Experimental investigation of V-type breakwater for protecting reef-fringed coasts against infragravity waves

As a result of sea-level rise and coral degradation, the capacity of coral reefs against extreme waves has been progressively declining. Although various wave-dissipating structures for the coral reef have been proposed through field and laboratory studies, none of them have been found to be effective in mitigating infragravity (IG) wave attack on the reef-fringed shoreline. To address this knowledge gap, this study proposes a small-footprint, perforated V-type breakwater that is specifically designed to attenuate IG waves, and systematically evaluates its performance through laboratory experiments under various wave conditions and varying breakwater configurations. The propagation and evolution of IG waves under the influence of the breakwater are analyzed by the cross-correlation method. This method effectively separates multiple incoming and outgoing IG waves, enabling the quantitative evaluation of wave reflection and dissipation induced by the breakwater. The results demonstrate that the V-type breakwater significantly reduces IG waves on the reef flat by reflecting wave energy and enhancing dissipation, achieving a maximum wave height reduction of 73%. Increasing the angle and the number of layers of V-shaped baffles improves the performance of IG wave attenuation. It is also found that to effectively reduce IG waves without raising the mean water level, the breakwater needs to have sufficient permeability and be positioned away from both the reef edge and the shoreline.