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the MOSE system for the safeguard of Venice: how it works

High waters

Since the beginning of the 1900s, high waters have becoming ever more frequent as the level of the land has dropped with respect to the sea.  Flooding causes inconvenience for inhabitants and damage to architecture and buildings. There is also an ever present risk of a catastrophic event such as the 4 November 1966 flood when Venice, Chioggia and other built up areas in the lagoon were completely submerged under more than a metre of water. 

 Some figures:

a) High waters above 140 cm recorded in Venice since 1966

4 November 1966: 194 cms
3 November 1968: 144
14 February 1979: 140
22 December 1979: 166
1 February 1986: 159
8 December 1992: 142
6 November 2000: 144
16 November 2002: 147

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b) Increase in the frequency of high waters in Venice from 1926 to 2005 (number of events equal to or higher than 110 cm per decade)

years:                         no. events
1926 - 1935:  7 events
1936 - 1945: 3
1946 - 1955: 11
1956 - 1965: 22
1966 - 1975: 31
1976 - 1985: 39
1986 - 1995: 23
1996 - 2005: 53

 What is the MOSE and how does it work?

Lagoon of Venice. The three inlets of Lido, Malamocco and ChioggiaThe Mose System is a project for the safeguard Venice from high waters and consists of mobile barriers able to temporarily separate the lagoon from the sea.  It is being constructed at the lagoon inlets of Lido, Malamocco and Chioggia, the three openings in the barrier island through which tides propagate in the lagoon. 
The mobile barriers consist of rows of gates.  In normal tidal conditions, the gates (a type of pontoon) rest in caissons on the bed in the inlets, completely invisible and without modifying exchanges between sea and lagoon. During high waters, they are raised and prevent the tide from entering.  At present, the tidal level at which the gates will be raised has been set at 110 cm, the level to which Venice has been protected by raising quaysides and paving.  This means that the gates would be activated an average of 3/5 times per year for a period of 4/5 hours each time.  However, the level at which the gates are raised can be changed whenever necessary. When the gates are in operation, the continuity of port operations will be guaranteed by a lock for large shipping being constructed at the Malamocco inlet. 

Mose system. Movement of the gates   Mose system. Detail of a row of gates in action

The above illustrate the movements of the gates of the MOSE system.

The Mose system can protect the lagoon and its cities from tides of up to 3 m and will therefore be effective even if the level of the sea rises significantly during the next few decades. 

Mose system: Progress

The go-ahead to construction of the Mose System was given by the "Comitatone" in April 2003, with the collaboration of all levels of State, Regional and Local Government.  Work has been underway for three and a half years and will last a total of eight years. A further ok was given by the comitatone in november 2006. According to the project, by 2012 (expected year of completion) Venice will be definitively protected from all high waters and the ever present risk of a catastrophic event such as 1966.

Work sites - For the last three and a half years, work has been proceeding in parallel at the three inlets of Lido, Malamocco and Chioggia.

Lido inlet - At the centre of the inlet, the new island which will act as the intermediate structure between the two rows of mobile gates has already been constructed.  At the side of the island, work is underway on the deep structure which will house one of the "abutments" for the row of mobile gates. The island will also accommodate the control buildings and barrier operation installations
The coast on the north side of the inlet (Cavallino- Treporti) has been extended and redesigned with the construction of two sizeable small craft harbours, large areas of protected water equipped with a lock to allow small craft to shelter and transit when the gates are raised during a high water event.  The sea side area of the small craft harbour has already been "impermeabilised" and will be used to construct the gate caissons.
Along the south side of the inlet (San Nicolò), the existing jetty has been enlarged to avoid siphoning and flow-over of water when the gates are raised to close the inlet.  The deep structures to house the "abutment" for the second row of gates are under construction.  For the last few months, major work has been underway to prepare the bed for installation of the gates. 

Malamocco inlet - Outside the inlet, a 1,280 m long curved breakwater has been constructed with the dual role of attenuating the vivacity of the tidal currents and creating a basin of calm water to protect the lock for large ships heading for Marghera, already finished some time ago.  The lock will avoid Mose interfering negatively with port activities during construction and when the gates are raised.  The size of the lock, present in numerous large ports in the north, allows the transit of large ships up to 280 m long and 39 m wide.
Beside the lock, a temporary area has been prepared to construct the gate housing caissons for this inlet. 

Works at the Malamocco inletIn the photo: the works at the Malamocco inlet. On the left, on the south side of the inlet (Pellestrina littoral), works for the construction of the abutment of the gates and for the creation of the navigation lock that will allow large ships to pass through when the barriers will be closed. In the foreground, the new breakwater (completed) outside the inlet. It attenuates the vivacity of currents nd creates a calm basin sheltered from wave motion and wash to facilitate the transit of boats. On the background, the city of Venice)

Chioggia inlet - Outside the inlet, a 520 m long curved breakwater has been completed.
Work at the north side of the inlet is also at an advanced state of completion, with construction underway of a protected small craft harbour with two locks to guarantee access to the lagoon for a large number of fishing vessels when the gates are in operation during a high water event. The "abutments" for the row of gates are also under construction. 
Lastly, large sections of the bed have been protected with layers of rock near the areas where the rows of gates will be installed.

 Employment - Currently about 700 people are employed directly, while after completion. When in full activity, the work sites will guarantee a total of about 1.500 direct jobs.


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