Although the problem of storm movement affecting flows (shape of hydrograph and peak discharges) has been recognized for a long time, most overland flow studies do not take into account the effect on the runoff response caused by the movement of the storm across the catchment. Ignoring of the storm movment can result in considerable over and underestimation of runoff volumes and peaks.
The main aim of this study was to assess the ability of simple geometric measure of thunderstorm rainfall in explaining the runoff response from the watershed. for calculation of storm geometric properties (e.g. position of storm centroid and the movment of storm centroied in time) spatial information of rainfall is needed.
The basin behavior was simulated based on recorded rainfalls and hydrographs in order to study the influence of storm movement on simulation of hydrographs.
Rainfall–runoff relations and flood routing in the channel were obtained by using curve number and Muskingum methods in HEC-HMS software respectively. Consequently, calibration and validation of the simulated model of watershed behavior were conducted.
The method of Inverse Distance Weighted (IDW) was used to estimate spatial distribution of rainfall.
Temporal distribution of rainfall was studied in two approaches. For the first case, the beginning of the rainfalls in all sub basins were considered the same in the nearest of recording gauge. For the second case, the rainfall event was shifted related to the distance between the gravity center of the sub basin and nearest recording gauge. The result showed that in most of rainfall–runoff records, temporal shift of the rainfall caused to increase in accordance between simulated and observed hydrographs.