Subansiri Runs Dry After Landslide

Lower Subansiri Hydroelectric Project

Why in News?

  • Massive landslide damages the under-construction Lower Subansiri Hydroelectric Project in October 2023, blocking the river flow downstream
  • The project has faced multiple delays and opposition from stakeholders due to environmental concerns

The under-construction 2000 MW Lower Subansiri Hydroelectric Project in Arunachal Pradesh and Assam border, was hit by a massive landslide on 27th October 2023. A large part of the hill slope on the left side of the dam collapsed into its reservoir, blocking the only functional diversion tunnel and stopping the flow of water downstream into the Subansiri river.

Here is a detailed analysis of Lower Subansiri Hydroelectric Project and the impact of recent landslide, by the UCN Team to give you the key concepts and insights.

This is the latest setback for the long-delayed project which has already faced multiple extensions of its commissioning deadline. The project construction had been stalled between 2011-2019 due to protests and opposition from local stakeholders over environmental concerns related to landslides, dam safety and downstream impact. The recent incident has renewed calls for reviewing the project’s safety mechanisms and environmental norms.

With over 90% of construction completed, the damage caused by the landslide and its impact on the river’s flow has highlighted the risks of ignoring expert advice. The project developer NHPC Ltd had not conducted slope stability assessments recommended by the Central Electricity Authority earlier this year. The recommendations were made after multiple landslide incidents at the dam site in 2022 and 2023. However, NHPC maintained that no further assessments were required. The latest incident is thus in news as it has exposed the flaws in risk management and lack of transparency that has plagued the implementation of this mega hydro project.

Subansiri River

  • The Subansiri River (Chayul Chu in Tibet) is a trans-Himalayan River and a tributary (right bank) of the Brahmaputra River.
  • It flows through Tibet’s Lhuntse County in the Shannan Prefecture, and the Indian states of Arunachal Pradesh and Assam.
  • The Subansiri is approx. 518 km (322 mi) long, with a drainage basin 32,640 square km (12,600 sq mi).
  • It is the largest tributary of the Brahmaputra contributing 7.92% of the Brahmaputra’s total flow.
  • The river holds importance due to the following factors:
    • It is a major tributary and contributes significantly to Brahmaputra’s flow
    • Has a large drainage basin spread across China, Arunachal Pradesh and Assam
    • Home to aquatic biodiversity including endangered Gangetic river dolphins
    • Source of livelihoods for local communities through fishing and agriculture
    • Site for hydropower projects like Lower Subansiri Hydroelectric Project
subansiri river
subansiri river

About Lower Subansiri Hydroelectric Project

Project Details

  • The Subansiri Lower Dam, officially named SLHEP, is an under-construction gravity dam on the Subansiri River in North Eastern India on the borders of Arunachal Pradesh and Assam.
  • Described as a run-of-the-river project by National Hydroelectric Power Corporation (NHPC) Limited, the Project is expected to supply 2,000 MW of power (eight 250 MW units) when completed.
  • NHPC Limited commenced construction work of the SLHEP in 2005 after obtaining forest clearance.
  • The project has key stakeholders including:
    • NHPC Limited – project developer
    • Central government – approval and oversight
    • Arunachal Pradesh and Assam state governments – project falls in both states

Issues and Controversies

  • There have been several issues and controversies related to the project:
  • Environmental concerns related to biodiversity, river flow impact downstream.
  • Changes in dam design like height reduction without public explanation.
  • Time and cost overruns – Expected completion pushed from 2018 to 2024. Cost escalated from ₹6,285 crore to ₹20,000 crore.
  • Previous instances of landslides at the dam site including in 2005, 2022, and now in October 2023.

Recent Landslide Incident

Events

  • In October 2023, a massive landslide occurred at the dam site, and the only functional diversion tunnel was blocked.
  • This stopped the river flow downstream into the Subansiri river.
  • The project developer NHPC Ltd had ignored recommendations of the Central Electricity Authority (CEA) to assess the impact of diversion tunnels on slope stability.

Impacts

  • The incident will likely cause further delays in project commissioning, which has already been pushed to 2024.
  • Aquatic life and environment downstream have been impacted due to the stoppage of river flow. There are reports of large numbers of fish dying.
  • The incident has renewed calls for review and more transparent assessment of the project’s safety mechanisms and environmental impact.
  • More extensive slope stabilisation measures will need to be taken to prevent future landslides.
  • Accountability needs to be fixed for ignoring expert advice on timely safety assessments.
  • The failure to follow protocol has exposed flaws in risk management of this mega project.

Way Forward

  • Review and strengthen the safety standards, design parameters and environmental norms for hydropower projects especially in earthquake prone and ecologically sensitive areas.
  • Address the concerns of local stakeholders and communities through proper public consultations.
  • Strengthen early warning systems and risk management protocols for landslides, floods and other natural disasters.
  • Ensure transparency and accountability at all stages of large dam projects. Independent safety audits should be mandatory.
  • Fix responsibility for ignoring expert advice and not taking timely preventive measures.
Hydroelectric Power Plant
Hydroelectric Power Plant

Final Thoughts

The UCN team is inclined to think that:

  • The Lower Subansiri project exemplifies the importance of balancing development needs and environmental sustainability.
  • It is a cautionary tale against the complacency of ignoring expert advice on safety assessments for large infrastructure projects.
  • The incident emphasises the need to learn from such experiences and incorporate lessons into planning of future dam building activities.
  • Safety mechanisms, risk assessment protocols and emergency preparedness need to be strengthened.
  • Participation of indigenous communities, transparency norms and environmental impact mitigation should get priority to avoid cost and time overruns.
  • With India’s ambitious plans for hydropower expansion in sensitive Himalayan regions, we must imbibe these lessons to prevent any future disasters.
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UCN Team
UCN Team

UCN Team: Combining expertise in UPSC Exams and Tech to deliver high-resolution, insightful content for aspiring civil servants

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