A UNDP situation analysis on vulnerabilities from GLOF in the two valleys states that about 10 percent of the country's population lives in these two valleys.
The report points out that, along the Punatsangchu, the country's longest river, were emerging townships, important historical structures, major hydropower projects, farmland and public infrastructural projects. Choskhor valley in Bumthang was emerging as an important urban, tourist and economic hub.
Geology and mines officials said that it was impossible to make any predictions as to how long they have to avert nature's wrath. "They pose no immediate danger," said the director of geology and mines, Dorji Wangda, adding that, at the same time, they could not procrastinate mitigation work.
geologist, Karma Toeb, who visits the glacial sites every year, said that
each time he saw new and disturbing developments.
While all the three glacier lakes, Thorthormi (Thortomi), Raphstreng and Luggye showed signs of bursting individually any time in future, geologists feared the worst case scenario, where two of the bigger lakes could merge and flow down as one giant GLOF.
Karma Toeb said that the Thorthormi (Thortomi) lake adjoining Raphstreng lake was slightly elevated and separated by just a 75-metre thick (at the top) moraine dam, which is a mass of earth and rock debris carried and left at the edges by melting glaciers.
The Thorthormi (Thortomi) glacier, Karma Toeb said, was solid ice in the 50s. "Glaciers are melting every year and several small ponds have formed, which are spreading and joining," he said. "The water from this lake is leaking into Raphstreng."
Recent studies suggest rates of glacial retreat in the Himalayas as high as 30 to 60 metres a decade.
The geology and mines director said that they wondered how long the moraine dams would endure until gradually giving into pressure from the meltingThorthormi (Thortomi) glaciers. "These moraine dams are cemented by the core ice, which is melting from global warming," said Dorji Wangda. "The dams will fail if global warming keeps increasing."
Should the two lakes join together, geology and mines officials said that it would burst open to unleash some 53 million cubic metres of floodwater.
During the 1994 flood in Punakha, the 140-metre deep Luggye tsho burst open and let out 18 million cubic metres of flood water, which damaged more than 1,700 acres of agriculture and pasture land, washed away five mills, 16 yaks and several houses, six tonnes of food grains, government infrastructure and killed 22 people.
Geologists said that rocks and material, occasionally dropping into the narrow gorge, which was the outlet created by the Luggye tsho when it burst in 1994, was blocking the thin passageway. This, they fear would allow water volume to rise until another flood hit the valley down stream.
To mitigate the threat from Thorthormi (Thortomi) lake, geology and mines officials will have to dig a channel at the outlet so as to reduce the water volume in the lake by five metres. "Whenever the water level rises, it'll flow out through the channel," said karma Toeb. "That won't allow hydrostatic pressures to build up in the lake," added Dorji Wangda.
The UNDP sanctioned a total budget outlay of US$ 7.8 million on April 8, for the mitigation work. Geology and mines officials said that the first phase, which begins this year, would be used to prepare logistics, stocking up food and carrying excavating materials and equipment to the glacial site.
"We can't use explosives, so everything has to be done manually," said Karma Toeb. The real work of excavation, which is expected to begin in the following three years after the first phase, would require about 300 workers.
According to UNDP officials, the project will look into building capacity for disaster risk management at the national, regional and local levels to address the need to incorporate climate change into ongoing disaster risk management decision-making and practices.
It will also work towards reducing the risk of GLOF from Thorthormi (Thortomi) Lake by artificially lowering its water level and enhance resilience of vulnerable populations in Punakha-Wangdue valley by establishing an early warning system for GLOF and other flash floods.
Glacial Lake Outburst Floods (GLOF) is one of the biggest hazards the country will continue to face given its numerous rivers which are glacial fed. Of the 2,677 glacial lakes in the country, 25 of them have been identified as potentially dangerous, posing threat of GLOF at any time.