Expert panel clears plan to rebuild washed away Teesta dam in Sikkim

Expert committee recommends reconstructing Teesta-3 dam in Sikkim with stronger concrete structure and improved early warning system.

Fourteen months after a devastating glacier lake outburst flood in Sikkim washed away the Teesta-3 dam — the State’s biggest hydropower project — and killing at least 100, an expert committee of the Environment Ministry has recommended that the dam be reconstructed.

Instead of the older structure that was part rock and part concrete, the new dam will be entirely concrete — reportedly to increase its strength — and its spillway will be capable of managing a peak flow of 19,946 cubic metres a second (cumecs), thrice the capacity of the former dam, which was 7000 cumecs.

The project developers, Sikkim Urja Limited (SUL), have also been asked to implement an early warning system in the upper catchment, such that in case of a flood, the gates of the dam can be opened well in time.

A major cause for the “overtopping” (dam breach) was that the flood gates could not be opened in time and this led to a deluge of water, debris and muck. “Had this been possible, even the previous rock-concrete dam would have survived. There would have been flooding but it couldn’t have been this bad,” a government official aware of proceedings told The Hindu. “The Teesta project was a successful one and commercially viable. The power equipment (to generate electricity) was found largely intact and so there was a strong case for commissioning it again, but with a stronger structure and an improved early alert system.” He said there was no proposal to abandon the project in the aftermath of the accident.

A pure concrete and concrete-rock structure had their own inherent advantages but “cost” also played a significant part, the person added. The new design incorporated a “worst-case scenario” — meaning the maximum possible rain in the upstream glacier lake, modelled by the India Meteorological Department, in the South Lhonak region over the next 100 years influencing further downstream modifications.

“To enhance the safety of the personnel working during project operations, SUL has plans to shift the dam control room to a higher elevation. Further, SUL will implement an early warning system in the upper catchment which gives sufficient time to shift the working manpower from the dam site and safely operate and open all dam gates in the event of a flood,” says the expert committee recommendation report.

The additional costs of restoring the dam is estimated to be ₹4,189 crore. The project cost in 2017, when the project was commissioned, was ₹13,965 crore.