Wind Erosion in Western Queensland Australia

Chapter 3 – Modelling Land Erodibility ReviewWEELS computes wind erosion as hourly assessments (thr -1 ). The model can be used to maperosion risk in terms of the duration of erosive conditions and corresponding maximumsediment transport rate. Simulated monthly and annual time series of wind erosion conditionswere compared with data from test sites in England and Germany (Böhner et al., 2003).Spatial and temporal patterns of modelled wind erosion were found to be in agreement withobservations of wind erosion. However, no quantitative assessments of the modelperformance have been published.3.3.2 Wind Erosion Assessment Model (WEAM)The Wind Erosion Assessment Model (WEAM) was the first integrated model developed inAustralia to quantify wind erosion rates (Shao et al., 1994). The model was designed tooperate at a moderate spatial resolution and predict dust emissions from the Murray-DarlingBasin in south-eastern Australia. WEAM combined current theories on the effects of climate,soil, vegetation and land use on wind erosion.WEAM quantifies land erodibility through the threshold friction velocity, with erosionoccurring when u * > u *t . The model computes streamwise sediment flux (Q) and vertical dustflux (F). It uses the saltation model of Owen (1964), a sand transport equation, to compute Q,which is adjusted using soil particle size distributions. The wind shear velocity (u * ) isdetermined from climatic conditions and the surface roughness height (Shao et al., 1996). Thethreshold friction velocity is calculated as a function of soil particle size, frontal area index ofsurface roughness elements, soil moisture, and the hardness of the surface crust:( d ,w,c)ut( ds,0,0,0)( ) H ( w) M ( s)*u* t s, = (3.20)Rwhere u *t (d s , 0, 0, 0) was approximated from the model of Greeley and Iversen (1985), R(λ) isthe ratio the bare threshold velocity over the covered (rough) threshold velocity, H(w) is theratio of the threshold velocity of the wet surface over the threshold velocity of the dry surfaceand, M(s) is a mobility coefficient describing the influence of the state of soil aggregation andcrusting, and the chemical binding strength which maintains this state.83