Saving Venice From Rising Tides

Johnny VonNeumann-Halchuk – Cavaille Stepanova – Natasha Blayney

Venice: La Serenissima. For the past six hundred years, this small island city floating in the northern Adriatic has held a mystique all its own that no other place on Earth has ever rivaled. From the Crusades to the Renaissance, Venice has overcome many obstacles and transitions in its past, but only in this century has it met a rival that could finally spell its ruin and, ironically, it’s the very thing that brought it great wealth and esteem so many centuries ago: water. Initially, it sounds absurd, that a city with such a rich and powerful history could just slowly disappear into the sea. That’s exactly what it’s doing, while a good number of people are already discouraged and packing their bags, eyes set for dry ground. The rest have remained behind and decided to fight the tide and find a way to save this beloved city from a slow and miserable decay.

Lavishly-dressed intellectuals debating philosophy and literature over dusty books and coffee at Cafe Florian won’t save Venice in this debacle. This time, she needs scientists and engineers to address the cause, or causes, behind this major problem. Experts from all over the world, in fields ranging from marine ecology to geology to civil engineering have chipped in their efforts and come to their conclusions, and a great variety of solutions have been proposed, but which one is the right one? Which will cost the least? Which will have minimal impact on the natural environment? Which will leave the cultural integrity of the city intact?

Venice’s rich collection of art, from paintings to sculpture and architecture, are all at risk of damage due to the harmful effects of saltwater on paints, limestone and marble, but the importance of Venice is not just sentimental. Tourism alone is worth $2 billion annually (Newman, 2009), and its importance in the professional fields of art conservation, commerce, and international trade is still very strong. Venice is but one city in the surrounding region of the same name, that boasts a population of nearly two-hundred thousand people (Newman, 2009), many of whom commute to Venice for work. The sinking of Venice, and its waste, also spells disaster for the surrounding ecosystems, which are particularly sensitive to the salinity of the lagoon.

This paper will address the many hardships endured by Venice, given both its current problems and the problems introduced by engineering projects put into action by the Italian government — namely, the MOSE Project, which will be described in later chapters; the history and causal analysis of flooding in the city; and the most promising solutions to the city’s high tides.

 

The History of Sea Level Rise in Venice

Built at sea level in 450 A.D. in the midst of Barbarian invasions, Venice was a refugee fortress that, even at the time, made for an already sensitive destination. One of many islands in the Adriatic Sea, whose unfortunate disposition has made Venice a flood-prone city, it has had to deal with sewage overflows and the corroding of buildings at high tides. It was only after the Venetians experienced the loss of priceless art and valuables from sporadic flooding events that a continuous pumping system was installed. The mechanism is initiated once two feet of water reach past the slowly sinking seawalls. The city has also seen a decrease in tourism due to the astonishing reality that there have been at least “10 events over 140 centimeters since 1950, including a devastating 1966 flood” (Ritter, 2013). In the past, Venice would average seasonal high tides around 7 times a year, but now, they are averaging around 100 (Poggioli, 2008). According to Juhola and Sirkku (2011), “[p]rojections of future sea level rise are also spatially variable, reflecting in large part the importance of thermal expansion. This term which contributes up to three-quarters of the projected sea-level rise by 2100, is calculated from the combined atmosphere-ocean general circulation models.” Francesca de Pol of Consorzio Venezia Nuova explains the loss of the lower level tenants and shops, due to the variant water levels: “windows have been [cemented] as they are too much exposed to the waters” (Poggioli, 2008). Due to Italy’s alliance with the European Union, cutting back on greenhouse gas emissions is more reasonable than it is in other developed countries, but Venice is in need of immediate action, making adaptation the more reasonable choice.

The only recorded instrumental observations from 1872 to 2000 are those that we can visually see to this day. Using photographic paintings, camera obscuras, as reference points to the earliest unofficial records, were made possible by Antonio Canal and his pupil Bernardo Bellotto. These have helped scientists gauge the amount of water Venice has experienced through the comparison analysis of the high tide markings made from laminaria alga. Using original paintings, the algal belt can be measured, but the amount of works that can actually be used are scarce due to the faint indication of where the high tide level is located due to restoration work or some kind of demolition took place.

With the expected sea level rise, the sinking of the ground due to the extraction of water from the subsoil, and the exchanges between sea and lagoon waters, Venice is currently facing problems that are all symptoms of the warming climate and an influx of overconsumption in the past century. It’s stated that “the problem has changed and has become dramatic since the middle of the past century when the works undertaken were not to protect the city, but to develop new trade routes that became unsustainable for the city” (Camuffo & Sturaro, 2004, p. 9). Scientists are using paintings as well as instrumental records to compile data needed to transform the city that is going to witness the most severe repercussions of the warming climate.

