Flood hazard zonation using HEC-RAS hydraulic model in Sarbaz River, Sistan and Baluchestan Province

Every year, floods destroy the economic and social structure of communities and cause a lot of financial and human losses. One of the effective factors in the occurrence of floods is the development of urbanization around rivers. Due to climate change, in recent decades, Sistan and Baluchestan Province with hot and dry climate, is prone to floods. The aim of the present study is to zoning the flood of Sarbaz Watershed using HEC-RAS hydraulic model. To conduct the research, the SCS model of the area was first determined according to satellite images, land use map and runoff curve number. Then, the flood discharge of the basin with 10, 25, 50 and 100 years return periods was simulated using the HEC-HMS hydrological model. The simulation results resulted in the occurrence of peak flood discharges of 3363.8, 4563.7, 54462 and 6359.3 m3s-1 for return periods of 10, 25, 50 and 100 years in the study basin, respectively. In order to evaluate the efficiency of the model in calibration and validation stage, Nash-Sutcliffe evaluation indices and the mean square error were used, the results of which indicate the optimal performance of the model. Then, the flood zoning map of Sarbaz Watershed in Rusk City was prepared in desired return period with the help of HEC-RAS hydraulic model. The results showed that with the return periods of 10, 25, 50 and 100 years, 366.86, 397.12, 449.95 and 580.78 hectares of flood zone of Sarbaz Watershed in Rask City area will increase, respectively.