A scientific team that had gone to assess a monsoon disaster that damaged Nepal’s most expensive infrastructure project northeast of Kathmandu itself had a narrow escape in a snowstorm this week.
The nearly completed $700 million Melamchi Water Supply Project designed to bring water from a glacier in Langtang National Park to Kathmandu through a 26.5km tunnel was badly damaged in a freak flash-flood in July.
The Asian Development Bank (ADB) that is the main funder of the scheme sent a research group to the headwaters of the Melamchi River to investigate the cause of the floods and assess future risk.
However, the 16-member team composed of geologists, glaciologists, support staff and porters which had helicoptered to the Bhemthang region of the valley two weeks ago to investigate the monsoon flood was itself trapped for 27 hours by a winter blizzard.
“It snowed continuously all day on Tuesday and till midnight, and there was more than 1m of snow,” said Sonam Lama, a mountaineering guide with 16 years of experience who knows the region well.
Heavy snowfall and small avalanches from above buried the team’s tents and equipment, and members were forced to spend the night under a rock overhang. The next morning the visibility was too poor for a rescue flight, and the helicopter finally arrived on the afternoon of 30 December.
The team had just finished carrying out a topographical scan and a geophysical survey of the depth of the fluvial deposits at Bhemthang from the July floods. The data will be processed to see if there is danger of more floods from the debris field, or the glaciers further up the Pemdang and Melamchi rivers.
“We scanned the sediment deposits up to a depth of 100m to see if there is a risk of it being washed down in future,” said Hari Ghimire, leader of the research team. “We measured the depth and volume of debris, but the data will take some time to be processed.”
Six international project staff lost their lives in the debris flow on 15 July, and 20 people downstream are still missing. The flood destroyed the headwork channel, sedimentation pond and other structures, causing Rs2 billion worth of damage.
However, engineers managed to close the main gate to the tunnel just before the flood waters rose, saving the scheme from much more serious destruction.
Results of the current investigation will determine what new structures need to be designed to protect the headworks from future floods. A study of the glaciers upstream will also be undertaken to see if there is any vulnerability.
Scientists say the July floods could have been caused by a combination of destabilised slopes after the 2015 earthquake, being exposed to record rainfall of 200mm in 24 hours on 15 July, and climate change.
The rain fell on fragile moraines and slopes which used to get snow earlier. Global warming has also melted the glaciers upstream creating numerous supraglacial ponds.
“This geophysical survey of the Melamchi watershed and other studies of the condition of the glaciers will provide us the information necessary to assess the nature of the catchment area so we can plan future action,” said Tajendra Pant, an engineer with the Melamchi project.
Melamchi Water Supply Project was damaged after its soft opening last year, even before it came into full operation to supply Kathmandu Valley with 170 million litres of water a day.
A proposed extension of the project to bring water from Yangri and Larke Khola with another 12km tunnel will increase the supply to 510 million litres a day. The tunnel is the second longest water supply tunnel in Asia.
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