Numerical investigation of hydro-morphodynamic characteristics of a cascading failure of landslide dams

A cascading failure of landslide dams caused by strong earthquakes or torrential rains in mountainous river valleys can pose great threats to people’s lives,properties,and infrastructures.In this study,based on the three-dimensional Reynoldsaveraged Navier-Stokes equations(RANS),the renormalization group(RNG)k-εturbulence model,suspended and bed load transport equations,and the instability discriminant formula of dam breach side slope,and the explicit finite volume method(FVM),a detailed numerical simulation model for calculating the hydro-morphodynamic characteristics of cascading dam breach process has been developed.The developed numerical model can simulate the breach hydrograph and the dam breach morphology evolution during the cascading failure process of landslide dams.A model test of the breaches of two cascading landslide dams has been used as the validation case.The comparison of the calculated and measured results indicates that the breach hydrograph and the breach morphology evolution process of the upstream and downstream dams are generally consistent with each other,and the relative errors of the key breaching parameters,i.e.,the peak breach flow and the time to peak of each dam,are less than±5%.Further,the comparison of the breach hydrographs of the upstream and downstream dams shows that there is an amplification effect of the breach flood on the cascading landslide dam failures.Three key parameters,i.e.,the distance between the upstream and the downstream dams,the river channel slope,and the downstream dam height,have been used to study the flood amplification effect.The parameter sensitivity analyses show that the peak breach flow at the downstream dam decreases with increasing distance between the upstream and the downstream dams,and the downstream dam height.Further,the peak breach flow at the downstream dam first increases and then decreases with steepening of the river channel slope.When the flood caused by the upstream dam failure flows to the downstream dam,it can produce a surge wave that overtops and erodes the dam crest,resulting in a lowering of the dam crest elevation.This has an impact on the failure occurrence time and the peak breach flow of the downstream dam.The influence of the surge wave on the downstream dam failure process is related to the volume of water that overtops the dam crest and the erosion characteristics of dam material.Moreover,the cascading failure case of the Xiaogangjian and Lower Xiaogangjian landslide dams has also been used as the representative case for validating the model.In comparisons of the calculated and measured breach hydrographs and final breach morphologies,the relative errors of the key dam breaching parameters are all within±10%,which verify the rationality of the model is applicable to real-world cases.Overall,the numerical model developed in this study can provide important technical support for the risk assessment and emergency treatment of failures of cascading landslide dams.

Particle size spatial distribution in landslide dams

The particle composition and spatial distribution of landslide-induced dam bodies are critical geotechnical parameters for studying the hazards of dam-break floods.However,current research often neglects the influence of the initial particle composition and spatial distribution of the landslide on the particle composition and spatial distribution of the landslide dam.This study investigated the impact of initial particle size distribution,volume,and sliding length on the energy and velocity changes of characteristic particles during the sliding process and the spatial distribution of particle sizes in the landslide dam body.Numerical simulations and physical models were employed to examine the effects of sequential gradient arrangements(where particle sizes decrease from top to bottom)and four other different initial particle arrangements on the energy and velocity changes of particles and the spatial distribution of particle sizes in the dam body.The study reveals the characteristics of translational and rotational energy of different particles and the laws of mechanical energy conversion,obtaining the spatial distribution patterns of particle sizes in landslide-induced dams.The results show that under the sequential gradient arrangement,the energy dissipation of the landslide movement is lower,with larger particles mainly distributed at the distal end and smaller particles at the proximal end of the landslide dam.In contrast,under the reverse gradient arrangement,the energy dissipation of the landslide movement is higher,and the distribution pattern of the dam particles is opposite to that of the sequential gradient arrangement.For the other arrangement modes,the spatial distribution of dam particles falls between the aforementioned two.There is a positive correlation between particle size and translational kinetic energy within the particle flow during the landslide process,and rotational motion increases energy dissipation.Under constant slope conditions,sliding length does not affect the movement pattern of the particle flow or the spatial distribution of particles in the dam body.The findings of this study provide a scientific basis for the accurate simulation and prediction of dam-break flood processes.

