Seti flash flood not from glacial lake outburst, suggest experts

The government has said that rainfall, along with a land mass slip in Machhapuchhre VDC, Kaski district, triggered an unexpected flooding in the Seti river on Saturday morning.
“The flash flood took place at around 9:55am. The latest information is that the volume of water in the river is receding,” said Shankar Prasad Koirala, spokesperson for the Home Ministry. “The government wants toinform concerned locals that the situation is improving now.”
Experts say the region is vulnerable to glacial hazards such as an avalanche, glacial lake outburst floods (GLOF), and debris flow, affecting millions of people downstream.
The Annapurna range, where the Seti originates, is extremely prone to avalanches particularly from March to mid-June, said Om Ratna Bajracharya, joint-secretary at the Department of Hydrology and Meteorology. “Due to the geographical condition and the gorge type structure, the region is highly vulnerable to avalanches,” he said.
An avalanche—the mass of snow, ice and rock that falls down the side ofa mountain—is common high up in the Himalayan region. “Cases of avalanches remaining for about
two weeks or even an entire season blocking the river flow have been reported,” said Mandira Shrestha, water specialist at the International Centre for Integrated Mountain Development.
Arun Bhakta Shrestha, climate change specialist at ICIMOD, said that in the event of a blockade of water upstream by an avalanche, the volume of water decreases significantly downstream.
When the avalanche can no longer hold water, a flood of boulders, debrisand mud, among others, causes flash floods downstream, he said. The volume of water in the Seti had decreased before the river was swollen all of a sudden on Saturday.
According to Arun Shrestha, preliminary reports and the nature of flooding negate the chances of the incident being a glacial outburst. No study suggests the existence of big glacial lakes in the region that could cause this level of flooding.
A 2010 ICIMOD study on glacial outburst risk assessment reports six glacial lakes in the Seti basin. Out of the 338 glacial lakes identified in and around the Gandaki River Basin, which includes the Seti, four are listed as potentially dangerous.
Experts have stressed that a field study is necessary for finding out more about the incident. “We neesd to enhance awareness on similar disasters among the communities and improve their capacity to react to such disasters particularly in vulnerable mountain communities,” Shrestha said. Access to locally available equipment to deal with disasters, establishment of shelters and empowerment of local disaster management committees or agencies are among things necessary to deal with disasters.
“This is a lesson. We need to work together for effective preparedness and relief
packages in the aftermath of a disaster,” said Shrestha.
Scientific evidences show a GLOF occurred on the Seti Khola about 450 years ago when a glacial lake located behind Mt Machapuchhre burst outin a seismic activity.