Wind and Sand Transport Across a Vegetated Foredune Slope

Vegetated foredunes are widespread aeolian landforms along wave-dominated sandy coasts. In contrast to previous advances in dune erosion during storm surges, there is a little empirical data and understanding of aeolian processes during foredune recovery and growth. Based on a comprehensive data set (airflow, sand transport, topography change, and vegetation cover) collected across a steep (1:2.5, 21.8°), high (20 m) foredune during a windy 5-week period at Egmond aan Zee, the Netherlands, we demonstrate in agreement with previous studies that shore-perpendicular winds accelerate by a factor of 3 from dune foot to crest but result in low aeolian mass fluxes that are maximum at the dunefoot, favoring local deposition. In contrast, oblique and alongshore winds up the foredune are accelerated less (or even decelerate) but are important in bringing sand from the dunefoot on to the foredune slope, where it is deposited when vegetation cover exceeds about 50% of the maximum density measured on the dune crest. Moreover, our data suggest that sediment flux at the dune foot is limited by fetch-induced sediment availability, whereas sediment flux at the dune crest is limited by transport capacity, which depends on the wind velocity and the distance traveled over vegetation. Our study thus highlights the importance of wind direction and vegetation cover to foredune growth and recovery.