Characteristics and interpretation of the seismic signal of a field-scale landslide dam failure experiment

Outburst floods caused by breaches of landslide dams may cause serious damages and loss of lives in downstream areas; for this reason the study of the dynamic of the process is of particular interest for hazard and risk assessment. In this paper we report a field-scale landslide dam failure experiment conducted in Nantou County, in the central of Taiwan.The seismic signal generated during the dam failure was monitored using a broadband seismometer and the signal was used to study the dam failure process.We used the short-time Fourier transform(STFT) to obtain the time–frequency characteristics of the signal and analyzed the correlation between the power spectrum density(PSD) of the signal and the water level. The results indicate that the seismic signal generated during the process consisted of three components: a low-frequency band(0–1.5 Hz), an intermediate-frequency band(1.5–10 Hz) and a highfrequency band(10–45 Hz). We obtained the characteristics of each frequency band and the variations of the signal in various stages of the landslide dam failure process. We determined the cause for the signal changes in each frequency band and its relationship with the dam failure process. The PSD sediment flux estimation model was used to interpret the causes of variations in the signal energy before the dam failure and the clockwise hysteresis during the failure. Our results show that the seismic signal reflects the physical characteristics of the landslide dam failure process. The method and equipment used in this study may be used to monitor landslide dams and providing early warnings for dam failures.

Influence of inflow discharge and bed erodibility on outburst flood of landslide dam

Accurate prediction of the hydrographs of outburst floods induced by landslide dam overtopping failure is necessary for hazard prevention and mitigation. In this study, flume model tests on the breaching of landslide dams were conducted. Unconsolidated soil materials with wide grain size distributions were used to construct the dam. The effects of different upstream inflow discharges and downstream bed soil erosion on the outburst peak discharge were investigated. Experimental results reveal that the whole hydrodynamic process of landslide dam breaching can be divided into three stages as defined by clear inflection points and peak discharges. The larger the inflow discharge, the shorter the time it takes to reach the peak discharge, and the larger the outburst flood peak discharge. The scale of the outburst floods was found to be amplified by the presence of an erodible bed located downstream of the landslide dam. This amplification decreases with the increase of upstream inflow. In addition, the results show that the existence of an erodible bed increases the density of the outburst flow, increasing its probability of transforming from a sediment flow to a debris flow.

一种S波段雷达通信电子战多功能宽带DAM的设计

本文创新性地提出了一种S波段多功能宽带DAM,首先介绍了该型DAM的顶层架构设计,接着介绍了各个功能组成模块的设计过程,最后给出了该型DAM的指标实现情况。该型DAM可以分时实现雷达、通信及电子战功能,最大瞬时带宽可达200MHz,支持任意波形产生,在多功能综合射频系统中具有良好的应用前景。

Analysis and Modeling of Slope Stability in the Three-Gorges Dam Reservoir (China)——The Case of Huangtupo Landslide

The water level in the Three Gorges Dam reservoir is expected to change between the elevations of 145 m and 175 m, as a function of the flood control implementation and the intensity of the annual flood. As a matter of fact, the hydraulical and mechanical loadings, related to the water level modifications, will result in alterations in the slope stability conditions. The town of Badong (Hubei), of 20 000 inhabitants, is one of the towns which was submerged by the impoundment of the reservoir. As a consequence, the new town of Badong was constructed on a nearby site which appeared to be partly an unstable site. A part of this site corresponds to an old landslide, the Huangtupo landslide, the base of which had to be submerged by the water of the reservoir. The analysis of the Huangtupo landslide, taking into account various events scenarios, drainage and reinforcement measures and monitoring devices, allows to illustrate the general process implemented all along the reservoir in order to mitigate the landslide hazard.

