Investigation of Flood Hazard Potential in Watersheds Using AHP(Case Study: Ilam City Watershed)

The aim of this study was to analyze the factors affecting the occurrence of floods and to prepare a zoning map of flood potential in two sub-watersheds of Arghavan and Kalanar, sub-watersheds of Ilam watershed, using AHP method. For this purpose, slope, vegetation, geology, soil permeability, drainage density and watershed shape as effective parameters in flooding in the studied sub-watersheds were selected. After the experts familiar with the watershed completed the questionnaire, these parameters were weighted. Using the results of weighting, the flooding potential zoning map was then calculated. Based on the results, the slope and shape indices of the watersheds had the highest (0.293) and lowest weight (0.072) and effects on flooding, respectively. According to the flood zoning plan, zones with very high flooding class are 1.45% of the area in Arghavan watershed and 14.77% in the sub-watershed of Kalanar, and zones with very low flooding class are 2.86% in Arghavan watershed and 1.25% of the watershed area in Kolanar. According to the final flood potential zoning map, Kolanar sub-watershed has a higher flood potential due to its high slope, impermeable formations, low vegetation and relatively round shape, as well as high specific discharge (0.52 m3/s.km2) compared to Arghavan sub-watershed (0.29 m3/s.km2) and the Arghavan sub-watershed contains a larger volume of floods due to its larger surface area than the Kalanar sub-watershed. As a result, experts should pay more attention to the Kalanar sub-watershed, which has a higher flood potential.