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e-Journal

 

Venice and the Environmental Hazards of Coastal Cities
(Released December 2006)

 
  by Carolyn Scearce  

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Urban maintenance and coastal defense

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The processes of subsidence and erosion, the increasing frequency of flooding, and the ravages of time and the elements have taken their toll on Venice. The Adriatic's encroaching waters do not represent the only threat to the city's integrity. Many of the city's historic buildings and walkways are compromised by factors such as the corrosive effects of sea water, the wearing influences of motor boat wakes, and soil erosion from beneath foundations. In order to address such problems Venice has instituted plans of urban maintenance, established warning systems for extreme weather events, and deliberated on various proposals considered for addressing the impact of rising sea waters.

map
Model showing currents in Venice Lagoon
For a city like Venice, built as it is in such a potentially changeable environment, failure to conduct regular maintenance represents an acute vulnerability to safety and functionality. During the 1970s and '80s, maintenance regimes were somewhat slack. By the early 1990s, many canals within the city had become choked with sediments, significantly impairing the navigability of the water system. To address this and other problems, plans were instituted and work began in 1993 to improve the waterways and city infrastructure, with completion scheduled for 2025. The first phase focuses on dredging and improving hydraulic and sanitary conditions within the canals. Other factors the plan addresses include improving structures of buildings and bridges, raising the height of pedestrian walkways, and updating utility services (Dolcetta, 2005). Over the centuries, as sea levels have risen relative to the city, walkways and bridges have traditionally been built up. This may be the last time this approach is feasible as doorways within the city will start to become inaccessible if the pavements are raised more than the projected few centimeters proposed by this project.

A dramatic storm surge experience by the city on November 4, 1966, focused considerable attention on Venice by forecasters and ocean modelers (Tomasin, 2005). Due to Venice's vulnerability to storm surge and unusually high tides, it is crucial for the city to have access to reliable forecasts of sea level conditions (Canestrelli and Zampato, 2005). To fulfill this need, the Centro Previsioni e Segnalazioni Maree (CPSM) provides a forecasting and warning system for Venice. CPSM includes observations of sea level and meteorology, short term sea level forecasts, tide information, and alerts for high water events.

diagram of mobile gate
Functioning of the mobile gates, know as MOSE, to be built to protect from flooding
Since the 1966 event, the increasing frequency of city flooding has demonstrated that warning systems alone will not be enough to protect the city. For this reason, the city has considered more active defensive measures for managing high water events. The proposal that officials have settled on as the most workable is known as (Modulo Sperimentale Elettromeccanico) MOSE. The project consists of a set of mobile gates to be built across the three inlets that provide access to the Adriatic Sea. According to the proposal, the gates would be open the majority of the time, in order to allow free exchange of water between the sea and the lagoon. However, during high water events, the gates would be raised to protect the city from flooding (Ravera, 2000). There has been some debate about the efficacy, impact, and expense involve in the MOSE project. However, it seems likely that the city will go forward with MOSE even though the project is not expected to buy the city more than another 100-200 years of sustainability under current conditions.

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