[52] sustain’ MAR/APR 2012 sustain’ MAR/APR 2012 [53]

very high tide

normal tide

sub-normal low tide

exceptional low tide

> 80 cm

< -50 cm

<-90 cm

A Century ago 0 cm

In a Century’s time + 75 cm

Average water level today + 25 cm

extreme high tide

exceptional high tide > 140 cm

> 110 cm

Astronomical tide today

a site of exceptional natural beauty and historic, artistic and cultural heritage.Over time, the Venetians

consolidated the marshes and banked the channels to create the islets and canals of which the city itself is composed. This began in about the 10th century and continued until the mid 20th century when land was reclaimed from the lagoon around its perimeter for expansion of the airport and Marghera industrial zone, as well as within Venice for some social-housing projects.An aerial view from the northern

part of the Venice Lagoon, where many of the original features persist, reveals the affinities between the sinuous form of the saltmarshes and a corner of the island famous for glass production, Murano. Many of the paved squares we find today were originally tidal pools amongst the swamps and the earliest houses were built on the perimeter where sediments accumulated towards the edges, reinforcing the ground and making it a slightly more elevated place to build. Over time, the pools silted up and became grassy fields for grazing livestock before the whole town was paved over during Napoleon’s brief occupation, followed by the Austrians.

Looking at Venice while thinking of sustainability requires double-vision. It is probably the only city where people can look at paintings from centuries gone by in a museum and then find themselves standing in the same scenes (to quote a recent visitor)! The forma urbis has hardly changed since medieval times; jumping through time, the views of Carpaccio, Canaletto or Turner are still identifiable today. So in architectural terms we can say that Venice was built in a remarkably sustainable way, in as much as

sustainability is synonymous with being adaptable and resilient. The same building – say a 16th

century palace – that housed a patrician family, their relatives and servants can now be found, subdivided into about 15 apartments for 21st century families with a fresh layer of paint, modern plumbing, a few extra walls to lower the ceilings and downsize the salons, a satellite dish out the window and even a lift in the courtyard in some cases. Boatyards have been seamlessly transformed into supermarkets

and contemporary urban planners come here from all over the world to be inspired by the pedestrian zone that is the whole of Venice (as more and more areas of inner cities elsewhere are closed off to motor traffic). An efficient water-bus service has replaced the wooden barges that plied the same Venice canal network. But the canals are still the same and a few traditional gondola ferry services still operate (10.50 to cross the Grand Canal at 5 or 6 strategic points).

Working and living with waterThe early Venetians were ingenious in their approach to creating Venice – amidst the mosquito-infested swamps, where they had been forced to take refuge from the invading barbarians – and they subsequently co-opted the natural dynamics of the lagoon system to create the collection of islands and canals that flourished for over a thousand years as the Republic of Venice and that remains today

A sinking feelingFor centuries, the city of Venice has lived in harmony with the waters that surround it. Indeed, the Venice Lagoon is symbolically and symbiotically interconnected with Venetian culture and history. However, as Jane da Mosto, Science Director at The Venice in Peril Fund has discovered, the impacts of climate change and sea-level rise are now threatening the harmony of that relationship. With the threat of rising waters and flooding now facing many of the world’s major cities, what lessons can we learn from Venice?

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Venice is at a critical point between its history and future. If present trends are allowed to continue, the distinguishing features that make Venice sustainable

and resilient will be washed away...

very high tide

normal tide

sub-normal low tide

exceptional low tide

> 80 cm

< -50 cm

<-90 cm

A Century ago 0 cm

In a Century’s time + 75 cm

Average water level today + 25 cm

extreme high tide

exceptional high tide > 140 cm

> 110 cm

Astronomical tide today

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PHOTO: Mimmo Jodice Rialto From the series Venice 2010. Courtesy of Galerie Karsten Greve.

PHOTO: Philip-Lorca diCorcia, Luci From the series, Venice, 2011. Courtesy of the artist and David Zwirner, New York.

[54] sustain’ MAR/APR 2012 sustain’ MAR/APR 2012 [55]

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Innovative buildingtechniquesBuilding foundations consist of wooden piles (2-3m long and 25-30cm wide) driven into the more stable layers of compressed mud. The poles do not decay since they are deep enough to never come into contact with air, which would make them susceptible to attack by micro-organisms. The iconic church of Santa Maria della Salute, designed by Longhena in the 17th century, reputedly rests on over a million poles. It is a significant landmark for Venice not just because it commemorates the end of a devastating bubonic plague, but also because it stands very close to the main tide gauge reference point!The ancient buildings also retain

a certain elasticity to adapt to the shifting mud substrate, ongoing geological subsidence and even in the case of earthquakes. Wooden boards and then thick blocks of Istrian stone (a form of white marble from the opposite coast of the Adriatic) form the base of the buildings. The rest of the building is made of lighter materials notably brick and wood, which reduce the pressure of subsidence. Floors are typically a mixture of lime and clay with marble fragments, known as terrazzo veneziano. Goats milk was used as a sealant.

Venice in Peril supported a brilliant research project a few years ago, in collaboration with the Municipality of Venice, which demonstrated how the use of traditional building materials and techniques was more durable and equally cost effective than modern restoration methods. An abandoned vernacular building was beautifully transformed into three apartments including a ground-floor flat suitable for a self-sufficient disabled person.

