Debris Flow Simulation Research Articles

An Integrated Approach for Simulating Debris-Flow Dynamic Process Embedded with Physically Based Initiation and Entrainment Models

Recent studies have indicated that the accurate simulation of debris flows depends not only on the selection of numerical models but also on the availability of precise data on the initial source location and depth. Unfortunately, it is currently difficult to obtain quantitative data on source locations and depths during field investigations or model experiments of debris flow disasters. Therefore, in this study, we propose an integrated approach for simulating the debris-flow dynamic process that includes the physically based slope initiation source estimation and the entrainment-incorporated process simulation. We treat the potential slip surfaces’ locations and depths as random variables to search for the critical surface corresponding to the minimum stability factor by Monte Carlo simulation. Using the spatial variation interval of the soil parameters, we estimate the range of possible critical slip surfaces and the interval of the initiation source volume. Moreover, we propose a wet/dry front treatment method applied to the finite difference scheme and integrate it into our entrainment-incorporated model to improve the stability and accuracy of the numerical solution over complex topography. The effectiveness of the method is demonstrated through a case study of the 2010 Hongchun debris flow event in Yingxiu town. The result indicates that our method is effective in simulating debris flow dynamics, including slope initiation source estimation and dynamic process simulation.

Numerical simulation of rainfall-induced debris flow in the Hongchun gully based on the coupling of the LHT model and the Pudasaini model

Numerical simulation of rainfall-induced debris flow in the Hongchun gully based on the coupling of the LHT model and the Pudasaini model

Study on the Prediction of Debris Flow Risk Using LS-RAPID

In this study, the LS-RAPID program was applied to evaluate the debris flow deposition area using the field surveyed topographical data in the areas of debris flow occurrence. In 2020, aerial photogrammetry was performed using an unmanned aerial vehicle in Seonseri, Osan-myeon, and Gokseong-gun. The erosion and deposition areas owing to debris flow were estimated using the orthographic images generated from photogrammetry and high-resolution Digital Surface Mode (DSM), and the extent of debris flow was accurately estimated. For debris flow simulation, the LS-RAPID program, with the apparent friction angle of the Coulomb's friction model as an important factor, was applied. The simulation results were significantly affected by the quality of the topographical data. It is essential to apply DSM data for obtaining a highly accurate simulation of the deposition area where damage generally occurs. To evaluate the performance of the simulation, the LSSI index with the deposition area as a factor was applied; it was found to be 65%, showing a superior predictive performance. In conclusion, it is possible to predict the debris-flow damage using LS-RAPID simulation, and the DSM data on deposition areas are required to generate a reliable disaster map.

Simulating Debris Flow and Levee Formation in the 2D Shallow Flow Model D‐Claw: Channelized and Unconfined Flow

AbstractDebris flow runout poses a hazard to life and infrastructure. The expansion of human population into mountainous areas and onto alluvial fans increases the need to predict and mitigate debris flow runout hazards. Debris flows on unconfined alluvial fans can exhibit spontaneous self‐channelization through levee formation that reduces lateral spreading and extends runout distances compared to unchannelized flows. Here we modify the D‐Claw shallow flow model in two ways that are hypothesized to generate levees. We evaluate these modifications with observations from a large‐scale flume experiment. We investigate model performance when including the effect of two different friction sub‐models, as well as the inclusion of segregation effects on granular permeability. Results show that, for a wide range of plausible model input parameters, simulations including the effects of segregation promoted modeled levee formation, whereas simulations without the effects of segregation did not create levees. Further, using a forward predictive framework, simulations with the effects of segregation were more likely to better model the magnitude of debris flow depth and runout distance, whereas simulation timing of the debris flow was affected by the choice of friction sub‐model. Our results indicate that including the effects of segregation on granular permeability can improve the likelihood of better predictions of debris flow depth and runout prior to an event occurring.

Numerical modelling of an alpine debris flow by considering bed entrainment

Numerical models have become a useful tool for predicting the potential risk caused by debris flows. Although a variety of numerical models have been proposed for the runout simulation of debris flows, the performances of these models in simulating specific events generally vary due to the difference in solving methods and the simulation of the entrainment/deposition processes. In this paper, two typical depth-averaged models have been used to analyze a well-documented debris-flow event that occurred in the Cancia basin on 23 July 2015. The simulations with and without bed entrainment are conducted to investigate the influence of this process on the runout behavior of the debris flow. Results show that the actual runout can be reproduced only by considering bed entrainment. If basal erosion is not taken into account, part of the debris mass deviates from the main path and both models predict unrealistic bank overflows not observed in the field. Moreover, the comparison between measured and simulated inundated areas shows that both models perform generally well in the terms of simulating the erosion-deposition pattern, although the DAN3D model predicts a greater lateral spreading and a thinner depositional thickness compared to Shen’s model. A simple numerical experiment obtains similar consequences and further illustrates the possible reasons that cause these differences.

