Glaciers: A multi-disciplinary team comprising officials from various government agencies will visit Lunana to reassess the glacier lakes.
The agencies concerned are the department of geology and mines, disaster management, department of watershed management, land commission and HydroMet Services.
Director of HydroMet services department Karma Tshering said the reassessment will focus on glaciological and geo-hydrological surveys of Lunana lake complex that will support lake breach and downstream hazard assessment.
“It would also be combined with vulnerability and risk assessment surveys,” he said. A detailed study on geomorphology, vulnerability and reassessment would be conduced to find out what could be done should there be a glacier outburst.
The reassessment is expected to take about 20 days to a month depending on the extent of work in colleting the required data and information for development of land use and disaster management plan for the Punakha-Wangdue valley.
Karma Tshering said that through the reassessment, it is expected that they would be able to sensitise changes in policy and practices. A case study would then be presented to the government for immediate relocation of Lunana settlement to a safer site nearby like the kame terraces above the present floodplain of upper Lunana.
Officials said that unlike Laya, lakes in Lunana possess more threat and could cause catastrophic threats downstream. Lunaps, particularly people of Thanza would be hit hard in case of a glacier lake outburst.
Officials said when the outburst of Lemthang lake with just about 0.37 million m3 water could shake people downstream, outbursts from Lunana could wash away everything from Punakha and Wangdue till Kalikhola, Dagana.
Karma Tshering said that the lakes in Lunana hold about 40-50 million m3 of water. “The glacio-fluvial situation is far more threatening compounded by huge extent of vulnerabilities and therein the risk associated,” he said.
He added that the Glacial Lake Outburst Flood (GLOF) magnitude expected is of exponential order, and the probability is comparatively higher. “The potential travel distance or probable run-out distance is much longer, that will impact lives, livelihood and infrastructure even beyond the Bhutan border,” he said, adding that the 1994 GLOF was from partial emptying of Lugge (18-20 million m3 only).
Officials said Punakha-Wangdue basin host habitation from the headwaters to right across the international border. Flood vulnerability has increased and so has the associated risks as human activities extended in areas that were not inhabited earlier.
Punakha-Wangdue basin makes more than 25 percent of the country’s land area and is home to more than 14 percent of its population. The two biggest Punatshangchu hydropower projects are also located downstream.
HydroMet officials said that in a worse case GLOF scenario (cascade breach of Luggee, Thorthormi and Raphstreng), no hydropower would survive it. Hence, the need to focus on other measures than early warning system.
According to International Centre for Integrated Mountain Development (ICIMOD) and DGM inventory of 2001, there were 677 glaciers and 2,674 glacial lakes, out of which 24 were considered potentially dangerous. There have been 12 GLOFs since 1966.
Experts from ICIMOD said that climate change has shrunk glaciers that feed most of the Bhutanese rivers since 1980. To monitor changes in the glaciers in Bhutan, a repeat decadal glacier inventory was carried out from land sat images of 1977, 1978, 1980, 1990, 2000 and 2010. The 2010 inventory shows 885 glaciers with a total area of 64216.1 km2. The glacier area is 1.6 percent of the total land cover in Bhutan.
Database report by ICIMOD stated that Bhutan’s glacial lakes increased by 8.7 percent while the actual size of the glaciers shrunk by 22 percent between 1980 and 2010. Within the same period, the glaciers receded from 860 sqkm to 671 sqkm in 2010 in Bhutan. These findings from remote sensing were corroborated by field investigation.
Bhutan makes up one percent of the Hindukush Himalayan range, contributing 1.1 percent of its glaciers. Glaciers occupy 1.7 percent or 671 sq km of the country.
Dawa Gyelmo, Wangdue