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Saving Venice From the Sea

High water, or acqua alta, is a persistent phenomenon throughout the Venetian lagoon. Over the centuries, the city's leaders, merchants, and residents have dealt with rising sea levels either by demolishing old buildings and erecting new ones on higher, impermeable-stone foundations, or by raising the entrances to buildings that line the dozens of canals criss-crossing the historic city. Or, on the then-rare occasions when the city was flooded by storm-driven tides, Venetians simply waited it out. The water went up, a few hours later it went down, and life, scarcely disturbed, went on.

ByJohn KeaheyNova

As Venice evolved from a mercantile republic into a living museum, city fathers preserved historic buildings rather than razing them to make way for new structures. It simply would not do to create a modern city atop the ruins of the old, as has been done throughout the world. Such a Venice would not be the Venice the world has come to cherish.

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The worst
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acqua alta in memory, the one that truly woke Venetians up to how bad things could get, occurred on November 3, 1966. The high tide that swept into all corners of the city that night lasted an astonishing 22 hours (typical high tides last six).
© Venice Water Authority/Consorzio Venezio Nuova

A city awash

The 20th century, with its rampant industrialization and its witnessing of climate shifts, changed all that (see Venice Under Siege). Many scientists believe that global warming driven by the burning of fossil fuels is primarily responsible for the rise in global sea level, which at Venice has resulted in higher and more frequent instances of acqua alta. To make matters worse, Venice has been sinking over the centuries, due to the natural settling of lagoon sediments and the indiscriminate pumping of freshwater from a deep aquifer beneath the city.

Sixteen hundred years ago, around the time of Venice's founding, the Adriatic's standard sea level was almost six feet below what it is today. For a millennium and a half, Venetians were able to cope with the problems associated with living in a water-dominated environment. As late as 1900, for example, water at extreme high tide covered St. Mark's Square only seven times a year.

Boats cannot navigate the canals during the highest tides because they cannot pass under bridges.

By 1989, however, such inundation occurred no fewer than 40 times a year. In 1996, water nearly as high as the average tourist's knee lapped 99 times at piles of sandbags placed to guard the doorways of the Doges' Palace and St. Mark's Basilica. More and more frequently, visitors must walk on elevated wooden walkways, or passarelle, as peak tides flow over the city's sidewalks. Boats cannot navigate the canals during the highest tides because they cannot pass under bridges.

St. Mark's Square
Visitors to Venice's famous St. Mark's Square in times of flood generally make their way along raised walkways called passarelle.
© Venice Water Authority/Consorzio Venezio Nuova

The high tides are not just annoying but damaging. Instead of merely washing against the impermeable marble that makes up the city's foundations, high waters are splashing with increasing frequency against the soft, permeable bricks that sit above the foundations. Saltwater from the Adriatic soaks into this brick, inching ever higher into the walls and creeping into interiors, destroying frescos and other irreplaceable relics. Unless they have been restored with new, waterproof brick, many of these buildings crumble imperceptibly.

What can be done about this unstoppable rise in sea level, which brings the waters of the Adriatic, borne on twice-daily tides, higher and higher against the stones of Venice?

walking through water
Some renegades in St. Mark's Square chose to go it alone amid the rising waters.
© Venice Water Authority/Consorzio Venezio Nuova

Gates of salvation?

City officials, the Italian government, and a consortium of Italy's largest construction and design firms believe they have the solution to this messy problem: line the bottom of the Venetian lagoon's three entrances with a series of 79 hollow steel gates that would be raised to hold back the sea in times of acqua alta.

When tides are low and weather calm, these gates would be filled with water and rest on the bottom of the three channels at the north and south ends of the Lido—the long, narrow island that separates lagoon and sea—and at the fishing village of Chioggia on the lagoon's southern end. When storms with strong winds roam northeasterly across Italy and Adriatic tides run high, engineers would activate a system that pumped compressed air into the gates. The air would force out the water, enabling the gates to rise on hinges and form a barrier against the surging seas.

