Debris Flow Model Research Articles

Small-scale study of Debris-Flows Interactions with a Lateral Debris Basin and Crossings: The Manival Torrent case study

Small-scale models are useful tools to study the interactions between debris flows and structures and channels. Small-scale modelling of debris flows remains however complicated because of the complex rheology and scaling challenges of these geophysical processes. An on-going study of a debris basin and the downstream channel where two fords and a bridge are located is presented in this extended abstract. The studied torrent is the Manival catchment, located near Grenoble in France. We present the catchment features, the scientific questions studied, some preliminary calibration results describing the mixtures used to model debris flows as well as results from three debris-flood and two debris-flow runs. In essence, the model highlighted that the structure enable a large share of the bedload transport to pass downstream. Debris flows can be more or equally trapped depending on their rheology which controls the surges dynamics and the deposition slope in the debris basin.

Impact of climate change on hydro-meteorological trigger conditions for debris flows in Austria

Debris-flow activity is expected to change in a future climate. In this study we connect a susceptibility model for debris-flows on a regional scale with climate projections until 2100. We use this to assess changes of hydro-meteorological trigger conditions for debris flows in six regions in the Austrian Alps. We find limited changes on an annual basis, but distinct changes when separating between hydro-meteorological trigger types and regions. While regions in the east and in the south of Austria may experience less days susceptible to debris flows in summer, there is a general trend of increasing susceptibility earlier in the year for both, rainfall-related and snow-related trigger conditions. The outcomes of this study serve as a basis for the development of adaption strategies for future risk management from this debris-flow hazard.

Risk Assessment of Transport Linear Infrastructures to Debris Flow

For the assessment of debris flow risk, it is essential to consider not only the triggering and propagation stages but also to perform analyses of its effects and consequences. The study aims at developing a procedure based on a quantitative risk assessments able to estimate the different levels of risk with reference to transport linear infrastructures. This includes numerical modelling for debris flows to determine the zones where the elements at risk could suffer an impact. 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 single-phase model (RASH-3D) with reference to the Enna area (Sicily). The results can be applied for the risk calculations. The purpose is to define a priority of intervention for the identification of the infrastructures exposed at risk, leading to the choice of safety measures.

Coupled Eulerian-Lagrangian Debris Flow Model with Flexible Barrier

Natural hazards such as large debris flow events can have catastrophic effects on the environment and critical infrastructure, posing a significant threat to human life. Debris flows often exhibit high velocity, high-pressure discharges due to their bulk volume, and the capacity to transport considerable volumes of large rocks, boulders, and woody debris. Although debris flow run-out simulations are commonly performed using hydraulic modelling software, these environments are seldom capable of assessing the interaction between the debris fluid, transported material, and protective structures. In this research, large deformation numerical models are calibrated using input parameters from hydraulic modelling software. Due to the computational cost of the large deformation models involving fluid-solid-structure simulation with flexible net barriers, an equivalent stiffness method is implemented to provide comparable performance through a membrane structure. The Coupled Eulerian-Lagrangian Finite Element method is used to model the impact forces of rocky boulders on the membrane, exhibiting damage characteristics consistent with flexible ring-net protective structures. The Coupled Eulerian-Lagrangian model results highlight the performance of the simplified membrane, as shown through a benchmark simulation of debris flow with boulders.

Integration of meteorology and geomorphology for enhanced understanding of post-fire debris-flow hazards

Through precipitation, the fields of meteorology and geomorphology are fundamentally linked, thus interdisciplinary efforts are needed to advance understanding and warning of rainfall-driven geohazards. With a focus on recent efforts specific to post-fire debris flows in California, our presentation provides an overview of the benefits and challenges of working in an interdisciplinary team of meteorologists and geomorphologists, as well as results of a recent project demonstrating advancement through the integration of these fields. In this project, we combine high-resolution ensemble precipitation forecasts with post-fire debris-flow models to explore the feasibility and potential value of providing probabilistic post-fire debris-flow hazard information over a burn scar. In sharing these examples, we emphasize the multi-benefit nature of these efforts, and encourage future interdisciplinary efforts that improve warning and mitigation of rainfall-driven geohazards.

