During our Ecology of Venice walk, our docents describe and explain the structural characteristics of Venice, the problems that the city faces, and some of the remedial measures currently being carried out. We spoke with docent Luca Zaggia, who has been working for the last 15 years as a coastal oceanographer for the National Research Council of Italy, Institute of Marine Science in Venice, and asked our three top questions regarding the challenges this city faces.
Context Travel: What accounts for the damaging effects of saltwater to the city’s various structures?
Luca Zaggia: Long term damage to the buildings due to salt expansion in building materials (“haloclasty”) is undoubtedly a result of the increased rate of the relative rise in sea-level. This is partly due to local subsidence (shrinkage of the deep soil layers which result in a loss of altitude), and partly due to the increase of the ocean level, which relates to the global climatic trends. So if in the past centuries the tide oscillations only affected the foundations of Venetian palaces, today the tidal range overcomes the protections invented by Venetians against capillary rising of seawater into the building structure, which were effective for such a long time. We can say that local processes and global warming together affect the architectural and artistic heritage of Venice accelerating the speed at which the structures are deteriorating and weathering and increasing the costs of safeguarding the city. There is nothing that the barriers against storm surges (the MOSE) can do to protect the city from this threat unless we decide to keep the barriers closed forever, which is, of course a crazy and unsustainable choice.
CT: Venetians have developed various ways to incorporate amenities such as electricity, phone lines, gas pipelines in the city – under walkways and under bridges. How has the city reacted to the rise in sea-level?
LZ: There are places, which I show visitors on the Ecology of Venice walk, where one can detect four different stages of elevation of urban surfaces (alleys and sotoporteghi – passages that connect streets). The city reacts to the increasing sea-level much like a coral reef by continually rebuilding structures on a higher level. The most recent step to do this was taken between 1995 and 2005 when Insula on behalf of the municipality, elevated almost all the urban surface to 110 cm over the local zero of the tide (that is 25 cm below the present days mean sea level). This elevation corresponds to the typical high tides, which are exceeded only by exceptional events and storm surges. Above this level we expect the barriers will be operated as soon as the works are completed.
CT: Boats play a crucial part in the daily lives of Venetians. Why is city maintenance so important for this form of transport?
LZ: Venice is a wonderful machine designed through the centuries to combine natural forces and human efforts in order to create acceptable life conditions in this unique environment. It must, however, be continuously maintained. If not dredged periodically, the canals will fill with sediments carried in by the tide and materials from weathered buildings. Navigation would be affected in low tide, so the city life would be greatly affected. It’s a kind of paradox, high tides are a threat for the city, but also low tides are also an obstacle for city life. So what we see today such as traffic of goods via the boats in canals, would be impossible if there was no funds to maintain the canals.
If you are looking to learn more about the ecology of Venice, Luca recommends the following resources:
- The book The science of Saving Venice by Fletcher and Da Mosto is quite a good introduction to the lagoon and its problems.
- The Venice safeguard website www.salve.it (the website of Magistrato alle Acque, the City water Authority) is also a good introduction.
- The video published by INSULA on VIMEO, is also a simple yet very informative introduction to the issues faced by the city: http://vimeo.com/21688538