Nagarjuna Sagar Dam

Nagarjuna Sagar Dam

నాగార్జునసాగర్ ఆనకట్ట
Nagarjuna Sagar Dam
Location of Nagarjuna Sagar Dam in India
Official name నాగార్జునసాగర్ ఆనకట్ట
Nagarjuna Sagar Dam
Location Nalgonda district, Telangana and Guntur district, Andhra Pradesh
Coordinates 16°34′32″N 79°18′42″E / 16.57556°N 79.31167°E / 16.57556; 79.31167Coordinates: 16°34′32″N 79°18′42″E / 16.57556°N 79.31167°E / 16.57556; 79.31167
Construction began 10 December 1955
(by SWE Infrastructures Ltd)
Opening date 1967
Construction cost 132.32crore rupees
Dam and spillways
Impounds Krishna River
Height 124 metres (407 ft) from river level
Length 1,550 metres (5,085 ft)
Reservoir
Creates Nagarjuna Sagar Reservoir
Total capacity 11,560,000,000 m3 (9,371,845 acre·ft)
Active capacity 5,440,000,000 m3 (4,410,280 acre·ft)[1]
Catchment area 215,000 square kilometres (83,000 sq mi)
Surface area 285 km2 (110 sq mi)
Power station
Commission date 1978-1985
Turbines 1 x 110 MW (150,000 hp) Francis turbines, 7 x 100.8 MW (135,200 hp) reversible Francis turbines
Installed capacity 816 MW (1,094,000 hp)

Nagarjuna Sagar Dam was built across the Krishna river at Nagarjuna Sagar where the river is forming boundary between Nalgonda district of Telangana state and Guntur district of Andhra Pradesh state in India. The construction duration of the dam was between the years of 1955 and 1967. The dam created a water reservoir whose gross storage capacity is 11,472,000,000 cubic metres (4.051×1011 cu ft). The dam is 490 feet (150 m) tall from its deepest foundation and 0.99 miles (1.6 km) long with 26 flood gates which are 42 feet (13 m) wide and 45 feet (14 m) tall.[2] Nagarjuna Sagar was the earliest in the series of large infrastructure projects termed as "modern temples" initiated for achieving the Green Revolution in India. It is also one of the earliest multi-purpose irrigation and hydro-electric projects in India. The dam provides irrigation water to the Prakasam, Guntur, Krishna, Khammam, West Godavari and Nalgonda districts along with hydro electricity generation. Nagarjuna Sagar dam is designed and constructed to utilise up to the last drop of water impounded in its reservoir of 405 TMC gross storage capacity which is the second biggest water reservoir in India.[1]

Foundation stone of Nagarjuna Sagar

History

The proposal to construct a dam to use the excess waters of the Krishna river was planned by the Nizam of Hyderabad and engaged British Engineers in 1903 to irrigate Telangana. Since then, various competing sites in Siddeswaram, Hyderabad and Pulichintala were identified as the most suitable locations for the reservoirs. The perseverance of the Raja Vasireddy Ramagopala Krishna Maheswar Prasad (Raja of Muktyala) and his logistics support paved way for the identification and selection of dam site.[3][4] The dam was built with local know how under the able engineering leadership of K.L. Rao.

Project construction was officially inaugurated by Prime Minister Jawaharlal Nehru on 10 December 1955 and proceeded for the next twelve years. The reservoir water was released into the left and right bank canals by Prime Minister Indira Gandhi in 1967.[4] Construction of the hydropower plant followed, with generation increasing between 1978 and 1985, as additional units came into service. In the year 2015, diamond jubilee celebrations of project's inauguration was celebrated remembering the prosperity the dam has ushered in the region.[5]

The construction of the dam submerged an ancient Buddhist settlement, Nagarjunakonda, which was the capital of the Ikshvaku dynasty in the 1st and 2nd centuries, the successors of the Satavahanas in the Eastern Deccan. Excavations here had yielded 30 Buddhist monasteries, as well as art works and inscriptions of great historical importance. In advance of the reservoir's flooding, monuments were dug up and relocated. Some were moved to Nagarjunakonda, now an island in the middle of the reservoir. Others were moved to the nearby mainland village.[6]

Data

Nagarjuna Sagar right Earth Dam

Effect of the project

The right canal (Jawahar canal) is 203 km (126 mi) long with maximum 311.5 cumecs capacity and irrigates 1.117 million acres (4,520 km2) of land in Guntur and Prakasam districts. The left canal (Lalbahadur Shastri canal) is 179 km (111 mi) long with maximum 311.5 cumecs capacity and irrigates 1.008 million acres (4,080 km2) of land in Nalgonda, Krishna, West Godavari and Khammam districts.[8] The project transformed the economy of above districts. 52 villages were submersed in water and 24000 people were affected. The relocation of the people was completed by 2007.

