Baskota estimates that some 150 cubic metres of fluvial, glacial or lacustrine deposits still sit on the river upstream at an elevation of 3,500m, and this is constantly being washed down by the river because of continuing heavy rains. On 11 July, a weather station in nearby Sermathang recorded 110mm of rain in 24 hours.
Some scientists blame the extreme weather events on climate change, and say that heavy downpours are now falling on higher altitudes where there used to be snowfall. Other researchers believe that in addition to heavy rainfall, a glacial lake higher up could have burst, adding material to the debris flow.
“It looks like there has not been an adequate disaster risk assessment of the catchment area,” Baskota says. “This means we have to study the glaciers above Yangri and Larke before starting the next phase of the Melamchi water project.”
There is a way to reduce the danger from future flooding along the Melamchi by building check dams along the river to slow the flow of the debris. But engineers admit it is a huge and expensive undertaking which has to start as soon as the monsoon ends to be prepared for next year’s rains.
Climate scientist Raju Pandit Chhetri says that the impact of global warming in the Himalaya is only going to increase, so current and future infrastructure along the mountains have to take the risk into account.
“Bridges, highways, water supply all have to be designed to withstand extreme events,” says Chhetri. “It may drive up the cost of the project, but it will prevent greater loss. Planning for a disaster like this would not have affected the Melamchi project as badly as it did.”