Mangde Chhu

The Mangde Chhu (Dzongkha: mang lde chu; sometimes Mangdechhu) is the main river of central Bhutan. It rises in the high country of Wangdue Phodrang district near Gangkhar Puensum, Bhutan's highest peak at 7,546 metres, and flows roughly north–south through Trongsa and into Zhemgang, where it joins the Drangme Chhu at Tingtinbi to form the Manas system that drains to the Indian Brahmaputra. Its basin covers approximately 3,339 square kilometres, draining the eastern slopes of the Black Mountains and the southern Bumthang highlands.^[1][2]

The river is the site of the 720 MW Mangdechhu Hydroelectric Project, commissioned in stages between June and August 2019 and inaugurated jointly by the prime ministers of India and Bhutan on 17 August 2019. The project is widely regarded as the most successful of Bhutan's recent Indian-financed hydropower projects, completed within a budget envelope close to the original estimates and ahead of comparable schemes that have run severely over time and cost.^[3][4]

This article covers the river's hydrology, the Mangdechhu Hydroelectric Project, and the basin's strategic and biodiversity significance.

Course and hydrology

The Mangde Chhu rises in alpine high country in northern Wangdue Phodrang and flows southeast across the southern fringe of the Bumthang range. Bhutan's lateral east–west highway crosses it about 8 kilometres west of Trongsa town, near the ridge on which Trongsa Dzong stands. South of Trongsa the river drains the eastern slopes of the Black Mountains and forms the eastern boundary of the Jigme Singye Wangchuck National Park (Black Mountains National Park) and the eastern edge of Royal Manas National Park further south.^[1][2]

The Trongsa–Zhemgang highway follows the right bank of the river south through the gorge towns of Tingtinbi and Panbang, leaving the Mangde at Tingtinbi where the road heads east towards Gelephu. The Bumthang River (Chamkhar Chhu) joins the Mangde from the east north of Tingtinbi. Below the confluence with the Drangme at the mouth of Royal Manas, the combined waters are conventionally referred to as the Manas Chhu.^[1][2]

Mangdechhu Hydroelectric Project (720 MW)

The Mangdechhu Hydroelectric Project is a run-of-river facility located between Trongsa and Tingtinbi. It was constructed by the Mangdechhu Hydroelectric Project Authority (MHPA), an India-financed special-purpose entity, under the Indian Government's 2009 commitment to support Bhutan's hydropower expansion. Construction began in June 2012, and the four turbine-generator units were commissioned between 28 June 2019 and 16 August 2019.^[3][5]

The project was formally inaugurated on 17 August 2019 by Indian Prime Minister Narendra Modi and Bhutanese Prime Minister Lotay Tshering. Commissioning increased Bhutan's installed electrical generation capacity by 44 per cent, raising the national total to approximately 2,326 MW. The plant generates an estimated 3,000 GWh per year and was projected to reduce greenhouse gas emissions across the regional grid by approximately 2.4 million tonnes annually.^[3][5] Operational responsibility was transferred from the MHPA to Druk Green Power Corporation in December 2022, completing the handover of the asset to Bhutanese ownership.^[6]

By comparison with the troubled Punatsangchhu I project — under construction since 2008 and still incomplete — and the partially commissioned Punatsangchhu II, Mangdechhu has been treated by the Bhutanese government as a working model for cross-border hydropower cooperation. Its success has been attributed to favourable geology relative to the Punatsangchhu sites, a comparatively simple run-of-river design, and active project management by MHPA during construction.^[3][7]

Strategic geography of the basin

The Mangde corridor was the heartland of the Trongsa Penlop's traditional jurisdiction. The dzong founded by Yongzin Ngagi Wangchuk in 1543 and rebuilt in the 17th century by Chhogyal Minjur Tempa controls the only practicable route across central Bhutan, sitting on a spur above the Mangde. The penlops who held the dzong — including Jigme Namgyel and his son Ugyen Wangchuck, the first king — used control of this corridor to consolidate national authority in the second half of the 19th century. The river basin therefore has a strong identification with the founding dynasty, and the Trongsa Penlop title remains the traditional designation of the Crown Prince today.^[8]

Biodiversity

The middle and lower Mangde basin lies within the buffer zones of two of Bhutan's most important protected areas — Jigme Singye Wangchuck National Park, which encompasses the Black Mountains massif west of the river, and Royal Manas National Park to the south. The forests of the basin support populations of the Bengal tiger, leopard, Asian elephant, gaur, golden langur and a range of pheasant and hornbill species. The Black Mountains complex is one of the principal corridors for tiger movement between Bhutan's eastern and western populations.^[2][7]

The hydropower scheme has raised concerns about altered downstream flow regimes and sediment dynamics affecting Royal Manas; project operators have undertaken studies of fish passage and minimum environmental flow, and these are referenced in subsequent project planning across Bhutan.

References

1. Mangde Chhu — Wikipedia
2. Bhutan — River Systems — US Library of Congress Country Studies
3. Mangdechhu Hydroelectric Project — Power Technology
4. Mangdechhu — Druk Green Power Corporation
5. Mangdechhu Hydroelectric Project Authority — official site
6. Bhutan DGPC handed keys to 720 MW Mangdechhu hydro project — Business Standard
7. DGPC takes over 720 MW Mangdechhu hydropower plant — Renewable Energy World
8. Karma Phuntsho, The History of Bhutan (Random House India, 2013), chapters on Trongsa and the rise of the Wangchuck dynasty