Movement pattern of debris flow

Debris flows are one of the perilous landslide-related hazards due to their fast flow velocity, large impact force, and long runout, in association with poor predictability. Debris-flow barriers that can minimize the energy of debris flows have been widely constructed to mitigate potential damages. However, the interactions between debris flows and barriers remain poorly understood, which hampers the optimal barrier installation against debris flows. Therefore, this study examined the effect of barrier locations, in particular source-to-barrier distance, on velocity and volume of debris flows via the numerical approach based on smoothed particle hydrodynamics (SPH). A debris-flow event was simulated on a 3D terrain, in which a closed-type barrier was numerically created at predetermined locations along a debris-flow channel, varying the source-to-barrier distance from the initiation point. In all cases, the closed-type barrier significantly reduced the velocity and volume of the debris flows, compared to the cases without a barrier. When the initial volume of source debris was small, or when the flow path was short, the barriers effectively blocked the debris flow regardless of the source-to-barrier distance. However, with a long flow path, installation of the barrier closer to the initiation location appeared more effective by preventing the debris volume from growing by entrainment. Our results contribute to a better understanding of how source-to-barrier distance influences debris-flow behavior, and show that the methodology presented herein can be further used to determine optimum and efficient designs for debris-flow barriers.

Debris flow which has rapid character and strong destruction is a common natural disaster in the mountainous areas of China. The terrain of our country is high in the west and low in the east, and the terrain is complex and changeable. Chinese alpine and high-altitude mountainous areas are widely distributed. In addition, various types of debris flow disasters occurred frequently, especially in summer. Based on the analysis of a large number of alpine mountain debris flow researches, we summarize some key issues of these special research problems:the formation conditions and development rules of the debris flow in the alpine natural environment, the disaster chain effect, and the alpine mountain debris flow research methods and prevention measures. Among them, the problem of debris flow caused by glacier-lake breakout and debris flow blocking rivers has attracted wide attention. In addition, the Qinghai-Tibet Plateau has also become an important focus of the study of debris flow in the alpine mountain areas. The paper also combines the main research problems and environmental change trends in recent years, and puts forward development suggestions for the study of debris flow in the alpine mountain area in the future.

Our aim is to determine the run-out distance of the debris flow that is crucial in the assessment, prevention and control of the debris flow hazard. Based on the variation characteristic of debris flow velocity in the alluvial fan, this paper proposes the calculation method of the velocity attenuation coefficient of the debris flow. By defining the velocity attenuation coefficient and deducing its calculating formula, this paper puts forward a new method to determine the run-out distance of the debris flow based on the velocity attenuation coefficient, and Gangou debris flow in Luding County, Sichuan Province is selected as a case for calculation and verification. Having 10 m as its measuring spacing, this paper measured 19 sections at the alluvial fan of the Gangou debris flow (among them, 11 sets of data are valid). And based on the measurement, this paper analyzes the characteristic of the velocity attenuation and calculates its velocity attenuation coefficient after the 2005 debris flow. The study indicates that when the velocity of Gangou debris flow at the alluvial fan is greater than 12 % of the initial velocity (at the mouth of gully), the attenuation is quite remarkable. But when the velocity at the alluvial fan is less than 12 % of the initial velocity, the attenuation is quite slow. Besides, when Gangou debris flow rushes out of the gully mouth (the initial velocity is 10 m/s) and when it attenuates to the 32 time, its velocity is less than 0.1 m/s, the debris flow is considered to stop flowing, and the run-out distance of Gangou debris flow is calculated to be 320 m. But the present alluvial fan of Gangou debris flow is measured to be 285 m in length, and the calculated run-out distance is 320 m, which is 35 m longer than its present length. This means when the debris flow runs out in 2005, it blocked up the main river (Dadu River) in some extent. And this finding is generally in accordance with that from the field survey. The findings can be of theoretical and practical significance in the debris flow hazard assessment, as well as its prevention and mitigation.

The predictive hazard analysis at a detailed scale for debris flow runout analysis can be improved significantly through reliable estimation of the input parameters. In this study, a method for database establishment of input parameters at a site-specific scale was laid out for the predictive-based debris flow hazard assessment under extreme rainfall. The adoption of the DAN-3D code necessitated the estimation of three main input parameters: initial volume, bulk basal frictional angle, and growth rate. The initial volume was assessed using a 3D coupled finite element seepage and limit equilibrium-based slope stability analysis. An artificial neural network-based model was developed using 27 debris flow events for predicting the basal bulk frictional angle and consisted of eight factors: plan curvature, profile curvature, percentage of fine content, D50, initial unit weight, initial volume, relative relief ratio, and channel length. Finally, the growth rate was estimated using the previously assessed initial volume, soil depth, and the approximate runout length. The proposed method was validated by application to the Raemian slope in the Woomyeon mountain region, Seoul, for the extreme rainfall event of 27 July 2011. The analysis yielded a final volume of 53,067.9 m3, a velocity upon arrival on the road of 26.81 m/s, and an approximately 0.5-m debris thickness concentrated near the Raemian apartments. The comparison of the predicted debris flow path and debris flow velocity with the actual event demonstrates good similarity and provides a conservative estimate of the volume. This study therefore illustrates the importance of an input parameter database in providing a reliable debris flow runout hazard assessment.

