Assams Subansiri Hydroelectric Project Faces Six Month Delay After NDSA Directive
In Assam The Subansiri Lower Hydroelectric Project, India’s second-largest hydroelectric undertaking, has hit yet another roadblock. Scheduled for commissioning in June 2025, the massive infrastructure project will now face a six-month delay after a directive from the National Dam Safety Authority (NDSA) ordering additional safety-related grouting work.
The project, which promises a capacity of 2,000 MW and has already seen multiple missed deadlines, continues to wrestle with engineering setbacks and regulatory hurdles. The recent delay comes after an NDSA inspection at the project site in Arunachal Pradesh’s Lower Subansiri district on June 20, where the authority flagged unfinished work on Diversion Tunnel 1. The order is the second in recent months; a similar directive was issued on April 11, asking the National Hydroelectric Power Corporation (NHPC) to conduct grouting at the inlet sections of the diversion tunnels to address potential safety concerns. With monsoon-induced high river flows currently submerging critical sections of the tunnel, work has been rendered impossible until at least mid-October 2025, officials confirmed.
According to NHPC and PWD sources, the critical delay involves plugging a 30-meter section of Diversion Tunnel 1, a component vital for stabilizing the dam structure before reservoir filling can be authorized. The tunnel, currently submerged due to heavy rains and elevated river discharge, requires dry conditions for concrete grouting work—a form of substructure reinforcement used in dam safety measures. “Plugging the tunnel is possible only when the water level recedes. With the current river flow, that won’t happen before October or even November. Only after that can we begin the concrete works necessary for final commissioning,” a senior NHPC engineer stated.
Grouting in hydroelectric projects is a standard but crucial practice. It involves high-pressure injection of cement into voids or unstable sub-surfaces, ensuring structural continuity between the dam’s concrete and the underlying rock strata. The practice helps address erosion-induced cavities and reinforces unbraced or weakened footings, preventing leakage and long-term instability. This delay marks yet another entry in a long list of missed timelines. Originally conceived in 2003, the Subansiri Lower Hydroelectric Project has suffered a two-decade-long saga of environmental protests, legal challenges, technical revisions, and bureaucratic inertia. Despite being hailed as a game-changer for India’s power grid in the Northeast, the project has rarely met its revised deadlines.
The NHPC had planned to bring the first three turbines online by June 2025, totaling 750 MW. However, with NDSA’s new conditions and monsoon delays, even partial commissioning is now pushed back to December 2025 or later, and full-scale commissioning is unlikely before March 2026. This continuous shifting of deadlines is proving costly—not just in terms of time but money. The cost overrun is reportedly running into thousands of crores, increasing the financial burden on both the central government and NHPC shareholders. Delayed power generation also implies revenue loss from power purchase agreements that have already been inked with multiple states.
Amid the setbacks, there is a silver lining. Sources indicate that by the time the site is finally ready for operation, the fourth turbine (250 MW) of the powerhouse will be installed and tested—allowing an immediate generation of 1,000 MW (4×250 MW) once the project receives a green light. This would provide a strong starting output and relieve power demand in Assam, Arunachal Pradesh, and other Northeastern states. NHPC also plans to integrate the dam into India’s North-East power corridor, designed to channel surplus electricity into the national grid, particularly during the monsoon season when hydropower generation peaks. That, however, will only become viable once the dam is fully stabilized, inspected, and greenlit for operations by NDSA and other safety boards.
While technical delays dominate headlines, it’s important to remember the legacy of environmental and public opposition that has surrounded the project. Local communities, particularly those downstream of the Subansiri River in Assam’s Dhemaji and Lakhimpur districts, have raised serious concerns about the dam’s impact on ecosystems, agriculture, and seismic vulnerability. “The project is being delayed for good reason. Safety must come before speed. If the grouting isn’t solid, you’re putting thousands of lives downstream at risk,” said an environmental activist associated with the Krishak Mukti Sangram Samiti (KMSS).
NDSA’s interventions are being widely viewed as a positive assertion of technical oversight in a politically sensitive and high-stakes project. As climate volatility continues to escalate across the region, the structural integrity of megadams like Subansiri will be more critical than ever. With October now being the next milestone, NHPC is racing against time and nature. The upcoming dry season offers a short window for technical fixes, safety inspections, and final approvals. Whether that window will be enough remains uncertain.
Until then, the Subansiri Lower Hydroelectric Project remains a towering reminder of both India’s energy ambitions and the sobering challenges of executing infrastructure in ecologically fragile and hydrologically unpredictable regions.
