Gerukamukh, a quiet village on the Assam–Arunachal Pradesh border, is emerging as a key site in India’s energy transition. Here, on the banks of the Subansiri river, work is nearing completion on the Subansiri Lower Hydroelectric Project (SLHEP) the country’s largest under-construction hydropower project with a capacity of 2,000 MW.
Major milestone after years of delay
Half of the project structures, including the main dam and water conductor systems, lie upstream in Arunachal Pradesh. The other half, including the power house where electricity will be generated, is located in Assam’s Gerukamukh.
Four of the eight turbines, each capable of producing 250 MW, are expected to begin commercial operations between mid-November and the end of December. One unit is already undergoing trial runs. The remaining four are scheduled for commissioning next year.
The project has been in progress for nearly two decades. Initially approved in 2003 and taken up for construction in 2005, SLHEP was expected to be completed by 2012 at a cost of Rs 6,285 crore. But large-scale protests, petitions before the National Green Tribunal and environmental concerns stalled work in 2011. Construction resumed only in 2019. The delays pushed the project cost to around Rs 27,000 crore.
Senior NHPC officials say the company incurred a loss of roughly Rs 5 crore per day when work remained suspended. Interest accrued during the construction period is estimated at around Rs 1,000 crore.
Safety and flood control concerns addressed
The Subansiri, the largest tributary of the Brahmaputra, has a history of sudden surges during the monsoon. To address fears of downstream flooding, NHPC has installed early flood warning systems upstream at Daporijo and Tamen. These systems provide a five-to-six-hour advance alert in case of high discharge, allowing time to regulate water release from the dam.
NHPC has also undertaken flood protection and riverbank strengthening at vulnerable downstream stretches. This work cost about Rs 522 crore. Officials say the dam was able to manage heavy upstream discharge in June 2023 and again in May–June 2024 without flooding villages in Assam.
Compensation and land concerns
The project did not involve displacement of settlements. However, agricultural land in two upstream villages was affected. Seventy-seven families were compensated, and the company paid around Rs 300 crore towards forest land value under the Net Present Value (NPV) norms. The total compensation package was around Rs 650 crore.
Key role in India clean energy goals
The Subansiri project is seen as central to unlocking Arunachal Pradesh’s hydropower potential, where several more hydroelectric projects are planned, including the proposed 11,200 MW Upper Siang multipurpose project. Together, these projects are expected to strengthen the region’s contribution to India’s renewable energy capacity.
NHPC chairman and managing director Bhupender Gupta said the completion of SLHEP will support India’s clean energy transition and the country’s target of achieving net zero emissions by 2070.
Once operational the project will not only supply power to the North-Eastern region but also act as a flood-moderating structure along the Subansiri–Brahmaputra basin, reducing the severity of monsoon flooding.
For now, Gerukamukh continues to witness round-the-clock engineering work. The final stages are underway, marking a crucial moment in a project shaped by two decades of environmental debate, political negotiation and technical challenges and one that stands to significantly reshape the energy landscape of North-East India.