Shadow from fallen Sikkim dam falls on India’s hydroelectric projects in Bhutan

Shadow from fallen Sikkim dam falls on India’s hydroelectric projects in Bhutan

Sikkim’s highest dam was washed away during flash floods, raising doubts about hydropower projects being developed, now with design changes, by the country, abroad

The Chungthang dam of Sikkim Urja Limited’s 1,200 MW Teesta-III hydroelectric project on river Teesta gave way on October 4, contributing to the death of at least 94 people in the downstream areas of Sikkim and West Bengal. The devastation has refreshed worries over two of three India-assisted, under-construction mega hydropower projects in Bhutan — the 1,200 MW Punatsangchhu Stage-I (Puna-I) and the 1,020 MW Punatsangchhu Stage-II (Puna-II). These projects, along with the 660 MW Kholongchu, are estimated to cost ₹21,637.28 crore, funded by India, benefiting States in northern and eastern India.

Doubts were raised in February 2023, when the Central Electricity Authority (CEA) uploaded a note on the projects completed, being constructed, and pursued under a 2006 agreement on cooperation in the field of hydroelectric power signed between the two countries. The status was updated in August, with hardly any changes.

The CEA note on the Puna-I that was started in 2008 and expected to be commissioned in 2024-25, said: “Project commissioning is being delayed due to movement/subsidence of right bank hill mass in the dam area. Treatment/stabilisation of the right bank and completion of dam work under progress. The option of providing a barrage in the upstream and abandoning of the dam is being studied.”

On the Puna-II, targeted for commissioning in 2023-24, the note said: “Poor geological strata and shear zone being encountered at left bank and foundation of dam and HRT [head race tunnel, a tunnel connecting water intake at dam site to power house for generation of hydro electricity]. Remedial measures are under progress.”

Experts weigh in

According to the CEA, the HRT for Puna-I was completed in June 2015, while 99.53% of the dam excavation and 98.05% of the underground powerhouse have been completed. In the case of Puna-II, 99.73% of the HRT and 97.49% of the concrete dam have been completed.

An Assam-based hydrologist, under condition of anonymity, said the rethink on the two Puna projects is likely to entail an expensive design change. In pushing for dams, it reflects the failure of several Indian agencies in comprehensively assessing the fragile Himalayan geology, similar to Sikkim and Arunachal Pradesh flanking Bhutan.

These agencies are the Central Water Commission, the Geological Survey of India, and WAPCOS, apart from the CEA. Earlier known as Water and Power Consultancy Services (India) Limited, WAPCOS is a consultancy service provider under the administrative control of the Ministry of Jal Shakti.

“Punatsangchhu has been a story of disaster with international landslide experts like Dave Petley having pointed out it was a blunder to start a dam at the location that seems to be on the debris of past landslides,” environmental activist and water expert Himanshu Thakkar said. “The Puna-I project is more or less a washout and hence they are considering the alternative of a barrage there. But that also does not seem to have been finalised. It is an admission of a major failure by these agencies,” he said.

CEA officials did not respond to emails seeking to understand whether the geological studies upfront had been poor, as well as the financial impact of the shift from the dam to a barrage.

Indian government officials said no final decision has been taken on the Bhutan projects, but experts are studying the “technical aspects” of the projects. “Geological aspects are being reviewed by experts for the dam option,” an official who spoke off the record, said.

Relook at geological survey

Reports in Bhutan said the governments of the two countries have tasked the eight-member Technical Coordination Committee (TCC) with reviewing and proposing a path forward for the Puna-I dam. A mutual decision was made to initiate geological investigation studies at the project site, Bhutan’s power officials said, indicating that the TCC would determine the extent of additional geotechnical investigations required at the dam site.

“We need to re-look at the geological survey of the (Puna-I) dam because many things have changed in 15 years. There have been many reasons for the delay, including technical issues and COVID. The (soil) stabilisation measures have not yielded the results they wanted. No expert will go on to do a project that is not technically, scientifically feasible,” Bhutan’s Prime Minister, Lotay Tshering told The Hindu.

He was, however, confident that the problems would be resolved. “There is no disagreement on the principles. Both the countries and the experts agree that the project must be completed, and they are sorting out the technical details that can potentially harm the dam’s future,” he said.

“Our technical experts have proposed that if the dam is not feasible, then probably a smaller dam or barrage is needed. The government of India experts have said the dam is feasible,” Dr. Tshering said.

According to a protocol signed in 2009, India agreed to import a minimum of 10,000 MW of electricity from a total of 13 financed projects with a total installed capacity of 12,241 MW.

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