Spatial Vulnerability Investigation by Morphotectonic Analysis of the Mandakini River Basin near Kedarnath, Uttarakhand, India using SRTM DEM in a GIS Platform and GPS Data

Abstract

Tectonomorphic study was carried out to evaluate the intensity of tectonic activity in and around the Mandakini River basin (1330 sq. km area) near Kedarnath. The area has witnessed several vulnerable landslides and devastating floods in the recent past. Quantitative parameters such as Bifurcation Ratio (BR), Asymmetry Factor (AF), Valley floor width Index (Vf), Hypsometric Integral (HI), Stream-length gradient Index (SL index), Sinuosity Index (Sp) and two qualitative parameters such as drainage orientation survey and the hypsometric curve is used to evaluate the spatial tectonomorphic susceptibility of the different watersheds of the Mandakini River basin. High BR, medium to high AF and low Vf show a very high vulnerability mostly close to MCT. High Sp and medium HI values are linked with continuous tectonic disturbances followed by erosion. High SL index demarcates high tectonic instability along different portions of streams which is prone to tectonic perturbation. The Index of Relative Active Tectonic also suggests variability in tectonic activities varies from very high tectonic activity to high tectonic activity. Regional geology and lower-order stream orientation survey of the study area revealed that the initial NE-SW shortening direction of the Himalayan orogeny is rotated to the N-S direction in the later stage. The resulting deformation style is expressed by the NW–SE and NE–SW striking lineaments and WNW–ESE striking thrust dipping moderately toward the north. Processed GPS data shows the rotation of the maximum principal compression direction and resultant readjustment of strains are linked with the revolving of the Indian Plate in the anticlockwise direction which is responsible for the orientation of different discontinuities, developing maximum shear stress conditions, weak internal friction and negligible resistance by low-strength rock. The present tectonic setup of the Kedarnath region is highly susceptible to devastating floods and vulnerable landslides.