Debris Flow Hazard Mitigation Research Articles

Towards a better understanding of debris flow sediment sources: Monitoring of an active rock slope at Spitze Stei, Switzerland

Rapid process cascades can lead to destructive debris flows. Identifying and characterizing the processes conditioning debris-flow occurrence will strongly contribute to the mitigation of debris-flow hazards. In recent years, the rock slope near “Spitze Stei”, in the Kandersteg region, Switzerland, has exhibited elevated displacement rates exceeding 10 cm per day, suggesting a growing instability up to 20 million m3. The accumulated sediments at the bottom of the Spitze Stei slope are mobilized as debris flows by melting snow and heavy summer precipitations. Here, we use seismology combined with an intelligent algorithm to automatically detect rockfall and landslides at the Spitze Stei rock slope. These mass movements act as primary sediment sources delivering sediments to a debris-prone channel. Our initial results quantify mass movement activity before two debris flow events that occurred in 2022 and identify their triggers. Such analysis can contribute towards mitigating debris flow hazards and extending warning time, especially for debris flows triggered by factors other than precipitation.

Geographic information system models with fuzzy logic for susceptibility maps of debris flow using multiple types of parameters: a case study in Pinggu District of Beijing, China

Abstract. Debris flow is one of the main causes of loss of life and infrastructure damage in mountainous areas. This hazard should be recognized in the early stage of land development planning. According to field investigation and expert experience, a scientific and effective quantitative susceptibility assessment model was established in Pinggu District of Beijing. This model is based on geographic information system (GIS) combined with grey relational, data-driven and fuzzy logic methods. The influence factors, which are divided into two categories and consistent with the system characteristics of a debris flow gully, are selected, but also a new important factor is proposed. The results of the 17 models are verified using data published by the authority and validated by two other indexes, as well as area under curve (AUC). Through the comparison and analysis of the results, we believe that the streamlining of factors and scientific classification should attract attention from other researchers to optimize a model. We also propose a good perspective to make better use of the watershed feature parameters. These parameters fit well with the watershed units. With full use of insufficient data, scientific calculation and reliable results, the final optimal susceptibility map could potentially help decision makers in determining regional-scale land use planning and debris flow hazard mitigation. The model has advantages in economically weak areas with insufficient data in mountainous areas because of its simplicity, interpretability and engineering usefulness.

Erosion Process of Multiple Debris Flow Surges Caused by Check Dam Removal: An Experimental Study

AbstractDebris flows are one of the most serious natural disasters on Earth and cause great losses in human life and property each year. Check dams have been widely utilized in debris flow hazard mitigation, and over time, some control projects have exceeded their designed service lifetime. However, the processes of stored sediment erosion with multiple surges of debris flows after check dam removal are unknown. Here, the stored sediment erosion processes associated with different reductions in the dam height (i.e., the removed height) were revealed by physical experiments. The results showed that erosion was concentrated on the stored sediment scarp formed by dam removal and that the erosion process mainly included undercutting and widening. The erosion efficiency of the debris flow gradually decreased with the development of erosion and was positively correlated with removed height, negatively correlated with the accumulated debris flow volume, and proportional to the remaining potential volume of sediment to be eroded. The erosion volume development process was well described by an exponential function model, and the physical meanings of the parameters in the model and their empirical values were clarified. Moreover, the distribution of the erosion volume along the flume was shown to satisfy the Weibull distribution, and the distribution parameters were related to the removed height, erosion volume, and sediment volume fraction of the debris flow. We anticipate that our results will serve as a starting point for the demolition and reconstruction of debris flow hazard mitigation engineering in mountainous areas.

