The failure of embankment dams due to overtopping

This article provides three numerical investigations on the overtopping failure of embankment dams which are modelled with non-cohesive fill material. The first investigation is based on a one-dimensional approach in order to calculate the outflow hydrograph during dam overtopping failure. The written program calculates the flow parameters by solving the one-dimensional Saint-Venant equation. Furthermore, the bed evolution is calculated by solving the Exner equation with the finite difference scheme. Here, the model accuracy is increased by dividing bed slopes into three categories: zero slope (0.0-1%), mild slope (1%-20%) and steep slope (>20%). At each time step based on the real bed slope the bed load transport is modelled. In the second investigation the two dimensional open-source TELEMAC software has been modified in order to model embankment dam failure. This modification is done by calibrating slope correction formula in the sediment part of this software. Finally, the influence of different geometrical parameters on the outflow hydrograph of dam failure is numerically modelled. Our modelling results show that the downstream slope has significant influence on the outflow hydrograph in comparison to the other geometrical parameters.

Proceedings of the 21st TELEMAC-MASCARET User Conference 2014, 15th-17th October 2014, Grenoble – France, 2014

In this paper two cases regarding the failure of homogenous embankment dams due to overtopping are presented. The simulations of the breaching processes were performed with the 2D depth-averaged hydrodynamic model TELEMAC-2D in coupled mode with the sediment transport model SISYPHE. The first case deals with the numerical simulation of a laboratory experiment in which the failure of a homogenous sandy dam due to overtopping was investigated. In a small sensitivity analysis the effects of different hydrodynamic and sedimentological parameters are tested. Comparing the experimental with the numerical results, the study shows that especially the type of transverse deviation correction has a definite influence on the shape of the erosion. The implementation of an alternative formulation for the factor beta in Talmon's deviation formula indicates a reliable improvement. Furthermore the transport stage dependent alpha coefficient in the Meyer-Peter & Müller bed load transport equation was investigated which gives an additional improvement. In the second case the findings of the first case are applied to the modelling of the breaching process in prototype scale of a water reservoir for snow production. The computed breach hydrographs are compared to the hydrograph calculated by a commercial breach parameter model. The study involving the two test cases reveals the excellent ability of the open source TELEMAC suite for the simulation of homogenous embankment breaching processes due to overtopping. I.

Hydrological Sciences Journal, 2001

A one-dimensional numerical model for dam failure due to flow overtopping is developed. The MacCormack explicit finite difference scheme is used to solve the one-dimensional equations of continuity and momentum for unsteady varied flow over steep bed slopes. In the computation of erosion process, sediment transport equations are considered and the modified Smart formula developed for steep bed slope is selected. The sliding stability of the overtopped dam is checked by modified ordinary method of slices. The model has been successfully calibrated and verified using laboratory experimental data. By comparing with the experimental results, it was found that the model accuracy depends largely on the sediment transport formula and pore water pressure coefficient. The model was found to predict actual breach outflow of the Buffalo Creek Dam reasonably well and closer than other existing numerical models.

Research & Reviews: Journal of Engineering and Technology, 2016

While there are many benefits to using reservoir dams, their break leads to destructive effects. From the viewpoint of International Committee of Large Dams (ICOLD), dam break means the collapse of whole or some parts of a dam; thereby the dam will be unable to hold water. Therefore, studying dam break phenomenon and prediction of its behavior and effects reduces losses and damages of the mentioned phenomenon. One of the most common types of reservoir dams is embankment dam. Overtopping in embankment dams occurs because of flood discharge system inability in release inflows to reservoir. One of the most important issues among managers and engineers to evaluate the performance of the reservoir dam rim when sliding into the storage, creating waves is large and long. In this study, the effects of floods which caused the overtopping of the dam have been investigated. It was assumed that spillway is unable to release the inflow. To determine outflow hydrograph resulting from dam break, n...

This paper provides new relationships for predicting fill dam failure based on available history of dam failures around the world. These new relationships provide estimation about maximum discharge and breach formation time for embankment dam which failure by overtopping. The relationship for maximum discharge was derived by introducing a new method for handling the outflow hydrograph. The relationship for predicting breach formation time was obtained by using regression analyses. For the outflow hydrograph, the flow duration curve is split into three simple shapes and superimposed for calculating the peak discharge. The accuracy of the peak discharge is improved by considering the influence of dam reservoir volume. Additionally the prediction of breach formation time can be improved considerably by introducing a parameter related to the dam type. This parameter is defined as the ratio of dam storage over the height of the water behind the dam. The gained results show more reasonable results compared with existing formula.

