Lithological Control on Landslide in the Siwalik Section of the Lakhandehi Khola Watershed of Sarlahi District, South-Eastern Nepal

Abstract

The main objective of this study is to research how landslide occurrence is controlled by lithology in a portion of the Siwalik of Nepal. This study further aims to observe the immediate and long-term consequences of increasing landslides in the Siwalik and Bhabar Zone of Lakhandehi Khola watershed, South-Eastern, Nepal, through inventory-based analysis. The Siwalik rock successions of the present study can be divided into four geological units as the Lower Siwalik, Middle Siwalik 1 (MS1), Middle Siwalik 2 (MS2) and the Upper Siwalik, from older to younger, respectively. The landslide frequency and landslide size frequency were found very prominent in the Lower Siwalik and least in the Middle Siwalik 2 (MS2). In recent years, the downstream section of the Lakhandehi Khola watershed has been suffered critically from the extreme sediment supply which is provoked by increasing landslides in the Siwalik Hills. This has resulted several effects on river morphology such as channel erosion, upstream and downstream incision, gravel scramming, bed armouring and channel instability. Subsequently, loss of agricultural productivity, failure of flood protection structures, deforestation and so forth have been already started in the watershed region and is embodying depressing future if proper landslide-controlled measures are not used properly.