Three thick stratigraphic sections and two small outcops have been studied in Mississippian rocks to NW Adamuz. These rocks have been interpreted as slope facies, containing a hemipelagic background sedimentation, with common olistolites, debris flows, slumps and turbidite beds. The majority of the olistolites and clasts embedded in the debris flows are assigned to the late Visean, but some olistolites, turbidite beds and wackestones of sponge spicules (Iikely also background sedimentation), exhibit foraminiferal and algal assemblages assigned to the Pendleian (early Serpukhovian). Thus, the age of the entire deposit is considered as Pendleian in age. Stratigraphic, biostratigraphic and sedimentological features of this area in Adamuz are similar to those described in the literature from the Guadiato Area, which contains one of the scarce record of Pendleian carbonate rocks in the region. However, some differences have been also recognised, and thus, the correlation between the Guadiato Area and Adamuz is questionable, because the tectonic conditions which controlled the sedimentation in both areas are slight1y different.

This paper examines the kinematical characteristics of the collapse-debris flow in red beds. It presents an evaluation method about spatial prediction of the collapse-debris flow in red beds. It takes the Kangsu collapse in red beds as an example. It uses the aerial photography of the unmanned aerial vehicle and the field geological survey, and combines them with the engineering geological elements of the collapse study area. It analyses the formation mechanism and the failure types of the collapse. The research shows that the collapse is the crack-type collapse. The collapse is mainly controlled by the combination of lithology of dangerous rock mass and structural plane of slope body. The hazard mode is given as follows: Firstly, rocks have the different weathering resistance under the conditions of wind and other external forces. Secondly, under the action of freezing and thawing, the rock mass structure is destroyed. Thirdly, when the unloading fracture zone is expanded further, the bottom of dangerous rock mass can be in an empty state. At last, under the action of gravity, the collapse occurs unsteadily and impacts to the slope surface to form debris flow. And the DAN-W model is used to simulate the motion process of the collapse-debris flow. The calculation results show that the duration of the collapse-debris flow movement is about 50 s, the average thickness about accumulation body reaches 2 m and the maximum speed is 11.5 m·s-1. And the longest impact distance is 315 m. The calculated results are in good agreement with the actual situation. It proves that DAN-W model can be used to analyze the dynamic hazard effects of the collapse-debris flow in red beds area. The paper providesareference for the analysis of the formation characteristics and movement effects of similar potential collapse-debris flow hazards in red beds.

Deposition morphology in large-scale laboratory stony debris flows

The authors predicted mudflow and debris flow velocities with 350 field and laboratory measurements and obtained a slight trend for V=u to increase with h=d50, and the ratio of V=u is approximately 10 and rarely exceeds 30. The logarithmic relationship of turbulent resistance agrees reasonably well with the measurements. Good results also are obtained with the Manning-Strickler approach. The dispersive stress equation also compares well with the measurements, but only when h=d50 < 50. For individual series data such as Hashimoto and Puerco, there is a trend for V=u to increase with h=d50. But for other individual series data, such as Davies, Rickenmann, Paris, St. Helens, Nevado del Ruiz, Wanglin, Wang, and Wenhai, there is a trend for V=u to decrease with h=d50 (Fig. 1 of the original paper). The discussers have some field data that also show the same phenomena, which are presented in Fig. 1. The database includes a total of 119 flow velocity measurements, in which each point includes flow depth, density (volume concentration), median grain diameter d50, grain size of less than 10% d10, and slope. The data of Jiangjia were obtained from the field measurements in Jiangjia Ravine, Yunnan, China, in 1999; the data of Hunshui were obtained from the field measurements in Hunshui Ravine, Yunnan, China, in 1976–1978; and the data of Liuwan were obtained from the field measurements in Liuwan Ravine, Gansu, China, in 1963–1964. Debris flow is a gravity flow, and the gravity force plays an important role in the movement of debris flow. So debris flow moves on a large slope and deposits on a small slope. Fei and Su (2004) showed that the main driving force of debris flow is provided by particles, not by water. When the volume concentration C 1⁄4 0:27 (or density ρ 1⁄4 1:46 g=cm3), the particle driving force is equal to the water driving force in debris flow. They defined that the minimum density of debris flow is 1:46 g=cm3, and 1:46–1:80 g=cm3 is the range of less viscous debris flow. Therefore, the minimum density of viscous debris flow is 1:80 g=cm3 (C 1⁄4 0:47) (Fei and Su 2004; Yu 2008a). Two types of shear stresses describe these two kinds of debris flows: (1) the viscous stress for viscous debris flow, and (2) the turbulent stress for less viscous debris flow (Fei and Su 2004). As the driving force of debris flow is provided primarily by particles, the coarse particle plays an important role in the movement of debris flow, especially for viscous debris flow with a large volume concentration. So the larger particle diameter, the larger is the velocity. There is a trend for V to increase with d50, and there is a trend for V=u to increase with d50=h. Two empirical equations of mean velocity of viscous debris flow described this relationship (Wu et al. 1993; Yu 2001): V u 1⁄4 27:57 d50 h 0:245 ð1Þ

