Flood partially damages guard wall of Lower Subansiri dam

OUR BUREAU

ITANAGAR/LAKHIMPUR: A guard wall at the powerhouse of the National Hydro Electric Power Corporation's (NHPC) 2,000-MW Lower Subansiri Hydroelectric Project along the Assam-Arunachal border collapsed due to the rising water level of the river Subansiri, officials said on Sunday.

The incident took place on Saturday late at night due to the overflowing of the Subansiri. The company has evacuated all its workers from the powerhouse, where all the machinery is located, the officials said.

"Heavy rainfall in the foothills of Arunachal Pradesh increased water volume at the project. As a consequence, a portion of the guard wall of the powerhouse collapsed," an official added. An NHPC employee said on condition of anonymity that the damage is a threat to the two turbines and other machinery of the project.

On Friday, one of the diversion tunnels at the project got damaged due to landslides. No person was injured in the incident, a senior official said.

According to NHPC consultant AN Mohammed, the landslides at the tunnel had no effect on the main Subansiri project.

"The cavity above the diversion tunnel No 2 is being filled up and stabilized, though the works are being hampered due to rainfall in the project area during the last few days," he said in a statement.

The company constructed five diversion tunnels as temporary measures to divert the river for the construction of the dam foundation. However, tunnel No 5 was blocked in the outlet in 2020 and tunnel No 2 was blocked near the entry point on September 16 this year due to landslides.

"As the dam construction is nearing completion with 88 per cent progress, the necessity of the diversion tunnels is over, and NHPC is planning to plug all the diversion tunnels after this monsoon," Mohammed said.

In June this year, a person was killed and another seriously injured when the roof of Intact Tunnel No 2 collapsed.

The Assam Government informed the State Assembly in March this year that partial commissioning of the 2,000-MW project has been postponed further till August 2022. However, it is yet to start.

Diversion Tunnel-5 of the project has been lying non-functional for a long period, and the overflowing water is affecting the catchment area and the Diversion Tunnel-3, sources alleged.

The company had earlier set a target of March 2022 for commissioning its biggest project, being constructed along the Assam-Arunachal Pradesh border.

Construction work of the ambitious project at Gerukamukh was stalled from December 2011 to October 14, 2019, due to protests by locals and many groups on safety grounds and downstream impact.

According to a company estimate in January 2020, the cost of the mega project, which was scheduled to be commissioned in December 2012, had escalated to around Rs 20,000 crore from the initial cost of Rs 6,285 crore.

The Centre had allocated a total of Rs 11,000 crore as of December 2010 for the construction of the dam.

The Subansiri Lower Hydro Electric Project is the biggest hydroelectric project undertaken in India so far and is a run-of-river project.

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