Thame Valley GLOF 2024 — Causes, Impacts and Future Risks

Summary

This 2025 technical publication by ICIMOD and Nepal's National Disaster Risk Reduction and Management Authority documents the 16 August 2024 Thame Valley glacial lake outburst flood. It combines satellite analysis, field investigation, UAV survey and post-event measurements to reconstruct the two-lake cascade and assess remaining hazards in the valley.

Key Findings

• The report attributes the disaster to successive releases from Upper Ngole Cho and Lower Ngole Cho, about 10 km upstream of Thame village.
• A rock avalanche entered Upper Ngole Cho and generated a displacement wave that eroded the moraine above its bedrock dam. The released flow then descended about 120 m and struck Lower Ngole Cho.
• The Lower Ngole Cho breach measured about 21.6 m deep and 51 m wide. Field and satellite measurements indicate that roughly 303,000 m³ of water was released from that lake.
• The flood developed into a hyper-concentrated flow that transported debris for more than 80 km along the Thame and Dudh Koshi rivers.
• Documented damage in Thame included homes, hotels, schools, agricultural land and the Khumbu hydropower intake. The report also records sediment deposition near the surge tank and continuing slope instability near hydropower infrastructure.
• The study identifies continuing avalanche, overflow and lake-instability hazards upstream; its risk classifications are specific to the lakes assessed in the Thame watershed.

Relevance

This is the direct technical source for the 2024 example on GLOF Risk. It also supports the event-specific references on Koshi Basin and provides hazard context for Dudhkoshi Storage Hydroelectric Project, without establishing the design basis or exposure of that proposed project.

Limitations

• This is an event-specific reconstruction and lake-risk assessment, not a Nepal-wide GLOF frequency study.
• Fieldwork took place in December 2024. Later geomorphic change, mitigation work or monitoring results are outside its evidence window.
• The report documents damage and physical processes but does not provide a project-level design flood, final repair cost, insurance assessment or financial-loss model for downstream hydropower.
• Regional climate-change evidence in the background section does not by itself establish a single-cause attribution for the triggering rock avalanche.