Venice Is Sinking: Struggles of the City Built on Water
Environmental Problems of Venice
Despite keeping its absolutely magnificent appearance, Venice has many daily challenges to face, some newer ones due to pollution and climate changes.
The complex eco-system in which Venice lays, makes the city slowly deteriorate and face several problems:
- The salty water from the sea slowly corrodes the brick walls that need continuous maintenance.
- Unnatural waves created by boats running in the canals increase the corrosion of walls and structures, even with the speed limit being set very low, the effects of the waves is still worsening the deterioration of the city.
- Emergency services are challenging. When there is an accident, ambulances and firefighters need to reach the location by boat and due to narrow canals, speed limits, and boat traffic, it can take a long time to respond.
- With the high tides, water infiltrates the building foundations, damaging the wood.
- During the XX century, with global warming melting of the glaciers, the sea level has increased by circa 1 millimeter each year. The sea level could increase by 50 centimeters by 2030.
- In addition to the water rising, the buildings are also slowly sinking into the mud on which they are built. It has been estimated that the city sunk about 23 centimeters in one century, and up to 1.5 meters since when it was founded.
- Like all big cities, Venice is not eluded by pollution. Particularly, the water in the canals is affected by industrial and agricultural waste deposited throughout the years. The canals are now only half the depth they were in the beginning, and the high presence of phosphorus and nitrogen stimulates algae multiplication.
- The algae infesting the canals destroy the oxygen in the water and then decompose, causing a bad odor during the summer months’ low tides. As if the small was not enough, it also attracts mosquitoes.
Acqua Alta – High Water
In Venice Acqua Alta, which literally translates as high water, means that the sea level rises of more than 80 centimeters (31.5 inches) and covers parts of the city.
Not every high tide causes acqua alta, a series of conditions are needed to influence the sea level: the astronomical tide, the meteorological contribution, the land's natural subsidence, and the rising of the sea level. Low atmospheric pressure on the Adriatic Sea and sirocco wind are also factors triggering the high water in Venice.
These conditions occur mainly in autumn and winter, in those months, in fact, there are most of the floods. In the worst cases, the water covers 90% of Venice.
An event of acqua alta lasts three or four hours, then the water recedes and everything goes back to normal. In the areas of the city that get flooded, Venetians set up raised walkways to permit transit.
However, if you have a pair of tall rubber boots you can still go pretty much anywhere and enjoy the city even during this peculiar time.
The Sea Level Has Been Rising Over the Past 20 Years
The rise of the average sea level around Venice over the period 1994-2016 (as a result of both eustatism and subsidence, definitions below) is 5.6 millimeters per year.
There had been a period of relative stability between 1970 and the early 1990s, but now we are back to values close to those that characterized the period prior to 1970, when aggressive industrial exploitation of the underground water reserves had caused the soil to collapse.
With the current warming of the atmosphere, we have to catastrophic effect for Venice.
- The increase in the temperature of the waters causes a partial expansion of the oceans with a consequent rise in the sea levels.
- The melting of the continental ice sheets (Greenland and Antarctica above all) resulting in of new liquid masses contributing to the sea level rise.
Worldwide changes in sea level, caused by the melting of ice sheets, movements of the ocean floor, sedimentation, etc.
The gradual caving in or sinking of an area of land.
Venice Is Going Down 1.5 mm Per Year
The subsidence component of the historic center of Venice in the period 1994-2016 is equal to -1.9 millimeters per year, in clear increase compared to the stability of the previous twenty years.
The recent increase in the subsidence speed of Venetian soil is supported by the latest up-to-date analyses of satellite data (GPS) which indicate a loss of altitude in the period 2010 - 2015 with a speed approaching -1.5 millimeters per year.
Troubling Predictions for the Sea Level
A study, published in Quaternary International in 2017 and reported in The Independent, predicted that if global warming isn't curbed in the coming decades, all of Venice will be completely underwater by 2100, as the Mediterranean Sea is expected to rise by up to 55 inches in that time.
High Water in Venice
How Venice Was Built on Water and Mud
In Venice, to raise any building, from the smallest house, to the Cathedrals and tall bell towers, the first phase of the contraction has always been to create a dry area for the foundations.
Then, they had to deal with the ever-present factors of salt water lapping the walls, foundations built on muddy sand, and long-term salt corrosion.
In the old days, they framed the area with two lines of wooden beams, distant about 30 inches from one line to the other, and filled the gap with mud. This would create a wall all around the lot, allowing the builders to drain the water inside the area.
Once dry, they planted tree trunks one next to the other, deep enough to reach solid ground. Once they leveled the tree heads, they would fill any gaps between the tree trunks with stones, rocks, broken tiles, and other materials mixed with cement.
Over the leveled trees they would put planks of larch and elm wood. This would increase even more the resistance of the trunks planted in the mud and cemented, to the point that they would keep in great condition for centuries.
Standing on Upside-Down Trees
Founded around year 450 AD by mainland populations escaping from the barbarian invasions of the Huns led by Attila, Venice is built on over 100,000 palafittes driven into the mud to lay a solid basis for the magnificent buildings.
Venice has been built on the Venetian lagoon, over a forest of upside-down trees.
With the absence of oxygen, the upside-down trees have become as hard as a rock. However, the mysterious uncertainty of this daring work has fed for centuries rumors of the city’s demise, but Venice survives intact through the centuries.
What Are the Palafittes?
In archaeology, palafittes are prehistoric huts built over a body of water and supported by wood beams driven into the muddy ground.
This kind of dwelling built on a wooden platform over water is still used in some regions of South-East Asia and Equatorial Africa.
In Venice, the tree trunks planted into the Lagoon form a foundation of palafittes for brick buildings.
Video: 10 Facts About Venice's Canals
Is Venice One Island?
The magnificent Venice, which seen from a plane looks like a single fish-shaped island, is actually made of 118 islands.
The Islands are separated by about 150 canals and connected by more than 400 bridges.
The main canal is the Canal Grande, that cuts through Venice as a big backward S, is crossed by only three bridges (ponti): the Ponte di Rialto, the Ponte dell'Accademia, and the Ponte degli Scalzi.
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© 2012 Robie Benve