Projecting the Longevity of Coastal Foredunes Under Stochastic Meteorological and Oceanographic Forcing

Coastal foredunes serve as a critical buffer between the ocean and beach-adjacent infrastructure, yet these features are at increasing risk of destruction from future storms and changes in sea level. Quantifying potential future hazards to dunes, which are influenced by both erosional wave-driven and accretional wind-driven processes, is complicated by an inability to forecast the exact sequencing and magnitude of future oceanographic and meteorological forcings. Here we use a stochastic weather emulator capable of generating time series of wind and wave properties to force a reduced complexity morphologic model to assess potential accretional and erosional dune volume changes over the next century. Stable beaches with low shoreline change rates are predicted to have net accretional dunes over the next century on average. Inclusion of background beach erosion rates and sea level changes instead drives more frequent net volumetric dune erosion. At decadal scales, volume changes of the dune are shown to be dominated by the magnitude of shoreline change rate in locations that are rapidly retreating. For stable and mildly eroding shorelines (<$\sim$ −0.3 m/yr), both shoreline changes and changes in the still water level influence timescales of dune destruction. Sets of probabilistic simulations are used to show that gradual wind-driven sediment gains can compensate for episodic wave-driven losses over the long term. However, in the case of higher sea levels, more frequent dune collision results in less time for dune recovery in between major storms in which case tipping points in future dune states can occur.