Research On Numerical Model Of Levee Breach And Dam Break Water Flow And Its Application

Flood is a major concern for many Chinese cities that are founded along rivers, and there exists a high risk of levee-breach due to low design criteria and poor maintenance. In case of levee-breach, the flood may induce serious losses of lives and properties. Therefore, it is of great significance to study the routing characteristics of flood caused by levee breach.A two dimensional numerical model based on Godunov method was developed to simulate levee-breach water flows over actual topographies. The Roe's approximate Riemann solver was used to calculate the flow flux based on the hybrid unstructured finite-volume method. TVD-MUSCL and Hancock methods were used to achieve the second accuracy. A robust procedure was adapted to efficiently and accurately simulate the movement of a wet/dry boundary without diffusing it. The time step was determined adaptively, based on the maximum instantaneous Courant number across the domain. The algorithm's stability, concordance and robustness were tested with several classical test cases. The test cases with actual topographies showed that the model can be used to deal with complex engineering problems.Dense buildings in urban areas exert great influence to flash flood, and they were treated in the model as, respectively, (1) solid wall boundaries, (2) grid cells with buildings top elevations, and (3) grid cells with artificially increased roughness. Comparison of the predicating performance of the model with three different approaches showed that approach (2) is more applicable.Analysis of flood release capacity of upstream detention areas and the probable maximum flood reveals that the risk of levee-breach in Harbin city still exists. The developed 2D model was then applied to describe possible flooding events due to levee breach in Harbin city. The results show that the model can simulate the levee-breach flood well. The invasion coefficient is put forward because the flash flood must invade into the residence block and buildings. In order to compute the invasion water, the side weir idea is used. In order to display the numerical results visually, the three dimensional levee-breach flood visualization system of Harbin is established by use of the Dll technology to link the numerical model into three dimensional visualization platform. Real-time display of levee-breach flood in the city was realized in the system, and this can help decision makers establish the best scheme about flood control and emergency repair easily and efficiently.