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Saving Venice

An ambitious plan seeks to prevent a modern Atlantis
St. Mark's Square



FABIO GATTA/1999 Consorzio Venezia Nuova
It is 6 a.m. on New Year¿s Day, 2001, in the picturesque city of Venice, Italy. Sirens blare across the piazza, warning of impending high tides. Venetians wake once again to the war against the waters. It¿s a war they are currently losing. Venice is sinking, and could be submerged by the end of the century.

Now Project Moses, a controversial $3-billion-dollar government-funded scheme to keep Venice above water, has finally been given the go-ahead by Italian officials. Construction of its novel floodgates is set to begin in December 2002, following years of false starts. But some scientists still object to the project, saying that it will damage local ecosystems and is doomed to obsolescence within years if the sea level rises as predicted by current climate-change models. Moses may yet have a few mountains to climb before parting Venice from the sea.

The Tide Turns

To better understand why Venice is so troubled, it helps to consider its history. Venice is a city on stilts. Built on 117 small islands in the middle of a lagoon that flows into the Adriatic Sea, the city has origins that stretch back to Attila the Hun¿s invasion of Italy in 452. People sought refuge on the lagoon¿s islands, and the tidal channels have guarded settlers for centuries since. In 810, Venice¿s watery ramparts blocked the forces of Pepin, a son of Charlemagne, who had rampaged through Italy, seizing land-based towns.

However, the waters that have defended Venice are now its greatest threat. In 1966, a meter of water blanketed the city, prompting the Italian government to label safeguarding Venice as a matter of "priority national interest." In the years that followed, the Consorzio Venezia Nuova (CVN), the private consortium of engineers and architects behind the floodgate project, was founded and charged with the task of keeping Venice from drowning.

Water, Water Everywhere

Venice is sinking about half an inch per century. Italy, as part of the African geological plate is drifting north, pushing under the European plate. This is causing the Alps to rise and Venice to sink. The subsidence was exacerbated by industries pumping groundwater from below the city, for manufacturing and agricultural purposes, after World War II. That practice--which was stopped in the 1970s--caused the city to sink a foot in two decades. As a result, the world-famous St. Mark¿s Square, the center of Venetian social life, stands just two inches above the normal high-tide level. The square stands under four inches of water in flood events that occur around 100 times a year. And things are getting worse. January 2001 saw the worst spate of sustained flooding in the city¿s history, which lasted more than a fortnight, with an eighth of the city underwater. Add to that the projected sea-level rises due to global warming, and the peril of a city sinking without a trace becomes depressingly clear.

Parting the Sea

Since 1951, 90,000 people have left Venice, and the 60,000 who remain live in fear of a repeat of the 1966 floods. The CVN¿s solution is the Mo.S.E. (Modulo Sperimentale Elettromeccanico, or Experimental Electromechanical Module) Project. It involves the construction of a set of 79 mobile floodgates that will separate the lagoon from the Adriatic when the tide exceeds one meter above the usual high-water mark. Similar gates have been constructed in London and Rotterdam, but they are large aesthetic intrusions on the landscape. The Italian government is adamant that the construction project should not have an impact on Venice¿s scenery. During normal tides, the 300-ton mobile gates are designed to lie flat on the seabed, inactive and filled with water, hidden from view. When a tide of one meter is forecast, air will be injected into the gates, pushing out the water and causing the gates to rise. As the tide drops, the gates will be refilled with water and return to rest on the seabed.

The mobile gates were first proposed more than a decade ago, so why has it taken so long for approval? The answer is that Project Moses has had to overcome many environmental objections. Italy¿s Green Party fears that closing the lagoon for long periods will cause it to stagnate, damaging marine life. To appease the Greens, the CVN has implemented many complementary projects to defend the city by alternative methods, often repairing damage caused by earlier makeshift attempts to stem the tides (see sidebar).

Raising Venice

The most ambitious such project involves raising the sidewalks and shores of the city¿s lowest-lying areas to a height of one meter. This should protect these vulnerable regions from flood levels that are high enough to cause damage but too low to activate the gates. Thus far, the CVN has raised 960 hectares of land, 80 percent of the target. So why are the mobile gates needed at all? Why not simply raise the city even higher to safeguard it from floods greater than one meter? "In historical Venice [which in parts dates back to the eleventh century] in particular it is difficult to raise up the level of pavements while maintaining the function of the building; it reduces the door size," answers Maria Teresa Brotto, an engineer with the CVN. St. Mark¿s Square cannot be raised without irrevocably--and unacceptably--altering its appearance. Instead, the CVN is raising up the surrounding embankments and placing a waterproof clay membrane under the square to stop water from rising up through the soil. And, Brotto adds, "raising pavements is a very expensive project."

The chosen height of one meter seems to be a good compromise. At that level 5 percent of the city¿s surface area must be raised, at a cost of around $40 million. However, to raise the pavements by just an extra 20 centimeters escalates costs to $2 billion, because 30 percent of the city would then need to be raised. The mobile gates, on the other hand, will protect the city from floods between one and two meters. And, Brotto stresses, the gates will only be called into action around seven times a year, minimizing effects on marine life.

The Threat of Obsolescence

But will the gates be enough if sea levels rise as predicted from global warming? No, says Paolo Antonio Pirazzoli, a geophysicist with the National Center for Scientific Research in France, who worked as a consultant to the city of Venice on the Mo.S.E. project during the 1990s. In the May 14, 2002, issue of Eos, published by the American Geophysical Union, he accused the CVN of failing to account for realistic sea-level rises over the next century, against which the gates will be ineffectual. Pirazzoli worries that the government is backing a superficial solution to improve its political image. "I do not know whether Mr. Berlusconi [the Italian Prime Minister] follows, on the Venice problem, a rationality much different from that of President Bush on the greenhouse-gases problem," he says. He predicts that the $3-billion construction will become obsolete within decades.

An environmental-impact study, commissioned by the CVN, comes to the opposite conclusion. Raphael Bras of M.I.T, the lead researcher on the 1997 study, states that the gates can successfully handle a rise of 50 centimeters in the next 100 years, which is a greater amount than many models predict for the Adriatic. But, Pirazzoli counters, the study ignored rainfall, river discharges and winds that will raise the lagoon level when the gates are closed. "This is simply not true," replies Bras. "Independent hydrologic studies¿have confirmed that this is not an issue." He explains that most of Venice¿s rivers were diverted to go around the lagoon 500 years ago, so lagoon flooding from the rivers is minimal. "For this peak [in rainfall and river discharge] to even coincide with the tide peak is almost inconceivable," says Bras.

Pirazzoli remains unconvinced. He is currently preparing a paper with four new case studies that he says will show that the mobile gates cannot cope with a 50-centimeter rise. He also questions why the M.I.T group chose to examine a worst-case scenario of a 50-centimeter rise at all, when the second IPCC report, published in 1996, predicated a potential sea-level rise of up to 90 centimeters by the year 2100. The third IPCC report, published in 2001, estimates a maximum rise of 88 centimeters. And so the debate rages.

For now, though, it seems that the Italian government will continue to support the project, which should take eight years to complete. That will at least help to relieve the suffering of the Venetians for many years after the gates become operational. And the CVN is confident about the gates¿ performance against potential sea-level rises. After all, says Brotto with a laugh, "with a 20-centimeter rise, all other parts of Italy will be flooded, but not Venice. Perhaps then Venice will be the only dry city!"


Zeeya Merali is based in Providence, R.I.
"Drowning New Orleans," by Mark Fischetti (Scientific American, October 2001), is available for purchase at the Scientific American Archive
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