[ AN Mohammed ]
For the people of Arunachal Pradesh, the Subansiri river is more than a geographical feature – it is a living presence that has shaped settlements, livelihoods, and culture across Upper Subansiri, Lower Subansiri and Kamle districts for generations.
Rising from the high reaches of Upper Subansiri and flowing through forested valleys and gorges, the river eventually enters Assam before joining the Brahmaputra. Today, with the part commissioning of the Subansiri Lower Hydroelectric Project (SLHEP) at Gerukamukh, this powerful river is entering a new chapter that carries both responsibility and opportunity for Arunachal.
The SLHEP, with an installed capacity of 2,000 megawatts, is India’s largest hydropower project under commissioning in the Northeast. More importantly for Arunachal, it marks a shift in how river-based development is planned and managed. Beyond electricity generation, its reservoir management strategy is opening new avenues for water tourism, fisheries development, flood security and biodiversity conservation – areas of direct relevance to communities living along the river in Upper Subansiri, Lower Subansiri and Kamle districts.
From mountain river to shared resource
Traditionally, large stretches of the Subansiri in Upper Subansiri and Kamle districts were marked by steep gradients, fast currents and limited accessibility. River use was largely confined to small-scale fishing and seasonal crossings. The construction of the 116 metre-high dam at Dollungmukh has transformed this reality by creating a long and stable reservoir upstream.
At full reservoir level, the Subansiri reservoir extends close to 60 kms, varying in width from 400 mtrs to 1 km, and covers about 33.5 sq km. This newly created water body now stretches into Arunachal’s upstream districts, introducing an inland lake-like system in areas where such calm waters did not exist before.
Unlike conventional dams, the SLHEP has been designed as a multipurpose reservoir. Stored monsoon water is released in a regulated manner throughout the year to balance power generation, flood moderation and environmental needs. For Arunachal, this means the Subansiri is no longer just a river flowing out of the state – it has become a shared natural asset with long-term value.
Flood moderation, upstream responsibility, downstream security
Flooding has been a recurring concern associated with the Subansiri, particularly during intense monsoon rainfall. Sudden surges from upstream catchments often caused damage downstream, affecting both Assam and the border areas of Arunachal.
Through scientific reservoir management, the Subansiri lower project now acts as a flood buffer. During peak monsoon months, reservoir water levels are deliberately maintained at lower elevations to create flood cushion. When heavy inflows occur, excess water is temporarily stored and released gradually.
This approach enables complete moderation of medium-scale floods and significantly reduces peak flood levels during larger events. While this requires sacrificing some power generation during the monsoon, the emphasis on public safety and river basin stability reflects responsible upstream stewardship – something of particular importance to communities in Lower Subansiri and Kamle districts.
Water tourism opportunities for Upper and Lower Subansiri
One of the most visible outcomes of reservoir creation is its potential for water based tourism – a sector with growing importance for Arunachal’s economy. The calm waters extending into Upper Subansiri and Lower Subansiri districts, combined with forested hills and scenic surroundings, provide ideal conditions for sustainable tourism development.
Activities such as boating, kayaking, eco-cruises, river safaris, bird watching and lakeside camping can be developed with proper planning and safety infrastructure. The reservoir also opens possibilities for improved river transport in remote stretches, enhancing connectivity for local communities.
For young people in the districts and surrounding areas, water tourism offers new livelihood options as boat operators, guides, hospitality workers and ecotourism entrepreneurs, while keeping development aligned with Arunachal’s strong conservation ethos.
“The state government has already announced plans to develop the Subansiri Lower pondage into a world-class mountain-cum-river immersive tourism hub, integrating ecotourism, adventure, culture, and sustainable livelihoods. It may be noted that on 28 March, Chief Minister Pema Khandu, along with colleagues and officials undertook a high-speed river journey spanning approximately 45 kms along the Subansiri river, from the SLHEP site in Dollungmukh to the Kamle-Subansiri confluence.” (The Arunachal Times, 24 April 2026)
Fisheries and pisciculture
The formation of the reservoir has altered local water conditions, making them suitable for reservoir fisheries and pisciculture. Calmer water, increased depth and improved nutrient retention create favourable habitats for both indigenous fish species and new varieties adapted to reservoir environments.
Scientific assessments indicate strong potential for cage culture and cooperative fisheries in stretches affecting Lower Subansiri and Kamle districts. With support from central and state fisheries schemes, these initiatives can provide steady income to riverine communities.
For villages that traditionally depended on forest resources and shifting cultivation, fisheries development offers a complementary livelihood -strengthening food security while reducing pressure on natural ecosystems.
Emerging habitat for migratory birds and aquatic life
Over time, large reservoirs often evolve into seasonal habitats for migratory birds. The Subansiri reservoir’s stable water regime, shallow inlet zones, and surrounding forest cover in parts of Kamle and Upper Subansiri districts create favourable conditions for wintering birds arriving from northern Himalayan regions and Central Asia.
At the same time, regulated releases from the dam ensure minimum environmental flows downstream throughout the year. This sustains aquatic life, supports plankton growth, and improves breeding conditions for fish even during the lean season.
Environmental experts believe that, if monitored carefully, the Subansiri reservoir and its downstream stretches could gradually develop into a biodiversity hotspot within Arunachal, enhancing both conservation and ecotourism potential.
Science-based management rooted in local reality
The reservoir operations at the SLHEP are guided by more than five decades of hydrological data. Seasonal regulation balances power generation with flood safety, environmental flows and sediment transport.
By keeping reservoir levels lower during monsoon months, sediment is allowed to pass naturally through the system. This reduces long term accumulation and helps maintain downstream river morphology – an important consideration in Arunachal’s fragile Himalayan terrain, particularly in erosion prone districts like Kamle.
A development model for Arunachal
The Subansiri Lower Hydroelectric Project represents a new generation of hydropower development – one that recognises rivers as living systems rather than mere energy channels.
For Arunachal, and especially for Upper Subansiri, Lower Subansiri and Kamle districts, the project demonstrates that large infrastructure can deliver multiple benefits: clean energy, flood safety, livelihoods, tourism and biodiversity conservation.
The Subansiri is no longer only shaping valleys and plains – it is shaping futures. Through responsible reservoir management, it is lighting homes across the country while opening new horizons for communities in Arunachal. (AN Mohammed is a consultant for hydropower development in Northeast India)
