Spatial variations of infragravity waves on fringing reefs are studied using a fully nonlinear Boussinesq equation model FUNWAVE-TVD. The effects of bottom roughness, forereef slope and tidal water level on significant wave height, wave setup and infragravity wave motion are investigated. Model results show that the cross-shore distributions of significant wave heights and setups are reasonably reproduced using the calibrated bottom friction coefficient. However, the infragravity wave heights over the reef flat are under-predicted. Spatial variations of infragravity waves at different tidal water levels exhibit distinct patterns. Spectral peaks and valleys on the reef flat, indicative of the generation of standing infragravity waves, are observed in the measurements and reproduced by the model. It is demonstrated that the model is capable of simulating the generation and propagation of infragravity motions on fringing reefs. The effects of relative submergence and inverse wave steepness on infragravity waves are investigated through a series of numerical experiments. The results demonstrate that the relative submergence has significant effects on the distributions of infragravity waves on the fringing reef. The maximum infragravity wave height decreases with increasing relative submergence at the reef edge. However, it increases with increasing relative submergence at the inner reef flat.
