Thousands at Risk of Himalayan Glacier Floods - Study
[WTN-L World Tibet Network News. Published by The Canada Tibet Committee. Issue ID: 02/04/15; April 15, 2002.]
Tue Apr 16, 1:04 PM ET
LONDON (Reuters) - More than 40 Himalayan lakes could burst their banks in five years' time, sending millions of gallons of floodwater down into the valleys and killing thousands, scientists said on Tuesday.
The lakes, formed by water from melting glaciers, are filling up faster and faster as glaciers succumb to global warming (news - web sites). Average temperatures in the Himalayas have risen by one degree Celsius since the 1970s.
Researchers at the United Nations (news - web sites) Environment Programme (UNEP) have identified at least 44 potentially dangerous glacial lakes in the tiny Himalayan kingdoms of Nepal and Bhutan.
"We have evidence that any one of these could, unless urgent action is taken, burst its banks in five to 10 years' time, with potentially catastrophic results for people and property hundreds of kilometres downstream," UNEP's regional glacier specialist Surendra Shrestha told a press conference.
UNEP's conclusions were based on a two-year study of old and new maps, aerial and satellite photographs and the evidence of old sherpas who saw what were tiny ponds in their childhood becoming large lakes two generations later.
One glacial lake, the Tsho Rolpa Lake in Nepal, has swollen from a surface area of 0.23 sq km in the late 1950s to 1.4 sq km now, solely thanks to a nearby glacier melting.
The researchers also found that catastrophic floods, once seen as a "500 year occurrence", had become a frequent phenomenon in the 20th century.
The worst in recent memory came in 1954 when the Sangwang Cho glacial lake at the head of Tibet's Nyangqu River burst its banks, sending 300 million litres (66 million gallons) of water into the valley below at 10,000 cubic metres a second.
The flood buried the upper valley in up to five metres (16 ft) of debris and damaged the cities of Gyangze and Xigaze 120 and 200 kilometres away, respectively.
With the lakes typically found between 4,000 and 5,000 metres above sea level -- at the upper altitude limit of most helicopters -- and in remote, rugged terrain, draining them is a complex and costly task.
A giant siphon made up of hundreds of pipe sections had been tried, but although it was successful at draining the lakes, it required carrying the pipes as many as seven days' walk from the nearest village, making it impractical, said Pradeep Mool, who is spearheading drainage work and flood warning system projects.
The favoured approach now was to dig slip-away channels through the glacial moraine, the mud and rock debris which forms the often unstable walls of the lakes, he said.
Work to lower the water level by 30 metres on Nepal's Tsho Rolpa Lake high above the Rolwaling and Tama Koshi valleys, had already started, although a lack of funds meant progress on other critical drainage projects was slow, Mool said.
UNEP's survey of Nepal and Bhutan accounts for less than 10 percent of the whole central Asian massif, which also runs through Afghanistan (news - web sites), Pakistan, India and China. Risk studies in these other countries are planned, the researchers said.
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