Staff Reporter

‘Masonry dam will be a better alternative'

VISAKHAPATNAM: With the State government yet to start the re-tendering process after pre-closing tenders for the multi-purpose Polavaram project, changes in the structure of the dam are suggested.

Experts veer around to the view that the flood inflow will be 60 lakh cusecs going by the studies made by the National Institute of Hydrology, Roorkee. The length of the surplus channel has to be increased in view of the high flood inflow.

The project design comprises earth and rock-fill dam. Retired deputy chief engineer A.V.L. Bhujanga Rao says the present design is intended to cut the cost of excavation by Rs.250 crores by reducing reflexive action. Consequently, the length of the spill way channel will be reduced. Mr. Bhujanga Rao contends that as a result the surplus water will impinge 200 m below the dam instead of 1000 m. It will be highly dangerous to the safety of the dam and the toe will be eroded by flood waters. Model studies will reveal the position, he says.

To deal with the problem, quoting his experience in an analogous situation for the Fore Bay Dam of the Lower Sileru Hydro Electric Scheme, Mr. Bhujanga Rao suggests erection of semi-hexagonal shape increasing linear length by 1.5 per cent and gates to 66. Mr. Bhujanga Rao sees scope for reducing the cost of excavation.

He contends that the earth and rock-fill dam of a length of 2,310 m necessitates huge transport of earth, rock, sand, gravel and metal involving huge cost and more time. Instead, masonry dam is a better alternative as suggested by Karl Terzagahi, a German engineer. The German who is credited with finding Science of Soil Mechanics visited the site and suggested construction of masonry dam.

The cubic contents of earth dam are 190 per cent more than that of a masonry dam and proportionately the cost increases,

Mr. Bhujanga Rao estimates. Masonry dam will be economic, 100 per cent safe, and can even withstand an earthquake.

The problems related to foundation to masonry dam can be solved with the latest techniques available.