Numerical Simulation Of Check Dam Failure Process Based On MIKE21 Model

The Loess Plateau is one of the most serious soil erosion areas in China.A large number of check dams has been built in the Loess Plateau,which has played an important economic and social role in preventing soil erosion,reducing the erosion of sediment into the Yellow River,and increasing grain production capacity.With the frequent occurrence of extreme weather in the Loess Plateau and the early construction of check dams,the drainage facilities are inadequate,and when the storage capacity is reducing,the overburden collapse of check dams often occurs,which has negative influence for flood security and people’s safety.Therefore,research on check dam break is of great significance for the safety of flood control and sediment management.In the field of dam break research,numerical simulation methods are still in the developing stage,and the difficulty lies in the evolution process simulation of the breach,which will greatly affect the flow discharge rate,the discharge rate will also affect the development of the breach and act on the downstream flood evolution process.In response to these issues,the research and the main results include the following two aspects:(1)The DB-IWHR model was used to calculate the evolution process of the breach and its corresponding discharge flow for a homogeneous check dam.On this basis,the downstream flood evolution analysis was carried out through the hydrodynamic model(HD)of the MIKE21,and the distribution characteristics of the downstream flow field were obtained.The results show that the discharge reaches the maximum value in a short time after the dam break,and then decreases exponentially with the passage of time.The peak discharge is positively correlated with the width and depth of the dam break.The maximum velocity of the factory building downstream of the breach ranges from 0.5m/s to 2.2m/s,where the velocity attenuation is mainly due to the flood detention area formed between the factory building area and the dam area,which greatly reduces the flood velocity.The peak velocity of dam break discharge depends on the width,depth and water level difference between upstream and downstream.When the breach is located in the main dam section,there is no flood detention area in the downstream area,and the elevation difference between the upstream and downstream is large.Therefore,the flow velocity and flow rate of the dam break are relatively large,and the maximum flow velocity can reach 7m/s.(2)Using the hydrodynamic model(HD)and sediment transport model(ST)by Mike21 software,under the condition of different bed load suspended load and different calculation formula,the effects of different thrust to suspension ratio,material porosity,particle size,angle of repose of sediment under water and spiral flow on the failure process of warping dam were discussed and analyzed,and reasonable calculation parameters and results have been obtained.The results show that the proportion of bed load and porosity are positively correlated with the scouring intensity;When the particle size is large,the breach is narrow and deep;The larger the angle of repose,the faster the gully develops;Considering the spiral flow,it has a certain influence on the evolution and curvature of scoured channel.The numerical simulation of the breach development process can be generalized into seven stages.