Multi- Hazard Risk Assessment of Khimti Watershed

Abstract

Many places of Nepal are vulnerable to multiple hazards. Past and recent evidences have shown that the area near the hydropower areas is more vulnerable towards flooding and landslide. As many hydropower structures are under construction near the Khimti region, studying the vulnerability of this area is of great importance. The basin is vulnerable to flooding, landslide and seismic hazards. This study therefore aimed to assess multi-hazard risk through integration of individual hazard maps of flood, landslide and earthquake. This study utilized geographic information system (GIS) in combination with Frequency Ratio Approach for landslide hazard mapping. Flood vulnerability and risk was mapped by developing flood-inundation mapping model in HEC-RAS. Earthquake hazard map was prepared using R-CRISIS tool. The multi- hazard map was created using analytical hierarchy process for assigning weights to individual hazard map (landslide, earthquake and flood). For assessing climate change impact on flood inundation, future climate was projected using a set of five CMIP6 Global Circulation Models (GCMs) under Shared Socio-economic Pathways (SSP) scenarios. Eleven causative factors were identified and evaluated using GIS, and a landslide susceptibility score was created based on each factor's prediction rate. Finally, a landslide susceptibility map was created with the use of the landslide susceptibility index, and it was divided into four categories (i.e., Low, Moderate, High and Very high). The areas under classified range Low, Moderate, High, and Very High susceptibility zones, respectively, are 41.0%, 28.2%, 21.0%, and 9.8%. Flood hazard map was prepared using depth grid for 100-year return period from HEC-RAS. The obtained flood hazard map was divided into three categories (i.e., Low (< 1 m), Moderate (1 – 3 m) and High (> 3 m)) based on inundation depth. The areas under classified range Low, Moderate, High zones, respectively, are 1.3 Km2 , 0.6 Km2 and 0.3 Km2