Subansiri Lower Hydroelectric Project Begins Power Generation After Two Decades

Power Generation Commences at Subansiri Lower Hydroelectric Project

Guwahati, Dec 4: The Subansiri Lower Hydroelectric Power Project has officially started generating electricity after a lengthy 20-year development phase, with its first unit successfully synchronized to the national power grid at 6:12 PM yesterday.

This ambitious 2,000 MW project, managed by NHPC, consists of eight units, each with a capacity of 250 MW. The second unit also began operations yesterday, and three additional units are expected to be operational within this month. The entire project is projected to be fully operational by March 2027.

According to project consultant AN Mohammad, the synchronization of the first unit marks a significant milestone in India's hydropower development.

The commissioning process for Unit 1 and Unit 2 began with mechanical tests on October 26 and November 6, respectively. The synchronization of Units 1, 3, and 4 will follow after thorough testing during wet commissioning, which is anticipated to add another 1,000 MW by December 2025.

The commercial operation date (COD) will be announced soon, with the final four units expected to be connected sequentially between 2026 and 2027, further enhancing energy supply and supporting national infrastructure.

Once completed, the Subansiri Lower HE Project is anticipated to generate 7.421 billion units of renewable energy annually, significantly contributing to India's energy sector and aiding in achieving the country's carbon neutrality goals.

Providing insight into the project's background, Mohammad noted that the Subansiri Lower HEP was conceived in January 2005 at Gerukamukh, located on the Arunachal Pradesh-Assam border, and has faced numerous challenges.

Construction was halted for eight years from 2011 to 2019 due to protests in Assam and legal disputes concerning dam safety and ecological concerns downstream.

However, with enhanced mitigation strategies, construction resumed in October 2019, turning skepticism into tangible progress.

To address these legitimate concerns, the Government of India established expert panels. The Technical Expert Committee (TEC), created by the Planning Commission in July 2012, effectively addressed the hydrological concerns raised by the Assam Expert Group.

In June 2013, the Dam Design Review Panel (DDRP) recommended crucial safety improvements, including widening the dam from 171 meters to 271 meters, extending upstream cut-off walls, and implementing downstream seepage barriers, along with intensive foundation grouting and rock anchors.

The National Committee for Seismic Design Parameters (NCSDP) also reviewed and approved the seismic safety measures for the project.

A significant study titled 'Cumulative Impact and Carrying Capacity Study of the Subansiri Sub-Basin, Including Downstream Impacts,' led by the Central Water Commission (CWC) in December 2014, emphasized the importance of ecological balance.

It mandated a consistent environmental flow of 240 cubic meters per second to support the river's aquatic ecosystem, ensuring the Subansiri remains vibrant for future generations.

The Subansiri River is known for its turbulent history, having caused significant flooding and erosion in Assam's plains for decades. The catastrophic earthquake in 1950 altered its course, leading to landslides that temporarily blocked the river in Arunachal Pradesh, resulting in devastating floods downstream. The project's reservoir, with a capacity of 1,365 million cubic meters (MCM), is designed to mitigate such extreme events.

It allows for unimpeded monsoon flows while ensuring minimum flows during non-monsoon periods to sustain downstream ecosystems.

A 15-meter flood cushion atop the reservoir, holding 442 million cubic meters, acts as a crucial buffer, while extensive riverbank reinforcements—spanning 60 km downstream—have increased the channel's capacity by 15-20%.

Additionally, downstream development initiatives worth over Rs 470 crores aim to enhance health, education, sustainable livelihoods, and infrastructure for affected communities.

Beyond its protective measures, the project promises to generate 7.421 billion units of clean, renewable energy annually, advancing India's clean energy initiatives.

As a national project, power distribution follows central hydropower regulations. Assam will receive a preferential allocation of 300 MW, in addition to its standard 208 MW share, along with 25 MW of free electricity. Arunachal Pradesh, as the host state, will benefit from a 12% allocation of free power according to national hydropower policy.

The remaining power will be distributed to other states, including those in Northeast India.

The project's cost has escalated from Rs 6,285 crores at 2002 prices to approximately Rs 26,000 crores at current prices, primarily due to the prolonged construction timeline, escalation costs, and interest during construction, as noted by Mohammad.