Sluice gate controling flow notch cut in moraine bank of Tsho Rolpa
Sluice gate controling spillway cut in moraine bank of lake.

Chronology of Tsho Rolpa GLOF Hazard Response








[  GLOF resources  ] [  Mountain Legacy  ] [ Rolwaling  ] 



A Gentler, Dryer Lake?





[Newsflash on Sunday, June 11, 2000; from Nepalnews.com, archived on Google 


Tsho Rolpa Dewatering Begins




Kathmandu, June 8  -- The Prime Minister could not make it by helicopter to the Rolwaling Valley Thursday morning for the official inauguration because of bad weather, but  the dewatering process on Tsho Rolpa Lake went ahead anyway.



Water is now gushing out of the glacial lake at a speed of up to 6000 litres per second, in a controlled draining of the lake designed to prevent a catastrophic outburst.



Tsho Rolpa is one of several glacial lakes in the Nepal Himalaya that are dangerously swollen due to global warming, raising fears of glaciallake outburst which could devastate downstream valleys. Glacial lake outburst floods (called GLOFs) regularly hit Himalayan valleys and have been known to cause great loss of life and property in historical times.


The lakes are dammed by the terminal moraine of Himalayan glaciers and as the ice recedes, water collects. The moraines are fragile dams, and give way easily due to pressure of water or because of earthquakes.


The dewatering process that began Thursday is expected to lower the level of Tsho Rolpa by 25 cm per day, taking 12 days for the water to come down by three metres. The next phase of the project will bring down the level of the water by 17 metres, after which the danger of an outburst is expected to be greatly reduced.


The lake is situated at an altitude of 4,600 metres in the scenic Rolwaling Valley under the shadow of Mt Gauri Shankar. Three years ago, panic spread across much of the valley of the Bhote Kosi and Sun Kosi rivers after rumours that Tsho Rolpa was about to burst, people rushed uphill and camped out.


Tsho Rolpa is seven times bigger than it was in 1959 and now covers 1.7 sq km and contains 80 million cubic metres of water.


The Tsho Rolpa drainage project was started last year and is supported by the Dutch government costing a total of Rs 190 million. Almost half of that money was spent just on flying up the equipment to the roadless Rolwaling Valley. 












Yes, the lake is perhaps three meters lower.  But is that enough?





The Tsho Rolpa Hazard Mitigation Project

Tsho Rolpa hazard mitigation project site, October 2000






Catwalk
Catwalk over the sluice gate.




Sluice gate

Engineers cut a notch in the moraine that holds back the lake;
 the notch was dammed and a sluice gate installed to allow controled release of water.





channel-1
Above and below: The outlet channel leading from the lake through the gate.

channel-2




channel-3








Water being released over moraine lip to join Rolwaling River below.




Water dropping from notch to join Rolwaling River below

Water dropping from notch to join Rolwaling River below; 

rocks have been stabilized with cables.

















This photograph, shot from the rim of Tsho Rolpa, is a reminder that the lake
 is both hundreds of meters deep and also perched hundreds of meters above the valley floor.
 If the moraine walls give way, the result would be catastrophic.







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