Flood Overtopping Research Articles

Study on the Evolution Characteristics of Dam Failure Due to Flood Overtopping of Tailings Ponds

There has been a frequent occurrence of tailing dam failures in recent years, leading to severe repercussions. Flood overtopping is an important element contributing to these failures. Nevertheless, there is a scarcity of studies about the evolutionary mechanisms of dam breaches resulting from flood overtopping. In order to fill this knowledge vacuum, this study focused on the evolutionary characteristics and triggering mechanisms of overtopping failures, utilizing the Heshangyu tailings pond as a prototype. The process of overtopping breach evolution was revealed by the conduction of small-scale model testing. A scaled-down replica of the tailings pond was constructed at a ratio of 1:150, and a controlled experiment was conducted to simulate a breach in the dam caused by water overflowing. Based on the results, the following conclusions were drawn: (1) The rise in water level in the pond caused the tailings to become saturated, leading to liquefaction flow and local slope sliding at the initial dam. If the sediment-carrying capacity of the overflowing water exceeded the shear strength of the tailings, water erosion would accelerate landslides on the slope, generating a sand-laden water flow. (2) The breach was primarily influenced by water erosion, which subsequently resulted in both laterally widened and longitudinally deepened breach. As the breach expanded, the sand-carrying capacity of the water flow increased, leading to a faster rate of failure. The breach process of overtopping can be categorized into four distinct stages: gully formation stage, lateral broadening stage of gully, cracks and collapse on the slope surface, and stable stage of collapse. (3) The tailings from the outflow spread downstream in a radial pattern, forming an alluvial fan. Additionally, the depth of the deposited mud first increased and subsequently declined as the distance from the breach grew. The findings of this research provide an important basis for the prevention and control of tailings dam breach disasters due to overtopping.

Research on model material selection based on inception similarity in impact analysis of flood overtopping on tailings dam

Research on model material selection based on inception similarity in impact analysis of flood overtopping on tailings dam

Impact of inundation range of overtopping dam break of tailings pond under actual terrain conditions.

Tailing ponds are a major hazard source with the risk of dam breaks. To predict the impact of tailings pond dam breaks more accurately, one needs to quantitatively understand the dam-breaking process of the tailings reservoir and its downstream impact. This study is based on an old tailings pond that is about to be put out of service and the proposed new tailings pond next to it. Study the inundation range of the new and old tailing ponds with simultaneous overtopping dam breaks under actual terrain conditions. First, fine-grained tailings and expanded perlite were selected as the model sand materials, and the appropriate model sand ratio was determined through laboratory tests. Second, the two tailings ponds were tested (at a scale of 1:200), for flood overtopping and simultaneous dam breaks. The dam break, flow, section morphology evolution, submerged elevation, and range were analyzed. Finally, a numerical model was developed using MIKE 21 to simulate the simultaneous overtopping and collapse of the new and old tailings ponds, and the impact of rainfall intensity on the inundation range of the simultaneous overtopping of the dam was analyzed. The research results will guide disaster prevention and mitigation in tailings reservoirs.

A Stochastic Conflict Resolution Optimization Model for Flood Management in Detention Basins: Application of Fuzzy Graph Model

Floods are a natural disaster of significant concern because of their considerable damages to people’s livelihood. To this extent, there is a critical need to enhance flood management techniques by establishing proper infrastructure, such as detention basins. Although intelligent models may be adopted for flood management by detention basins, there is a literature gap on the optimum design of such structures while facing flood risks. The presented study filled this research gap by introducing a methodology to obtain the optimum design of detention basins using a stochastic conflict resolution optimization model considering inflow hydrographs uncertainties. This optimization model was developed by minimizing the conditional value-at-risk (CvaR) of flood overtopping, downstream flood damage, and deficit risk of water demand, as well as the deviation of flood overtopping and downstream damage based on non-linear interval number programming (NINP), for four different outlets types via a robust optimization tool, namely the non-dominated sorting genetic algorithm-III (NSGA-III). Conflict resolution was performed using the graph model for conflict resolution (GMCR) technique, enhanced by fuzzy preferences, to comply with the authorities’ priorities. Results indicated that the proposed framework could effectively design optimum detention basins consistent with the regional and hydrological standards.

