Gorkha [Nepal], October 11 (ANI): The International Centre for Integrated Mountain Development (ICIMOD) has identified the failure of a temporary landslide-induced river blockage as the probable cause of flash floods in Nepal's Budhi Gandaki river corridor.

In a press release, the regional intergovernmental learning and knowledge sharing centre said the flash flood "may have been triggered by the failure of a temporary river blockage created by a landslide near Chumchet in Gorkha district, according to preliminary accounts from Nepal's authorities..."

In its preliminary assessment, ICIMOD estimated that the flooding began at around 4 am Nepal time on October 11, carrying mud, sediment and debris downstream through the Budhi Gandaki corridor.

Recounting the early-morning evacuation, Kamala Duwadi, a resident of Arughat in Gorkha district, told ANI that she and other residents moved to higher ground after receiving warnings about the approaching flood.

"In the morning, an alert was issued to us. I was inside my home and I came out hearing the sounds outside; the police were making public announcements for the evacuation. It was around 4:30 in the morning. I own a shop here and some of the workers who live upstream also called and warned about the incoming flood situation and explained that they also ran to higher ground for safety and asked us to move to safe ground. The fear of the Bhotekoshi Flood is still in mind; we quickly moved out from here to the higher ground up in the hills," Duwadi said.

Initial reports indicate that people are missing, houses have been washed away, bridges have been lost and riverside infrastructure has been damaged. Damage has also been reported at the 341 MW Budhi Gandaki hydropower site at Selleri, although the full extent of the losses remains under assessment.

The latest incident comes shortly after the Gyirong-Rasuwa disaster, highlighting the risks posed by cascading mountain hazards, in which one event can trigger another and amplify the impact on communities and infrastructure.

The latest flooding follows another major flood-generating event in the same valley in April 2024, when a massive ice avalanche from the snout of the Manaslu Glacier plunged into Birendra Tal, triggering a sudden overflow into the Budhi Gandaki River.

A detailed ICIMOD-led assessment found that the event was caused by displacement of lake water following the ice avalanche, rather than a glacial lake outburst flood (GLOF). 

"Together, the two events highlight the range of hazards capable of generating destructive floods in Himalayan river systems and the importance of monitoring multiple sources of risk," ICIMOD stated.

"Coming so soon after the Gyirong-Rasuwa disaster, this event is another reminder of how exposed mountain communities and river corridors remain to sudden, cascading hazards," said Pema Gyamtsho, Director General of ICIMOD. 

"While response efforts must remain the immediate priority, understanding what triggered this flood will be critical for reducing future risks and strengthening resilience."

The Budhi Gandaki flood also highlights the vulnerability of settlements, transport networks, energy infrastructure and essential services located along mountain river corridors. 

As response efforts continue, understanding the interaction between slope instability, river dynamics and downstream exposure will be crucial for risk reduction, infrastructure planning and recovery efforts across the Himalayan region.

"Current analysis points to the possible failure of a temporary landslide blockage that released a heavily sediment-laden flood downstream," said Qianggong Zhang, Strategic Lead on Climate and Environmental Risks for ICIMOD. 

"Events like this demonstrate why monitoring and evaluating unstable slopes and river systems together is essential in steep mountain catchments, where hazards can develop rapidly and affect communities far downstream."

ICIMOD notes that future risk assessments, infrastructure planning and recovery efforts should account for multiple hazards, their triggering mechanisms and their cascading downstream impacts, particularly in river corridors where settlements, transport networks, energy infrastructure and essential services remain highly exposed to sudden-onset hazards. (ANI)