pore-pressure dissipation in debris flows

Debris flows are typically saturated mixtures of debris grains and interstitial slurry consisting of water and clay. Pore pressure in slurry plays a crucial role in the characteristic behavior and runout of debris flows. However, the mechanisms that cause pore pressures to diffuse are still uncertain. Here we report consolidation tests to investigate the effects of debris composition (uniformly graded and widely graded) and slurry density on the dissipation of pore pressure. Pore pressures of debris flows were found to dissipate at contrasting rates ranging from a few seconds to dozens of hours and dissipation time strongly depended on slurry density. We observed an abrupt change in pore-pressure dissipation time at a critical slurry density. We propose that a critical pore throat controls the permeability of a debris material and regulates the pore-pressure dissipation based on percolation theory. This hypothesis is verified by pore-network models from a micro-computed tomography analysis with high resolution. The critical pore throat of the uniformly graded debris material is larger than that of widely graded debris material due to the difference in the porosity. The permeabilities and hydraulic diffusivities of debris flows significantly decrease once critical pore throats are blocked, resulting in a change of pore-pressure dissipation. Critical slurry density is approximately linearly correlated with the porosity of debris flows. Our results highlight opportunities to use micro-structural properties for interpreting debris-flow behavior.

Testing applicability of image analysis for measurements of sediment concentration in laboratory experiments

Flume experiments are typically conducted to reveal the detailed behavior of debris flows. Direct sampling at the lower end of a flume has been used to measure sediment concentrations in flume experiments; however, direct sampling measurements under non-steady or non-equilibrium conditions are difficult. In contrast, image analysis methods can acquire spatiotemporal high-resolution data in a non-contact manner. In this study, we conducted experiments in which a homogenous sediment concentration field of 0 ~ 20 % was prepared in a water tank with a depth of 10 cm using coarse and fine sediments. We filmed the experiments and verified the relationships between sediment concentrations and image features in a fixed area. As a result, the mean of pixel values for coarse sediments depends on the sediment concentration of up to 10 % and the number of mode pixels for fine sediments depends on the sediment concentration of up to 20 %. We then analyzed factors influencing image features and identified three processes. Furthermore, we analyzed the effects of the sediment grain size on image features, and the results show that both the brightness index and brightness uniformity index of images are affected. In conclusion, these findings indicate that image analysis can be used to clarify both sediment concentration and grain size.

기후변화를 고려한 토석류 재해취약지역 레질리언스 강화를 위한 연구

Recently, climate change has caused serious natural disasters at the vulnerable areas with many mountainous regions. This study analyzes the behavior of debris flow with respect to time elapse by applying various precipitation, mountain slope change, and the categories of vegetation loosened in mountainous areas. The behavior of debris flow is debris flow discharge and water depth. In addition, the runout length of debris flow passed through the channel and reached the downstream according to the change of the water supply and slope was measured. The larger the supply flow, the higher the debris flow discharge, and the second peak value became faster as the supply flow increased, and the slope became steeper. In the category where the multiplier of vegetation for debris flow is large, the fluctuation period was made long, and the amplitude of the fluctuation was also made large. As for the debris flow runout length, the supply flow was large and it was spread in a considerable range on steep slopes. This study will provide various information such as establishing measures for debris flow occurring in vulnerable areas to natural disasters due to climate change, or establishing a plan for strengthening resilience.

Influence of Debris-Flow Impact on the Structural Stability of Check Dams

Small check dams are widely used in the Republic of Korea to mitigate and prevent sediment-driven damages by mountain torrents. This study aimed to quantify the combined effects of debris-flow impact forces and earth pressures from dam sedimentations on the structural stability of a dam by incorporating the change in the longitudinal profile of the channel bed owing to sediment deposition. A debris-flow simulation model (Hyper Kanako) was used to reproduce the debris-flow behavior from the 2011 Mt. Umyeon landslide (Seoul, The Republic of Korea). Finite element analysis was conducted to analyze the structural stability of the check dam under various debris discharge and sedimentation scenarios. The magnitudes of impact forces that were exerted on the check dam ranged from 81.76 kPa under a non-deposition scenario to 123.04 kPa under a 100% deposition scenario. The resultant tensile and compressive stresses were found to be up to 0.80 and 0.35 MPa, respectively, which were lower than the maximum allowable strengths of the dam, securing sufficient strength for the dam stability. Overall, the proposed approach can be applied to obtain a better understanding of the resultant internal stresses experienced during debris flow and sediment deposition, thereby providing valuable information for the structural analysis and safety assessment of check dams.

