Improving the Simulation of Surface Runoff Hydrograph by Storm Movement Approach (Case study: Amirkabir Dam Basin)

Rainfall characteristics are different spatially and temporally and this issue has impact on runoff. So, considering the spatial and temporal distribution of rainfall is one of the most important factors in the simulation of rainfall-runoff. Spatial and temporal distribution of rainfall is not same in a basin due to its topographic and climatic variations, but to simplify the calculation of storm movement in sub basins, this issue is not considered in most studies and is led to the under or over estimate of the peak discharge of runoff. So, in this research, at first spatial distribution of rainfall was calculated in each sub basin using the recorded data of rainfall in daily rain-gauge stations of Amirkabir dam basin and Inverse Distance Weighting (IDW) method. Temporal distribution of rainfall was examined in two cases. At the first case, that is a widespread method for regions without station, the used rainstorm in all sub basins considered as same as the nearest stable rain-gauge station and in the second case, time of rainfall occurrence in sub basins has been estimated based on the distance of the center of gravity of sub basins from the nearest rain-gauge station to the study area and the time of rainstorm in the other rain-gauge stations and then was shifted based on the hyetograph of rainfall in sub basins. To evaluate the impact of temporal shift of rainfall on peak discharge, simulated runoff was compared in two stable and moving storm cases. Results of rainfall simulation for five selected storm events showed that temporal shift of rainfall (second case) significantly has improved the estimation of peak discharge and time to peak of the rainfall compared to the first case.