Reduce Subansiri dam height: expert panel

Will National Hydro Power Corporation heed report?

By Bharat Lal Seth
Published: Tuesday 13 July 2010

An eight-member expert committee has recommended a thorough review and redesign of the 115-metre high dam on 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. The committee was set up by the Assam government in December 2006. It comprised members from IIT Guwahati, Dibrugarh University and Gauhati University and was asked to study the downstream impact of the ongoing Subansiri dam project. The project is 40 per cent complete.

In its final report submitted on June 29 to NHPC, the committee expressed reservations over the dam, which it believes, could adversely impact downstream areas of Assam. The report revealed inadequacies in the dam's design. The spillway for releasing floodwaters has been designed incorrectly, the committee said. The spillway is based on the maximum discharge of 12,024 cumec, whereas the maximum discharge recorded on July 11, 1971 was more than 21,230 cumec, the report said. “Clearly the dam has not been designed for the highest discharge,” said Chandan Mahanta, of IIT Guwahati, one of the committee members. This can compromise the structure and spell disaster for downstream areas, he added.

The panel recommended reduced dam height and power generation capacity to minimise its adverse economic and environmental impacts. If the present design parameters are followed, the dam construction will impact biodiversity and lead to siltation. To deal with this, the report has recommended a minimum flow of 320 cubic metre per second and a minimum depth of 3 metre in the dolphin habitat stretches area of the river. To minimise dam induced flash floods, the report has recommended flood cushioning in the reservoir.

The report sparked protests. Various environmentalist groups and All Assam Students Union (AASU) demanded immediate stoppage of work on the dam. The activists believe even after redesigning, the dam will create environmental and socio-economic problems. To show their resentment, they are planning to hold a dharna in Dispur before the assembly session begins. “We are now in a strong position to pressurize the government to stop all construction activity,” said Ravindra Nath, founder member of River Basin Friends, a campaign front in Assam.

Officials at the NHPC headquarters in Faridabad, near Delhi, said they were yet to receive their copy. “When it arrives we will look in to 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 the 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 Ravindranath.

Panel's key recommendations

  1. Upstream catchment area needs to afforested while maintaining slope to minimise soil erosion

  2. To minimise dam induced flash floods, proper and adequate cushioning be kept in the reservoir.

  3. Re-examination and redesigning of spillway

  4. Attention to riparian rights and indigenous people

  5. Minimum discharge of 320 cumec to be maintained

  6. Embankments of the river be suitably raised and strengthened

  7. A minimum 3-metre depth in the dolphin habitat stretches

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