Rising waters: Can a massive barrier save Venice from drowning?

Source(s): Yale School of the Environment
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A retractable barrier designed to protect Venice from sea level rise and storm surges is set to be operational next year. But the project’s engineering limitations and cost overruns are raising questions about the mega-projects that many coastal cities are hoping can save them.

By Jeff Goodell

It’s tempting to believe that the devastating sequence of hurricanes in the Atlantic this year has blown in a new awareness of the risks of rising waters and increasingly powerful storms on our rapidly warming planet. In a rational world, the destruction wrought by these storms would inspire us to redouble our efforts to cut carbon pollution as quickly as possible and begin planning for an orderly retreat to higher ground. 

But with a few exceptions, that’s not happening. Instead, we’re hunkering down in our SUVs and building walls. Sea walls are going up all over the East and Gulf coasts, and engineers and urban planners are musing about larger barriers that could, in theory, protect entire cities. In Texas, where Hurricane Harvey ravaged Houston in August, a $15 billion project known as the Ike Dike, which would create 55 miles of sand dunes and sea walls around Galveston Bay, is being proposed, as well as an 800-foot wide retractable barrier at the mouth of the Galveston shipping channel. In New York, the U.S. Army Corps of Engineers has long had plans for a similar barrier around Jamaica Bay to protect vulnerable neighborhoods nearby. In Boston, a city-sponsored reportlast year recommended considering a barrier across the outer harbor. And this is not an America-only trend. Even in water-friendly European cities like Copenhagen, walling off the harbor is seen by some urban planners as inevitable.

Today’s barriers aren’t your grandfather’s sea walls – they are massive, complex infrastructure projects that cost billions of dollars and take decades to complete. The Thames barrier near London, for instance, which protects the city from storm surges pushing up the river, is a marvel of modern engineering, with rotating gates that allow operators to control the flow of the river. The Maeslant Barrier in the Netherlands, which is located at the mouth of the Rhine, has two Superman-like arms that swing closed to stop the sea from pushing up the river and flooding surrounding farmland and cities. 

But in a world of quickly rising seas, even the most sophisticated engineering is not always sophisticated enough. Consider the case of a barrier known as the Modulo Sperimentale Elettromeccanico in Venice, better known as MOSE, an acronym deliberately designed to invoke Moses, the Bible’s great parter of the waves. The MOSE barrier, which is scheduled to be operational in 2018, was designed to protect Venice from a storm surge and save the sinking city from oblivion. In fact, MOSE’s engineering short-comings and colossal expense raise a number of questions about the wisdom of these mega-projects. 

The genesis of MOSE can be traced back to November 4, 1966, when gale-force winds in the Adriatic Sea pushed a wall of water into the Venice lagoon. Venetians awoke to find their city under 5 or 6 feet of water. From its founding in the 5th Century, flooding had been commonplace in Venice. But groundwater pumping had caused the ground under the city to subside, and dredging of the lagoon for container ships had changed the tidal dynamics, making Venice more vulnerable to storm surges. “It had always been a fragile place of exquisite beauty and slow death. It was now an emergency,” historian Thomas Madden wrote. “Venice was descending beneath the all-consuming waves, and something needed to be done — immediately.”

A ban on groundwater pumping halted the city’s subsidence (or at least slowed it to its current rate, 1 millimeter or so a year). But that was just a first step. To come up with solutions to protect Venice from the sea, a group of construction and engineering firms banded together with the government to form Consorzio Venezia Nuova (Consortium for a New Venice). After years of study, CVN proposed the construction of high-tech mobile barriers that would rise to protect the city when needed, then lower to allow the lagoon to remain connected to the sea. In 1994, Italy’s Higher Council of Public Works approved the plan, and in 2003, construction began.

The MOSE barrier is actually three separate flood barriers, one at each of the three inlets of the lagoon. Each barrier is made up of about 20 individual gates, which are bound by a hinge on the floor of the lagoon and are hollow, allowing them to fill with water. In calm weather, the water-filled gates sit at the bottom of the lagoon. But when an exceptionally high tide threatens — Venetians call it acqua alta — the water is pumped out of the gates and replaced with air, allowing the gates to float up to the surface and create a barrier capable of stopping a storm surge as high as 9 feet. When the surge passes, the air inside the gates is released and replaced with water, causing the gates to sink back to the bottom of the lagoon.

