14 months after glacial lake flood, Sikkim’s Teesta dam gets environment nod for rebuild without public hearing

On October 4, 2023, the South Lhonak glacial lake in Sikkim burst, causing a flood that Ministry panel clears Sikkim dam structure despite own concerns killed 40 people across four districts of Sikkim. The flood also washed away the 1,200 MW Teesta-III Chungthang Dam located 55 km downstream.

The EAC nod for the new dam comes in the backdrop of concerns the panel had itself raised over the structure’s safety and stability.

Late in December 2024, an EAC sub-committee comprising the panel’s chairman, a Central Electricity Authority official, a senior ministry official and an official of the Central Water Commission (CWC) visited the site to evaluate the planning and feasibility of the proposed concrete gravity dam in place of the earlier concrete rock-filled dam.

A concrete gravity dam is made entirely out of concrete and is generally considered stronger than a concrete rockfill dam, but is more expensive to construct. A concrete rockfill dam has a core of concrete that is surrounded by rockfill material.

Days after the December site visit, at its meeting on January 10, the EAC approved Sikkim Urja’s proposal even as it noted – according to the minutes of the meeting of that day – that the “design directorate of CWC has suggested to carry out a revised study of the PMF (probable maximum flood) and diversion flood and get it approved through concerned hydrology directorate of CWC”.

The EAC also set conditions for the new dam – including the setting up of early warning systems and the mapping of glacial lakes and landslide spots – while noting that the design aspects were yet to be approved by the CWC, Geological Survey of India and the Central Soil and Materials Research Station.

Proposal documents and the minutes of the January 10 meeting showed that one of the key concerns of the EAC was centred on the capacity of the new dam to withstand flooding in the event of an incident of the nature of the October 2023 GLOF. In its response, however, Sikkim Urja Ltd stated that the proposed dam’s spillway capacity (which allows draining of excess water) has been enhanced from 7,000 cumec (cubic metre/second) to 19,946 cumec while taking into consideration both eventualities — a probable maximum flood as well as another GLOF event.

Back in the mid- to late-2000s, when the project was being appraised, it was warned that a low spillway capacity risked overtopping, which is what eventually happened when the South Lhonak lake burst in the early hours of October 4, 2023.

When the EAC asked Sikkim Urja about the hazards of glacial lakes upstream, the company claimed that of the 119 glacial lakes identified in the catchment area, 50 big lakes, with an expanse of 10 hectares or more, were shortlisted for evaluation. “After a detailed study, 13 potentially dangerous glacial lakes were identified based on water spread area (40 ha or more), volume and distance,” the company submitted to the EAC. The EAC’s minutes did not specify who authored the study on the glacial lakes.

According to the minutes of the meeting, a“worst-case” scenario was worked out using different combinations for GLOF events and it was calculated that a breach in two lakes would release a combined volume of 109.44 million cubic metres of water and the eventual GLOF flood value would be 12,946 cumecs. “The value has been approved by CWC,” the company submitted to the EAC.

Calls and messages by The Indian Express to EAC Chairman Professor Govind Chakrapani, seeking comments on the panel’s decision, and to Yogendra Kumar, ED – Incharge and President, Sikkim Urja Limited, went unanswered.

An email sent to the Greenko Group seeking its response on the EAC’s decisions too did not elicit any response. Promoted by the Sikkim government until last year, Andhra-based Greenko Group now owns the majority stake in Sikkim Urja Limited.

Independent expert Himanshu Thakkar of the South Asia Network on Dams, Rivers and People questioned the “hurry” in clearing a project with a history of disaster, especially when the revised probable maximum flood studies were awaited. “This proposal should be treated as a fresh proposal in the context of changing rainfall patterns, the GLOF vulnerabilities. The EAC should have ordered for a fresh environmental impact assessment when the Central Electricity Authority and CWC are considering it in a fresh way. They are also using old data for floods by their own admission. There should be fresh calculations for peak flood levels based on recent data,” Thakkar said.

The EAC did not seek a fresh public hearing on the grounds that no fresh land acquisition, displacement was involved and because a public hearing was conducted in August 2006.