Assessment Performance of HEC-HMS Hydrological Model for the Lumped and Semi-distributive Watershed (Case Study: Kohsukhteh Catchment)

For modeling, the concept of the system and the system boundary is necessary. The system is defined as a group of objects that in order to fulfill a specific purpose in the framework relationship or interdependence of regularly are interconnected. Systems rainfall - runoff from rainfall in the basin is started and after applying the types of losses (evaporation, infiltration, etc) it will become runoff. In the study of the HEC-HMS model for show the effectiveness of the sub-basin in runoff of the watershed is used; so SCS curve number method for losses method and SCS unit hydrograph method for transmission method were used. In beginning distribution basin model with three sub-basin then as an lumped basin model was run. The results show that the accuracy of the model in the watershed by taking sub-basin is more than lumped basin model..