Patterns of sand transport on vegetated foredunes

The aeolian development of coastal foredunes is studied at two sites along the Dutch coast. Amounts of sand transport are measured in cross-sections over the foredunes, and changes in surface height are monitored. Sand transport decreases rapidly landward of the vegetation boundary. Near the dunefoot, changes in surface roughness and topography generate turbulence and upward flow, causing a small part of the sand to be transported in suspension. Patterns of transport are found to be closely related to air flow, which in turn is related to topography and vegetation density. With steeper topography, the amounts of sand transported landward from the dunefoot increase, if vegetation density is low. During oblique onshore winds, most of the sand accumulates at the dune front. During perpendicular onshore winds, a large proportion of the sand is deposited landward of the slope. When deflection of flow occurs, landward transport of sand is interrupted.