Influence of offshore fringing reefs on infragravity period oscillations within a harbor

The main objective of this paper is to systematically study the influence of offshore fringing reef topography on the infragravity-period harbor oscillations under the condition of wave breaking occurring over the reef. The infragravity (IG) period oscillations inside an elongated harbor excited by bichromatic wave groups are simulated using a fully nonlinear Boussinesq model. Based on a wave analysis technique, influences of plane reef-face slope, reef-face profile shape and reef ridge on the maximum IG period component amplitude, the bound and the free IG waves and their relative components inside the harbor are comprehensively investigated. Results show that under the condition of wave breaking occurring over the reef, all the four above-mentioned variables increase gradually with the reef-face slope, and tend to increase first, then decrease, and then increase again with the mean water depth over the reef face. For the reef-face profile shapes with relatively large mean water depth (equal to or larger than 3.0 m), the existence of the reef ridge always significantly enhances the bound IG waves inside the harbor, while its influences on the maximum IG period component amplitude and the free IG waves both depend on the incident primary wave amplitudes.