Abstract: Flood propagation after dam break in urban areas is greatly different from that in mountainous areas because of disparities in terrain, boundary, and roughness coefficient. Areas in the downstream of urban reservoir has numerous buildings and complex roughness, so it’s difficult to process urban terrain data. To solve this problem, we built a high fidelity digital elevation model (DEM) by using GIS technology, and assigned different coefficients of roughness corresponding to different land surfaces, and generated a roughness field. Subsequently we took Longkou Reservoir in Shenzhen City as a case study to built a model of flood propagation caused by sudden dam-break suitable for urban area based on Hydrodynamics of MIKE21. Computation result demonstrates that the model could well simulate the backwater affected by buildings, and could reflect the guidance of urban trunk road for flood propagation, and also explains the rapid rise and regression of flood in some local areas. High fidelity DEM and multivariate distribution of roughness coefficients could improve the accuracy and rationality of simulating flood propagation after dam-break in urban areas.

Key words: dam-break, model of flood propagation, numerical simulation, MIKE21, GIS