Looking out over Rolwaling Valley from the lip of Tsho Rolpa

Chronology of Tsho Rolpa GLOF Hazard Response

The Dutch Connection

Fears about the danger from Tsho Rolpa increased in July 1991, when the moraine dam restraining nearby Chubung lake collapsed. Six houses in Beding village were impacted in the ensuing flood. After the Chubung disaster, the Sherpas of Rolwaling asked for help.

In October 1991, Summit Trekking Nepal (a Dutch outfitter operating in Rolwaling) and the Netherlands-Nepal Friendship Association became involved. At Summit's request, Professor R. De Meyer of the University Of Gröningen (Neth.) and a group of experienced trekkers surveyed the lake. Their report was received with alarm.

Subsequently, geomorphologist Michiel Damen of the International Institute for Aerospace Survey and Earth Sciences ITC in Enschede, Netherlands, together with a Nepalese student at ITC, Pradeep K. Mool, undertook a study of Tsho Rolpa. In May and June, 1992, Damen came to Kathmandu to discuss the problem with Sherpas from Beding and Na and with official agencies. In June, he and the Sherpas took measurements of water level, discharge, and slope and moraine stability in order to assess the GLOF hazard. A preliminary map of Rolwaling valley and its glacier system was made using the ILWIS Geographical Information System.

Damen and Mool concluded that the moraine dam was extremely unstable. Water was seeping through the moraine in several places. At the western lip of the lake, the water was scarcely two meters below the rim of the retaining wall, and in one place a stream was already flowing over the edge. Large rocks falling into the lake posed a threat quite similar to the situation at Dig Tsho: such an avalanche would cause a shock wave six meters high, certainly capable of breaching the wall. International experts agreed that the safest and only possible solution was to lower the water level without altering the moraine dam. (These experts included J. Hanisch, of the German Geological Advisory Group in Kathmandu; J.M. Reynolds, his counterpart in Peru; and, Professor H. Th. Verstappen, president of the International Geographical Union.)

In 1993, Pradeep Mool and the Japanese glaciologist Tsutomu Kadota from the Japanese International Cooperation Agency (JICA)undertook another survey to evaluate the condition of the moraine. They took stereoscopic photographs, measured the lake's depth, and installed the equipment to gather meteorological, glaciological, and hydrological data. Mool and Kadota reported that the lake is considerably larger than indicated on current maps, and quite a bit deeper than had been estimated: 132 meters. In terms of volume, approximately 70 million m³, Tsho Rolpa had to be considered the largest glacier lake in the Himalayas. As a result, it was accorded top priority for research, and that same year a second JICA expedition visited Tsho Rolpa together with the Nepalese Water & Energy Commission Secretariat (WECS). From May to October 1995, two geology students of the Free University of Amsterdam conducted further research on the moraine walls and the slopes around the lake; their period of research was selected in order to allow observations before, during, and after the monsoon.

In early 1994, the Sherpas of Rolwaling presented a petition, signed with their fingerprints, to authorities and organizations in the Netherlands through the Netherlands-Nepal Friendship Association. They requested help in preventing a flooding disaster in their area.

In order to assure continuing research, DGIS [=?] in The Hague granted 6 scholarships for Nepalese experts in the field of mountain hazards. A seven-month course was announced for the ITC in Enschede, beginning in September 1995, followed by a three-month course in spring, 1996, in cooperation with the Geographical Faculty of the Tribhuvan University in Kathmandu. Mapping GLOF risk areas with remote sensing and GIS technology was to be one of the major elements of the courses. An expedition to Lake Tsho Rolpa was part of the field course. [We do not know whether this course was actually carried out.]

The Siphon Experiment

Due to the absence of electricity and the impracticality of heavy diesel machinery, there was no question of simply pumping the water out of the lake. An action committee was formed to find a way to prevent a GLOF event at Tsho Rolpa. Participants included the Netherlands-Nepal Friendship Association; Summit Nepal Trekking; ITC; and Wavin Overseas, located in Zwolle (Netherlands), the leading manufacturer of plastic pipe systems in Europe. J. A. van Ness of Wavin and Damen, designed a siphon installation for Tsho Rolpa. Wavin, then celebrating its fortieth anniversary, donated the pipes, couplings, and other material, and shipped them to Nepal at their own cost.

Siphoning in such a situation presents many difficulties.