Mobile barriers are to sea level rise as condoms are to sex: a device you use to protect yourself in a heated moment. Unlike an actual wall or dike, a mobile barrier like MOSE is designed to be deployed only when necessary to protect the city from a surge. It doesn’t cut Venice off from the sea. It doesn’t impede tidal flow in the lagoon. It’s not a monstrous industrial structure on the Venetian horizon. And yet, if a big storm is coming, it can be raised in 30 minutes, creating a temporary wall against the sea.

That’s how it is supposed to work, anyway. In reality, the project has been delayed, tangled in a high-profile corruption scandal, and victim to engineering problems that have led many thoughtful observers to wonder if it will ever work. To top it all off, cost overruns have raised the price tag from $2 billion to $6 billion — and counting. At one conference I attended in Venice, Pier Vellinga, a climatologist at Wageningen University in the Netherlands, called the MOSE barrier “a Ferrari on the seafloor.” It wasn’t clear whether he meant this as a compliment.

Earlier this year, I visited the CVN offices in the Venice arsenal, a restored medieval boatyard with beautiful arched colonnades. I met with Monica Ambrosini, one of the organizations’s media handlers, in her brick-walled office. Over an espresso, she explained the current state of construction: So far, gates had been installed in only one of the three lagoon inlets. I asked her if she could take me out to see the installation, but she shook her head. “It has been tested, but it’s not operational now, so there is nothing really to see. It is all underwater now.” She explained that she would like to take me to see the control room of the MOSE barrier, but unfortunately it was not built yet. “But I can show you a couple of gates that have just arrived,” she offered.

Ambrosini was eager to show off progress on MOSE in part because the organization has taken a lot of fire in recent years for wild cost overruns, as well as a corruption scandal that left many Venetians wondering how much money went into the design and construction of the barrier and how much went into the design and construction of vacation homes for the politicians and industry executives who were involved with the project. In June 2014, 500 officers raided 140 offices from Venice to Tuscany and Rome as part of a probe into the alleged rigging of contracts. More than 35 people were arrested, including politicians and business executives who were accused of bribery and other forms of corruption. The investigation eventually led to the indictment of the mayor of Venice, as well as the governor of the Veneto region. No one knows for sure how much was siphoned off by corrupt officials, but a good estimate is close to $1 billion.

When I asked Ambrosini about all this, she blushed and asked if she could go off the record — then explained, basically, that she couldn’t justify or explain it, but that bad people had been involved and now those bad people were gone. Back on the record, she said, “We have completely changed the structure of the organization and put new people in charge and new rules in place so it cannot happen again.”

With that, we put on our hard hats and orange safety vests and headed out through the backwoods of the arsenal. Workers scurried around; a forklift carrying concrete pipes rolled by. Ambrosini led me toward a chain-link fence, behind which were two enormous slabs of metal. They looked like 100-foot-long, 15-foot-wide teeth extracted from a creature on planet Gargantua. One was painted bright yellow, the other aqua. Ambrosini pointed to the aqua one. “It weighs about 330 tons,” she explained. The mobile barrier at the central inlet would be made up of 21 of these gates, each hinged to the ocean floor and working together.

That was when the scale and ambition of this project became clear to me. These gates were designed to do nothing less than hold back the sea, one of the primal forces of nature. That humans could even contemplate building such a tool was evidence either of the power of technological innovation or of the folly of human hubris — or both.

I asked Ambrosini when she estimated that the entire MOSE barrier would be installed and ready to defend the city.

“By 2018,” she said. Then she added, “That’s the hope, anyway.”

The MOSE barrier may or may not be operational by 2018, but even assuming that the $6 billion project works as planned (a big assumption), its design and construction bring up a number of issues that are worth considering.

