The Raidāk River (also called Wang Chhu or Wong Chhu in Bhutan) is a tributary of the
Brahmaputra River
The Brahmaputra is a trans-boundary river which flows through Southwestern China, Northeastern India, and Bangladesh. It is known as Brahmaputra or Luit in Assamese language, Assamese, Yarlung Tsangpo in Lhasa Tibetan, Tibetan, the Siang/Dihan ...
, and a
trans-boundary river
A transboundary river is a river that crosses at least one political border, either a border within a state or an international boundary. Bangladesh has the highest number of these rivers, with at least 58 major rivers that enter the country from ...
. It flows through
Bhutan
Bhutan, officially the Kingdom of Bhutan, is a landlocked country in South Asia, in the Eastern Himalayas between China to the north and northwest and India to the south and southeast. With a population of over 727,145 and a territory of , ...
,
India
India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
and
Bangladesh
Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...
.
Course
Bhutan
The Wang Chhu, or Raidāk, rises in the
Himalayas
The Himalayas, or Himalaya ( ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the Earth's highest peaks, including the highest, Mount Everest. More than list of h ...
. In its upper reaches it is also known as the Thimphu Chhu. The main river is a rapid stream, running over a bed of large boulders. Between
Thimphu
Thimphu (; ) is the capital and largest city of Bhutan. It is situated in the western central part of Bhutan, and the surrounding valley is one of Bhutan's '' dzongkhags'', the Thimphu District. The ancient capital city of Punakha was replac ...
and the confluence with the
Paro Chhu
The Paro Chhu is a river of western Bhutan. It is a tributary of the Wong Chhu, which is known as the Raidak in its lower reaches.
Course
The Paro Chhu rises to the south of Chomo Lhari (mountain of the Goddess). Its glacial waters plunge torre ...
, the course of the river is not severely confined but, after leaving the confluence, it runs through a narrow defile between very steep cliffs. It subsequently flows southeast through a comparatively open valley, its course strewn with large boulders against which the water foams violently. It is joined by several small tributaries flowing from nearby mountains. Just above
Paro Dzong a considerable feeder, the Ta Chhu, joins it from the left. To the west, the
Ha Chhu drains into the Wong Chhu. At
Tashichho Dzong the bed of the river is about above sea level and at the point of its exit in the
Dooars
The Dooars or Duars () are the alluvial floodplains in eastern-northeastern India and southern Bhutan that lie south of the outer foothills of the Himalayas and north of the Brahmaputra River basin. This region is about wide and stretches ov ...
its elevation is only .
West Bengal and Bangladesh

It debouches into the plains in
Jalpaiguri district
Jalpaiguri district () is a district of the Indian state of West Bengal. The district was established in 1869 during British Raj. The headquarters of the district are in the city of Jalpaiguri, which is also the divisional headquarters of Ja ...
and then flows through
Cooch Behar district
Cooch Behar district (), also known as Koch Bihar district, is one of the List of districts of West Bengal, 23 districts of the state of West Bengal in India. The district is the part of Jalpaiguri division, Jalpaiguri Division. Cooch Behar ci ...
in
West Bengal
West Bengal (; Bengali language, Bengali: , , abbr. WB) is a States and union territories of India, state in the East India, eastern portion of India. It is situated along the Bay of Bengal, along with a population of over 91 million inhabi ...
. The Raidak confluences with the Brahmaputra at
chainage
The chain (abbreviated ch) is a Units of measurement, unit of length equal to 66 foot (unit), feet (22 yard (unit of length), yards), used in both the United States customary units, US customary and Imperial units, Imperial unit systems. It is su ...
327 km in
Kurigram District
Kurigram District () is a district of Bangladesh in Rangpur Division. The district is located in northern Bangladesh along the country's border with India. Under British rule, the area was organized as a mahakuma and was not established as a dis ...
in
Bangladesh
Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...
, where it is sometimes referred to Dudhkumar River.
The total length of the main river is but along with its tributaries, it covers a length of nearly in Bhutan alone.
[
]
Chukha hydel plant
The 336MW Chukha hydel project, which harnesses the waters of the Wang Chhu or Raidak River, was historically one of the largest single investments undertaken in Bhutan, and it represented a major step toward exploiting the country's huge hydroelectric potential. It was built by India on a turnkey basis, with India providing 60% of the capital in a grant and 40% in a loan at highly concessional terms and conditions. In the arrangement, India receives in turn all the electricity generated from the project in excess of Bhutan’s demand at much cheaper prices than India’s generation cost from alternative sources. Located between Thimphu
Thimphu (; ) is the capital and largest city of Bhutan. It is situated in the western central part of Bhutan, and the surrounding valley is one of Bhutan's '' dzongkhags'', the Thimphu District. The ancient capital city of Punakha was replac ...
and the Indian border, a diversion dam was built at Chimakoti village, upstream of the confluence of the Ti Chhu and Wong Chhu rivers. From the dam water was diverted through long tunnels to a fall of more than to Chukha power house for generation of electricity. Construction started in 1974 and completed in 1986–88.
Tala hydroelectric plant
Tala Hydroelectric Power Station is a run-of-the-river
Run-of-river hydroelectricity (ROR) or run-of-the-river hydroelectricity is a type of hydroelectric generation plant whereby little or no water storage is provided. Run-of-the-river power plants may have no water storage at all or a limited amou ...
type hydroelectric
Hydroelectricity, or hydroelectric power, is Electricity generation, electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other Renewable energ ...
power station
A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the electricity generation, generation of electric power. Power stations are generally connected to an electr ...
on the Wangchu River in Chukha District
Chukha District (Dzongkha: ཆུ་ཁ་རྫོང་ཁག་; Wylie: ''Chu-kha rdzong-khag''; officially spelled "Chhukha" ) is one of the 20 dzongkhag (districts) comprising Bhutan. The major town is Phuentsholing.
Languages
In Chu ...
, Bhutan
Bhutan, officially the Kingdom of Bhutan, is a landlocked country in South Asia, in the Eastern Himalayas between China to the north and northwest and India to the south and southeast. With a population of over 727,145 and a territory of , ...
. The station consists of a tall gravity dam
A gravity dam is a dam constructed from concrete or stone masonry and designed to hold back water by using only the weight of the material and its resistance against the foundation. Gravity dams are designed so that each section of the dam is ...
which diverts water through a long headrace tunnel to the power station, which contains six Pelton turbine
The Pelton wheel or Pelton Turbine is an impulse-type water turbine invented by American inventor Lester Allan Pelton in the 1870s. The Pelton wheel extracts energy from the impulse of moving water, as opposed to water's dead weight like the t ...
-generators. The Tala dam is located about 3 km downstream of Chukha power house.
References
{{DEFAULTSORT:Raidak River
Rivers of Bhutan
Rivers of West Bengal
Tributaries of the Brahmaputra River
International rivers of Asia
Rivers of Bangladesh