Study on the effect of entrainment on the behavior of debris flows using a 3D Coupled Eulerian–Lagrangian finite element method

Study on the effect of entrainment on the behavior of debris flows using a 3D Coupled Eulerian–Lagrangian finite element method

Discussion on erosion and accumulation behaviours in the process of soil-rock flow migration with deep learning experimental analysis method and numerical simulation

The frequency of debris flows occurring has increased in Taiwan and mitigation strategies are important to protect property and save lives. Dr Shih-Hao Chou is a research scholar based in the Department of Mechanical Engineering, National Central University, Taiwan, is exploring how AI and deep learning can be applied to the mitigation of debris flow. He is investigating the physical mechanisms of debris flow, as well as migration behaviour and the potential scale of future disasters, which includes analysing flow behaviour and comparing it with an occurrence model. In their work, Chou and his collaborators are using a deep learning experimental analysis method to observe the current situation of debris flow in real time, and further predict the downstream debris flow behaviour. The researchers are also utilising numerical simulation in order to observe the internal movement behaviour in the earth-rock flow field and the damage caused to engineering facilities. Chou is conducting this research in collaboration with Professor Hsiau Shusan from the Department of Mechanical Engineering, National Central University. Chou is also looking at erosion transport or sedimentation behaviour in the process of collapse and flow, responding to a knowledge gap in this area. This involves studying the erosion and sedimentation behaviour of an artificial dam-break particle flow field on the bottom bed and, following the dam break, studying the particles in the collapse process using image and particle tracking technology and numerical simulation technology, looking at avalanche speed, avalanche time, erosion and sedimentation phenomena.

Global debris flow susceptibility based on a comparative analysis of a single global model versus a continent-by-continent approach

Debris flows, and landslides in general, are worldwide catastrophic phenomena. As world population and urbanization grow in magnitude and geographic coverage, the need exists to extend focus, research, and modeling to a continental and global scale. Although debris flow behavior and parameters are local phenomena, sound generalizations can be applied to debris flow susceptibility analyses at larger geographic extents based on these criteria. The focus of this research is to develop a global debris flow susceptibility map by modeling at both a continental scale for all continents and by a single global model and determine whether a global model adequately represents each continent. Probability Density, Conditional Probability, Certainty Factor, Frequency Ratio, and Maximum Entropy statistical models were developed and evaluated for best model performance using fourteen environmental factors generally accepted as the most appropriate debris flow predisposing factors. Global models and models for each continent were then developed and evaluated against verification data. The comparative analysis demonstrates that a single global model performs comparably or better than individual continental models for a majority of the continents, resulting in a debris flow susceptibility map of the world useful for in-depth research, international planning, and future debris flow susceptibility modeling and determining societal impacts.

Long‐Runout‐Landslide‐Induced Debris Flow: The Role of Fine Sediment Deposition Processes in Debris Flow Propagation

AbstractLandslide‐induced debris flows can travel long distances. Many field studies, laboratory experiments, and theoretical studies have been conducted to clarify the mechanisms of long‐runout landslides. However, information concerning landslide‐induced debris flows is still inadequate despite several explanations proposed. Thus, we collected various forms of data, including video images and light detection and ranging data, for a landslide‐induced debris flow that occurred on 28 July 2015, in Fukaminato River, Japan, and clarified the debris flow behavior from initiation to deposition. We showed that the water content of the debris flow should only be approximately 30% immediately after landslides occurred at the site. However, a fluid phase‐dominated flow flowed over 1.2 km, expanding the damaged area. We inferred that the fine sediments behaved as part of the interstitial fluid in the debris flow and that, during debris flow deposition, some fine sediments were stored in the interstitial space of the riverbed and did not contribute to forming the skeleton of deposits. We conducted a numerical simulation to test the processes of fluid phase‐dominated flow propagation, focusing on the flow and deposition of fine sediments. Our simulation results suggest that fine sediments' flow and depositional processes significantly influence both the initiation of fluid phase‐dominated debris flow and the travel distance of landslide‐induced debris flow.

Simulation of runout behavior of submarine debris flows over regional natural terrain considering material softening

Evaluation of regional submarine debris flows is critical for quantitative assessment of vulnerable areas and reasonable design of geohazard mitigation measures. In this article, an efficient numerical model for kinematics of regional submarine debris flows is developed. The proposed model can simulate the runout process and morphological evolution of submarine debris flows over natural 3D terrain by solving 1D depth-averaged governing equations in a geographic information system (GIS). A strength softening equation is introduced to capture the degradation of sliding material strength during the runout process. The model is validated by a flume test, two slump tests, and a real case history of submarine debris flow (St Niklausen slide). Applications to Shenhu area, South China Sea, are presented to demonstrate the ability of the proposed model over complex natural terrain and the importance of considering material softening. Results show that the proposed model is capable of simulating the whole debris flow process and tracking the propagation of the sliding material. Simulation of submarine debris flow without material softening will underestimate the disaster consequences. In addition, the influences of the ambient fluid and the yield strength of the sliding material on its runout behavior are also discussed.

