Wind Erosion in Western Queensland Australia

Chapter 5 – Land Erodibility Model DevelopmentChapter 4 of this thesis established a framework for modelling soil erodibility. Due to aninability to parameterise the framework, this factor is kept spatio-temporally constant inAUSLEM at short (daily to monthly) time scales. This creates a problem in circumstanceswhere vegetation cover and soil moisture are low, and where land erodibility is controlled bysoil erodibility, for example on a dry lake bed or playa. If a crust is present on the soil surfaceand the supply of saltation material is limited, soil erodibility will be considerably lower thanif the surface were disturbed (Houser and Nickling, 2001a; Langston and McKenna Neuman,2005). These effects vary depending on soil texture and crust characteristics. An a prioriassumption in modelling land erodibility with AUSLEM is that at seasonal to annual timescales regional variations in soil surface conditions in rangeland environments are reflected ingrass cover and soil moisture conditions. During wet periods when cover and moisture arehigh, soil aggregation and crust cover are likely to be higher than in dry seasons and periodsof drought (Chapter 4). At these times inter-particle binding by moisture will be low, andcrusts and soil aggregates are likely to be most disturbed by photo-degradation and tramplingby livestock (McTainsh and Strong, 2007). So, at seasonal to annual time scales regionaltrends in land erodibility modelled with vegetation cover and soil moisture are likely toreflect actual land erodibility. Interpretation of AUSLEM output should therefore be confinedto the examination of trends in output at time-scales longer than one month.A soil texture mask (E tx ) has been included in the current model formulation (Figure 5.3). Themask assigns a scaling factor (provisionally set to 3.0) to areas with soil clay content less than7.0 %. All other soils are assigned a factor of 1.0. The scaling factor forces sandy soils forwhich crusting and aggregation are likely to play a minor role in determining erodibility tohave a consistently higher susceptibility to mobilisation than soils with high clay content forwhich crusting and aggregation have greater potential effects on erodibility (Breuninger et al.,1989; Belnap and Gillette, 1997; Leys and Eldridge, 1998).Stone Cover EffectsThe effects of stone cover on land erodibility are considered by the addition of a mask thatassigns an erodibility value of 0 (not erodible) to areas with extensive stone cover. Theinclusion of the mask was considered important as significant areas (i.e. the Sturt StonyDesert) of the study region are covered by a dense stony pavement. Experimental wind tunnelresearch by Gillette et al. (1980) demonstrated that this type of dense stone cover is effectivein protecting surfaces from deflation. While wind erosion on stony floodplain and playa141