Crossing the Shoreline Divide: Toward modeling the co-evolution of dune, beach and nearshore systems

Under calm conditions, nearshore hydrodynamics determine the timing and rate of delivery of sand to beaches and thus partly determine the availability of sand for dune building. During storms, nearshore processes erode beach and dune sand and may reset dune formation. At the same time, even when sand supply to dunes is potentially large, wetting and drying affect the transport of sand from beaches to dunes, and processes related to salt spray and groundwater availability alter the viability and growth of vegetation important in dune formation. Just as dune formation is partially controlled by nearshore hydrodynamics and sediment transport, the details of subaerial topography provide a crucial boundary condition for determining hydrodynamics and sediment transport during storms. Duran and Moore (2013) recently extended the model of Hermann et al. (2008) to create an aeolian eco-morphodynamic model (the Coastal Dune Model, CDM) to simulate the formation of coastal foredunes. De Vries et al. (2014) initiated development of a model to simulate the influence of supply-limiting factors on aeolian transport (now the AeoLiS model). Roelvink et al. (2009) developed a modelling approach to dune erosion, overwashing and breaching (XBeach), which connects the upper shoreface with dune systems during storms. Despite the importance of interactions that occur across the spatial domains and range of conditions represented by these process-based models, CDM and AeoLiS treat storm erosion in a schematized way and XBeach does not address inter-storm development of topography. Thus, we are collaborating to develop WindSurf, consisting of: (1) XBeach (2) CDM and (3) AeoLiS. In addressing both subaqueous and subaerial sediment transport and erosion during storms as well as inter-storm evolution of subaerial topography, the resulting coupled model will allow, for the first time, process-based simulation of event- and decadal-scale co-evolution of nearshore, beach and dune systems.