Journal of Watershed Management Research

Flood is one of the natural hazards that its frequent occurrence has increased in the recent years and the damages of it, had affected apart of country in every year. Prioritization of sub basins has an important effect in watershed management. The purpose of prioritization of sub basins is offer a pattern for control and decrease flood hazards and evaluating the role of each sub basin in peak discharge of outlet flood hydrograph of basin. In this study, NEKA basin was selected as study area, because of several floods was occurred in it and with combining GIS and HEC-HMS hydrological model, the contribution of each sub basin in outlet flood from total basin based on SCS method, was determined. For this purpose, at first design rainfall hyetograph for different return periods was computed and after calibration the HEC-HMS model and estimate optimal value of the parameters, outlet flood hydrograph from each sub basin of NEKA basin and also outlet flood hydrograph from all over the basin for different return periods was simulated by HEC-HMS. For prioritization of sub basins, after removal of single sub basin in HEC-HMS environment, two indexes of parcenary contribution of each sub basin in outlet flood of basin and parcenary contribution of each sub basin in outlet flood of basin per unit area was used. for this purpose,  the 100 years return period flood was used. The results showed that the contribution of sub basins in flooding potential will be not only affected by its area but also the place of each sub basin and flood routing in main reach have remarkable effect on flooding regime of basin. Also determine the severity of flooding per unit area of sub basins, in prioritization flood control operation for cost and facilities, can be more efficient than other. Finally was observed, the sub basins that are located in the central part of basin, have most effect on the total basin's flooding.