The Sinking City Game Length
Bartley Trowbridge
Not quite land, not quite sea, Venice seems to float in its own world. Aworld that at first glance appears immune to the passing of time. Thenine-hundred-year-old St. Mark's Basilica presides over a giant public squarethat's changed little since the days of Casanova and Vivaldi. But in recentyears, the illusion that is Venice has begun to crack, and this idyllic cityhas been showing a darker side.
The trouble began on November 4, 1966, when an extremely high tide sweptinto Venice and refused to leave. For 15 hours, Venice was inundated by thesea. In historic Saint Mark's Square the water was four feet deep. Luckily, noone was killed. But the place was a disaster zone.
EDMUND PENNING-ROWSELL (Flood Hazard Research Center): It'shappening. It's happening now. Venice is a trigger. Veniceis the first major city in the world to face sea level rise, because it's builtright at sea level.
CHARLES E. MCCLENNEN (Colgate University): The Venice you knowtoday cannot be preserved as it is today. It was built on a salt marshat sea level, in a sinking area, and unfortunately, sea level is rising.
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Between October and January, the lowest parts of Venice flood almost everyday, and much of the city is inundated half a dozen times. During this wetseason, Venetians rarely venture far without their rubber boots. Andsometimes even that's not enough. They call it "acqua alta," high water.
ALBERT AMMERMAN (Colgate University): It's this sort of slimy,murky water, which isn't very pleasant. But it also contains quite a bitof pollution. So you really don't want to stick your hand in this wateror have this water in your entry to your house, in your hallway. Schoolscan't run. Boats have troubles getting under the bridges. There'sa whole series of dysfunctional things which happen with acqua alta.
NARRATOR: It's not just inconvenient. The tide is insidious,creeping into every building without regard for its historical value. Saltwater eats away at floors and walls, no matter what century they were built inor what genius architect designed them. The front of St. Mark's Basilica,perhaps the most famous Venetian landmark, is adorned with stones from aroundthe Mediterranean. All of it is being corroded by floods, almost on a dailybasis.
Venice is famous as the city of romance, the city of Casanova, where loversforget their worldly woes. It was once an extremely rich and powerful city,built by merchants and bankers who controlled a shipping empire throughout theMediterranean. Her wealth and beauty flowed directly from the sea.
So how is it that the water is now threatening to undo all that it made? Inthe case of Venice, it comes down to "location, location, location." If youwere planning to build a city, you could hardly pick a less practical spot.
At the northern tip of the Adriatic Sea, historic Venice sits on what isactually several dozen islands, within a 200-square-mile shallow lagoon. A longchain of barrier islands guards the lagoon from the sea, but three openings inthe chain allow ships, and the tide, access to the city. Flooding occurs whenexceptionally high tides break through these inlets.
Normally, the tides are controlled by the moon, but the sun also plays arole. These astronomical tides are easily predicted, and they aren't veryextreme. The difference between high and low tide in Venice can be as little asan inch or two, or it can be more than three feet, during a full or new moon.But you can't blame the moon for Venice's flooding problems.
CHARLES E. MCCLENNEN: The acqua alta, those extreme high tides, arecaused primarily by the weather, strong winds out of the south driving Adriaticwaters to the north and forcing it into the lagoon and causing flooding.So predicting acqua alta is really based on predicting storms. Andit's not that easy.
NARRATOR: Bad weather was the cause of the 1966 deluge. Windand low pressure created a giant storm surge that pushed water into the lagoonand wouldn't let it out. The flood was a complete surprise.
Since then, Venice has paid much more attention to the weather and itseffect on the tides. Out on the Adriatic, twelve miles from shore, thisplatform collects data 24 hours a day. Temperature and humidity, wind speed,atmospheric pressure, anything that contributes to a storm surge. All thisinformation is relayed to a team within the city. If flooding ispredicted then alarms go off.
These events are becoming more frequent. A century ago, St. Mark's Square,the lowest point in Venice, flooded about nine times a year. Nowadays,it happens about 100 times. Buildings in Venice were constructed to withstandsome contact with the sea, but these floods are pushing them beyond theirlimits.
