Battling to keep Venice's floodwaters at bay

Road Trip 2011: The famous Italian city gets flooded up to five times a year, and a massive infrastructure project is under way to protect it against the rising tides, as well as to save its beaches and marine habitats.

A $6.7 billion infrastructure project could be completed by 2014 that could protect Venice, Italy, from the increasingly common high tides that threaten the island city with floods and continued erosion. Special gates could keep the Adriatic Sea at bay.

VENICE, Italy--Not far beyond this famous city, just at the border between the Venice Lagoon and the Adriatic Sea, a group of concrete behemoths is under construction. A lot of very smart people think they will be part of the solution that could save the island town from drowning.

The notion that Venice is sinking has been around for a long time, and in fact, it has lost 23 centimeters of land over the last 100 years. But these days, it faces a troika of what may be more insidious challenges: rising tides that each year bring more and more floods; the degradation of beaches and shore areas; and gradual pollution of its marine environment.

To tackle this, the Italian Ministry of Infrastructure and Transport, in conjunction with the Venice Water Authority and the Consorzio Venezia Nuovo--a group of local engineering firms--have embarked on a giant infrastructure project known as Mose that, it is hoped, will keep the rising waters at bay and begin the process of permanently protecting Venice. The group hopes to have the system up and running in 2014.

The heart of the project is a system of 78 disappearing, oscillating, buoyancy flap gates that will be activated when tides rise higher than 110 centimeters inside the lagoon. There are three inlets to the 500 square-kilometer lagoon. Forty-one gates will be installed at the Lido inlet (21 at Lido-Treporti, and 20 at Lido-San Nicolo), while 29 will be installed at the Malamocco inlet and 18 at the Chioggia inlet.

"Normally, the barriers [will be] full of water and rest on the sea bed," according to information provided by the Consorzio Venezia Nuova. "When flooding is forecast, compressed air [will be] pumped into the gates, emptying them of water and causing them to rise up and emerge, blocking the tide as it enters the lagoon. When the tide drops, the gates [will be] filled with water again and return to their housing. Thanks to its operational flexibility, the Mose [will be able to] cope with floods in various ways--by simultaneously closing all three inlets during an exceptional event, by closing one inlet at a time, or partially closing each inlet (the gates are independent) during medium to high tides."

The highest tide on record to hit Venice was 194 centimeters, in November 1966, and the Mose gates are expected to be able to handle tides of up to 300 centimeters. Yet, even if a major storm hits the area and the gates are all raised--for as much as five hours, the average expected closure time--normal shipping activities should not need to be interrupted. That's because part of the project includes a large lock at Malamocco that will be able to handle even the largest ships. And smaller locks have been built at the two other inlets for smaller boats.

As part of Road Trip 2011, I got a chance to visit some of the biggest infrastructure construction of the Mose project, and while the gates have yet to be made, they're still very much a part of the future reality of this iconic city.

Just adjacent to the mouth of the Malamocco inlet, for example, a massive artificial pier has been built to handle the fabrication of the caissons--or basements--that will house the gates when everything is ready to go. The caissons themselves may well be the biggest part of the effort, since they are giant concrete and steel boxes that will rest on the sea bed, and on top of each will be three of the 20-meter-wide gates.

Once built, they will be moved on a system of 84 trolleys to what is known as the Syncrolift, a tremendous launching bay where the caissons will be lowered into the water--they have many large hollow sections, so they'll float--and then get towed to their final resting place nearby. Later, the gates will be brought out and connected at special hinge points.

At Lido, which I also visited, the process is different. There, the area of the canal where the gates will be installed was drained, and the caissons were built in place. Next spring, I was told, the area will be re-flooded, and prepared for the gates.

It's too early to tell, of course, if the Mose project will have the desired effect. But the consortium of the Italian government, the local water authority, and leading engineering firms has bet a lot of money--up to $6.7 billion--and a lot of prestige on the idea that these gates can keep Venice's rising tides from impacting the city, its shorelines, or its marine environment.

And if it works, and Venice becomes safe even in the biggest storms, the long-held belief that the city is sinking may itself finally be ready to be put out to sea.

 

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