Worldwide coasts are globally threatened by the effects of shore erosion, with increasing consequences from both a social and economic point of view. In recent decades the use of environmentally friendly artificial submerged barriers have been receiving an increasing interest from the research, due to a high biological compatibility associated to shore protection. Among them, Reef BallTM (RB) represents one of the most commonly used environmentally friendly modules. The latter was originally employed for biological enhancement, and more recently for the shoreline stabilization of high valued sites. To this specific aim, RBs modules can be arranged in rows, according to different configurations, to realize submerged breakwaters even of significant width.
However, in spite of the clear environmental benefit deriving from the adoption of similar structures, their application is still affected by large uncertainties in the estimation of the hydraulic characteristics of the wave-barrier interaction. In particular, very limited studies exist providing equations for the prediction of the effectiveness of Reef ball structures, generally focused on very peculiar and uncommon configurations.
In order to produce a systematic characterization of the hydraulic properties of these breakwaters, and overcome the abovementioned limitations, a wide experimental campaign consisting in 1,440 tests has been conducted with irregular waves in the flume of the Department of Civil, Architectural and Environmental Engineering (DICEA) of the University of Naples “Federico II”. In these tests a wide range of submergences, wave attacks and configurations was investigated, in order to analyse the behaviour or RB barriers under breaking and non-breaking waves. To the Author‟s knowledge, this represents the widest experimental investigation on this specific type of submerged barrier.
The most relevant aspects related to the wave-barrier interaction have been addressed, namely the wave breaking , the rate of energy dissipation, the wave set-up and the variation in the wave spectrum.
In particular, predictive equations have been proposed for the estimation of the transmission coefficients defined both in terms of wave heights and periods. More specifically, the comparison between the DICEA data and literature equations allowed to develop a new conceptual approach for the assessment of the rate of energy dissipation of RB barriers.
Furthermore, the analyses performed allowed a better comprehension of the overall hydraulic behaviour of these structures, especially for what concerns breaking occurrence and typological characterization, and RB barrier‟s influence on nearshore circulation.