Sun Koshi

The Sun Koshi ('golden river') is the trunk into which the Koshi system's western rivers drain. Its principal headstream, the Bhote Koshi, descends from Nyalam County in Tibet through the Arniko Highway corridor; at Dolalghat the Indrawati joins, and from there the river turns east along the foot of the Mahabharat range, absorbing the Tama Koshi, Likhu and Dudh Koshi one after another on its long run to Tribeni, where it meets the Arun and Tamor to form the Sapta Koshi.

It is a corridor that lives with Himalayan hazard. On 2 August 2014 a massive landslide at Jure in Sindhupalchok killed around 155 people, destroyed more than a hundred houses, and dammed the river outright — the impounded lake submerged the highway and the blockage cut power generation until the army blasted a channel through the debris.

The Sun Koshi's long, continuous whitewater is its other claim to fame: the classic multi-day rafting expedition runs about 272 km from Dolalghat (620 m) down to the Chatara gorge (115 m) on grade III–IV rapids, and is regularly ranked among the world's great river journeys.

The river also works hard. The Bhote Koshi corridor carries a string of hydropower plants, and in Sindhuli the river is the donor for the Sunkoshi–Marin Diversion, a National Pride Project since January 2020: a 13.3 km tunnel — bored by TBM and broken through on 8 May 2024, well ahead of schedule — will divert a design flow of 67 m³/s into the Marin Khola of the Bagmati basin, irrigating some 122,000 ha across five Madhesh districts and generating 38.62 MW on the way.