New Delhi: A proposed hydroelectric project in Arunachal Pradesh has brought into focus the environmental costs of expanding hydropower infrastructure in the Eastern Himalayas, with official documents showing that its implementation could require the diversion of 3,278 hectares of high-conservation-value forest and the felling of more than 23.4 lakh trees.

State-owned National Hydroelectric Power Corporation (NHPC) has approached the Union Environment Ministry for forest clearance for its 1,720 MW Kamala Hydroelectric Project, planned on the Kamala River, a right-bank tributary of the Subansiri River. The project, estimated to cost ₹23,764.01 crore, is among several hydropower developments planned in the Subansiri river basin.

The Ministry’s Forest Advisory Committee (FAC) is scheduled to examine the forest-diversion proposal on October 23, according to its official agenda. The proposal covers forest areas across Kra Daadi, Kurung Kumey and Kamle districts in the lower Himalayan region of Arunachal Pradesh.

The scale of the proposed diversion is considerable. Documents submitted for the project identify 23,40,213 trees for felling, including approximately 15.08 lakh in the Hapoli forest division and 8.31 lakh in the Kra Daadi division.

The proposal has raised questions about the ecological consequences of a large infrastructure project in a predominantly hilly landscape covered by dense forests, particularly when the compensatory afforestation intended to offset the loss is proposed in another state.

A forest-rich landscape faces a massive intervention

Of the 3,278 hectares of forest proposed for diversion, 439 hectares are classified as very dense forest and another 1,119 hectares as moderately dense forest.

The project's environmental impact assessment, based on field surveys conducted across different seasons, recorded 155 plant species belonging to 69 families in the study area. These include trees, shrubs, herbs, grasses, climbers and ferns.

The figures offer a glimpse of the biological diversity of the area that could be affected by the project. The implications of clearing such an extensive forest area, however, extend beyond the number of trees identified for felling.

Forests in the Eastern Himalayas form part of interconnected ecosystems in which vegetation, wildlife habitats, river systems and animal movement routes are closely linked. Large infrastructure projects can alter these relationships through land clearing, reservoir submergence and the construction of associated facilities.

A site inspection report prepared by officials of the Environment Ministry’s regional office in Shillong acknowledged that the project site does not fall within a national park, wildlife sanctuary, biosphere reserve or elephant corridor.

However, the report cautioned that the absence of such a protected-area designation does not eliminate the project's potential impact on wildlife.

The report observed that the project “will undoubtedly affect the habitats of various wildlife. Moreover, the increased width of the submerged area will adversely affect the migration of wild animals from one bank to the other.”

The officials consequently called for a wildlife mitigation plan or biodiversity conservation plan.

The concern is particularly relevant in a landscape where the movement of animals between forested areas is essential to maintaining viable habitats. Reservoir submergence and associated infrastructure could alter the continuity of these habitats, making the effectiveness of mitigation measures an important consideration in the clearance process.

The price of compensating for forest loss

One of the most consequential aspects of the proposal is the plan to undertake compensatory afforestation in Madhya Pradesh rather than Arunachal Pradesh.

According to the latest Indian Express report, NHPC has proposed compensatory afforestation over 7,018 hectares across several districts of Madhya Pradesh.

The arrangement reflects the difficulties of identifying suitable land for compensatory plantations in a state with extensive forest cover. Under the applicable forest-conservation framework, compensatory afforestation can be undertaken outside the state where forest land is being diverted when the prescribed conditions are met.

Where equivalent non-forest land cannot be made available, the applicable rules provide for plantations over twice the diverted area on degraded forest land.

The proposal therefore involves a substantial plantation programme intended to compensate for the loss of forest cover in Arunachal Pradesh.

But the location of the plantations raises a broader ecological question: how far can afforestation in another state compensate for the loss of a mature forest in the Eastern Himalayas?

The environmental functions of an existing forest depend on more than the number of trees it contains. Its vegetation, habitat structure, species composition and relationship with the surrounding landscape contribute to its ecological value.

