Tributaries
The Pabbar River is a tributary of the Tons River connecting to it from the west. The Pabbar River is the westernmost river that drains east to the Ganges. The Sutlej River is the next watershed over and is the easternmost river that drains west into the Indus.
The Asan River is a tributary of the Tons that is often named (incorrectly) after this great river as the Tons. The Asan river is a confluence of two small river systems; one comprising streams flowing south from the Himalayan range running from Vikas Nagar towards Tehri (with Mussorie in the centre), and the other comprising streams flowing north-west from the lower Shiwalik hills (that separate Dehradun and Saharanpur districts). The misnomer Tons stands for the river originating from the Mussorie hills, flowing down through Robber's cave, Bijapur canal and Tapkeshwar Mahadev, before emerging into a broad valley behind IMA. This river receives substantial waters from several streams flowing south from the Himalayan slopes. It goes on west beyond the locality of Premnagar to finally join the streams from the lower Shiwaliks and flow toward the Yamuna, which it joins near Poanta Sahib. Asan barrage is constructed just before this confluence.
Read more about this topic: Tons River