In News:

India’s largest hydroelectric venture, the 2000 MW Subansiri Lower Hydroelectric Project, has officially entered its commissioning phase after years of delays, protests, and structural overhauls. Located at Gerukamukh on the Arunachal Pradesh–Assam border, the project marks a crucial milestone in India’s renewable energy expansion, especially in the Northeast.

Overview of the Project

• Type: Run-of-the-river hydroelectric project
• Capacity: 2000 MW (8 × 250 MW units)
• River:Subansiri River, a major tributary of the Brahmaputra
• Developer: National Hydroelectric Power Corporation (NHPC)
• Location:Gerukamukh, in the foothills of the Himalayas
• Construction Timeline: Work began in 2005; commissioning initiated in 2025
• Financing Structure: 70% equity and 30% debt; Central government provided budgetary support as equity

When fully operational, it will be India’s single largest hydroelectric power plant, providing a major boost to national energy security and clean energy capacity.

Engineering Features

• Concrete Gravity Dam:
  • Height: 116 m from riverbed; 130 m from foundation
  • Length: 284 m
  • Reservoir Storage Capacity: 1.37 km³
• Power Generation System:
  • Eight Francis-type turbines, each generating 250 MW
  • Eight headrace tunnels, eight surge tunnels, and eight circular penstocks
  • A 35 m-long, 206 m-wide tailrace channel to release water back into the river

Recent Developments – Commissioning Phase

On the first mechanical run, Unit-I generated 250 MW, marking the start of wet commissioning and its synchronization with the national grid. NHPC described this achievement as a “landmark moment for India’s hydropower landscape,” signalling steady progress toward bringing the remaining units online.

• Three additional units are expected to be commissioned within the year, adding 1,000 MW of clean energy to the grid.
• Once all 8 × 250 MW units become operational, the project will light millions of households and reinforce India’s push toward sustainable, reliable, and carbon-free energy.

Historical Delays and Controversies

The project’s trajectory has been far from smooth:

• Original commissioning target: December 2012
• Sanctioned: 2003
• Work halted: 2011–2019 due to widespread protests

Concerns raised by local communities and civil society groups:

• High seismic vulnerability of the region
• Potential ecological disruption
• Fear of downstream flooding
• Impact on riverine ecosystems and local livelihoods

Organisations such as the All Assam Students’ Union (AASU) demanded a complete reassessment of safety and environmental impacts.

Expert Review and Redesign

During the eight-year suspension:

• Expert committees from IIT Guwahati and the National Dam Safety Authority (NDSA) evaluated structural integrity and proposed design modifications.
• Recommended changes led to:
  • Enhanced seismic reinforcements
  • Additional grouting
  • Redesign of spillways
  • Strengthened safety protocols

The redesign ensured compliance with updated safety, hydrological, and structural norms before work resumed in October 2019.

Cost Escalation

The prolonged delays and modifications caused a substantial budget escalation:

• Initial Estimate: ?6,285 crore
• Revised Estimate: ?26,075 crore
• Cost Increase Drivers:
  • Inflation
  • Monsoon-induced damage
  • Prolonged suspension of civil works
  • Safety overhaul and redesign

Strategic Importance

• A cornerstone of India’s renewable energy strategy in the Northeast
• Strengthens national energy security with clean, baseload hydro capacity
• Supports grid stability and contributes to India’s climate goals
• Symbol of engineering resilience and India’s capability in executing large-scale infrastructure projects

NHPC leadership hailed the achievement as an emblem of “India’s unstoppable march towards a cleaner and self-reliant energy future.”