There is no perfect balance between mitigation and adaptation when it comes to negotiating national policies. Most developed countries, who are legally committed through the Kyoto Protocol, find that their focus on mitigation tactics are enough when it comes to reducing greenhouse gases in the atmosphere. Due to the inevitable circumstances, Venice is undertaking a different approach to their changing climate: Adaptation. So far Italy doesn’t have a National Adaptation Plan, but Venice has uprooted from a municipal level. From the extraction of groundwater and burning of methane, the city built in a lagoon has managed to cope with the ongoing sinking of its’ islands in combination with their seasonal high tides, referred to by locals as Acqua Alta, but it has always been a constant struggle. The best balance between mitigation and adaptation is a process best achieved through the understanding of worst-case scenario climate models from the Intergovernmental Panel on Climate Change (IPCC) as well as having the financial compliance from other countries that can afford a reduction in fossil fuel reliance. Without some form of divestment and new infrastructure implementation, Venice will have to undergo a drastic change that will undoubtedly hurt it’s tourism, leave thousands of residents homeless, and forcing many to flee to the mainland.

 

How to protect the city: the debate

One of the first instances an adaptation project had been proposed came from the Mayor of Venice in the form of a formal request (letter no.13102). This piece of legislation would be shut down, due to the fact that people were concerned the popular “MOSE” (Modulo Sperimentale Elettromeccanico or the Experimental Electromechanical Module) project would be “advocating extensive structural works that would turn the lagoon into a highly artificial area” (Langer, 1995). The MOSE system is a series of gates put into the bed of the Venice Lagoon that could be raised during periods of high tides to stop the lagoon from filling with water. It was also important to remind those, that soon the lagoon would have to be protected in such a way that if not through artificial protection, then preparatory measures would have to be taken, such as “closing the lagoon to petrol tankers and reorganizing the harbor canals” (42/43). Although the barriers are able to deflate when ships enter the lagoon, Venice will still run into the probability that a more frequent Acqua Alta will occur. This could be problematic for the residents of the city due to the location of the island: the runoff from the rivers, pollution from the large industrial complexes, and the silt sand sedimentation will have nowhere to drain. Additionally, ships carrying passengers and cargo will have to be diverted elsewhere, until the barriers are no longer protruding out of the water. There was also talk of narrowing the entries, but even with the redistribution of land, the fact that there would be a need to dig up “millions of cubic meters of seabed and replace it with cement [suggests that such a project] could seriously alter the ecosystem” (Poggioli, 2008. pp 28).

 

Main Claim

The MOSE system has been set up by the Italian government as a means to prevent the flooding of the Venice Lagoon with too much seawater during high tide; however, the MOSE system is an inadequate means of protecting the city. The system is in no way a long term solution and will have huge economic, environmental and cultural impacts if global sea level rise continues. According to Pirazzoli (2002), the MOSE project “was officially put forward in 1981 and has not been subsequently adapted to the predictions of greenhouse gas buildup-related sea-level rise, which have been foreseen since 1982” (p. 217), and also does not take into account flooding caused by river divergence and raising of sea level caused by wind.

According to Vergano, Umgiesser and Nunes’ (2010) report on the economics of the MOSE system, a large part of Venice’s economy is based off of the shipping of goods and tourists that occurs through the ports into the lagoon (p. 343). Not looking at the cost of building and maintenance of the MOSE system, the interruption of shipping alone could cause major issues for the Venetian economy, as the raising of the barriers impedes any shipments from coming in or out of the lagoons (Umgiesser & Matticchio, 2006, p. 320). This has a direct increase on “costs imposed on ships waiting in the roadstead to enter the lagoon or staying at the quay waiting to leave the lagoon (Vergano et al., 2010, p. 344). These interruptions in shipping will not only have these direct effects but will also have a negative effect on Venice’s reputation as a trading port, as the costs associated with shipping, and consequently, living there rise, the already emptying city will look more unappealing to residents, visitors and businesses. Although Vergano et al. (2010) conclude that the “direct costs… by the operation of MOSE are relatively small” they use an estimated sea level rise that is based on the lowest estimate made by the National Academies Press (2010) based on projections from the Intergovernmental Panel on Climate Change , and is only beneficial when compared to the costs associated with taking no action (Vergano et al., 2010, p. 344; National Academies Press, 2010, p. 244).

Venice is a city known globally for its canals and water lining the city, and as stated by Roberto Suro (1988) “Water is what gives Venice much of its charm” (Suro, 1988, para. 2). According to Suro(1998) the Venetian lagoon is susceptible to high waters (acque alte) from storms, tides, and river overflows, this problem is exacerbated by the shipping canals leading into the lagoon ( 1988, para. 3) Another problem facing Venice is that between tides the water in the lagoon stagnates due to the man made structures that now cover a large portion of the lagoon. This stagnation can be damaging to lagoon ecosystems and is made worse by the pollution from the city that settles into the water. Many of the projects first presented after the major flood in 1966 would have been environmental disasters, but due to the increasing environmental mindedness of Italians during the 1980’s the considerations for solutions became slimmer as the impacts of each project had to be considered (Suro, 1988, Para. 11-12). This stagnation of sediment causes serious problems in lagoon environments and will have a negative impact on local shellfish and nesting waterfowl in the Venetian lagoon.