Effects of river flow velocity on the formation of landslide dams

Natural dams are formed when landslides are triggered by heavy rainfall during extreme weather events in the mountainous areas of Taiwan.During landslide debris movement,two processes occur simultaneously:the movement of landslide debris from a slope onto the riverbed and the erosion of the debris under the action of high-velocity river flow.When the rate of landslide deposition in a river channel is higher than the rate of landslide debris erosion by the river flow,the landslide forms a natural dam by blocking the river channel.In this study,the effects of the rates of river flow erosion and landslide deposition(termed the erosive capacity and depositional capacity,respectively)on the formation of natural dams are quantified using a physics-based approach and are tested using a scaled physical model.We define a dimensionless velocity index vde as the ratio between the depositional capacity of landslide debris(vd)and the erosive capacity of water flow(ve).The experimental test results show that a landslide dam forms when landslide debris moves at high velocity into a river channel where the river-flow velocity is low,that is,the dimensionless velocity index vde>54.Landslide debris will not have sufficient depositional capacity to block stream flow when the dimensionless velocity index vde<47.The depositional capacity of a landslide can be determined from the slope angle and the friction of the sliding surface,while the erosive capacity of a dam can be determined using river flow velocity and rainfall conditions.The methodology described in this paper was applied to seven landslide dams that formed in Taiwan on 8 August 2009 during Typhoon Morakot,the Tangjiashan landslide dam case,and the Yingxiu-Wolong highway K24 landslide case.The dimensionless velocity index presented in this paper can be used before a rainstorm event occurs to determine if the formation of a landslide dam is possible.

Evaluation of potential landslide damming: Case study of Urni landslide,Kinnaur, Satluj valley, India

This work aims to understand the process of potential landslide damming using slope failure mechanism,dam dimension and dam stability evaluation. The Urni landslide, situated on the right bank of the Satluj River, Himachal Pradesh(India) is taken as the case study. The Urni landslide has evolved into a complex landslide in the last two decade(2000-2016) and has dammed the Satluj River partially since year 2013,damaging ～200 m stretch of the National Highway(NH-05). The crown of the landslide exists at an altitude of ～2180-2190 m above msl, close to the Urni village that has a human population of about 500.The high resolution imagery shows ～50 m long landslide scarp and ～100 m long transverse cracks in the detached mass that implies potential for further slope failure movement. Further analysis shows that the landslide has attained an areal increase of 103,900 ± 1142 m^2 during year 2004-2016. About 86% of this areal increase occurred since year 2013. Abrupt increase in the annual mean rainfall is also observed since the year 2013. The extreme rainfall in the June, 2013; 11 June(～100 mm) and 16 June(～115 mm),are considered to be responsible for the slope failure in the Urni landslide that has partially dammed the river. The finite element modelling(FEM) based slope stability analysis revealed the shear strain in the order of 0.0-0.16 with 0.0-0.6 m total displacement in the detachment zone. Further, kinematic analysis indicated planar and wedge failure condition in the jointed rockmass. The debris flow runout simulation of the detached mass in the landslide showed a velocity of ～25 m/s with a flow height of ～15 m while it(debris flow) reaches the valley floor. Finally, it is also estimated that further slope failure may detach as much as 0.80 ±0.32 million m^3 mass that will completely dam the river to a height of 76±30 m above the river bed.

Rapid Geometry Analysis for Earthquake-induced and Rainfall-induced Landslide Dams in Taiwan

Stability analysis of the dam is important for disaster prevention and reduction. The dam's geometry plays an important role in understanding its stability. This study develops a rapid landslide dam geometry assessment method for both earthquake-induced and rainfall-induced landslide dams based on nine real cases collected in Chinese Taipei and 214 cases collected worldwide. For simplification purposes, a landslide dam is classified into triangular or trapezoidal. The rapid landslide dam geometry assessment method in this paper uses only satellite maps and the topographic maps to get landslide area, and then analyze the dam geometry. These maps are used to evaluate the area of the landslide and the slope of the river bed. Based on the evaluation information, the proposed method can calculate dam height, the length of the dam, and the angles of the dam in both upstream and downstream directions. These geometry parameters of a landslide dam provide important information for further dam stability analysis. The proposed methodology is applied to a real landslide dam case at Hsiaolin Village. The result shows that the proposed method can be used to assess the landslide dam geometry.

Landslides at Qingjiang River in the Downstream Area of Shuibuya Dam Site, China

To enhance the general knowledge of landslides in China, the DAAD （German Academic Exchange Service） is financing an investigative project. As part of this project, at the Qingjiang （清江） River, a 10 km^2 area downstream of the Shuibuya （水布垭） dam site was geologically and geotechnicaUy mapped to gather information concerning landslides and their correlation to lithology, slope angles and texture. The geological mapping contained the characterization of the lithological units. The characterization of the shape of landslides and the classification of rocks into units with similar geotechnical behavior is contained in the geotechnical map. Samples were taken and investigated using X-ray diffraction to identify the clay minerals and geotechnical tests to determine the effective shear angle and cohesion of rocks and soils. Geotechnical mapping showed a close connection between lithology, slope angle and texture concerning the occurrence of landslides. Most landslides occur on the northern bank of the Qingjiang River where the dip angle of the bedding is nearly parallel to the slope, resulting in potential and effective slide planes. On the southern bank only sporadic and small landslides occur because the bedding is antipodal to the slope angle. This pilot work is a base for further and more detailed investigations in this area.

