A recent flash flood in Dharali, Uttarakhand, has dramatically altered the course of the Bhagirathi River, with the river returning to its old path. Triggered by the erosion of a debris fan on Kheer Gad, a tributary of the Bhagirathi, the high-magnitude flood reshaped the river's morphology, widening stream channels and pushing the Bhagirathi towards its right bank.
Satellite images from the Indian Space Research Organisation (ISRO) reveal the extent of the damage. Comparing data from June 2024 and August 7, 2025, the images show a vast, fan-shaped debris deposit, roughly 20 hectares in size, at the confluence of Kheer Gad and the Bhagirathi, just above Dharali. These images show extensively altered river channels, submerged or buried buildings, and major topographical shifts. Analysis of satellite data indicates that approximately 148 buildings were damaged, and about 16 hectares were affected. The imaging also highlighted damage to critical infrastructure, including one bridge and nearly 0.95 km of roadway, leading to significant disruptions in connectivity and emergency response.
The flash flood eroded an entire fan deposit, and Kheer Gad reclaimed its previous course. The debris has pushed the Bhagirathi's flow towards the right bank. Hydrologists warn that such sudden geomorphic changes could have cascading effects far downstream. Altered river channels can increase flow velocity, change sediment transport, and destabilize banks kilometers away from the flood site. Over time, this can create new erosion hotspots, threaten bridges, and change floodplains, forcing riverside communities to adapt to a new hydrological pattern.
The disaster has raised concerns about the growing vulnerability of Himalayan settlements. Rapid tourism growth and the pilgrim influx over the last decade, along with commercial activity near the road, had prompted settlement on the alluvial fan. Encroachments and constructions within the riverbed altered the flow dynamics, and when the powerful mudflow struck the built-up areas, it collided with buildings with immense thrust and force, causing catastrophic loss of life and property. Unplanned expansion into ecologically sensitive and disaster-prone zones has increased the risk exposure of local communities.
Experts are cautioning that the scale of destruction seen in Dharali was amplified due to human intervention in the river's natural course. The width needed for the mudflow to pass was missing due to construction in and around it, which worsened the disaster. This raises critical questions about why constructions in such vulnerable riverbed zones were allowed, highlighting the consequences of unchecked urbanisation driven largely by tourism development in the region.
So far, 566 people have been rescued since Tuesday, when torrents of mud swallowed homes, hotels and cars. Sixteen people, including nine Army personnel and seven civilians, were listed missing. Dharali is the main stopover on the way to Gangotri, from where the Ganga originates, abounding in hotels, homestays, restaurants and guest houses.
The event underscores the need for sustainable development practices in the Himalayas, balancing tourism and infrastructure with environmental protection. It also highlights the importance of disaster preparedness and early warning systems to mitigate the impact of such events in the future.