Study on Hydraulic Incipient Motion Model of Reinforced Tailings

Once the flood overtopping accident of a reinforced tailings dam occurs, it will cause great property losses and serious environmental pollution to the downstream residents. In order to further study the microscopic characteristics of the hydraulic erosion of reinforced tailings dams, considering that the beginning of reinforced tailings particles is the basis of flooding and erosion of reinforced tailings dams, in this paper, a reinforced tailings hydraulic erosion facility was used to carry out the tailings particle start-up test with reinforcement spacing of 5.0, 2.5, 1.7, 1.3, and 1.0 cm, and the influence the law of critical incipient velocity of tailings particles with different reinforcement spacing was revealed. The test results show that, the smaller the reinforcement spacing, the larger the incipient velocity of the reinforced tailings sample. Based on the sediment incipient motion theory, it is assumed that the resistance direction of particle incipient motion is opposite to the particle motion direction. A reinforcement coefficient is introduced to establish the incipient velocity formula of reinforced tailings particles. This model can provide theoretical support for the study of the hydraulic erosion rate of a reinforced tailings dam.

Overtopping process and structural safety analyses of the earth-rock fill dam with a concrete core wall by using numerical simulations

Earth-rock fill dams are the most widely used dam type all over the world, and flood overtopping is the key reason causing dam burst. However, since an earth-rock fill dam with a concrete core wall is a modified new dam type, overtopping studies on these dams are rather deficient. The overtopping process and structural safety analyses of this new dam type have been studied in this paper by using a CFD-FEM coupled method based on the three-dimensional model of the Fangtianba reservoir expansion project. The scouring characteristics of the earth-rock fill dam, the variation trend of the downstream scouring depth, and the deformation as well as stress of the core wall have been obtained. Overtopping burst failure of the earth-rock fill dam with a concrete core wall is greatly affected by the downstream scouring depth, and tensile stress will occur on the upstream side of the core wall near the scour hole. When the downstream scouring depth is small and its growth is slow but stable, the tensile stress cannot exceed the allowable value in the early period of overtopping, and the concrete core wall may be able to support the dam body for a period of time, which might delay the occurrence of destructive collapse and overall burst. However, a sudden collapse may occur in the later period of overtopping; thus, reinforcement and emergency measures should be taken in time before the overall dam bursts.

Experimental Study of Landslide Surge Wave Overtopping an Earth Dam

In this study, the experimental investigation on whether the landslide surge waves can influence the dam failure process caused by flood overtopping was presented. The experiments were conducted in a large width flume with length of 50 m, width of 4 m and height of 2 m. The time between the start of the earth dam break and the surge wave reaching the dam site was set to 80 s. During this period, the water depth of the reservoir constantly decreased. The experimental results showed that the surge wave height decreased while the propagation velocity increased slightly as the surge moved to the dam site. Several surge waves could overtop the dam crest and the shear height of the dam crest caused by each surge wave was a function of the surge wave height, which could be described non-dimensionally by Δz* = 0.946 Hs*2.113. The surge wave influenced the water level falling velocity and breach width expanding speed from the time of the overlay of the breaking dam. The surge wave could lead to a large instantaneous peak discharge that exceeded the dam failure peak discharge of the experiments with no surge wave.

Overtopping Risk Analysis of Earth Dams considering Effects of Failure Duration of Release Structures

For modern high earth dams, sufficient safety margin is considered in the designs of flood discharge capacity and dam crest elevation to prevent flood overtopping. However, for high earth dams which may induce catastrophic consequences, during their long operational period, extremely hazardous scenarios which could occur and threaten dam safety need to be considered. For the earth dams located in areas with intensive seismicity, there is a possible scenario that the release structures fail due to seismic landslides and gate failures caused by a severe earthquake when the flood begins to enter the reservoir. Thus, it is desirable to investigate the influence of failure duration of release structures on dam overtopping risk. Based on the Bayesian network, a methodology for overtopping risk analysis of earth dams considering effects of failure duration of release structures is proposed. The overtopping risk of the PBG earth-rockfill dam was analyzed to illustrate the methodology. The critical release structures which dominate the dam overtopping risk are identified. The dam overtopping risk is most sensitive to the failure duration of the spillway. The tolerable failure duration of the spillway is approximately 3 days, and when the failure duration of the spillway reaches 4 days, the dam overtopping risk drastically rises to an unacceptable level. The case study suggests that the proposed methodology could be helpful to analyze the influences of possible failure durations of release structures on dam overtopping risk and could facilitate preparation for emergency plans.

