The effective factors in occurrence and zonation of landslide in Alamut-Rud Watershed

Alamut-Rud watershed is located in northeast of Qazvin (central Alborz mountains). In order to landslide hazard zonation, based on the areal photos in scale of 1:40000 and field studies the instability distribution map in scale of 1:25000 was prepared. Different instabilities and their causes as well as other characteristics were recorded on single page questionnaires. Then the instability distribution map according to different factors and occurrence of landslides in the study area, information layers such as lithology, slope, aspect, vegetation cover, mean annual precipitation, distances from the road, fault and river and elevation in Arc GIS is provided and finally by bivariate statistical techhniques the zonation of landslides were prerformed. For evaluation of zonation map, the landslides distribution map was used which showed this method for zonation is suitable. Totally, this investigation shows 447 slope movements cases (328 landslides, 21 falls, 13 flows and 85 complex movements), which occupied 32% of the Alamut-Rud watershed and with the study of the whole factors in occurrence of landslides within this basin, out of 424 due to erosion and undercutting, 371 due to layering, 316 due to fractures, 278 due to faulting and other factors such as agriculture, destruction of lean, water resources structures, land use change, etc. have been affected less than 20% of the watershed.