Subansiri lower hydroelectric project faces fresh six month delay after NDSA directive

Guwahati, July 5: The Subansiri Lower Hydroelectric Project will miss yet another deadline, with its commissioning getting delayed by another six months.

This follows a directive by the National Dam Safety Authority (NDSA) to the National Hydroelectric Power Corporation (NHPC) to do some additional grouting work in the inlets of the diversion tunnels.

The project was scheduled for commissioning in June this year.

The NDSA had upon a site inspection on June 20 directed the NHPC to complete the remaining portion of about 30m plugging of Diversion Tunnel 1 in the outlet side. Earlier on April 11, the NDSA had issued a similar directive, mandating some additional grouting work in the inlets of the diversion tunnels.

Official sources told The Assam Tribune that the plugging of Diversion Tunnel 1 by concrete would be possible only when river flow is reduced. As of now, the tunnel stands submerged and work is unlikely to start be-fore mid-October.

"Work can resume only by mid-October or even later depending on the water lev-el of the river. We expect rainfall to subside sufficiently from mid-October on-wards, enabling grouting works as mandated by NDSA," sources added.

As the NDSA may give clearance for reservoir filling only after the full plugging of the tunnel, the commissioning of the project will be delayed and cannot be expected earlier than in December, sources said. In all probability, it will be commissioned next year, they said.

Repeated missed deadlines have triggered a huge cost escalation of the project, resulting in wastage of public money and revenue loss for the government.

On the positive side, by the time of commissioning, the fourth unit of the power house will be completed and 1,000 (4x250) MW power will be generated immediately.

Grouting work refers to foundation consolidation drilling following which it is filled up with cement. Voids caused by scour and erosion are common in water-based infrastructure and grouting reconnects the structure with its footings and subsurface piling. In some cases where there are unbraced lengths of piling, grouting is used to establish a long-term reinforcement.

India's second largest hydropower dam, the 2,000-MW Subansiri Lower Hydroelectric Project's three units totalling 750 MW were scheduled for commissioning in June but has missed the deadline. Full capacity commissioning of the project is expected by March 2026.