The evolution of the Samaoding paleolandslide river blocking event at the upstream reaches of the Jinsha River, Tibetan Plateau

A large number of landslides have occurred in the upstream reaches of the Jinsha River, Tibetan Plateau due to the intensity of tectonic movement in the area. Remote sensing and field investigation indicate that one of them, the Samaoding paleolandslide, previously blocked the river. Various river-blocking phenomena are well preserved, including the old landslide dam and deposits, fluvial sediments, and hydrostatic sandy sediment. To better understand the evolution of the Samaoding landslide, the authors carried out thermoluminescence (TL) dating and numerical simulations. The TL analysis shows that the landslide occurred at 10.6 ± 0.5 Ka BP. Discrete element method (DEM) simulation of the landslide based on landform restoration provided results that are consistent with field observations. The simulation indicates that the entire landslide process lasted for 80 s, and the sliding mass reached a maximum velocity of 64 m/s. The landslide formed a landslide dam with a length of 1900 m, a width of 600 m, and a depth of 200 m. The simulation results show that the level of the riverbed at that the time of the landslide was at least 25 m higher than it is today. On the combined basis of the simulation results and field observations, the authors propose explanation that the following valley evolution sequence occurred after river blocking. The landslide dam experienced flood overtopping and then was eroded until it had mostly had been transported away by river flow, and the river then rapidly incised the bedrock to form the present-day landform. Based on the field investigations, the authors summarize the failure mechanism of steep-inclined antidip rockslides and found that tectonics play an important role in the formation of landslide dams (or trigger of landslides) and the failure of landslide dams in an active tectonic environment of Tibetan Plateau.

Quantitative Vulnerability Model of Earth Dam Overtopping and its Application

Dam failure constituted a considerable threat to human life and created corresponding losses. Hence, this paper proposed a quantitative vulnerability evaluation model to estimate the consequences of dam overtopping, including loss assessment and vulnerability degree calculations. A composite normalized function was applied to convert dam overtopping loss to a vulnerability degree ranging from 0 to 1. In addition, many complex factors were simplified in the loss estimation, and the thresholds of various types of losses were proposed and adapted to the national and regional conditions. Then, loss of life, economic loss, social loss and environmental loss were incorporated into the vulnerability degree model based on a comprehensive evaluation method and were further assigned weights. Finally, vulnerability degree grading criteria was divided based on three significant cut-off values, and the corresponding guidelines for vulnerability evaluation were explained in detail. The methodology was applied to Chengbihe Reservoir in China to illustrate the assessment process of flood overtopping loss and to evaluate the vulnerability degree of the area. The results indicated that (1) dam overtopping vulnerability degree of the Chengbihe Reservoir was 0.89, which was within the range of “extremely high vulnerability” and (2) countermeasures were necessary; for example, early flood warning and forecast systems must be developed for the reservoir so that people and property in flooded areas can be safely evacuated during the process of emergencies.

Sensitivity Analysis for the Inverted Siphon in a Long Distance Water Transfer Project: An Integrated System Modeling Perspective

Long distance water diversion projects are developed to alleviate the conflicts between supply and demand of water resources across different watersheds. However, the significant scale water diversion projects bring new challenges for the water supply security. This paper presents the flood risk of inverted siphon structure which is used for crossing transversally in the water diversion project through sensitivity analysis. Soboĺ and regionalized sensitivity analysis are used to investigate the sensitive parameters of the integrated model and the sensitive range of the parameters, respectively. The integrated system model consists of the hydrologic model, the sediment transport model and the siphon hydraulic model to determine the flood overtopping duration and volume, which are used to quantify flood risk in this study. The flood overtopping duration and volume indicators are used to quantify flood risk in the sensitivity analysis. The South to North Water Diversion Project in China is used as a case study. The results show the mean rainfall and roughness coefficient of the pipe are the most sensitive parameters in the integrated models, while the sensitive range of these two parameters are distinct. The sensitivity analysis of the inverted siphon provides an insight into the significant contributions to the flood risk. The analysis can provide the guidance for the system operation security.

Simulasi genangan banjir menggunakan data ASTER DEM pada alur Sungai Cilemer

The Cilemer River is a river which flowing to Lada Bay in west coast of Pandeglang District, Banten Province. The influence of the tide, the high flood discharges and settlements located at the flood plain has caused flooding every year. In order to understand flood overtopping mechanism and inundation map, numerical model simulation for flood and inundation area were conducted. The numerical model of the river were conducted using cross sectional of the river, result of these simulations were further integrated with Geographical Information System (GIS). The objective of this study is to obtain inundation map area. The input for GIS is a Digital Elevation Model which is obtain from Advanced Spaceborne Thermal Emission and Reflection Radiometer Digital Elevation Model (ASTER DEM). The simulation results shows the capacity of Cilemer River upstream is 210 m3/s while on the downstream segment was only 100 m3/s. Simulation shows with overtopping of the dike of 0,96 m generate 546 Ha of inundation area for 2 year return period of flood discharge. The overtopping of 1,1 m has generated 592 Ha of inundation area for 5 year return period of flood discharge. With overtopping of 1,26 m of 10 year return period flood discharge has caused 682 Ha inundation area, while 2,56 m overtopping has generated 912 Ha inundation area for 25 year return period of flood discharge. Effect of flood control structure on the outlet of bypass has generated 19 cm increase of water level.

