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Sinking City of Venice

See the Gates in Action
Illustrated Transcript


Venice homepage

This is the Venetian lagoon with the city at its center. These are the three lagoon inlets. They are the openings, which connect the lagoon to the sea. This is where the mobile defenses will be installed—a system of gates designed to solve the problem of high water, which is becoming increasingly frequent and intense.

Imagine that the system is already in place and let us draw nearer onboard a helicopter. We're at the Malamocco inlet, framed by two long jetties. The tide is at a normal level and the gates, which come into operation only when tides higher than 100 cm [40 inches] are forecast, are completely invisible in the bed of the canal. The only structures visible merge with the surrounding landscape and are of modest dimensions, like this building.

Now on a small bathyscaphe, which gives us an idea of the dimensions of the gates, we reach the bed. The seat of the line of gates is set into a trench on the bed of the inlet. The gates have one side attached to their base by means of two hinges. Special paint is applied to their exterior, which protects them from the aggression of the marine environment.

Now, let's go and see how they're made inside. Inside we see the modular metallic structure, which assures maximum resistance of the gates to the pounding of the wave motion. But how do they function exactly?

When exceptionally high water is forecast, compressed air is pumped into the gates to empty the water that keeps them on the seabed. As the water is expelled, the gates, rotating around the axis of the hinges, rise until they emerge and isolate the lagoon from the sea. When the high water ebbs and the water in the lagoon and the sea reach the same level the gates are filled once again with water until they return to their original position.

The mobile defenses, on average, come into position about seven times a year and remain functioning only during high water. The system protects the Venetian lagoon, its inhabitants, its extraordinary city, and its invaluable historical, artistic, and environmental patrimony from all high waters as well as from the risks of extreme events.

Opening the gates, which we see here, is carried out according to precise procedures, with which the possible increase in the water level of the lagoon, resulting from the flow of the rivers, from rain, from local increases due to the wind, and water passing between one gate and another, is also taken into account.

The gates are 20 meters [66 feet] wide, 5 meters [16.5 feet] thick, and a maximum length of 30 meters [99 feet] where the bed is deepest. The time needed to open the entire line of gates is 30 minutes, and 15 minutes to close it. At the end of the raising phase the upper part of the gates emerges until it forms a continuous line, which closes the inlet, preventing the tide from entering and maintaining the water in the lagoon at a safe level.

The system is designed to sustain a difference in level between the sea and the lagoon of up to two meters [6.5 feet]. It will therefore also be effective in the case of relevant increase in sea level during the next century. Fishing boats, emergency vessels, or leisure boats can enter the lagoon through a refuge haven with a lock created at the side of the inlet canal. The functions and the control plant are also installed here.

The mobile defenses, chosen after comparison with many other defense systems, do not reduce the exchange of water caused by the tides and are compatible with the ongoing and future environmental equilibrium interventions of the lagoon and with the development of the port. Building the system will take eight years at a cost of 3,700 billion lire [$1.9 billion] and will directly employ about 1,200 workers a year. This development of new activities and new qualified work also implies the safeguarding of Venice.

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Map of three lagoon inlets

The gates would be installed at the three lagoon inlets, the gaps in the coastal strip through which the tides flow into the lagoon.







Barrier diagram

When in operation, the gates form a continuous barrier that blocks the flow of the tide, keeping the water level in the lagoon at a safe height.







In normal tidal conditions the gates are filled with water and rest on the canal bed. When high water is expected, the gates are temporarily emptied of water until they emerge to isolate the lagoon from the sea.








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