Detailed measurements of horizontal (U) and vertical velocity (W) and flow directionrnfrom ultrasonic anemometers were taken during an oblique-alongshore (incident angle 31°) sandtransportingrnevent over a vegetated foredune in May 2002. The experiment was part of a largerrnstudy on the sedimentary dynamics of a beach-dune complex in the Greenwich Dunes, PrincernEdward Island, Canada. Topographic steering of flow toward the foredune occurred at the lowerrnstoss slope then deflection back toward crest parallel at the crest. Thus, sand transport pathwaysrnover the foredune deviate greatly from those on the beach. Flow acceleration due to topographicrnforcing did not occur, rather flow decelerated up the windward slope due to a rougher vegetatedrnfetch compared to the beach. Time-series of U and W show that as incident flow becomes lessrnoblique, U and W increase due to enhanced topographic forcing and vertical lift in the lowerrnstoss slope region. As flow becomes more oblique topographic forcing effects are reduced as therndune is effectively less steep to oncoming flow. Variability in U and W show that flowrnsteadiness decreases up the stoss slope in contrast to measurements over desert dunes. Strongrngusts in U and upward W maintained sand transport via saltation into and over the foredune.rnGrain suspension was not observed. Flow deceleration and vegetation roughness reduced sandrntransport at the dune toe promoting accretion. Up the stoss slope transport declined sharply tornthe crest but was maintained by short-lived gusts and slight speed up at the crest.
展开▼
