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
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 11.56×10^9 m3 (9×10^6 acre·ft)
(408 Tmcft)
Active capacity 5.44×10^9 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
Operator(s) TSGENCO
Commission date 1978-1985
Turbines 1 x 110 MW Francis turbine, 7 x 100.8 MW 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 forms the boundary between Nalgonda District in Telangana and Guntur district in Andhra Pradesh states 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 billion cubic metres (405.1×10^9 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]

History

The perseverance and logistics support of Raja Vasireddy Ramagopala Krishna Maheswar Prasad paved the way for the construction of the Nagarjuna Sagar project. He came to know that the Government of Madras Presidency had made plans to divert water from the Krishna river to Madras by linking the Krishna and Pennar rivers. He embarked upon a tour of nine districts of Andhra Pradesh and visited each and every village to collect the signatures of people in favour of the Nagarjuna Sagar Dam project. He traveled through the thick and inhospitable jungles near Macherla to visit the site of Nandikonda and formed a team of retired engineers at his own expense to make the project plans and designs. The government of Madras tried to scuttle his plans, but the Raja established the 'Krishna Farmers Welfare Society' and exerted pressure on the Government of India in favour of the Nagarjuna Sagar Dam. The Government of India instituted the Khosla Committee but the committee refused to visit the site on the excuse that there was no motorable road to Nandikonda. The Raja gathered villagers and volunteers from twenty five villages and made a road by labouring day and night for a week at his own expense. The Khosla committee visited the site and found it to be the most ideal location to build a gigantic dam across the river.

Foundation stone of Nagarjuna Sagar

There were attempts to suppress the report of the Khosla committee. The Raja went to New Delhi and with the support of N. G. Ranga, Moturi Hanumantha Rao and Kotha Raghuramaiah resurrected the report, distributed it to important people and urged the Planning Commission (Government of India) to take cognizance.

The Raja made a matching grant of fifty two lakh Rupees (one hundred million British Pounds) and several thousand acres of ancestral land for the construction of the dam. The dam was built with local know how under the able engineering leadership of K.L. Rao a member of parliament from Vijayawada constituency.

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.[3] 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.[4]

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 called Anupu.[5]

Data

Nagarjuna Sagar right Earth Dam

Tourism

Nagarjunasagar Dam is one of the popular weekend getaways from Hyderabad. Thousands of tourists visit Nagarjunasagar when the dam gates are open in monsoon season (around September / October). Hotel Vijay Vihar, operated by Telangana Tourism is one of the best places for accommodation in Nagarjunasagar.[7]

There are several other places around Nagarjunasagar that can be visited as a one-day trip from Hyderabad.

Effect of the project

Irrigation

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. 54 villages (48 in Nalgonda and 6 in Guntur) were submersed in water and 24000 people were affected. The relocation of the people was completed by 2007.

Alimineti 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 with pump house located near Puttamgandi village on the left bank of Krishna river also supplies nearly 20 TMC water for the drinking water needs of Hyderabad city.[10][11] 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 flood flow 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.[12] The tail pond is under advanced stage of construction to put to use the pumped storage features of 7 x 100.8 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.

Environmental aspects

The artificial lift irrigation based diversion of the river from its natural delta area into Nalgonda district caused erosion of the Florine rich volcanic rocks in Nalgonda and contaminated its ground water supply. It also caused uncertain flows of water into the Krishna river delta area and a shrinkage of the natural wonder "The Kolleru Lake".[13] The use of erosion resistant canals interfered with the natural silting process of a river to the deltas and created long term ecological issues to the health of the delta lands. Reduced flows into the sea resulted in land salination and sea encroachment of coastal lands in Diviseema. The diversion of Krishna water for 200 km to Hyderabad resulted in massive evaporation losses especially in summer and reduced the size of Krishna river. The river water needs to be lifted 1600 ft above its natural flow for it to reach Hyderabad, power consumption that is unjustifiable given that there are cheaper ways to get water to Hydearabad. Nagarjuna sagar, Srisailam, Almati and Ujjani dams together successfully halted the flow of Krishna River before it reaches the delta and is good case study of how to kill a mighty river with poor environmental oversight - the fourth largest in the country. Hamsaladeevi the point where Krishna used to meet the ocean does not have Hamsalu (swan) and the Deevi (island) will merge into the ocean in the next decade. Desertification of various flood plains is already recorded. Many forest preserves along the natural Krishna flow are now categorized as "completely degraded" forest areas. Krishna river once home to an ecological wonderland of fresh water fish and aquatic population is now completely depopulated. The river stopped being navigable since the year of Nagarjuna sagar construction. The death of river Krishna is now a matter of time.