Aliminati Madhava Reddy lift irrigation canal draws water from the Nagarjuna Sagar reservoir to irrigate 0.37 million acres (1,500 km2) of land in Nalgonda district.[9] This lift scheme also supplies nearly 20 TMC water for the drinking water needs of Hyderabad city. Nearly 80% of the Nagarjuna Sagar water used in Hyderabad city is available for irrigation use in Nalgonda district in the form of regenerated water/treated sewage water. In addition, the high level canal drawing water from the left side shore of the reservoir also supplies irrigation water in Nalgonda district.

Power generation

The hydroelectric plant has a power generation capacity of 815.6 MW with 8 units (1x110 MW+7x100.8 MW). First unit was commissioned on 7 March 1978 and 8th unit on 24 December 1985. The right canal plant has a power generation capacity of 90 megawatts (120,000 hp) with 3 units of 30 megawatts (40,000 hp) each. The left canal plant has a power generation capacity of 60 megawatts (80,000 hp) with 2 units of 30 MW each.[10] The tail pond is under advanced stage of construction to put to use the pumped storage features of 7x100.8 MW units.

Many times, it happens that power generation from the 150 MW canal based units is not optimised when the Nagarjunasagar reservoir is overflowing on its spillway and very less water is required for irrigation from the canals during the monsoon floods. Power generation from canal based hydro units can be optimised by running these units during the flooding period by releasing the water fully into the canals. The unwanted canal water can be released into the natural stream when it is crossing the major stream. Thus run off power can be generated from the water going down unutilised into the river by the canal based power units also.

The water level in the Nagarjunasagar reservoir shall be maintained above the minimum level required for these units in most of the time by releasing water from the upstream Srisailam reservoir to optimise the power generation from the canal based units during dry season.

Tapping dead storage potential

The left and right bank canals sill level is fixed at 490 feet (149 m) MSL to supply irrigation water to two million acres. The unutilized storage capacity is nearly 180 TMC below the canals sill/bed level.[11] Nagarjuna Sagar reservoir also meets the Krishna delta water requirements to the extent of 80 TMC by letting water down stream into the river. Nearly 1.3 million acres (5,300 km2) is irrigated under Krishna Delta Canals. There is a possibility to utilize most of this idle dead storage capacity to store the river flood water further and to use as carry over storage. Nearly 150 TMC idle storage up to 380 feet (116 m) MSL, can be used leaving 30 TMC for silt settlement. This is possible by installing Water Powered Pump[12] (WPP) units at the base of the dam.

WPP units are to be located at the toe of the Nagarjuna Sagar dam with tail water level of 240 feet (73 m) MSL on either side of the river. The WPP units can be connected below 380 feet (116 m) MSL level to the reservoir with the technique called under water reservoir / lake tapping.[13] Under water lake tapping method was implemented successfully in Koyna Hydroelectric Project to install additional hydroelectric units without emptying the Koyna reservoir. The cost would be Rs 15 billion for utilizing 150 TMC storage additionally. If the same storage is created under a new reservoir, it would cost not less than Rs 200 billion. Water can be supplied to high level canals at sill 580 feet (177 m) MSL on both right and left banks without consuming electricity with WPP units to irrigate dry lands further in Nalgonda, Warangal, Khammam, and Guntur districts. As a further cheaper solution to utilise the available dead storage water partially (up to 50 TMC), the existing river chutes available on both sides of the dam at sill level 450 feet (137 m) MSL, can be used for providing water supply to the WPP units without the need of lake tapping.[8] There is no need of lake tapping on the left bank side and the existing river diversion tunnel can be used to supply water to the WPP units for pumping water into Nagarjuna Sagar left canal.

