Debris Flow Movement Research Articles

Numerical investigation of debris flows using a two-phase continuum model incorporating a visco-inertial rheology

The motion of debris flows is controlled by the interaction of their fluid and solid components. In this work, a general two-phase model framework (Pudasaini, 2012) is adopted which captures the coupled effects of the individual phase dynamics to the overall mobility. While solving the model equations, the fluid phase is treated as a viscous Newtonian liquid while the solid phase is considered to be a granular material obeying a recently developed visco-inertial constitutive rheology. Solid and fluid components in the mixture are coupled through the interaction forces, namely buoyancy, drag, and virtual mass. The model is calibrated against results from instrumented flume experiments and from field measurements of saturated, channelized debris flows. The numerical model captures the enhanced mobility of debris flows due to the presence of interstitial fluid and provides better predictions of the flow dynamics relative to those obtained from single-phase frameworks. Better modeling agreement is obtained for granular-fluid flows with relatively high fluid content. The model is then used to simulate real debris flow events, including a case that occurred in the proximity of the Sichuan-Tibet Railway, where good agreement with reported field measurements is obtained. This modeling framework is expected to improve mitigation strategies for debris flows hazards.

Rheological characteristics of marine sediments from the Ulleung Basin, East Sea to estimate the mobility of submarine landslides

In estimating the geohazards posed by submarine landslides, the rheological properties of marine sediments are of significant importance for their postfailure dynamics. We report an experimental study of the rheological behavior of marine sediments taken from the Ulleung Basin, East Sea and their influence on numerical simulations of debris flow runout. Marine sediments exhibit a typical yield stress behavior, such as that of low-activity clays. For the materials examined, different yield stresses are observed depending on the shearing methods. Steady-state and oscillatory shear tests were conducted for different volumetric concentrations of sediment. According to the test results, the Bingham yield stresses under controlled shear stress and shear rate range from approximately 100 Pa to 1500 Pa, but the yield stresses under oscillatory shear loads range from approximately 25 Pa to 3500 Pa for a given sediment concentration. In the latter cases, the value obtained in the elastic region is approximately doubled. Experiments under steady-state and oscillatory shear loads can be helpful in determining the yield points in the elastic and viscous regions and in explaining changes in the structure of the soil sample due to shear. We apply the range of measured yield strength values to numerical simulations of debris flow runout using a Herschel-Bulkley model and find that only the lowest values of yield strength, despite the low sediment concentrations, could account for the observed runout and thickness distribution. We infer that significant wetting must occur during debris flow motion to attain the observed runout.

An optimized volume of fluid method for modelling three-dimensional debris flows. Implementation in OpenFOAM, validation, and application in the Aiwa Watershed, Beijing

Debris flows are a common type of geological hazard. They move down slopes at rapid speeds, causing severe damage to buildings and humans. It is of great significance to study the development and movement characteristics of debris flows. In this study, we developed a numerical method of simulating the movement of debris flows. The phase fraction was used to represent the contents of the debris flow components. The Herschel–Bulkley–Papanastasiou model was used to simulate the movement of the fine particle–water mixture in the debris flow, and the pressure-dependent Coulomb viscoplastic model was used to describe the movement of the gravel-size particles. The interface between the debris flow and the air was obtained using the volume of fluid method. The above models were implanted in OpenFOAM. Finally, indoor experimental data were used to verify the numerical method developed in this study, and the experimental and simulation results were found to be in good agreement. The proposed method was then applied to debris flow prediction in the Aiwa Watershed, Beijing. The homogeneous flow model developed in this study can significantly reduce the number of calculations required and can be used for the three-dimensional simulation of large-scale debris flows.

Largest scale successful real-time evacuation after the Wenchuan earthquake in China: lessons learned from the Zengda gully giant debris flow disaster

A catastrophic debris flow occurred in the Zengda gully, a branch of the Dajinchuan River in Zengda town, Jinchuan County, Sichuan Province, China. The successful implementation of a real-time evacuation avoided 820 casualties for people living in 200 settlements. This was the largest-scale successful real-time evacuation for a debris flow disaster after the Wenchuan earthquake in China. In order to better reveal the causes of the successful real-time evacuation process of the giant debris flow disaster, the characteristics, formation and movement process of the debris flow were studied using multi-temporal remote sensing images, field investigation, laboratory analysis, and empirical formula calculations. It was found that the successful real-time evacuation was possible because of a well-executed monitoring system, timely release of early warning information, a highly effective operation disaster prevention system, and decisive and advanced avoidance. It also transferred strategies through in-depth analysis of several important stages in the real-time evacuation process. Finally, an exemplary mode of community-based warning is proposed based on the Zengda gully giant debris flow disaster real-time evacuation. Specifically, the mode was led by government, implemented by local residents and proceeded with the guidance by experts in the field. The experience and effective risk avoidance mode presented in this paper can be shared and employed by other countries or regions at serious risk for debris flow disasters.

