Rangit Dam

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Dam in India

title: "Rangit Dam" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["dams-in-sikkim", "hydroelectric-power-stations-in-sikkim", "dams-in-the-brahmaputra-river-basin", "dams-completed-in-1999", "1999-establishments-in-sikkim", "20th-century-architecture-in-india"] description: "Dam in India" topic_path: "arts" source: "https://en.wikipedia.org/wiki/Rangit_Dam" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Dam in India ::

::data[format=table title="Infobox dam"]

Field	Value
name	Rangit Dam
image	Ranjit Dam & Reservoir on Rangit River.jpg
image_caption	Rangit Dam and Reservoir
name_official	Rangit Hydropower Project, Stage III
dam_crosses	Ranjit River
location	Legship, Sikkim, India
dam_type	Concrete Gravity
dam_length	100 m
dam_height	45 m
spillway_type	Gated Overflow
spillway_capacity	2725 m³/s
opening	January 2000
owner	NHPC
operator	National Hydroelectric Power Corporation
res_name	Rangit Reservoir
res_capacity_total	1.175 million cubic metres
res_catchment	979 km2
res_surface	12.9 ha
plant_operator	National Hydroelectric Power Corporation
plant_turbines	3×20 MW
plant_capacity	60 MW
plant_annual_gen	340 GWh (Firm Power 39 MW)
plant_type	R
plant_commission	January 2000
location_map	India Sikkim
coordinates
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| name = Rangit Dam | image = Ranjit Dam & Reservoir on Rangit River.jpg | image_caption = Rangit Dam and Reservoir | name_official = Rangit Hydropower Project, Stage III | dam_crosses = Ranjit River | location = Legship, Sikkim, India | dam_type = Concrete Gravity | dam_length = 100 m | dam_height = 45 m | dam_width_base = | spillway_type = Gated Overflow | spillway_capacity = 2725 m³/s | construction_began = | opening = January 2000 | cost = | owner = NHPC | operator = National Hydroelectric Power Corporation | res_name = Rangit Reservoir | res_capacity_total = 1.175 million cubic metres | res_catchment = 979 km2 | res_surface = 12.9 ha | res_max_depth = | plant_operator = National Hydroelectric Power Corporation | plant_turbines = 3×20 MW | plant_capacity = 60 MW | plant_annual_gen = 340 GWh (Firm Power 39 MW) | plant_type = R | plant_commission = January 2000 | plant_decommission = | location_map = India Sikkim | location_map_caption = | coordinates = | website = | extra = Rangit Dam (Hindi: रन्गीत् बाँध Bāndh), which forms the headworks of the Rangit Hydroelectric Power Project Stage III, is a run-of-the-river hydroelectric power project on the Ranjit River, a major tributary of the Teesta River in the South Sikkim district of the Northeastern Indian state of Sikkim. The project's construction was completed in 1999. The project is became functional in 2000. The project was built at a cost of Rs 4922.6 million (Rs 492.26 crores) (at US$1 = Rs 45, this is US$109.39 million). The average annual power generation from the 60 MW (3x20 MW) project is 340 GWh with firm power of 39 MW.

Topography

| align = left | image1 = Rangit and Rathong chu Rivers meet upstream of Dam.jpg | width1 = 150 | alt1 = | caption1 = | image2 = IMG 4144 A Chorten at the Confluence.jpg | width2 = 150 | alt2 = | caption2 = | footer = Left: Confluence of Rangeet River and Rathong chu rivers upstream of the Rangit Dam. Right: A chorten above the confluence of the two rivers The Ranjit River, on which the Rangit Dam is located, is a major right-bank tributary of the Teesta River in Sikkim. The river arises from the Talung glacier, and it meets the Teesta river at Melli after a travel of 61 km from its source. At the dam site, the catchment area drained is 979.02 km2 (rain-fed catchment is 712 km2 and the balance area is snow-fed, above 4570 m); the elevation of the catchment area varies from about 600 m to about 7338 m at North Kabru Peak and is delimited between and . A number of perennial streams originate in glacial fields of the river basin; important snow-fed rivers which constitute the Rangit basin above the dam site are the Rathong Chu, Rimbi Chu, Prek Chu, Ralli Chu, Rongdon Chu, and Kayam Chu. The drainage pattern is sub-dendentric.

The dam is located at a distance of 130 km from Siliguri and 70 km from Gangtok. The dam is downstream of the confluence of Rathong Chu and Rangit Rivers near the Legship town, and the powerhouse of the project is near Sagbari village.

Hydrology

The annual inflow in the river at the location of the dam has been estimated as . The maximum flood discharge has been adopted as 3395 m3/s, while the design flood discharge adopted for the spillway is 2725 m3/s. The dependable discharge adopted for diversion from the reservoir for power generation is 1717.8 m3/s (without considering contribution from the upstream Stage II project, which is yet to be implemented).

Climate

The climate of the Rangit River basin is cold and humid. The climatic seasons of the basin represented in the project area are: spring season–late February, summer season–March, premonsoon showers–April and May; monsoon season–May to September, sometimes extending to October. Snow, at higher elevations of the catchment, falls between December and February. Winters are very cold with mist and fog lasting from November to February.