Our proposal

We’ve already assessed that Venice’s problems with flooding stem primarily from rising sea level and local natural and artificial subsidence, and because sea level rise itself is a much more expensive, not to mention global issue, many professionals have suggested a more localized solution. This promising long-term solution for Venice in fact comes from a practice that has existed for over half a century (Teatini et al., 2011): through the injection of fluid into the underlying rock layers.

Nine hundred meters under Venice, there is a 200-meter thick layer of impermeable clay that was deposited roughly 4 million years ago. Geologists have named this layer Santerno, and it is what Teatini et al. (2011) call “a natural hydraulic barrier” that ensures an even distribution of injected fluid under the city, thereby eliminating, or at least reducing, any risk to the city’s infrastructure. Directly above this layer of clay lie several layers of porous sedimentary rock whose depths, thicknesses, and permeabilities indicate what Comerlati et al. (2004) call “a quite promising formation for a seawater injection project.”

Figure 1 (Comerlati et al., 2004) gives a vertically-exaggerated depiction of the underlying rock layers beneath Venice in the northern Adriatic. The lowermost band is the Santerno clay formation, and the alternating bands labeled “A” are the aquifers into which fluids will be injected to elevate the city and surrounding lagoon.

 

While Teatini et al. (2011) argues that “[t]he subsurface injection of fluid occurs… [only to] mitigate anthropogenic land subsidence,” Comerlati et al. (2004) takes it a step further to argue that fluid injections can raise Venice’s land elevation to even greater levels than it was over a century ago. Comerlati et al. (2004) proposes the strategic installation of 12 vertical injection wells in the surrounding lagoon which will raise the city of Venice 11 to 40 centimeters within the next ten years. This exceptionally wide range is due to the discovery that the permeability of the Santerno clay layer matters less than the permeability of the adjacent layers of sand and the compressibility of the rock. In other words, more research into the structural mechanics of the rock layers under Venice is needed to more accurately determine how high Venice will be by the end of this project. However, Comerlati et al. (2004) state that “the most likely value is 25 cm.” According to Carbognin et al. (2009), this uplift should save Venice from the predicted devastation in flooding over the next century.

Fluid injection is already underway in several parts of the northern Adriatic. Oil companies, like the Italian ENI-E&P compensated for the natural gas they extracted from the Malossa fields west of Venice (Comerlati et al., 2004, p. 3), and they are currently hoping to tap into the gas fields several kilometers south of Venice, near the town of Chioggia, where they hope subsidence will be reversed thirteen years after the cessation of gas withdrawal (Teatini et al., 2011).

Figure 2 (Teatini et al., 2011) shows the predicted outcomes in elevation in Chioggia, with seawater injections shown in dotted lines and without injections shown in solid lines.

 

Some experts have argued, however, that fluid injections still pose a significant risk of creating uneven terrain and consequently endanger the structural stability of Venice’s old buildings; however, recent technological developments have dramatically boosted the accuracy and efficiency of monitoring devices. Teatini et al. (2011) suggest satellite technology, which offers a “relatively inexpensive, spatially distributed, and accurate methodology to detect ground movements.” (Comerlati et al, 2004, p. 5) adds that the deeper the injection, the more even the distribution; that the current depths of the injected rock layers, between 600 and 800 meters, poses minimal threat to the city, as all experimental models show promising results; and that engineers can make adjustments to further minimize risk. Finally, unlike the MOSE project, fluid injections provide no foreseeable threat to the ecosystems on the surface, and will in fact restore salinity levels and improve overall water quality both in Venice and the surrounding lagoon (Comerlati et al., 2004). Other efforts to improving Venice’s situation with flooding include the reconstruction of over one hundred wetland sites in the surrounding area, through reuse of dredged sediments. The apparent absence of continued subsidence in the southern lagoon indicate that such projects are already partially successful (Bock, Wdowinski, Ferretti, Novali, Fumagalli, 2012).

 

Figure 2 (Comerlati et al., 2004) show five predicted increases in elevation over a course of 10 years given a variety of structural conditions in the rock layers under Venice. Figure A shows the minimal outcome, with a localized elevation in Venice of 25 cm; Figure B shows a broader region of increase of 15 cm; Figures C through E show a broader region of increase greater than 30 cm. Figure E shows the maximal outcome, with a localized increase of 40 cm.

 

Conclusion

In short, Venice will sink due to rising sea levels and regional subsidence if nothing is done, and while current projects, such as MOSE, may remedy flooding short-term, they will only cause more economic, ecological, and cultural problems, by threatening water quality, trade, and tourism, and by draining federal funds through both construction and future maintenance. A more viable, long-term solution that doesn’t pose these same threats is the proposal to inject water into rock layers beneath the city, which not only avoids any problems associated with stagnated canals and lagoons, but also may improve the state of Venetian structures and is the best means of elevating the city through human intervention.

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