Spatial Analysis of the Instability slope in Mahabad Dam watershed

Recently, Use of fuzzy sets has been considered by geomorphologists. due to consider a range of possibilities instead of numbers, no limits on quantitative methods and a more accurate prediction of the instability slopes. The aims of this study are identify areas with high susceptibility of instability slope in Mahabad watershed has been done using fuzzy model. At first, the factors affecting on the occurrence mass movement were determined. These effective factors were mapped with satellite image (ETM), topographic map (1/50000), geological map (1/100000), and field surveys. Then, the additive and multiplicative algebraic function fuzzy, carried out on factors and overlaps were done. Finally, based on the best possible gamma (Gamma 0.7), the final mass movement susceptibility map has been obtained. The results showed that about 33.8 percent (equal to 254.64 km2) of the total area of Mahabad watershed have “high” and “very high” the susceptibility of mass movements. Comparison of the final maps with the effective factors indicating that the areas with the possibility of very high are according to areas of slope degrees of over than 20 percent, elevation of sea of over than 2300 meters, regions with a high density of faults and the steep terraces river.