Project MOSE, the acronym for the experimental model created to test the gates' performance (Modulo Sperimentale Elettromeccanico), has been the only proposal proffered by engineers, contractors, and consortium scientists since the early 1970s. (Watch a video about the proposed gates.)

Designers say that the proposed mobile gates, when raised into their upright position, would hold back the incoming tide up to a level of six feet or more above the water level in the lagoon.
© Venice Water Authority/Consorzio Venezio Nuova

In December 2001, the government announced plans to build the gates at a cost of between $2 billion and $3 billion. Supporters of the project said design work would begin this fall (2002), with construction getting under way within a few years. The most ardent supporters said they believed the gates would be in operation between 2007 and 2010. On September 23, 2002, however, the Venice City Council voted to reconsider its support for the gates and raised the specter that the project should be reevaluated. This was stunning news, and whether the project will ever regain its standing remains in doubt.*

It is political reality in Italy that governments do not last long; 58 governments have come and gone since 1945.

The project has long had a bevy of critics: Italian and international environmentalists, along with scientists who for three decades have disapprovingly followed the path to the MOSE solution. Those opposed believe that relentlessly rising seas will make MOSE obsolete within a few years. They also worry that officials would need to raise the gates so often that the normal ebb and flow of the cleansing tides would dramatically affect aquatic life within the lagoon and make the city unlivable for long periods, as sewage normally flushed from the lagoon remains behind. These critics want more studies conducted on the gates' potential environmental impact, and they want the international scientific and engineering community to come up with new solutions that would protect Venice for the next century rather than for just the next few decades.

Even if gates advocates can somehow reverse the stance of the Venice City Council, the national government faces many other hurdles before it could ever consider construction. First is the question of financing the project. The current Italian government, in power since early 2001, has also announced plans to rebuild the nation's freeway system, expand the national high-speed train system, and construct a suspension bridge from the Italian mainland to Sicily. All this comes at a time of budget crisis and no identifiable means of raising the billions of euros needed to launch these projects.

Italians tend to wink at such grandiose pronouncements. It is political reality in their country that governments do not last long; 58 governments have come and gone since 1945, and new elections will likely take place by 2004. An administration that does not support these projects might well come to power.

Venice from above
How wet will Venice get in the coming years? Only time—and the result of ongoing passionate debate—will tell.
© Corbis Images

Tide of optimism

But through this climate of political infighting and uncertainty, hope for Venice springs eternal. City officials backed by the Italian government have quietly appropriated significant sums of money separate from the gates project to improve the infrastructure of the historic center. Crews are dredging a century's worth of accumulated muck from the city's dozens of canals and are rebuilding and waterproofing canal sides. They are restoring bridges and fountains. And they are raising fondamente, or sidewalks, along the canals and edges of the surrounding lagoon to levels above routine high-water marks.

Plans are afoot as well to improve Venice's treatment of sewage, which for centuries has been dumped directly into the canals. Venetians are now installing septic tanks as buildings and market areas undergo renovation, and authorities hope that within the next two decades, traditional sewer pipes can deliver the city's waste to mainland water-treatment facilities. Finally, St. Mark's Square, the city's lowest point and most frequently flooded area, is slated for a $50 million project to rebuild its drainage system.

The debate over how to safeguard Venice and preserve its buildings and art treasures for successive generations will not end soon. Indeed, it will likely be years before construction of any kind begins, whether of the mobile gates or some entirely different solution.

*On May 15, 2003, Silvio Berlusconi, Italy's Prime Minister, officially launched the gates project, which is expected to take eight years to complete at a cost of $4 billion.

Editor's Notes

This feature originally appeared on the site for the NOVA program Sinking City of Venice.

Major funding for NOVA is provided by the David H. Koch Fund for Science, the NOVA Science Trust, the Corporation for Public Broadcasting, and PBS viewers.