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Venice is at risk of succumbing to its sinking foundations and rising sea levels. To avert disaster, the city is making changes. Venice is a stunning oddity. It is a city built atop around 120...
- Venice floods: Climate change behind highest tide in 50 years ... - BBC
The recent flooding in Venice was caused by a combination of...
- Venice floods: Climate change behind highest tide in 50 years ... - BBC
Apr 1, 2023 · Venice is sinking. The tectonic plates under the city are naturally settling, a process accelerated in the 20th century by the pumping of groundwater for use in the industrial port of...
Rising sea levels because of climate change coupled with Venice’s well-documented sinking make the city built amid a system of canals particularly vulnerable. The sea level in Venice is 10 centimeters (4 inches) higher than it was 50 years ago, according to the city’s tide office.
Nov 15, 2019 · Venice suffered the worst flooding in half a century, with 70% of the city submerged and seagulls swarming the square. Climate scientists warn that Venice is a harbinger of the problems facing all coastal cities, as sea levels rise and the city sinks.
- Overview
- How Moses works
- The cost of keeping Venice dry
- How to degrade a salt marsh
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A system of moveable walls, called Moses, protects Venice from colossal high tides that are worsening with climate change. But they’re also destroying the marshes that keep the lagoon alive.
Venice, ItalyThe cataclysmic flood of November 12, 2019, washed unremarkably into Venice, Italy’s Piazza San Marco around 6 a.m. Two hours later, the rising waters began to tail off at about three feet above normal sea level, leaving 90 percent of the city untouched. Venetians breathed a collective sigh of relief. It was just another mildly unpleasant acqua alta, high tide, in the lagoon.
The calm lasted until 4 p.m., just before night fell. Sirens began to sound, and within an hour the ancient squares and narrow walkways along the city’s 26 miles of canals had vanished under ferocious torrents of seawater. “This wasn’t simply a tide,” says Marco Malafonte, who co-owns a property management firm with his wife, Caroline Gucchierato. “It was a colossal wave, something we’d never seen before. A tsunami."
The couple split off in separate directions, joining ad hoc rescue teams. In the San Marco quarter, Venice’s lowest-lying district, Gucchierato came to the aid of an elderly French tourist standing up to her neck in the raging flood, pinned against a stone wall. She had perched her infant grandson on a ledge, holding onto him until help arrived. Vaporettos, the iconic 80-foot-long Venetian water buses, “were thrown up onto walkways and bridges like children’s toys,” recalls Malafonte.
At 8 p.m., the surge finally crested at just over six feet, with 85 percent of the city submerged. It was the second highest flood tide ever registered in Venice, nearly eight inches above the average height of its residents.
Before the world climate crisis began building in the 1970s, that terrible November night might have been written off as a freakish disaster. But in 2022, Venice—La Serenissima—is a poster child for climate change. The occasional destructive acqua alta, which occurred just a few times per century before 2000, has become the new normal as sea levels rise around the globe. Of the 25 worst acque alte registered in Venice in the past 100 years, each topping 4.5 feet, more than half have happened since December 2009.
Moses began taking shape in 1987. It is a system of mobile tide barriers formally called the Experimental Electromechanical Model, but its acronym invokes the biblical prophet who parted the Red Sea, allowing the Israelites to escape captivity in Egypt.
The project has engaged some of Europe’s largest construction firms, under the direction of an Italian government-sponsored consortium called Venezia Nuova (New Venice). Its cost to date has ballooned to more than $6 billion from an initial euro budget projection equivalent to $4.5 billion. The price tag is highly controversial in Italy, as is a long string of work stoppages due to unpaid debts and political scandals.
In 2014, then Venice mayor Giorgio Orsoni was arrested on charges of accepting over half a million dollars in illegal campaign contributions from Venezia Nuova in return for alleged influence in contract allocations. Although the judicial verdicts were inconclusive, Orsoni and 24 city council members subsequently resigned from their posts.
The Italian Ministry of Infrastructure and Transport, in conjunction with the consortium, began manufacturing the system’s components in 2003. On-site installation opened in 2008. The long-term goal is to protect Venice until at least the end of the century, when sea levels are expected to have risen another two feet. Although Moses will not be fully operational until December 2023, by late 2020 its partially completed barriers were ready for live testing.
The functional heart of the project is a battery of four gigantic surge barriers that span three inlets to the lagoon from the Adriatic Sea. The two largest barriers, comprised respectively of 21 and 20 steel gates, are separated by a control center on an artificial island and stretch a combined half mile across the Lido inlet, just east of the main islands of urban Venice. Each is outfitted with a lock that allows small vessels to leave or enter the lagoon when the barrier is raised.
A third set of 19 gates was installed 7.5 miles south at the 46-foot-deep Malamocco inlet, where a much larger adjacent lock provides access to the lagoon during high tides for cargo freighters and industrial ships. The fourth set, with 18 gates, lies near the port of Chioggia on the lagoon’s southern limits, with a double lock serving fishing boats, pleasure craft, and emergency vessels.
