The Effect of Beach Vegetation on Aeolian Sand Transport

by Alan W. Niedoroda, Environmental Science &, Engineering Inc, Gainesville, United States,
D. Max Sheppard, Environmental Science &, Engineering Inc, Gainesville, United States,
Alfred B. Devereaux, Environmental Science &, Engineering Inc, Gainesville, United States,

Abstract: The effect of coastal vegetation on aeolian sand transport is examined through consideration of the governing aerodynamic processes. Local scale processes without the effect of ground relief are considered. The atmospheric surface boundary layer is represented as three sublayers consisting of a constant stress layer above the plant canopy, a constant turbulent mixing length layer within the canopy, and a near-ground constant stress layer. This representation is used to compute the fluid shear stress acting on the sand surface and the consequent entrainment and transport of sand. Published aerodynamic coefficients for vegetation similar to coastal plants are used in computations of the ratio of the aeolian sand flux in vegetated and bare-ground conditions. The results show that vegetation type, height, and spacing, as well as wind speed, grain size and gradation, control sand transport beneath a canopy. Closely spaced vegetation results in such a large reduction of the boundary shear stress that no sand transport occurs, even with strong winds. However, many types of coastal vegetation tend to be sparse so that varying amounts of sand transport occur. The spatial transport gradient is large between bare and vegetated zones for wind speeds slightly exceeding the grain entrainment threshold conditions and smaller for stronger winds. Typical spacing of sparse coastal vegetation normally reduces sand transport, even during high winds.

Subject Headings: Vegetation | Sand (hydraulic) | Sandy soils | Sediment transport | Shear stress | Canopies | Soil stress

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