In 1999, to ensure uninterrupted power from the 1,960 MW hydro-electric project at Koyna dam, the state government commissioned and built an underground tunnel to augment water supplies. Now, nearly eight years later, the time has come to think of the future and take correctives — extend the tunnel by another 4.5 km.
The reason: With requirements for irrigation constantly on the rise, stage IV of Koyna dam that generates 1,000 MW may have to be shut down during the peak summer months of March to May if water is diverted for farming.
‘‘So, we are extending the tunnel and will be opting for a second ‘lake tapping (the reservoir is tapped to bring in more water through underground tunnels)’ in May 2007. This is to protect power generation between March and May,’’ Koyna project executive engineer V M Soman said as he stood inside the 4.5km tunnel, almost 80 metre below ground level.
With changes in the State’s water management policy, Koyna reservoir that used to cater to the western parts will now also irrigate the eastern parts. ‘‘This means the reservoir will deplete faster. By March, stage IV will be exposed and we will be left with no option but to make it dysfunctional till May,’’ he said.
The State is already reeling under a severe power crisis with a shortfall of nearly 4,000 MW. The Koyna dam that has a total capacity of 98.78 TMC (thousand million cubic feet) uses 67.5 TMC for power generation and the rest for irrigation.
So tapping the reservoir at a lower level will lead to an additional 20 TMC of water which could be used for irrigation. ‘‘However, the total water available for power generation — 67.5 TMC — will remain the same,’’ Soman said while on an 8km boat ride from the base of the dam to the tunnel construction site.
The Rs 500 cr project envisaged in 2000 was to go on stream by this year. ‘‘There were some delays, but the drip irrigation projects for which the demand is envisaged will take a few years. We are working in advance to tackle the situation,’’ Soman said.
While the State will construct nearly 1-km stretch of the tunnel, Hyderabad-based Soma Enterprises has been awarded the Rs 176.1-crore project for the remaining 3.5-km stretch. ‘‘We are on target and 90 per cent of the work is complete. Our job will be ready by September,’’ Soma Enterprises director Ankineedu Maganti said.
The tunnel
The Koyna dam tunnel is being extended to augment water supplies and ensure uninterrupted power supply. The tunnel:
* will cost Rs 500 cr
* is 80-mt below ground, 4.5 km long
* in the shape of a horseshoe with 9.5 mt diameter
* has a totally concrete structure, with a discharge carrying capacity of 260 million cubic per second
Dam strengthening
The second phase of strengthening of the Koyna dam that commenced on October 15, 2005, is expected to be completed by May 31. As reported by Pune Newsline on in October 2005, Hyderabad-based Soma Enterprises in a joint venture with a Russian firm is strengthening the portion of the dam that’s above ground and working to stabilise the river basin so that it becomes more sturdy and is safe from quakes. Once the work is over, the dam will be able to withstand earthquakes up to a magnitude of 6.9 on the Richter scale.