𝐒𝐢𝐩𝐡𝐨𝐧 𝐓𝐞𝐜𝐡𝐧𝐨𝐥𝐨𝐠𝐲 𝐭𝐨 𝐁𝐞 𝐓𝐞𝐬𝐭𝐞𝐝 𝐭𝐨 𝐑𝐞𝐝𝐮𝐜𝐞 𝐆𝐋𝐎𝐅 𝐑𝐢𝐬𝐤 𝐟𝐫𝐨𝐦 𝐓𝐡𝐨𝐫𝐭𝐡𝐨𝐫𝐦𝐢 𝐋𝐚𝐤𝐞

By Kezang Choden

The National Center for Hydrology and Meteorology (NCHM) is on track to test siphon technology aimed at reducing the risk of Glacial Lake Outburst Floods (GLOF) from Thorthormi Lake in Lunana. The key components of the siphon system High-Density Polyethylene (HDPE) pipes have already reached Lunana. The materials were transported from the Punakha helipad by the Drukair Helicopter Services Division on May 10, 2025. An assessment phase is scheduled for May and June this year. Based on its findings, the full testing of the siphon system is planned between September and October this year. The project is part of Bhutan’s ongoing efforts to mitigate climate-induced risks in vulnerable highland regions.

According to the NCHM, the rapid melting of glaciers in Bhutan and around the world is primarily driven by climate change and rising temperatures. Recent studies show that glaciers in eastern Bhutan are retreating at a faster rate compared to those in the west, with a loss of 15 to 30 percent in area over the past three decades. This rapid retreat has raised serious concerns about long-term water security and the increasing risk of GLOFs. Beyond the immediate threat of GLOFs, the continued loss of glaciers poses a grave danger to Bhutan’s biodiversity and fragile ecosystems. As highlighted in the Thorthormi Flood Incident Action Taken Report from NCHM’s assessment on Thorthormi Lake, four glacial lakes in the Lunana region(Luggye, Thorthormi, Rapstreng, and Baytso) have been identified as potentially dangerous. These lakes are among nine glacial lakes in the headwaters of the Phochhu River that are considered to pose a significant risk.

Karma, a specialist from the Cryosphere Services Division under the NCHM, has confirmed that a test phase for siphon technology will begin in September and continue through October this year. The siphon will be used to reduce the GLOF hazards in Bhutan. According to Karma, the use of siphon technology is still relatively new in Bhutan, and it has not been widely tested in similar glacial environments. Therefore, before implementing the siphon system, a reassessment of the lake will be carried out to evaluate current conditions and determine the best course of action. “We are not certain whether the test phase will be successful,” Karma stated. “However, if the siphon works as planned, we will proceed with lowering the lake’s hazard in a gradual and controlled manner.” The NCHM will continue to monitor the situation closely and update the test progresses.

A rapid assessment team deployed to Lunana following a glacial lake outburst flood (GLOF) event from Thorthormi Lake has confirmed significant changes in the lake and glacier structure. The team observed that the entire ablation area of the Thorthormi glacier has disintegrated into ice blocks. According to the report, the current dimensions of Thorthormi Lake are approximately 4.33 kilometers in length and 1.3 kilometers in width, with a surface area of 4.33 km². The partial breach of the lake led to a water level drop of 46 centimeters, releasing an estimated 1.98 million cubic meters of water downstream. In response to the event, the NCHM has reinforced the monitoring system at the lake site. The damaged Automatic Water Level Station (AWLS) has been temporarily restored to ensure continued surveillance of the lake’s condition. Authorities are closely monitoring the situation to mitigate further risks and ensure timely updates for downstream communities.

Kaka, the Gup of Lunana Gewog under Gasa Dzongkhag, stated that the NCHM is making significant efforts to reduce the risk of GLOFs in the region. This follows a major flood event in the past caused by the Thorthormi Lake, which raised concerns among the local communities and authorities. In response, the NCHM is now preparing to test a siphon-based technology designed to lower the water levels in Thorthormi Lake. The system is expected to help drain excess water in a controlled manner, thereby minimizing the chances of a sudden outburst. According to the Gup, this approach is a proactive measure to protect both lives and properties downstream, particularly as climate change continues to accelerate glacial melting in high-altitude regions. He emphasized that Lunana remains one of the most vulnerable areas in the country to GLOF events, and such interventions are crucial for the safety and wellbeing of the residents. If the siphon technology proves effective, it will mark a promising step forward in disaster risk reduction and climate adaptation for the people of Lunana.

Karma explained that the primary reason for testing this method is to find innovative ways to reduce hazards posed by glacial lake outburst floods (GLOFs) and other water-related threats. According to him, the ultimate goal is to safeguard critical infrastructure, including the historic Punakha Dzong and hydropower projects located downstream. “This year’s testing is crucial,” Karma said. “If the siphon technology proves effective in lowering water levels in glacial lakes or diverting excess flow, we will intensify our work in the following year to ensure the safety of key national assets.” The siphon method involves using tubes to draw down water levels from potentially dangerous glacial lakes without requiring large-scale construction. If successful, this technique could serve as a cost-effective and environmentally friendly approach to disaster risk reduction in Bhutan’s highlands, where climate change continues to accelerate glacial melt. Karma added that protecting vital infrastructures is not only about preserving historical and economic assets but also about ensuring the safety and wellbeing of communities living downstream.

The Gup expressed optimism regarding the efforts being made by experts to prevent future floods caused by glacial lake outbursts. He stated that if the initiatives being undertaken prove successful, they will not only bring safety to the local community but also ensure greater prosperity for all those living downstream. He highlighted the critical importance of addressing the risk of glacial lake outburst floods, which have been a recurring concern in the region due to the impact of climate change on high-altitude lakes. According to the Gup, the community is fully committed to supporting the team from the NCHM in their ongoing efforts to avert potential disasters. The Gup added that while the efforts so far are commendable, the true impact of the interventions will only be known after the completion of the siphon technology testing, which is scheduled for later this year. He emphasized that the residents remain hopeful and stand ready to cooperate with technical experts in any way necessary to protect lives, livelihoods, and infrastructure.

Once fully tested and implemented, this technology is expected to serve as a long-term solution to mitigate flood risks in vulnerable areas. The Gup reiterated that preparedness and collaboration are key to reducing disaster risks, and he thanked the relevant agencies for their continued support and dedication to the safety and well-being of the communities living in flood-prone zones.