An equilibrium-based shoreline rotation model

Abstract

The rotation of beaches is important and should be more pronounced under high energy conditions with significant changes in wave direction. Shoreline rotation occurs when one end of a beach accretes, while the opposite retreats. This phenomenon is attributed to periodic or long-term changes in wave climate. To simulate the variability of the shoreline orientation in a simple and efficient way, the aim of this paper is to present a new equilibrium-based shoreline rotation model derived from a shoreline migration formulation. This model assumes that beach rotation is induced by the incoming wave power and direction.The proposed model was applied to two embayed beaches with different hydrodynamic and morphodynamic contexts located in the South Pacific Ocean. Almost fifteen years of shoreline positions extracted from hourly time-averaged images captured at Tairua Beach, New Zealand, and thirty-seven years of shoreline position data acquired from beach profile surveys at Narrabeen Beach, Australia, were used to evaluate the model performance. The results from the last beach have been compared and discussed with respect to an existing semi-empirical model, which has shown to successfully reproduce the time-varying shoreline rotation on embayed beaches.Overall, the results demonstrate that the proposed model successfully represents the general shoreline orientation variability both qualitatively and quantitatively. Nevertheless, observations from different sites with diverse beach characteristics and wave conditions are needed to broadly validate the proposed model.