Impact failure models and application condition of trees in debris-flow hazard mitigation

Impact failure models and application condition of trees in debris-flow hazard mitigation

The relationship of human activities and rainfall-induced landslide and debris flow hazards in Central China

Human activities have been recognized as one of the significant influencing factors on natural hazard, yet studies of quantitative relationship between human activities and natural hazard have been limited. The relations of human activities and hazards (landslide and debris flow) induced by heavy rainfall are quantitatively analyzed in this study and suggestions are provided for the integrated hazard mitigation management in the study area of Central China. The results show that human activities index (HAI) is an effective indicator to characterize spatiotemporal changes of human activities. The relations of rainfall-induced landslide, debris flow hazards and human activities are significant as shown in spatial distribution. The probability of rainfall-induced landslide, debris flow hazards is highly correlated with the intensity of human activities and the changes of HAI. However, in terms of temporal relations, human activities have more direct impact on rainfall-induced landslide hazard than on rainfall-induced debris flow hazard, as the frequency of landslide hazard shows a 2-year delay with HAI changing, in general, according to the cross-wavelet transform analysis. In comparison, no significant correlating period is shown between the changing human activities and the frequency of rainfall-induced debris flow hazard. Specifically, there are three types of time relationship between the changing human activities and rainfall-induced landslide, debris flow hazards in the affected counties: (1) concurrent changing, accounting for 30% of landslide and 18% of debris flow; (2) lagging relationship, accounting for 54% of landslide and 30% of debris flow; (3) no direct relationship, accounting for 16% of landslide and 52% of debris flow. The results in this study suggest that HAI is a simple and effective index for the local governments to manage human impacts on rainfall-induced landslide and debris flow hazards, and integrated prevention measures are suggested to be executed when HAI reaches 0.072. In addition, the types of human activities also impact landslide, as the ratio of Economy factor to Land use factor (E/L) is significantly (P < 0.05) higher in counties with concurrent relationship of changing human activities and frequency of rainfall-induced landslide hazard. The results should assist the policy-making for integrated mitigation of rainfall-induced landslide and debris flow hazards at local/regional level, while balancing economic development and natural hazard.

An artificial neural network model to predict debris-flow volumes caused by extreme rainfall in the central region of South Korea

In South Korea, the risk of debris-flow is relatively high due to the country's vast mountainous topographical features and intense continuous rainfall during the summer. Debris-flows can result in the loss of human life and severe property damage, which can be made worse due to the poor spatiotemporal predictability of such hazards. Therefore, it is essential to research the preemptive prediction and mitigation of debris-flow hazards. For this purpose, this study developed an ANN model to predict the debris-flow volume based on 63 historical events. By considering the morphology, rainfall, and geology characteristics of the studied area in central South Korea, the data of 15 debris-flow predisposing factors were obtained. Among these data, four predisposing factors (watershed area, channel length, watershed relief, and rainfall data) were selected based on Pearson's correlation analysis to check for significant correlations with the debris-flow volume. To determine the best performing ANN model, a validation testing was carried out involving ten-fold cross-validation with MSE and R2 using both training and validation datasets, which were randomly split into a 7:3 ratio. The model performance validation results showed that an ANN model with two hidden neurons (4×2×1 architecture) had the highest R2 value (0.828) and the lowest MSE (0.022). In addition, in a comparative study with other existing regression models, the ANN model showed better results in terms of adjusted R2 value (0.911) using all datasets. Furthermore, 94% of the observed debris-flow volumes from the ANN model were within 1:2 and 2:1 lines of the predicted volumes. The results of this study have shown the potentiality of the developed ANN model to be a useful resource for decision-making and designing barriers in areas prone to debris-flows in South Korea.

Measurements of Velocity Profiles in Natural Debris Flows: A View behind the Muddy Curtain

ABSTRACT The internal deformation behavior of natural debris flows is of interest for model development and model testing for debris-flow hazard mitigation. Up to now, only a few attempts have been made to measure velocity profiles in natural debris flows due to the low predictability and high destructive power of these flows. In this contribution, we present recent advances to measure in-situ velocity profiles together with flow parameters like flow height, basal normal stress, and pore fluid pressure. This was accomplished by constructing a fin-shaped monitoring barrier with an array of paired conductivity sensors in the middle of Gadria Creek, Italy. We present results from two natural debris-flow events. Compared to the first event on July 10, 2017, the second event on August 19, 2017, was visually more liquid. Both debris flows exhibited significant longitudinal changes of flow properties like flow height and density. The liquefaction ratios reached values up to unity in some sections of the flows. Velocity profiles for the July event were mostly concave-up, while the profiles for the more liquid event in August were linear to convex. These measurements provide new insights into the dynamics of real-scale debris flows.

