I was in Venice when the acqua alta struck on 28 October 2018. I noted in my diary: “It happened today. The first big acqua alta of the year, with a siren at 09.17, followed by two steady tones. One tone is for 1.1 metres, two 1.2 metres, three 1.3 metres and four 1.4 metres or more. The tidal chart says the level should peak just after noon. At 12.30 I put on my green rubber boots. Stepping out along the canals, I found the water above my ankles and immediately had to re-learn how to walk. Walking at normal speed causes the water to splash over your boots and on to your legs. I slowed down, finding I also needed to watch out for little waves from the boats on the canal, which rode up right over the submerged pavement.

“Tourists used bin bags or fluorescent pink plastic booties over their shoes, walked barefoot or just got their shoes wet. Judging by the laughs and picture taking, high water looked fun, but not for the tourists who held heavy suitcases to their chests to keep them dry as they walked. One woman, who had given up, was dragging hers through the water. They looked really stressed. People carried small dogs and children, while a man hefted an old woman on to one of the raised board walkways set up for pedestrians. Many shops are open, some with thigh-high ‘flood’ barriers at the door, even as clerks mop up, pushing water out with wiper blades on sticks or setting up pumps to spew water back out on to the street. In a pizzeria, waiters shuffled through the water to serve customers.

“By the time I got to St Mark’s Square, hip-booted policemen urged people on the walkways to move along and not to stop for selfies. The water in the square was too high for my boots, nearly knee-high, so it spilled over the top and poured in. Cold. The crowd in the square seemed to be enjoying the spectacle, even when it started to rain.”

The next day, another acqua alta of 1.56 metres broke a record, flooding 75% of the city, giving Venetians a real scare, but now, a year on, that has paled in the face of a new record flood recorded on 12 November 2019, of 1.87 metres, the highest in more than 50 years, flooding over 85% of the city. Lesser record highs hit in the following days. The flood caused millions in damage, and two deaths – one man who tried to restart a water pump was killed by electrocution, and another was found dead in his home. The extended flooding has disheartened many among the city’s depleted population of 53,000, with some now thinking that there is no future for Venice.

But the threat from flooding has been growing for some time. The problem first came to global attention on 4 November 1966, with the record 1.94 metre acqua alta flooding 96% of the city. The city was unprepared, and waist-high, stinking, muddy, oily water destroyed housing, shops, goods and art treasures on all the islands and lagoon shorelines.

The catastrophe sparked an international outcry that led the Italian government to pass a special law in 1973, officially recognising that the fate of Venice and the lagoon that surrounds it need to be considered as one entity. This legislation aimed to turn back the environmental devastation of the last century. It promised to restore the lagoon’s physical and ecological integrity by rescuing the salt marshes, ending land reclamation and curbing pollution.

Faced with subsidence under Venice and the threat of bigger tides, the authorities planned gigantic dams to be constructed at the three openings where the lagoon meets the sea. In the decades since, another force has picked up that is much more threatening: sea-level rise. The Venice area is among the low-lying coasts of the world that, like the Netherlands, have been saved from the sea by human effort, via the use of dykes and pumping out water, and much of it is very sensitive to sea-level changes.

The average sea level rise predicted by the IPCC, the United Nations body for assessing climate change, is 0.43 metres by the end of the 21st century, and it could be as high as a metre or more. In Venice, higher water levels, adding to the effect of subsidence, are creating new, possibly unsustainable, stresses on the lagoon defences and the city. Already, higher water levels cause rising damp in Venice’s ageing walls, crumbling the bricks and rusting the ties that hold up the buildings. The effect of higher water is also aggravated by lagoon erosion. While the tides took between 90 minutes and two hours to enter a century ago, now they enter in an hour. With the lagoon an average of 1.5 metres deep, twice what it was, the tides not only rise higher but also move faster and in greater volume on entering and leaving. The number of acque alte have also been rising since the last century: the number of floods over 1.1 metres have doubled since the 60s, due not only to subsidence and sea level rise, but also to increase in wind, waves and storms related to the climate crisis.