A study of the disaster model and movement process simulation of debris flow in the Zhixi River of Deqin County

Deqin County is one of the areas suffering the most serious geological disasters in Yunnan Province. Based on the development characteristics of the debris flow in the Zhixi River, this study identifies five disaster-generating modes for the debris flow in the Zhixi River: Collapse - clastic flow, rock landslide-clastic flow, soil-rock mixture landslide-clastic flow, loose accumulation layer -bedrock contact surface landslide-clastic flow and landslide in loose accumulation layer-clastic flow. The FLO-2D model is used to simulate the debris flow movement in the Zhixi River under the rainstorm cycle of 10, 20, 50 and 100 years, and the maximum flow velocity, the maximum accumulation depth, the accumulation distance and the volume scale in different rainfall return periods are quantitatively analyzed. The results show that the debris flow is characterized by high acceleration, fast velocity, strong destructive force, and long circulation area when it erupts. When the debris flow occurs once in 100 years, its maximum velocity reaches 3.07 m/s, the maximum mud depth is 2.27 m , the volume of debris flow washed out is 84419 m3, and the disaster area reaches 91600 m2. The results provide quantitative data reference for the prevention and control of debris flow disasters in Zhixi River, and also provides an important basis for the design of disaster prevention and mitigation projects in Deqin County.

Debris flow hazard assessment of the Eryang River watershed based on numerical simulation

The middle reach of Taohe River, in the south part of Gansu Province, China is severely threatened by debris flow hazard. Eryang River is an important branch of Taohe River. On May 10, 2012, many debris flows were triggered by extreme heavy rainfall (1% frequency), resulting in serious losses of human lives and properties. In order to recognize the hazard of debris flows in small watersheds, six key debris flow gullies in Eryang watershed, Lalonggou, Zhalonggou, Yizigou, Jiehagou, Lalugou, Paizuigou, were selected as the research area. The numerical simulation software FLO-2D was used to analyze the debris flow movement and accumulation characteristics of each debris flow gully under the actual ‘5.10’ rainfall conditions, so as to reconstruct the ‘5.10’ debris flow disaster scenario. Numerical simulation results show that the flow speed increased to the maximum after 15-30 minutes since the outburst. The flow lasted for about 3 hours. The speed in the moving section was very high, and decreased sharply at the gully-mouth, then deposits accumulated in the river valley. According to the satellite images and field investigations, the simulation results were compared with the actual situations. The comparison shows the simulation effect is good, the deposition area, the discharge process, and the main damage area were well-reconstructed by FLO-2D simulation. Then, the same method and parameters are used to simulate the accumulation range, depth and velocity of debris flows under the precipitation of 2 % and 0.2 % frequency (fifty and five hundred years rainfall, respectively), and then the risk zoning map is produced using the simulation data. The potentially threatened houses and properties were outlined. The threatened area is 37900m2 and 60500m2 under 2% and 0.2% rainfall frequencies. There are 22 houses in the highest hazard level. This provides direct reference to the local government to control the debris risk. This work also provides a practical approach for the debris flow hazard assessment.

Grain Configuration Effect on Pore Water Pressure in Debris Flow

The generation and development of excess pore water pressure directly affects the grain interaction in debris flow, which can significantly reduce the friction strength and promote the movement of debris flow. It has been found that coarse grains favor the increase in excess pore water pressure, but the effect due to grain configuration is missing in studies. In order to study the influence of grain configuration, field investigations and laboratory tests were carried out for two typical cases, i.e., flow with coarse grains evenly mixed (case I) and flow with coarse grains floating on the surface (case II). The results show that case II generates much higher excess pore water pressure than case I. The variation of relative excess pore water pressure (Ur) with time (t) satisfies the power function relationship: Ur = mt–n. Case II often has a smaller n value, meaning a low dissipation rate of excess pore water pressure. This study is helpful for a better understanding of granular effects in debris flow.

