Investigation the effect of geological formations on slope instabilities of Babolrood Watershed

Abstract

Landslides are among the most costly and damaging natural hazards in mountainous regions of Babolrood Watershed. The watershed is one of the major water basins in Mazandaran Province in which drain the water of northern part of Alborz Mountain into Caspian Sea. Due to the high density of population, farm lands, forests and infrastructure installations such as dams, roads and power lines, it is necessary to carry out the investigate of slope instabilities in the area. The aim of this work is to obtain an estimate of areas susceptible to landslide and to suggest mitigation methods to reduce the destruction effect of the hazard. Although many factors affect the instabilities of slopes, but in this research only the type of rock and the related geological formation is considered as a main factor. In this regards the locations and the type of landslides occurrence are distinguished and the information were plotted on geological based map. Then by the aid of ARC-GIS-9 program, and the use of Area Density Method, the percentage of landslide events in each geological formation was identified. The results show that marl, mudstone and siltstone of Neogene's deposits have high potential of Area Density of landslides. On the other hand, Shemshak Formation presents the highest number of landslide events. Carbonate rocks of Delichai, Lar, and Elika Formations were among the most resistible to landslide. It is also concluded that due to high rate of annual precipitation in the area, rocks with high percentage of clay minerals are more susceptible to landslide than others.