Wind Erosion in Western Queensland Australia

Chapter 2 – Land Erodibility Controlsparticle entrainment and quantifies susceptibility to wind erosion through the thresholdfriction velocity (u *t ) at which particle entrainment will occur. This method is frequently usedin process-based wind erosion modelling (e.g. Marticorena and Bergametti, 1995; Shao,2000). Computation of u *t to assess erodibility provides a measure that is independent of, butaccounts for the dependence of wind erosion on wind erosivity.Aeolian abrasion processes can affect assessments of soil and land erodibility. This isrelevant to assessing erodibility through soil erosion rates, but has not always beenconsidered in these studies. Aeolian abrasion (described in Section 2.2.7) is the process bywhich fine clay-sized particles are emitted into the atmosphere. The process is a response tosaltation (Section 2.2.1), whereby bouncing (saltating) particles and/or particles on the soilsurface break down or become detached due to particle impact forces. Soils with high sandcontent are typically mobile and are considered highly erodible (Table 2.2). However, they donot necessarily produce large quantities of dust. This may be the case if the relativeproportion of fine (clay) particles in the soil is low (Pye, 1987). Soils with high clay contentmay have a low erodibility due to strong inter-particle binding or surface crusting. However,with the introduction of some abrasion mechanism to release the fine particles, clay soils canbe significant dust emitters. The presence of abrasion material is governed by soil surfaceconditions, and the availability of sand size particles, for example from a neighbouring dunesource. When assessing erodibility it is important to recognize and separate potential soilmobility measured by erosion rates as distinct from potential dust production induced byaeolian abrasion (e.g. McTainsh et al., 1999 – Land Erodibility Index).2.1.3 Definitions of ErodibilityThe terms ‘soil erodibility’ and ‘land erodibility’ will be used in this thesis to describe theseparate but related conditions of soil and land susceptibility to wind erosion. The terms aredefined as follows:Soil Erodibility:The susceptibility of a soil to mobilisation by wind. Soil erodibility is spatially variable andtemporally dynamic, and is a related to the availability of loose erodible material (< 0.84 mm)on the soil surface as determined by aggregation (aggregate size distribution and aggregatestability), surface crusting and soil moisture content. Factors controlling soil erodibility are31