Coupled empirical–mechanical modeling of debris flows occurred in small ungauged basins

On 28 July 2013, an intense torrential rainfall occurred at the boundary of Yamaguchi and Shimane Prefectures in western Japan, and triggered a debris flow on an ungauged hillslope to bury the entrance of Shirai tunnel and to shutdown railway service in that region for 1 year. To assess this disaster, this study aims at numerically modeling this debris flow event through a methodology incorporating empirical hydrologic analysis and mechanical debris flow model. For hydrologic analysis, the SCS-CN method implemented by HEC-HMS was used to obtain direct runoff hydrograph with high-resolution precipitation data reanalyzed using observations from radars and rain gauges. Then, the obtained runoff-discharge information was applied as an input for numerically simulating the debris flow movement from source to deposition areas. The simulation result is verified by the field evidence from field survey. The study demonstrates the applicability of the proposed empirical–mechanical approach for assessing debris flows in ungauged basins.

Characteristics and risk analysis of debris flow movement in a strong earthquake area - Sichuan earthquake stricken area as an example

It is very likely that debris flow will break out in a strong earthquake area under the stimulation of a large-scale rainfall, and its risk needs to be analysed. This study analysed the debris flow in a single gully in Wenchuan, introduced the natural environment, geological conditions, and travel conditions and movement characteristics of debris flow in Wenchuan, and then analysed the risk of debris flow using two methods. It was found from the results of a risk calculation based on evaluation factors that the risk of the study area was 0.76, which was high. It was found from the results of a risk calculation based on intensity that the debris flow in the study area had XL level risk, which needed long-term control and monitoring. The research results verify the high risk of debris flow in a strong earthquake area and provide some theoretical bases for debris flow control in that area.

A TWO DIMENSIONAL COUPLED MODEL FOR SUBMARINE DEBRIS FLOW AND ITS INTERACTION WITH SUBSEA INSTALLATIONS

Debris flow are gravity driven mass flows which can create catastrophic geohazards along their overriding paths. Driven by the gravity, debris flow can travel long distances on favorable continental slopes. Their frontal velocity can be very high which may pose significant threat to offshore installations such as subsea pipelines, communication cables and offshore platforms (Yuan et. al., 2012). Therefore, understanding their dynamic behavior is critical in order to mitigate potential geohazards. The specific objective of this paper is to present a coupled two dimensional numerical model that characterizes debris flow movement, rheological properties and its interaction with subsea installations. For demonstration purpose, the coupled model has been applied to schematized settings representing generalized continental shelves with canyons.Recorded Presentation from the vICCE (YouTube Link):

Characteristics and risk analysis of debris flow movement in strong earthquake area-taking Sichuan earthquake stricken area as an example

It is very likely that debris flow will break out in a strong earthquake area under the stimulation of a large-scale rainfall, and its risk needs to be analysed. This study analysed the debris flow in a single gully in Wenchuan, introduced the natural environment, geological conditions, and travel conditions and movement characteristics of debris flow in Wenchuan, and then analysed the risk of debris flow using two methods. It was found from the results of a risk calculation based on evaluation factors that the risk of the study area was 0.76, which was high. It was found from the results of a risk calculation based on intensity that the debris flow in the study area had XL level risk, which needed long-term control and monitoring. The research results verify the high risk of debris flow in a strong earthquake area and provide some theoretical bases for debris flow control in that area.

Superelevation analysis of the debris flow curve in Xiedi gully, China

The superelevation phenomenon is common in the movement of debris flows around curves. This paper presents a new method to calculate the superelevation of debris flow when it encounters obstacles in the flow process. The calculation method is based on the Bingham Model for debris flow determination. In this paper, physically significant internal and external roughness coefficients are determined by analysing the internal characteristics and external channel boundary conditions of viscous debris flows in Xiedi gully, China. According to the situation of debris flow passing through the bend, when the debris flow moves to the sidewall of the gully with velocity, the movement state is divided into two parts: radial and normal. One part of the mud rock fluid continues to move in the tangential direction and generates superelevation, and the other part moves in the radial direction and generates upward climbing along the sidewall. Thus, the formula for calculating the superelevation of debris flow bend is derived. Based on the debris flow physical and dynamic parameters, such as density and weight of the debris flow, cohesion, internal friction angle, yield stress and dynamic viscosity of liquid-phase slurry, the reliability of the formula is verified, which provides a theoretical basis for future studies of debris flow disaster prevention and control in similar areas.

Effect of viscosity changes on the motion of debris flow by considering entrainment

Debris flows are typical two-phase flows that commonly occur with entrainment. By involving sediment materials, the fluid viscosity of debris flow may change significantly along with the variety of solid volume fraction, which further influences debris flow routing. To address this issue, a two-phase model is incorporated with a correlation for the apparent viscosity of the mixture and an entrainment formula, which is applied for studying how the changing fluid viscosity affects the interaction force between the solid and fluid phases during flow propagation. A second-order accuracy numerical scheme based on the finite volume method is applied to solve model equations. The numerical results correlate well with the available experimental data, and indicate the importance of viscosity changes in debris flow routing.

