Controls on the geomorphic response of beach-dune systems to water level rise

This paper offers a synthesis of the disparate evidence on the importance of the magnitude and duration of water level rise in both lacustrine and marine environments in relation to other long-term controls on coastal response (e.g., wind climatology, vegetation growth, geological context). A brief review of two 'equilibrium profile' models (i.e., the Bruun and RDA models) is provided as a conceptual foundation before considering a range of complicating factors that are important to determining how sandy coasts may evolve in the future under rates of relative water level rise (RWLR) similar to recent increases in sea level. Key processes controlling beach-dune interaction are reviewed, especially the rates of morphodynamic action relative to the inundation potential driven by water level increases, leading to the conclusion that transgression distances due to RWLR are small in comparison to characteristic shoreline excursions driven by storm events and subsequent reconstruction phases. Much of the available evidence suggests that the beach and foredune (together with the nearshore profile) will migrate landward intact, keeping pace with relatively slow rates of RWLR similar in magnitude to those predicted by current sea-level scenarios. However, the documented response of shorelines in the Great Lakes to several episodes of relatively rapid rates of RWLR over a period of about a decade indicates that landward migration of the foredune through aeolian processes may be too slow to keep pace with this magnitude of shoreline transgression, and therefore the foredune will be over-run by the translating beach and nearshore profile.