New Insights on Coastal Foredune Growth: The Relative Contributions of Marine and Aeolian Processes

Coastal foredune growth is typically associated with aeolian sediment transport processes, while foredune erosion is associated with destructive marine processes. New data sets collected at a high energy, dissipative beach suggest that total water levels in the collision regime can cause dunes to accrete-requiring a paradigm shift away from considering collisional wave impacts as unconditionally erosional. From morphologic change data sets, it is estimated that marine processes explain between 9% and 38% of annual dune growth with aeolian processes accounting for the remaining 62% to 91%. The largest wind-driven dune growth occurs during the winter, in response to high wind velocities, but out of phase with summertime beach growth via intertidal sandbar welding. The lack of synchronization between maximum beach sediment supply and wind-driven dune growth indicates that aeolian transport at this site is primarily transport, rather than supply, limited, likely due to a lack of fetch limitations. Plain Language Summary Coastal dunes are prevalent features along much of the world's sandy ocean coastlines. As these landforms serve as the first line of protection against storm-induced coastal flooding, understanding when and why dunes erode and/or recover has significant societal importance. This study investigates beach and dune evolution at a field site in southwest Washington, USA, by utilizing (1) a long-term data set of coastal change and (2) detailed information on local waves, tides, and winds. Although high water levels impact the dune frequently during the winter as a result of a high-energy wave climate, the dunes at this location are growing rapidly. Here we show that high water levels are not necessarily destructive to dunes and instead under certain conditions they can contribute, along with wind induced sediment transport, to dune growth.