Flow modelling and determination of sub-watersheds contribution in flood Hydrograph in Amoughin watershed, Ardabil province

The focus of watershed management practices should be in the runoff control, flood prediction and determination of sub-watersheds contribution in producing flood with the aim of reduction its destructive losses. Proposing of practical management solutions of flood control needs the examining of rainfall-runoff models to simulate flow hydrograph, especially in ungauged watersheds. The aim of this study was to evaluate the effectiveness of HEC-HMS model in the rainfall-runoff simulation of Amoughin watershed and determination of sub-watersheds contribution in outlet flow hydrograph. Toward this attempt, the HEC-HMS model was run with SCS-CN method (loss module), SCS-Unit hydrograph method (rainfall-runoff transformation) and Muskingum method (flood routing) through 9 rainfall-runoff events. The input parameters of the model were optimized through applying 6 storm events considering Nash-Sutcliffe objective function and the mean values of the input parameters were used as input for three excluded storm events during the validation stage. In order to prioritize the potential flooding of sub-watersheds, the calibrated HEC-HMS model was employed by removing the sub-watersheds in each run with the 25-year design rainfall, then the flooding potential indices calculated. According to the results, the average value of Nash-Sutcliffe statistical criterion 0.63 in the validation stage demonstrates that the accuracy of HEC-HMS model in flood simulations of Amoughin watershed. The result of flooding potential indices showed that B1, B2, and B3 sub-watersheds have more effect on the flooding potential of Amoughin watershed. In conclusion, it can be said that flooding potential sub-watersheds are not affected only by sub-watersheds area. While, the physiographic characteristics, land use related factors, spatial location and flow routing through sub-watershed to outlet should be considered in determining the flooding potential of sub-watersheds in future studies.