Reduce Subansiri dam height: panel

Will National Hydro Power Corporation heed report?

By Bharat Lal Seth
Last Updated: Saturday 04 July 2015

imageAN EIGHT-MEMBER expert committee has recommended a thorough review and redesign of the 115-metre high dam on the Subansiri river, a tributary of the Brahmaputra.

The National Hydro Power Corporation (NHPC) is developing the 2,000 MW Lower Subansiri Hydro Power project in Dhemaji district of Assam.

In its final report submitted on June 29 to NHPC, the committee expressed reservations over the dam, saying it could adversely impact downstream areas. The report revealed inadequacies in the dam’s design. The spillway for releasing floodwaters has been designed incorrectly, it said. The spillway is designed for a maximum discharge of 12,024 cumec, whereas the maximum discharge recorded on July 11, 1971, was more than 21,230 cumec.

“Clearly the dam has not been designed for the highest discharge,” said Chandan Mahanta of IIT Guwahati, a panel member. This can spell disaster for downstream areas, he added. The panel recommended reducing dam height and power generation capacity to minimize its adverse economic and environmental impacts.

If the present design parameters are followed, the dam will impact biodiversity and lead to siltation. To deal with this, the report recommended a minimum flow of 320 cumec and a minimum depth of three metres in the dolphin habitat stretches of the river. To minimise dam-induced flash floods, the report has recommended flood cushioning in the reservoir.

The Assam government had set up the expert committee in December 2006. It comprised members from IIT Guwahati, Dibrugarh University and Gauhati University, and was asked to study the downstream impact of the dam project. The project is 40 per cent complete.

The report sparked protests. Environmentalist groups and the All Assam Students Union demanded immediate stoppage of work. They believe even after redesigning, the dam will create environmental and socioeconomic problems. They are planning protests in Dispur.

Officials at the NHPC headquarters in Faridabad, near Delhi, said they were yet to receive the report. “When it arrives we will look into all the concerns and the remedial measures suggested by the committee,” said a senior official. Earlier this year, Union Power Minister Sushil Kumar Shinde had assured activists that the Subansiri dam project would be reviewed on the basis of the final report.

“My feeling is that either the committee will compromise the report or it will simply be discarded since more than Rs 500 crore has already been spent,” said Ravindra Nath, founder member of River Basin Friends, a campaign front in Assam.

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  • The appeal of Assam Chief

    The appeal of Assam Chief Minister to the Prime Minister as reported in News papers on 25-10-10 for setting up a technical committee to study the safety aspects of Subanasiri dam of 2000 MW capacity is fraught with dangers because the improper location of a such a major dam in the worst seismic zone with a seismicity of 8.5 magnitude on the Richter scale will ultimately result in its collapse during its life time. This 115 high concrete dam over the tributary of the Brahmaputra river is highly under designed as the spillway is designed for peak flood of 12,000 cumecs even though the historical maximum flood of 21200 cumecs occurred in July 1971. As per International Standards the Spillway Design flood must be atleast 2 to 3 times this historical flood ,amounting to atleast 50,000 cumecs. Even then the dam remains under designed from the structural safety angle because the seismic coefficient used for the design of the dam is 0.4 as against the anticipated peak value of 1.0. Under these circumstances the dam is going to burst and cause flash floods that wipe out of existence many villages and towns downstream of the dam including,Gawahati, the state capital of Assam .Many villages and towns will get inundated on an unprecedent scale due to extreme floods caused by not only the collapse of the lower Subanasiri dam but also because of flash floods from other dams in the upper catchment areas of Brahmaputra due to a maximum credible earthquake or extreme floods due to the environmental backlashes like increased deforestation resulting in siltation and aggradation of bed levels and cloud bursts due to intensfied cyclonic storms consequent to the impacts of climate change. Under the circumstances the Government of Assam and Union Governments must take into consideration not only public safety but also the dam safety and the consequential inestimable economic losses that make the project highly unviable from the ecological, environmental, economical and national security perspectives. The height of the project must be reduced from the proposed 115 meters to a much smaller level that can store enough water to generate hydro-power on the premise that even if the dam were to burst the degree of damage to the environmental assets and the people living downstream must be within tolerable limits.

    Prof.T.Shivaji Rao
    Director, Center for Environmental Studies, GITAM University,visakhapatnam.

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