Posted on February 26 2018
Venice sits at the northern end of the Adriatic Sea, an arm of the Mediterranean.
The origins of Venice are rooted in simplicity and desperation. Simple, because the earliest inhabitants of the many lagoon islands at the northern end of the Adriatic Sea were those making a basic living off the sea—fishermen and sea salt miners. But as the Roman Empire came under attack by invaders from the north, desperation became a motivation. People from cities along the coast would flee the invaders, at least temporarily, heading into the watery safety of the low-lying islands. When traveling armies had moved on, the locals might return to their homes, but as the foreigners began to take over everywhere, the lagoon population swelled with those seeking long-term refuge. Because the barbarians at the gate had no experience with watercraft or the sea, they did not come after the refugees. In time, Venice absorbed the rulers, aristocrats, thinkers, and artisans of overrun cities on the mainland, and when things settled out, the city’s detachment provided autonomy from Italian politics and papal rule. Avoiding the entanglements of their wars allowed the Venetians to develop trade with the Far East, and become a wealthy city state.
The water-filled canals and pedestrian walkways form the streets of Venice, a city with no automobile traffic.
In time, Venice developed its own conflicts with other powers, and has a long and very complicated history of culture and politics. One adversary that has been there since the first day, and which has always played an ambivalent role, is the sea itself. Provider of food, safety, and salt in the early days, it was also Venice’s route to trade and naval power. In addition, it made possible the city’s unique transportation system—the canals and gondolas which are synonymous with the place. But Venice has always been at the mercy of its surrounding waters, and grows more so all the time. High tides and storm surge bring anxiety for its residents, and probably have since its early days. The lowest-lying parts of the city have long gotten a bit of water on them during these high-water events, known as “acqua alta,” but a flood in 1966 brought home the seriousness of Venice’s predicament. Storm surge from persistent winds across the Adriatic combined with high tides to push excessive water into the lagoon and canal systems, raising water levels more than six feet. The flooding of ancient buildings and the damage or loss of a great deal of priceless art shocked the world, and spurred planning to avoid another such disaster.
Part of Venice’s problem is that it has long been sinking. The weight of the city on marsh soils guaranteed some subsidence, but for a long time groundwater was pumped from below it to feed the city, and that caused a great deal of downward movement. The practice was halted by law after 1966, but the city, the surrounding islands, and nearby lands are still sinking by one or two millimeters a year. Part of it is plate tectonics—the land sits on a plate that is slowly subducting under another, which may also account for a slight eastward tilt that careful measurements have detected. Compaction continues to push Venice down, but more of a factor than all this land drop, is sea-level rise. Dredging deep channels in the lagoon to allow the passage of ever-larger container ships didn’t help matters. Storm surge now has an easier path to travel.
Piazza San Marco just slightly submerged by acqua alta.
Sometimes it gets deeper.
The years since The Great Flood, as the 1966 event came to be known, have found the famed Piazza San Marco more and more frequently turned into a shallow pond at high water. Elevated boards are routinely put in place so that people can keep their feet dry as they cross inundated areas. These would be minor inconveniences except for the fact that the situation only worsens over time. Even before sea-level rise was much on anyone’s radar, Venice decided it needed a mechanism by which it could control the highest tides and occasional storm surge events that most threatened it. These conditions are intermittent, and the health of the lagoon depends on having access to the open sea, so they decided that rather than building a solid seawall, they would engineer an as-needed solution. It was a long process, but by 2003, construction had begun on an ambitious and unique feat of engineering.
Venice lagoon, with its three entrance points, the sites for the MOSE project.
The lagoon surrounding Venice has three entrances from the sea. In each of these passages through the thin strip of land that defines the eastern edge of the lagoon, structures will be emplaced which are like giant hinged gates. These gates aren’t hinged to swing open and shut like the ones in your garden. Rather, they are hinged to massive bases on the lagoon floor, and swing up or down to block or allow the passage of sea water. It might take enormous engines to drive such movement, but these “gates” are hollow. When at rest on the bottom, they are filled with water. When needed, they will be pumped full of air, which will cause them to float up, swinging into place to create a barrier. When the threat of incoming water has passed, the hollow structures will be re-filled with water, and they will sink back down. The different openings will have 18, 19 and 41 individual gate modules. It takes about a half-hour to emplace these barriers, quick enough to avoid the predictable rises in water level. The project is named MOSE, for Modulo Sperimentale Elettromeccanico. Mose is the Italian form of Moses, who is famously credited with parting the Red Sea. But will MOSE work?
How MOSE works—the gates float up from the lagoon floor and block the incoming high water.
First, it will have to get built. The target date of 2012 came and went, and now 2018 has been replaced by 2020, or possibly 2022, as opening day. And new snafus continue to arise with regularity. The cost estimates, which started at $2 billion, have ballooned to $6 billion. Not surprisingly, that much money was more than corrupt politicians and engineering companies could resist, and millions if not billions have been siphoned off into private pockets. Arrests followed, but prison for the bad actors has so far been avoided. The inevitable design problems and construction delays that accompany such a massive and unprecedented project have only driven up the cost and raised doubts about its eventual efficacy. In addition, predicted maintenance costs are climbing rapidly, thanks to the expectation that the gates will need to be raised more frequently than earlier thought. Some of the structures already in place on the seabed are corroding badly, such that the gates do not rise up properly, and some are fouled with sediment and mussel growth, impeding them from lying down as they should. Other mechanical failures are accumulating, and this in advance of any pressure from critical operational situations.
Concerns are also rising over MOSE’s effect on the lagoon environment, given the dredging that has had to be done just to build bases for the gates. Tides, fish, birds, and all the rest of the ecosystem are feeling the changes brought on by this unnatural engineering, and a lot will need to be done to mitigate future changes. In the city, the acqua alta events occur ever more frequently. Raising the gates to hold them back will interfere with yet another system, or really, the lack thereof. The city of Venice has no sewer operation. Individual buildings do some filtration, but a lot of pretty nasty water gets sent right into the canals, where tides, um, flush it out to sea. Impeding this ages-old process could make a sketchy situation worse.
Whether the grand design actually functions as envisioned, or causes a myriad of unintended consequences, won’t be fully known until it is completed. But more worrisome than its proper mechanics is the question of its adequacy. While it was originally designed to hold back a roughly 9-foot storm surge that seemed prudent at the time, nature has been busily moving the goal posts. Sea level changes that continually astonish climate scientists also lend more elevation to storm surge levels. MOSE was thought to be sufficient protection for the next 100 years, but if the sea outpaces it, water will come into the lagoon by overtopping not only the gates, but other points along the narrow land barrier fronting the lagoon. So Venice may be fighting a very expensive losing battle. It is unfortunate that such a staggeringly rich trove of architecture and art is centered in such a vulnerable place. The art can be moved. But the buildings and culture that make Venice so precious will one day very likely be reclaimed by the sea.
Thinking of going to visit Venice before it slips under the rising sea? Fill your head with historic info and smart travel tips with this comprehensive guide by Lonely Planet, available from Maps.com by clicking here:
PHOTO CREDITS:
caption: Venice lagoon, with its three entrance points, the sites for the MOSE project.
caption: Piazza San Marco just slightly submerged by acqua alta.
caption: Sometimes it gets deeper.
caption: How MOSE works—the gates float up from the lagoon floor and block the incoming high water.
The post Geo-Joint: Venice—Treading Water and Waiting for a Life Preserver appeared first on Journeys by Maps.com.
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