Information Entropy Embedded Back Propagation Neural Network Approach for Debris Flows Hazard Assessment

The purpose of the study is to propose a new method to assess debris flow hazard by embedding Shannon’s information entropy in back propagation neural network. The procedure was divided into two parts. One was to establish a mathematical model for debris-flow hazard assessment based on Shannon’s information entropy forming input and output data sets of back propagation neural network. The other was to establish a back propagation neural network technique for characterizing debris flow dynamic hazard. The proposed method was employed to assess debris flow hazard of Shenxi gully basin, Sichuan province, China. The result shows that the assessed result of proposed method is highly consistent with the result of field surveys. The proposed method can reflect the interaction, nonlinearity and dynamic process of background variable factors and can be used to debris flow hazard assessment, risk management and mitigation of debris flows.

Predictability of Naïve Bayes classifier for lahar hazard mapping by weather radar

The aim of this study is to develop lahar hazard vulnerability as a warning system by introducing radar-rainfall observation to data mining technique of Naïve Bayes Classifier (NBC). NBC is used to estimate lahar occurrences based on the posterior probability of rainfall, topographic factor, soil moisture, and soil type as predictors. Rainfall intensity and working rainfall were obtained from a weather radar. The soil moisture is derived from SMAP satellite imagery. A river on Mount Merapi, a very active volcano in Indonesia, was selected as the target basin. Observed rainfall and recorded lahar events in Gendol River from October 2016 to February 2018 were divided into a training dataset and a testing dataset. Qualitative evaluation through visual assessment of the hazard map product reveals that the model could estimate the occurrences of lahar. The performance of the model in terms of accuracy, Brier score, and quantitative dichotomous quality indices showed a reasonable skill. The study suggests that the NBC technique is advantageous for estimating lahar occurrences that are displayed on hazard maps. This work is expected to contribute to debris flow hazard mitigation by the data mining approach in volcanic regions.

Case study on debris-flow hazard mitigation at a world natural heritage site, Jiuzhaigou Valley, Western China

The Jiuzhaigou earthquake on 8 August 2017, led to a significant increase in the amount of loose, solid material, which has been a rich source of debris-flow activity. In this paper, a comprehensive debris-flow prevention and control system consisting of stabilization, blocking, and deposition structures is proposed based on the topographic features of the debris-flow gullies in the Jiuzhaigou Valley. Taking the Xiajijie Lake gully as a case study, the history and formation of debris-flow disasters were analysed. This study proposes the main principles of debris-flow prevention and control as well as implementation measures, consisting of lateral diversion and deposition at the outlet of the gully. In addition, several environmental mitigation measures are proposed. Galvanized wire gabions can be placed in front of trees to lessen the debris-flow impact force, and bushes can be planted in front of deposition retaining walls to increase their aesthetic value. Alternatively, steel structures can be constructed on deposition retaining walls and filled with nutrient soil, and grass can be planted in these structures for an enhanced aesthetic appeal.

Regulation effectiveness of a window-check dam on debris flows

Window-check dams are widely used to regulate sediment transport in debris-flow hazard mitigation. However, the effectiveness of window-check dams on modulating debris flows is still unclear. In this study, dimensional analyses combined with physical experiments were conducted to evaluate the sediment-trapping and particle-regulating functions of a window-check dam. Results showed that both of the attenuation ratio of unit weight and (the difference between upstream and downstream divided by upstream) the retention ratio of mass (upstream divided by downstream) decreased with an increase in openings area, drain holes width, and bottom slope. However, the increase in inflow unit weight of debris-flow led to larger retention ratio of mass. Besides, an optimal attention ratio corresponding to dimensionless unit weight of 1.8 was found. Also, the particle sizes sorted by the window-check dam were found to be associated with the median grain size of sediment. Furthermore, two improved expressions were obtained to assess the effectiveness of window-check dams on trapping sediments. The comparison between these expressions and laboratory data is in reasonable agreement, serving a useful reference for the optimal design of check dams.

