Sunday, 27 April 2008

Not too late nor early either

26 April, 2008 - Settlements and infrastructure along a 147-km stretch, from Punatsangchu to Lhamoizingkha (Kalikhola) in the southern foothills, will feel the impact of 53 million cubic metres of water thundering down the mountainside if the Thorthormi and Raphstreng glacial lakes in Lunana merge and burst its banks.

This is a worst-case scenario, but with signs of a merger already visible at the lakes, officials of the geology and mines have mapped out the hazard zones to work on mitigation measures.

The hazard zones are marked red, yellow and blue, with red for high risk to lives of people, whether within or outside their homes, and destruction to structures; yellow indicating danger to people outside their homes and damage or possible destruction to structures; and blue, low or no danger to people and structures.

Geology and mines officials have identified 117 buildings, 362 people, 58 livestock, 16 historical monuments, a bridge and 5.22 km of road under the red zone (see box).

One mitigation measure, which will begin this year, is to dig a channel at the outlet to reduce water volume in the lake by five metres each time it rises because of glacial melt.

Geologist Karma Toeb said that they only had four working months for four years, between June and September. For the rest of the year, the passes were closed by snow.

The main work of reducing the impact of GLOF downstream, installing early warning systems (EWS), is yet to begin.

Although a manual system, using wireless communication, already exists, geologists suggest that an automatic EWS was a must since the appetite for destruction of the expected GLOF was unfathomable. The project manager of DGM-UNDPGEF, Dowchu Dukpa, said that the manual system would be used along with the automatic.

He said that, during the 1994 flood in Punakha, which occurred in the early hours of a weekend, the manual EWS failed because people in Lunana, while trying to contact and inform those in Punakha of a GLOF gushing their way, found nobody to receive the information.

“Today we’ll install fully automatic systems, but we’ll also use the manual as a back-up,” said Dowchu Dukpa. According to him, they intend to plant early warning systems with three different types of sensors, one that picks up signals of GLOF from water pressure, another from water levels and a third through ground vibrations.

The sensors, which will be planted at different intervals upstream, will first pick up signals in case of a GLOF outbreak, send the signal to the data logger, which will then be transferred to a communication system and eventually hit the different towers all together, which will instantly sound the alarm.

A sensor each will be planted, one 13 km upstream of Samdingkha, a second at Khuruthang, which is about 11 km from Samdingkha, and the third at Wangdue-Bajothang about 19 km from Samdingkha. Each of these places will have two alarm towers erected.

Based on calculations derived from the 1994 flood, geology and mines officials calculate that should a GLOF occur, it would first hit Samdingkha, which will leave about 54 minutes for people downstream to run to safety, followed by Khuruthang, where people will have about an hour and 40 minutes, and Wangdue-Bajothang will have about 2 hours and 14 minutes.

“Between Lunana and Punakha, there is about 100 km, which the floods in 1994 took about seven hours to reach Punakha from Lunana,” said Dowchu Dukpa.

But Karma Toeb added that, if a GLOF should occur, it would reach Punakha in a much shorter time because the 1994 flood had cleared all natural barriers that existed.

Pacifying people’s concern over the damage the GLOF could do to the upcoming Punatsangchu project, the secretary of economics affairs ministry, Dasho Sonam Tshering, said that the dams of the plant were designed to handle 11,500 cubic metres of water a second.

“The speed of the 1994 flood was recorded at 2,000 cubic metres a second,” said Dasho Sonam Tshering. “If Lunana lets out about 53 million cubic metres of water, it can pass through Punatsangchu gate within an hour and a half.”

He said that the dams had several gates, which opened in the event of a flood to allow the floodwater to pass through without damaging the plant.

“But, to do that, we need proper early warning systems in place,” Dasho Sonam Tshering said. “It’ll take almost two hours to open the dam gates totally because of the pressure.”

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