A Case Study on the Closed-Type Barrier Effect on Debris Flows at Mt. Woomyeon, Korea in 2011 via a Numerical Approach

Debris flows are capable of flowing with high velocities and causing significant economic and infrastructural damage. As a hazard mitigation measure, physical barriers are frequently installed to dissipate the energy of debris flows. However, there is a lack of understanding on how barriers affect and interact with debris-flow behavior (e.g., velocity and volume). This study investigated the changes in debris-flow characteristics depending on the installation location of barriers. Mt. Woomyeon, which is located in Seoul, Korea, was the site of a major debris-flow event in 2011. This study modeled this event using DAN3D, numerical software based on smoothed particle hydrodynamics (SPH). Our numerical approach assessed changes in debris-flow behavior, including velocity and volume, as the debris flow interacts with four closed-type barriers installed at separate points along the flow path. We used DAN3D to model the barriers via terrain elevation modifications. The presence of a closed-type barrier results in the reduction in the debris-flow velocity and volume compared to when no barrier is present. Most notably, the closer a barrier is installed to the debris source, the greater the velocity decrease. By contrast, a barrier that is constructed further downstream allows the debris flow to undergo entrainment-driven growth before confronting the barrier, resulting in a larger debris deposition volume that can often cause overflow, as shown at our particular study site. The presented results highlight the effectiveness of barriers as a method of hazard mitigation by providing insight into how such installations can alter debris-flow behavior. In addition, the findings can provide a reference for future debris-flow barrier designs, increasing the effectiveness and efficiency of such barrier systems.

DebrisFlow Predictor: an agent-based runout program for shallow landslides

Abstract. Credible models of landslide runout are a critical component of hazard and risk analysis in the mountainous regions worldwide. Hazard analysis benefits enormously from the number of available landslide runout models that can recreate events and provide key insights into the nature of landsliding phenomena. Regional models that are easily employed, however, remain a rarity. For debris flows and debris avalanches, where the impacts may occur some distance from the source, there remains a need for a practical, predictive model that can be applied at the regional scale. We present, herein, an agent-based simulation for debris flows and debris avalanches called DebrisFlow Predictor. A fully predictive model, DebrisFlow Predictor employs autonomous subroutines, or agents, that act on an underlying digital elevation model (DEM) using a set of probabilistic rules for scour, deposition, path selection, and spreading behavior. Relying on observations of aggregate debris flow behavior, DebrisFlow Predictor predicts landslide runout, area, volume, and depth along the landslide path. The results can be analyzed within the program or exported in a variety of useful formats for further analysis. A key feature of DebrisFlow Predictor is that it requires minimal input data, relying primarily on a 5 m DEM and user-defined initiation zones, and yet appears to produce realistic results. We demonstrate the applicability of DebrisFlow Predictor using two very different case studies from distinct geologic, geomorphic, and climatic settings. The first case study considers sediment production from the steep slopes of Papua, the island province of Indonesia; the second considers landslide runout as it affects a community on Vancouver Island off the west coast of Canada. We show how DebrisFlow Predictor works, how it performs compared to real world examples, what kinds of problems it can solve, and how the outputs compare to historical studies. Finally, we discuss its limitations and its intended use as a predictive regional landslide runout tool. DebrisFlow Predictor is freely available for non-commercial use.

Monitoring Debris-Flow Surges and Triggering Rainfall at the Lattenbach Creek, Austria

ABSTRACT Debris-flow events often comprise a sequence of surges, sometimes termed “roll waves.” The reason for this surging behavior is still a matter of debate. Explanations include the growth of hydraulic instabilities, periodic sediment deposition and release, or grain size sorting. High-resolution field measurements together with triggering rainfall characteristics are rare. We present results for 3 years of monitoring debris-flow events at Lattenbach Creek in the western part of Austria. The monitoring system includes a weather station in the headwaters of the creek, radar sensors for measuring flow depth at different locations along the channel, as well as a two-dimensional rotational laser sensor installed over a fixed cross section that yields a three-dimensional surface model of the passing debris-flow event. We find that the debris flows at Lattenbach Creek were all triggered by rainstorms of less than 2 hours and exhibited surges for each observed event. The velocities of the surges were up to twice as high as the front velocity. Often, the first surges that included boulders and woody debris had the highest flow depth and discharge and showed an irregular geometry. The shape of the surges in the second half of the flow, which carried smaller grain sizes and less woody debris, were rather regular and showed a striking geometric similarity, but still high velocities. The results of our monitoring efforts aim to improve our understanding of the surging behavior of debris flows and provide data for model testing for the scientific community.

Role of the Rheological Parameters in Debris Flow Modelling

Nowadays, the debris flow model has become an essential part of risk analysis and impact engineering. Coupled with field observations and historical records, these models have proven powerful tools to understand the behaviour of debris flow in complex terrain. However, their application poses several new challenges to scholars and engineers. A detailed understanding of the debris flow phenomena requires a sound knowledge of the shallow water equation and rheological model used to simulate the debris flow hazard. In this study, important rheological models used to analyse the debris flow process and their limitations have been highlighted. Furthermore, the suitability of the Voellmy-Salm rheological model has been studied for 2D pyroclastic flow taking different combinations of the coefficient of friction namely coulomb friction coefficient \\i,and turbulent coefficient of friction £ using IMEX SFLOW 2D dynamic continuum model. It was found that velocity and runout distances are significantly influenced by the variation of the coefficient of the turbulent friction © at a large scale. It is then concluded that the identification of a suitable rheological model is necessary to simulate the precise behaviour of complex and heterogeneous debris flow