The water level flowing out of Thorthormi lake in Lunana was normal as of yesterday night. However, the stability of the moraine walls surrounding the main lake is uncertain.
The chief of hydrology and water resources division, Sangay Tenzin said this is because of the two subsidiary lakes that breached on the evening of June 20. There is erosion and an outflow from the subsidiary II lake, which could destablise the moraine dams of the main Thorthomi lake.
A special team of experts would visit the lake site today to make rapid assessment of the lakes and the surrounding areas.
A press release from the Department of Disaster Management (DDM) stated that concerned authorities conducted a coordination meeting last night to consider precautionary measures and made the decision.
Officials at the National Centre for Hydrology and Metereology (NCHM) are constantly monitoring the situation through its early warning systems (EWS) and two field officials deputed at the site in Lunana.
“Our priority right now is to provide accurate and timely information to the people if a GLOF occurs,” Sangay Tenzin, said.
NCHM officials intensified the monitoring after the Thorthomi glacial lake outburst flood (GLOF) EWS’s remote monitoring station detected a rise in water level at 6:55pm on June 20 and alerted the flood monitoring and command room.
The water level increased from 6.55ms at 6.05pm to 8.04m at 7:20pm and receded to 5.36m at 10:40pm.
Sangay Tenzin explained that the unusual receding is dangerous, as it indicates GLOF scenario as per the GLOF EWS system logic.
NCHM’s field observers stationed at Thanza walked up to the lake to verify and reported that the bed and channel erosion at subsidiary lake II is intensive. “Due to this, there are chances of destablising the main Thorthormi lake.”
Officials say civil servants in Lunana are assisting the NCHM officials. Without any villagers around, there is no one to take food to the officials who are monitoring the lake.
With the gauge post at Thorthormi damaged, officials in Lunana are using boulder marks to study the water level.
Officials explained that it would be difficult to assess the moraine stability and what caused the breaching of the two subsidiary lakes as of now. “It could be because of geophysical activities like avalanches or anything else but we don’t want to make any assumptions now,” Sangay Tenzin said.
Meanwhile, the residents of Thanza and Tenchey village in Lunana evacuated themselves to the mountains since the night of June 20.
Lunana gup Kaka said that while most of the villagers have gone to the mountains to harvest cordyceps, those residing in the village comprising mostly of elderlies and children moved their rations and shelters to the yak sheds. Some have pitched tents.
He said that two bridges have been washed away in Thanza and Tenchey. “The water level has not decreased.”
But people living downstream along the banks of Phochu are not much worried.
With DDM and NCHM issuing flood warnings and alerting people, residents in Gasa, Punakha, Wangduephodrang and Dagana said local leaders would inform them if anything happens through WeChat.
It was learnt that students were not informed about the matter since it’s exam time.
In Punakha and Khuruthang, people were doing their usual chores yesterday afternoon. They said it would take the flood about six hours to reach their place.
Sangay Lhamo, 59, from Khuruthang hired labourers to transplant paddy saplings and said she is sure the flood won’t reach their area before they return home.
In Samdingkha, a shopkeeper, Pem, said she only noticed the change in the colour of the river. “Our family would spend the night in the gup’s office.”
In Dagana, Tsangkha gup and Sunkosh town residents conducted a meeting to discuss the action plan if a GLOF occurs. Sunkosh town has about 15 households.