A numerical model for wave erosion spatial variability at a Headland-Bay scale on rock coasts: Development and testing with synthetic and measured bathymetries

Abstract

In this work, we studied the spatial variability of wave erosion (ET) caused by periodic waves through the development of a simple numerical model on a large-scale (headland – bay scale) over a short-term (annual scale). This model used a wave ray tracking approach and parametrization for wave breaking based on slope and incident wave conditions to investigate the influence of nearshore geometric characteristics: bathymetric planform and cross-shore geometry, on the wave energy transfer from offshore to the shoreline. The model estimated (1) the location of the breaking point and the establishment of the surf zone, (2) the erosive force of those waves reaching the shoreline, and(3) the alongshore and intertidal variations of wave-driven coastal erosion. Synthetic bathymetries simulating straight and sinuous planform rock coasts, the latter with and without alongshore slope variability, were used in the initial tests. In addition, measured bathymetries of two natural rock coast examples were used to examine the model representation of the general wave erosion behavior. Model results showed that the spatial variability of wave energy transfer and the consequent erosion are strongly influenced by the geometry of nearshore bathymetry and deep-water wave regime (height and period). Findings indicated that some segments of a sinuous shoreline may be eroded at higher (headland apex and flanks) and lower (bay center) rates. A conceptual model that describes the spatial variability of wave erosion as a result of the relative influence of geometric characteristics and oceanic settings was developed in this work. Despite its simplified assumptions, the model showed how the nearshore bathymetric geometry influences wave dissipation and the subsequent alongshore distribution of wave erosive force.