Due to the enormous quantity of water to be moved, one needs very large-bore tubes and/or many separate siphons. These would have to be quite long, also, in order to contrive a pressure differential capable of powering the siphons. But delivery of such material to a high and remote destination is expensive and logistically difficult; beyond certain dimensions, delivery would of course be impossible.
Such materials are useful to local people in other construction projects. We have seen piping used in bridges, irrigation and water supply, and fencing. Pilfering is therefore a problem.
The material had to be able to resist extreme cold, extreme fluctuations of temperature, intense ultra-violet radiation, and physical battering.
Because the tubes would be too long to transport intact, coupling devices would be needed, and these would have to be particularly resistant.
Ways would have to be found to avoid blockage of the intake.
Cavitation (air pockets that disrupt the vacuum necessary for siphoning) would be a problem with large-bore piping.
Waves from avalanches could damage or destroy the siphons.
As water level dropped, the siphons would have to be repositioned, and adjustments to the moraine wall would have to be made -- by hand.
Maintenance would require effective participation of local people.

The first Wavin siphon installation, supervised by project manager Mr. J. N. van Rijswijk and technical coordinator Mr. J. A. van Nes on behalf of Wavin, was under considerable pressure due to the importance of completing the operation before the onset of the monsoon. According to negotiations led by Honorary Consul De Stoppelaar of the Netherlands, the Nepalese Ministry of Water Resources agreed to take end-responsibility for the project.

Our information as to the specifications of the siphon, derived primarily from Wavin press releases, is inconsistent. In an announcement before the installation, Wavin said they would manufacture 100 plastic pipes 5 meters long with a diameter of 160mm. These would be assembled to form a 500-meter long pipeline, with the eventual installation to be eight times that size (meaning, presumably, seven additional siphons). According to a release after the installation, the first siphon was only 300 meters long.

The test siphon was included 3 separate inlets (entailing a specially-designed fitting) to increase the speed. The siphon was assembled from 100 HDPE plastic pipes (plus couplings) lugged up to the site by Sherpas from the threatened villages. This plastic was light enough so that a length (3 meters? or 5 meters??) could be carried by a single porter, flexibile enough to accommodate the broken terrain, and rugged enough to withstand the extreme pressure, temperature, and unusually high UV radiation. Assembly was simplified so as to be feasible without skilled labor or special tools.

The three inlet pipes were submerged 15 meters below the surface in the deeper part of the lake. Water was carried up over the moraine dam, 1.5 meters above the surface of the lake, and then released at a stable site along the river 200 meters.

Tests of the trial installation confirmed that water was being evacuated at 170 liters/second. However, it was estimated that an outflow at least 30 times greater would be required to lower the lake level by 3 meters per year.

The siphon worked for 14 months without any maintenance. By May 1996, the pipe was dislocated at 3 points, and by September '96 it had ceased functioning. Two months later, the siphon started working again. In August 1997, another joint separated. It continued to function under less than optimal conditions.

In June, 1997, HMG installed five locally-manufactured siphons. On September 4, a large wave from a calving glacier severely damaged one of them.

The following July 1999 communication from Jaap van Rijswijk of Wavin Overseas describes the project:

In principle, as far as the siphoning is concerned it is quite simple and logical and therefor we planned to do the job with the help of the local people.

The trick is good quality material, fit for the purpose and time management to install and adjust the siphons at the right time.

Due to the reported instability of the end-morene (the dam), we decided to avoid the danger of a GLOF caused by ourselves if we should try to move material on the waterline and by doing that, get an uncontrolled spillway.

SO, FIRST SIPHONING OVER AN INTACT RIM, let the water level drop about 4 meters during autumn and winter, and AFTER THAT MAKE A NEW SPILLWAY AT THE LOWER WATERLEVEL in early spring before the melt.

Repeat that procedure for about 4-5 years and the danger has gone.

To prove that siphoning on that altitude and also during winter was feasible, we installed a trial early june 1995 which is still functioning as far as I have been informed. Only the outlet what was originally about 250 m long down the outer slope to improve suction-power and avoid erosion high on the slope, is now much shorter.

Some couplers slipped loose due to too much temperature tolerance in the fixing rod and chamber. In summer outside temp. 40C and inside water temp 4C.

We adapted the design for the final coupler, but in the mean time the government officials decided that they did not need us any more I got word a few weeks ago that at last the final signatures were placed now. They almost doubled the budget and are prepared to start digging in the moraine directly without siphoning.

The early warning system was a political decision to calm the local people. Some military or police man are spread along the river with walky-talkies and/or a satellite telephone to report a GLOF and hope for the best to tell the people to run from the river uphill to save their lives.

Upon local Nepalese pressure, together with the early warning system, some five additional syphons were installed from domestic material. At least three of them could not stand a tidal wave when a big piece of the melting glacier dropped in the water and were damaged against the rocky rim of the lake.

We hope for the best of the Rolwaling people that all goes well and cross our fingers.

We had hoped that this combined siphoning project could set an example how to act in similar circumstances at high altitude and were prepared to document our findings and procedings internationally, but now our help is denied any further, it is of no use any more, and for my company a waste of time.

[ Next ]