Plan to save Venice from the sea draws praise, doubts

By December, engineers expect to begin building a movable wall of 79 huge gates.

The last thing Venice needs now is a dose of what the rest of the Europe has endured over the past two-and-half weeks: heavy rains and high flood waters. Those rains raised sea levels around Venice by some 35 inches, threatening to worsen the city's longtime battle against rising tides.

The latest threat comes as plans are being completed for a project that supporters say will fend off just such climatic events and protect "the bride of the sea" and its architectural treasures. But critics say the project won't do the job.

Built on a series of islands in a large lagoon, Venice has been slowly sinking under its own weight throughout its thousand-year history. In the 20th century, relative sea level in Venice increased by more than 9 inches. Green algae grow on the porous brickwork of many of the palaces along the Grand Canal.

After decades of debate and study, the Italian government is offering a solution. The centerpiece, approved in December, is a $3 billion project to build 79 huge hinged gates to separate Venice and its lagoon from the Adriatic.

The gates will lie flat on the sea floor inside the three entrances to the lagoon. In conditions of "acqua alta" – an especially high tidal surge produced by certain wind conditions – the gates will swing up to form a temporary wall against the water. The gates are designed to protect the city from flood surges of up to 6 feet. That's sufficient to keep up with sea-level rise for at least 70 years, says Giovanni Cecconi, an engineer with the New Venice Consortium, an alliance of Italian engineering firms charged with designing, building, and operating the project. "It's not the final solution, it's just a way to protect the city during this century until another solution can come into place," he says.

Supporters point to similar multibillion-dollar flood-control projects already built by Britain and the Netherlands.

But the project's most prominent critic, Colgate University archaeologist Albert Ammerman sees "fundamental flaws" in the consortium's scientific studies.

Mr. Ammerman and his colleagues found that the city has been sinking much faster than previously thought. Throughout the city they found layer upon layer of pavements and foundations laid over the centuries in a constant effort to keep the city above water. Using new carbon- dating techniques, his team calculated the rate of relative sea-level rise going back 1600 years. Ammerman says the sea will gain 12 to 39 inches relative to Venice's streets within a century.

The problem, Ammerman says, is that the gates will have to be closed far more often than their planners say. Since most of Venice's sewers empty into the city's canals and lagoon with little or no treatment, frequent lagoon closures could trigger serious environmental consequences. "In a bad year [in the mid-21st century] you could have the gates closed for 100 or 120 days a year, with two-thirds of them in the three-month flood season," Ammerman says. He predicts the resulting pollution crisis will shorten the project's lifespan to 30 or 40 years.

Monica Ambrosini, a consortium spokeswoman, disagrees. "The problem of sea-level rise is very real, and the designs take it into account," she says. The company expects to start construction by the end of the year.

Meanwhile, after 50 years of neglect, Italian authorities have started dredging canals, raising city pavements, and repairing damaged seawalls. Italy expects to spend about $40 million a year for the next decade on such projects in an effort to reduce the number of times the planned gates would need to be closed.

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