Quantitative analysis of debris-flow flexible barrier capacity from momentum and energy perspectives

In-depth understanding of debris-structure interaction is hindered by a lack of physical data of debris flow impacting structures. This study reports a set of centrifuge experiments investigating the impact load exerted by debris flow on rigid and flexible barriers. A combination of high-speed imagery and load-displacement sensors enabled a comprehensive grasp of the impact details, including flow depth, velocity, impact pressure, bending moment, and cable force-elongation of flexible barrier. Test results reveal that the debris-structure interaction plays a major role in the energy dissipation and impact load reconstruction. The built-up of static load behind the barrier occurs simultaneously with the grow-up of impact force. As a result, the momentum flux of incoming flow is not merely a surrogate of the impact force. A quantitative analysis from the energy perspective has been conducted. Under the experimental conditions of this study, debris flow impact results in over 90% of debris energy dissipated through the internal and boundary shearing, leaving <10% absorbed by the flexible barrier. Findings from the energy and momentum perspectives could facilitate the optimization of flexible barriers in mitigation of debris flow hazards.

Experimental study on characteristics of trapping and regulating sediment with an open-type check dam in debris flow hazard mitigation

Beam dams are a highly effective and commonly used open-type check dam in debris-flow hazard mitigation. In this study, dimensional analysis was used to obtain empirical equations for quantitatively determining the sediment-trapping and flow-regulating characteristics of a beam dam. To determine the coefficients of the empirical equations, flume experiments were conducted to simulate the trapping and regulating processes. The flow pattern, trapping, and regulating characteristics were investigated when debris flows passed through a beam dam. Debris-flow bulk density and peak discharge, and sediment-trapping ratios, were measured directly and indirectly. The results showed that three blocking actions occurred, and that blockage-breaking considerably influenced the trapping and regulating performance of the beam dam. The relative opening size and the sediment concentration were the two main factors affecting the performance of the beam dam. The ratio of trapping sediment decreased with relative opening, and increased with sediment concentration as well as reducing ratio of bulk density and reducing ratio of peak discharge. The sediment concentration and relative opening were the leading factors influencing the trapping and regulating sediment of a beam dam, followed by flume gradient. The results showed that the calculated values obtained using empirical equations were in good agreement with the values derived from the experiments, and that the deviation was acceptable. Finally, taking Zechawa Gully as an example, using the empirical equations we designed the opening size of a beam dam aimed to trap sediment and regulate peak discharge of debris flow in the main gully.

Numerical Simulation on the Dynamic Characteristics of a Tremendous Debris Flow in Sichuan, China

The mega debris flow that occurred on 13 August 2010 in Zoumaling Valley in Mianzhu County, China has done great damage to the local inhabitants, as well as to the re-construction projects in the quake-hit areas. Moreover, it is of high possibility that a secondary disaster would reappear and result in worse consequences. In order to maximize risk reduction of this problem, the local government planned to construct seven debris-resisting barriers across each ditch for mitigation of debris flow hazards in the future. In this paper, the numerical simulation fields of flow velocity, pressure, and mud depth of the Zoumaling debris flow had been computed by using finite volume method software based on computational fluid dynamics (CFD). The Bingham fluid was chosen as the constitutive model of this debris flow. The debris flow geometry model was a 3D model. The initial conditions, boundary conditions, control equations, and parameters were determined and adjusted by the actual conditions and analyses. The flow field data obtained from numerical simulations were substituted into the finite element software ANSYS. Then the calculations of fluid-solid coupling action between the flow and dam had been done. All these results of simulations and analyses could be the guide and suggestion for the design and construction of prevention engineering of Zoumaling debris flow.

