Teesta hydro project, devastated in glacier disaster, to reopen

Teesta hydro project, devastated in glacier disaster, to reopen

Teesta hydro project, devastated in glacier disaster, to reopen ByJayashree Nandi Jan 27, 2025 05:18 AM IST Share Via Copy Link The project in Mangan district was destroyed following a GLOF in October 2023 that washed away the dam and flooded the underground powerhouse, halting its operations

An expert appraisal committee of the Union environment ministry has recommended an amendment in the conditions for environmental clearance for the Teesta Hydroelectric Project Stage-III (1200 MW) by Sikkim Urja Limited, granting it the go-ahead to resume operations.

The flood in October 2023 killed nearly 100 people. (PTI)

The project in Mangan district was destroyed following a Glacial Lake Outburst Flood (GLOF) in October 2023 that washed away the dam and flooded the underground powerhouse, halting its operations.The disaster meant that the plant needed a fresh design, which in turn necessitated a fresh clearance.

Sikkim Urja Limited, which runs the plant,in its application for the clearance said that the amendment “is requested” to ensure the project is brought back “in operation at the earliest”.

“The water conductor system is mostly unaffected in the (2023) flash flood, hence, other than the dam most of the components can be restored in a year’s time. As most of the components would be ready in a year, there is a case for restoring the dam and bringing back the Project in operation at the earliest for which EC amendment is requested,” the EC application by Sikkim Urja Limited said.

The amendment includes changing from a concrete-faced rockfill dam to a concrete gravity dam, a design tweak that would accommodate the safe release of water in the event of larger floods. Around 265 families will be relocated as part of the new design. 

While the project has been recommended for renewed operations with several environmental conditions, minutes of EAC’s January 10 meeting show that a comprehensive study for identification of potential threats due to glacial lakes has been carried out.

A total 119 glacial lakes were identified in the catchment, and of these, 50 lakes with area of 10 ha or more were shortlisted for further evaluation. The project is located on the main Teesta River in the Mangan district, utilizing drop of about 800m in the river between Chungthang and Sankalang villages.

“After detailed study, 13 potentially dangerous glacial lakes were identified based on the water spread area (40 Ha or more), volume and distance. During criticality analysis, a combination of lakes was studied to find out the worst-case scenario,” the EAC minutes show. The 13 are part of the 50 that were identified for further evaluation.

“Three different combinations were studied, and worst combination was considered for GLOF. In the worst-case combination, highest volume outflow from simultaneous breach of two lakes of 12,946 cumecs was considered. This GLOF capacity has been added to the probable maximum flood (PMF) for deciding the spillway capacity,” the minutes show.

The January 10 meeting followed a decision to defer the proposal to grant a nod for amendment to EC conditions at the 19th EAC meeting held in November last year.

The January 10 meeting observed: “…The EAC expressed serious concerns regarding the dam’s design and stability; its ability to withstand potential natural disasters in the future. The committee emphasized the need for a thorough review of the proposed modifications to ensure the structural resilience and safety of the dam, particularly given the region’s susceptibility to extreme hydrological events. It was therefore recommended to get comments from the Central Electricity Authority (CEA) on the proposed modifications. Therefore, the EAC opined to conduct a site visit by sub-committee of EAC members before giving any further recommendation to the project...”

Responding to these concerns, Sikkim Urja said that the type of dam has been changed from concrete face rockfill dam to concrete gravity which is a much more resilient structure minimizing the chance of dam failure due to overtopping.

“SUL is employing various measures like jet grouting, permeation grouting to improve the ground conditions and control seepage for the Stage I works. Dam spillway capacity has been enhanced from 7,000 cumecs to 19,946 cumecs by considering both GLOF and PMF. The spillway crest is lowered to enhance spillway safety in operation. To enhance the safety of the personnel working during Project operations, SUL has plans to shift the Dam control room to a higher elevation,” say the minutes.

The minutes also recorded the SUL response.

Additionally, the EAC has recommended a preliminary study of catchment area for implementation of early warning system and fixing of location of sensor stations. The Environmental Management Plan (EMP) has a proposed budget of ₹8,189.42 lakh, including a capital cost of ₹5,273.54 lakh and a recurring cost of ₹2,915.88 lakh.

Additionally, ₹1,423 lakh has been allocated for Local Area Development.

The EAC observed that the total land requirement for the project is 213.8831 hectares, which is already in the possession of the Project Proponent (PP). It was further noted that as per the initial Environmental Clearance (EC) dated 04.08.2006, the total land requirement was around 196.96 hectares, comprising 80.288 hectares of forest land.

EAC has recommended that the project meet various environmental conditions including on muck management; disaster management; biodiversity conservation, among others.