Explanation:

 Tons River :
This river is an important tributary of the Yamuna river and joins it at Kalsi in the North-Western part of Dehradun valley ( approximately 48 km. away from Dehradun ). It rises as the following two feeder streams - the Supin river rises from in the Northern part of the Tons catchment near the Himachal Pradesh and Uttar Pradesh border and the Rupin river rises from a glacier at the head of the famous Har-Ki-Dun valley in the North-North Eastern part of the Tons catchment.