The Subansiri Lower Hydroelectric Project, otherwise known as India’s largest hydel project currently under construction, encountered a recent setback due to a landslide that obstructed its only working diversion tunnel. This incident not only halted the flow of water downstream of the dam into the Subansiri River – a principal tributary of the Brahmaputra – but also caused the river bed to dry up and threatened aquatic life. Questions regarding the project’s safety and viability have resurfaced as a result of these occurrences. The ambitious project has faced multiple delays and opposition since its initiation in 2005.
About the Subansiri Lower Hydroelectric Project
The Subansiri Lower Hydroelectric Project is a “run-of-river” scheme that aims to produce 2,000 MW of power by harnessing the potential energy of the Subansiri River. This river flows along the boundary of Arunachal Pradesh and Assam. A run-of-river dam is designed in such a way that the flow of water downstream remains identical to the upstream flow. The National Hydroelectric Power Corporation (NHPC) is responsible for the project’s execution.
Project Structure and Expected Output
The hydroelectric project’s design involves the construction of a 116-metre high concrete gravity dam, a reservoir spanning 34.5 kilometres, five diversion tunnels, eight spillways, and a powerhouse equipped with eight 250-MW units. Due to the dam’s design maximizing the weight of the concrete or cement, it can successfully resist the horizontal pressure of the water pushing against it. It is anticipated that the project will generate approximately 7,500 million units of power annually in a 90% dependable year. Besides electricity generation, the project is also predicted to provide flood moderation, irrigation, and drinking water benefits to downstream areas.
Construction Timeline and Challenges
NHPC Limited started the construction work of Subansiri Lower Hydroelectric Project in January 2005. However, due to resistance from local stakeholders, work was halted from December 2011 until October 2019. Following clearance by the National Green Tribunal, the construction resumed on October 15, 2019.
Subansiri River: A Powerhouse in Waiting
Known as the “Gold River,” Subansiri is the largest tributary of the Upper Brahmaputra river. Originating in the Tibetan Himalayas, the river enters India through the Miri Hills of Arunachal Pradesh. Varying topographical features along its course offer significant opportunities for exploiting hydropower potential in the region.
Previous Examination Questions
In a previous UPSC Civil Services Examination, a question related to the topic was asked: “Consider the following rivers: Barak, Lohit, Subansiri. Which of the above flows through Arunachal Pradesh? (a) 1 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3.” The correct answer was option (b).
