Wave overtopping and flooding hazards represent critical issues for coastal areas. To contain their related risks, which will be seemingly amplified by various climate change effects, the engineering community is resorting to so-called “adaptive solutions”, namely, the enhancement of existing defensive structures. In this study, we investigate the efficacy of two different adaptive solutions in reducing the mean overtopping discharge at a vertical seawall. Specifically, this study examines either a wall protected by rubble mound breakwaters or rubble mounds combined with ReefBall modules; while a few studies have recently addressed the former solution, the second one represents a novelty.

To analyze the behavior of these two layouts, we have performed a physical experimental campaign in the small-scale flume of the University of Naples Federico II. Four regular wave conditions have been run to measure the mean overtopping discharge at both an unprotected and a protected vertical wall. In particular, we have tested different rubble mound configurations by varying geometrical features, as well as several arrangements of ReefBall modules on the crown of the breakwater. Laboratory results have indicated that rubble mounds do not exhibit a significant overtopping reducing power, especially for submerged structures. On the other hand, the presence of ReefBalls remarkably lessens the mean flow rate at the wall, especially for certain modules’ dispositions. The present work, hence, explores and highlights the effective capabilities of these adaptive solutions in reducing coastal flooding risks.