17. Water Hazards in the Trans-boundary Kosi River Basin

The Kosi River is an important tributary of the Ganges that passes through China, Nepal and India. With a basin area of 71,500 km², the Kosi River has the largest elevation drop in the world (from 8848 m of Mt Everest to 60 m of the Ganges plain) and covers a broad spectrum of climate, soil, vegetation and socioeconomic zones. The basin suffers from multiple water-related hazards including glacier lake outburst, debris flow, landslide, flood, drought, soil erosion and sedimentation. This paper describes the characteristics of water hazards in the basin based on the literature review and site investigation covering hydrology, meteorology, geology, geomorphology and socioeconomics. Glacier lake outbursts are a huge threat to the local population in the region, and they usually further trigger landslides and debris flows. Floods are usually a result of interaction between man-made hydraulic structures and the natural environment. Debris flows are widespread and occur in clusters. Droughts tend to last over long periods and affect vast areas. Rapid population increase, decline of ecosystems and climate changes could further exacerbate various hazards in the region. The paper has proposed a set of mitigating strategies and measures. It is a huge challenge to implement them in practice. More investigations are needed to fill in the knowledge gaps.