Study area

The Alaknanda originates from two glaciers, the Satopanth and Bhagirath Kharak glaciers (elevation 3800 m). The Bhagirathi originates from Gomukh, (elevation 3920 m), the snout of the Gangotri glacier. After flowing for approximately 225 km, these two rivers join at Devprayag and are subsequently known as the Ganga [36]. The Ganga is the largest river in India (the fifth-longest in the world). It has a length of 2525 km [37]. Two major dams, at Tehri and Koteshwar, have been constructed across the Bhagirathi, whereas the Srinagar dam is constructed across the Alaknanda [38–40].