Sylvia Poggioli, NPR 7 Jan 08;
As the Earth warms up, rising sea levels will increase the threat of storm surges and flooding. In some places, that will make existing problems worse. Venice, Italy, offers a glimpse at what may lie ahead.
For years now, Venice has topped the world's most endangered cities list. Built 1,300 years ago on mudflats in the center of a lagoon, the sinking city is subject to increasingly frequent winter flooding, from high tides known as "acqua alta" in Italian.
A major engineering project has now begun aimed at protecting the Venetian lagoon from rising sea levels, but most Venetians seem to take high water in stride.
Elevated walkways ensure dry feet, boutiques provide fashionable rubber boots, and residents are comforted by the conviction that nothing evil can come from the sea, Venice's oldest friend and protector.
MOSE Project Aims to Part Venice Floods
by Sylvia Poggioli
A boat ride in the Venice lagoon is a discovery of how humans and nature have created one the world's most extraordinary experiments.
Starting in the 16th century, the Venetians diverted major rivers outside of the lagoon to prevent silt from filling it up.
Left alone, lagoons like the one in Venice either tend to dry up and become land or they are overwhelmed by the sea and turn into bays.
The lagoon covers 212 square miles. Along with the city of Venice in the center, there are some 50 smaller islands, as well as dozens of mudflats and sandbanks — havens for thousands of aquatic birds that flock here even in winter.
This delicate and fragile ecosystem is the largest wetland in the Mediterranean.
If Venice is to be saved, the lagoon must be protected.
But today, rising seas threaten the Venice lagoon. All along the Grand Canal, windows of buildings near sea level have been closed and filled with cement.
"Those windows have been closed as they are too much exposed to the waters," says Francesca de Pol of Consorzio Venezia Nuova, the consortium entrusted with the task of safeguarding Venice.
Moving Upstairs
No Venetian lives on the ground floor any more.
In the last century, the city sank 11 inches, mostly due to the pumping of groundwater and methane gas for local industries. But it has also being affected by rising sea levels.
What that means is that the same tides that were not flooding the city 100 years ago are now high-tide events. It's called acqua alta.
High water afflicts Venice mostly in the winter. A century ago it happened seven times a year, now it's more like a hundred.
The visionaries who first began building Venice 1,300 years ago used materials for the foundations that could withstand water. But with the seabed sinking, brick walls on the ground floors are being corroded and waterlogged buildings are crumbling.
Sophisticated technology is now being used to rescue the lagoon. MOSE, the acronym in Italian for experimental electromechanic module, is the biggest public works project in Italian history.
MOSE is also the Italian word for Moses, recalling the biblical parting of the Red Sea.
The project is building 78 floodgates at the three inlets that link the Venice lagoon to the Adriatic Sea. Del Pol says one of the gates' characteristics is their flexibility.
Depending on the type of tides, there are differing ways to manage the gates.
"You are not obliged to close the whole lagoon," she says. "You can close one inlet and not the other.
"In case of wind coming from a certain direction, you can chose not closing the whole system but only parts of the gates for certain types of tides.
"So you continue to have an exchange of water, not totally blocked."
Giant Gates Filled with Air
At the Malamocco inlet, the walls of the MOSE project are being built just like the original walls in Venice. But workers are driving 125-foot-long steel and concrete pilings into the lagoon bed, instead of wooden pilings.
When the giant doors are at rest, they will be lying on the bottom of the inlet channel, invisible to the world. Each gate will be up to 92 feet long, 65 feet wide, and will weigh 300 tons.
When a dangerous tide is forecast, compressed air will be released inside the gates, emptying the gates of water. They will then rise and block the entrance of the tide.
In another effort not to alter the landscape, the worksite is on a specially built artificial island that will be demolished once the project is completed.
Protests Fail to Slow Construction
A debate over the floodgates has been under way for nearly four decades. The design was finally approved by the Italian government in 2003. Costs now stand at $7 billion.
Claudio Mantovan, supervisor at the Malamocco worksite, says the project is on schedule. Some 37 percent of the work has been completed, and MOSE should open as planned in 2012. One key element already finished is a navigation lock to allow large ships to enter the lagoon when the gates are up.
Mantovan says a few days of work have been lost due to peaceful protests by environmentalists and others.
"In order to build trenches for the MOSE gates, they are going to dig up millions of cubic meters of seabed and replace it with cement, which could seriously alter the ecosystem," says Alberto Vitucci, a journalist who has been covering the project for years.
"The entire mechanism will be underwater, making maintenance extremely difficult and costly. And the authorities never took any alternative projects into serious consideration."
Other proposals to control flooding in Venice have included narrowing the inlet channels to reduce the water flow from the sea into the lagoon, and banning tankers and large ships from entering.
Some criticize the project as irreversible and outdated. They say it was designed without taking into account predictions on rising sea levels over the next century.
MOSE engineers respond that the mobile gates are designed to last at least a century and to protect Venice from a difference in water level between the sea and lagoon of up to six and half feet.
The latest prediction of the United Nations Intergovernmental Panel on Climate Change is for a one- or two-foot increase by the end of this century.
Despite opposition, the MOSE project is moving ahead, and it's being closely watched not only by Venetians.
Coastal cities all over the world, from New Orleans to Singapore to Bombay, know that due to rising sea levels, Venice's seasonal flooding could soon become a shared, global phenomenon.
