The Department of Hydrology and Meteorology (DHM) has launched an investigation to identify the cause of the massive flash flood that struck the Bhotekoshi River, a tributary of the Trishuli River, in Rasuwa district in the wee hours of Tuesday.
Binod Parajuli, Chief of the Department’s Flood Forecasting Division, said that satellite image analysis has been initiated to determine the potential cause of the flood and assess its impact along the riverbanks.
He noted that several glacial lakes exist in the Bhotekoshi River’s upper catchment area in Tibet, China. However, based on preliminary assessments and data from meteorological centers, heavy rainfall is not believed to be the cause of the flood.
“The Kyanzing meteorological station near the Nepal-China border and the Dhunche station recorded only sporadic rainfall,” said Parajuli. Weather radar data from Palpa also did not indicate significant precipitation in the Rasuwa border region. Similarly, satellite-based rainfall guidance from the World Meteorological Organization confirmed that the area did not receive heavy rainfall in the 24 hours preceding the flood.
A sudden surge of water entered the Bhotekoshi River, which is also known as Lhendekhola, from the Tibetan side at around 3:00 am, causing the water level at Timure in Rasuwa to rise by 3.5 meters.
According to Parajuli, riverbank areas in Rasuwa and Trishuli have been severely affected, while impacts in downstream areas from Nuwakot to Benighat in Dhading district are moderate to minor. Although the water level has been receding, he urged the public to remain cautious.
Meanwhile, the International Centre for Integrated Mountain Development (ICIMOD) has stated that it is too early to determine the exact cause of the flood. “We can confirm that extreme rainfall was not the cause,” ICIMOD said in a statement, adding that a comprehensive investigation is needed once the monsoon cloud cover clears to allow for high-resolution satellite imagery analysis.
ICIMOD emphasized the need for a multidisciplinary team—including geologists, glaciologists, hydro-meteorologists, and remote sensing analysts—to jointly investigate the event. While a Glacial Lake Outburst Flood (GLOF) or a Landslide Lake Outburst Flood (LLOF) is suspected, ICIMOD said there is no conclusive evidence yet.
According to its 2021 inventory, one glacial lake in the upstream Trishuli River basin in the Tibet Autonomous Region of China has been categorized as high risk and requires close monitoring. Due to persistent cloud cover, optical satellite analysis has been hindered, and experts must wait for clear, high-resolution imagery to verify whether the lake has breached or undergone a sudden volume change, ICIMOD said. -- RSS