Peak flood estimation under overtopping and piping conditions at Vahdat Dam, Kurdistan Iran

Estimation of maximum discharge and time of transfer dam break wave are among the main factors in provision of emergency action plan and safety assessment of dams. Most dam breaks begin with a breach in the body of the dam or flood overtopping. Estimation of maximum discharge for determining affected areas and also determination of hazards due to the dam break are essential issues. In this research, the dam break of Vahdat Dam located in Kurdistan, Iran, and in neighborhood of Sanandaj City was simulated by integrating ArcMap and HEC-RAS software and field observations. The necessary data was collected from the corresponding organizations. The Manning coefficient of the Gheshlagh River at downstream of the dam was estimated using the Manning coefficient relationships and field observations and measurements. The breach dimensions were determined using the conventional empirical relationships. The dam breaks in both overtopping and piping states were simulated. The maximum discharge values obtained from the modeling and empirical relationships were compared. The results indicated the substantial effect of selecting break types on the hydraulic characteristics of dam break wave in the river and downstream areas. While in the case of break due to the breach, selection of the methods for calculation of breach dimensions would affect the break and these relationships in various conditions would give different breach dimensions.

Submerged area of typical torrential flood and debris-flow disasters in Mengzong Gully, China

ABSTRACTThe torrential flooding and debris flow disasters associated with global climate change pose not only serious threat to individual lives and property, but also impact economic development. Accurately simulating flood scenarios can help to reduce the losses caused by torrential flooding and debris flow by making early warning, evacuation planning, and risk analysis possible. In this study, HEC-RAS software and HEC-GeoRAS module were employed in GIS (geographic information system) to simulate the flood overtopping in the Mengzong Gully of Batang River in flood scenarios occurring once in 20, 50, and 100 years, respectively. The simulated floods provided valuable information including scope and depth of submersion via 2D visualization.

关于堤坝坝顶高程计算中安全加高的讨论

安全加高是确定堤坝坝顶高程的重要参数，直接影响防洪安全和经济性。本文基于现行规范和防洪工程资料，分析讨论了堤坝工程设置安全加高的必要性、取值原则和方法。研究表明，影响洪水漫顶的安全因素，基本上都可以定量确定，计算静水位以上的超高时没有必要再单独考虑安全加高。安全加高的规定与当前防洪工程发展形势不适应，与欧美发达国家通行做法不一致。建议构建柔性综合防洪体系，取消安全加高的规定，安全超高由浪高和风壅增高直接确定。 Safety freeboard, one of the important parameters to determine the crest elevation of levee, de-termines the safety and economy of flood control engineering in a great way. Based on the current design codes and some research materials, the necessary and selections of the safety freeboard corresponding to different structures and different typical flood are studied. The results show that the main factors of flood overtopping can be quantitatively determined, so there is no need to es-timate safety freeboard in calculating dam height above static water level. Now, stipulation of safety freeboard is in some contradiction with flood control development and not consistent with the prevailing practice in western developed countries. It is necessary to revise applicable design codes and standards. When constructing a flexible comprehensive flood control system and canceling safety freeboard in calculating crest elevation, safety height is just equal to sum of heights by waves and the wind.

Risk assessment of earth dam overtopping and its application research

The problem of dam safety is one of the most important research topics of water conservancy projects, and many researchers pay much attention to study the risk of earth dam overtopping. This paper synthesizes in the definition of risk the probabilities of dam failure and the corresponding losses, including the probability estimation, losses evaluation and criteria exploring risk approaches. Then, a comprehensive risk assessment system of dam flood overtopping is established, which is widely applicable. Gate failure, randomness of flood, initial water level and time-varying effects are incorporated in the failure probability model. Many complex factors are simplified in losses estimation. In addition, thresholds of various types of losses are proposed and are adapted to the national conditions. The methodology is applied to the Lianghekou hydropower station in China to illustrate the assessment process of flood overtopping risk and to evaluate its safe loophole with a view to the failure of spillway gates. Monte Carlo simulation and JC method programs are adopted to solve the model based on MATLAB tools and DELPHI. The results show that the losses pose significant impact on the risk assessment and should be considered in the assessment of risk. Probability calculation and loss estimation could be well combined with standards, providing a basis for risk management and decision-making.

