Geological controls on shoreface morphodynamic state and implications for coastal barrier evolution

The morphodynamic response of coastal sedimentary barriers to sea level changes is determined by a multitude of factors that range from dynamic forcing by waves and currents, sediment type and supply and their complex interaction through morphodynamic process-response mechanisms. These factors and mechanisms are significantly influenced or even controlled by the underlying geological framework, which remains mostly disregarded when modelling decadal to centennial barrier evolution. As sea level rises and barriers migrate landwards, the shoreline is transgressed and the shoreface is subjected to wave ravinement (erosion and scour by waves along the shoreface). The stratigraphic surface created by wave ravinement becomes an important geological control, as it defines the basal surface over which transgressive shoreface deposits accumulate.

In this work, we explore a variety of geophysical datasets obtained from multibeam and shallow sub-bottom seismic surveying in diverse coastal areas, and model shoreface profiles based on sediment type and dominant sediment transport processes to investigate the significance of wave ravinement surfaces in the morphodynamic state of contemporary shorefaces and discuss the implications for barrier evolution. Our results demonstrate that in many cases the modern shoreface closely mirrors the slope and topography of the wave ravinement surface, even in contexts of abundant sediment supply. This reflects depositional patterns that preferentially follow the antecedent shoreface topography. The dependence of the modern shoreface on the underlying surfaces implies that contemporary shoreface morphodynamic state and large-scale coastal behavior are at least partially controlled by antecedent wave ravinement. Likewise, the future evolution of coastal barriers under accelerated sea level rise will be at least partially controlled by the geological framework of the coastal area to be transgressed and the extent to which future wave ravinement is effective in modifying the shoreface configuration. This work highlights that progress in understanding and predicting barrier response to future sea level rise requires the explicit consideration of the geological framework, including the configuration of significant stratigraphic surfaces.