Landslide Hazard Zonationb by Using AHP (Analytical Hierarchy Process) Model in GIS (Geographic Information System) Environment (Case Study: Kordan Watershed)

Landslides are one of the critical phenomena that frequently lead to loss of human life and property, as well as causing severe damage to natural resources. Kordan watershed located in the Alborz province, which including areas that are prone to landslide. The area under investigation is located from 50 ° 45' to 05' ° 51' east longitude and 35° 55' to 36° 05' North with expansion of about 488 km2 and elevation ranges from 1320 to 3900 m. The purpose of this study is to identify factors in landslides and zonate landslide hazard of Kordan watershed using AHP (Analytical Hierarchy Process) model in GIS environment. In this study, 4 factors, namely geology, hydrology, human and geomorphology were identified as important factors that could play an important role in Landslide watershed. In this study, geological mapping, using topographic maps and satellite images of the study area and data layers of various factors including lithology, fault, land use, roads, residential areas, slope, aspect, elevation, rainfall, temperature, congestion and drainage system in GIS using Arc GIS software has been developed and weight and relative importance of each factor in landslide hazard zonation with Analytical Hierarchy Process (AHP) were determined. Among the effective factors, sub-criteria of lithology, distance from the river, distance from fault, landuse and rainfall, respectively, with weights 0.314, 0.219, 0.105, 0.086 and 0.054 have been identified as the most important factors in the development of landslide in study area that In total,form up more than 75 percent of the total weight. The role of other factors reduces according to their weights in landslide. The final cumulative map of study area was categorized into four hazard zones and classified as zone I to IV (very low risk, low risk, medium risk and high risk). According to presented model and final zonation map, about 34 percent (30 km2) of Kordan watershed area have the occurrence of high risk and about 29.16 percent (142.386 km2) have the occurrence of moderate risk. As a result of the zonation performed according to the layers, most sensitive parts of the landslides are locted in the basin Quaternary deposits and the banks of rivers. The landslide hazard zonation map is useful for landslide hazard prevention, mitigration, and improvement to society, and proper palnning for land use and construction in the future.