Wind Erosion in Western Queensland Australia

Chapter 2 – Land Erodibility Controls• Particle weight; and• Inter-particle cohesion.Figure 2.1 illustrates the effect of these forces on a particle. Airflow around the particles andover the soil surface results in the lift and drag forces. The particle moment represents acombined rotational effect resulting from these forces. A decrease in fluid static pressure(Bernoulli Effect) combined with a steep velocity gradient over the surface determines themagnitude of the lift forces (Lancaster, 1995). The lift, drag and moment forces act in favourof grain entrainment. Opposing these forces are the effects of particle weight and interparticlecohesion. A number of environmental conditions affect the strength of these factors.These include: soil texture and grain size distribution; grain weight; particle packing density;soil moisture content; soil chemistry; and soil organic matter content. These factors controlthe susceptibility of a soil to entrainment – the soil erodibility.Figure 2.1 Forces acting on soil particles exposed to the air-stream, including lift (L), drag (D), interparticlecohesion (C), particle weight (W) and the particle moment (M) (after Bagnold, 1941).In order for wind erosion to occur the forces of lift and drag incident on a particle mustexceed the opposing forces of particle weight, inter-particle cohesion and surface friction(Pye, 1987). While turbulent airflow characterises the wind profile, flow close to the surfaceis also non-linear. Soil particles that protrude into the flow create a layer of zero velocity33