Abstract: Watershed flood simulation is a focus of flood analysis and prediction and a fundamental issue in flood control and disaster reduction. In this study, flood propagation process in a small basin is calculated by coupling a distributed hydrological model and a hydrodynamic model on the platform of SWAT and HEC-RAS. In a case study of the Longxi River basin in Chongqing, different scenarios of rainstorms over a small watershed are predicted through runoff generation, confluence calculation, and two-dimensional numerical simulation of floods, considering meteorological, topographic, and underlying surface conditions. The calculations show that this coupling model can simulate effectively the confluence process over the basin under complicated conditions and it is useful to the decision of disaster reduction when combined with disaster loss assessment and flood risk analysis.

Key words: geographical information system, hydrologic-hydrodynamic model, flood damage assessment, flood risk analysis, Longxi River basin