The river rises near Tibet and is joined by the Bhoti Kosi just downstream from Barbesi. Most raft trips start at Dolaghat. The Sun Kosi flows eastwards in Nepal through the great valley between the Mahabharat Lekh mountains and the Himalayas.

The volume increases considerably draining flows from his Himalayan tributaries. In November, the flow at Dologhat is about 100 cumecs. Lower down the river, through the big rapids of the Jungle Corridor, it would be about 400 cumecs, which is appr. 11,000 cft, a typical low flow on the Grand Canyon of the Colorado.

At the end at Chatra, the flow is a super 800 cumecs, in November, which makes it one of the major rivers of the world in monsoon.

A nice thing about Sun Kosi is that the general standard of the river gets progressively harder as you descend it so there is time to practice your skills on easy water before the more interesting, bigger and continuous rapids lower down the river.