Nagarjuna Sagar Dam

Nagarjuna Sagar Dam is a masonry dam on the Krishna River at Nagarjuna Sagar in the border of Guntur and Nalgonda districts of Andhra Pradesh. The construction duration of the dam was between the years of 1955 and 1967. The dam created a water reservoir whose capacity is 11,472 million cubic metres. The dam is 490 ft (150 m). tall and 1.6 km long with 26 gates which are 42 ft (13 m). wide and 45 ft (14 m). tall. Nagarjuna Sagar was the earliest in the series of large infrastructure projects initiated for the Green Revolution in India; it also is one of the earliest multi-purpose irrigation and hydro-electric projects in India. The dam provides irrigation water to the Nalgonda, Prakasam, Khammam, Krishna and Guntur districts along with electric power to the national grid.

The proposal to construct a dam to use the excess waters of the Krishna river was planned by the British Engineers in 1903 on the supervision of Hyderabad Nizams. 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 of Muktyala paved way for the site identification, design and construction of the dam. Nagarjunasagar was the earliest in the series of "modern temples" taken up to usher in the Green Revolution in India.

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. Construction of the hydropower plant followed, with generation increasing between 1978 and 1985, as additional units came into service.

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 Nagarjuna's Hill, now an island in the middle of the reservoir. Others were moved to the mainland.

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 MW with 3 units of 30 MW each. The left canal plant has a power generation capacity of 60 MW 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 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 in to the canals. The unwanted canal water can be released in to the natural stream when it is crossing the major stream. Thus run off power can be generated from the water going down unutilised in to the river by the canal based power units also.

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.