Flood Zoning, Using Hec-Ras Model in Broudjerd Seilakhor Floodplain

Flood is a complex natural disaster and a destructive phenomenon that causes considerable annual damage. Floodplain and lands alongside river beds are always at the exposure of flood, while most of economic activities are also concentrated in these areas. Therefore, in these regions, flood zoning is indispensable. Flood zoning maps, could be a suitable and well as lawful tool for use in determination of development strategies. In this research, a map of flood zoning with different return periods was prepared. Hydrological data and information were collected and analyzed. Natural unit hydrograph (N.U.H) was derived. In addition, 262 cross sections were surveyed for Broudjerd Seilakhor River and its branches. Some floodplain characteristics, such as situation of bed and river banks as well as vegetation cover were noted. Flood routing was carried out in different branches and reaches employing Muskingum-Cunge method. Finally, by using HEC-RAS model, flood-zoning maps with a scale of 1:50.000, water surface profiles and flow characteristics in different reaches and for different return periods, were derived. Then, the accuracy and precision of maps, by use of historical films and pictures and through regional investigations, were evaluated. The results indicated that by even considering the HEC-RAS limitations, the final flood maps were still accurate enough for the aim followed in this kind of study.