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Context

• A massive landslide at NHPC's much-delayed 2,000 MW Subansiri hydro project along the Assam-Arunachal Pradesh border on Friday completely blocked the only functional diversion tunnel, thereby significantly obstructing water flow through the river.

About

• It is the largest hydroelectric project ever constructed in India.
• It is a run-of-river system on the Subansiri River.
• The project is located near North Lakhimpur on the Arunachal Pradesh-Assam border.
• Capacity: 2000 MW
• It will produce up to 7.4 billion kWh of electricity per year.

• The project includes the construction of a surface powerhouse and a 116m-high concrete gravity dam from the river bed level.
• The dam will be 284 meters long.
• The dam is in Assam's Dhemaji district, but the powerhouse is in Arunachal Pradesh's Subansiri district.
• The National Hydro Power Corporation (NHPC) is in charge of its development.

About the Subansiri Lower Hydroelectric Project (SLHEP):

• SLHEP is a gravity dam under construction (almost 90% of the work has been finished) with a capacity of 2000 MW (8x250 MW).
• It is India's largest hydroelectric project to date, and it is a run-of-river scheme on the Subansiri River.
• A run-of-river dam is one where the flow of water downstream of the dam equals the flow of water upstream of the dam.
• In other words, the dam does not hold/store water behind it; rather, it flows with the river.
• National Hydroelectric Power Corporation (NHPC) Limited is in charge of the SLHEP's construction.

Subansiri River

• The Subansiri River, sometimes known as the "Gold River," is the greatest tributary of the Upper Brahmaputra River.
• It originates in the Tibetan Himalayas and flows into India via Arunachal Pradesh (Miri Hills).
• It runs from the Himalayan Mountains to the east and south-east of Arunachal Pradesh before reaching the Assam Valley.
• Finally, it meets the Brahmaputra River in the Assam district of Lakhimpur.
• It meets the Brahmaputra in the mysterious confluence of Majuli Island, the world's largest populated river island.

Controversy regarding SLHEP

• The project has been stalled due to local agitation over several dam safety and administrative issues involved in its implementation, such as:
• SLHEP violates the 1980 Brahmaputra Board Act by transferring the work of the Subansiri Basin Water Resources Department from the Brahmaputra Board to the public and private sectors.
• There is also the question of rising seismic threat levels to the dam, according to IIT-Roorkee.

Other Contentious Dams

The Sardar Sarovar:

• The Sardar Sarovar Dam is a gravity dam on the Narmada River near Navagam, Gujarat.
• It is the world's second-largest concrete gravity dam by volume.
• The dam provides water and electricity to Gujarat, Madhya Pradesh, Maharashtra, and Rajasthan.
• The dam is said to have displaced over 2.5 lakh locals.

Mulla Periyar Dam:

• This gravity dam on the Periyar River in Kerala's Idukki district is owned and administered by the Tamil Nadu government.
• The height of the dam is a point of disagreement between the governments of Kerala and Tamil Nadu.

Polavaram project:

• It is a multi-purpose national project under construction on the Godavari River in Andhra Pradesh's West Godavari and East Godavari districts.
• Villages in Chhattisgarh and Odisha will be submerged as part of the project.

Kishanganga Hydroelectric Plant

• It is a run-of-the-river hydroelectric system in Jammu and Kashmir that is designed to move water from the Kishanganga River to a power plant in the Jhelum River basin.
• The World Bank's Court of Arbitration was unable to settle the dispute between India and Pakistan over the Indus water treaty.

PRACTICE QUESTION Discuss the environmental, social, and economic implications of large dam projects in India, taking a specific case study as an example. (250 words)