India’s largest hydroelectric project, the 2000-MW Subansiri Lower Hydroelectric Project, has begun its commissioning phase.

About Lower Subansiri Hydroelectric Project
The  Lower Subansiri Hydroelectric Project (LSHEP) is India's largest hydroelectric project, with an installed capacity of 2,000 megawatts. Operated by the state-run National Hydro Power Corporation (NHPC), the project is a run-of-the-river scheme built on the Subansiri River, a tributary of the Brahmaputra. 
Location and structure

• Location: The LSHEP is situated at Gerukamukh on the border between the northeastern Indian states of Arunachal Pradesh and Assam.
• Dam type: It features a concrete gravity dam that is 116 meters high from the riverbed and 130 meters high from its foundation.
• Powerhouse: Located on the right bank of the river, the powerhouse contains eight Francis-type turbines, each with a capacity of 250 MW.
• Tunnels: The project includes eight headrace tunnels and eight surge tunnels to direct water to the powerhouse for power generation.
• Reservoir: The dam has created a reservoir with a gross storage capacity of 1.37 cubic kilometers. 

Project history and timeline

• Construction begins: NHPC started construction in January 2005.
• Construction suspended: Following protests and concerns over environmental and downstream impacts, construction was stalled from December 2011 to October 2019.
• Work resumes: The project resumed construction on October 15, 2019, after clearance from the National Green Tribunal.

Key milestones:

• 2023: Construction of the dam to its top level was completed.
• October 2025: The project began its wet commissioning and test run. 

Controversies and issues
The project has faced significant opposition and delays due to several issues: 

• Downstream impact: Local groups in Assam, including the All Assam Students' Union (AASU) and Krishak Mukti Sangram Samiti (KMSS), have protested against the potential environmental and social consequences downstream.
• Geological concerns: The dam is located in a highly seismic zone, Zone V, which has raised safety concerns.
• Ecological impact: The reservoir will submerge forests, wildlife habitats, and agricultural land, impacting the local ecosystem.
• Landslides: The project has been impacted by landslides, including one in October 2023 that blocked a diversion tunnel.
• Cost overruns: Due to the prolonged delays, the project's estimated cost has significantly increased from the original budget. 

Benefits and output
Once fully operational, the project is expected to deliver the following benefits:

• Annual generation: It is expected to generate approximately 7,500 million kilowatt-hours (kWh) of power annually.
• Energy security: It will supply power to 17 states in India, strengthening the renewable energy capacity of the North-East region.
• Development: NHPC has implemented various development programs in the local area, including skill training and infrastructure improvements.

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