Nagarjuna Sagar Dam
Nagarjuna Sagar Dam is a masonry dam across the Krishna River at Nagarjuna Sagar which straddles the border between Nalgonda district in Telangana and Palnadu district in Andhra Pradesh. The dam provides irrigation water to the Nalgonda, Suryapet, Krishna, Khammam, West Godavari, Guntur, and Prakasam districts along with electricity generation. Constructed between 1955 and 1967, the dam created a water reservoir with gross storage capacity of . The dam is tall from its deepest foundation and long with 26 flood gates which are wide and tall. It is jointly operated by Andhra Pradesh and Telangana. Nagarjuna Sagar Dam  was the earliest in a 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 hydroelectric projects in India. History. The Nizam made the British engineers begin the survey work for this dam across the Krishna River in the year 1903. The project's construction was officially inaugurated by Prime Minister Jawaharlal Nehru on 10 December 1955 and proceeded for the next twelve years. Raja Vasireddy Ramagopala Krishna Maheswara Prasad, popularly known as late Muktyala Raja, was instrumental in the construction of  the Nagarjuna Sagar Dam through active political lobbying and the donation of crores of rupees (fifty-two lakhs in those day's money) and fifty-five thousand acres of land. It was the tallest masonry dam in the world at that time, built entirely with local know-how under the engineering leadership of Kanuri Lakshmana Rao. The reservoir water was released into the left and right bank canals by Prime Minister Indira Gandhi on August 4, 1967. Construction of the hydroelectric power plant followed, with power generation increasing between 1978 and 1985 as additional units came into service. In 2015 , diamond jubilee celebrations of project's inauguration were held, alluding to the prosperity the dam has ushered into the region. 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 and the successors of the Satavahanas in the Eastern Deccan. Excavations there yielded 30 Buddhist monasteries as well as artwork and inscriptions of historical importance. Prior to 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 of Anupu. Utilisation. Irrigation. The right canal (Jawahar canal) is long with maximum 311.5 cumecs capacity and irrigates of land in Guntur and Prakasam districts. The left canal (Lalbahadur Shastri canal) is long with maximum 311.5 cumecs capacity and irrigates of land in Nalgonda, Suryapet, Krishna, West Godavari and Khamman districts. The project transformed the economy of above districts. 54 villages (48 in Nalgonda and 6 in Guntur) were submersed in water and 24,000 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 of land in Nalgonda district. 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. 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 with 3 units of each. The left canal plant has a power generation capacity of with 2 units of 30 MW each. The tail pond is under advanced stage of construction to put to use the pumped storage features of 7 x 100.8 MW units. And it will be useful for the irrigation 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. 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. There are several other places around Nagarjunasagar that can be visited  as a one-day trip from Hyderabad. Environmental aspects. The artificial lift irrigation based diversion of the river from its natural delta area into Nalgonda district caused erosion of the fluorine-rich volcanic rocks in Nalgonda and contaminated its groundwater supply. It also caused uncertain flows of water into the Krishna river delta area and a shrinkage of the natural wonder "The Kolleru Lake". 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. 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. 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. 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 MSL to supply irrigation water to two million acres. The unutilized storage capacity is nearly 180 TMC below the canals sill/bed level. 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 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 MSL, can be used leaving 30 TMC for silt settlement. This is possible by installing Water Powered Pump (WPP) units at the base of the dam. 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. The sill level of the right bank canal power house (3 x 30 MW) is at MSL. It is possible to draw water from the dead storage by tapping water from the penstocks to feed water to  a pump house (3 x 15 MW) located on the left side of the power house. The pump house will have three pump sets each of 5000 cusecs flow capacity to feed into the NS main right bank canal. Power generation from the 90 MW power house is no way affected since its units can only operate when reservoir level is above 540 ft MSL and the pumping units need to operate below the 508 ft MSL to draw water from the dead storage. Thus nearly 50 TMC water can be utilized during the drought years. The power generation units  are normally in operation for five months in a year when the water level is above its minimum draw down level at MSL. During the drought years, the additional water availability is more valuable than the pumping power consumption. The consumed pumping power is compensated fully by the enhanced generation from the 44 MW capacity mini hydel plants located on the downstream canals. Pumped storage hydro power potential. Nagarjuna Sagar reservoir, serving as low level reservoir, has potential to install nearly 2,18,000 MW high head pumped storage hydroelectric plants on its right side. 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. 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. 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 where the Bhimanapalli Vagu tributary is  joining the Krishna river. The minimum draw down level (MDDL) of the PH is MSL below which water can not be pumped from NS reservoir. 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. 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 just upstream of the Puttamgandi PH approach channel. This new dam with FRL 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. Godavari water transfer via Nagarjuna Sagar left canal to Krishna river. The Nagarjuna Sagar left canal supplies nearly 130 TMC of 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 a total of  210 TMC of 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 the Nagarjuna Sagar reservoir and 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 ) 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 MSL with least possible total pumping head. 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.