Experimental Investigation of Infragravity Wave Propagation on a Porous Reef

A laboratory experiment is carried out to study the generation mechanism and the evolution process of an infragravity wave (IG wave) on a typical permeable fringing reef. Fifteen capacitance wave gauges are installed along the reef model to record the water surface elevation under irregular wave action. Based on the experimental data, both IG wave generation and strong IG wave interaction are systematically analyzed. The experimental results indicate that the IG waves are generated by the time-varying breakpoint mechanism at the reef edge, and the tidal modulations on the IG wave height are mainly influenced by wave breaking and wave dissipation. Around the reef edge, the tidal modulation is controlled by wave breaking and the IG wave height monotonously decreases with the increase of the tide level. At the shoreline, the tidal modulation is controlled by wave dissipation at the low tide level and wave breaking at the high tide level. Therefore, the IG wave height first increases and then decreases with the increase of the tide level, and the maximum IG wave height occurs at the middle tide level.