Description

Source: PIB

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Context

Lower Subansiri Hydroelectric Project a 2GW facility developed by NHPC on Subansiri River between Arunachal Pradesh & Assam is set to be one of Indian largest hydropower stations.

Key Highlights

Aspect	Details
Project Type	2000 MW run of river hydroelectric project
River & Location	Located on Subansiri River a tributary of Brahmaputra; at Arunachal Pradesh–Assam border
Developer	National Hydro Power Corporation (NHPC) A state-run public sector undertaking
Dam Specifications	Concrete gravity dam 116 m high from riverbed (130 m from foundation); 284 m in length
Reservoir Storage	1.37 km³ gross storage capacity
Powerhouse	Located on left bank of river; contains 8 x 250 MW Francis turbines (total 2000 MW)
Head Race Tunnels	8 tunnels, horseshoe-shaped, diameter 9.5 m, lengths vary from 608 m to 1,168 m
Surge Tunnels	8 tunnels, horseshoe-shaped, diameter 9.5 m, length 400 m to 485 m
Penstocks (Pressure Shafts)	8 circular shafts, diameter 7 m to 9.5 m, length 195 m to 215 m
Tailrace Channel	Discharge water channel, 35 m long & 206 m wide
Estimated Cost	₹20,370 crore (~£2.21 billion)
Annual Energy Output	7.4 billion kWh
Construction Started	2005; paused due to environmental concerns; restarted in 2019
Commissioning Timeline	Targeted for August 2023
Strategic Significance	Will address Northeast India's power demand & reduce fossil fuel dependence

Concept & Components of a Hydroelectric Power Project

Component / Concept	Description
Hydroelectric Power	Generation of electricity by converting kinetic energy of flowing water into mechanical energy via turbines then to electrical energy using generators.
Types of Projects	Storage-based (dam/reservoir) Run of river (minimal storage, uses natural river flow) Pumped storage (reversible flow for peak demand)
Dam	Structure built across a river to store water or create hydraulic head. Provides elevation for gravitational flow.
Reservoir	Water body created by dam to store water. Ensures consistent flow during dry seasons.
Intake	Opening that allows water from reservoir into tunnels leading to turbines.
Head Race Tunnel	Conveys water from intake to surge tank or pressure shaft. Optimized for minimal friction losses.
Surge Tank	Relieves pressure fluctuations caused by sudden load changes in system. Prevents water hammer effect.
Penstock	High-pressure shaft/pipeline that delivers water to turbines. Must withstand intense water pressure.
Turbines	Rotating machines (e.g. Francis, Pelton, Kaplan types) which convert hydraulic energy into mechanical energy.
Generators	Convert mechanical energy from turbines into electrical energy. Coupled directly to turbine shaft.
Tailrace Channel	Path for discharged water to return to river after passing through turbines. Must ensure minimal backflow.
Control Systems	Automates turbine operation, water gates, power output monitoring, etc. Includes SCADA & MIS systems.
Environmental Concerns	Impact on aquatic biodiversity, seismic risk (especially in Himalayan regions), displacement of communities, sedimentation, deforestation.

Major Hydroelectric Projects in India

Project Name	River	Location	Installed Capacity (MW)	Developer/Operator	Status	Type
Tehri Hydroelectric Project	Bhagirathi	Uttarakhand	2,400 (Tehri Stage I + II)	THDC India Limited	Operational	Storage + Pumped Storage
Lower Subansiri	Subansiri (Brahmaputra)	Arunachal Pradesh–Assam border	2,000	NHPC	Nearing Completion (2025)	Run of River
Koyna Hydroelectric Project	Koyna (Krishna tributary)	Satara, Maharashtra	1,960	Maharashtra State Electricity Board (MSEB)	Operational	Storage
Bhakra Nangal	Sutlej	Himachal Pradesh–Punjab	1,325	BBMB	Operational	Storage
Sardar Sarovar	Narmada	Gujarat	1,450	Narmada Control Authority	Operational	Storage + Irrigation
Nathpa Jhakri	Sutlej	Himachal Pradesh	1,500	SJVN	Operational	Run of River
Dibang Multipurpose Project	Dibang (Brahmaputra)	Arunachal Pradesh	2,880 (planned)	NHPC	Under Development	Storage + Flood Control
Etalin Hydroelectric Project	Dibang tributaries: Dri & Tangon	Dibang Valley, Arunachal Pradesh	3,097 (planned)	Jindal Power Ltd. (under JV)	Environment Clearance Stage	Run-of-River
Karcham Wangtoo	Sutlej	Himachal Pradesh	1,000	JSW Energy	Operational	Run-of-River
Uri-I & II	Jhelum	Jammu & Kashmir	720 + 240 = 960	NHPC	Operational	Run-of-River

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Sources: NSENERGY

PRACTICE QUESTION

Q. Hydroelectric power plays a dual role in India energy & water security. Discuss strategic significance of projects like Tehri, Subansiri & Dibang in this context.