Nagarjunasagar-Somasila Link

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Krishna (Nagarjunasagar) – Pennar (Somasila) Link project envisages diversion of 12146 Mm3 of water from Nagarjunasagar, part of it (8167 Mm3) through the link canal and the balance through the existing Nagarjunasagar Right Bank Canal (NSRBC). Krishna (Nagarjunasagar) - Pennar (Somasila) link canal (N-S link) taking off from the Nagarjunasagar reservoir is proposed as a contour canal running for a total length of 393.02 km before it tails into the Somasila reservoir on the Pennar river. It is proposed to run parallel and adjacent to the existing NSRBC on its right for the initial 202.75 km, at the end of which the NSRBC is proposed to amalgamate into the link canal. Thereafter the link canal runs as a single canal upto the Somasila reservoir. The proposed link canal is designed to discharge 488 cumec at head, 565 cumec at RD 202.75 km and 498 cumec at the tail end. Out of the 3979 Mm3 diverted through NSRBC, 2356 Mm3 would be to meet part demand of the existing command area of NSRBC. The remaining part of the demand (1623 Mm3) is proposed to be met from the Godavari (Inchampalli) - Krishna (Pulichintala) link canal.

The Project comprises of the following components:

  • The existing storage reservoir at Nagarjunasagar across the Krishna with FRL 179.83 m, gross storage capacity of 11560 Mm3, live storage capacity of 5733 Mm3 and minimum draw down level of 155.45 m;
  • The existing 202.75 km long Nagarjunasagar Right Bank Canal (NSRBC);
  • The proposed 393.02 km long link canal taking off from the Nagarjunasagar reservoir which runs parallel and adjacent to the existing NSRBC on its right side to a distance of 202.75 km.
  • Existing Nagarjunasagar Right Bank Canal head regulator, power block and power house of installed capacity 3×30 MW.
  • Proposed head regulator, power block and powerhouse of installed capacity 3×30 MW and one standby unit (30MW) for the link canal.
  • The existing Somasila reservoir across the Pennar river with FRL of 100.58 m, gross storage capacity of 2208 Mm3 and live storage capacity of 1994 Mm3. The MDDL of the reservoir is 82.30 m.

The total requirement of NSRBC is 3979 Mm3, out of which part requirement of 1623 Mm3 will be provided through the proposed Pulichintala Right Bank Canal which is proposed to be brought through Godavari (Inchampalli) – Krishna (Pulichintala) link canal. The balance requirement of 2356 Mm3 (3979 - 1623) will be met from the diverted water through NSRBC. As the existing NSRBC was designed to carry 3979 Mm3 of water annually, it is proposed to divert 3979 Mm3 through this canal as against the balance requirement of 2356 Mm3 under this canal. After meeting the balance requirement of 2356 Mm3 under NSRBC, it is proposed to transfer the remaining quantity of 1623 Mm3 (3979 - 2356) to the link canal at the tail end of NSRBC at RD 202.75 km. Thereafter, the Krishna (Nagarjunasagar) - Pennar (Somasila) link canal will carry 9790 Mm3 (8167 + 1623) from RD 202.75 km and will tail off into Somasila reservoir at RD 393.02 km with FSL 101.102 m. It is envisaged that enroute, the Nagarjunasagar – Somasila link canal will provide irrigation to a culturable command area of 168017 ha utilizing 908 Mm3 of water besides providing 124 Mm3 of water for meeting domestic and industrial requirements. The link canal powerhouse with an installed capacity of 90 MW will generate 377 million units of power annually on the average.

The link canal traverses through Guntur, Nellore and Prakasam districts of Andhra Pradesh passing through the river basins of Krishna, Gundlakamma, Streams between Gundlakamma and Pennar, and Pennar. The existing reservoirs at Nagarjunasagar, at the off take point, and Somasila, at the tail end, are proposed to be utilised for the intended diversion, without any change in their storage capacities. The monthly simulation studies of the Nagarjunasagar reservoir carried out shows that the quantity of 12146 Mm3 of water could be diverted annually at a success rate of 80%.

The link canal will provide irrigation to an area of 168017 ha in the districts of Prakasam and Nellore. Apart from irrigation, it is also proposed to provide for future domestic and industrial water requirements in the command area. Additional domestic and industrial requirements, projected to 2050 AD, are estimated to be 55 Mm3 and 69 Mm3 respectively.

Transmission loss in the link canal is estimated to be 332 Mm3. It is envisaged that after meeting the above requirements, a quantum of 8426 Mm3 would be finally transferred to the Somasila reservoir. The link project envisages construction of a canal head powerhouse at the head of the link canal. The powerhouse will have an installed capacity of 90 MW with three units of 30 MW each and one standby unit of the same capacity. The link canal is designed as a lined canal with trapezoidal shape. The maximum carrying capacity of the canal is 565 cumecs with corresponding cross section of 67.5 m of bed width and 6m of full supply depth. In the initial reaches the link canal passes through a tunnel of 1.265 km length. The canal passes mostly through agricultural fields except for a few minor reaches through forest area.

As no new reservoir or additional storage is envisaged in this proposal, any adverse environmental impact is not anticipated. Suitable provision under R&R component to take care of the proposed measures of rehabilitation due to alignment of link canal has been made in the estimate for construction of the link canal. Direct benefits per annum from the link project due to irrigation, domestic and industrial water supplies are estimated to be Rs. 18529 lakh.

The capital cost of the link canal is estimated to be Rs. 632054 lakh at 1998-99 price level. Based on the quantity of water consumed enroute the link canal, apportioned capital cost is worked out to be Rs. 88061 lakhs and the annual cost to be Rs. 9938 lakh. The Benefit Cost Ratio works out to 1.86. The B.C. ratio may undergo a change if the cost of transferring surplus waters from the upstream link canals is also considered.

Source:National Water Development Agency (NWDA)

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