To understand why, just look at a typical Venetian foundation. Here, acanal has been pumped dry for repairs, revealing a few of the secrets of thecity's success and some of its major weaknesses. Strip off the outer layers ofthe foundation and you'll find a forest of wooden pylons. These logs werepounded through the soft mud, 10 or 15 feet to the bedrock below. Surroundingthe pylons are several layers of water-resistant stone. As long as the seawashes against this lower level, the structure above is well protected.
But now, the flooding is rising beyond the stone foundation to the buildingitself, which, in most of Venice, is made of brick. The bricks, sometimescoated in stucco, are soft and porous and much more vulnerable to corrosion.Chemists at the University of Venice are studying how this works.
GUIDO BISCONTIN (University of Venice): It's very interesting tosee the effect of the water on the sample, which is no different from whathappens to the walls in Venice. I'm immersing the brick in a fewmillimeters of water that contains a small quantity of salt.
NARRATOR: The salt travels up through the brick. As the waterdries, the salt crystallizes. With every new flood, the salt dissolves onceagain and bores a little more into the brick. Eventually, the brick willcrack and crumble away. This is what's happening inside all the walls ofhistoric Venice.
Almost everywhere, ground floors are damp and moldy. Many residents havemoved upstairs or out of town. Since the 1950s, Venice has lost over half itspopulation. Today, fewer than 70,000 people live here.
GIANFRANCO VIANELLO (Restaurant owner): Just look at theNetherlands, the whole country's below sea level and not a drop gets in.I don't see why we, who are nearly three feet above sea level in St Mark'sSquare, are not able to stop this water.
NARRATOR: The Netherlands used to be one of the mostwaterlogged nations on earth, with more than half the country below sealevel. Since the 1600s, legions of windmills have powered water wheelsthat lift water up into canals. These channels flowed back to the sea,which was held at bay by earthen dikes.
But this system was not foolproof. In January 1953, hurricane-force windsand an unusually high tide blasted the Dutch coast, collapsing the protectivebanks. Eighteen hundred thirty five people were drowned and 70,000 wereleft homeless. A third of the Netherlands was under water.
And so the Dutch came up with this: two mobile gates that can swing out toblock the river whenever the North Sea gets out of hand. To withstand the fullforce of the sea, the structures must be gigantic. Each gate has a steelbarrier, seven stories tall, which holds back the water. The arms are as longas the Eiffel Tower is high.
PIER VELLINGA (Vrije University, Amsterdam): When the North Seais rough, we are very vulnerable. And we had the choice between raisingall the dikes three, four, five meters, and rebuilding part of the old citiesor a one-time mobile barrier. And the population was much in favor of thismobile barrier because it is safer and it has less effect overall on thelandscape.
NARRATOR: When the sea's calm, the barriers rest in canals onthe riverbank. If a major storm is predicted, the huge arms will rotate towardthe center of the river until they almost meet in the middle. Then the barriersfill with water and sink into the riverbed.
Finished in 1997, the gates haven't been tested against a real storm yet,but it's predicted they will be needed, on average, once every 10 years. TheDutch system of dams and gates has been hailed as an engineering marvel, butcould it work for Venice?
NARRATOR: The Venetian flood plan calls for several sets ofmobile gates placed at the three large entrances to Venice's lagoon. Most ofthe time, the steel gates lie flat in a special housing on the bottom of theinlet. When extremely high tides threaten the city, compressed air is pumpedinto the hollow gates, causing them to tilt upwards to the surface.
Each gate measures about 65 feet wide, about 12 feet thick, and 65 to 100feet tall. They're designed to hold back a high tide more than six feet abovenormal. When in use, they are supported by the water on both sides. After thetide recedes, water flows into the gates, sinking them back into place.
CHIANG C. MEI:The design of the mobile gate system is veryinnovative. When it's in use, the elements of the barrier are allowed toswing back and forth with the waves. In this way, much of the wave forceis transmitted back to the water on both sides, and very little force istransmitted to the foundation and to the supporting structure. So inthis aspect, I think this is very, very clever.
Since the flood of 1966, Italians have been talking about how to protectVenice. Talking. And talking. But somehow, they've been unable to make adecision. Instead, the gates have become a political hot potato, tossed fromone administration to the next. And that's meant a lot of tossing. Since 1966,there have been more than 35 different governments in Italy.
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