Glacial Lake Floods Prevented in Bhutan

Lowering Thorthormi glacial lake in Bhutan
Bhutanese work to artificially lower Thorthormi glacial lake, which is threatening to overflow due to the rapid melting of ice and snow. Photo credit: Patrick Fries/Arrowhead Films

The glacial melt waters that sustain hydro power in Bhutan are also a potential source of destruction. Communities in Bhutan’s Punakha-Wangdue and Chamkhar Valleys have been living with the threat of glacial lake outburst floods (GLOF) due to the rapid rate of glacial melting resulting from rising global temperatures. These areas - populated by emerging townships, hydropower plants, infrastructure projects, and farmland - could suffer extreme human and economic devastation should a glacial lake flood occur.

In fact, a glacial outburst flood ripped through the village of Punakha in 1994, leaving 21 dead and destroying a year’s worth of crops. “Even today I don’t like to go near the river because I’m very afraid of another flood happening,” said Sonam, a horseman who survived the catastrophic glacial lake flood.


  • A new early warning system shares data with neighbouring states in India
  • More than 2,500 people in vulnerable communities are now more aware of GLOF early warning systems
  • A predicted GLOF disaster at Thorthomi Lake was averted due to the controlled drainage

UNDP is supporting the Government of Bhutan by bringing long-term glacial lake flood risk reduction plans into existing disaster prevention policies and practices. Among the achievements of this Global Environment Facility initiative is the construction and installation of a new automatic GLOF Early Warning System.

The system includes sirens, automatic water level and weather stations.  In addition, a flood warning control station, linked to Bhutan’s flood warning system, is monitored 24 hours a day and shares water level data with neighbouring Assam and West Bengal states in India.  To complement the early warning system, awareness raising activities have been conducted to over 2,500 people from vulnerable communities, schools, government and religious institutions so they are better prepared for any impending disasters.

The effort also provides employment. Every year from June to September, approximately 200-250 people trek to Thorthomi glacial lake to increase controlled water drainage from the lake using pickaxes and shovels. As a result, pressure from the melt water has been reduced on the thinning moraine dam.

“In the Himalayas, this is the first time this work is being done,” says Yeshi Dorji, Director General, Bhutan Department of Geology and Mines. “Quite a lot of countries like Nepal, Pakistan, India are observing us and how we are doing and how successful we will be.”

The overall target of the project was reached when the lake water level was lowered by five metres. While initial surveys conducted before the beginning of the project have predicted a GLOF event from Thorthomi Lake as early as 2010, the project has successfully managed to avert this disaster. A recent survey of the project’s impact on awareness and response capacities of the local population has revealed that 90% of GLOF-prone communities are already aware about the efforts of the project, and will be benefiting from the services provided by the early warning system even beyond the project lifetime.


Photos from our documentary 'Revealed: The Himalayan Meltdown'
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  • Bangladesh 3
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  • Bhutan 1
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