Seismic Measurements of Roll Waves in Debris Flows

Accurate debris-flow modelling depends on the ability to simulate surging and pulsing behaviour. However, our understanding of these phenomena is starved of observational constraints. Here we propose the use of seismic measurements, which resolve the arrival of coarse-grained roll wave fronts in debris flows at Illgraben, Switzerland. Roll waves likely play a key role in flow pulses but are typically only observed with point measurements like depth gauges. We compare in-torrent force plate measurements with near-torrent seismic records and discuss how these data can test existing roll wave theories.

Predicting burn severity for integration with post-fire debris-flow hazard assessment: a case study from the Upper Colorado River Basin, USA

Background Burn severity significantly increases the likelihood and volume of post-wildfire debris flows. Pre-fire severity predictions can expedite mitigation efforts because precipitation contributing to these hazards often occurs shortly after wildfires, leaving little time for post-fire planning and management. Aim The aim of this study was to predict burn severity using pre-fire conditions of individual wildfire events and estimate potential post-fire debris flow to unburned areas. Methods We used random forests to model dNBR from pre-fire weather, fuels, topography, and remotely sensed data. We validated our model predictions against post-fire observations and potential post-fire debris-flow hazard estimates. Key results Fuels, pre-fire weather, and topography were important predictors of burn severity, although predictor importance varied between fires. Post-fire debris-flow hazard rankings from predicted burn severity (pre-fire) were similar to hazard assessments based on observed burn severity (post-fire). Conclusion Predicted burn severity can serve as an input to post-fire debris-flow models before wildfires occur, antecedent to standard post-fire burn severity products. Assessing a larger set of fires under disparate conditions and landscapes will be needed to refine predictive models. Implications Burn severity models based on pre-fire conditions enable the prediction of fire effects and identification of potential hazards to prioritise response and mitigation.

Bidirectional Coupling Analysis of Support Pipeline for Shock Damping of Dilute Debris Flow

With the frequent occurrence of geological disasters and extreme weather, pipeline failure accidents and secondary disasters caused by debris flow continue to occur. Aiming at the impact of thin debris flow on support pipeline, a multi-physical coupling model of debris flow and support pipeline with vibration reduction is established based on the expansion flow model. The expansive fluid model is used to simulate the stress of the support pipeline under the action of thin debris flow. The results show that the impact effect of thin debris flow slurry on the support pipeline is concentrated at the inlet surface of the pipeline and the support, and gradually decreases to both ends. As the velocity of debris flow slurry increases, the stress acting on the support pipeline also increases. When the flow field tends to be stable, the load acting on the support pipeline maintains a stable value. The leading effect of debris flow slurry is the most serious damage to the support pipeline. The research results have a certain reference value for the impact of dilute debris flow in support pipeline.

A coupled SPH-DEM approach for modeling of free-surface debris flows

A Lagrangian mesh-less model is proposed to simulate fluid–solid flows with multiple-sized solids, i.e., millimeter-sized particle and larger-sized debris. Considering the difference in the size of solid phases, a hybrid resolved and unresolved model is established based on the coupling method of smoothed particle hydrodynamics (SPH) and discrete element method (DEM). SPH is used to model fluid, and the locally averaged Navier–Stokes equations are adopted as governing equations. DEM is used to model the particle–particle interactions, and the unresolved description of hydrodynamic forces including drag and buoyancy is established. The large-sized debris is modeled as the rigid body, which is discretized by particle elements having both SPH and DEM characteristics, where SPH particle elements are involved in the closure of the SPH fluids, and DEM particle elements interact with the solid particles following the contact law. The numerical model is validated and verified by several examples, including single-particle sedimentation, collapse of cylinder columns, and debris dam break. Results show that the present model reproduces general features of the complex fluid–solid flow with free surfaces. The advantage of the hybrid model is that it can deal with the fluid–solid flow problem with both small particles and large objects at a suitable resolution, and it is especially good at dealing with the free surface flow problem. A discretization for the modeling of debris flows is proposed based on the coupled SPH-DEM method. The novelty of the work is a coupled resolved–unresolved scheme for the free surface flow with multi-sized solids. The present scheme allows using a uniform resolution by bridging the size difference between small-scale solid particles and large-scale debris. The unresolved model of fluid-particle flow is efficient because the fluid resolution can be configured comparably to the particle size. The unified nature of the model allows the combination of resolved and unresolved simulations in the same computational domain.

