Development of Flood Forecasting and Early Warning System for Karnali and Narayani River Basins of Nepal

The Karnali and Narayani River Basins together drain over 82,500 km² of the Himalayas — the Narayani (Gandaki) covering 36,430 km² in central Nepal, fed by glaciers below Dhaulagiri (8,167 m), Manaslu (8,163 m) and Annapurna-I (8,091 m) via the Kali Gandaki, Trishuli and Marsyangdi tributaries; and the Karnali covering 46,148 km² in western Nepal, Nepal's longest river, originating in Tibet and descending to the Terai plains near Chisapani. Both basins concentrate roughly 80% of their annual rainfall in the June–September monsoon, creating recurrent devastating floods across the Terai districts of Chitwan, Nawalparasi, Bardiya and Kailali — affecting millions of people with inundation, bank erosion and sedimentation losses.

The Department of Hydrology and Meteorology (DHM) engaged the IWM–TMS–IES Joint Venture to replace Nepal's existing experience-based and gauge-to-gauge flood forecasting approach with a fully operational, model-driven Flood Forecasting and Early Warning System (FFEWS). IES Nepal is a technical partner in this joint venture, contributing expertise across field surveys, topographic and cross-section survey, hydrological monitoring, geo-spatial analysis and capacity building.

The project — running from October 2022 to September 2026 — delivers six integrated scope packages: a comprehensive baseline database; coupled HEC-HMS hydrological and HEC-RAS hydraulic models for both basins; a central database and web-based system; a Decision Support System (DSS) with web dashboard and mobile application providing 10–15 day lead-time flood forecasts; operational verification and maintenance; and knowledge transfer and capacity building for DHM hydrologists and technicians to sustain the system as a life-saving tool long after project completion.