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The Flood Gates of Venice

A watery jewel in Italy's gem-studded crown, Venice is no stranger to the problems of high tides. After almost four decades of debate, the fragile city is to be equipped with 21st century flood gates.

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Water fills St. Marks Square, Venice

Italian Prime Minister, Silvio Berlusconi marked the start of work on Venice's tidal defenses on Wednesday, when he aptly laid a foundation stone from a boat. The project, which is know as "Moses," an acronym for its technical title, is designed to save the lagoon city from tidal flooding.

The plight to prevent Venice from sinking under water was born way back in 1966 after many of the city's cultural treasures were devastated by the highest tidal wave on record. But it wasn't until the city had been pounded by a further series of high tides -- or acqua alta, as they are known locally -- that the Italian government sat up and took notice. In 1973 the government declared it in the national interest to save the city, but it then took another three decades of studies and proposals before any final decision was made on an appropriate plan of action.

Modern technology

The titanic new project, expected to cost some $7 billion, will see the construction of a mobile dyke that will cover the four main outlets from the lagoon into the Adriatic Sea. A total of 78 water-filled steel barriers, which will lay dormant on the seabed, allowing normal tides to ebb and flow as normal, will only respond to threateningly high tides. As a high tide approaches, the barriers will be pumped up with air, causing them to float and create protective dam.

As sea levels across the globe continue to rise, there is concern amongst Venetian port workers that the extravagant Moses project could affect their livelihoods if the new flood barriers prevent ships from entering the city's waterways. The head of the city's port authority, Claudio Boniciolli, says he is worried that if boats have to queue to enter the city, they might opt simply to skip Venice altogether, which could have serious implications for the 18,000 local port employees.

Environmental Opposition

Such skepticism for the project is shared by environmental groups in Italy, who fear the mobile dyke will damage the fragile ecosystem of the shallow lagoon on which Venice is built. They claim that if global warming continues to push up sea levels as expected, the flood gates will remain perpetually closed, which will prevent the natural flow of the sea and ultimately render the beautiful sparkling waters upon which Venice sits into nothing short of a cesspool.

Perilous waters

Constructed on millions of wooden piles pounded into marshy ground, Venice was never a risk-free zone, but flooding was very rare until the mid-1900s. Since then, the acqua alta have been gradually but steadily increasing, both in number and in depth, and last year the city of gondolas recorded its worst swamping ever.

There are various theories surrounding the sinking of the city, but scientists say the greatest contributing factor dates back to the 19th century when the British occupiers carved out the lagoon to enable ships to pass through on their way to port. The effect of this early engineering was to drastically shift currents, removing the natural barrier for high tides, leaving them to hurtle in and suck out the very sediment which creates the foundation of the city as they retreat.

Environmentalists and engineers believe that restoring the lagoon to its natural state, with its original depth, could significantly reduce high tides and lower levels of the highest floods.

But such views have been overlooked in favor of hi-tech underwater engineering, which is estimated to render Venice a flood-free zone by the year 2011.

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