The Bailong River catchment is located in the intersection of Tibetan Plateau,Loess Plateau and Sichuan Basin.It is also the cross point of the east-west and north-south seismic zones.Due to complex geological structures,the region is characterized by steep slopes,high relative reliefs and deep incised valleys.Weak rocks,which are widely distributed,and heavy rainfalls made the region one of the four areas in China most severely affected by landslide and debris flow disasters.Based on the data from field investigation and on-going research projects,this paper deals with the characteristics of landslides and debris flows,and their genetic mechanisms.The management of monitoring and early-warning systems and hazard prevention in this region are also discussed,with the purpose to encourage further researches on geohazards and mitigation measures in the region.

Debris‐flows are widespread natural phenomena characterized by high mobility (high velocity and long runout distance) and impact forces, which frequently cause human casualties and significant damage to infrastructure. To better understand the dynamics of such events, analyzing in particular the effect induced by the valley geometry on flow velocity, runout and mobilized volumes, in this work we reconstruct a real debris‐flow event through numerical modeling. Specifically, we used a modified version of the BING model, a fluid‐dynamic depth‐integrated numerical model for debris flows, which has been properly modified to account for width changes along the valley. The studied event, which occurred in Scaletta Zanclea (Messina, north‐eastern Sicily, Italy) on October 1, 2009, is exceptionally well constrained by field and topographic information. In this respect the flow velocity, estimated from two specific locations on the basis of field evidence, the distribution of erosional and depositional areas along the Racinazzo valley, based on the comparison of pre‐ and post‐event digital elevation models (DEMs), and the runout distance were used as constraints to calibrate the model. Furthermore, we report a detailed description of the main event characteristics based on hydrological records and witness reports. The numerical modeling results are consistent with witness reports and the severe damage recorded in the Scaletta Marina village, and highlight the effect of the valley geometry on both the debris flow velocity and the erosion/deposition processes. The effect of changing valley width has been also quantified, resulting in accelerations of the debris in correspondence of the valley narrowing and stagnations at the plateaus. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Gravitational mass movements, such as debris and mud flows, are among the most destructive natural hazards, leading to substantial fatalities and extensive economic damage worldwide. Improving our understanding and modeling of these processes is essential for developing effective risk management and early warning strategies. When debris and mud flows pass through a curved channel, centrifugal forces may cause a difference in flow height between the inner and outer banks of the channel. This height difference, known as superelevation, can be described using analytical models that establish a relationship between the superelevation height and the flow velocity.Analytical models often employ a forced vortex approach, incorporating parameters such as the cross-sectional slope of the flow surface, flow width, and bend radius. These models, however, rely on assumptions such as a linear flow surface between mud deposits on the banks, a rectangular cross-section, and neglect both complex rheological behaviors and solid-fluid interactions. As a result, an empirically determined correction factor is required within the formula. The absence of a clear mechanical rationale for this correction factor presents challenges, as it is currently derived only through field investigations and laboratory experiments.This study presents an enhancement to the existing forced vortex approach by incorporating insights from numerical modeling. A coupled SPH-DEM numerical model is employed, where DEM particles represent coarse solid particles, and SPH accounts for the fluid phase, comprising fines and water. The SPH-DEM coupling is based on the no-slip interaction model, with simulations performed using a GPU-based solver to ensure enhanced computational efficiency. To validate the approach, a parametric test is conducted, initially back-calculating laboratory-scale experiments. The study further involves varying the water content in debris and mud flows to examine its impact on flow behavior and superelevation. Larger water contents lead to an increased superelevation angle. Results from the parametric test reveal a clear correlation between water content and the flow surface shape in curved channels. Specifically, mud flows are characterized by convex upward surface shapes, whereas more granular debris flows typically exhibit concave downward shapes.The distribution of material within the cross-section of the flow is governed by the equilibrium between boundary forces and centrifugal forces acting on the flow, which directly influences the superelevation. Numerical investigations are conducted to determine a correction factor and assess the extent to which inertial effects contribute to this correction factor for different material mixtures. Furthermore, we demonstrate that the effect of the flow surface shape is significant and is currently only accounted for by the empirical correction factor. This study offers new physical insights for the back-calculation of debris flow velocities in curved sections marked by mud deposits. Large-scale SPH-DEM simulations of a real debris flow event at Illgraben (Switzerland) are performed, showing good agreement with field data and its potential for further real-scale modeling.

