Determination of Flood Plain Zoning in Zarigol River Using the Hydraulic Model of HEC-RAS

ABSTRACT: Several methods have been presented to flood administration and reduction and the results of flood risks until now. One of the employed methods is the Flood Plain Zoning (FPZ) method using hydraulic analysis that is based on a hydraulic model. Hydraulic models can draw the water surface profile in each arbitrary section. At first, the flood period is given; then the water surface level in different cross sections is calculated using the model, subsequently these points over the topographic plan of the zone are compared, to find the flood plain zone; and finally we can make required predictions to flood administration on the risk of flood. The current case study is an interval of Zaringol river in Golestan province in Northern Iran which is 24,210 meters long. Golestan province is the first region in Iran with the most detrimental floods and is always at risk because of its position, so presentation of accurate methods to determination of the accurate plain zone of flood is necessary to prevent the probable risks. To this end, in this paper, the hydraulic model of HEC-RAS to hydraulics calculations and the ArcView software are employed to extract the cross section using topographic plans of river and FPZ in Geographical Information System (GIS) with flood periods:2, 5, 10, 50 & 100 years and the scale of plans is 1:10000. The zones that were at risk were determined and finally several methods were recommended to prevent the zone reduction and the detriments of flood. This inquiry completely showed that incorporation of the hydraulic model of HEC-RAS and GIS is a useful implement to analyze FPZs.