Wind Erosion in Western Queensland Australia

Chapter 2 – Land Erodibility Controls2.2.7 Dust Emission by Aeolian AbrasionThe entrainment of particles from an exposed soil surface takes place through two processes.These processes occur primarily as a result of impacts by saltating grains and include: 1)deflation, whereby incoherent sediment is entrained by lift and drag forces or are “splashed”into the air stream by ballistic particle impacts; and 2) abrasion, whereby consolidated,cohesive materials including both mobile aggregates and crusted surfaces are worn down(Livingstone and Warren, 1996).Significant dust emission is dependent on a supply of loose sediment that can act throughabrasion to release fine particles (Houser and Nickling, 2001a). This may occur as clay oriron oxide coatings are worn from sand grains, or as clay particles are released from a crustedsurface. While sandy soils tend to have loose and mobile surfaces, soils with high claycontent tend to be supply limited in particles that can saltate, abrade and emit dust. Supplylimitation of particles that can abrade exposed soil surfaces results from aggregation andcrusting, while an increase in supply may result from photo-degradation, mechanicalbreakdown and disturbance of aggregates and crusts.The supply of sediments that can abrade a surface is critical to determining the susceptibilityof a surface to wind erosion (Gillette, 1977; Hagen, 1991; Zobeck, 1991; McKenna-Neumanet al., 1996; Rice et al., 1996, 1997, 1999). Abrasion efficiency is also related to the size ofsaltating grains, their kinetic energy, and the physical characteristics of the surface, includingcrust presence, strength and modulus of rupture (Greeley et al., 1982). Houser and Nickling(2001a, 2001b) reported that abrasion efficiency is inversely related to average crust strengthby a power function, implying that as crust strength increases it becomes more difficult forsaltating grains to abrade a surface.2.2.8 Roughness Effects of VegetationNon-erodible elements like vegetation cover affect wind erosion in a number of ways. Theseeffects are manifested through interactions with the air stream and sheltering of the soilsurface. Vegetation affects the wind shear velocity (erosivity), soil properties (e.g. organicmatter content) controlling crust formation and aggregation (erodibility), and interacts withthe processes of particle entrainment, transport and deposition. The effects of vegetation on54