- Why in news
- On 16 March 2026, the Minister of State for Power told the Rajya Sabha in a written reply that two of eight units of the Subansiri Lower Hydroelectric Project are commissioned and the rest are planned by Dec 2026.
- Location
- The project is on the Subansiri River at the border of Arunachal Pradesh and Assam.
- Capacity and developer
- Installed capacity is 2000 MW in eight units of 250 MW each. NHPC Limited is implementing it.
- Dam safety oversight
- Dam safety is ensured under the Dam Safety Act, 2021, with guidance from the National Dam Safety Authority.
Don’t confuse with Subansiri Lower vs Subansiri Upper: Subansiri Lower is the 2000 MW project on the Arunachal-Assam border. Subansiri Upper is a separate, planned project further upstream in Arunachal Pradesh.
Places in the news: 26 Prelims questions since 2013, rising (12% of news questions in 2022–26); they test location and why it matters.
Why it matters
- Adds large firm hydro capacity in the Northeast and gives peaking power to balance variable solar and wind.
- Offers flood moderation in the Brahmaputra Valley.
Problems
- Downstream erosion and flood concerns in Assam have drawn local protest and delayed the project.
- Large dams in a seismic Himalayan zone raise safety and ecological questions.
Way forward
- Strict dam safety monitoring under the Dam Safety Act, 2021 and continued downstream erosion control.
- Transparent environmental and community engagement with downstream Assam.
Put in your answer
Dam safety framework: The Dam Safety Act, 2021 sets up the National Dam Safety Authority to oversee dam safety.
- 2013Mains GS3 · Q17Explain run-of-river hydroelectricity and how it differs from other hydro projects.
- 2016Mains GS3 · Q14Discuss measures to mitigate rehabilitation of human settlements from major projects.
- 2018Mains GS4 · Q5What rational policy for dam construction in forested, ethnically inhabited valleys facing contingencies?
- 2005Prelims Q134Which statements on Pathrakkadavu hydro project and Silent Valley are correct?
- 2008Prelims Q72In which state are the Tapovan and Vishnugarh hydroelectric projects located?
- 2014Prelims Q45Which rivers among Barak, Lohit and Subansiri are correctly identified?
UPSC’s own questions that come close to this issue, from our Prelims and Mains banks.
No practice question for this one; the card may still help an answer. Why: 2000 MW project on Arunachal-Assam border by NHPC; worth a card, but progress update has few fresh testable facts. Places are 8% of Prelims.
Worth revising until Prelims 2027: most news questions come within two years of the event.