Wind Erosion in Western Queensland Australia

Chapter 3 – Modelling Land Erodibility ReviewThe effects of water content are defined through an exponential relationship derived fromwind tunnel experiments by Shao et al. (1996):H( w) u ( )/u ( w) = exp( 22. w)= (3.21)* t0* t 7where w has the units m 3 m -3 . Roughness effects are computed by the drag partition model ofRaupach et al. (1993). The effects of surface roughness and cover are defined by:0.50.5( ) = ( 1) ( 1+ ) R (3.22)rm rrwhere β r is the ratio of the drag coefficient for isolated roughness elements over the dragcoefficient for the surface, σ r is the basal-to-frontal area ratio and m r is a parameter ≤ 1accounting for non-uniformity in the surface stress (Chapter 2, Section 2.2.8). The frontalarea index is estimated from fractional cover f c by the equation:( ) = c ln 1(3.23)f cwhere c λ is an empirical constant related to the distribution of roughness elements (a value of1 is assigned implying elements are uniformly distributed and isotropically oriented). Theeffect of dry, loose soil on u *t is computed by the scheme of Greeley and Iversen (1985):u( d ) A F( ) G( d )( g) 0. 5= (3.24)* t1Retdwhere g is the gravitational acceleration, σ is the particle-to-air density ratio, A 1 is anempirical coefficient, F(Re t ) and G(d) are empirical functions, and Re t is the thresholdparticle Reynolds number. The parameters R(λ), H(w) and Sc are estimated based on windtunnel experiments carried out in the study area (Shao et al., 1996). The model is linked to aGIS which contains input data on soils, vegetation, land management and climate across theMurray-Darling Basin.The M parameter (Equation 3.20) and particle size distributions are linked to the soil data inthe GIS database, with the M values being assigned to soil texture classes based ondescriptions of soil properties in the Australian Natural Resources Atlas. While WEAM does84