Combined longshore and cross-shore shoreline model for closed embayed beaches

This research focuses on the development of a simple and efficient transect based long-term shoreline model. The new modeling tool is a combination of a model for the shoreline changes due to the gradients in longshore drift and a heuristic cross-shore shoreline model. The cross-shore part of the model uses an up-to-date semi-empirical shoreline evolution model based on the equilibrium beach state assumption. A physics-based longshore shoreline model is developed on the same premises as the one-line type approach based on the longshore sand budget and assumes no loss of sediment of the embayed system. The derivation of the longshore part of the model explicitly decouples the average shoreline position from its fluctuating components. An important result is that the equilibrium shoreline orientation is shown to depend on the time correlation between the incoming wave power and the difference between the instantaneous and the time average wave incidence. As a test case, the combined shoreline model is calibrated with the wave and shoreline data of the embayed beach of Narrabeen, Australia. A separate analysis of each contribution reveals that the long-term trend is mostly a longshore drift contribution and surprisingly, part of seasonal shoreline variability is attributed to longshore drift processes.