Earthquake and Monsoon Induced Slope Failure Effects on Hydropower Projects - An Analysis Along the Sunkoshi Valley, Nepal

Abstract

Due to various reasons like fragile geology, steep topography, highly varying climate and rainfall, many slope failures of varying sizes are very common in Nepal. Every year a lot of those events occur which cause a huge loss of life and property. Jure rockslide, which took place on 2nd of August 2014, is one of the most devastating disasters related to slope instability in the recent years in Nepal. Therefore, it is chosen as the representative case to carry out slope stability assessment. During the evaluation, kinematic, limit equilibrium, as well as numerical modeling are conducted. From the analyses, it has been confirmed that the slope failure in the Jure rockslide is caused by the combination of the main discontinuity set and raised groundwater level due to rainfall. Moreover, Gorkha earthquake (M = 7.9) hit Central Nepal on 25th of April 2015 which is the largest earthquake to strike Nepal after the 1934 Nepal-Bihar earthquake. Apart from the loss of lives, the major infrastructures suffered heavy damages. So, the Sunkoshi Valley, being one of the hardest hit areas, is chosen to document the damages in hydropower projects due to the earthquake. From the documentation of damages, it has been observed that the most damages were caused due to the quake-induced rock and debris fall or shallow landslides rather than the shaking itself. Hence, from both case studies, the slope failure processes induced by monsoon and earthquake are analysed and their effects on the hydropower projects are studied. Also, it is concluded that the earthquake and monsoon-induced slope failures greatly influence the efficient functioning of a hydropower project.