It enters Himachal Pradesh at Khadar Majri in Sirmaur district. Yamuna river is the largest tributary of the Ganga. The Yamuna river has mythical relation to the Sun. It rises from Yamunotri in Gharwal hills and forms the Eastern boundary with Unttar Pradesh. The Yamuna is the Eastern-most river of Himachal Pradesh. Its famous tributaries are Tons, Pabbar and Giri or Giri Ganga. The Giri Ganga rises from near Kupar peak just above Jubbal town in Shimla district, Tons from Yamunotri and Pabbar from Chandra Nahan Lake near the Chansal peak in Rohru tehsil of Shimla district. Its total catchment area in Himachal Pradesh is 2,320 km. It leaves the state near Tajewala and enters into the Haryana state.
The main geomorphic features of the Yamuna valley are interlocking spurs, gorges, steep rock benches and terraces. The latter have been formed by the river over the past thousands of years. The area drained by the Yamuna system includes Giri-Satluj water divide in Himachal Pradesh to the Yamuna Bhilagana water divide in Gharwal. To be more precise the South-Eastern slopes at the Shimla ridge are drained by the Yamuna system. The utilization of water of the river system is being done by the way of transportation of timber logs, irrigation and a hydel power generation. After Himachal Pradesh, the river flows through the state of Haryana, Delhi and Uttar Pradesh where it merges with the Ganga river at Allahabad. The Yamuna is 2,525 km. long.
Important Tributaries of river Yamuna :
Jalal River :
Jalal river is the small tributary of the Giri river in Himachal Pradesh. It rises from Dharti ranges adjoining Pachhad and joins Yamuna at Dadahu from the right side. It also joins the river Giriganga at Dadahu. The origin and entire course of this river lies in the lower Himalayas. This is the rainfed river and has abrupt flow during the rainy season. A number of human settlements have come up along the Jalal river. These include Bagthan and Dadhau.
Markanda River :
Markanda is a small river of Nahan area of the Sirmaur district. It rises from the Southern face of the lower Himalayas on the Western extremity. of the Kiarda dun ( Paonta ) valley. The lower Himalayan hills of Nahan occur on the right flank of the Markanda valley while the low rolling Shivalik hills are on its left flank. It is a rainfed river and has very low flow in the winter and summer months, but rises abruptly in the monsoon.
Andhra River :
This is a tributary of the Pabbar river which in turn drains into the Tons river. This river rises from a small glacier tenated in a cirque of the lower hills of the main Himalayas in the area to the North-West of Chirgaon in Shimla district. Thereafter it flows in a general direction towards South-East and merges with the Pabbar river at Chigaon.
Giri River :
The river Giri is an important tributary of the Yamuna river. It drains a part of South-Eastern Himachal Pradesh. The Giri or Giriganga as it is famous in the Jubbal, Rohru hills that rises from Kupar peak just above Jubbal town after flowing through the heart of Shimla hills, flows down in the South-Eastern direction and divides the Sirmaur district into equal parts that are known as Cis-Giri and Trans-Giri region and joins Yamuna upstream of Paonta below Mokkampur. The river Ashni joins Giri near Sadhupul ( Chail ) while river Jalal which originates from Dharthi ranges adjoining Pachhad joins it at Dadahu from the right side. The waer from the Giri river is led through a tunnel to the power house of Girinagar and after that it is led into the Bata river.
Asni River :
The Ashni river is a tributary of the Giri river which in turn drains into the Yamuna river. This river flows along a deep V shaped valley whose side alopes vary from steep to precipitous. It has carved a steep gorge across the off-shoots of the Nag Tibba ridge. Numerous small spring fed tributaries join the Ashni river at various places along its course.
Bata River :
This river originates in the boulders below the Nahan ridge in the South-Western corner of Himachal Pradesh as the Jalmusa-Ka-Khala. It is mainly fed by the rain water that is cycled as underground water before finally coming up on the surface as a spring. The river flows below the surface for a part of its length in its upper reaches, thereafter the water flows on the surface. Large and wide terraces have been formed by it. The small tributaries which join the Bata river in the Paonta valley are Khara-Ka-Khala flowing in a Southerly direction from the Nahan ridge, and Kanser-Khala originating from the Southern slopes of the Nahan.
Pabbar River :
The Pabbar river is a tributary of the Tons river, which in turn drains into the river Yamuna. This rises from the Dhauladhar range ( South facing slopes ) near the border of UP and Himachal Pradesh and the extreme North-Eastern of Shimla district. The main stream is fed by the Chandra Nahan glacier and springs originating from underground waters. It joins the Tons river at the base of the Chakrata massif near the border of Uttar Pradesh and Himachal Pradesh.
Patsari River :
It is a small spring fed tributary of the Pabbar river. This river rises from the lower Himalayan hills near Kharapathar in Shimla district of Himachal Pradesh. This river joins the Pabbar river near the mountain hamlet of Patsari about 10 km. upstream of Rohru. Its bed is strewn with boulders of various sizes. Small villages and hamlets have come up along this river.
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. These two feeder streams merge near the mountain hamlet of Naitwar and the channel downstream of Naitwar is known as Tons river. The river flows along a V shaped valley. A number of settlements have come up along the Tons river such as Tuni, Naitwar and Menus.