Wave energy distribution and morphological development in and around the shadow zone of an embayed beach

Abstract

BackgroundThe curved shoreline shape of embayed beaches is one of its most notable characteristics and can be described using the parabolic bay shape equation (PBSE). Wave diffraction in and around the shadow zone is often regarded as the primary forcing mechanism leading to the prominent curvature of the shoreline. However, wave climate variables (wave direction, directional spreading and wave height) are shown to be influential in redistributing wave energy throughout the bay and in the shadow zone. MethodsIn this study, a process-based morphological model (Delft3D) is used for hydrodynamic and morphodynamic simulations of a schematic embayed beach. Wave forcing conditions are systematically varied between a mixture of time-invariant and time-varying cases. ResultsThe role of diffraction is shown to be dominant only when the wave conditions are both narrow-banded (<20°) and when the PBSE angle β is high (>30°). Otherwise, as little as 6% variation in wave direction within a 90° range can account for the shoreline curvature in and around the shadow zone. ConclusionThe degree to which wave direction and directional spreading vary through time therefore has a large effect on the equilibrium orientation and shoreline planform of the bay.