Debris flow simulation 2D (DFS 2D): Numerical modelling of debris flows and calibration of friction parameters

Debris flows are rapid mass movements with a mixture of rock, soil and water. High-intensity rainfall events have triggered multiple debris flows around the globe, making it an important concern from the disaster management perspective. This study presents a numerical model called debris flow simulation 2D (DFS 2D) and applicability of the proposed model is investigated through the values of the model parameters used for the reproduction of an occurred debris flow at Yindongzi gully in China on 13 August 2010. The model can be used to simulate debris flows using three different rheologies and has a user-friendly interface for providing the inputs. Using DFS 2D, flow parameters can be estimated with respect to space and time. The values of the flow resistance parameters of model, dry-Coulomb and turbulent friction, were calibrated through the back analysis and the values obtained are 0.1 and 1000 m/s 2 , respectively. Two new methods of calibration are proposed in this study, considering the cross-sectional area of flow and topographical changes induced by the debris flow. The proposed methods of calibration provide an effective solution to the cumulative errors induced by coarse-resolution digital elevation models (DEMs) in numerical modelling of debris flows. The statistical indices such as Willmott's index of agreement, mean-absolute-error, and normalized-root-mean-square-error of the calibrated model are 0.5, 1.02 and 1.44, respectively. The comparison between simulated and observed values of topographic changes indicates that DFS 2D provides satisfactory results and can be used for dynamic modelling of debris flows. • A new numerical model called Debris Flow Simulation 2D (DFS 2D) is developed. • The proposed DFS 2D is useful for understanding the runout process of debris flows. • DFS 2D considers three different rheologies and the effect of entrainment. • The model is user-friendly and the outputs are saved in interactive formats. • Proposed two different approaches for calibration of friction parameters.

Numerical Simulation of Debris Flow and Driftwood with Entrainment of Sediment

Unlike general landslides, debris flow has a high water content, due to large floods and rainfall. On steep slopes, it behaves like a large specific-weight sediment–water mixture, rather than general fluid. Thus, its momentum rapidly increases, damaging human lives and properties. This study developed a numerical model of debris flow considering driftwood and entrainment erosion, and performed numerical simulations based on the 2011 observation data of Mt. Umyeon. To develop the debris-flow model, the Nays2DFlood model, which is a flooding model based on the shallow-water equation, was coupled with the advection and diffusion of the sediment–water mixture, debris-flow bottom shear-stress, and entrainment-erosion modules. The simulation better reproduced the depth, flow velocity, and debris-flow volume of Mt. Umyeon. In particular, the driftwood generation and motions, by debris flow, were well demonstrated in the numerical simulation. Moreover, the driftwood partially reduced the drag force, and the shielding effect of the forest caused a delay in the runoff duration-time. The results of this study are expected to help establish measures to reduce debris disasters that can respond to the current situation, wherein debris damage is increasing, owing to the increased rainfall because of climate change. This subsequently increases the possibility of debris flows and the consequent damage. In particular, the predictive methodology of the refined model expands the understanding of numerical treatment for debris flow and driftwood, by reflecting the detailed physical regime.

