Mapping hazards in Nepal’s Melamchi river: Catchment to enhance Kathmandu’s water security

This technical report assesses the string of events that triggered Nepal’s Melamchi River floods in 2021 and highlights threats to the catchment area that provides vital drinking water to Kathmandu’s fast-growing population. The report explains how floods damaged key water supply infrastructure and analyses risks posed by earthquakes, glacial lakes, and landslides, as climate change complicates conditions in the fragile Himalayas.

The present study proposes the following mitigation measures to reduce the hazard intensity of extreme debris and flash floods in the Melamchi catchment:

• Future headworks designs consider a peak flood discharge and sediment concentration that incorporates hazards and climate change impacts.
• Comprehensive monitoring of the river and catchment and establishment of a multihazard early warning system (EWS).
•  Setting up of a disaster risk management (DRM) plan that also involves local residents in river monitoring.
• Introduction of solutions to reduce landslide risks and offer broad community costbenefits.
• Establishment of an integrated river basin management plan to identify, prioritize, and implement local hazard protection solutions at vulnerable sites.