The Morpho-dynamics of a Beach Protected by Detached Breakwaters in a High Energy Tidal Environment

This contribution uses a numerical modeling system (MIKE21) to examine the mechanisms causing changes to beach morphology that have been observed in the analysis of video data. In this paper storm scale effects are concentrated upon since such conditions often associated with catastrophic erosion and so are of considerable interest to the coastal manger and engineer. An Argus camera system has been used to evaluate morphological changes under varying wave conditions. A fully coupled hydrodynamic, wave and sediment transport model has been used to investigate the effect of mean wave and tide conditions on the beach morphology. The model produced similar morphological changes to those displayed in the video data. Similar (but opposite) longshore tombolo displacement shown by storms of opposite incidence was shown to be produced by different mechanisms: under northerly incident storms sediment was transported in a down drift direction whereas under easterly wave incidence a gyre formed which moved sediment in an up-drift direction. This emphasizes the influence of tidal currents on wave driven circulation patterns. The importance of tidal currents in modulating near-shore circulation is not often incorporated in design guidelines which may explain the failure of design guidelines in some tidal environments.