A noted environmentalist and expert from Andhra Pradesh has demanded re-design and reduction in height of the 115-metre Subansiri dam in Assam to minimise its adverse environmental impacts.
“This 115-high concrete dam over Subansiri river, a tributary of Brahmaputra is highly under-designed as the spillway is designed for peak flood of 12,000 cubic metre per second, even though the historical maximum flood of 21200 cumec occurred in July 1971,” Professor T. Shivaji Rao, Director, Center for Environment Studies, GITAM University and Expert, Cloud seeding project in Andhra Pradesh said in a release here.
Also, the 2000-MW hydel project is fraught with danger because of its location in a highly seismic zone which may ultimately result in its collapse, he said.
As per international standards, the Spillway Design flood must be at least 2-3 times this historical flood amounting to at least 50,000 cumec. 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, Mr. Rao said.
Under these circumstances, the dam is going to burst and cause flash floods that will wipe out many villages and towns downstream of the dam including Guwahati, he said.
Many villages and towns will get inundated on an unprecedented scale due to extreme floods caused by not only the collapse of the lower Subansiri 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 intensified cyclonic storms consequent to the impacts of climate change, the release said.
Hence, the Centre and the Assam government must take into consideration not only public safety but also dam safety and the consequential inestimable economic losses that make the project highly unviable from the ecological, environmental, economical and national security perspectives, he said.
“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,” Mr. Rao, former HOD, Civil Engineering and Principal of College of Engineering, Andhra University, said.