ENGINEERS IN Nepal are racing against extreme Himalayan weather conditions in an attempt to avert the catastrophic collapse of a 150m tall glacial dam.
The natural structure, formed by a terminal moraine in the Rolwaling Valley 110km north-east of Kathmandu, is holding back a 110Mm3 lake of glacial meltwater known locally as Tsho Rolpa (NCE 19 June 1997). Geo-technical experts believe it could fail at any time, endangering 7,000 lives and threatening the Khimti hydroelectric plant 80km further down the valley.
Sixty site staff, equipped with only handtools and one back-hoe excavator, are attempting to lower the level of the water by 3m before the onset of winter. But the work has already been delayed a month by bad weather and logistical problems caused by the Nepalese general election.
Technical adviser to the Nepalese government Dr John Reynolds, of Reynolds GeoSciences, said it would be a battle to complete the work by November when the weather would be too extreme to continue.
He said: 'The site is at an altitude of 4,500m so we are facing all the normal hazards of the Himalayas. Our main concern is the stability of the dam as there is only 1.5m of freeboard. It could collapse at any moment either by overtopping caused by an avalanche into the lake, or by failure of the moraine's ice core.'
Work to lower the water level involves excavating a 5m deep notch in the top of the moraine and constructing a 100m long concrete lined spillway with three specially designed sluice gates. The £1.8M scheme, funded by the Dutch government and designed by BPC Hydroconsult, is seen as only a temporary measure. The water level will have to be reduced by a further 15m in the next few years to make the moraine safe, said Reynolds.
Global warming is putting pressure on dozens of glacial lakes in Nepal, Bhutan, Northern India, China and South America. In 1994 a moraine failure in Bhutan caused flooding up to 200km downstream and killed 27 people.