Influence of Dredged Channels on Wave Penetration into Harbors: The Malamocco Inlet Case

A natural or dredged channel extending outwards an harbor entrance may strongly influence wave penetration into the harbor itself. Bottom refraction and diffraction induced by the channel boundary slopes can actually cause either concentration or dispersion of wave energy at the harbor entrances, depending on the direction of incoming waves. Wave penetration may therefore depend on directional spreading of incoming wave energy more than on its frequency spreading. The present paper illustrates the results of an investigation carried out on the Malamocco inlet of the Venice lagoon - Italy - by means of a 2D fully elliptic mild-slope equation FEM model, alongside a study intended to support a barrier-system design aimed at protecting Venice from storm-surge flooding. Being characterized by a natural channel extending outwards its entrance actually makes this inlet a particularly suitable case of study. Both frequency and directional spreading have been simulated by means of the superposition principle, either taking into account or not taking into account wave breaking. The results confirm the smoothing effect on both wave concentration and attenuation due to the directional spreading, and show that wave attenuation is to be expected for waves traveling along direction nearly parallel to the channel axis (0°–10° to the channel axis), whilst wave concentration arises when the wave direction is about 20°–30° to the channel axis.