Works delayed as water level reaches 570 feet and minor leakages develop beneath the gates
Over 90 per cent of works to repair the Nagarjunasagar dam spillway in its glacis and bucket portions, have been completed after much delay because of the last year's floods and rise in water levels. The works are scheduled to be closed by soon.
M.A. Saleem, Executive Engineer, Nagarjunasagar dam, told The Hindu that repairs were launched in March last year, but were delayed because contractor had approached the Andhra Pradesh High Court when the water level reached 570 feet, and also due to minor leakages under the gates.
The court permitted execution of work in May by the same contractor. Mr. Saleem said during the construction of the dam itself there was a difference in profile and construction. This had not been exposed for 35 years. The damage was revealed after 40 years as small patches started coming off. After 45 years, it increased because of the floods.
The floods continued every year from 2005. On October 4, 2009, as much as 10.23 lakh cusecs (a record) was released. By now the damage, ‘due to negative pressure in the construction and design profile', increased to 90 per cent. A six-foot concrete got eroded and up to four or five feet of masonry work was washed away, warranting immediate repairs.
Authorities realised that the damage could pose a major threat to the structure and that precautions should be taken. All masonry eruptions were filled with ‘M 60 concrete' as also a special ingredient silica fume. Steel fibre reinforcements were added.
He said flood water had been passed to test the dam safety in September, October and November last year.
The test was successful after it was found that there was no damage in the vents where repairs were done.