Numerical study of irregular wave propagation over sinusoidal bars on the reef flat

Abstract

Irregular wave propagation over sinusoidal bars on the reef flat is studied based on a fully nonlinear shock-capturing Boussinesq model FUNWAVE-TVD. The model was first verified with existing experimental, theoretical, and numerical data to confirm its robustness in predicting irregular propagation over the reef bathymetry and Bragg reflection of irregular waves induced by sinusoidal bars on the horizontal bottom. A series of numerical experiments were then performed based on the verified model to investigate the Bragg reflection effect induced by sinusoidal bars set on the reef flat for irregular waves. Model results show when the natural frequencies of sinusoidal bars fall in the sea-swell wave band, sinusoidal bars on the reef flat can induce a Bragg reflection of sea-swell waves. However, no certain primary reflection peak is observed for sea-swell waves, and a substantial part of sea-well wave energy can still transfer to infragravity wave energy before reflection so that the reduction effect of infragravity waves is barely satisfactory. In this situation, increasing the amplitude of sinusoidal bars can still enhance the Bragg reflection of irregular waves while increasing the number of sinusoidal bars has no regular effect. When the natural frequencies of sinusoidal bars fall in the infragravity wave band, the reduction effects of both infragravity waves and sea-swell waves are better, but still no primary reflection peak is observed. In this situation, increasing the amplitude of sinusoidal bars can also enhance the Bragg reflection of irregular waves. Overall, the results presented in this paper show that the efficiency of idealized sinusoidal bars on the reef flat to reduce infragravity waves is not as good as expected.