The Tons river originates from the Ruinsara snout and flows through Garhwal, the western part of the Himalayan state of Uttaranchal, edging Himachal Pradesh. Ruinsara snout is located below the Dhum Dhar kandi ridge which further leads to the Kalanag and Bandarpoonch and is one of the most major perennial Indian Himalayan rivers. Tons river is the major tributary of Yamuna river. In Fact it carries more water than the Yamuna itself, which its meets below Kalsi near Dehradun. Tons river join Yamuna river in the north-western region of Doon valley.
A new dam has been planned to be constructed on Tons river on the Himachal Pradesh-Uttarakhand border to meet nearly two-thirds of Delhi’s projected additional demand for water by 2023.
Tons river flows in a V shaped downstream. The end point of the river course of Tons river is DakPathar in Dehradun. It further flows through Tethan Himalaya rocks before connecting to the Pabbar River. The Tons river merges into the Yamuna River after crossing into the Sub-Himalaya Sequence.