The Bhutanese Leading the way.
Bhutan is preparing to test an innovative siphon-based water management system to reduce the risk of a Glacial Lake Outburst Flood (GLOF) from Thorthormi Lake in Lunana, one of the most dangerous glacial lakes in the country.
The pilot project, led by the National Center for Hydrology and Meteorology (NCHM), represents a potentially groundbreaking shift in Bhutan’s strategy for dealing with GLOF hazards.
The siphon system uses High-Density Polyethylene (HDPE) pipes to draw water from the surface of the glacial lake and discharge it safely downstream, thereby gradually lowering the lake’s water level without the need for heavy excavation or explosives.
Siphon method, simply put, is like when you are trying to take out water from a drum using a pipe by sucking on the pipe and creating a vacuum which leads to the flow of water.
The aim is to create a sustainable, low-impact method to reduce pressure on moraine dams, which is a barrier made of ice and loose rocks, holding these lakes back, and minimize the chances of a catastrophic outburst.
The materials for the siphon system are currently being airlifted from the Punakha helipad to the high-altitude region of Lunana by Drukair’s Helicopter Services Division. The first round of transportation began on 10 May 2025, and will continue over the coming weeks due to the remote and rugged terrain of the area.
According to the NCHM, an initial assessment phase will be conducted between May and June 2025 to study lake conditions, monitor flow behavior, and finalize system installation plans. The full testing of the siphon system is scheduled for the autumn season, from September to October 2025, when glacier melt rates are typically high and water levels peak.
Thorthormi Lake, situated at over 4,400 meters above sea level, has long been identified as a major threat due to its unstable moraine dam and proximity to other glacial lakes. The big danger is that its moraine dam wall could give way one day and pour into the fully melted Rapstreng Tsho or lake below.
This potential outburst could impact communities as far downstream as Punakha and Wangdue, endangering lives, infrastructure, and farmland.
While Bhutan has invested in GLOF early warning systems and lake monitoring since the 2000s, physical mitigation has mostly involved manual lake lowering through digging or controlled drainage channels, both logistically difficult and expensive. The siphon approach offers a potentially more cost-effective and less invasive method, especially suitable for remote, high-altitude locations like Lunana.
“This is the first time Bhutan will test siphon technology for GLOF risk reduction,” said a senior official from NCHM.
According to the Chief of the Cryosphere Division, only 500 meters of HDPE pipes will be used for the testing phase at Thorthormi Lake. The pipe diameter is 100 to 150 mm.
“There is no exact amount of how much water will be taken out during the siphoning phase,” he added. The volume will be determined based on the performance of the test. If successful, the team will proceed with a full-scale implementation, including evaluating how much manpower will be required for the expanded operation.
The siphon method has been tested in other parts of the Himalayas, including Nepal, but Bhutan’s extreme altitudes and logistical challenges make this a particularly ambitious undertaking. The success of this project could open the door to broader regional collaboration on climate adaptation strategies in the Himalayas.
As climate change continues to accelerate glacier melt in the region, proactive and adaptive solutions like the siphon system are becoming increasingly vital for protecting downstream communities and preserving Bhutan’s environmental security.
