Morphological effect of spring-neap tidal variations on macrotidal beaches

A simple morphodynamic model is presented which adopts an energetics based approach for the determination of cross-shore structure of sediment transport for the investigation of beach profile evolution. This approach is not new, but the translation of a transport function across the beachface, emulating the dynamic regime of a macrotidal environment, represents a departure from previous contributions. The development of this stable, high resolution model facilitates the investigation of the morphodynamic effect of a large tidal range and the interaction of various harmonic components, which become significant outside of a microtidal regime. The model predicts the formation of bars at the approximate break-point, although these formations only occur at tidal standing positions. Once formed, high and low water bars converge, with offshore movement of the high water bar. Interestingly, with the introduction of a second tidal component at S2 frequency, formations occur at the break-point positions relating to high and low water of full springs and full neaps, suggesting that a period of several tidal cycles is required for the establishment of these formations. Temporary formations occur in the interim tidal standing locations but are quickly broken down by the translation of the surf and shoaling zones. The model offers many possibilities for investigating the morphological effect of wave/tide interaction, as well as surf/shoaling dominance and tidal harmonic interactions.