Dams for Venice

Venice, as every visitor learns, is built on low islands in a huge, protected lagoon. When exceptionally high tides strike--which occurs about 25 times a year--the charming Italian city is flooded. Last week for instance Venetians had to cross the Piazza San Marco on wooden gangplanks; the great square was once again ankle-deep in sea water. Though floods have plagued Venice for centuries (one was recorded in A.D. 885), lately they have been getting worse. Main reason: to permit the passage of large ships, the Italians have widened and deepened the three channels through the 38-mile-long barrier beach that protects the Venetian lagoon from the high tides of the Adriatic Sea.

Dead Serious. Now engineers have devised a solution that sounds like the punch line of some sort of Italian joke: rubber dams. But the sponsors of the plan--Pirelli, the famous tire company, and Furlanis, a construction firm--are dead serious about it. They propose installing hollow, expandable dams made of rubber-coated fabric across the three channels. The dams, which would measure from 1,698 ft. to 3,000 ft. in length, would lie on the seabed, held firmly in place by steel cables anchored to concrete pilings. Most of the time they would remain flat, allowing ships to pass over them into the lagoon and normal tides to flush the waters.

But at the first sign of abnormally high tides, enormous pumps would force sea water into the dams, causing them to expand like hot-water bottles. Once full, they would protrude just above the surface of the sea, thus sealing the lagoon. When the danger subsided, so would the dams.

"The project is technically feasible," says Pirelli Engineer Attilio Angioletti. Lab tests have shown that the tirelike rubber fabric has a tensile strength of 2.5 tons per sq. in.--enough to withstand the battering of any sea. To test the system further, Pirelli and Furlanis are now building a 220-ft.-long "baby" dam at the mouth of another lagoon. If it works as well as expected, the Italian government will consider funding dighe di gomma for Venice.

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