Wangchhu River

The Wangchhu (also written Wang Chhu, Wong Chu; called the Raidak in India and the Tro Chu in its Tibetan headwaters) is the principal river of western Bhutan. It rises north of the Bhutanese border on the Tibetan plateau, descends through Thimphu and the Wang valley, and exits Bhutan at Phuentsholing into the Indian state of West Bengal, where it joins the Brahmaputra system as the Raidak.^[1]

Within Bhutan the river is the main drainage of Thimphu, Paro, Haa and Chhukha dzongkhags. It carries about 7 per cent of Bhutan's total river discharge and underpins three of the country's flagship hydropower stations: Chhukha, Tala and the original Wangchhu Hydroelectric Project.^[2]

Although shorter and less voluminous than the eastern Manas system, the Wangchhu is the most economically and politically important river in Bhutan. The Thimphu–Chukha–Phuentsholing corridor it defines is the spine of the country's road network, urban population, industrial estate and electricity exports.

Course and basin

The Wangchhu rises in the Phari area of Tibet's Chumbi Valley and crosses into Bhutan through the upper Haa and Thimphu sub-basins. In its upper Bhutanese reaches it is known locally as the Thimphu Chhu. It flows south through the Thimphu valley past the capital, then west to the confluence at Chuzom (literally "the meeting of waters"), where the Pa Chhu draining Paro and the Wang Chhu draining Thimphu join. From Chuzom the combined river is the Wangchhu proper.^[3]

The river then descends sharply through Chhukha dzongkhag, dropping more than 1,500 metres before reaching Phuentsholing on the Indian border. Below the border it is renamed the Raidak and enters Cooch Behar district in West Bengal. Total length to its confluence with the Brahmaputra in Bangladesh is roughly 370 kilometres, of which about 200 kilometres are inside Bhutan.^[1]

Major tributaries inside Bhutan include the Pa Chhu (Paro), the Haa Chhu, the Thimphu Chhu, and smaller streams such as the Bjemina and Pipingchhu. The basin covers around 4,600 square kilometres of Bhutanese territory, the most densely populated drainage in the country.^[3]

Hydropower

The Wangchhu is the most heavily dammed river in Bhutan. Three large run-of-the-river plants on its main stem account for a substantial share of national generation:

• Chhukha Hydropower Plant (336 MW) — Bhutan's first mega-project, commissioned in 1986 with Indian financing and operated by Druk Green Power Corporation.
• Tala Hydroelectric Power Station (1,020 MW) — commissioned in stages between July 2006 and March 2007. Tala remained Bhutan's largest power station until the recent Punatsangchhu projects in the Wang Chhu's neighbouring basin.^[4]
• Wangchhu Hydroelectric Project (570 MW, planned) — a joint venture under the India–Bhutan hydropower programme, repeatedly redesigned since 2014 and not yet under construction as of 2026.

Smaller mini- and micro-hydel installations on tributary streams supply isolated rural loads. The Basochhu plant, operated by Druk Green, sits on a Wangchhu sub-tributary in Wangdue Phodrang.

The river and Thimphu

The capital city of Thimphu sits along a 12-kilometre reach of the Wangchhu (locally Thimphu Chhu) at altitudes between 2,200 and 2,400 metres. Successive city plans have treated the river as a green corridor, with the Centenary Farmers' Market, Memorial Chorten precinct and Changlingmithang stadium all sited within sight of the river. Periodic floods, most notably in 1995 and 2009, have prompted bank stabilisation works and dredging in the southern reach near Babesa.

Water quality in the Thimphu reach has degraded since the 1990s. The Wangchhu River Basin Management Plan, prepared by the National Environment Commission and updated in 2016, flags municipal sewage, urban run-off and industrial effluent in Pasakha as the principal pressures.^[3]

Biodiversity and downstream impacts

The Wangchhu basin spans temperate broadleaf and conifer forests in the upper reaches and subtropical forests near the Indian border. Brown trout were introduced to the Pa Chhu and upper Wangchhu in the 1930s and persist as a managed sport fishery; the native snow trout (Schizothorax) and golden mahseer occur in lower reaches.

Below the Indian border the Raidak runs through a heavily cultivated floodplain and is prone to flash flooding linked to monsoon discharge from the Bhutanese Himalayas. Joint India–Bhutan flood warning protocols, operated through the Central Water Commission and Bhutan's National Centre for Hydrology and Meteorology, have been progressively expanded since 2009.

References

1. Raidāk River — Wikipedia
2. Energy in Bhutan — Wikipedia
3. Wangchhu Basin Management Plan 2016 — Ministry of Energy and Natural Resources
4. Tala Hydroelectric Power Station — Wikipedia
5. Chhukha Hydropower Plant — Druk Green Power Corporation
6. Status of hydropower dams in Bhutan — International Rivers