Experimental study on blocking and self-cleaning behaviors of beam dam in debris flow hazard mitigation

Blocking is one of the important features when a beam dam intercepts debris flow, while self-cleaning is another when managing suspended debris flow. Both features determine the debris flow control benefits of beam dam but the latter often is not considered in practical engineering design. In this paper, a series of specially designed flume experiments were done to simulate blocking and self-cleaning processes. The blocking ratio and deposition features were measured to contrast the blocking and self-cleaning performance before and after artificial self-cleaning. The experimental results reveal that the beam dam net opening, particle diameter of sediment, sediment concentration, and gradient of the channel are the main factors affecting blocking performance. A new criterion of blocking performance of beam dams that considers the interaction of multiple factors and can provide guidance to practical project design is proposed. For all three types of blocking, sediment deposited upstream of a beam dam can be effectively transported downstream by erosion from post-debris-flow floods, Self-cleaning performance is most efficient for temporary blocking, followed by partial-blocking, and total-blocking. The efficiency of self-cleaning largely depends on the change of the sediment deposit due to erosion. Finally, a discussion is given for the optimal design of an open-type check dam and the feasibility of synergistic effects of self-cleaning in combination with artificial cleaning. Some supporting artificial silt-cleaning should be implemented in practice. A beam dam will, thus, have more storage capacity with which to control the next debris flow event.

Dynamic Process Analysis and Hazard Prediction of Debris Flow in Eastern Qinghai-Tibet Plateau Area—A Case Study at Ridi Gully

ABSTRACTProcess analysis and hazard prediction are essential for the prevention and mitigation of debris-flow hazards in mountainous areas. Many villages and ongoing infrastructure projects in China are vulnerable to large debris flows during heavy rainfall or glacier lake outbursts. Without emergency management planning, such contingencies can lead to extensive loss of life and egregious property damage. In the eastern Qinghai-Tibet Plateau area, debris-flow disasters are a common phenomenon. Taking Ridi Gully in the Sichuan Province of China as a case study, we analyzed the process of debris-flow events by running a dynamic erosion model. Because of the dynamic nature of the process, we needed to take into account many variables. Some of these variables include strong erosion in the origin area, scouring and downward erosion in debris-flow path, and siltation in accumulation area. Subsequently, we analyzed the elements underlying the hazard formation conditions and proposed a systematic and quantitative method of debris-flow hazard prediction based on kinetic energy and flow depth. Finally, we predicted the hazard and damage potential induced by the debris flow triggered by a 100-year and 200-year return period precipitation in Ridi Gully. The simulation results indicate that debris flow will cause great damage to the Sichuan-Tibet railway (or highway) and the residential area on the alluvial fan. This strongly suggests that, given the high level of debris-flow hazard predicted, the proposed method may serve as pertinent and timely support in planning measures to prevent or reduce the debris-flow hazard, both in the eastern Qinghai-Tibet Plateau area and beyond.

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

A key objective in debris-flow hazard mitigation is the reduction of the potential depositional area in the fan. From this point of view, forested areas are able to provide a protective function hindering the flow motion and promoting the surge deposition. Despite extensive research on Alpine forests and their protective functions, relatively few studies in the literature have quantitatively focused on the relationship between debris-flow depositional features and vegetation. In light of the above, our research investigates how vegetation characteristics in the fan area interact with debris-flow deposition. Field investigations were carried out in two Alpine fans where debris-flow events occurred in the summer of 2012. By recording the characteristics of 1567 involved trees and the associated deposit thicknesses, this paper provides a data set that contributes to the improvement of the knowledge of these interaction processes. The integration of literature findings and the analysis of the collected dataset adds insights into the relationships between tree characteristics and the dynamics of debris flow during the runout path. The main results prove the capacity of the forest of uniformly promoting flow-energy dissipation, presence of high species diversity in debris-flow deposits when comparing disturbed and undisturbed forest stands, tree mortality largely affecting small diameters <10cm in the upper/medium part of the cone, and deposit thicknesses depending on the trunk diameter only if the debris-flow regime was collisional. Based on the field results and their analysis, some criteria for the management of protection forests in alluvial fans are suggested.

