The National Centre for Hydrology and Meteorology (NCHM) officials confirmed that the small flood reported from Cherichhu in Thimphu on the night of August 13 was a flash flood and not glacial lake outburst flood.
NCHM’s In-Charge for Flood Monitoring and Command Room (FMCR), Sangay Tenzin, explained that the flood did not start from the water source but because of landslide and continuous heavy rainfall.
The flash flood that started around 8:45pm panicked people living downstream of Thimchhu after few people shared about the flood on social media.
Sangay Tenzin explained that the Cheri flash flood occurred after heavy logs and debris clogged the river, which narrowed the water channel.
He said that the water flux had risen to about 30-40 cm, causing the flash flood. “It, however, did not cause any impact.”
NCHM had issued a flood advisory on August 12.
Sangay Tenzin said that flash floods are unpredictable. “When precipitation is high and goes above normal then there are high chances of flash floods.”
The Chief of Hydrology and Water Resource Services Division, Karma Dupchu, said that such floods are normal during monsoon season. “This kind of flash floods occur in almost all river basins.”
He said that the Cheri base is not inhabited and because of narrow valley when there is heavy precipitation, landslides and flash floods occur almost every time.
Meanwhile, NCHM is planning to set up comprehensive early warning system near Wangchhu basin.
Sangay Tenzin said that early warning system has become the need of the hour. “Vulnerability is increasing with more settlements.”
NCHM has put forward a project proposal to Japan International Cooperation Agency for establishing an early warning system in Wangchhu.
There are four major early warning systems in four major river basins in Bhutan today, Phochhu and Mochhu basin of Punatsangchu, Chamkharchhu and Mangdechhu.