Rangit Dam
Encyclopedia
Rangit Dam which forms the headworks of the Rangit Hydroelectric Power Project Stage III, is a run-of-the-river power project on the Ranjit River
, a major tributary of the Tista River in the South Sikkim district of the Northeastern Indian state of Sikkim
. The project's construction was completed in 1999. The project is fully functional since 2000. The project was built at a cost of Rs 4922.6 million (Rs 492.26 crores) (at 1 USD = Rs 45, this is 109.39 million USD). The average annual power generation from the project is 340 GWh with firm power of 29 MW.
after a travel of 61 kilometres (37.9 mi) from its source. At the dam site, the catchment area drained is 979.02 square kilometre (rain-fed catchment is 712 square kilometre and the balance area is snow fed above snow line contour of (4570 metres (14,993.4 ft)); elevation of the catchment area varies from about 600 metres (1,968.5 ft) to about 7338 metres (24,074.8 ft) (North Kabru Peak) and is delimited between (27.275°N 88.0141°E) and (27.6195°N 88.42°E}. 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 kilometres (80.8 mi) from Siliguri and70 kilometres (43.5 mi) from Gangtok. The dam is located downstream of the confluence of Rathong Chu and Rangit Rivers near the Legship
town and the powerhouse of the project is located near Sagbari village.
comprising gneisses and granitoides. Recent alluvium
of sandy loam, silt
y loam
and clay
ey material of varying thickness overlay the rock formations. The banks of the Rangit River depict silty clay material with large rock blocks. Many land slides are observed in the catchment, which add to the siltation problems of the reservoir.
Generating Units of 20 MW capacity each, through the MIVs. The tailwaters from the turbines are lead back into the river through a combined short tailrace channel. The firm power generation is of 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: in the reservoir, Full Reservoir Level (FRL) of 639 metres (2,096.5 ft) and Minimum Draw Down Level (MDDL) of 627 metres (2,057.1 ft)), the Normal Tail Water Level (NTWL) in the Tail Race Channel from the Powerhouse of 512 m and under an operating gross head of 127 m. Since it is funded by the central government, 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 its parastatal organization namely, 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 (3×40 MW = 120 MW capacity) and Jorethong HEP (96 MW); the last two projects are now under construction.
, 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 pari passu (concurrently) with the implementation of the Hydropower 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 800–1800 m (2,624.7–5,905.5 ft)), East Himalayan wet temperate forests (elevation range of 1800–2700 m (5,905.5–8,858.3 ft)), Oak
and Rhododendron
forests (elevated above 2700 metres (8,858.3 ft)), mixed coniferous forests (in elevation range of 2700–3750 m (8,858.3–12,303.1 ft)) and alpine
scrubs/pastures (above 3750 metres (12,303.1 ft)). There are 35 reserve forests in the catchment, out of which 29 are in West Sikkim district and six (6) 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 hectares (32,309 acre)) was identified for implementing engineering and biological treatment measures. These measures were implemented, starting with 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 hectares (45.7 acre)) to provide saplings/seedlings for plantation in the sub-watersheds of the catchment identified for treatment.
town.
Rangeet River
Rangeet or Rangit is a tributary of the Teesta river, the largest river in the Indian state of Sikkim. The Rangeet river originates in the Himalayan mountains in West Sikkim district. A perennial river, it is fed by the melting snow of the Himalayas in early summer and the monsoon rains in...
, a major tributary of the Tista River in the South Sikkim district of the Northeastern Indian state of Sikkim
Sikkim
Sikkim is a landlocked Indian state nestled in the Himalayan mountains...
. The project's construction was completed in 1999. The project is fully functional since 2000. The project was built at a cost of Rs 4922.6 million (Rs 492.26 crores) (at 1 USD = Rs 45, this is 109.39 million USD). The average annual power generation from the project is 340 GWh with firm power of 29 MW.
Topography
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 MelliMelli
Melli is a town on the West Bengal-Sikkim border near the River Teesta.The appellation Melli in Nepali means "the place where the dead are cremated". Melli is one of the few towns in India that lie in two different states. A bridge named Jawaharlal Nehru Bridge connects the two parts of the town....
after a travel of 61 kilometres (37.9 mi) from its source. At the dam site, the catchment area drained is 979.02 square kilometre (rain-fed catchment is 712 square kilometre and the balance area is snow fed above snow line contour of (4570 metres (14,993.4 ft)); elevation of the catchment area varies from about 600 metres (1,968.5 ft) to about 7338 metres (24,074.8 ft) (North Kabru Peak) and is delimited between (27.275°N 88.0141°E) and (27.6195°N 88.42°E}. 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 kilometres (80.8 mi) from Siliguri and70 kilometres (43.5 mi) from Gangtok. The dam is located downstream of the confluence of Rathong Chu and Rangit Rivers near the Legship
Legship
Legship is a small town in West Sikkim district in the Indian state of Sikkim. The Rangit Dam lies up stream, a dam which the people of Legship were partly responsible for.Another famous place of interest is the Kirateshwar Mahadev Temple....
town and the powerhouse of the project is located near Sagbari village.