Flooding – a feature of Venice lifeSo having praised Venice for its foresighted “structural” resilience, it is now time to mention the other dimension: inevitable limits to its symbiotic relationship with the lagoon, and water in particular. Being relatively impermeable to water, the stone bases of the buildings are a fundamental element of defence for Venice’s buildings from water infiltration – this is not only a problem of humidity but the saltiness of the lagoon water together with the wet/dry cycles of the twice-daily tides in the lagoon, as well as periodic flooding, causes corrosion. Flooding has always been a feature of life in Venice. The earliest recorded occurrence was in the 13th century. The critical issue, from the point of view of urban maintenance, is the rising average water level, a combined result

of natural, long-term geological subsidence (approximately 0.5mm/year), human-induced subsidence caused by groundwater extraction that compressed ground-level (more than 10cm between the 1950s and 1970s) and of course sea-level rise – not necessarily that associated with greenhouse-gas emissions and global warming, but also the significant variations produced by variations in atmospheric pressure, other weather conditions and major climate cycles.Venice has been battling with the

debilitating impacts of upwardly creeping water levels that come into contact with building walls and permeate bricks and plaster, above the impermeable stone bases and via capillary rise reach as far as causing the rusting of metal tie beams, that are often placed at first-floor level to consolidate old buildings, as well as causing precious decorative plasterwork to fall off, fresco paintings to crumble and even the mosaics in St Mark’s Basilica fall off its ceiling. The graph below shows the increased frequency of water levels at which saltwater infiltration of the fabric of Venice affects a large proportion of buildings – from an average of less than 100 times per decade at the end of the 19th century, chronic water levels are now experienced more than a hundred times in a single year.

A critical point betweenhistory and futureThe global ocean system, Mediterranean Sea, Adriatic and Venice Lagoon are nothing other than interconnecting chambers and basic physics tells us how water will find its own level across all of them. So sooner or later, one way or another, the forecast 60cm rise in average sea level will be felt in Venice around the turn of the next century. That extent of sea-level rise is increasingly being accepted as a relatively conservative estimate, taking into account the fact that observed changes are in line with the upper UN projections that, in turn, did not incorporate the increase in sea volume that ice melt in Antarctica especially is contributing.This trend, together with what we

know about the impacts of climate change and sea-level rise, brings us back to thinking about the role and future of the Venice Lagoon. It is not just symbolically and symbiotically interconnected with Venetian culture and history, it is also Italy’s largest coastal wetland and one of the most important regions in the entire Mediterranean basin in terms of birdlife and other biodiversity. Parallels with New Orleans and the delicate Louisiana coastline, for example, tell us about the significance of saltmarsh as a buffer to storm surges, the importance of freshwater sediments for coastal systems, and their potential to attenuate tidal exchanges. What kind of role will the Lagoon have in Venice’s future when considering measures to mitigate and adapt to the effects of sea-level rise?

Economic interests associated with petrochemical processing at Marghera (in decline since the latter part of last century) and latterly intensification of activities at Venice’s commercial port and exponential growth in the cruise sector have intensified pressures on the lagoon by endorsing the necessity for deep navigation channels and ongoing dredging that exacerbate an existing trend towards erosion of the lagoon.Venice is at a critical point between

its history and future. If present trends are allowed to continue, the distinguishing features that make Venice sustainable and resilient will be washed away by a reductionist economic structure and tourist floods that will preserve, at best,

the building fabric in the form of some variant of a theme park. Venice in Peril firmly believes that a more viable future is possible for both the city and lagoon. For more than a decade we have been engaged in building and maintaining an independent platform for analysing and discussing the wealth of relevant scientific research in an objective and integrated framework to promote a process of long-term strategic planning and articulated thinking to plan the future for Venice that she deserves, and desperately needs. This work is not easy, but we carry on nonetheless, true to the Venetian expression: the appetite grows as you eat!

Venice is a city facing a range of threats. Sound information is vital if there is to be worthwhile long-term planning for the city of Venice in all areas important to its survival: protection from the waters; reduction of pollution emanating from the territories around the lagoon; tourism management and transport; finance; change of use of buildings; demographics and employment. Venice in Peril finances essential studies and publications into such issues, as well as disbursing millions of pounds for the restoration of Venetian monuments, buildings and works of art. To find out more, visit: www.veniceinperil.org

fig. 1 – Average Water Level in Venice

Livello media dell’acqua a Venezia

fig. 2 – Annual Frequency of water level of at least 80 cm measured in Venice since 1872 (when records began)

Distribuzione annuale delle maree di almeno 80 cm a Venezia da 1872 (inizio seria storica)

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2012

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2010

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0

1872

1882

1892

1902

1912

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1972

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2002

2012

1870

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1900

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1920

1930

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1950

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2010

Lagoon Intelligence #6 – Illustrations

Venice in Peril

MAIN PHOTO: Tiina Itkonen Ca’Sagredo From the series At the time of the Bora Wind, Venice, 2011. Courtesy of Michael Hoppen Contemporary, London. BOTTOM LEFT: Sinuous Venice. RIGHT: Tim Parchikov, Venice 2009 From the series, Venice, 2005-2011. Courtesy of the artist.