The dam was constructed in a deep gorge in the Nallamala Hills in between Nandyal and Nagarkurnool districts, 300m (980ft) above sea level. It is 512m (1,680ft) long, 145 metres (476ft) maximum height and has 12 radial crest gates. It has a reservoir of 616 square kilometres (238sqmi). The project has an estimated live capacity to hold 178.74 Tmcft at its full reservoir level of 885 feet (270m)MSL. Its gross storage capacity is 6.116 cubic km (216 tmc ft). The minimum draw-down level (MDDL) of the reservoir is at 705 feet (215m) MSL from its river sluice gates, and corresponding dead storage is 3.42 Tmcft.[4] The left bank underground power station houses 6 × 150 megawatts (200,000hp) reversible Francis-pump turbines for pumped-storage operation (each turbine can pump 200 cumecs) and the right bank semi-underground power station houses 7 × 110 megawatts (150,000hp) Francis-turbine generators.
Tail pond dam/weir located 14km downstream of Srisailam dam is under advanced stage of construction to hold the water released by the hydro turbines and later pump back into the Srisailam reservoir by operating the turbines in pump mode.[5] The weir portion got breached in November 2015 unable to withstand the normal water release from the hydropower stations.[6] Tail pond weir was completed during the year 2017 and pumping mode operation is being done even when the downstream Nagarjuna Sagar reservoir water level is below 531.5 feet (162m) MSL. The tail pond has nearly 1 tmcft live storage capacity.[7]
History
The Srisailam project began in 1960, Initially only as a power project. After several delays, the main dam was finally completed twenty years later in 1980 July 26. [citation needed] In the meantime the project was converted into a multipurpose facility with a generating capacity of 770 megawatts (1,030,000hp) by its second stage which was completed in 1987. [citation needed] The dam is to provide water for an estimated 2,000 square kilometres (770sqmi). Under the right bank branch canal 790 square kilometres (310sqmi) in Kurnool and Kadapa districts will have assured irrigation. From the initial modest estimate of ₹38.47 crore for a power project the total cost of the multipurpose project was estimated to cross ₹1000 crore in its enlarged form. The dam has alone cost ₹404 crore together with the installation of four generating sets of 110 MW each. The right bank branch canal is estimated to cost ₹449 crore and the initial investment of ₹140 crore has been provided by the World Bank. The projected cost-benefit ratio of the project has been worked out at 1:1.91 at 10% interest on capital outlay.[citation needed]. In 1998 a coffer dam was over topped by flooding. The power house required repairs and did not generate power for a year. On 2 October 2009, Srisailam dam experienced a record inflow which threatened the dam.[8] It was built under the engineering leadership of Kanuri Lakshmana Rao.
Srisailam left bank canal will receive water by gravity through tunnels to irrigate lands in Nalgonda district. Tunnel work is not complete and the required water has been provided to most of the project area by lifting water from the downstream Nagarjuna Sagar reservoir.
Dam Maintenance and Safety
Systematic Neglect and absence of diversion of funds is evident in maintenance of the dam and lack of any modernization attempts of the Powerhouse. The officers report a shortage of maintenance staff.[11]
Safety concerns to the 2nd largest Hydroelectric project in the country have been raised over the years[12][13] and have been assessed false subsequently.[14] In 2009, the dam, designed for a maximum flood of 19 lakh cusecs, endured a flood of 25.5 lakh cusecs. According to a survey conducted in the summer of 2018, the scouring resulted in the formation of a huge pit in the apron downstream the dam. And a structure protecting the ‘toe’ and foundation of the main dam has weakened. Efforts are not yet made to repair and maintain the dam.[15]
Power generation optimization
At present, the initial inflows into Srisailam reservoir are stored excessively without being used for power generation. The flood water fills the remaining empty Srisailam reservoir quickly and most of the flood water overflows into the downstream Nagarjunasagar reservoir without being used for power generation.[16] The endeavor shall be to fill the Nagarjuna Sagar reservoir fully with the uniform water released through the power generating units.
The existing right bank power station (770 MW) can be converted into pumped storage hydroelectric power (PSHP) to operate in pumping mode when the downstream Nagarjuna Sagar reservoir level is above 560 feet (171m) MSL. The PSHP can be used for energy storage purposes on daily basis and to transfer Godavari water to the Srisailam reservoir during drought years. Alternately, the tunnel of the existing power station can be used for a new PSHP station to pump water from the Nagarjuna Sagar reservoir to the Srisailam reservoir.
This article uses material from the Wikipedia article Srisailam_Project, and is written by contributors.
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