Why in the News?

The National Hydroelectric Power Corporation (NHPC) has begun the wet commissioning of the first 250 MW unit of the Subansiri Lower Hydroelectric Project (SLHEP), India’s largest hydropower installation.

About Subansiri Lower Hydroelectric Project (SLHEP):

Overview: A run-of-the-river hydroelectric project located on the Subansiri River at Gerukamukh, straddling Arunachal Pradesh and Assam in the Lower Subansiri district.
Developer: Implemented by the National Hydroelectric Power Corporation (NHPC) Limited, India’s leading central public-sector hydropower enterprise.
Installed Capacity: 2,000 MW (8×250 MW), the largest hydroelectric project in India upon completion.
Dam Structure: A concrete gravity dam, 116 m high from riverbed (130 m from foundation) and 284 m long, built to withstand high flood discharge and seismic activity of the Eastern Himalayas.
Reservoir & Components: Features a 34.5 km reservoir, five diversion tunnels, eight spillways, and a surface powerhouse on the right bank.
Power Output & Benefits: Expected to generate 7,500 MUs annually (90% dependable year), contributing to clean power supply, flood moderation, irrigation, and drinking water for downstream Assam.
Timeline: Construction began 2005, stalled 2011 due to environmental protests, resumed October 2019 after NGT clearance and PMO intervention.
Recent Milestone: In October 2025, NHPC began wet commissioning of the first 250 MW unit, marking the project’s operational phase.

Back2Basics: Subansiri River

Overview: Arises in the Tibetan Himalayas, flows southeast through Miri Hills (Arunachal Pradesh), entering Assam, and joins the Brahmaputra at Lakhimpur.
Tributary Importance: Largest right-bank tributary of the Brahmaputra, contributing ~7.9% of total river flow.
Catchment Area: Covers 32,640 sq. km, combining steep Himalayan terrain and fertile plains.
Local Name: Known as the “Gold River” due to historic alluvial gold traces in its sands.
Ecological Significance: Supports endemic fish species, riparian forests, and floodplain livelihoods across Dhemaji and Lakhimpur.
Strategic Relevance: Its high gradient and perennial discharge make it ideal for renewable hydropower, central to Northeast India’s energy security.

[UPSC 2024] Recently, the term “pumped-storage hydropower” is actually and appropriately discussed in the context of which one of the following? Options: (a) Irrigation of terraced crop fields

(b) Lift irrigation of cereal crops

(d) Rainwater harvesting system

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