Alternatively, floating/barge mounted pumps can be installed along with associated piping on the reservoir bed to pump water from the reservoir's dead storage into left and right bank canals and the approach channel of the existing pump house of Hyderabad water supply scheme during drought years. During the good monsoon years, when the reservoir water level is above the dead storage level, the same barge mounted pumps can be used regularly to pump water into the existing high level (flood flow) canal (near 16°39′27″N 79°15′43″E / 16.65750°N 79.26194°E / 16.65750; 79.26194) located on the left bank of the reservoir in Nalgonda district. Similarly, during the good monsoon years, a lift irrigation scheme can be taken up with the help of the same barge mounted pumps to lift water from the reservoir (near 16°21′41″N 79°14′31″E / 16.36139°N 79.24194°E / 16.36139; 79.24194) by 45 m height for irrigating nearly 200,000 acres of uplands situated adjacent to the reservoir in Guntur district. Thus all the installed barge mounted mobile pump houses can be used for regular pumping needs to maximise the water use from the reservoir every year.

The minimum draw down level (MDDL) of the river based hydro power units is approximately 125 metres (410 ft) MSL with minimum 50 meters head available for power generation.[11] Through the hydro power units, water can be released into the down stream river / tail pond to further pump into the existing right and left canals by installing pump houses on both sides of the river. Thus nearly 100 TMC of dead storage water available below the canals MDDL (155 metres (509 ft) MSL) can be utilised for irrigation purpose. However the minimum head required for the hydro power units is 75 meters to generate power at grid frequency of 50 Hz. It is technically feasible to generate power by the existing hydro turbines from lower head (75 to 50 meters) at lower frequency and the lower frequency power can be upgraded / converted to normal grid frequency (50 Hz) by installing HVDC converters before feeding power into the grid. The unused converter stations of HVDC Sileru–Barsoor transmission link can be relocated and utilised for this purpose. With minor modifications to the electrical systems of hydro power units, nearly 100 TMC water available in the dead storage of the reservoir can be put to use every year.

The reservoir dead storage water below the 125 m MSL can be released into the downstream river through the existing diversion tunnel which was in use to divert the river flow during the dam construction.[8]

Godavari water transfer via Nagarjuna Sagar left canal

Nagarjuna Left Canal deep cut before entering the gravity tunnel

The Nagarjuna Sagar left canal is presently supplying nearly 130 TMC water for irrigation needs in Telangana and Andhra Pradesh states. This is a contour gravity canal with gradual downward gradient (≃ 1:10,000) along the water flow direction. This canal can be used for transferring nearly 80 TMC Godavari river water into the Nagarjuna Sagar reservoir in addition to supplying the Godavari water under its entire command area. Thus total 210 TMC Godavari water can be used in the Krishna basin of Telangana state from Srisailam and Jurala reservoirs for the new projects with 100% water dependability. Godavari water transferred into Nagarjuna Sagar reservoir/Krishna main river can also be used for the proposed Palamuru lift irrigation and Nakkalagandi lift irrigation schemes in Telangana.

This is possible by re-engineering of the left canal to reverse its water flow direction from the location (near 17°22′13″N 80°21′43″E / 17.37028°N 80.36194°E / 17.37028; 80.36194) where Godavari water would be pumped into this canal. The canal embankments would be raised to facilitate flow reversing towards Nagarjuna Sagar reservoir and intermediate pumping stations (with low head & high flow concrete volute pumps) would be installed near the Paleru balancing reservoir, Pedda Devulapalli balancing reservoir, left canal head regulator on the rim of Nagarjuna Sagar reservoir and the existing major aqueducts across Halia, Musi and Munneru tributaries. The cost of this canal redesigning and the associated pump houses would be one third of a new scheme to transfer Godavari river water into Nagarjuna Sagar reservoir at its FRL 590 feet (180 m) MSL with least possible total pumping head.[14] The above re-engineering of the canal is similar to modifications carried out to reverse the water flow of ancient Grand canal under Eastern Route project of South to North Water Transfer in China.[15]

See also

References

External links

Media related to Nagarjuna Sagar Dam at Wikimedia Commons

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