The type of cofferdam approved by the Polavaram Dam Design Review Committee allows water to be diverted into the project’s canals even before completion, explains Irrigation Engineering-in-Chief M. Venkateswara Rao.
Minister for Water Resources D. Umamahesw
ara Rao asked the Engineering-in-Chief to explain to the media the nuances of the project here on Friday.
Mr. Venkateswara Rao said that the cofferdam (temporary enclosure built with a body of water to allow the enclosed area to be pumped out for creation of a dry work environment) approved by the committee would be able to withstand a flood of 28 lakh cusecs in the river.
Though it was huge, the cofferdam was temporary and meant to be removed after completion of the regular dam, he explained.
Two types of cofferdams were usually employed in the construction of dams — one which allows work only in the dry season and the other that allows work all through the year.
Limiting work only to the dry season took a long time for the completion of the project and resulted in increased overheads and, therefore, not viable.
A combination of the cofferdam and the spillway could be used to impound water and create enough head to divert water into the Polavaram Right and Left canals, Mr. Venkatewara Rao said.
The time for completion of the project would be further reduced by working on the cofferdam, the main dam, and the gates simultaneously as suggested by Chief Minister N. Chandrababu Naidu, the engineer said.
Giving technical details, he said that the crest of the spillway was 25.72 metres above Mean Sea Level (MSL).
“The level of the spillway canal will be 17 m above MSL, but the crest of the spillway will be 25.72 m. This can be used to divert water. If building of piers and manufacturing of gates is also taken up simultaneously, water can be impounded up to the level of 35.5 m above the MSL,” he explained.
The cofferdam was designed to withstand a flood of 28 lakh cusecs and water level of up to 41 m above MSL, Mr. Venkateswara Rao said.
Dig at Congress
Mr. Umamaheswara Rao said that Congress leaders, who could not even get the designs of the dam finalised, had no moral right to criticise the Telugu Desam government, which was leaving no stone unturned.
But for the efforts of the TDP government, which was quick to get vacated nine villages that were an obstacle for work, there would have been no progress, he said.
The Congress government, which was unable to get the villages vacated, simply gave up and delayed the project by 10 years, he alleged.
