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Glaciers are retreating

On a clear blue morning of October 7, 1994, Dechen Tshering, a Class X student of Punakha High School, was standing at the confluence of the Pochhu and Mochhu rivers when he heard a rumbling sound.

He didn't give it a second thought assuming that convoys of trucks was passing by but when the water level of the Punatshang chhu touched the stones where he had positioned himself he literally flew to safety.

"All I could see was a river of logs, boxes, haystacks," he recalled. "In minutes the river ravaged everything on its way. It changed course, destroyed parts of the dzong, and flooded the school soccer field and ripe paddy fields with fish," he said.

The October flood had claimed more than a dozen lives, damaged acres of farmland, and government and private property worth millions of ngultrums.

The flood was caused by a glacial lake that had burst high up in Lunana nine days walk from Gasa dzong.

Mochhu Valley Gasa Dzong

Since then several attempts have been made to reduce the risks of another glacial lake outburst flood (GLOF), but geologists say the dangers are far from over with changes in climate.

Since the last inventory of glaciers and glacial lakes in Bhutan by the International Centre for Integrated Mountain Development (ICIMOD) in 2001, 106 new glaciers and 120 glacial lakes have formed in the mountains.

In the past 15 years, 16 new glaciers and 82 glacial lakes had formed in the headwaters of the Phochhu alone.

About 140 glaciers and four new glacial lakes had also formed in the headwaters of the Mochhu, according to Glaciologist, Karma Toeb, who presented the impact of climate change on glaciers and glacial lakes in Bhutan Himalayas.
If the present trend of climate change continues, there is a possibility of another GLOF," the glaciologist said. "It is difficult to say when, but the glaciers are melting at an alarming rate." According to geology experts, the number of lakes posing dangers had increased from 24 to 25.

Karma Toeb, who has visited Lunana eight times said that they have identified nine potentially dangerous lakes in the Phochhu sub basin, seven in Mangde chhu, five in Mochhu, three in Chamkhar, and one in Kuri chhu.


The more impending dangers could come from fast retreating glaciers

Karma Toeb said that the glacier retreat rate in Himalaya of Bhutan was more rapid than the retreat rate in Nepal. "Glaciers are retreating at a rate of 7.36 metres in a year," he said. "There is an average of 10.7 percent shrinkage in glacier area and 3.28 percent increase in the lake area," he said.

According to geology officials, the Thorthormi ( Thorthormi) lake, 4,500 metres above the sea level, has become critical and poses potential dangers. "The debris covered glacial lake is expanding because the glaciers are melting," Karma Toeb said.

The Thorthorm (Thorthormi) lake is located between the Luggye lakethat flooded in 1994 and the Raphstreng lake. "The moraine dam between Thorthormi and Raphstreng is not thick," the glaciologist said. "There is ice core in the moraine and the moraine will become weak with the ice melting."

The Thorthormi lakes left lateral moraine was eroded during the 1994 flood. "The Raphstreng lake where artificial canalising had been carried out would not be able to hold the water from the Thorthormi (Thorthormi) lake incase the lake leaks because of the melting moraine," said Karma Toeb.

According to geomorphologist Deo Raj Gurung, in a worst-case scenario, there could be a chain reaction if one of the lakes burst in Lunana. "The volume of water in the reservoir is about 18 million cubic metres, therefore it is only wise to secure the downstream now," he said.

Glacial lake
A hazard zonnation for GLOF along the Puna tsangchhu from Khuruthang in Punakha to Kalikhola is among various mitigation and risk management measures, the department of geology and mines (DGM) with the Netherlands Climate Assistance Programme (NCAP) had prepared.
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The project, which would begin soon, is one of the adaptation methods to climate change according to the director DGM, Dorji Wangda.

"A base map on the hazards related to GLOF along the Puna tsangchhu can be used as a tool by policy makers and planners in taking decisions, designing and planning developmental activities along the river," he said.

Presenting the project to stakeholders, Deo Raj Gurung said that many important installations and monuments lie along the Puna tsangchhu like the Punakha dzong, new Wangduephodrang township, Basochhu project, Puna tsangchhu project besides thousands of settlements.

Mochhu Valley Punakha Dzong: Confluence of Mo Chhu and Pho Chhu
Punakha Dzong Punatsangchhu Valley near Basochhu

The hazard zonnation map along the Puna tsangchhu would delineate areas along the river into different zones of different degrees of hazards from GLOF in future.

Meanwhile, the Global Environment Fund had agreed to fund US$ 3.5 million for hazard zonnation map in Chamkhar chhu in Bumthang, establishment of an early warning system along the Punakha-Wangdue valley, and artificial lowering of theThorthormi ( Thorthormi) lake.

Contributed by Ugyen Penjore, KUENSEL, Bhutan's National Newspaper, 2006
Punatsangchhu Valley near Wangdue Phodrang Wangdidzong
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