Numerical Simulation Of Cascade Earth-rock Dam Breach

It is of a low probability and high risk to the dam failure,once the dam burst accident,and which will cause great damage to the downstream area,causing huge casualties and economic losses.As the main dam type,the earth rock dam accounted for 95% of all kinds,while domestic break accidents happened in dams,the earth rock dam accounted for 98%.At present,13 large hydropower bases have been planned in our country,in which there were 310 large and medium-sized reservoirs,and most of the dam types in the basin are earth rock dam and face rock-fill dam.The distribution of super high dams was relatively concentrated.Considering the current development situation of China's cascade reservoir dam,it was of important practical significance to simulate and study the continuous burst of the stepped earth dam.For cascade reservoirs,research on the failure mechanism of earth dam,and being based on the influence of dam break process of upstream dam and dam break flood in the lower reaches of the reservoir,the cascade dam break even numerical model was established,which had important significance for dam break risk analysis,reservoir flood control operation,safety prevention and control of cascade River Basin and determination of engineering grade of reservoir group.In this paper,based on the study of single reservoir dam break model,coupling flood routing calculation and flood routing analysis,the numerical calculation model of cascade dam was established.The main research contents and results are as follows:(1)The mathematical model of dam break of earth rock dam was identified based on the comparative analysis of dam break model of earth rock dam.According to Summarize the characteristics of the existing dam break model,five kinds of dam failure mechanism model and a parameter model were selected: Mike11 DB model,HEC-RAS model,BREACH model,DAMBRK model,DB-IWHR model and rapid assessment model of weir dam collapsed.Through the simulation of typical dam break cases,the calculation accuracy and parameter sensitivity of each model were the focus of analysis and comparison.According to the comparative analysis,it was found that the DB-IWHR model was applied to study the mechanism of the dam,adequately considering the impact of the geometric parameters,material properties,initial conditions of breach,etc.And solving the problem of existing dam break model which could not break development of autonomic computing and too many known parameters,which was more practical significance and greater application value for the prediction of dam break.So,the DB-IWHR model was selected as the embankment dam break model.(2)The downstream evolution model of dam break flood was established.By studying on numerical calculation method of one-dimensional dam break flood,and based on the theory of Preissmann four point implicit difference scheme for solving Saint Venant equations,the open channel unsteady flow calculation program was compiled.Different examples showed that this procedure was applicable to different boundary conditions of the channel gradient flow and blast flow.The evolution process of the dam break flood was calculated by using the unsteady flow evolution program,and the results were compared with the results of Mike 11 software,which proved the accuracy and reliability of dam break flood evolution model.In this paper,taking the emergency treatment of the dam in the Tang Jia Shan as an example,through the application of dam break flood evolution program,the downstream flood risk analysis is carried out on the condition of different recurrence periods.(3)The mathematical model of cascade dam collapse was constructed.Based on Four order Runge Kutta method,the reservoir flood routing model was established,The change process line of downstream reservoir water level was calculated,and whether the upstream dam break flood was caused by the collapse of downstream cascade dams.By the DB-IWHR model the downstream dam break process was calculated,based on the model of single reservoir dam break,the flood routing and flood routing the process were coupled,the dam break mathematical model of cascade reservoirs was established.With the example of the cascade reservoirs in the Tang Da Da Da Li,the continuous collapse simulation of cascade earth rock dam was carried out,and the conditions of continuous collapse which was the downstream reservoir with early warning and different discharge capacity.The results showed that additional flood discharge facilities and very early warning all gate discharge increases flood storage capacity were taken,though the flood tolerant the dam did not break and continuous burst of cascade reservoir dam was avoid.