Gandak Basin

The Gandak Basin is bounded on north by the Himalayas. On the south by the River Ganga, On the east by the Burhi Gandak Basin and on the west by the Ghagra Basin.

River Gandak known as Kalie or Krishna Gandaki in the upper reaches rises in the glacial of southern Tibet at altitude of 7,620 mt. near Tibet Nepal border to the south east of Dhaulagiri at north latitude 29°18” and east longitude 83°85”. After receiving a number of tributaries like Mayangadi, Bari and Trisuli, Gandak debouches into the plains of West Champaran district of Bihar at Triveni (Valmikinagar). At this point two more tributaries viz. Panchand & Sarhad join the river. Thereafter, the river flows in a southerly direction and forms the boundary between Uttar Pradesh and Bihar for about 45 km. It then flows through Bihar and finally joins the River Ganga opposite Patna.

The catchment area of river Gandak is trapezoidal in shape upto Triveni. Out of its total catchments area of 45.731 Sq. km, 5.687 sq. km is in Tibet,30.882 sq.km in Nepal, 1874 sq.Km in U.P. and 7.288 sq. Km in Bihar. It runs a course of 380 km in Tibet & Nepal and about 250 km in India.