Possible Defenses Against a Sea-Level Rise in the Venice Area, Italy

Abstract

Already flooded several times a year by ordinary storm surges, the Venice area would be greatly endangered by even a very small, additional rise in sea level. In this paper, after a brief presentation of the gee-hydrologic context of the coastal plain of northeast Italy and of the lagoon of Venice, computation of the frequency and return periods of present-day extreme tide levels in the city of Venice and beyond the lagoon, at sea, is discussed. If a rise in sea-level occurs in the next century, as predicted by certain models, the construction of mobile gates at the lagoon passes could help maintain harbour and other activities in the lagoon and protect the historical city from flooding. This protection, even with navigable locks, would be adequate only if the sea-level rise is less than 0.3 m, however, and if at the same time the lagoon is completely cleared of existing water pollution. In order to avoid floodings during the periods when the lagoon has to be closed provisionally to the sea, fresh-water discharges from minor rivers and drains received in the lagoon, attaining up to 1000 m3/s at the time of extreme rainfall events, must be collected and pumped away. For a sea-level rise greater than 0.3 m, a system of powerful dykes, permanently separating the lagoon from the sea, will be necessary if the area is to remain inhabited. At present, whatever the climatic scenario may be, the most urgent priority is to reduce water pollution.