NEW DELHI: Days after an environment ministry expert panel gave its conditional nod to resume construction of Sikkim’s 1,200 MW Teesta III hydroelectric project, a study published in the international journal ‘Science’ has warned that the increasing number of such projects near glacier lakes in the Himalayas amplifies GLOF risks.
It was the catastrophic glacial lake outburst flood (GLOF) of Oct 3 in 2023, resulting from the collapse of the northern lateral moraine into the South Lhonak Lake, that transformed into a devastating flood and destroyed the project downstream post-midnight on Oct 4.
Findings of the study, jointly carried out by 34 scientists and researchers from nine countries, show that the surroundings of South Lhonak Lake, located in the Upper Teesta basin, have been unstable for a long time and remain “highly susceptible” to future GLOF events.
“The modified slope geometry following the 2023 collapse, particularly at the moraine crest, increased the likelihood of further failures,” said the study on the ‘Sikkim flood of Oct 2023’. The team of researchers, led by an IIT Bhubaneswar scientist Ashim Sattar, used high resolution satellite imagery and modelling techniques to investigate the intricate cause of the extreme event.
“The South Lhonak outburst once again demonstrates the vulnerability of Himalayan hydropower to extreme natural events. Hydropower projects exposed to glaciers and glacial lakes increase the risks of being impacted by outburst floods. With changing climate and global warming, we will likely see similar disasters in the future,” said co-author Wolfgang Schwanghart from the Institute of Environmental Science and Geography, University of Potsdam, Germany.
Citing the study, the other co-author Kristen L Cook from the University Grenoble Alpes in France, highlighted the possibility of “more GLOF in future years” in the Himalayan region. “It is critical that we use the findings from our study to better anticipate the full chain of GLOF hazards, including the compounding effects of landslides and sediment mobilisation on the flood and its impacts,” said Cook.
The study also reveals the role of a low-pressure system (LPS) that made its way from the Bay of Bengal towards Sikkim and brought heavy rainfall along the Teesta valley. Since it intensifies the impacts of the flood cascade especially in West Bengal and Bangladesh, the paper highlights the critical need for monitoring LPS activity and its role in flood cascades in the Himalaya and its foothills.
Flagging those concerns, the study underlined that the energy policies of Himalayan states should be more considerate of these potential risks and act towards mitigating such glacier-related risks.
“As we work to reduce the risks of GLOFs in the Himalayas, it is clear that we need a multi-faceted approach, including early warning systems, strengthened regulatory frameworks, a paradigm shift in GLOF modelling approaches, and robust preparation programmes and community education,” said Sattar.
The environment ministry’s panel, while giving its nod to resume construction of the Teesta III Hydroelectric Project, also underlined setting up early warning systems as one of the conditions. The minutes of the meeting of the panel said that the project proponent will have to install and operationalize a Telemetric Early Warning System (TEWS) to monitor and report real-time data on environmental parameters such as water levels, rainfall, and seismic activity.
The project, located on the main Teesta river in the Mangan district, was commissioned in February 2017 and was in successful operation till October 3/4 October 2023 when it faced a flash flood which led to the washing away of the dam and flooding of the underground powerhouse leading to halting of its operations.
Since the underground powerhouse, electro-mechanical equipment and most of the components of the project can be restored to their original condition in about 10-12 months, amendment in the environment clearance was sought by the project proponent to bring it back in operation at the earliest.
One of the key amendments in the Environmental Clearance (EC) to the project include redesigning the dam and replacing the earlier ‘concrete faced rockfill dam’ with a ‘concrete gravity dam’ which is considered as a much more resilient structure minimizing the chance of dam failure due to overtopping.
The panel, however, made it mandatory for the project proponent to obtain “all necessary permissions from Central Electricity Authority (CEA)/Central Water Commission (CWC) or any other agency with respect to project design and other safety parameters” before starting the project construction work.
