Venice, Italy


The city of Venice is an engineering marvel of the world. The city houses almost 300,000 people and is one of the most visited places in Europe. Today, Venice is a tourist city. It has become world famous due to its architecture and famous waterways. The city is made up of 118 islands and 150 canals. It is home to over 400 bridges and in this city, the only way to travel is either on foot or by boat. Venice truly is one of the world's most unique cities.

Some History

Long ago the buildings were built by using long wooden piles (about 60’ long) driven deep into the ground. These piles go deep down into the soil, reaching past the weak silt and dirt to a portion of the ground that was hard clay which could hold the weight of the buildings placed on the piles above.  The piles were also driven into the water which normally would have been a disaster as wood rots normally. The wood used in the construction of the piles was very water resistant but even so the wood should have rotted away eventually. However, several things happened which kept the wood intact for over 500 years.  The first is that wood rots only when both air and water are present, so in the oxygen starved environment of the water underneath the buildings, the wood was protected until the second thing happened.  The waters of the lagoon carried an extremely large amount of silt and soil and the wood was being blasted by this sediment for years.  The wood absorbed the sediment and quickly petrified into basically stone at an accelerated pace.  The wood used in the construction of the piles was also very water resistant such as oak or larch. 

The manner in which the piles were laid is also important.  The piles were placed as closely together as the soil of the ground would permit. Stone and rock was thrown in between the piles which kept the silt from rising up during subsequent pilings;two layers of wood was added on top of the piles which is where the masonry starts. Marble is one of the candidates used in the masonry because it is impermeable to water. 

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Recently, the pile system has shown some drawbacks. Drinking water has always been a problem for the city since the water surrounding Venice is salt water from the Mediterranean Sea. During the 1960’s artisan wells were opened across the city which were drilled deep underground for potable water. However, as the water was drained from underneath the hard clay in which the foundations were piled into, the city began to sink at an increased rate. Drilling was halted and artisan wells were banned across the city because the damage done could never be fixed. Another large issue with the piling method concerns the rising tides across the planet. This is something that the residents of this city have come to regard as a fact of life, and are not immensely troubled by it.

Challenges Today

Venice has been sinking over the years due to steadily rising sea levels. Compared to sixteen hundred years ago. Venice's standard sea level has dropped six feet, which has led to increased flooding. As industrial activity and pumping from the aquifer beneath the city has increased, erosion surrounding the lagoon has reached critical levels. The Italian government has decided to work alongside Ocean and Construction Engineers in safeguarding Venice by building mobile barriers across the lagoon inlets surrounding the city.

"Project MoSE"
- "In 2001, a plan was finally put in motion to keep back the high waters. “Project MoSE,” as it was nicknamed, called for the construction of 79 steel gates to be installed along the sea floor at the three inlets of the lagoon." - Redux

The design plan for Project MoSE (Modulo Sperimental Elettromeccanico) includes seventy-eight hinged steel box gates placed throughout the inlets at Lido, Malamocco, and Chioggia. The gates will first be flooded in seabed caissons. A hinged gate proved to be the most suitable gate typebecause of its ability to be out of sight when not in use and low cost for production. When the tides reach 110 centimeters air will flow through the gates, emptying the water, and allowing the gates to pivot upward. One challenge in the project was trying to predict the right amount of barrier height to accommodate for sea level rise. After consultation with the United Nation's Intergovernmental panel on Climate change, a 60 cm sea-level rise was accounted for. The 300-ton gates will be 4m to 5m thick, 22m to 30m in length, and 20m wide. Hinges in the gate will have a spherical shape and will be made up of ducts for air compression. The Caissons will be placed on piles in trenches with dimensions of up to 60 meters in length, 10 meters in depth, and 45 meters in width. The soil at each inlet will be strengthened with jet grouting and the ground around the caissons will be secured with rock mattresses. For the construction of the caissons a craft harbor and 16 hectare casting yard will be used in the lagoon. Caissons will be built on platforms which will include trolley-mounted jacks. This will allow the caissons to be rolled to ship lifts, which will lower the caissons into the water.

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The overall budget for the project came to 4.7 billion dollars. Once the project is complete in 2014 the gates will protect the city of Venice from flooding and further erosion. During high tides these gates can raise up to six feet and depending on the weather conditions the system will be able to provide complete or partial closure for each inlet.                                                                                                         

Will it work?
Taking a look at Venice, Italy we see that Venice has always been vulnerable to flooding, especially at high tide. But where as something that used happen a few times a year, now happens a hundred times a year has many people worried for the future of Venice. Even though construction for a solution to these on going floods has begun, there has been a significant amount of environmental concerns, and the project has been opposed by many environmental groups.

Concerns about interference with normal tides can increase the levels of toxic chemicals, such as mercury, in the waters of Venice. This could threaten the lives of both marine life and the health of the people who eat the local fish. Since Venice does not have sewers, most of their "household waste flows into the canals and is washed out into the ocean twice a day with the tides"  (Fletcher,2005). So, there is no telling what effects the gates can have on the city's natural waste system.

Environmental, Water Resources, Ocean, Geotechnical, and several other engineers are working hard to solve any potential problems with the project. Some say that the project will be a total failure because it would have a negative affect on Venice. Then there are also those who say that this project will have a positive impact on the city. Since the project is rather new, and completion for the project isn't for another 3-4 years, one will only be able to know the true impact of the project until it is put into effect. There are several professionals working on the project and since there are yet to be any true uncertainties with the project, construction will continue as normal. Hopefully, the project can create a prospective future for the city of Venice.


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