After a scare of a glacial lake outburst flood from Lunana last night, the water level at the Thanza Flood Warning Station is currently reported normal. According to the National Centre for Hydrology and Meteorology (NCHM) there is no imminent threat downstream as the water level is still below the risk level. However, the NCHM staff from its Tenchoe base, who spent the whole of last night at the Thorthormi Lake site, found the Thorthormi Automatic Water Level Sensor damaged by yesterday’s GLOF incident.
At 7:20 in the evening, yesterday, the water level at the Thorthormi Automatic Water Level Sensor recorded a sudden decrease in water levels within a space of five minutes, indicating a breach of the Thorthormi Lake.
Similarly, between 7:45 and 8:00 pm, the water level at the downstream station in Thangza village increased between 40 to 50 centimetres. Thangza is the first village at risk.
Soon after the alarms were triggered at the National Weather Flood Warning Centre in Thimphu and GLOF Early Warning System Control Room in Wangdue Phodrang. Staff from NCHM’s Lunana base in Tenchoe village then began to walk towards Thorthormi Lake for field verification.
The field verification staff, who reached the site at around 11:00 pm found abrupt changes in the water level of the Thorthormi Lake.
Visual observations also found huge displacement of icebergs and new erosion on the moraine walls of Thorthormi’s subsidiary lakes I and II.
A team of three experts from the NCHM, who flew to Lunana this morning, are currently at the site to study the potential cause of the lake outburst.
According to the director of the NCHM, while the adjacent Raphstreng Lake is fully formed, the Thorthormi Lake is still in its forming stage.
The director also added that there are possibilities of the Thorthormi Lake spilling over into the Raphstreng Lake.
“We will not be able to specifically tell the cause yet. In yesterday’s incident, the system detected the event and to further verify, we have deputed the team in Lunana. The earliest studies have shown that there are high possibilities since the ridge between the Raphstreng and Thorthormi lakes is decreasing. In a worst-case scenario, the chances of Thorthormi breaching into the Raphstreng would cause a catastrophe,” said Karma Dupchu, Director of the National Centre for Hydrology and Meteorology.
Soon after the incident yesterday, the GLOF Early Warning System Control Room in Wangdue Phodrang informed the Local Governments of Punakha, Wangdue and Gasa, and Hydropower Projects downstream.
According to the NCHM, a team led by the secretary of the Ministry of Energy and Natural Resources and NCHM talked with the Local Governments and monitored the ground situation.
Residents living along the PhoChhu and Punatsangchhu basins are advised to exercise vigilance and stay informed about the situation.
“The Tshogpa called us and alerted us about the situation. We stayed awake till 11 pm. We packed all our important belongings and documents in a bag if in case a flood happens. However, we did not go outside,” said Namgay Wangmo, a resident of Samdingkha in Punakha.
“We tried to escape carrying our bags. Then someone from the village called the people in Lunana and inquired about the situation. We were then told that the situation was not so grave. We also received some video clips to assure that. Then we headed home,” said Pasang Dema, another resident.
The last time Bhutan experienced a devastating glacial lake outburst flood was in October 1994 when a partial burst of the Luggye Lake wreaked havoc downstream along the Punatsangchhu basin.
Should the imminent convergence of Thorthormi and Raphstreng happen, Punakha will experience a more severe flood, nearly three times more severe than the 1994 GLOF.
According to the NCHM, Thorthomi and Raphstreng are two of the 17 glacial lakes in Bhutan that pose serious GLOF risks.
Bhutan has more than 700 glacial lakes.
Deki Lhazom
Edited by Sherub Dorji
