A rising crisis for Venetians


Venice: Since the devastating floods of 1966, all sorts of plans to protect the city from high water have been on the table. Most have been stalled by a bureaucratic logjam.

March 27, 2001|By Tom Hundley | Tom Hundley,CHICAGO TRIBUNE

VENICE -- In the 16th century, the doges of Venice faced an urgent crisis. Silt carried by the Brenta and Piave rivers was slowly filling the Lagoon of Venice; unless immediate action was taken, the city would be left high and dry.

"After about a hundred years of discussions between the Greens and the engineers of that time, it was finally decided to divert the rivers. The lagoon was saved," says Ignazio Musu, a professor at Venice's Ca' Foscari University.

These days, the doges are in a similar quandary, only this time the problem is too much water.

The vestibule of St. Mark's Basilica, the most famous building in the city, was ankle-deep in water for 250 days last year. On Nov. 6, the city weathered its third highest flood in 100 years as tides in the lagoon rose 57 inches above the normal level. That put most of the city knee-deep in murky gray-green water.

Already this year, the city has experienced 15 consecutive days of acqua alta, high water.

Since the devastating floods of 1966 that caused billions of dollars in damage to the city's architectural and artistic treasures, all sorts of plans to protect Venice from flooding have been on the table.

The most ambitious -- and the one that has received the most international attention -- is a $2.5 billion project to erect a series of mobile flood barriers that would shut the lagoon off from the Adriatic Sea when flood conditions threatened. But building the mobile barriers has been stalled for 30 years by a three-way debate between politicians, environmentalists and engineers.

In that respect, little has changed since the days of the Serenissima. Venetians still take a long time to make up their minds.

Not Mayor Paolo Costa, who took office about nine months ago. Unlike some of his famously indecisive predecessors, Costa knows exactly what he wants to do.

"I made up my mind years ago," he says. "It is not a question of mobile barriers or some other diffuse interventions. We need both. There is no alternative."

To break the bureaucratic logjam, Costa has given the go-ahead for construction of a network of unobtrusive dykes around the perimeter of St. Mark's Square. The dykes will be about 8 inches high -- and the slope will be so gradual that few tourists will notice -- but the extra inches should reduce the number of days the famous piazza is flooded, from more than 80 last year to about six or seven.

Construction is scheduled to begin this month, according to Maria Teresa Brotto, an engineer with the New Venice Consortium, a business group that was formed in 1984 to develop various flood protection projects.

In addition to raising the perimeter of St. Mark's, workers will first repair and then seal a newly discovered network of drainage tunnels beneath the square that tended to back up when the square was flooded, compounding the problem. They also will install a 16-inch layer of clay beneath the surface of the square to act as a shield against groundwater that rises with the tides.

Venice, built on a shifting pile of mud in a shallow lagoon, has always been flood-prone. Since 1900, the ground on which it sits has subsided by about 8 inches, while at the same time the sea that surrounds the city has risen about 4 1/2 inches. Scientists who have been studying global warming trends warn that the sea will rise by at least 8 inches over the next 50 years.

The acqua alta has become so routine and predictable that electronic message boards along the Grand Canal tell residents exactly when they can expect water to come sloshing over the side. An elaborate network of elevated walkways can be quickly assembled throughout the city at the first sign of flooding.

The work around St. Mark's Square is only a Band-Aid measure, according to Costa. As former national minister of public works in the previous government, Costa has long been a supporter of what has been dubbed "Project Moses."

Although it would part the seas in biblical fashion, Project Moses owes it name to the Italian acronym for electro-mechanical experimental model -- MOSE.

The project envisions a series of flood barriers formed by a row of hollow metal flaps, 98 feet high, hinged to pilings embedded in the sea floor. At normal water levels, the flaps rest on the sea bottom.

But when a storm surge threatens, compressed air is pumped into the flaps, causing them to rise and block off the lagoon. At a 45-degree angle, the barrier can hold back 6 feet of water. London, Rotterdam and Hamburg, three cities vulnerable to flooding, already have installed similar barriers in anticipation of high waters caused by global warming.

In Venice, the barriers would shut off the three entrances where the sea enters the lagoon. They would be activated only when storm surges in excess of 3 feet are anticipated. Under present circumstances, that would be about seven to 12 times a year. But as the sea level continues to rise, the number could triple by 2030.

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