Erosion profiles due to particles entrained by wind: Application of an eolian sediment-transport model

Abstract

Erosion by impacts of particles entrained in the wind scales with the kinetic energy of impacting grains. A recent model of eolian sediment transport permits calculation of expected erosion patterns in objects of simple geometry. The modeling of vertical erosion profiles, in turn, provides an exacting test of the transport model. Realistic distributions of liftoff velocities for saltating grains give rise to kinetic-energy–flux profiles characterized by a strong maximum as much as .1–.4 m above the bed during strong winds. Kinetic-energy flux due to suspended grains also peaks above the bed; the height and strength of the maxima depend very strongly on the grain-size distribution. As grain size diminishes, increased particle deflection by the air flow around an obstacle reduces delivery of kinetic energy to the surface. For both saltating and suspended grains, kinetic-energy flux scales with the fifth power of the wind shear velocity. Erosion profiles in man-made obstacles are well modeled with only slight modification of the saltation model to account for the relatively high elasticity of actual deflationary surfaces, lending considerable support for the model. The modeling also elucidates several aspects of ventifaction. As small ventifacts (.1–.2 m in diameter) and the lower portions of larger ones are predominantly eroded by saltating grains, upwind surface irregularities are quickly damped, leading to facets that dip upwind and sharply truncate lee surfaces. Sandblasting by suspended grains dominates along the upper portions of large ventifacts, where grain paths are partially deflected by the obstacle, and may lead to radially symmetrical flutes and grooves.