Evidence of the formation of landslide-dammed lakes in the Zagros Mountains range,Iran

Alternation of high and low resistance sedimentary beds,active tectonics,large rivers,and slope erosion in valleys consequently resulted in landslide in dammed lakes within the Zagros range.This study presents the results in the analysis of geological and topographic data,satellite imageries,morphotectonics and hydrodynamics of drainage networks about the landslide dammed lakes.There are four landslides in central Zagros(Zagros FoldThrust Belt,ZFTB)which have formed five dammed lakes named,Seymareh,Jaidar,Shur,Shimbar,and Godar.According to the results,damming landslides occurred in the active-tectonic regions on the slopes of anticlines and in valleys with undercutting effects of rivers on their slopes consisting of alternations of loose and resistant beds.The studied landslide dams in narrow valleys are formed as a result of blocking river by sliding debris slopes and rock slides.This study also indicates the formation of Jaidar and Godar in one stage and the presence of Lake Terrace sequence in Seymareh,Shur and Shimbar lakes.The observed sequences of terrace formation in these lakes are caused by four Seymareh Landslides followed by the three-stage excavation of Shur andShimbar lakes.

Rapid prediction models for 3D geometry of landslide dam considering the damming process

The geometry of a landslide dam plays a critical role in its stability and failure mode,and is influenced by the damming process.However,there is a lack of understanding of the factors that affect the 3D geometry of a landslide dam.To address this gap,we conducted a study using the smoothed particle hydrodynamics numerical method to investigate the evolution of landslide dams.Our study included 17 numerical simulations to examine the effects of several factors on the geometry of landslide dams,including valley inclination,sliding angle,landslide velocity,and landslide mass repose angle.Based on this,three rapid prediction models were established for calculating the maximum height,the minimum height,and the maximum width of a landslide dam.The results show that the downstream width of a landslide dam remarkably increases with the valley inclination.The position of the maximum dam height along the valley direction is independent of external factors and is always located in the middle of the landslide width area.In contrast,that position of the maximum dam height across the valley direction is significantly influenced by the sliding angle and landslide velocity.To validate our models,we applied them to three typical landslide dams and found that the calculated values of the landslide dam geometry were in good agreement with the actual values.The findings of the current study provide a better understanding of the evolution and geometry of landslide dams,giving crucial guidance for the prediction and early warning of landslide dam disasters.

Analysis of Landslide Dam Geometries

The geometry of a landslide dam is an important component of evaluating dam stability.However,the geometry of a natural dam commonly cannot be obtained immediately with field investigations due to their remote locations.A rapid evaluation model is presented to estimate the geometries of natural dams based on the slope of the stream,volume of landslides,and the properties of the deposit.The proposed model uses high resolution satellite images to determine the geometry of the landside dam.These satellite images are the basic information to a preliminary stability analysis of a natural dam.This study applies the proposed method to two case studies in Taiwan.One is the earthquakeinduced Lung-Chung landslide dam in Taitung,and the second is the rainfall-induced Shih-Wun landslide dam in Pingtung.

Reproduction of the Sedimentary Disturbance Phenomenon of the Diexi Ancient Landslide-Dammed Lake under Earthquake

Valuable geological and environmental information can be obtained from the 200 m thick lacustrine sediments in the Diexi lake(an ancient landslide-dammed lake) of the Minjiang River. The shaking table test method was employed to study the disturbance phenomena which occurred in the Diexi lake sediments. The results show that the disturbance phenomena were caused by liquefaction-induced flows in the unconsolidated lacustrine sediments, due to triggering by earthquakes. The deformations only occurred in unconsolidated sediment layers and not in consolidated layers. This means that a consolidated layer cannot be liquefied and disturbed again by an earthquake for a second time. The disturbance on one layer corresponds to only one earthquake. The temporal occurrence of earthquakes could be determined by disturbance layers generated at different ages. In total, 10 disturbed layers were found in the lacustrine sediments of the Diexi lake. The experiments showed that there were more than 10 earthquakes between 30 ka B.P. and 15 ka B.P. in the Diexi lake area based on the dating of the disturbed sediment layers.