Geology

Precambrian formations of the Daling series of quartzites and phyllites dominate the area. This rock type is overlain by crystalline Darjeeling Gneiss comprising gneisses and granitoides. Recent alluvium of sandy loam, silty loam, and clayey material of varying thickness overlay the rock formations. The banks of the Rangit River have silty clay material with large rock blocks. Many landslides are observed in the catchment, which add to the siltation problems of the reservoir.

Project features

::figure[src="https://upload.wikimedia.org/wikipedia/commons/b/bb/An_aerial_view_Rangit_Dam_&_Reservoir_on_Rangit_river.jpg" caption="Aerial view of Ranjit Dam and related works"] ::

The Rangit Dam is a 45 m concrete gravity structure, 100 m long. The reservoir created behind the dam has a storage capacity of . The storage created is used for hydropower generation at a surface powerhouse on the left bank of the Rangit River. The diversion of flow from the reservoir to the surface powerhouse is effected through an intake leading to a concrete-lined headrace tunnel (HRT) of 4.5 m diameter (horseshoe-shaped and concrete-lined) of 3 km length, a surge shaft (14x60 m) at the end of the HRT with control arrangement followed by one main penstock pipe (3.5x270 m) trifurcating into three lines of 2 m diameter each to connect to the three Francis turbine generators of 20 MW capacity each, through the MIVs. The tailwaters from the turbines are fed back into the river through a combined short tailrace channel. The firm power generation is on the order of 39 MW, corresponding to annual energy generation of 340 GWh (in a 90% dependable year).

The ruling levels for power generation are:

Full reservoir level (FRL): 639 m
Minimum draw-down level: 627 m
Normal tail-water level in the tailrace channel from the powerhouse: 512 m
Operating gross head: 127 m

Since it is owned by Coastal Projects Ltd, the power generated is shared and Sikkim gets a share of 13.33%.

The project was funded by the Government of India and built by the National Hydroelectric Power Corporation (NHPC). The construction of the project was completed in December 1999, and operation started in January 2000. Operation and maintenance of the project is also with the NHPC.

This power project was the third stage of the five-stage cascade development conceived on the main stem of the Rangit River, and was the first to be built in the series of Rangit Stage I to IV initially conceived by the Central Water Commission. Three other projects on the Rangit River planned and under development are the Rangit Stage II (60 MW capacity), Rangit Stage IV (120 MW capacity), and Jorethong HEP (96 MW); the last two projects are now under construction.

Environmental aspects

In river-valley reservoir projects, the gravity of the siltation problem induced by to catchment degradation is serious and needs to be suitably addressed. For this purpose, the Ministry of Environment and Forests of the Government of India have made it obligatory for the project authorities to implement physical engineering and biological measures in the catchment area of the project to be taken up concurrently with the implementation of the project. This activity involves several works defined under the Catchment Area Treatment (CAT) plan.

For evolving the CAT plan, the status of the reservoir catchment was analysed. The reservoir catchment consists of five types of forests namely, the East Himalayan Sub-Tropical wet hill forests (elevation range of 800 -), East Himalayan wet temperate forests (elevation range of 1800 -), oak and rhododendron forests (elevated above 2700 m), mixed coniferous forests (in elevation range of 2700 -), and alpine scrubs/pastures (above 3750 m). There are 35 reserve forests in the catchment, out of which 29 are in West Sikkim district and six are in South Sikkim district. The entire catchment area was analysed in detail to assess the degraded areas to be treated under the CAT plan to reduce siltation problems. An area of 13075 ha was identified for implementing engineering and biological treatment measures. These measures were implemented, starting in 1995–96, by the Forest Department of the Government of Sikkim involving engineering treatment measures (included agricultural land, forest land and water land) and biological treatment measures. 15 nurseries were established covering an area of 18.5 ha to provide saplings/seedlings for plantation in the sub-watersheds of the catchment identified for treatment.

Recreation

The reservoir created by the Rangit Dam has been developed into a recreational water park named Rangit Water World. It is a popular venue for picnics, fishing, boating and rafting. The recreational centre was developed due to the initiative of the local people of Legship town.

Notes

References

"Welcome to Rangit Power Station". NHPC Limited.
Kaushish, S.P.. (2002). "Silting Problems in Hydropower Plants". Taylor & Francis.
Jain, Sharad K.. (16 May 2007). "Hydrology and Water Resources of India". Springer.
"Hydroelectric Power Plants in India – Northeast". Powerplants around the World.
"Rangit Power Station". Scribd.
Kaushish, p.12
"Energy & Power Department Government of Sikkim". Government of Sikkim.
"Jorethang Loop HE Project". Dans Energy.
"Project". Jal Power Corporation Ltd.
"Gammon initial offering to fund India's 66-MW Rangit 2". Hydroworld.
Kaushish, p.10
Kaushish, pp.15–17
"South Sikkim". Digital Himalaya.
"Legship".

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