Modeling of Hydraulic Behavior of Kashkan River and Determination of Floodplain Limits Using HEC-Geo-RAS

Prediction, controlling, and reduction of the flood plain have crucial role in integrating watershed management. The flood damage analysis and designing control plans need to identify floodplain limits around the main river according to different return periods. Kashkan River in Lorestan province has been challenged frequently by dangerous floods. Since numerous villages and also agricultural lands are existed near the both sides of the river, they are exposed in flooding hazard. The aim of this study is preparing the floodplain maps of this river for a reach length of 5000 m using HEC-Geo-RAS for different return periods. For this purpose, digital elevation map (DEM) with scale of 1:150, topographic map with scale of 1:50000, cross-sections geometry, and peak discharge data recorded in the hydrometric station in upstream of the reach were incorporated. The peak discharge corresponding to return periods 2- to 1000-years are estimated as 227 to 5000 m3/s using fitting a three parameters person distribution. Simulation of the hydraulic behavior of the Kashkan River using the HEC-RAS model indicates that the floodplain area for discharge with return period 25-years are 75% of one obtained for 1000-years. Additionally, the floodplain area for the upstream of the study reach is greater than the other where. This reveals that construction of the villages and changing the land use in the river borders threaten with low period floods (e.g. 25-years).