Several decades after the laws intended to protect Venice came into effect, much has been accomplished, but the hopes they raised have taken a battering in the face of inaction, resistance and inertia.

The 1966 flooding disaster that led to special laws for Venice launched decades of studies and planning and opened a multibillion-euro tap of funding that would go into housing refurbishment, art restoration and a two-part programme to save the lagoon. One part dealt with acqua alta up to 1.1 metres by bolstering the shock-absorbing effect of the salt marshes and sea fronts while building smaller barriers and localised adaptations in Venice and on other islands. The other part, for flooding over 1.1 metres, when the sirens sound, envisioned the massive dams dubbed Mose (pronounced Mosé), a strained acronym for Modulo Sperimentale Elettromeccanico (Experimental Electromechanical Module).

The word “experimental” was included in the barriers’ name in a nod to the law’s requirement that the solution be “gradual, experimental and reversible”. This was because solutions to managing the lagoon have historically been found with an element of trial and error. In reality, however, the massive, bright yellow, semi-submerged barriers under construction since 2003 are built on a foundation of millions of tonnes of concrete fixed with enormous piles driven into the sea floor, with no room for changing of minds. Mose also refers to the biblical Moses who held back the tides in Egypt, allowing the Jews to escape the pharaoh – which sets expectations rather high. So, the naming has not been a great boon, and already the flood gates have far surpassed their estimated cost, with more than €5.4bn spent.

Facebook Twitter Pinterest Works for the Mose flood protection project. Photograph: Giuseppe Cacace/AFP/Getty Images

Initially expected to be finished by 2011, decades after being conceived, plans were set back even further after a corruption scandal that broke in 2014 – one of the largest in Italian history – and are now only stuttering forward. The dams are still unusable, but now projected to be finished by the end of 2021. When the dams are ready, and a way to fund their €100m annual maintenance bill is found, they will then face their real test: whether they are up to the job – and serious doubts have been raised.

Many of the “soft” measures to control flooding up to 1.1 metres were completed decades ago, such as new sea walls on the littoral islands of Lido and Pellestrina and a “baby” Mose dam in the lagoon-side town of Chioggia. Housing has also been adapted. In 1966, many people lived in ground-floor accommodation, but that has since been banned. Now Mose gets all the attention and most of the money, often to the exclusion of other needs.

“The challenge,” said Dario Berti, the lead mechanical plant engineer on Mose until 2017, “was this: to have a system that could intervene in the tides with minimal impact, but only those over a certain level, because those below should be allowed to come and go.” The dams also needed to have a minimal impact on the scenery at the ports and on the lagoon.

Solutions like ones in Rotterdam (two movable storm surge barriers, each a half-moon shape almost as big as the Eiffel Tower) and the Thames barrier in London (10 gates, high as a five-storey building), both of them huge and visible, “would have too much environmental impact in this context,” including destroying much of the natural dune reserves along the coastline, Berti said.

Venice’s Mose project, selected after decades of study and political controversy from a number of alternatives, is unprecedented in design: separate dams at the Lido, Malamocco and Chioggia port openings, with a total of 78 rectangular flood gates over the three openings, each attached to the bottom by massive hinges. At the Lido opening, an island has also been constructed in the middle of the channel as part of the dam structures. When required, the hollow steel barriers – each as big as six or seven railway carriages laid side by side – are filled with air, causing them to float up to 45 degrees. Together they form a barrier designed to hold back the tide coming from the Adriatic. When the tide subsides, the air is let out and they sink back on to the bottom, out of sight and allowing the flow of water and naval traffic to resume.

Berti called the design “courageous and innovative … There is no magic solution. This is a good compromise.” In the wake of the latest floods, the government promised money to accelerate Mose and related efforts.

Good though it may be, Mose may not be good enough. Long mired in controversy, it was originally pushed through by politicians who wanted a quick solution.

“Mose is a costly, useless project with no guarantee that it will function well. It will require expensive management and maintenance, is unsustainable for national finances and will be difficult to control,” said Venice University professor Antonio Rusconi, a civil engineer, formerly of the Magistrato alle Acque, a civic body that used to be in charge of maintaining the lagoon, and the National Hydrology Service. A long-time critic of Mose, he is not alone. After a very fraught, politicised design selection process, the environment ministry’s own environmental impact commission had rejected the plan in 1988.

