The Torsa River, known as the Amo Chhu in Bhutan, is a transboundary river of 358 kilometres that originates in the Chumbi Valley of Tibet, flows through western Bhutan, and enters the Indian plains near Phuentsholing before joining the Brahmaputra system. It is significant for hydropower potential, border demarcation, and recurring monsoon flooding.
The Torsa River is a transboundary waterway of approximately 358 kilometres that originates in the Chumbi Valley of Tibet, flows south through western Bhutan — where it is called the Amo Chhu (Dzongkha: ཨ་མོ་ཆུ) — and enters India near the border town of Phuentsholing. From there it crosses the Duars plains of West Bengal and eventually joins the Brahmaputra system. The river's course spans three countries (China, Bhutan, and India) and a fourth, Bangladesh, before its final discharge, making it one of the more geopolitically notable rivers in the eastern Himalayas.
Course and Tributaries
The river rises on the Tibetan Plateau in the Chumbi Valley, a narrow corridor of Chinese territory wedged between Bhutan and the Indian state of Sikkim. Approximately 113 kilometres of the river's length lie in Tibet, where it collects water from the Tangka Chu, Khangphu Chu, and Tromo Chu before entering Bhutan through Haa District. Within Bhutan, the Amo Chhu flows roughly 145 kilometres, passing through Haa and Chhukha districts in deep, forested gorges that drop steeply from alpine elevations to the subtropical lowlands at Phuentsholing (approximately 300 metres).[1]
After crossing into India, the river enters the flat alluvial Duars plains. It flows past the towns of Jaigaon and Hasimara in West Bengal and through the Alipurduar district. Significant tributaries on the Indian side include the Kaljani River, a left-bank stream originating in the Bhutanese foothills that joins the Torsa near the India–Bangladesh border, and the Ghargharia River, which drains from the highlands and merges in Tufanganj subdivision. Other minor tributaries include the Holong and Chhoto Torsa streams in the Indian foothills.[2]
Flooding
The Torsa is one of the more flood-prone rivers in the eastern Himalayan foothills. During the monsoon season (June to September), discharge increases dramatically and the river carries heavy sediment loads from its mountainous catchment. Downstream communities in the Duars — particularly around Cooch Behar and Alipurduar — face recurrent inundation. The floods of 1968, 2000, and October 2025 were especially damaging, displacing thousands and destroying agricultural land.[3]
In October 2025, severe flooding on the Torsa triggered by a low-pressure system over the Bay of Bengal affected both Bhutan and West Bengal. The Indian Army launched helicopter rescue operations from Sevoke Road Aviation Base after Phuentsholing and surrounding areas were inundated. In addition, the Tala Hydropower Dam on the nearby Wang Chhu overflowed during the same event due to a gate malfunction, compounding downstream concerns. The transboundary nature of the river complicates flood management: upstream land-use changes and hydrological events in Tibet and Bhutan directly affect Indian communities downstream.[4]
Hydropower
The Amo Chhu has been identified as a potential site for large-scale hydropower development. The Amo Chhu Hydroelectric Project, initially assessed at 620 MW and later scaled to 540 MW, has been under bilateral discussion between Bhutan and India. The National Thermal Power Corporation prepared the detailed project report, which was approved by India's Central Electricity Authority in January 2013. However, the project has remained stalled: India has expressed security concerns about a dam situated in close proximity to the China–India–Bhutan trijunction. As of 2026, the project remains valid in Bhutan's hydropower planning documents but has not begun construction.[5]
Ecology and Conservation
In Bhutan, the Amo Chhu basin falls partly within the Jigme Khesar Strict Nature Reserve and the Torsa Strict Nature Reserve, protecting temperate and subtropical forest ecosystems. On the Indian side, the river flows through or near Buxa Tiger Reserve and Jaldapara National Park, the latter home to one of the largest populations of Indian one-horned rhinoceros outside Kaziranga. The river supports freshwater ecosystems including several mahseer species. Any future dam construction would need to address fish migration and downstream flow alteration.[6]
Border and Strategic Significance
At Phuentsholing, the Amo Chhu/Torsa marks part of the international boundary between Bhutan and India. The river's headwaters in the Chumbi Valley place it at the junction of Chinese, Indian, and Bhutanese territorial interests — a factor that figured in the 2017 Doklam standoff between Indian and Chinese forces. Any upstream diversion or development in Tibet could affect water availability in Bhutan and India, adding a layer of hydro-diplomacy to the river's significance.
References
See also
Amochhu River
The Amochhu, also called the Toorsa or Torsa, is the westernmost major river of Bhutan. Rising in the Chumbi Valley of Tibet, it flows through Haa and Samtse before entering West Bengal as the Torsa, draining a sparsely populated and steeply incised western corridor.
places·4 min readWangchhu River
The Wangchhu, known as the Raidak below the Bhutanese border, is the principal river of western Bhutan. Rising in Tibet and flowing through Thimphu and Chukha before entering West Bengal, it has been the backbone of Bhutan's hydropower programme since the 1980s.
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Cheri Monastery (Chagri Dorjeden), founded in 1620 by Zhabdrung Ngawang Namgyal, is the first monastery established in Bhutan and the birthplace of the Central Monastic Body. Located on a forested hillside north of Thimphu, it remains one of the most important meditation centres of the Drukpa Kagyu tradition.
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