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Safeguarding Venice: a sea defence system project against climate change impacts

Venice Water Authority

On 4 November 1966,Venice and the entire lagoon area were completely submerged under more than a metre of water.The damage to the extraordinary historical, artistic and environmental heritage of the city and lagoon was incalculable and it was clear that the very survival of towns and villages in the lagoon area could not be guaranteed if action was not taken to protect them.

The problem: increasing high tides

Although lucky weather conditions have prevented the concrete and ever present risk of similar or even more catastrophic events, the common image of the sinking and flooded city is a reality and is set to become an even worst threat as the climate changes.

Since the beginning of the 1900s, the relationship between land and water has changed radically and, because of a combination of a drop in land level (subsidence) and a rise in sea level (eustatism), Venice has “lost” more than 23 cm with respect to the sea. As a result of those few centimetres, vitally important for a city built on the water, the frequency and severity of high waters have intensified. In the future, the phenomenon could be further aggravated by the predicted rise in sea level produced by the “greenhouse effect”. Action has been necessary to counteract increasing high tides and the risk of catastrophic events.

The Chioggia inlet with work underway. On the north bank of the inlet you can see the work underway to construct the small craft harbour and locks to allow the transit of fishing boats, emergency vessels and small craft when the gates are in operation during high waters
The Chioggia inlet with work underway. On the north bank of the inlet you can see the work underway to construct the small craft harbour and locks to allow the transit of fishing boats, emergency vessels and small craft when the gates are in operation during high waters

After four decades of much heated debate around the 1966 flood, work began in 2003 on the Mose system, a system of mobile barriers at the three lagoon inlets to definitively safeguard Venice from all high waters, including both exceptional events threatening the city’s survival and the more frequent floods which erode its physical structures and quality of life. The arrangement of concealed barriers and defence of the entire sea front with reinforcement of the littoral and restoration of the jetties have been designed to withstand a rise in sea level of at least 60cm in the next 100 years and cope with even the most pessimistic of scenarios predicted by international bodies. The Worldwatch Institute mentions Venice and the Netherlands in their January report State of the World 2006 as the two places already implementing projects which deal with climate change impacts.

The solution: the Mose System

The mobile barriers consit of rows of gates full of water and completely invisible in normal tidal conditions, hinged and lying in caissons at the bottom of the channels leading to the lagoon. When a high tide is forecast, compressed air is pumped into the gates to empty them of water, they thus rise above the surface, creating a continuous barrier dividing the sea and the lagoon for the necessary length of time. Mose includes small craft harbours and locks to let ships to enter the lagoon when the barriers are raised, with small locks for pleasure and fishing boats at Lido and Chioggia and a large lock for ships heading for the port at Malamocco.

The work will last a total of eight years and, by 2012,Venice will be absolutely protected from all high waters. It is one of the largest sea defence projects underway anywhere in the world. Managers, scientists and technical experts from the Thames barrier in England, the Sheld and Rotterdam barriers in the Netherlands and St.Petersburg in Russia (with its experience of defending itself from the Neva) are involved in meetings and work with the Mose designers and technical experts, and follow with great interest the work and innovations, including in terms of management and economic repercussions.

Detail of a row of gates in action, Venice, Italy
Detail of a row of gates in action

The Mose system is at the heart of a vast plan of interventions delegated by the Special Legislation to Safeguard Venice to the State and implemented by the Ministry of Infrastructure and its local technical office, the Venice Water Authority, via the Consorzio Venezia Nuova. The Plan of Interventions is divided into separate but interrelated lines of action: defence from high waters and sea storms, restoration of morphology and improvement of the lagoon water and sediment quality.

The entire project is in an advanced stage of implementation and represents a fundamentally important environmental defence, restoration and management programme, not just in terms of quantities, but also the know-how acquired. The Italian State’s commitment to Venice goes back many years. As well as central government, other authorities – including the Veneto Region responsible for pollution abatement and the local authorities of Venice and Chioggia, responsible for urban maintenance – take a role in generally safeguarding the city and protecting the lagoon ecosystem.

Thanks to Mose,Venice will soon be safe. But at the same time, the city has a great opportunity for high quality development through the specific activities of study, experimentation, monitoring and implementation inherent in such a complex sea defence project. In short, in the era of the greenhouse effect and rising sea level,Venice will become the city which once again, as in the times of the Serenissima, teaches the world how to survive the force of the sea.

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