The major challenge for the dams is that acqua alta is never flat. When there is wind – and there is always wind – the surface is high here and low there, and it can even push water out of one port opening and into another, said Rusconi. “The wind crams the water into certain places, raising it up by as much as 40cm. Controlling this system will involve fights and legal issues. It will be impossible to manage, not just technically. This is where things will get unclear and unclean, because this is a political choice – and we know that these choices get made because the big companies are paying.” The waves will cause the raised barriers to flap, creating “multi-directional stress” that will cut the lifespan of the hinges, he said, while every storm will send sand, mud and debris into the wide grooves that cradle the barriers under the water, preventing them from re-closing.

Facebook Twitter Pinterest Tourists in Venice during the record acqua alta of November 2019. Photograph: Miguel Medina/AFP via Getty Images

The motive for building them under the water was to avoid sullying the landscape. This was a mistake, Rusconi said, “because on the surface there will also be a huge pontoon boat for maintenance, which is uglier even than the yellow gates”. He believes that something visible but more easily managed, as in London or Rotterdam, would have been better.

Sea level rise will make it necessary to close the barriers ever more often, eventually impeding shipping traffic and causing pollution, as the water cannot be refreshed by the tides. There are also concerns about how the barriers will deal with rain. In 1966, water falling on the lagoon and draining from the land caused the water level in the lagoon to resurge. The wind could cause a sloshing-bathtub effect, where the water shifts uncontrollably from one part of the lagoon to another, interfering with floodgate management. “In short,” Rusconi said, “the system is too complex. Mose might work for small storms, lasting two or three hours, but if a very strong one comes, like 1966, it will fail. But the small storms were not the objective – the big ones were.”

So why did the whole project go ahead?

“Incredibly, because the ministries were corrupt,” said Rusconi. “Their judgments were bought. In many cases, the corruption was not a matter of money. It also happens by means of promotions, career advancement, illegitimate awards … favours, jobs for the offspring of ministry officials who were hired by Consorzio Venezia Nuova. In Italy we call it parentopoli – nepotism.”

The scandal broke on a warm June morning in 2014, with 36 arrests of politicians, officials, magistrates, businessmen, professionals and technicians linked to Consorzio Venezia Nuova, the company responsible for Mose, who had, since 2005, created a slush fund of €25m for bribes to politicians and magistrates. The minister of public works in Rome, the then-mayor of Venice, the governor of the Veneto region and state engineers who should have been checking on the work were among those investigated for corruption, fiscal fraud and illegal financing of political parties.

“The state’s mechanisms of control over the management of the money were weak, and this allowed the robbery of state funds,” said public prosecutor Paola Tonini, who ordered the crackdown. But why in this case – a massive state construction project – was such laxness possible? She blamed the set-up of the Consorzio Venezia Nuova as a monopoly with nebulous management controls and lack of competitive bidding for jobs, adding: “Stealing from the state was probably part of the plan from the beginning.” (The Consorzio is now being run by a new administration under anti-corruption rules.)

The need for the dam reflects the historical relationship between Venice and the lagoon. For centuries the Venetian republic husbanded its natural resources, keeping the lagoon from filling in through sedimentation and protecting its water quality. That care fell away in the 19th and especially the 20th centuries, when land reclamation gobbled up a third of the lagoon – most of it rare natural habitat – in order to build an industrial port. Petrochemical plants at Marghera on the mainland opposite Venice caused the worst damage and health hazards, dumping millions of tonnes of toxic waste, including heavy metals and dioxins, into the lagoon for decades. Most of it remains in the mud under the surface. By the 1990s, market forces had killed off these toxic industries, leaving an industrial wasteland, mostly contained by 8km of metal piles driven in around the industrial area to prevent further poisoning.