Plantations established elsewhere may help meet compensatory-afforestation requirements, but they cannot automatically reproduce the ecological characteristics of the forest being diverted.

The Environment Ministry's expert appraisal committee has itself expressed concern over the proposed tree felling and called for a precise and well-managed ecosystem-restoration plan, including adequate mitigation and compensatory measures.

The committee stressed that these measures would need to be developed in consultation with the state Forest and Wildlife Department, ecology and wildlife experts, and local people.

The effectiveness of the proposed afforestation and restoration measures will therefore be central to assessing the project's environmental implications.

A 216-metre dam and a reservoir in the Subansiri basin

The Kamala project is conceived as a run-of-the-river project with storage facilities. It involves the construction of a 216-metre-high concrete gravity dam equipped with flood-moderation features.

The reservoir and dam-top areas are expected to occupy nearly 2,960.49 hectares of forest land, according to the project documents cited by The Indian Express.

The project is designed to harness the flow of the Kamala River for electricity generation, while the storage component and designated flood cushion are intended to provide flood-moderation benefits.

Hydropower projects of this scale can contribute to electricity generation, but their environmental implications depend on the extent of land required, the area submerged, the changes to river systems and the measures adopted to protect surrounding ecosystems.

The Kamala project is part of a wider cascade of hydropower developments planned in the Subansiri basin. The 2,000 MW Lower Subansiri project, located at Gerukamukh on the Assam-Arunachal Pradesh border, lies downstream on the main Subansiri River.

The development of multiple projects within the same river basin makes the cumulative effects of infrastructure particularly relevant. Individual clearances may examine the impacts of specific projects, while the wider ecological consequences can also depend on how several developments interact across the river system.

The Kamala proposal thus forms part of a larger debate over how hydropower potential in the Eastern Himalayas can be developed while accounting for forest conservation, biodiversity and the needs of local communities.

Thousands of families across 126 villages

The project's potential impact is not confined to the forest landscape.

According to its Social Impact Assessment report, 5,440 families across 126 villages are expected to be affected by the development.

The affected villages are spread across Kamle, Kra Daadi and Kurung Kumey districts. The area is predominantly hilly, with dense forests forming a significant part of the surrounding landscape.

The implications for local communities will depend on the project's land requirements, construction activities, rehabilitation arrangements and the effects on livelihoods and access to natural resources.

The project's environmental and social assessment is therefore important not only for identifying ecological impacts but also for establishing the measures required to address the concerns of people living in the affected area.

Public hearings were conducted as part of the environmental-clearance process, and the project has been considered by the Environment Ministry's expert appraisal panel.

However, the implementation of rehabilitation, compensation and environmental-management commitments will remain an important part of determining the project's eventual impact on the region.

Environmental clearance is not the final hurdle

The Kamala project has undergone several rounds of investigation and changes in configuration over the years.

The Brahmaputra Board began investigating the project area in 1996. NHPC subsequently undertook feasibility studies and prepared a detailed project report. The project was later transferred to Kamala Hydro Electric Power Company Limited, which pursued an earlier version with an installed capacity of 1,800 MW.

The project subsequently stalled after unresolved issues led to the return of the detailed project report and the rescinding of earlier clearances in 2018.

The Arunachal Pradesh government approved the project's allotment to NHPC in 2023. NHPC later revised the installed capacity to 1,720 MW, and the Central Electricity Authority concurred with the revised detailed project report in May 2025, according to the Environment Ministry's appraisal records.

In January 2026, the ministry's expert appraisal committee recommended the project for environmental clearance, subject to obtaining in-principle forest clearance.

That recommendation did not amount to final forest clearance or permission to begin felling the trees identified in the proposal.

The forest-diversion application is being considered separately by the Forest Advisory Committee. The latest report in The Indian Express says the committee is scheduled to examine the proposal on October 23.

The distinction matters because the environmental appraisal and forest-clearance processes are separate regulatory steps. The proposed tree felling remains contingent on the necessary approvals.