Laboratory study on the characteristics of large wood and debris flow processes at slit-check dams

Large wood (LW) in debris flows during flooding can cause significant damage to check dams, bridges, and other major infrastructure in its flow path. When LW accumulates and forms logjams, large volumes of sediment can be deposited, resulting in increased backwater. The logjams can then suddenly collapse, with the deposited sediment and accumulated water increasing the magnitude of debris-flow peak discharge. To better understand the characteristics of debris flow discharge caused by LW accumulation and collapsed logjams, as well as the associated magnitude amplification effects, a series of experiments was carried out in a laboratory experimental channel. The main purpose of this study was to analyze the process of LW accumulation and collapse and to determine the magnitude amplification ratio of the debris flow peak discharge with LW. The results revealed three types of debris flow movement with LW: flow with no clogging or breakage, flow with clogging but without breakage, and flow with both clogging and breakage. The results indicated a significant effect on the magnitude amplification ratio caused by LW clogging and breakage. The maximum magnitude amplification ratio was 1.60 in the experiments, with a relative LW length and volume of 0.875 and 0.75, respectively, during the clogging and breakage process.

Effects of loose deposits on debris flow processes in the Aizi Valley, southwest China

Loose deposits, rainfall and topography are three key factors that triggering debris flows. However, few studies have investigated the effects of loose deposits on the whole debris flow process. On June 28, 2012, a catastrophic debris flow occurred in the Aizi Valley, resulting in 40 deaths. The Aizi Valley is located in the Lower Jinsha River, southwestern Sichuan Province, China. The Aizi Valley debris flow has been selected as a case for addressing loose deposits effects on the whole debris flow process through remote sensing, field investigation and field experiments. Remote sensing interpretation and laboratory experiments were used to obtain the distribution and characteristics of the loose deposits, respectively. A field experiment was conducted to explore the mechanics of slope debris flows, and another field investigation was conducted to obtain the processes of debris flow formation, movement and amplification. The results showed that loose deposits preparation, slope debris flow initiation, gully debris flow confluence and valley debris flow amplification were dominated by the loose deposits. Antecedent droughts and earthquake activities may have increased the potential for loose soil sources in the Aizi Valley, which laid the foundation for debris flow formation. Slope debris flow initiated under rainfall, and the increase in the water content as well as the pore water pressure of the loose deposits were the key factors affecting slope failure. The nine gully debris flows converged in the valley, and the peak discharge was amplified 3.3 times due to a blockage and outburst caused by a large boulder. The results may help in predicting and assessing regional debris flows in dry-hot and seismic-prone areas based on loose deposits, especially considering large boulders.

A combined method for modeling the triggering and propagation of debris flows

This study describes a combined method for rainfall-induced debris flow initiations (landslides) and propagations including a series of numerical analyses. In this study, the debris is assumed as a mixture of soils and water which is physically non-Newtonian fluid. The emphasis is placed on applying the effect of the combination of rainfall-induced landslides and debris flows to the numerical analysis. An analysis of rainfall-induced landslides is conducted to identify the thickness and location of the initial volume of debris flow. The movement of debris flow is subsequently simulated considering entrainments affected by the initial wetting condition (wetting front) estimated from the rainfall-infiltration analysis. The proposed method can simulate a sequential process from the initiation of the debris flows to the deposition based on the prediction of slope failure by rainfall, fluid dynamics based on Navier–Stokes equation, and the analysis of entrainments by considering the effect of the weight of debris and the wetting condition of soil beds. Based on the numerical results of this study, the proposed method could be applied to the analysis of regional-scale landslides and debris flows.

Debris flows originating from colluvium deposits in hollow regions during a heavy storm process in Taining, southeastern China

On 8 May 2016, eight debris flows occurred in Taining County, Fujian Province, China. Thirty-six people died as a result of the largest catastrophic debris flow (DF3), which occurred in the Luankeng gully and has attracted the attention from scholars all over the world. A field investigation was conducted, and site measurements were obtained to identify the processes of debris flow formation, movement, and deposition. The precipitation seepage was analyzed by numerical simulation with the Geo-Studio software. The mechanism that transforms the colluvium deposits in hollow regions (CDHs) into debris flows was studied by a stability analysis of the CDH in the initiation zone. The results showed the following: (1) the CDH instability was triggered by the combined effects of rainfall and flow concentration at the end of the hollow, and the CDH slide occurred along the interface between the bedrock and hollow, which transformed into a debris flow; (2) the debris flow discharge was amplified 6.5 times due to blockage by boulders distributed in the gully; and (3) the confluent area of the hollow region and the CDH slope gradient and thickness impart significant impact on the CDH stability. The CDH will experience failure when the slope gradient and thickness exceed the critical values of 30.5° and 1.25 m, respectively. The confluent area of the hollow may supply as much as four times the normal amount of water, which may trigger a debris flow during heavy rainfall.

