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Lunana's glacial lakes: Thorthormi Tsho
Thorthormi Mitigation Project

Work on Lunana lake is delayed

Work to prevent the flooding of the largest glacial lake in Lunana has been delayed by the shortage of funds.

The lake - Thorthormi (Thortomi) - meanwhile, is becoming more vulnerable, according to experts, because its body of glacier is melting fast and filling up the lake.

"We must start the mitigation works before the situation becomes critical," the director of the geology and mines department, Dorji Wangda said.

In 1994 one of the glacial lakes in Lunana - Luggye Tsho - formed by the melting of glaciers, partially burst, causing the Pho Chhu to flood.

It killed 23 people in the Punakha valley and cost the government more than Nu. 43 million on flood relief measures.

The government then sent several expeditions to the Lunana region to assess the risk of glacial outbursts. A Bhutan-India team discovered that a glacial lake - Raphstreng Tsho - was on the brink of rupture. The water from the lake was quickly drained and the risk of an outburst reduced.

A Bhutan-Austrian team later, in 2000, saw a threat about 60 meters above the Raphstreng Tsho. Situated at 4,500 metres above sea level, the Thorthormi (Thortomi) glacier was melting and had created multiple lakes at its terminal. The team after studying the glacier for more than three years concluded that, in 10 years, these numerous lakes would extend and grow into one huge lake in the region.

Given that the Thorthormi (Thortomi)'s southern flank, also called its left lateral moraine dam, was eroded by the 1994 flood and thus weakened, the pressure from the growing water body could cause the lake to give way. If that happened, the team's findings stated, the Raphstreng Tsho, another large glacial lake situated downstream, could be pressured to burst as well because of the weak moraine ridge separating the two lakes.

The team pointed out that, if the two lakes erupted they would unleash about 53 million cubic meters of water and carry a large volume of debris. That is about three times the ferocity of the 1994 Punakha flood.

Thorthormi (Thortomi) and Raphstreng are both sources of the Pho Chhu.

In 2003, the team urgently submitted their findings to the government and recommended three projects in the region to mollify the threat. The first and an immediate one was to manually lower the water level of the Thorthormi (Thortomi) Lake by draining out the water from an outlet. The second was to install a "glacial lake outburst flood" technical early warning system which could warn settlements downstream like Punakha within ten minutes of the impending outburst. The third was to map and identify places which could be affected in case of an outburst.

The projects are yet to take off.

Officials of the geology and mines department said that the cost was very high and the government did not have the funds.

Manually lowering the lake alone is estimated to cost Nu. 121.6 million (almost US$ 3 million) in addition to about Nu. 17 million (US$ 400,000) to install a warning system.

"We are trying to seek external funding," said Dorji Wangda. His department was also monitoring the glacial lakes every year, he added.

Officials in the department of local governance, under the Ministry of Home and Cultural Affairs, which is at present working on the "disaster preparedness" policy, maintained that they have not received the proposals to mitigate the glacial threats.

Meanwhile the Thorthormi (Thortomi) Lake is filling up because rising temperatures are melting the glaciers and surrounding snowfields that feed it, said glaciologist, Karma, of the geology and mines department. "Every year we see the same thing: Thorthormi (Thortomi) lake is growing bigger and bigger," he said.

Source: Kencho Wangdi, Kuensel 2005
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