Simulating the Impact of Sea-level Rise and Offshore Bathymetry on Embayment Shoreline Changes

Abstract : LX-Shore is a reduced-complexity shoreline change model driven by cross-shore and longshore processes which can account for man-made or natural non-erodible areas such as groynes and headlands. Here we describe and further test the implementation of two recent developments allowing to account for (i) real and non-erodible offshore bathymetric features such as rocky outcrops and canyons affecting offshore wave transformation and, in turn, shoreline variability and (ii) shoreline retreat due sea-level rise. After a description of the numerical developments, the benefits of these new developments are demonstrated with the application of LX-Shore to an idealized embayed beach exposed to real wave climate during a 10-yr period. Three simulations are conducted to test the impact of an outcrop in the middle of the embayment and of a gradual 1-m sea-level rise on shoreline spatial and temporal modes of variability. Results show that the equilibrium planview shoreline and the shoreline variability are strongly impacted by only slightly modifying the bathymetry and varying the mean sea level. These results show the potential of LX-Shore to better understand and further predict shoreline change along real coasts exhibiting mixed (sandy/rocky) and complex seabed morphologies and undergoing sea-level rise.