In addition, modern-day industrial and agricultural runoff from the river basin to the north adds to lagoon pollution. Since the 1970s, better treatment facilities and a requirement for new buildings in Venice to install local septic tanks has improved water quality markedly, but the city still lacks a sewer system. So half of the buildings pour human waste, detergents and household chemicals directly into the canals.

However, the most devastating damage is hidden. To make way for bigger ships, the openings to the sea separating the littoral islands of Lido and Pellestrina were deepened and a channel called the Canale dei Petroli was dredged in 1960-69 to a depth of 17 metres. Enlarging the openings and dredging the new channel caused massive surges of tidal water that are washing away the silty lagoon bottom. In the southern lagoon, they have gouged out an ever-widening crater and destroyed natural channels that feed the lagoon ecosystem. This, with the added erosion from ships and illegal clam fishing, is fundamentally altering the lagoon, diminishing its prized wetlands and converting the lagoon into a sterile branch of the Adriatic Sea.

The key actor in the fate of the lagoon – and of Venice – is its port, visited by thousands of container ships and tankers, along with some 700 cruise ships every year.

Facebook Twitter Pinterest A cruise ship towering over a canal in Venice, June 2019. Photograph: Miguel Medina/AFP via Getty Images

As the industrial role of the port has diminished, it has grown into a commercial hub, riding a wave of Chinese exports, of everything from toys to motorbikes. At the same time, the old Stazione Marittima at the eastern end of historic Venice, once the commercial port, has been given over to cruise-ship tourism.

Unlike commercial shipping, cruise ships steam directly through the city’s Giudecca canal instead of bypassing historic Venice on the Canale dei Petroli. These giants, whose scale makes Venice look like a Lego-built mini-city, not only cause erosion and pollution, but risk accidents by passing close to the city as they move through the Giudecca canal and past St Mark’s Square. Each one, on average 10 storeys high, is a floating resort city, with casinos, shopping centres, restaurants, nightclubs, cinemas, gyms, theatres and ice-skating rinks.

Tending to arrive on the busiest weekends, each liner can pour as many as 5,000 passengers into Venice, and sometimes there are six or seven in port at once. Venice is already straining under the weight of 30 million tourists a year. The ships generate terrible air pollution, and most of them burn “bunker fuel”, which has up to 2,000 times more sulphur content than diesel. On entering and exiting, they make waves that erode seawalls and foundations. Their propellers stir up and wash away lagoon sediments, turning the water brown.

After the Costa Concordia ran aground and capsized off the Tuscan coast in January 2012, killing 32 people, Italy passed a law forbidding ships to come closer than two miles from the coast, except where there was no alternative – so it did not apply to Venice. The government banned ships of more than 40,000 tonnes from the Giudecca canal, but has insisted, for economic reasons, that passage for such boats should continue until other arrangements can be made. The exception has prompted international protest, regular demonstrations in the city and expressions of concern from Unesco over the risk to Venice, which is a World Heritage Site. When a 275-metre cruise ship, the MCS Opera, collided with a dock and tourist boat after losing control in the Giudecca canal in June, attention was refocused on the need to deal with cruise ship routes.

Since the mid 1990s, cruise ship tourism has been growing fast; shipyards around the world have an estimated 124 new ships that can carry more than 5,000 passengers each coming onstream in the next few years. Cruise ship passenger numbers worldwide have risen from 11 million a year in 2009 to 28.5 million in 2018. The industry insists that it provides jobs, and that air pollution can be reduced, and denies that erosion from its ships damages the lagoon. Even so, the ships have become the most visible symbol of how tourism is eating away the social and cultural fabric of the city. And the prospect of sea-level rise has led to the reluctant realisation that, in coming decades, the lagoon may have to be closed to protect Venice.

The port authorities, “have not understood that, within 10 or 20 years, their internal port will be unusable,” said a lagoon hydrologist from Padua University, Luigi D’Alpaos. “Because either you choose to let ships enter the port, or you choose to defend Venice from acqua alta. This is the great contradiction Venice has always lived with. If I want to save the Venice lagoon, I cannot, at the same time, protect the activity of the port, because the solutions required for these two problems are absolutely opposite.”

