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. Five points have been used at different locations across the two study areas and three different indices were used such as Normalized difference water index (NDWI), Normalized difference turbidity Index (NDTI), and Normalized difference chlorophyll index (NDCI), to analyze changes in water quality. Spectral signatures and backscattering coefficients derived from Sentinel-2 Optical and Sentinel-1 Synthetic-aperture radar (SAR) data were also compared to study the changes in water quality. It was evident from the water quality indices and spectral signatures that the flood plains changed significantly. Using spectral signatures and different indices, the water level in the Chilla dam canal near Haridwar was found to decreased after the Chamoli disaster event as the flood gates were closed to stop the deposit of sediments in the canal. 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. This study is a preliminary qualitative analysis showing changes in river flood plain and water quality after the Chamoli disaster.
Highlights
In the northern parts of India, the Himalayan rivers are glacier-fed and pass through the Indo-Gangetic plains (IGP) and plunge into the Bay of Bengal
We present the abrupt changes in the water quality using Sentinel-2 multi-spectral and Synthetic-aperture radar (SAR) data along the confluence of the Dhauli Ganga and the Alaknanda rivers up to Haridwar in the northern part of India after the deadly Chamoli disaster of 7 February 2021
The quality of water has been analyzed using various indices derived from the Sentinel-2 optical data and Sentinel-1 SAR data to evaluate the changes in the water quality of the river after the Chamoli disaster
Summary
In the northern parts of India, the Himalayan rivers are glacier-fed and pass through the Indo-Gangetic plains (IGP) and plunge into the Bay of Bengal. We have analyzed the pre- and post-event Sentinel data to examine changes in water quality along the rivers (Fig. 1) in four sections, along the Rishi Ganga, Alaknanda and near Haridwar along the Ganga River. We analyzed changes in the water index, turbidity, and Chl-a concentration at five locations (Table 4) near Tapovan and Haridwar.
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