An Ordinal Scale Weighting Approach for Susceptibility Mapping Around Tehri Dam, Uttarakhand, India

Abstract

The landslides are natural hazards, which cause damage to both property and life every year, especially in the Himalayas. Detailed studies of landslide susceptible areas are instrumental in getting fast and safe mitigation actions and doing future planning for any construction work. The study area lies under the Lesser Himalaya in the Tehri-Garhwal region of Uttarakhand, India. This area consists of weak and unstable lithology, highly fragile rocks due to the complicated tectonic settings; consequently, landslide movement is a common phenomenon in the area. We have used several landslide controlling factors such as slope, lithology, thrust buffers, relative relief, land use land cover, lineaments, and stream buffer in order to generate a susceptibility map. We have prepared these parameters from geological (structural and lithological) maps, Landsat TM, and ASTER GDEM data and field investigation data. We have integrated the data based on the ordinal scale weightage rating technique to generate the landslide susceptibility index (LSI) values. The LSI frequency distribution is divided into five zones (i.e., very low, low, moderate, high, and very high susceptibility) based on the geometric interval as well as the standard deviation to enhance the classes with minimal frequency. These zones account for 3.30%, 20.88%, 47.99%, 41.13%, and 1.83% of total area respectively. Furthermore, the final susceptibility map is validated using the field data of landslide occurrences, which depicts that more than 50% of landslides occur in very high and high zones. These zones lie in the north-eastern side of the Tehri reservoir, which is traversed by North Almora Thrust (NAT), while just 16% of landslides have fallen in low and very low susceptible zones.