Flood Hazard Zonation of Babolrud River Using Hydraulic Model of HEC-RAS in a Geographical Information System Environment (GIS)

Extensive areas of productive agricultural lands of river banks, due to flooding, destroy every year. Therefore, for river path training and management, beside evaluation of flow hydraulic behavior, flooding locations, flooded area percentage, flood height relative to land surface digital elevation, and flood characteristics during different return periods should be determined. Therefore, this research is aimed to map and delineate Babolrud flooding areas. For this purpose an attempt has been made to use GIS technique and HEC-RAS software for the assessment of flood risk zonation, from Anarestan to western Daroonkola village in a 4- kilometre length. To conduct this study digitalized topographic maps of 1:1000 scales were prepared and the TIN map of the mentioned area, was prepared using ARCVIEW and Hec-GeoRas environments. By identification of river and 113 cross sections geometry characteristics, the flow and Mining roughness coefficients were introduced to the model, therefore the flood return periods of 2, 5, 10, 25, 50, 100 and 200 years were calculated and ultimately flood zonation was determined. Finally, based on the flood zonation maps, it was determined that 80.3% of the flooded areas within the studied zone were affected with 25 years or less return periods. It reveals that the Babolrud banks are flat and more vulnerable to high frequent floods.