Subansiri Lower Hydropower Project

Subansiri Lower Hydroelectric Project (SLHEP) is India's largest run-of-river hydropower project under construction — a 116 m concrete gravity dam on the Subansiri river in Assam, designed to generate 2,000 MW of hydroelectric power. The project has been one of India's most politically contentious infrastructure projects, with construction halted for 8 years (2011-2019) due to environmental opposition.

NHPC sanctioned the project in 2003 and began construction in 2005. The dam's location at Gerukamukh — on the Arunachal Pradesh-Assam border, downstream of which the river enters the Assam plains — caused major concerns from Assam's anti-dam groups + Brahmaputra-system ecologists. Concerns included: downstream flood risk, fisheries impact, sediment trapping, seismic vulnerability (the project is in Zone V), and inadequate environmental impact assessment.

The Krishna Pal-led Standing Committee on Energy + Subansiri Lower Project Expert Body recommended major design changes in 2010-11, after which the project was halted. Construction resumed in 2019 after revised EIA + dam-safety reviews. Total cost has escalated from original ₹6,285 crore to current estimate of ₹19,992 crore — representing one of India's largest hydropower cost overruns.

The dam, when complete (target 2026), will generate 2,000 MW (8 × 250 MW units) — among India's largest hydropower facilities. Significant project elements include a 460 m long spillway with 11 radial gates, 8 km of pressure tunnels, and a 600 m underground powerhouse.