Wind Erosion in Western Queensland Australia

Figure 1.9 Flow chart of the thesis structure, linking the thesis chapters to theresearch objectives. ..........................................................................................23Chapter 2: Land Erodibility to Wind: Systems AnalysisFigure 2.1 Forces acting on soil particles exposed to the air-stream, including lift(L), drag (D), inter-particle cohesion (C), particle weight (W) and theparticle moment (M) (after Bagnold, 1941).....................................................33Figure 2.2 Modes of particle transport by wind, including: creep; reptation;saltation; and suspension (after Pye, 1987)......................................................36Figure 2.3 Graph of the threshold friction velocities (u *t ) for a range ofgrain/particle sizes (after Bagnold, 1941). The two curves illustrate thedifference between fluid and impact thresholds. .............................................38Figure 2.4 Graph illustrating the effect of soil clay content on sediment transportfor soils in cultivated (disturbed) and non-cultivated (crusted)conditions (after Leys et al., 1996). .................................................................40Figure 2.5 Diagram illustrating the dependence of soil textures on drought toexperience a significant increase in soil erodibility. The dependence ofclay textured soils on drought is due to the requirement for long dryperiods that enable the breakdown of aggregates to occur (afterGillette, 1978) ..................................................................................................42Figure 2.6 Illustration of probability distributions of the energy delivered to a soilsurface by saltating grains, P[Ei], and the local energy required tobreak surface crusting, P[Es] (after Rice et al., 1999). ....................................53Figure 2.7 Graph illustrating the effect of wheat stubble cover on sand discharge(after Leys, 1991a). ..........................................................................................56Figure 2.8 Graph illustrating the effect of Spinifex (Triodia spp.) grass cover onsand discharge for a range of wind velocities (after Wasson andNanninga, 1986)...............................................................................................57Figure 2.9 Illustration of the effects of vegetation on surface roughness and thedrag partitioning model (after Chepil and Woodruff, 1963). (a) showsthe relationship for a bare surface, (b) for a surface with sparsevegetation cover, and (c) for a densely vegetated surface. ..............................59Figure 2.10 Space-time plot illustrating the spatial and temporal scales over whichwind erosion controls operate. .........................................................................64xv