پهنه بندي خطر سيل در بخشي از محدوده رودخانه زيارت در حوزه آبخيز شهري گرگان

Flood hazard zonation in a part of Ziyarat river in Gorgan urban watershed

Flood events cause extensive human and financial losses in the world every year. The process of land use change, urdanization, inappropriate construction and occupation of river side lands have great effects on this hazard. This study was carried out in Ziyarat river flood plant which, large area of Gorgan city is located in its floodplain. For this reason, first topographic and land use maps of the urban watershed of Dorgan has been digitized for using in GIS. According to topographical conditions, the study area was divided into 15 sub-watersheds. Also, according to hydraulic and hydrological conditions of river, this river was divided into 9 reaches. Then flood hydrographs in 2, 5, 25, 50, 100 and 200 years return periods estimated by Muskingum-Gunge method. Geometrical characteristics of reaches in 55 cross sections have been determined by field surveying. Water surface profile in each has been calculated, using HEC-RAS software for every return period. Then flood hazard maps of the study area have been prepared in ArcView G1S. With overlaying flood hazard land use maps, the flooded area and mean depth of floods have calculated. Finally, according to the results of this research, suitable management approaches have been proposed.