Keynote lecture. Towards reliability-management for debris flow risk assessment

Recent progress in data-integrated simulation methods excelled our understanding of debris flows including triggering mechanisms and dynamic run-out behavior. Research groups and geohazard practitioners worldwide successfully integrate advanced simulations into workflows for hazard mapping. However, many challenges remain in predictively applying such tools for accepted decision support. One reason is our lack of a systematic approach to managing the simulations’ reliability. In this contribution, we present results on an investigation to which extent the choice of data used for calibration influences the simulation’s reliability. We start with introducing building blocks of a modular and extendible data-integrated debris flow simulation toolchain developed by our group. Next, we introduce reliability as one quality measure of a holistic debris flow simulation and discuss how it can be assessed. Based on a synthetic example, we then show how different types of observed calibration data, such as impact area, deposit volume or localized velocity measurements impacts on the subsequent forward simulation’s posterior probability distribution, hence the simulation’s reliability. We conclude by discussing how linking a debris flow simulation’s reliability to type, scope and resolution of the calibration data could offer a novel pathway towards reliability management for debris flow risk assessment.

FaDebrisFOAM validation using field data surveyed in Crucecita (Chile) alluvial fan for the event of 13th May 2017

The openFOAM solver faDebrisFOAM was recently developed to simulate debris flows with the finite area method. This new solver includes, among other capabilities, a variable density for the solid-liquid mixture, erosion and deposition processes, and a terrain modification algorithm. To test the performance of this new solver, we simulate the debris flow event that occurred in the Crucecita alluvial fan on the 13th May 2017 in the Atacama Desert, Chile. Thanks to pre- and post-event topographies, we have an accurate measure of the morphological changes that took place. Comparing the field data and our numerical model results shows that faDebrisFOAM can reproduce the main flooded, eroded, and deposited areas. Once the model is calibrated, we study the behavior of the terrain modification algorithm. Finally, we discuss the advantages of using this model to reproduce erosion and deposition processes together with changing rheologies for a debris flow event.

The effect of sediment density parameter values on the debris flow velocity parameters

Debris flow is a phenomenon where the material from the eruption is carried away by the flow of water due to rain in the upstream area of the river and usually crashes into watersheds around the volcano. The potential for large debris flows can be caused by high rainfall and sediment deposits that occur during debris flows. Rainfall and sediment carried by water flow can affect the volume and velocity of debris flows. A debris flow simulation was carried out to anticipate casualties and damage using SIMLAR V2.1 by modifying rain intensity and the density of sediment carried by the debris flow. Based on the result, we can obtain the results of the velocity, volume, and area affected by the debris flow. The flow velocity values obtained for testing with rainfall intensity of 162 mm with a density of sediment 1370 kg/m3, 2340 kg/m3, 2635 kg/m3, and 2820 kg/m3, respectively, were 2.72 m/s, 2.16 m/s, 2.50 m/s, and 2.57 m/s. The volume values with the same intensity and density of sediment are 186,381 m3, 311,116 m3, 274,030 m3, and 294,987 m3. Based on the test results, it can be concluded that sediment density significantly affects the velocity and volume of the debris flow. Where sediment density is inversely proportional to the flow velocity, the higher the sediment density, the slower the flow velocity, while the volume is directly proportional to the sediment density. The higher the density of the sediment, the higher the volume.

Bridge obstruction caused by debris flow: A practical procedure for its management in debris-flow simulations

Bridge clogging due to a debris flow is a phenomenon scarcely studied but critical in hazard mapping in the mountain area. Since a rational and systematic approach is still missing, we propose a practical method to deal with this phenomenon in a numerical framework. We tested this methodology by using, as a numerical model, the two-phase, mobile-bed model TRENT2D and, as a site test case, the village of Voueces in the north-west part of the Italian Alps. The application shows reasonable results and highlights the importance of a mobile-bed approach.

Finite difference lattice Boltzmann method for modeling dam break debris flows

A finite difference lattice Boltzmann method (FDLBM) for the simulation of mud and debris flows for one-dimensional cases has been introduced. The proposed FDLBM recovers the generalized equations of mud and debris flows, that is, an unsteady one-dimensional Saint-Venant equation, including the effects of the non-Newtonian behavior of the mixture of water and soil, contraction–expansion losses (or large eddy loss), wind force, various geometries, and lateral inflow or outflow. The proposed FDLBM can be implemented for various non-Newtonian viscoplastic constitutive models of the studied mud and debris flows. The method is validated against previous studies for several benchmark cases, including steady-state problems, hydraulic jump tests, dam breaks with dry and wet beds, and slope dam break floods. Finally, the Anhui debris dam failure flood was investigated by this approach, and the results demonstrated a good agreement with the observed computational and field tests.

Modeling the runout behavior of the July 23rd, 2015 Cancia debris-flow event using two numerical models

On 23 July 2015, a typical volume-enlarging debris flow was triggered by heavy rainfall that occurred a few days before the event. The available data corresponding to this event is obtained from detailed field investigations conducted before and after the event, as well as the monitoring station installed in June 2014. This study aims to reproduce the July 23 debris-flow event using two different numerical methods, analyse the influence of entrainment on the runout behavior of the debris flow and compare the performance of different numerical methods when simulating the same debris-flow event. The results showed the following: (1) The expanded inundated area and unrealistic overflowing were observed in the scenario without entrainment while the simulation that takes entrainment into account presented more perfect results. It illustrates that entrainment is a non-negligible factor for the simulation of these volume-enlarging debris flows. (2) Two models considering the entrainment performed a good match between the simulation and the field survey. However, some noticeable differences can be observed in terms of the erosion-deposition distribution because different numerical schemes were adopted in the two models. Specifically, the DAN3D code always gives higher mobility and larger lateral spreading relative to the Shen model.

