This paper studies, with a numerical approach, the wind waves that are expected at the quay in front of "Piazza S.Marco", namely the main square of Venice (IT). Essential part of this applied research is focused on the mitigation of the flooding risk of the Piazza. Water level and waves in the lagoon are simulated, with the Advanced CIRCulation (ADCIRC) and the STeady-state spectral WAVE (STWAVE) models, that are driven by a constant and spatially uniform meteorological forcing, taking into account different wind speed and directions. In short, the first model evaluates the set-up and the second model evaluates the waves propagating on such levels. It is found that the observed waves in front of the Piazza, that are generated by winds of 25 m/s, occurring approximately once every 10 years, are approximately 0.50 m.
A recurrent problem in the lagoon of Venice is the flooding caused by high-tide events. The well-known Mose gate system (www.mosevenezia.eu) was designed to mitigate this problem and isolate the lagoon from the sea in case of extreme events.
Obviously, the water level in the lagoon cannot be described by a single value and, for instance, the wind set-up may cause significant differences between points located at the north and south ends. Similarly, the level is expected to vary in time due, for instance, to the rain contribution or to the variability of the aforementioned wind set-up.
When the Mose will be in operation, a set of numerical models of different nature will predict the tide, surge, wave and wind setup, rain, etc., in order to conveniently anticipate the gate closure. The level in front of the main square, named "Piazza San Marco", should be kept below the threshold +1.1 m with reference to the "Punta della Salute" topographic cornerstone, ZMPS (Zero Mareografico Punta della Salute). Note that the Mose, in order to meet other environmental constraints, cannot be designed to preserve a lower threshold. This level is suited to preserve economic and navigation activities, with acceptable environmental impacts but, at present, it would not be sufficient to maintain the Piazza completely dry, since approximately 12% of the city of Venice is inundated when the water level in front of the Piazza is +1.10 m (Canestrelli et al., 2006, Boato et al. 2009).