NEW DELHI: A flash flood in Chamoli district of Uttarakhand that ravaged through the valleys of the Rishi Ganga, Dhauliganga and Alaknanda rivers last month was triggered by a massive rockslide just below Ronti peak and the energy of the fall melted the ice creating the source of flood, said scientific findings of an intergovernmental body, International Centre for Integrated Mountain Development (ICIMOD).
The findings, released on Friday, said the energy of the fall of about 22 million cubic metres of rock mixed with ice and snow “remobilised the debris and ice on the valley floor deposited by previous events, pushed the stream water and created an excessive flood wave”.
Referring to images from Maxar portal accessed through the USAID SERVIR programme, the ICIMOD researchers found that the rockslide had an approximate width of 550 metres at the upper edge at 5,500 metres above sea level.
Noting that the event was definitely not caused by a ‘glacial lake outburst flood’ (GLOF) as there were no significant glacial lakes in the area, the report said a couple of days prior to the February 7 event, a strong western disturbance resulted in heavy precipitation in the area, which increased the flood magnitude downstream.
The Kathmandu-based ICIMOD has eight member countries, including India, Nepal and China, on board which is considered as the most authoritative voice of scientists in the Hindu Kush Himalayan (HKH) region.
At least 70 people have been confirmed dead and another 134 persons reported missing in the disastrous incident that also swept away the unfinished Tapovan Vishnugad Hydropower Project and inflicted substantial damage on the Rishi Ganga Hydropower Project in the ecologically fragile region.
The findings of a team of seven ICIMOD researchers, led by climate change specialist Arun Bhakta Shrestha, observed that infrastructure in the flood path, particularly hydropower projects, exacerbated the impact of the flood.
About the link of the incident with climate change, the ICIMOD said, “While a hazard event like the flood at Chamoli cannot be directly attributed to climatic changes, the increased thaw-freeze cycle of permafrost could have partially contributed to the event.”
On the factors which could have triggered the rockslide, the report referred to a strong western disturbance that passed across Kashmir and northwest India from 4 to 6 February. “It was fully charged with convective instability that may have contributed to the heavy precipitation… Numerical simulation of some of the attributes have been carried out which depict strong evidence of heavy precipitation contributing to high flows downstream,” it said.
Recommending comprehensive monitoring of mountain environments, the report suggested that infrastructure development in fragile mountain environments should consider a sustainability framework, including environmental sustainability.
Noting that infrastructure such as roads and hydropower projects are rapidly penetrating mountain landscapes, the report said, “The interplay between natural hazards with human settlements and infrastructure is an important aspect, which can significantly escalate the impacts of events like the Chamoli flood.
“Disaster risk management therefore needs to incorporate a multi-hazard risk assessment approach. In the aftermath of recent disaster events, the role of infrastructure, especially hydropower and its interplay with natural hazards has emerged as a topic of strong debate.”