As Sikkim picks up pieces, Teesta-III reservoir, opening of its gates under lens

Sikkim Urja Limited, the company that developed and ran Teesta-III, is scrambling for damage control mode. On Saturday, it announced a financial relief package of Rs 70 crore for four GLOF-affected districts. This package, tweeted Tamang, was in addition to the relief aid provided by the state.

As reported by The Indian Express on Friday, the Rs 13,965-crore project has a history of dodgy compromises. This includes an allocation of only Rs 2 crore, pointed out the CAG back in 2009, towards its mandatory disaster management plan.

The GLOF warning, it is learnt, came from the ITBP between 12-40 and 1 am on October 4. While this gave time to move people away from the river in Chungthang before the waters reached the village, efforts to open the dam’s spillways apparently did not succeed.

Sources said a team of staff members of the Teesta-III project reached the dam site to open the spillways but were daunted by the rapidly rising waters. This has raised questions about dam maintenance since spillways are electronically controlled and are not supposed to require manual intervention.

“A dam of this size does not involve mechanical spillways. At roughly 15 meters per second, the flood must have taken over an hour to reach the dam site from the lake and around half an hour from the flood monitoring station at Lachen. That’s enough time to operate the gates through remote control unless the spillways were damaged or stuck for some reason,” said an engineer with the Central Water Commission (CWC).

Sunil Saraogi, the executive chairman of Sikkim Urja Limited, confirmed that Teesta-III’s spillways were indeed operated electronically. “We have been hearing a lot of things in the last few days but I will be able to verify only when communications are restored,” he said.

Investigators are also likely to probe if Teesta-III was operating above its capacity on October 3. “If it was so, the dam’s storage was probably full. That would have left no space to absorb the initial impact of the flood but could have made it a lot worse by contributing the additional water,” said an SDMA official.

Saraogi could not confirm the dam’s storage status when the GLOF hit. Teesta-III had a gross storage capacity of 5.08 million cubic meters and a live storage capacity of 3.3 million cubic meters.

The combined discharge of storage water and GLOF from Teesta-III hit NHPC’s 510 MW Teesta-V – Teesta IV is at the proposal stage — and the under-construction 500 MW Teesta-VI downstream in about an hour, causing extensive damage, and washing all the bridges in its way.

The GLOF overtopped the Teesta-V dam, obliterating the approach road and the control room for remote operation, knocking down multiple transmission towers and drowning the power station where one casualty was reported. All connecting roads to the project site and parts of the residential colony were severely damaged.

The GLOF, subsequently, disrupted ongoing works at Teesta-VI where flood water entered the powerhouse and the transformer cavern, washing out bridges connecting the right and left banks at the barrage as well as the powerhouse.

A former NHPC official familiar with the developments underlined how Teesta-V’s concrete dam, with spillways of 12,500 cumec, withstood the overtopping. “In contrast, with spillways of just 70,00 cumec, the concrete-face rock-filled dam of Teesta-III was unlikely to survive the impact of this 8-10,000 cumec GLOF that also carried massive boulders. But opening the gates and emptying the reservoir in time could have reduced the damage downstream,” he said.

Himanshu Thakkar, coordinator of the South Asia Network on Dams, Rivers and People, said that the Teesta-III dam was not included in the CWC’s National Register of Large Dams (NRLD). “Commissioned in 2017, it is inexplicably missing in the NRLD compiled in 2019. There is no information on the Dam Safety Mechanism of Teesta-III and the last inspection of the dam and its spillway gates,” he said.