“The commissioning of the Subansiri Lower Hydro Electric Project (SLHEP) has been further delayed till May 2026” NHPC has now acknowledged. In a report filed by PTI, the project developer has acknowledged on June 12 2025 that the controversial 2000 MW Hydropower project on Subansiri River in Brahmaputra basin on Assam-Arunachal border “has suffered “minor damages” during the recent monsoon rains”. The suggestion that the damages were minor may not be accurate considering the consequences of project delay.
Instances of damages in 2020-2024 The project has been suffering multiple instances of damages and disasters each year since 2019 when the work on the project was resumed after prolonged agitation against the project in Assam. In year 2020, for example, project suffered damages. In June and July, in 2021, it suffered damages in Aug, in 2022 the incidents including those in March, June, flashfloods and landslide in Sept and on landslide on Oct 12 2022. The report from the Central Electricity Authority in Apr 2022 listed the earlier instances. In April 2023, the project suffered landslide. In Oct 2023, a massive landslide damaged the project once again. In May 2024, the SLHEP suffered. Another landslide leading to death and destruction.
Damages in June 2025 A June 1 2025 report noted: “But a massive landslide on the right bank of the fragile Gerukamukh hills has further intensified the crisis, reportedly causing flash flood-like conditions at the project site… NHPC’s reassurances have fallen flat in the face of nature’s fury… Local sources report visible signs of distress, with villagers along the Subansiri belt in constant fear of sudden flooding. Many are urging authorities to conduct immediate safety reviews of the project and put public safety above power generation goals.”
On June 12 2025, Assam Tribune also reported that National Dam Safety Authority (NDSA) has not yet given clearance to commissioning of SLHEP. It quoted officials saying: “National Dam Safety Authority is reviewing progress on the grouting work on left bank. Once it is completed, we expect the approval from the authority for commissioning… We expect all work to be accomplished within June and after that we will get the NDSA nod for commissioning”. Grouting becomes necessary to fill up the “voids caused by scour and erosion”. This report also thus confirms that scheduled commissioning of 3 units, each of 250 MW in June 2025 is now no longer possible. The official also accepted: “There is some scouring in the lip of the spillway No. 6.” This report also said: “Full capacity commissioning of the project is expected by March 2026.” This now is further postponed to May 2026 as per Rediff report above, sourced from PTI news, generally considered reliable.
A day before, on June 11 2025 Assam Tribune reported about what it described as “a major structural setback”: “A section of the guard wall beneath Spillway Gate Block No. 6 was washed away by the strong currents of the Subansiri River, triggering fresh safety and stability concerns… According to preliminary reports, the river’s powerful flow eroded critical structural components located beneath the spillway gate, causing part of the protective guard wall to collapse… emergency response and technical assessment teams have been mobilized to the site. Engineering experts are now examining the extent of the damage and the potential implications for the structural integrity of the dam… This latest incident adds to a long list of challenges that have clouded the SLHEP since its launch”.
Another report on the same date said: “A major structural issue has been reported at the SLHEP, raising serious safety concerns ahead of its commissioning. The incident has occurred at Block No. 6 of the main dam. According to reliable sources within the NHPC, a portion of the guard wall at the spillway has collapsed due to intense water pressure from the Subansiri River. Technically, NHPC officials have termed the issue as a failure of the “spillway lip.” There are apprehensions that the base floor of the spillway near Gate No. 6 may also have sustained damage. The development poses a significant technical challenge for NHPC… Sources further revealed that visuals from May 31 and June 10 inspections clearly indicate signs of the structural fault. Experts believe this could be an early warning of a more serious risk to the integrity of the dam. The Subansiri project, already delayed by years due to environmental and technical concerns, now faces fresh hurdles”. The rolling of boulders and wooden logs has damaged the upper surface of the spillway no. 6 glacis and lip portion.
In Conclusion It is clear that SLHEP has faced very large number of instances of damages, we can see instances in each year since 2019 when the project work resumed. This is far from usual. This has not only led to cost and time overruns, but also created questions about the project among all concerned. It is good that NDSA has not given NHPC permission to commission the project. However, the reports based on which NDSA has taken this decision must be in public domain. Any issue or report related to dam safety has to be in public domain as these are subjects of public interest. It may be good idea for the government to institute an independent inquiry into what is going on this largest and costliest hydropower undertaken by India so far, leaving aside some projects taken up in recent years.
SANDRP
SANDRP 