Combining TRIGRS and DEBRIS-2D Models for the Simulation of a Rainfall Infiltration Induced Shallow Landslide and Subsequent Debris Flow

TRIGRS revealed the responses of the total pressure heads and factors of safety with a depth change under a rainfall infiltration occurring on the Daniao tribe’s hill. The depth distribution of the collapsed zone could be identified under the condition where the factors of safety Fs = 1, and the results could calculate the area and volume. Afterward, DEBRIS-2D used TRIGRS’s results to assess the hazard zone of the subsequent debris flow motion. In this study, the DTM variation analysis results from both of before and after the Daniao tribe’s landslide are used to validate TRIGRS’s simulation, the area and the volume of the collapse zone within 8% and 23% errors, respectively. The real disaster range was depicted from the aerial photo used to validate the hazard zone simulation of DEBRIS-2D within 25% errors. In spite of that, the hazard zone from the simulation still included the real disaster range. The combining method for a rainfall infiltration induced a shallow landslide and subsequent debris flow, which was well-matched on a real disaster range on the Daniao tribe’s hill. Therefore, we believe that the TRIGRS and DEBRIS-2D combining methods would provide a better solution for an assessment of a rainfall infiltration inducing shallow landslide and subsequent debris flow motion. TRIGRS could, therefore, provide the area and depth distribution of the collapsed zone, and DEBRIS-2D could use TRIGRS’s results for subsequent debris flow hazard assessment. Furthermore, these results would be of great help in the management of slope disaster prevention.

Dynamic Modeling of Sediment Budget in Shihmen Reservoir Watershed in Taiwan

Qualifying sediment dynamic in a reservoir watershed is essential for water resource management. This study proposed an integrated model of Grid-based Sediment Production and Transport Model (GSPTM) at watershed scale to evaluate the dynamic of sediment production and transport in the Shihmen Reservoir watershed in Taiwan. The GSPTM integrates several models, revealing landslide susceptibility and processes of rainfall–runoff, sediment production from landslide and soil erosion, debris flow and mass movement, and sediment transport. For modeling rainfall–runoff process, the tanks model gives surface runoff volume and soil water index as a hydrological parameter for a logistic regression-based landslide susceptibility model. Then, applying landslide model with a scaling relation of volume and area predicts landslide occurrence. The Universal Soil Loss Equation is then used for calculating soil erosion volume. Finally, incorporating runoff-routing algorithm and the Hunt’s model achieves the dynamical modeling of sediment transport. The landslide module was calibrated using a well-documented inventory during 10 heavy rainfall or typhoon events since 2004. A simulation of Typhoon Morakot event was performed to evaluate model’s performance. The results show the simulation agrees with the tendency of runoff and sediment discharge evolution with an acceptable overestimation of peak runoff, and predicts more precise sediment discharge than rating methods do. In addition, with clear distribution of sediment mass trapped in the mountainous area, the GSPTM also showed a sediment delivery ratio of 30% to quantify how much mass produced by landslide and soil erosion is still trapped in mountainous area. The GSPTM is verified to be useful and capable of modeling the dynamic of sediment production and transport at watershed level, and can provide useful information for sustainable development of Shihmen Reservoir watershed.

The Seismic Signature of Debris Flows: Flow Mechanics and Early Warning at Montecito, California

AbstractDebris flows are concentrated slurries of water and sediment that shape the landscape and pose a major hazard to human life and infrastructure. Seismic ground motion‐based observations promise to provide new, remote constraints on debris flow physics, but the lack of data and a theoretical basis for interpreting them hinders progress. Here we present a new mechanistic physical model for the seismic ground motion of debris flows and apply this to the devastating debris flows in Montecito, California on 9 January 2018. The amplitude and frequency characteristics of the seismic data can distinguish debris flows from other seismic sources and enable the estimation of debris‐flow speed, width, boulder sizes, and location. Results suggest that present instrumentation could have provided 5 min of early warning over limited areas, whereas a seismic array designed for debris flows would have provided 10 min of warning for most of the city.