FLOATING BREAKWATERS COMBINED WITH SHEET PILES. AN APPLICATION FOR THE DEFENSE OF SAN MARCO SQUARE (VENICE, IT)

The Lagoon of Venice is the largest of the Mediterranean area with a unique and fragile ecosystem. It is the result of its long-term management, that dates back to the fourteenth century, when the Venetians decided to divert the major tributaries (Adige, Bacchiglione, Brenta, Sile, Piave rivers) out of the lagoon, so that they discharge their fresh water and sediments directly into the sea, reducing the siltation of the lagoon (Gatto and L. Carbognin 1981). These monumental hydraulic works, decisive for the splendor of Venice, gave rise to several other variations: subsidence was not compensated for by the alluvial deposit, deepening of the lagoon increased the erosion processes, diversion of freshwater caused an increment of the salinization, etc. As a result, a unique lagoon environment developed, that however cannot survive without constant management. Today, at the three inlets that connect the lagoon with the Adriatic Sea, impressive hydraulic works, storm surge barriers named Mo.S.E. (from the Italian acronym for “Experimental Electromechanical Module”, www.mosevenezia.eu) are present. They are crucial to prevent coastal flooding caused by high water levels during extreme storm events. The system started to be operative in October 2020 (Mel et al. 2021) and since then the barriers were activated more than 50 times.