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Sikkim’s Teesta Dam Gets Environmental Approval for Rebuild 14 Months After Glacial Flood, No Public Hearing

Sikkim January 28, 2025: Over a year after the devastating glacial lake outburst flood (GLOF) in Sikkim, which washed away the 60-meter-high rockfill concrete dam of the 1200-MW Teesta-III hydel project, the Environment Ministry’s panel has approved the proposal to construct a new 118.64-meter-high concrete gravity dam in its place. The approval was granted without a fresh public hearing, and the design aspects of the new dam are yet to be finalized.

On January 10, the Ministry’s Expert Appraisal Committee (EAC) for River Valley and Hydroelectric Projects approved the proposal submitted by Sikkim Urja Ltd., the project operator. The approval was made under the provisions for ‘expansion or modernisation’ of existing projects.

The flood, triggered by the October 4, 2023, burst of the South Lhonak glacial lake in Sikkim, resulted in the loss of 40 lives across four districts. The flood also destroyed the 1,200 MW Teesta-III Chungthang Dam located 55 kilometers downstream. Despite concerns regarding the structure’s safety and stability, the EAC granted approval for the new dam.

A concrete gravity dam, made entirely of concrete, is typically stronger but more costly than a concrete rockfill dam, which has a core of concrete surrounded by rockfill material.

During its site visit in December, the EAC raised concerns about the dam’s safety in light of the 2023 GLOF event. The panel noted that the “design directorate of CWC has suggested a revised study on the probable maximum flood (PMF) and diversion flood, which needs approval from the hydrology directorate of CWC.” The EAC set several conditions for the dam’s construction, including the installation of early warning systems and mapping of glacial lakes and landslide-prone areas. However, the design aspects of the dam have yet to be approved by the Central Water Commission (CWC), Geological Survey of India, and the Central Soil and Materials Research Station.

Documents from the January 10 meeting revealed that one of the key concerns raised by the EAC was whether the new dam could withstand the kind of flooding caused by the 2023 GLOF event. Sikkim Urja Ltd. assured the panel that the proposed dam’s spillway capacity has been increased from 7,000 cubic meters per second (cumec) to 19,946 cumec, taking into account both the PMF and another potential GLOF occurrence.

Earlier appraisals of the project had warned that a low spillway capacity could lead to overtopping, as occurred when the South Lhonak lake burst in October 2023.

Regarding the hazards posed by glacial lakes upstream, Sikkim Urja Ltd. reported that of the 119 glacial lakes in the catchment area, 50 large lakes covering 10 hectares or more were shortlisted for evaluation. The company identified 13 potentially dangerous lakes based on their water spread area, volume, and proximity. The EAC’s minutes did not specify the authors of the glacial lake study.



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