Detrmining the Flooding Points and Prioritizing Subcatchments of Barajin Catchment of Qazvin Using Hec-HMS and GIS

The first step to reduce the flood risk is flood control at the upper parts of watershed. So it is necessary to identify the flood prone regions within watershed، because performing the treatment activities at all over the watershed is impossible due to high expansion of the catchments. In this study، the potential map of flooding was prepared using SCS and overlaying data in GIS. The results showed that the coefficient of flood maintenance is low and the risk of flood occurrence is high due to characteristics of land use and soil hydrological units and the high weighted curve number equal to 78. The flooding potential map indicated that the risk of flood occurrence is really high، especially at the margins of north regions and upper parts of watershed duo to unsuitable land use type، high slope and outcrops without vegetation cover. Therefore، the priority of such regions for watershed engineering operations is more than other parts of watershed. The results of HEC-HMS model has also showed that fifth-sub catchment has the first flood control priority because of the high slope and CN number of 89.