Study of Flash Flood in the Rishiganga and Dhauliganga Catchment in Chamoli District of Uttarakhand, India

The present study is an attempt to investigate a flash flood that occurred on the morning of 7 th February 2021 in the Rishiganga and Dhauliganga Catchments in Chamoli District of Uttarakhand. A catastrophic flood was triggered due to a massive rock-cum-snow avalanche caused by Antecedent Snow falls in the region. A huge flash flood was generated as a tremendous quantity of rockslide, comprising deposited ice and snowmelt, rolled down the Ronthi Glacier and flowed downstream into the glacier valley. This massive flash flood hit the NTPC's Tapovan-Vishnugad hydel project and the Rishiganga Hydel Project, bridges, roads, and communities in and around Raini, Tapovan and Joshimath regions in the Chamoli district of Uttarakhand. The mud and slush-inducing elements resulted in the development of a dammed lake, which momentarily blocked one of the Rishiganga's tributaries. Temporal satellite image has been used to access the information of disaster damage assessment in the region. The high-resolution satellite image clearly showing flash flood watermarks in the region and on the avalanches site rock outcrops reaching up to 50–130m height on the way to Raini Gaon. As part of our analysis, we have also looked at the valley's slope profile, which clearly shows the valley's height following the destruction. It is estimated that more than Rs 4,000 crore infrastructures loss due to this flash flood in the region. Besides, two bridges have also been lost. Hydometeriological analysis was also carried out in order to obtain the trend of rapid increase in temperature in the valley where disaster occurred. Using remote sensing (RS) and Geographic Information System (GIS) techniques, thematic layers were generated for obtaining information on the flash flood.