Sombe-Lewara River is a tributary of Palu River which lies at the most downstream part of Palu River which has 112.38 Km 2 of catchment area and 28.11 Km of river length. Sombe-Lewara River comprises three reaches, i.e. Sombe River, Lewara River, and Sombe-Lewara River. In order to control the debris flow disaster, six sediment control structures have been built in Sombe River and another two were built in Lewara River. The sand mining activity in Sombe-Lewara River has caused river degradation and to some extent damaged sediment control structures. In order to prevent the river from further degradation and decrease in environment condition, a proper sediment management is therefore considered necessary. This paper illustrates the sediment balance analysis which applies the empirical formula of sediment supply at the upstream of sediment control structure and storage characteristics of sediment control structures, the initiation of debris flow occurrence and the sediment volume controlled by sediment control structures. The sediment balance was studied based on the sediment flow within the period of 2000 through 2009, at the existing infrastructures and the further development of sediment control structures. The results show that at 10 mm rainfall depth over the catchment, the average annual sediment supply at Somber River and Lewara River was found to be approximately 240,195 m 3 and 112,500 m 3 respectively. Within the above period, the sediment volume passing through control point 1 was approximately 105,890 m 3 . Furthermore, the sand mining activity at Sombe-Lewara River has caused severe river degradation and damage on the existing sediment control structures. Keywords : Sediment balance, sediment control structures, sand mining.

The design of appropriate mitigation measures to protect from landslides require the knowledge of the physical and mechanical processes governing their propagation. This knowledge can derive from experience, carefully verified and modeled through specific rheological models that take into account the main physical and mechanical properties referred to normal stream flows, hyperconcetrated flows, mudflows, debris flows, rock avalanches and their multiphase nature (flow like or granular).To predict the speed evolution and distance travelled by fine-grained material flows, an analytical (sliding block) model is proposed. The model takes into account (i) the (curved) geometry of the sliding surface; (ii) the mass variation due to possible erosion or deposition processes; iii) the interstitial pressures and, in particular, the evolution of the excess pore water pressures (generation, initially due to several phenomena and during the motion to the slope curvature, coupled to undrained and oedometric conditions; dissipation, due to consolidation process).The governing ordinary differential equation has been numerically solved. The role played by the main model parameters on the kinematics of rapid fine - grained material flows is evaluated through parametrical analyses and the range of their admissible values is investigated and defined. Model validations using laboratory measurements and analysing some documented cases are finally developed and carried out.

Debris flow can cause serious damages to roads, bridges, buildings and other infrastructures. Arranging several rows of deceleration baffles in the flow path can reduce the flow velocity and ensure better protection of life and property. In debris flow prevention projects, deceleration baffles can effectively reduce the erosion of the debris flow and prolong the running time of the drainage channel. This study investigated the degree to which a 6 m long flume and three rows of deceleration baffles reduce the debris flow velocity and affect the energy dissipation characteristics. The influential variables include channel slope, debris flow density, and spacing between baffle rows. The experimental results demonstrated that the typical flow pattern was a sudden increase in flow depth and vertical proliferation when debris flow flows through the baffles. Strong turbulence between debris flow and baffles can contribute to energy dissipation and decrease the kinematic velocity considerably. The results showed that the reduction ratio of velocity increased with the increase in debris flow density, channel slope and spacing between rows. Tests phenomena also indicated that debris flow density has significant influence on the mobility and deposition characteristic of debris flow. The deposit amount first increased then decreased when the flow density rises, and the deposit amount of debris flow density of 1500 kg/m3 reached the maximum when the experimental flume slope is 12°.

In order to effectively prevent and control debris flow disasters, it is one of the most effective engineering measures to construct a blocking project in the valley section of the circulation section to actively reduce the flow and velocity of debris flow. The check dams is taken as a control structure to intercept the solid materials of flush flood and debris flow in the channel, which play an important role in debris flow prevention and control project. However, the huge impact force of debris flow often causes the check dam to be destroyed. Based on the theory of fluid–solid coupling, by means of structural dynamics simulation software, fluid dynamics simulation software and coupling plane data transfer software, numerical simulation of the interaction between debris flow and the check dam has been carried out. Research results indicate that (1) the overflow section is subjected to the impact of the debris flow greater than the abutment; (2) debris flow impact only has a greater impact on a certain depth of the check dam, and the impact beyond this range is less. The numerical simulation results can provide data support for the design and optimization of the check dam.