Evaluation of Debris-Flow Vibration Signals Recorded at the Aiyuzi Stream in Shenmu Taiwan Using Machine Learning Methods

In recent years, due to the frequent occurrence of extreme weather due to climate change, the Taiwan region has often suffered from landslides and debris flows in the past 20 years. This study used the ground surface vibration signals collected by the geophone from seven debris flow events in the Shenmu area. Data were processed to represent the time series of velocity and accumulated energy per second. Datasets were established for model training and validation. In this study, Support Vector Machine (SVM) and Random Forest (RF) algorithms were used for comparison. After analyzing the data through balance processing (Synthetic Minority Oversampling Technique, SMOTE), a signal model of debris flow was established. The research results showed that the models using SVM and RF training had good accuracy, recall, and AUC values when choosing input data average of every 6 s and the 10-s time interval within which the data were marked as the occurrence of debris flow. The performance of SVM was better than that of RF after validation. Through the aforementioned research, the vibration signals of debris flow can be regarded as a reference factor, and the model established by the SVM method had acceptable performance and can be used for early-warning of debris flow.

Numerical modeling of debris flows using basic equations in generalized curvilinear coordinate system and its application to debris flows in Kinryu River Basin in Saga City, Japan

Each year, structures installed in rivers and valleys (e.g., bank protections, bridges, and sabo dams) are damaged by debris flows; therefore, it is necessary to predict the flow characteristics of debris flows accurately to design river and valley structures that are robust against such debris flows. In recent years, several two-dimensional models have been developed to simulate debris flow. However, the basic equations in the numerical simulation models are in the Cartesian coordinate system, and the shape of each numerical analysis grid is square or rectangular. It is impossible to use numerical grids that match the horizontal shape of the river or valley structures, such as bank protections and sabo dams, when employing square or rectangular grids. This makes it difficult to calculate the fluid forces acting on river or valley structures. In this study, the basic equations of debris flow are provided in the generalized curvilinear coordinate system and a numerical simulation model of debris flow designed using an orthogonal curved grid along the horizontal shape of rivers and valleys is developed. Numerical simulations of a periodical meandering valley are conducted using the basic equations in the generalized curvilinear and Cartesian coordinate systems; the difference between the two results is discussed. Further, numerical simulations of the debris flow that occurred in the Kinryu River Basin in Saga City, Japan, in 2019 are performed using the basic equations in the generalized curvilinear and Cartesian coordinate systems, and the difference between the two simulation results is discussed. The numerical simulation results of debris flow in a periodical meandering channel suggest a slow propagation of debris flow when equations in the Cartesian coordinate system are used; this is attributed to the rough boundaries of debris flow when a square grid is used, which causes numerical energy dissipation that does not exist physically. The inundation areas and land surface deformation of debris flow in Kinryu River Basin were reproduced well by the developed numerical analysis model; the basic equations were written in the generalized curvilinear coordinate system. The development and decrescence of debris flows were reproduced using the developed model; the first debris flow in Kinryu River Basin was stopped in the upstream mild slope area, while the second flowed into the residential area. Reproducing the flow depth, velocity, and discharge could be improved by the model using basic equations in the generalized curvilinear coordinate system, as compared with those reproduced using basic equations in the Cartesian coordinate system. When the Cartesian coordinate system was used, the volume of the debris flow was evaluated to be small and the travel distance of the debris flow was evaluated to be short; thus, the debris flow does not arrive at the residential area and the risk of debris flows is underestimated.

Analysis of the formation mechanism of debris flows after earthquakes – A case study of the Legugou debris flow