The first is the time required to design and build the barrier. After the 1966 flood, it took more than 50 years to settle on a plan to protect the city, then get it approved, funded, designed, and partially built. That kind of time scale might not be important if you are building, say, a new bridge. But when you’re constructing something that has to adapt to climate change, 50 years is like 50 centuries. In 1966, sea level rise was something that only a few scientists thought about. Today, it’s an existential threat to cities around the world. Yet even though the design for MOSE was not finalized until 2002, the estimates for sea level rise then used are now woefully out of date. According to a UNESCO report, during the project planning phase, three sea level rise scenarios for 2100 were considered. The estimate cited as “most probable” was 16 centimeters (about 6 inches); the one cited as most “prudent” was 22 centimeters (about 8 inches); the third scenario, labeled “pessimistic,” was 31.4 centimeters (about a foot). Planners recommended using the prudent scenario for design purposes. In a world where respected scientists are now suggesting that sea level rise by 2100 could be as much as 6 feet, designing a barrier for 8 inches of sea level rise looks, in retrospect, either like startling naïveté or startling incompetence.

The second issue is cost. When you spend $6 billion in tax dollars to fix a problem, it had better work, because at that price, it’s unlikely you’ll get a do-over. But costs don’t stop there. There is also the question of maintenance. MOSE might be a Ferrari on the seafloor, but Ferraris require a lot of work to keep them rolling. Initial estimates for maintenance charges were $12 million to $18 million a year. Ambrosini suggested that $50 million a year is a more appropriate figure; others have suggested it could go as high as $80 million a year, depending on how often the gates are used. This money is like a ransom that has to be paid every year — if maintenance lags and the gates fail, Venice could be inundated.

The most important question, of course, is whether the barrier will actually protect the city — and if so, for how long. That is not a simple question to answer, because it depends on how you define “protect.” If the barrier is completed and functions as advertised, it will likely spare the city from storm surges like the one in 1966 — for the next few decades, anyway. But because the gates will only rise when the tide in the lagoon reaches 110 centimeters, they will not stop the flooding that already happens in low spots in Venice (such as Piazza San Marco) when the tide gets above 80 centimeters or so. This could be solved by raising the barrier at lower tides, but that would have a big impact on the health of the lagoon, and would also increase operational wear and tear on the barrier, which would raise maintenance costs.

In the longer run, questions about the protection of the barrier depend, like much else in this world, on how far and how fast sea levels rise during the 50-year design-life of the barrier. Although MOSE was designed to protect from tidal surges as high as 9 feet, it was only engineered to handle less than a foot of sea level rise. This is an important issue, not only because rising seas increase the chances of higher storm surges, but also because higher seas would require the barrier to operate more frequently, as well as putting additional stresses on the barrier that it was not designed to handle.   

Right now, engineers expect the MOSE barrier to be closed about 10 times a year, usually for about five hours, until the tidal surge passes. Georg Umgiesser, an oceanographer at the Institute of Marine Sciences of the Italian National Research Council, estimates that with 50 centimeters (1.6 feet) of sea level rise, it will be closed once a day. With 70 centimeters (a little more than 2 feet), Umgiesser’s research suggests, the gates will be closed more often than they are open. More frequent closing means not just higher maintenance costs, but ever-greater dependence on the barrier to prevent massive flooding in the city. An outright failure could be catastrophic. And of course, if the gates are closed all the time, the whole point of a $6 billion Ferrari on the seafloor is moot. Why not just build a solid wall at a fraction of the cost and be done with it?

After our visit to the gates, Ambrosini and I returned to her office, where she spread out a map of the Venice lagoon. I brought up the problem of protection from sea level rise.

“In the end, I guess the big question is, how much sea level rise can MOSE protect the city from?”

“We believe Venice will be protected up to 60 centimeters of sea level rise,” she told me.

This was more than the MOSE design parameters suggested, but I let that go. It was still shocking to hear her admit this so bluntly. Some scientists believe we could have 60 centimeters (about 2 feet) of sea level rise as early as 2050.

“And after that?”

Ambrosini’s professional demeanor shifted and she suddenly looked worried. She pointed to the map, sweeping a finger over the northern edge of the lagoon. “After that, the sea will come in from other places to the north and the south. There is nothing we can do to stop it.”

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Hazards Storm surge
Country and region Italy
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