Venice Is Sinking: Issues of the City Built on Water
The Challenge of Building a City on Water and Mud
Since the beginning, to fabricate a building Venetians had to deal with water, corrosion by the salt, mud, and sand.
To build any building, from the smallest house, to the Cathedrals and tall bell towers, the first phase of the contractions was to frame the area with two lines of wooden beams, distant about 30 inches from one line to the other, and fill 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 trees trunks one next to each other, deep enough to reach solid ground. Once the 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.
How Was Venice Built?
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 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 archeology, 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.
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 backwards S, is crossed by only three bridges (ponti): the Ponte di Rialto, the Ponte dell'Accademia, and the Ponte degli Scalzi.
(see map below)
10 Facts About Venice's Canals
Map of Venice Italy
Environmental Problems of Venice
Despite staying absolutely magnificent, 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 fire fighters need to reach the location by water, 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.
- As all big cities, Venice is not eluded by pollution. Particularly, the water in the canals is affected by industrial and agricultural waste that 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.
High Water in Venice
Acqua Alta – High Water
In Venice Acqua Alta, which literally translates as high water, means that the sea level raises of more than 80 centimeters and covers parts of the city.
Not every high tide causes acqua alta, a series of conditions are needed to influence the level of the sea: the astronomical tide, the meteorological contribution, the land's natural subsidence, and the raising 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 the most cases of acqua alta. In the worst cases the water covers 90% of Venice.
An event of acqua alta lasts three or four hours, then water recedes and everything goes back to normal. In the areas of the city that get flooded, Venetians will set up raised walkways to permit transit.
However,if you have a pair of rubber boots you can still go pretty much anywhere and enjoy the city even during this peculiar time.
Do you know the environmental issues of Venice?
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© 2012 Robie Benve