Laboratory experiments on transforming emerged into submerged breakwaters

Traditional emerged breakwaters are frequently used to protect coastal regions from wave-induced damage. Although they are effective at mitigating transmitted wave energy, their advantages are not always evident, and they often have negative environmental impacts, such as seascape degradation, water stagnation, and unintended nearshore currents. In addition, most of these rigid structures around the world are nearing the end of their technical lifespan, consequently requiring significant financial investments for their refurbishment or removal. Sustainable management solutions and alternatives for their upgrading or removal are needed. In the current study, a novel approach to designing submerged breakwaters is introduced: the new submerged crosssection is obtained by reshaping the pre-existing emerged breakwater, i.e., maintaining the same volume and construction materials. The result is a constant-volume hydraulic analysis of different breakwater configurations under various wave climates, analysed through 2-D physical model tests conducted at the University of Campania "L. Vanvitelli" (IT). The comparison serves as a useful preliminary guideline for designers to choose the best solution based on specific wave climate conditions. The transmitted wave energy is analysed using spectral analysis, providing insight into the shape and peak frequency of the transmitted spectrum for each breakwater configuration. By considering the transmitted spectrum, designers can make informed decisions about the most effective shape for submerged breakwaters in different wave climates and to balance the compromise between improved water and sediment circulation patterns, panorama restoration and storm protection.