2015

Both numerical and experimental investigations are conducted to study the failure of earthen dams and levees. Boussinesq equations describing one-dimensional unsteady flow including non-hydrostatic pressure distribution are solved numerically along with Exner equation for the sediment mass conservation to include the effects of the streamline curvature on the failure of non-cohesive earthen embankments. In addition, the effects of the steep bottom slope on the flow variables during the failure are studied by solving the SaintVenant equations modified for steep bed slope along with the Exner equation to simulate non-cohesive earthen embankment failure due to overtopping. The Boussinesq equations are solved by using the two-four finite-difference scheme which is second order accurate in time and fourth order accurate in space, while the modified Saint-Venant equations are solved by using the MacCormack finite-difference scheme which is second order accurate in time and space. The perf...

In this thesis four different instances of embankment dams affected by overtopping flow are investigated. In the first investigation new relationships for predicting fill-dam failures based on the available history of dam failures around the world are introduced. These new relationships facilitate the estimation of the maximum discharge and breach formation time in the embankment dams which failed due to overtopping flow. The relationship for maximum discharge estimation is derived by introducing a new method for handling the outflow hydrograph. In this method, the flow duration curve is split into three shapes and superimposed to calculate the peak outflow discharge. The relationship for predicting the breach formation time was obtained by using regression analysis. The accuracy of the breach formation time is improved considerably by introducing a parameter related to the dam construction type. In the second investigation a one-dimensional program is developed in order to calculate the breach outflow hydrograph during embankment dam failure. This program calculates the flow parameters by solving the one-dimensional Saint-Venant equation. Furthermore, it calculates bed evolution by solving the Exner equation with finite difference method. Herein, the model accuracy is increased by dividing the bed slopes into three categories: small slope (0.0–1%), mild slope (1–20%), and steep slope (> 20%). At each time step, based on the real bed slope, bed load transport is modelled by using the relevant equations. In addition, the two-dimensional open-source TELEMAC software has been applied and a subroutine modified in order to model the embankment dam failure. This modification is done by calibrating the slope correction formulas in the sediment part of this software. In the third investigation of this study, the influence of different geometrical parameters on the breach outflow hydrograph are numerically modelled and compared with each other. The modelling results infer that the downstream slope has more influence on the breach outflow hydrograph in comparison to the other geometrical parameters. Finally, two new relationships are introduced in order to estimate the hydraulic parameters of the flood resulting from a dam breach which travels through channels and floodplains. The first relationship is concerned about calculating the peak outflow discharge curve. This curve is obtained by connecting the maximum values of cross section hydrographs downstream of a dam. The second relationship calculates the flood wave arrival time using a new method. In this method, it is assumed that arrival time increases linearly along the channel. This means that by calculating the slope of this line, arrival time can be calculated at each point of the channel. In conclusion, to evaluate the accuracy of the empirical and numerical approaches, reliable dam failure data are collected from a variety of sources around the world. The final results show that estimation of the breach outflow hydrograph and flood wave parameters have been improved by using the new approaches. These improvements are demonstrated by comparing the new approaches results against the existing formulas and observed results.

KSCE Journal of Civil Engineering, 2020

Numerical models are valuable tools for predicting the extent of floods associated with embankment overtopping. The paper presents and compares the results of two widely used dam breaching numerical models: NWS-BREACH and HR-BREACH. The focus of the study is to understand the sensitivity of key geotechnical parameters and their effect on breaching outflow rate, its geometry as well as its temporal and spatial characteristics. Results show that NWS-BREACH produces outflow hydrographs with a generally smaller lag-time where the rise-time was too short, suggesting a rather instantaneous breach. The multiple peaks in the outflow hydrograph using HR-BREACH simulations highlight new concepts that take into account the side-slope failure assessment using the embankment's material tensile and shear strength versus the Culmann method used by NWS-BREACH.

The Enhanced HLLC scheme as a robust approximate Riemann solver is used for numerical modeling of three different test cases of mobile bed and stepped mobile bed in dam failure and dam overtopping conditions. The current research has been done in the frame of the finite volume method using shallow water equations along with the Exner equation for sediment continuity. The Ribberink, Wong and Parker formulations have been used for the modelling of bed load movement. A convenient approach based on the Boussinesq hypothesis is deployed for considering turbulence effects in the second case. The affections of stepped and slope condition for the flow bed are considered through a corrected version of the HLLC flux components. Finally, the model is applied for modelling overtopping in the third case. The results of the present model are relatively reasonable by comparing with the experimental data.