Evaluation On Cascade Dam Breach Flood:Analytical Model And Case Studies On Xiaogangjian Barrier Lakes

Reservoir dams are the most important engineering measures for regulating the spatial and temporal distribution of water resources,optimizing the allocation of water resources,and preventing floods and disasters.In recent years,cascading development model of river basin has gradually become the dominant method of engineering construction to make fuller and more reasonable use of the water resources and meet the growing needs of production and living.Although the cascade reservoir dam brings huge benefits,its risk of breach and the possible damage caused by cascading dams breach flooding are inestimable.The problem of dam breach involves many disciplines such as hydraulics,sediment dynamics,soil mechanics,and slope stability analysis,etc.And the dam breach flood has strong nonlinearity and non-constant characteristics.Since the last century,a great deal of research has been conducted on a single dam breach flood.However,the researches on cascading dams breach are relatively few and have not been systematically carried out now.Therefore,on the basis of the study of a single dam breach,we will establish a calculation model for cascading failures flood of embankments and landslide dams,which will be used to design calculations,improve the risk emergency management level,prevent floods disasters.The main research contents and achievements of this paper are as follows:(1)Based on historical cases of the cascading breach of embankment dams,check dams,and landslide dams,the failure characteristics of these cascade dams in the basin had been analyzed.And a serious of scouring tests were conducted by a Cylindrical Erosion Test Apparatus to quantitative measure the erosion characteristics of dam material.The test results can be used to simulate the dam breach process.(2)The analysis of the breach of a single dam is the basis for the calculation of the cascading dams breach flood.A detailed analysis of the calculation principle of the DB-IWHR model was presented,including the calculation of the overall water balance,the calculation of the erosion rate of the dam material in the form of a hyperbolic curve,and the arc-shaped instability analysis of the breach slope.And a further analysis on the effects of extreme floods in the upper reaches,longitudinal development of dams,and erosion of dam foundations were considered.(3)Collect and back analysis the breach process of Banqiao dam.The characteristics of the hydrodynamic parameters used in the calculation model were analyzed to obtain the parameters that were more sensitive to the calculation results.The results found that the coefficient b of hyperbolic erosion model and falling coefficient m had an greater effect on the peak flow rate of about 20%.Based on the possible reasonable range of the parameters b and m,a instability analysis method for dam breach flood was proposed in combination with the Monte Carlo statistical test method,using the optimized GF deviation sampling.(4)Based on the single dam breach model(DB-IWHR model),a cascading dam breach model(DBC-IWHR model)was established combining the one-dimensional evolution calculation method(DBFL-IWHR)and the reservoir flood regulation calculation,which can be used to calculate the breach flood and analyze the risk of cascade dams failure in river courses.(5)The paper introduced the basic conditions of Xiaogangjian_up-Xiaogangjian_down-Yibadao cascading dams formed during the Wenchuan earthquake for the first time,including the structural characteristics,geological structure characteristics,hydrological data,the risk emergency plan and the draining process by blasting;The risk level was determined according to the risk analysis methods at home and abroad;The topography data of Xiaogangjian_up and Yibadao dams after the dam breach were acquired through the three-dimensional laser scanning technology;The draining process of the cascading dam was obtained through multiple field investigation,.(6)A back analysis was performed using the established cascading dams breach model.And the effect of flood overlapping,the discharge channel formed by blasting and flood return period were analyzed.It proved that this model can provide scientific technical support for risk analysis and design calculation of cascading dams.