The Zoning of danger of landslide by using the fuzzy region(the case study: the Watershed in Cham Gordlan dam in Ilam)

Geographically, the studied region in Ilam dam watershed is between 46°16'36'' to 46°38'32'' eastern longitude and 33°23'27'' to 33°38'54'' northern latitude. The area of case study is476.5 km2 with the highest and lowest height as 2400 m and 640 m above sea level. In this study, in order to map the landslide hazard zonation of Ilam Cham Gordalan dam basin by weighting the main criteria and using fuzzy membership functions in Arc GIS and establishing the best relationship functions between the presence and absence of landslides, a set of parameters is used. Then, each of the factors affecting landslides in the under-study area such as slope, slope direction, elevation, geology, land use, distance from roads, distance from drainage network, distance from the fault, and rainfall map has been digitized in the software environment of ArcGIS and are used in the fuzzy analysis. Landslide hazard in the under-study area has been zoned using fuzzy operators (Gamma, Product, Sum, Or, And). After the fuzzy fiction phase, the effective measures in the landslide occurrences in the area have been prepared using the above-mentioned method through Gamma fuzzy operators with Lambda 0.2،0.5، 0.8and 0.9 and by comparing final maps, the ideal model for the landslide hazard zonation in the area has been selected. The results show that among the above-mentioned operators, the Gamma operator with Lambda 0.9 is considered to be the most appropriate method for zoning the landslides in this area due to its fine fuzzy fiction of each criterion based on the distribution maps of occurred landslides and the way of separating risk classes.