Environmental and morphologic controls on wave-induced dune response

The Pacific Northwest of the United States exhibits complex spatial patterns of storm-induced coastal fore dune erosion. Using oceanographic and morphologic data from three field sites encompassing a range of subaqueous and subaerial coastal profile configurations, a relationship is found between morphologic characteristics and dune volume changes during storm events producing high water levels. The data suggest that dune erosion increases with increasing backshore beach slope and that, under particular oceanographic forcing conditions, wave-driven processes can grow the lower portion of dunes on low sloping, dissipative beaches. These observations of environmental and morphologic controls on storm-induced dune impacts are further explored using XBeach, a state of the art numerical model capable of simulating interactions between hydrodynamics and morphology. Consistent with the field data, model simulations indicate that wave-driven dune growth may occur on low sloping beaches in cases where the dynamic still water level (still water level plus wave setup) is lower than the dune toe. However, these accretional processes are restricted to events where limited incident wave energy impacts the dune. Cases with steep backshore beach slopes or dynamic still water levels exceeding the dune toe instead typically result in dune erosion. Additionally, the model simulations suggest that morphologic properties of the shelf, nearshore, and the dune itself influence storm-induced dune volume change. Therefore, morphologic features far from the dune face, including shelf geometries shaped in part by the regional historical sediment budget, may have important implications on the susceptibility of coastal foredunes systems to storm impacts. (C) 2019 Elsevier B.V. All rights reserved.