Chamoli Disaster: Pronounced Changes in Water Quality and Flood Plains Using Sentinel Data

Abstract

The Himalayan rivers are vulnerable to devastating flooding caused by landslides and outbreak of glacial lakes. On 7 February 2021, a deadly disaster occurred near the Rishi Ganga Hydropower Plant in the Rishi Ganga River, killing more than 100 people. During the event, a large volume of debris and broken glacial fragments flooded the Rishi Ganga river and washed away the Rishi Ganga Hydropower plant ongoing project. This study presents the impact of the Chamoli disaster on the water quality of Rishi Ganga river in upstream near Tapovan and Ganga river in downstream near Haridwar through remote sensing data. We used five points at different locations across the two study areas and used three different indices, Normalized difference water index (NDWI), Normalized difference turbidity Index (NDTI), and Normalized difference chlorophyll index (NDCI), to analyze changes in water quality. We also compared the spectral signatures and backscattering coefficients derived from Sentinel-2 Optical and Sentinel-1 SAR data. It was evident from the water quality indices and spectral signatures that the flood plains changed significantly. Using spectral signatures and different indices, we also found that the water in the Cheema dam canal near Haridwar decreased after the Chamoli disaster event as the flood gates were closed to stop the deposit of sediments in the canal. Our results suggest changes in water quality parameters (turbidity, chlorophyll concentration, NDWI) at the five locations near the deadly site and far away at Haridwar along the Ganga river. Our study is a preliminary qualitative analysis showing changes in river flood plain and water quality after the Chamoli disaster.