Impact on Hyderabad water security

Water planning for Hyderabad city started in 1920 with the tapping of Musi river for 15 Mgd. It progressed to tapping Esi (Himayat Sagar 1927 - 11mgd) and Manjira (1965 - 1993 - Majira and Singur dams) for another additional 130 Mgd. It took a huge leap during 1995 - 2004 with the commissioning of Krishna river water project (Phases I - III) at a total cost of over ten thousand crores to supply an additional 190Mgd to Hyderabad from Nagarjuna sagar away from the Krishna Delta and the Kolleru lake.[14] The project incurs an additional evaporation and leakage loss of 64 Mgd. About 30% of the water naturally flowing to Krishna Delta before 1995 is now diverted to Hyderabad.

Future potential

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.[15] 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[16] (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.[17] 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. This option is best suitable for feeding the right canal as it is not consuming any power for pumping water and some water is to be released for Krishna delta needs by AP state.

There is a cheaper possibility to pump water into the left canal when the reservoir water is below its sill level 490 feet (149 m) MSL by using the reversible turbines (7 x 100 MW) of existing hydro power station on the left bank of the river. Water would be released into the down stream tail pond through the hydro power station or the existing diversion tunnel. When water is to be pumped into the left canal, the water released into the downstream tail pond is pumped back into a contour canal which connects the hydro power station and the left canal intake point.[15] This contour canal is nearly 10 km long and located inside the Nagarjunasagar reservoir area situated at 510 feet (155 m) MSL. Only three units of the reversible turbines are required to feed nearly 12,000 cusecs water to the left canal at its MDDL level and rest of four reversible units can be used for power generation by releasing water into the tail pond. The pen-stock inlets of the three unit at 125 metres (410 ft) MSL are to be connected with the extension piping (4.8 m diameter) to feed the contour canal at 510 ft MSL. The extension piping is disconnected when water pumping to left canal is not required to restore the hydro power units normal working. When reservoir level is at its FRL level, the canal and the extension piping get submerged under water without undergoing any damage as the contour canal is away from the spillway of the dam or flood flow path. Thus both Telangana and AP states can use the reservoir dead storage water fully to ensure water supply for the command area under the left canal even during drought years.

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 (Flood flow canal)) 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 (Proposed lift scheme)) 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.

Another option is to separate a small portion of the reservoir by constructing a weir up to 510 feet (155 m) MSL along with an underground pumping station at 16°37′21″N 79°16′01″E / 16.62250°N 79.26694°E / 16.62250; 79.26694 (Underground pumping station) to maintain gravity flow to the left bank canal side from the lower level dead storage water of the main reservoir. When the reservoir water level is above 510 ft MSL, the weir would get submerged and water flows to left canal without any pumping as usual.

One more option is to use water transferred from Srisailam reservoir by the SRLBC tunnel to Akkampalli balancing reservoir for feeding NS left canal when the dead storage water is being used for the NS right bank needs. Water would be released downstream from the Akkampalli reservoir and picked up by a 6 km long feeder canal from a diversion weir at 16°45′11″N 79°14′01″E / 16.75306°N 79.23361°E / 16.75306; 79.23361 (Diversion weir at Battugudam) to feed into the NS left canal near Alwala. NS left bank side flood flow canal can also be supplied water by gravity from the Srisailam reservoir in a similar way when NS reservoir water level falls below the full supply level of the flood flow canal.