Hydrology
The annual inflow in the river at the location of the dam has been estimated as 696,000 cubic metres. The maximum flood discharge has been adopted as 3395 cubic metre/s while the design flood discharge adopted for the spillway of the dam is 2725 cubic metre/sec. The dependable discharge adopted for diversion from the reservoir for power generation is 1717.8 cubic metre/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. The snow season, 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 GneissGneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
comprising gneisses and granitoides. Recent alluvium
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
of sandy loam, silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
y loam
Loam
Loam is soil composed of sand, silt, and clay in relatively even concentration . Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silty soils, and are easier to till than clay soils...
and clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
ey material of varying thickness overlay the rock formations. The banks of the Rangit River depict silty clay material with large rock blocks. Many land slides are observed in the catchment, which add to the siltation problems of the reservoir.
Project features
The Ranjit dam is 45 metres (147.6 ft) high concrete gravity structure of 100 metres (328.1 ft) length. The reservoir created behind the dam has a storage capacity of 1,175,000 cubic metres. The storage created is utilized for hydropower generation at a surface Powerhouse located 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 Head Race Tunnel (HRT) of 4.5 metres (14.8 ft) diameter (Horse shoe shaped and concrete lined) of 3 kilometres (1.9 mi) length, a Surge Shaft (14 metres (45.9 ft) diameter and of 60 metres (196.9 ft) depth at the end of the HRT with control arrangement followed by one main penstock pipe (of 3.5 metres (11.5 ft) diameter and length of 270 metres (885.8 ft)) trifurcating into three lines of 2 metres (6.6 ft) diameter each (with a total length of all three lines is 59 metres (193.6 ft)) to connect to the three Francis TurbineFrancis turbine
The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, Massachusetts. It is an inward-flow reaction turbine that combines radial and axial flow concepts....
Generating Units of 20 MW capacity each, through the MIVs. The tailwaters from the turbines are lead back into the river through a combined short tailrace channel. The firm power generation is of 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: in the reservoir, Full Reservoir Level (FRL) of 639 metres (2,096.5 ft) and Minimum Draw Down Level (MDDL) of 627 metres (2,057.1 ft)), the Normal Tail Water Level (NTWL) in the Tail Race Channel from the Powerhouse of 512 m and under an operating gross head of 127 m. Since it is funded by the central government, the power generated is shared and Sikkim gets a share of 13.33%.
The project was funded by the Government of India
Government of India
The Government of India, officially known as the Union Government, and also known as the Central Government, was established by the Constitution of India, and is the governing authority of the union of 28 states and seven union territories, collectively called the Republic of India...
and built by its parastatal organization namely, the National Hydroelectric Power Corporation
National Hydroelectric Power Corporation
NHPC Limited , A Govt. of India Enterprise, was incorporated in the year 1975 with an authorised capital of Rs. 2000 million and with an objective to plan, promote and organize an integrated and efficient development of hydroelectric power in all aspects...
(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 (3×40 MW = 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 due to catchment degradation is serious and needs to be suitably addressed. For this purpose, the Ministry of Environment and ForestsMinistry of Environment and Forests
The Ministry of Environment and Forests is an Indian government ministry. The Minister of Environment and Forests holds cabinet rank as a member of the Council of Ministers...
, Government of India
Government of India
The Government of India, officially known as the Union Government, and also known as the Central Government, was established by the Constitution of India, and is the governing authority of the union of 28 states and seven union territories, collectively called the Republic 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 pari passu (concurrently) with the implementation of the Hydropower 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 800–1800 m (2,624.7–5,905.5 ft)), East Himalayan wet temperate forests (elevation range of 1800–2700 m (5,905.5–8,858.3 ft)), Oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
and Rhododendron
Rhododendron
Rhododendron is a genus of over 1 000 species of woody plants in the heath family, most with showy flowers...
forests (elevated above 2700 metres (8,858.3 ft)), mixed coniferous forests (in elevation range of 2700–3750 m (8,858.3–12,303.1 ft)) and alpine
Alpine climate
Alpine climate is the average weather for a region above the tree line. This climate is also referred to as mountain climate or highland climate....
scrubs/pastures (above 3750 metres (12,303.1 ft)). There are 35 reserve forests in the catchment, out of which 29 are in West Sikkim district and six (6) 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 hectares (32,309 acre)) was identified for implementing engineering and biological treatment measures. These measures were implemented, starting with 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 hectares (45.7 acre)) 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 LegshipLegship
Legship is a small town in West Sikkim district in the Indian state of Sikkim. The Rangit Dam lies up stream, a dam which the people of Legship were partly responsible for.Another famous place of interest is the Kirateshwar Mahadev Temple....
town.