Flood mapping using HEC-RAS hydraulic model in part of Khorramabad watershed

Flood prone area identification in the watersheds is one of the basic solutions for destructive flood control and mitigation. Flood mapping is one of the best methods for flood prone area planning and identifying. For this purpose, flow boundary conditions, peak instantaneous discharge with different return periods, cross sections and their distance and roughness coefficients for each cross section were entered to HEC-RAS hydraulic model in Khorramabad watershed located in Lorestan province, Iran, and this model was then run and flood water surface profile at different return periods were estimated. The results obtained from flood mapping showed that flood prone area in return period of 2-year with 145.125 m3s-1 and return period of 100-year with 553.781 m3 s-1 effect 8.63 and 10 km2 in area, respectively. So that about 4.4 km2 of the total rain-fed farming area, 2.4 km2 of total rangeland area and 1.4 km2 of total residential, 1.6 road area and 0.2 km2 abandoned effect by flood in return period of 100-year. Similarly for other flood return periods was also observed that the most flood prone areas are related to rain-fed farming, rangeland, road, residential area and abandoned the land.