Why in news?
The 2,000‑megawatt Subansiri Lower hydroelectric project, India’s largest, started commissioning its first unit in October 2025. Situated on the Subansiri River at Gerukamukh on the Assam–Arunachal Pradesh border, the project has faced delays for more than a decade due to environmental concerns and seismic risks.
Background
Construction of the Subansiri Lower project began in 2005, but public protests and legal challenges over ecological impacts and seismic safety halted work in 2011. An expert committee recommended design changes, including reinforcement of the dam and an improved spillway to handle floodwaters. Work resumed in 2019 after these modifications were incorporated. Developed by the state‑run National Hydro Power Corporation (NHPC), the project will ultimately comprise eight 250‑MW turbines.
Project features
- Run‑of‑the‑river design: The project uses river flow to generate electricity while minimising large‑scale reservoir flooding. A concrete gravity dam 116 metres high from the riverbed (130 metres from the foundation) and 284 metres long creates a modest reservoir with a gross storage capacity of about 1.37 cubic kilometres.
- Powerhouse: Eight Francis‑type turbines, each rated at 250 MW, will generate a total of 2,000 MW of electricity. Water is channelled to the turbines through horseshoe‑shaped headrace tunnels and returned via a tailrace channel.
- Financing: The project is funded through a mix of equity and debt. The central government provides budgetary support for a portion of the equity, with NHPC raising loans for the rest. Costs have risen from an initial estimate of around ₹6,300 crore to over ₹26,000 crore due to delays and redesign.
Significance
- Renewable energy: Once fully operational, the plant will supply clean electricity to the northeastern region, reducing dependence on fossil fuels and helping India meet its renewable‑energy targets.
- Economic development: Improved power availability can spur industrial growth and improve living standards in Assam and Arunachal Pradesh.
- Environmental concerns: Critics worry about the dam’s impact on river ecology, sediment flow and downstream communities. The project illustrates the tension between energy needs and environmental protection.
Conclusion
The commissioning of the Subansiri Lower project marks a milestone in India’s hydropower expansion. Balancing the benefits of clean energy with ecological safeguards will be key to ensuring that the project contributes positively to regional development.
Source: The Times of India