By means of the Graphic Method, Gray Correlation Method and Frequency Method, the total amount of loose solid materials, the amount of loose solid materials per unit area in the source area, and the risk degree and critical rainfall of the study area are determined, respectively. On the basis of the calculation results, the total amount of loose solid materials is 57.2 × 104 m3, the amount of loose solid materials per unit area is 0.13 m3/m2 (greater than 0.1 m3/m2), which better meets the initiation conditions for dilute debris flow. The Hazard Evaluation Model of Debris Flow in earthquake areas is established by the gray correlation method and the hazard index H = 0.725 is determined. According to the hazard classification standards for debris flows in earthquake areas, the debris flow in Lecugou was moderate after the earthquake. The critical rainfall value of 1H, calculated by the frequency method, ranged from 17.45 to 22.21 mm (Re = 25 mm) and 8.17 to 13.01 mm (Re = 50 mm). The critical rainfall value at 10 min ranged from 6.23 to 8.44 mm (Re = 25 mm) and 2.92 to 5.13 mm (Re = 50 mm), respectively. The maximum rainfall intensity of 45.5 mm/h was reached between 10:00 and 11:00 on July 29, 2019 and the cumulative rainfall reached 144 mm, far exceeding the critical rainfall of Legugou. Under the influence of earthquakes and human activities, the loose solid source amount and loose solid source amount per unit area increased greatly, and the critical rainfall for debris flow after earthquakes decreased sharply, which induced debris flows under the influence of heavy rainfall. This research will be helpful for the establishment of monitoring and early warning systems based on artificial intelligence methods, and can greatly improve the effectiveness of disaster prevention and mitigation.

Debris flow modelling and hazard assessment for a glacier area: a case study in Barsem, Tajikistan

Debris flow modelling and hazard assessment for a glacier area: a case study in Barsem, Tajikistan

Physically based modeling of co-seismic landslide, debris flow, and flood cascade

Abstract. The 2008 Wenchuan earthquake lead to various complex multi-hazard chains that included seismically triggered landslide initiation, landslide runout, river damming, dam breaching, and flooding. The modeling of the interactions between such hazardous processes is challenging due to the complexity and uncertainty. Here we present an event-based physically based model that is able to simulate multi-hazard land surface process chains within a single unified simulation. The final model is used to simulate a multi-hazard chain event in the Hongchun watershed, where co-seismic landslides led to a landslide dam and, 2 years later, a debris flow that breached the landslide dam. While most aspects of the multi-hazard chain are predicted well, the correct prediction of slope failures remains the biggest challenge. Although the results should be treated carefully, the development of such a model provides a significant progress in the applicability of multi-hazard chain simulations.

Study on dynamic response of debris flow to pipeline with defect

Based on the Finite Element Method (FEM) and the Smooth Particle Hydrodynamics (SPH) coupling method, this paper established full-size multi-physical field coupling model of debris flow impacting pipeline. By simplifying mud into Bingham fluid, this paper studied the dynamic response law of pipeline with defect and intact pipeline (pipeline without defect) under the joint action of mud and block stone, established the displacement equations of the pipeline under impact, thus obtained the displacement, stress and strain characteristics of different pipeline positions at different impact moment. The results showed that numerical simulation of dispersing mud into SPH particles can well simulate the movement process of mud splashing and detour flow. The maximum displacement occurred in the middle part of the pipeline. For the intact pipeline, the main failure was caused by the instantaneous impact of the mud, however, for the pipeline with defect, the dominant failure factor changed from the mud impact to the stone impact. This study provided a new pathway and theoretical reference for disaster prevention and control of pipelines in debris flow section.

The effect of seepage flow on movable solid materials research in debris flow experiments

Debris flows is one of the most common natural disasters in mountainous areas, posing a seriously risk to local people’s life and property. It is fundamental basis to study the criteria for movement of solid materials subjected to seepage flow and surface flow for the purpose of prevent this hazard. Therefore, mechanical analysis methods and laboratory experiments were used to study the effect of seepage flow on movable solid materials in debris flow. First, the definition of movable solid materials was proposed. Then, a geological model of debris flow is established considering saturated seepage flow. Finally, through mechanical analysis, formulas for dynamical force and resistance force are derived. The results show that the dynamical force and resistance force increase linearly with depth when the geologic model is homogenous and the seepage flow saturates the entire debris layer. It also indicated that pore-water pressure is one of the most important factors for causing debris flow, especially when the slope angle exceeds 12°. Through comparing the results of tests and theoretical analysis under saturated seepage flow, the discrepancy is only 1.3%–24.2%, showing that the formulas are fairly reliable. The motion of the solid materials should be described as a mechanical problem rather than a statistic qualitative description. The research contributes to the source volume calculation of small debris-flow watersheds and advances the study of the movable solid materials in complex dynamic conditions.