Evaluation of the overflow failure scenario and hydrograph of an embankment dam with a concrete upstream slope protection

The standard procedure in Quebec, Canada, for evaluating the failure of an embankment dam, per the Loi sur la securite des barrages, specifies a 30-min-long failure scenario with a breach width equal to four times the maximal height of the dam. We demonstrate a new method for evaluating the flood overtopping failure scenario for embankment dams with concrete upstream slope protection, using Toulnustouc dam for example computations. Our new methodology computes safety factors for a range of potential failure mechanisms taking into account geotechnical, hydraulic, and structural factors. We compile the results of our investigations of the various dam failure mechanisms and compare the corresponding dam failure hydrographs to the current hydrograph specified in the standard analysis procedures. Our investigations tend to invalidate the current standard procedures for evaluating the failure of rock-fill dams with concrete upstream faces, by indicating that the current standard procedures underestimate the peak failure discharge and overestimate the time to the peak discharge.

Structural master plan of flood mitigation measures

Abstract. Flood protection is one of the practical methods in damage reduction. Although it not possible to be completely protected from flood disaster but major part of damages can be reduced by mitigation plans. In this paper, the optimum flood mitigation master plan is determined by economic evaluation in trading off between the construction costs and expected value of damage reduction as the benefits. Size of the certain mitigation alternative is also be obtained by risk analysis by accepting possibility of flood overtopping. Different flood mitigation alternatives are investigated from various aspects in the Dez and Karun river floodplain areas as a case study in south west of IRAN. The results show that detention dam and flood diversion are the best alternatives of flood mitigation methods as well as enforcing the flood control purpose of upstream multipurpose reservoirs. Dyke and levees are not mostly justifiable because of negative impact on down stream by enhancing routed flood peak discharge magnitude and flood damages as well.

PHYSICAL MODELING OF OVERTOPPING EROSION AND BREACH FORMATION OF COHESIVE EMBANKMENTS

The formation process and timing of a dam embankment breach caused by flood overtopping can dramatically impact the rate at which water is released from a reservoir and directly impacts the hazard to life and property downstream of a breached dam. Therefore, dam embankment erosion processes and the rate of breaching from overtopping events are important to both engineers and planners alike, who must predict impacts on local communities and surrounding areas affected by flooding. There is a distinct difference between the erosion processes of non-cohesive and cohesive embankments during overtopping. The USDA-ARS has conducted seven large-scale overtopping failure tests on cohesive embankments ranging in height from 1.5 to 2.3 m. The purpose of this study is to: (1) establish a better understanding of the erosion process of overtopped cohesive embankments, and (2) provide detailed data for future numerical model development, validation, calibration, and testing. Three soils were tested, two non-plastic SM silty sand materials and a CL lean clay. A four-stage breach erosion process was observed for cohesive embankments. The primary erosion processes observed and reported in this article for cohesive embankments during stages 2 and 3 were headcut migration and erosion widening. The rate of these two processes was observed to vary by several orders of magnitude and was observed to be strongly dependent on the soil material properties.

Overtopping Reliability Models for River Levee

Wind setup and wave run-up heights are important considerations in determining the total height of a river levee system. In this study, two generalized reliability models for a levee system are developed considering the inherent uncertainties associated with wind as well as hydrologic and hydraulic processes. The generalized models can be simplified to reliability models when only hydrologic and hydraulic uncertainties are incorporated. By using the concept of a wind-flood damage ratio, reliability values of a levee system can be obtained and discussed on the same economic basis. A higher ratio of wind-flood damage requires a higher total levee height to obtain the same reliability value as for a lower wind-flood damage ratio. The total reliability decreases with an increase in service period of the hydraulic structure and/or the wind-flood damage ratio if the total levee height remains the same. The models enable the performance of a levee system to be predicted in terms of reliability. When the total levee height is specified, different options exist for the flood levee height to protect flood overtopping and for the freeboard allowance to withstand wind-generated wave overtopping. The best option can be chosen on the basis of a maximum reliability value. An example application of the models shows how the flood levee height and freeboard allowance may be determined to yield maximum reliability.