D’Alpaos calculates that with as little as a 30cm rise in sea level, the Mose flood gates would have to close for 70 hours a month, and at 50cm the rate of closures would hit 166 hours a month. This would cause significant obstruction to shipping and cruise vessels. It would also prevent the twice-daily tides from cleansing the lagoon, as they do at present. Mose’s usefulness could be diminished by as early as 2040 – and it has not even been completed yet. But intermittent closure would not necessarily mean the end of the port: it could be moved outside the lagoon.

The port authorities have looked at other ways to avoid such disruption. They continue dredging the Canale dei Petroli to keep the routes open for ships, probably adding to lagoon erosion. They have backed a plan for cruise ships to use a long detour to reach the maritime terminal. The mayor of Venice, Luigi Brugnaro, among others, supported this option after the 2019 cruise ship collision.

Neither plan addresses the issue of sea-level rise, and both face vociferous opposition because they would require dredging of canals, accelerating erosion of the lagoon and spreading pollution. The mud around the Vittorio Emanuele canal, along the road and rail bridges to Venice, is particularly contaminated. “This mud absolutely must not be moved, because if it is, it will stir up the poisons,” said lagoon biologist Lorenzo Bonometto. “This is why I think the idea of dredging Vittorio Emanuele is insane and reckless.” Apart from that, re-digging the canal would prevent tidal diffusion, starving the area of oxygen, he said. The water there “would degenerate in the summer heat, giving the entrance route to Venice a horrible stink – not to mention that it would damage the ecology”.

A new port just outside the lagoon, on or near the coast with the Adriatic Sea, could serve either cruise ships, or commercial shipping, or both. It might emulate the Maasvlakte 2 project outside Rotterdam on the North Sea, or the offshore river delta container port in Shanghai. Supporters believe it could resolve both the cruise ship issue and the future challenges of sea level rise, since a port outside the lagoon could eliminate the need for new dredging, and stop cruise ships traversing Venice, while continuing the port’s economic functions.

One idea, which has support from environmental groups and the former transport minister, Danilo Toninelli, is to set up a port outside the lagoon, solely for large cruise ships. Passengers would use environmentally friendly electric ferries to get from the vessels to Venice. “This means the port workers will continue to do what they do now at the maritime terminal,” said environmental advocate Armando Danella – ie, the abandonment of the old port would not need to result in job losses.

But the idea for a cruise ship port outside the city faces opposition from the beach communities nearby, especially Cavallino-Treporti, which sits on a spit of land north of the Lido opening, an area popular with tourists. The main criticisms concern logistics. Venice is a transit port, not a get-off-look-around-get-back-on port. Cruise passengers tend to begin or end journeys in Venice, travelling onward by train, plane or car. This could cause mind-boggling local transport issues, as several cruise ships arrive a day, each carrying 4,000 or more people and their luggage, all needing to be transferred to and from Venice and the airport. The resultant extra traffic could cause major congestion on the single road that runs along the peninsula.

As the sea rises, these problems – along with the huge costs that building new ports and closing the lagoon would involve – await serious study.

Lidia Fersuoch, president of the Venice branch of Italia Nostra, the oldest and largest environmental group in Italy, believes the issue will be forced by sea-level rise. When I met her, she was frustrated with the political process and “totally pessimistic” about saving the lagoon and Venice in the short term. She has, however, “a little seed of optimism, and my optimism is a response to global warming,” she said. “I hope that the sea-level rises will be such that the lagoon will finally be closed. It’s absurd to say this, but nothing else will achieve useful action.”

Global warming is already out of control, Fersuoch added, which means that “in 50, or even 20 years, the lagoon will have to stay shut, and then how will it function? We need to think about that, about how to create the system, the engineering, ways to activate the tides artificially. It won’t be easy,” she said, adding that these questions should take precedence over Mose, “but I see no one talking about them.” Perhaps the most recent floods will change that.

This article is based on Neal E Robbins’s forthcoming book Venice, Revisited

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• This article was amended on 20 January to correct the total of bribes paid by Mose to €25m. It had previously stated the figure was €21.5m.