Modeling of individual debris flows based on DEMNAS using Flow-R: A case study in Sigi, Central Sulawesi

On 2018 September 28, 18:03 a local time (10:03 am UTC), the Mw 7.5 earthquake with a focal depth of about 20 km devastated the Palu region in Central Sulawesi, Indonesia resulting in a catastrophic disaster and many casualties. The Palu earthquakes triggered widespread landslides upstream, contributing to the sizeable material volume accumulated in rivers and mountain slopes. After the Palu earthquake, from September 28, 2018, until December 2021, at least 24 events of debris floods have occurred, which have spread to 15 villages. As of late, the empirical debris flow model Flow-R, software for susceptibility mapping of debris flows at a regional scale, was published. While Flow-R's applicability on a regional scale has been confirmed in several studies, the calibrated case using back-analysis of individual debris flow events in Indonesia based on DEMNAS with a spatial resolution of 8.3 m has never been conducted. Local debris flows modeling using Flow-R was evaluated with three well-documented debris flow events on the break slopes on the west and east sides of the Palu Valley. Quantitative analysis was carried out in this study to assess the accuracy, positive predictive value, and negative predictive value of models. First, the result shows the individual back-analysis model of debris flows found good agreement between debris-flow paths predicted and documented debris flow path extent. However, the parameters for rheological properties and erosion rate required in the software are limited. Second, the quantitative analysis shows accuracy, positive, and negative predictive value, which varies considerably. Based on the study, Flow-R is not suitable for comprehensive hazard mapping but provides a direct information about possible run-outdebris flow paths. Furthermore, lateral spreading and friction of Flow-R model results can be used to calibrate the process with rheological properties and erosion rate in other numerical modeling software, either for forward or back analysis.

Review of Investigations on Hazard Chains Triggered by River-Blocking Debris Flows and Dam-Break Floods

The Tibetan Plateau suffers from various types of geohazards (collapses, landslides, and debris flows.) due to abrupt changes in complex topography and weather conditions. Global warming and frequent high-intensity earthquakes in recent years have exacerbated the situation. Collapses and landslides provide vast amount of soil and debris which are conveyed downstream by runoff caused by extreme rainfalls to form large-scale debris flows; then, the debris flows block rivers and finally form dam-break floods, that is, a hazard chain triggered by debris flows. Along the evolution direction of the hazard chain, the affected areas are constantly amplified. This study first summarizes the related research studies on river blockage, debris-flow dam failure, and the hazard chain triggered by debris flows and then points out the drawbacks of existing research studies. Overall, the research (including mechanism, risk assessment, key prevention, and control technologies) on the hazard chain triggered by debris flows is still in its infancy and is disconnected among single hazard types in the hazard chain; meanwhile, the understanding of the mechanism of debris flow blocking the river is not enough; the established model and discriminant have minimal application scope, and there is no empirical model and dynamic model of debris-flow dam failure. Finally, several key scientific issues of this field were raised: 1) it is necessary to elaborate the coupling mechanism of debris-flow dam formation and construct the discriminant and numerical model of debris flow blocking the river with high precision and a wide application range. 2) It is necessary to further study the failure mechanism of a debris-flow dam, construct the numerical model of the failure process of a debris-flow dam, and accurately simulate the outburst flood hydrograph. 3) It is necessary to clarify the critical transformation conditions and dynamic evolution process of the hazard chain caused by debris flows, complete the accurate quantitative simulation of the whole disaster chain process, then establish a complete risk assessment system of the hazard chain, and finally develop some key prevention and control technologies suitable for the hazard chain.