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.

Keynote lecture. The debris flow event of 29 October 2018 in the Rio Rotiano (Italy) and its challenges for the mathematical and numerical modelling

The debris flow that interested the Rio Rotiano, a creek located in the Province of Trento (Italy) on 29 October 2018, is an event that, because of its peculiar features, presents formidable challenges in terms of mathematical and numerical modelling. Here we present some results of our research, which required both physical and mathematical modelling, aimed at developing a numerical tool necessary to face the back analysis of the event and the validation of the planned protection works. Exploiting some results of the laboratory tests and coupling an advanced description of the debris flow dynamics (TRENT2D model) over fixed and mobile bed with a sub-surface flow model, we obtained a model that can be defined as a mobile-bed rainfall-runoff model, where the runoff is composed by both water and sediments and represents a new paradigm in the field of debris flow simulations. First applications give promising results but some further developments are required before completing the back analysis of the Rio Rotiano event.

Development of an open source Debris Flow Simulator for “Sabo” (DFSS)

We report the development of an open source “Debris Flow Simulator for Sabo” (DFSS). DFSS consists of three models corresponding to three geomorphological regions (mountain hillside slopes, mountain-to-plain river channels, and lower plains). A 2D rainfall-runoff (RR) model is adopted mainly for hillside slopes; a 1D debris flow runoff (DR) model is used for the river channel; and a 2D debris flow flooding or inundation (DF) model is adopted for the lower plains. These models are weakly coupled such that one can modify the overall model to fit diverse problems. In this article, we provide a detailed introduction to the models comprising DFSS, and demonstrate its utility.

MurGame: Protect your village from debris flows!

Past debris flow events, like in Bondo (2017) and Brienz (2005) in Switzerland have been heavily covered in the (Swiss) media, illustrating how destructive such events can get. Protection measures play an important role in dealing with natural hazards. Debris flows are considered to be very rare, complex and multidimensional processes. Imagining and foreseeing the course and progression of a debris flow as well as estimating the potential damage and the influence of protection measures is a difficult task. Serious games offer a possibility to simulate these kinds of situations. With the MurGame, we have developed an application for natural hazard prevention. In the three-dimensional, interactive game, a village is created by selecting different objects, such as residential buildings or schools. Debris flow simulations show, which buildings would be destroyed and what damage would occur in the event of a debris flow. Different protection measures can be implemented to protect the village and their effectiveness can be monitored during the simulations. After the event, it is necessary to evaluate which measures offer the desired protection, what they may cost and how the needs of the population are met. The MurGame can be played online at www.murgame.ch.

Probabilistic Prediction Method of Erosion Volume and Deposition Area from Rainfall Observation Data

We propose a methodology to estimate the spatial distribution of the probability of sediment deposition due to debris flow from rainfall data by combining the probability prediction of erosion volume based on an ordinal logistic regression and a sediment transport simulation. By using the Receiver Operating Characteristic (ROC) curve and Area Under Curve (AUC) we have selected the best combination of shortand long-term rainfall indices used as explanatory variables in the ordinal logistic model. The results showed that the regression model using 60-minute and 48-hour rainfall indices performed well and that the regression model using three events improved the predictability of local disasters in 2014. Furthermore, we performed Monte Carlo debris-flow simulations using rainfall data from 2014 using the model. We confirmed that the spatial distribution of disaster probability is consistent with the actual damage.

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.

An extended CFD-DEM model based on micropolar fluid and its application in geological engineering

CFD (computational fluid dynamics)-DEM (discrete element method) model has been widely applied in the simulation of the multiphase flow involving granular materials, but it’s time-consuming for the calculation of a large number of particles with different sizes in DEM. In this study, a model based on the computational micropolar fluid dynamics and discrete element method, viz. a CMFD-DEM model, is proposed to describe the coupling system that consists of gas–liquid two phases and discrete particles with different sizes. In this model, micropolar fluid model is employed to describe the mixture of the pure fluid with fine particles, while discrete element method is used to calculate the motion of the larger particles. In addition, VOF (volume of fluid) method is adopted to track the free surface of the liquid. The implementation of the CMFD-DEM model is based on the open source software, OpenFOAM and LIGGGHTS, and is validated in single particle sedimentation and particles pouring into quiescent water cases. Then, the simulation of debris flow and bank collapse are carried out. The results show that the average velocity and runout of the debris flow are decreased with the increase of micropolar parameter N/L, the collapsed ratio of the bank is smaller under the CMFD-DEM model comparing to that under the DEM-VOF model. Through the comparisons to the exiting results, it suggests that CMFD-DEM model is capable to describe the multi-size effect of the granular materials in the geological phenomena.

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.

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.