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.[15] 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.[18] 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]

Assured water supply to Hyderabad city

At present nearly one Tmcft per month or 250 million gallons per day or 350 cusecs is supplied to the Hyderabad city from Nagarjuna Sagar (NS) reservoir.[19] The water supply is nearly 50% of the total city water requirement . This water pumping scheme is part of Alimineti Madhava Reddy lift irrigation project with its foreshore pumping station at Puttamgandi which has nearly 2400 cusecs pumping capacity.[20] The water supply to the Hyderabad city is nearly 15% of its total capacity. The approach channel from the reservoir to the Puttamgandi pump house (PH) is located at 16°34′31″N 79°07′51″E / 16.57528°N 79.13083°E / 16.57528; 79.13083 (Puttangadi PH approach channel) where the Bhimanapalli Vagu tributary is joining the Krishna river.[21] The minimum draw down level (MDDL) of the PH is 502 feet (153 m) MSL below which water can not be pumped from NS reservoir.[22] The reliability / dependability of the PH for supplying assured water supply to Hyderabad city, is not adequate due to meagre inflows into the NS reservoir in some years and the need to deplete the NS reservoir water below 502 ft MSL for other purposes. In these circumstances, adequate water is to be stored above the 502 ft MSL to maintain 100% assured water source without depending totally on NS reservoir.[23]

This is possible by constructing a balancing reservoir by separating some area of the NS reservoir with a new dam across the Bhimanapalli Vagu tributary at 16°34′33″N 79°06′53″E / 16.57583°N 79.11472°E / 16.57583; 79.11472 (Proposed dam location) just upstream of the Puttamgandi PH approach channel. This new dam with FRL 590 feet (180 m) MSL, would not submerge any additional area other than the area already submerged by the NS reservoir. The water inflows from the Bhimanapalli Vagu tributary joining the NS reservoir are first impounded by the new dam and if found excess over flows into the downstream NS reservoir. This new balancing reservoir's live capacity is nearly 6 Tmcft above the 502 ft MDDL which is equal to six months water supply to the Hyderabad city. This reservoir would have provision to receive water from the Puttamgandi PH when inflows from the Bhimanapalli Vagu tributary is not satisfactory and water is at adequate level in NS reservoir during monsoon months. When water level of NS reservoir goes below the 502 ft MSL, water is fed to the Puttamgandi PH approach channel from the new balancing reservoir for pumping water needs of Hyderabad city. The cost of this new dam project would be nearly 1.5 billion rupees only which will provide 100% assured water supply to the Hyderabad city without depending on the water availability from NS reservoir during the non monsoon months and drought years.[23]

See also

References

  1. 1 2 "India: National Register of Large Dams 2009" (PDF). Central Water Commission. Retrieved 7 August 2011.
  2. ↑ "Nagarjunasagar". Archived from the original on 2007-01-24. Retrieved 2007-01-25.
  3. ↑ The Hindu : Magazine / Focus : Taming the Krishna
  4. ↑ "Nagarjuna Sagar dam completed 60 years". Retrieved 11 December 2015.
  5. ↑ "Nagarjunakonda". Retrieved 2007-01-25.
  6. ↑ Brief Profile of Nagarjuna Sagar Dam
  7. ↑ Nagarjuna Sagar Travel Guide
  8. 1 2 3 "Nagarjuna Sagar project". Retrieved 22 September 2015.
  9. ↑ "Aliminati Madhava Reddy Project (AMRP)". Retrieved 22 September 2015.
  10. ↑ "Expert suggests for full use of Puttamgandi pump house for Dindi project". Retrieved 22 April 2016.
  11. ↑ "Pumping station proposal in doldrums over funding delay". Retrieved 22 September 2015.
  12. ↑ Andhra Pradesh Hydel Power plants
  13. ↑ . The Hindu. The Hindu http://www.thehindu.com/news/national/andhra-pradesh/worries-grow-as-kolleru-shrinks/article8235423.ece. Missing or empty |title= (help)
  14. ↑ Provisioning of Drinking water to Hyderabad. JNU University Press. p. 155.
  15. 1 2 3 "Technical data of Nagarjunasagar dam" (PDF). Retrieved 22 September 2015.
  16. ↑ Nagarjuna Sagar Water Powered pump (WPP) Units
  17. ↑ Lake tap
  18. ↑ "Converting to full - power". Retrieved 22 December 2016.
  19. ↑ "Water to be Pumped From Dead Storage Level". Retrieved 22 April 2016.
  20. ↑ "Alimineti Project Fourth Pump Commissioned)". Retrieved 22 September 2015.
  21. ↑ "Krishna Middle Sub-Basin map" (PDF). Retrieved 22 April 2016.
  22. ↑ "AP, Telangana staring at severe water crisis". Retrieved 29 April 2016.
  23. 1 2 "Water level in Prakasam Barrage head pond dips to half". Retrieved 29 April 2016.

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