Upper Subansiri Hydroelectric Project

Context

The Expert Appraisal Committee (EAC) under the Ministry of Environment, Forest and Climate Change (MoEFCC) has recommended environmental clearance for the 1,605 MW Subansiri Upper Hydroelectric Project (SUHEP) in Arunachal Pradesh, subject to Stage-I forest clearance.

Project and Hydropower Cascade

1. Developer & Location: National Hydroelectric Power Corporation (NHPC) Limited is developing the 1,605 MW project near Menga, Upper Subansiri district, Arunachal Pradesh.
2. Key Features: It is a run-of-the-river project with storage, with a 237 m high dam and a reservoir extending about 50 km at FRL.
3. Purpose: The project aims at power generation and flood moderation.

4. Cascade: SUHEP is part of a hydropower development plan in the Subansiri basin, including Dengser, Oju, Niare, Naba and Nalo upstream and Subansiri Lower Kamala HEP, earlier called Subansiri Middle, is located on the Kamala River, a tributary of the Subansiri.

Subansiri River

1. Nature: A trans-Himalayan River and a major right-bank tributary of the Brahmaputra.
2. Origin & Course: Originates in Tibet and flows through Arunachal Pradesh and Assam before joining the Brahmaputra.
3. Name: Known as the “river of gold” due to the presence of gold-bearing sediments.
4. Tributaries: Major tributaries include Kamla, Tsari, Jiyadhol, Ranganadi and Dikrong.

Environmental and Disaster Risks

1. Forest Loss: Diversion of 2,733 ha of forest land and felling of nearly 1.36 lakh trees may cause habitat fragmentation and biodiversity loss.
2. Wildlife Impact: Fragmentation may disrupt wildlife movement, habitat connectivity and ecosystem services.
3. Flood Risk: The project is vulnerable to GLOFs and extreme flood discharge, requiring adequate dam-design safeguards.
4. Cascade Risk: A dam breach could affect the downstream Subansiri Lower Project, highlighting the need to assess cumulative basin-level risks.

Mitigation and Compensatory Measures

1. Biodiversity Management: NHPC must implement a site-specific, time-bound Ecosystem Restoration and Biodiversity Management Plan as directed by the EAC.
2. Compensatory Afforestation: 5,466 ha of degraded forest land in Madhya Pradesh has been identified for afforestation under the applicable forest-clearance provisions.
3. Local Conservation: Restoration measures should prioritise habitat connectivity, wildlife movement and ecosystem recovery around the project area.
4. Compliance: Timely implementation and monitoring of forest-clearance and compensatory-afforestation obligations are essential to address ecological impacts.

FAQs

Q1. What is the Subansiri Upper Hydroelectric Project?
Ans. It is a 1,605 MW NHPC project on the Subansiri River in Arunachal Pradesh for power generation and flood moderation.

Q2. Why is the Subansiri River geographically important?
Ans. It is a trans-Himalayan River originating in Tibet and flowing through Arunachal Pradesh and Assam before joining the Brahmaputra.

Q3. What is a Glacial Lake Outburst Flood (GLOF)?
Ans. A GLOF is the sudden release of water from a glacial lake, causing potentially destructive downstream flooding.

Q4. Why is the Subansiri project considered part of a cascade?
Ans. It is part of a basin-wide series of hydropower projects, including Oju upstream and Subansiri Lower downstream.