The vaporetto that ferries passengers from Piazza San Marco sails east along the two largest spans of Moses and the high-security command center on the artificial island between them. The gates themselves are hidden in their cradles. But their land-based operative infrastructure, clusters of giant compressors, warehouses, and office buildings, fills the skyline.
A team of four University of Padova marine research scientists meets me at the Punta Sabbioni wharf, near the tip of the 12-mile-long—and barely three-feet-high— peninsula separating the northern end of the lagoon from the Adriatic. Just to our west are the deep-green fields of Sant’ Erasmo, the fertile garden island that provides Venice with its best artichokes, zucchini, and tomatoes. We board a small, rented launch, piloted by hydraulic engineer Alvise Finotello, which carries us to the San Felice salt marsh. We don mud boots and step ashore.
At low tide on a sun-struck morning in May, San Felice is an airy field of salicorn, cord grass, sea lavender, and other estuarial plants waving in the morning breeze. The lagoonal waters have retreated into a web of narrow channels teeming with small fish, crabs, and seagrass. By early evening, the entire marsh will be fully submerged by the tide, its flora and fauna busily capturing nutrients necessary to their health—as well as the lagoon’s.
This is the universe that Moses threatens, one of “halophytic” vegetation, salt-tolerant plants that spend part of each day on land and part underwater, where they are nourished by clouds of incoming and outgoing tidal sediment that the flood gates block when in place. The sediment enables the plants to grow, and in the process, reinforce the sand banks and structure of the lagoon: its very existence. The salt marshes are “hotspots for biodiversity,” D’Alpaos says; without them and the ecosystems they foster, the lagoon would die. They also account for one of nature’s most critical roles in the struggle to confront climate change.
“They are extraordinarily efficient at sequestering carbon dioxide and storing it in the soil as organic carbon,” says geologist Massimiliano Ghinassi. “One square kilometer of the Venetian marshes annually removes 370 tons of carbon dioxide from the earth’s atmosphere, at a rate 50 times greater than that of tropical forests,” such as those in the Amazon.
Finotello, fellow hydraulic engineer Davide Tognin, and team leader Andrea D’Alpaos, an environmental engineer and leading authority on the lagoon, provide me with background, while Ghinassi inserts a long, T-handled cylindrical tool into the spongy ground. The cross-disciplinary mixture of experts is deliberate, D’Alpaos explains. “Eliminating the walls between pure science and engineering brings diverse perspectives into our work—and better results.”
In the 1920s, Italian economic planners undertook a “modernizing” program that transformed the continental shore of the Venetian Lagoon into one of Italy’s most heavily industrialized regions. Scores of manufacturing plants and refineries were built. Deep channels were gouged through the lagoon bed to accommodate heavy freighters bound for the port of Marghera, just two miles west of La Serenissima’s main island, and more recently, huge 5,000-passenger cruise ships.
The industrial facilities extracted immense amounts of groundwater from compressed sediment under the lagoon, causing Venice to subside 4.5 inches in the 20th century, at the same time Adriatic sea levels rose by four inches. Although the Italian government closed most of the wells in 1970, the subsidence is irreversible and slowly increasing.
Put bluntly, environmentalists now fear that Moses’ efforts to save urban Venice from crumbling into the sea may complete the destruction of the very ecosystem that gave birth to the city and sustained it for 15 centuries.
The chief threat, they say, endangers the crucial interaction of the marshes with tidal currents. The Padova team accumulated extensive data on the first 15 tests of the flood gates, focusing on San Felice and two other marshes between October 3, 2020, and the following winter. Their analysis suggests that the barriers could reduce the annual supply of sediment to the marsh plants by 25 percent, with potentially fatal effects on the future of the lagoon, since the sediment distributed by the tidal ebb and flow—the “sedimentary budget” —shores up the existing land and lagoonal banks.
What’s more, notes Davide Tognin in a related study, 70 percent of the lagoon’s necessary sedimentation occurs during episodes of high winds—precisely when the barrier tends to be raised.
"It is clear that the defense of the city of Venice and of the inhabited centers from high waters is an indispensable issue, and not under discussion,” says D’Alpaos. “We don’t question this need.” Instead, researchers urge that the barriers be raised when the tide reaches a slightly higher level—4.3 feet rather than 3.6 feet, which they say would reduce the loss of sediment to an environmentally sustainable 10 percent.
Venice faces a dilemma as it struggles to protect itself from rising sea levels and frequent floods. The moveable walls of Moses, a $6 billion project, may be the only solution, but they also threaten the ecology of the lagoon and its salt marshes.
- Frank Viviano
Jun 19, 2024 · The scientists predict parts of Piazza San Marco, Venice ’s most famous square, will be under 70 centimetres of water. The west side of the city will also be one of the first affected - it...
Nov 13, 2019 · The recent flooding in Venice was caused by a combination of high spring tides and a meteorological storm surge driven by strong sirocco winds blowing north-eastwards across the Adriatic Sea.
