The Karnali River Basin lies between the mountain ranges of
Dhaulagiri in
Nepal and
Nanda Devi in
Uttarakhand.
Dhaulagiri II, elevation , is the highest point of the entire basin. In the north, it lies in the rain shadow of the
Himalayas. The basin formed by the river has a total catchment area of , of which 45 percent is in India.
Tributaries Chhoti Gandak is a groundwater-fed meandering river originating near Dhesopool, Maharajganj district of
Uttar Pradesh. It travels a distance of about and joins Ghaghara near Guthani, Siwan district of
Bihar. The Chhoti Gandak River Basin is located between 26°00' to 27°20' N latitude and 83°30' to 84°15' E longitude.
Right bank tributaries are Khekhra, Hirna, Jethan, Maun, Duhari, Kanchi and Koilar rivers; Khanua river joins from the left bank. The discharge of Chhoti Gandak is mainly controlled by rain, which is very high during the
monsoon season and low during the summers. It has been observed that whenever precipitation is high in the catchment areas, there is flood in the downstream part of the Chhoti Gandak River Basin. The region exhibits upland terrace surface, river valley terrace surface, present-day river channel with narrow flood plains, natural levee, and point-bar deposits. All these geomorphic features are depositional in nature and made up of alluvium of different ages. The main tributaries of the Karnali are
Seti and
Bheri. == Administrative zones and districts ==