Flow dynamics over a foredune at Prince Edward Island, Canada

Time-averaged windspeed profiles at eight locations over a relatively high (8 m), vegetated, topographically simple foredune were measured using cup and ultrasonic anemometry during an onshore wind event in May 2002. The experiment was part of a larger study on the sedimentary dynamics of a beach-dune complex in the Greenwich Dunes, Prince Edward Island (PEI), Canada. The foredune is vegetated with Ammophila breviligulata, and vegetation density ranged from 0% on the foredune ramp to upward of 70% at the dune crest. Topographic forcing and resulting flow acceleration was observed distinctly in windspeed profiles, and linear speedup occurred for all elevations above the vegetation canopy. A distinct inflection point is evident in normalized windspeed profiles over the dune indicating a net momentum sink below the vegetation canopy top, and systematic speed-down within the vegetation was observed up the foredune stoss slope. Wind speed profile structure was consistent for the range of incident wind speeds measured. A comparison of normal and slightly oblique incident winds indicated that for similar approach winds, wind speeds are consistently higher during oblique flow conditions. The implications for foredune morphodynamics and sedimentation are discussed.