Assessing Flood Hydrograph by Using Simulated Runoff-Rainfall (Case Study: Evan Watershed)

This research was performed in the watersheds of Evan in Ilam province. Flood hydrograph was simulated by using HEC HMS model in HECGEO HMS and ARC MAP9.3 software. To this purpose¡ data of flood, discharge, daily and hourly rainfall were used in the 30 years period (1981-2011). Then all watersheds was divided to 4 smaller unit (E1, E2, E3, E4) and the maps were prepared like topography, vegetation, hydrologic soil groups in ARC MAP environment. The next step land use and hydrological soil group maps were combined and the result was CN map. As a result, E2 has the most runoff, On the other hand, the participation rate of sub areas in runoff aren’t direct relationship with area. Average cure number is 80 for sub area of study and this is significant cure number that showed that every rain, lots of its volume is flowing in the ground. Increasing height of runoff displayed that more changes in soil, waste of Plant available water in this area. This result is following changing land use from forest to grassland.