Prevention and Mitigation of Debris Flow Hazards by Using Steel Open-Type Sabo Dams

This paper presents the findings of an investigation on the prevention and mitigation of debris flow hazards by using steel open-type dams. First, the actual cases of trapping hazardous debris flow by steel open-type dams were surveyed. Through a field survey of actual cases, we classified them into four distinct scenarios based on the trapping type of debris flow: Scenario A (wooden debris + rocks + sediment), Scenario B (wooden debris + sediment), Scenario C (rocks + sediment) and Scenario D (wooden debris only). Second, recent trapping cases on protection and mitigation by various steel open dams were introduced. Third, trapping scenarios A, B, C and D were confirmed by performing physical model tests. Finally, a safety check of a steel open dam against a large rock was verified by two impact analyses, the finite element method (FEM) impact analysis using ANSYS Autodyn software, and the three dimensional (3-D) impact frame analysis.

Weights-of-evidence method based on GIS for assessing susceptibility to debris flows in Kangding County, Sichuan Province, China

Assessing susceptibility to debris flows is of great importance for hazard prevention and mitigation. Kangding County, a region with a high occurrence of destructive geological events, was selected as the study area, to evaluate the area’s susceptibility to debris flows using the weights-of-evidence method based on ArcGIS. First, the determination method of training points was revised. The unit cells covered by the debris flow catchments were set as the training points, rather than using one point to represent the debris flow catchment. Then, the landforms, lithology, faults, earthquakes, and river systems were selected as evidential themes for the analysis. The optimum buffer zones cutoff distance of the faults and rivers was determined by the maximum studentized value of the contrast. Finally, the map of the susceptibility to debris flow in Kangding County was obtained by combining the evidential themes. The susceptibility was categorized as low, moderate, and high susceptibility. The low-susceptibility zones cover an area of 6253 km2, accounting for 53.93 % of the county area. The moderate-susceptibility zones cover an area of 3323 km2, accounting for 28.67 % of the county area. The high-susceptibility zones cover an area of 2018 km2, accounting for 17.40 % of the county area. The moderate-susceptibility zones surround the high-susceptibility zones. The assessment results agree well with field data, demonstrating that the revised method is more suitable for debris flow assessment than the previous method. The assessment results can be used as guidelines for policy makers regarding prevention and mitigation of debris flow hazards.

Engineering measures for debris flow hazard mitigation in the Wenchuan earthquake area

Avalanches and landslides caused by the Wenchuan earthquake in the Longmen Mountains area provide abundant loose solids for debris flows, and a large number of debris flows have occurred during the period 2008–2012. The engineering measures in certain gullies failed, causing serious damage and loss of life. Judging from the debris flow characteristics in the Wenchuan earthquake area, engineering measures should be better constructed after the active period of debris flows in severely affected areas. To reduce debris flow disasters, this paper proposes a mitigation method and design principle based on the transport capacity of the main river. A series of check dams with various opening sizes was designed by investigating and analyzing existing cases. Furthermore, a new type of drainage channel with prefabricated reinforced concrete boxes is proposed. Finally, a case study of the Xiaogangjian Gully, which is a typical debris flow gully in the Wenchuan earthquake area, is presented. This system of engineering measures is based on the main river's transport capacity and consists of five check dams with various opening sizes, a drainage channel with sidewalls constructed of prefabricated reinforced concrete boxes, and a debris flow basin at the base of the main gully. The debris flow mitigation measures constructed in the Xiaogangjian Gully effectively resisted a debris flow with a 50-year return period that was triggered by rainfall on July 26, 2012. Specifically, these measures effectively protected a highway and minimized debris flow damage. Thus, the layout and engineered structures involved in this new engineering technique can provide a reference design for debris flow hazard mitigation.