Variation of Wave Groupiness across a Fringing Reef

Abstract

A new definition of wave groupiness factor is proposed here based on wave-height history of wave trains. This new definition takes into account the dual roles of both zero-downcrossing wave height and wave period in the spatial and temporal evolution of the wave groupiness. It is demonstrated that the new groupiness factor is less sensitive to the operational definition and can describe the groupiness degree of not only linear wave trains but also highly nonlinear ones. The variation of the wave groupiness across a laboratory fringing reef was investigated. Results showed that in the nonlinear shoaling zone, the groupiness became more pronounced. Decreasing of the groupiness was triggered by wave breaking in the vicinity of the breakpoint. The groupiness decreased rapidly shortly after breaking, whereas it increased in the inner surf zone. Infragravity wave modulation of short-wave water depth was the main source of groupiness after breaking.