Wind Erosion in Western Queensland Australia

Chapter 2 – Land Erodibility Controlsgeometry between spherical grains (one particle on top of another) was used, notrigonometric correction was required for the direction of the cohesive force as in theMcKenna-Neuman and Nickling (1989) model. The model performed well for low soilmoisture, but does not hold true as moisture content increases and pore spaces between grainsbegin to fill.Fécan et al. (1999) developed a theoretical model to account for soil moisture effects on u *tusing a similar model for particle contacts (i.e. between cones) and grain binding (i.e. bycapillary forces) as McKenna-Neuman and Nickling (1989). Their model was simplified todirectly include soil moisture content and an expression to calculate the threshold moisturecontent at which entrainment is initiated. The model was developed from a regressionanalysis of data presented by Belly (1964), Bisal and Hsieh (1966), Saleh and Fryrear (1995)and Chen et al. (1996), and is of the form:(%clay) 2 + 0.17( clay)w ' = 0.0014%(2.23)where w’ is the threshold moisture content for particle entrainment. The expression is used inthe calculation of the wet threshold friction velocity for two scenarios:uuuu* tw=* td* td1( w ) 0. 68* tw1+1.21 w'= for w > w’for w < w’ (2.24)where u *tw /u *td is ratio of the wet to dry threshold friction velocity.Cornelis and Gabriels (2003) tested a number of the models described above, finding largedifferences between output values for set input conditions. To address this issue, Cornelis etal. (2004a) developed another expression to quantify the effects of soil moisture on u *t .Developments in the new model included: 1) it considers inter-particle forces as the sum ofdry and wet binding forces, rather than computing the wet threshold friction velocity as anadjustment to the dry threshold; 2) it takes into account both capillary forces between soilparticles and adhesive forces due to absorbed water films; and 3) it uses a more general48