Analysis of landslide damage caused by the 2008 Wenchuan earthquake using strong motion data: A case study in the Beichuan county town

The county town of Beichuan county, China, experienced catastrophic destruction due to landslides induce by the 2008 Wenchuan earthquake. In consideration of the special location of the county town, this paper selected the landslides induced in the town as representative of large-scale near-rupture landslides, and quantitatively analyzed why the landslide damage was so destructive in the town by using strong motion data obtained from the Wenchuan earthquake in the Longmenshan area. Three methods were employed to estimate the landslide damage using strong motion data. （1） Peak ground accelerations （PGAs） on the hanging wall were used to evaluate the PGAs on the landslide sites in the town. The evaluated average PGAs were all greater than I g, indicating that the ground motion intensity was very strong during the earthquake. （2） Acceleration time histories, from another station with similar geological conditions to the town, were used to evaluate the critical acceleration changing range, and the estimated values showed the geological conditions were very susceptible to earthquakes. （3） Acceleration time histories, from two stations on the hanging and foot walls of the rupture, and near the town, were used to calculate the Newmark displacements, and all the evaluated displacements indicated that landslides were very likely. The results show that the slopes, susceptible to earthquakes in the Beichuan county town, were easily triggered under such strong ground-motion intensity and developed into large-scale catastrophic events.

The Calculation Method for the Volume of Landslides and Dammed Lake Sediments Triggered by a Strong Historical Earthquake in the Loess Plateau:A Case Study of Qiuzigou, Gansu Province, Northwest China

The quantitative calculation of the volume of large earthquake-triggered landslides and related dammed lake sediments is of great significance in the study of secondary disasters and focal parameters of strong historical earthquakes.In this study,the dammed lake induced by Qishan M7 earthquake(Lingtai County,Gansu Province,Northwest China)is selected as the research object.Based on the information collected from the 4 boreholes in the dammed lake area,we further take advantage of the lowlevel Unmanned Aerial Vehicle(UAV)photogrammetry and the morphology recovery method,to calculate the volume of the dammed lake and landslides,respectively.Finally,major conclusions are obtained as follows:①the AMS-14C age at the bottom of the Qiuzigou Dammed Lake sediments is 2890±30 BP,which coincides with the 780 BC Qishan earthquake;furthermore,the Qiuzigou Landslides seem to have been triggered by the earthquake,forming an enclosed dammed lake deposition environment after the upstream sediments accumulate;②the Qiuzigou landslides are opposite-sliding landslides that have blocked the river valley;in detail,landslide volumes at the right and left banks are 235×104 m3 and 229×104 m3,respectively.The length of the dammed lake is 2.6 km,with a thickness of approximately 43 m near the landslides,and the total sedimentary volume is 573×104 m3;③the erosion rate of Qiuzigou Landslide Dammed Lake is 0.44 mm/a,the accumulation rate is 15.05 mm/a,and the soil erosion modulus is 593 t/(km2/a),characterized as slight erosion.Quantitative research on the formation of landslides and dammed lakes from strong historical earthquakes is vital for increasing our understanding of the vibrational characteristics and surface action processes of these types of earthquakes.

Controls on the regional distribution of landslide dams and implications for fluvial landform evolution in Bhutan and its surrounding area

