- Nepal will lower water levels in four high-risk glacial lakes to prevent catastrophic outburst floods and protect vulnerable downstream communities.
- The $50 million project involves building controlled drainage channels and gated structures, with preliminary design work starting by July 2027.
- The initiative includes installing monitoring sensors and early-warning systems to mitigate risks from avalanches, earthquakes, and extreme Himalayan weather events.
- This urgent action follows recent devastating floods, addressing growing dangers posed by melting glaciers and unstable natural dams in mountain regions.
Kathmandu, Nepal: Nepal is preparing to lower the water levels of four high-altitude glacial lakes in an effort to reduce the risk of sudden floods in mountain valleys and communities downstream.
The plan will target Thulagi, Lower Barun, Lumding Tsho and Hongu II, four lakes that authorities consider among the country’s most dangerous. They are located at elevations ranging from about 4,050 metres to 5,483 metres above sea level.
The proposed work will not completely drain the lakes. Instead, engineers plan to build controlled drainage channels and gated structures to gradually lower their water levels and release water into nearby rivers. The aim is to reduce the pressure on the natural dams holding the lakes and limit the amount of water that could rush downstream if a dam fails.
“Our aim is to lower the risk of the lakes breaching their natural dams and reduce the risk of downstream floods,” Subash Tuladhar, an expert at Nepal’s Centre for Hydrology and Water Resources Research, told Reuters.
Preliminary design work and detailed studies are expected to begin during the fiscal year ending in July 2027. The actual drainage work could take up to six years once the necessary assessments and designs are completed, according to Sanjeeb Baral, executive director of the research centre.
The project is expected to cost about $50 million, with funding from the Green Climate Fund, the United Nations Development Programme and the Government of Nepal. The wider programme will also support monitoring systems, flood forecasting and early-warning measures for communities at risk.
The work will be difficult. All four lakes are located in remote and high mountain areas where workers must cope with low oxygen levels, freezing temperatures, steep terrain and limited access. There is also a risk of sudden flooding while the drainage structures are being built.
Engineers will therefore need to study each lake and its surrounding terrain carefully before construction begins. A drainage system that releases water too quickly could create a new flood threat downstream, while an unstable natural dam could make construction dangerous.
Nepal has some experience with such projects. The country lowered the water level of Tsho Rolpa in Dolakha by about three metres in 2000 to reduce the risk of a glacial lake outburst flood. A similar project was later completed at Imja Lake in the Everest region.
The four lakes now selected are considered high-risk because of their location, size and the possible consequences of a sudden outburst. A 2020 assessment by the United Nations Development Programme and the International Centre for Integrated Mountain Development identified them among the potentially dangerous glacial lakes in the region.
Glacial lake outburst floods occur when water held behind a natural dam of ice, rock or debris is suddenly released. An avalanche, landslide, earthquake, heavy rainfall or rapid changes in the lake can damage the natural dam and trigger a flood.
Such floods can travel rapidly through narrow mountain valleys, carrying large amounts of mud, rock and debris. Communities far from the lake can be affected because rivers can carry the flood far downstream.
Samjwal Ratna Bajracharya, a retired ICIMOD expert on glaciers and glacial lake outburst floods, said lowering the water level could substantially reduce the risk. But he also warned that the lakes would continue to face threats from avalanches, earthquakes, changing weather and other disturbances.
That is why the government’s plan goes beyond drainage. Monitoring sensors will be installed to track changes in the lakes, while flood forecasting and warning systems will be developed to alert downstream communities.
Such systems could be critical because lowering a lake does not remove every possible danger. Even after the water level is reduced, a landslide or avalanche could enter the lake and cause a sudden rise in water levels.
The urgency has increased following the devastating floods and landslides in August, when a glacier collapse triggered a series of landslides and flash floods in valleys along the Nepal-China border. More than 1,400 people were reported dead, while search teams continued looking for thousands of people who remained missing.
The disaster also damaged roads, bridges, homes, farmland and hydropower facilities, highlighting the vulnerability of communities and infrastructure in Nepal’s mountain regions.
The recent disaster has also renewed attention on the effects of a changing Himalayan climate. As glaciers retreat and meltwater accumulates, some glacial lakes are growing. At the same time, extreme rainfall and unstable mountain slopes can increase the risk of sudden floods.
Nepal has recorded about 26 glacial lake outburst flood events over the past four decades, according to officials. The country has thousands of glacial lakes, although only a smaller number are considered to pose a serious threat.
Lowering four of the most dangerous lakes will not solve Nepal’s wider glacial flood problem. The country will still need to monitor other lakes, improve warning systems, strengthen vulnerable infrastructure and prepare communities living along rivers and in flood-prone valleys.
For now, the government is focusing on the four lakes where it believes engineering work can reduce the danger. The task will be slow, costly and technically difficult, but officials say reducing the volume of water held behind unstable mountain dams could give downstream communities greater protection from a future disaster.
