| Raidāk River/Wang Chhu | |
|---|---|
 | |
 Relief map showing the passage of the Raidak River into the larger Brahmaputra | |
| Location | |
| Country | |
| Physical characteristics | |
| Mouth | |
• location | Brahmaputra River |
| Length | 370 kilometres (230 mi) |
| Basin features | |
| Progression | Thimphu,Rinpung Dzong, Chukha hydel project, Tala hydel project,Tufanganj |
TheRaidāk River (also calledWang Chhu orWong Chhu in Bhutan) is a tributary of theBrahmaputra River, and atrans-boundary river. It flows throughBhutan,India andBangladesh.
The Wang Chhu, or Raidāk, rises in theHimalayas. 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. BetweenThimphu and the confluence with theParo Chhu, 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 aboveParo Dzong a considerable feeder, the Ta Chhu, joins it from the left. To the west, theHa Chhu drains into the Wong Chhu. AtTashichho Dzong the bed of the river is about 2,121 metres (6,959 ft) above sea level and at the point of its exit in theDooars its elevation is only 90 metres (300 ft).[1][2][3]
It debouches into the plains inJalpaiguri district and then flows throughCooch Behar district inWest Bengal. The Raidak confluences with the Brahmaputra atchainage 327 km inKurigram District inBangladesh,[4][5][6][7] where it is sometimes referred to Dudhkumar River.[8]
The total length of the main river is 370 kilometres (230 mi) but along with its tributaries, it covers a length of nearly 610 kilometres (380 mi) in Bhutan alone.[1][9]
The 336MWChukha 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 betweenThimphu and the Indian border, a 40 metres (130 ft) diversion dam was built at Chimakoti village, 1.6 kilometres (0.99 mi) upstream of the confluence of the Ti Chhu and Wong Chhu rivers. From the dam water was diverted through 6.5-kilometre (4.0 mi) long tunnels to a fall of more than 300 metres (980 ft) to Chukha power house for generation of electricity. Construction started in 1974 and completed in 1986–88.[10][11][12][13][14]
Tala Hydroelectric Power Station is arun-of-the-river typehydroelectricpower station on the Wangchu River inChukha District,Bhutan. The station consists of a 92-metre (302 ft) tallgravity dam which diverts water through a 22 km (14 mi) longheadrace tunnel to the power station, which contains six 170 megawatts (230,000 hp)Pelton turbine-generators. The Tala dam is located about 3 km downstream of Chukha power house.