The regional distribution of landslide dams can provide valuable insights into the interactions among various factors,including lithology,topography,climate,and fluvial landforms in tectonically active mountains.Himalayan rivers are frequently impacted by large-scale landslide damming,which profoundly influence fluvial geomorphology.In this study,we identified 1652 landslide dams in four major rivers of Bhutan and its surrounding area by remote sensing interpretation.Notably,approximately 71%of these landslide dams are found in regions composed of quartzite or gneiss.Fault-related tectonic activity plays a significant role in governing the distribution of these landslide dams,as approximately 83%of the mapped landslide dams are found within a 10 km radius of the nearest fault.The majority of the identified landslide dams are situated in areas with relatively modest local relief,ranging from 227 m to 327 m.These dams tend to cluster in the tributaries,and the stream power of almost 95%of them is typically below 1×10^(6) kg m^(2) s^(-3).Our data,combining the erosion rate and kernel density map of the landslide dams,reveals that regions with high erosion rates do not consistently align with the major high-density distribution of landslide dams.It is shown that the distribution of landslide dams is strongly influenced by the valley form.In comparison to U-shaped valleys,V-shaped valleys exhibit a higher density of landslide dams.Intriguingly,we also find a positive correlation between the landslide-dam distribution density and the erosion rate only in relatively arid regions with mean annual rainfall less than 500 mm.Moreover,the length of the upstream reach protected by the knickpoint associated with both lithology and landslide damming is about three times longer than that protected by the knickpoint associated only with landslide damming.

Laboratory-scale investigation of the material distribution characteristics of landslide dams in U-shaped valleys

Material distribution characteristics during sliding and depositing is particularly significative to investigate the internal structure and spatial variation of landslide dams,which are fundamentally determining the mechanical and hydraulic behavior and the susceptibility to cause dam failure.However,limited by longevity shortages and special geographic environments,the material distribution characteristics and their formation mechanisms are difficult to observe in the field.Therefore,an experimental apparatus modeling a landslide dam was developed in this paper,designing three sampling methods with two valley states.The internal deposit characteristics,void ratio variation and relative content of the particle size range(PSR)were analyzed,and the mechanics of deposit structure were also delicately ascertained.The results indicate that granular material deposited in valley shows a structure of inverse grain size accumulation in both vertical and horizontal directions,exhibiting spatial variability of particle gradation and void ratio.The characteristic PSR decreases from 22-30 mm in the two-dimensional state to 10-14 mm in the threedimensional state.Vibration excitation and vibration sieve are the intrinsic mechanisms of granular flow segregation,intrinsically inducing the formation of inverse grading deposit structures.Consequently,spatial variability in size is mainly trig gered by segregation,whereas coarse particle content and deposition boundaries merely exacerbate the difference degree.

Insights into the long-term stability of landslide dams on the eastern margin of the Tibetan Plateau, China——A case study of the Diexi area

Landslide dams,especially long-term stable landslide dams,have been recognized as important contributors to regional geomorphological evolution.Here,the Diexi area,a long-term stable dam-prone area located in upstream of the Minjiang River on the eastern Tibetan Plateau,was adopted to reveal reasons that landslide dams are concentrated in this area and maintain long-term stability via detailed field investigations,landslide dam sampling,unmanned aerial vehicle(UAV)images,and digital surface models(DSM).The results show the controlling factors that the slopes are prone to sliding and rock mass structure deterioration including lithological combination mode,slope structure,topographic conditions,a series of NNE-trending radial fissures and hydrological conditions.Fault activities,which have caused many earthquakes,are the main inducing factor.Landslide dams are prone to occurrence in the Diexi area owing to the combined effect of the narrow channels,the large landslide dam volume and the rock fragments.The river flow,and the landslide dam volume,material,structure,and parameters control the stability of landslide dams.The landslide dam consists of various sizes of boulders and all landslide dams exhibit an obvious inverse grading sequence,and this size combination could consume most of the flow energy,and consequently protect the dam from incision.Additionally,a total of seven knickpoints were formed by landslide dams,and the longitudinal gradient upstream of every landslide dam was found to decrease by the action of knickpoint.In the eastern margin of the Tibetan Plateau,there are numerous landslide dams existed for hundreds or thousands of years.Studies on the long-term stable landslide dams in the Diexi area could provide experience for studying similar kinds of landslide dams in this region.

Landslide Dam Forming Hazard Analysis Based on Geological and Induced Factors

Landslide dams and lakes can cause great casualties and economic losses.A landslide dammed lake named Tangjiashan by Wenchuan earthquake in China was well known all over the world since May 12,2008. Many other landslide dams or lakes can also formed by rainfall or water fluctuation besides earthquake. Landslides along the river or branch banks in the Three Gorges Reservoir area face dam or lake forming possibility especially within the water