SOIL FLUX MEASUREMENTS USING A PORTABLE WIND EROSION TUNNEL

A portable wind erosion tunnel was used to measure the wind erodibility of a range of soil types under two treatments (bare uncultivated and bare cultivated) in south-west New South Wales. The erodibility was characterized by the soil flux function Q(u*) where Q is the streamwise soil flux (measured with a modified Bagnold soil trap) and u* is the friction velocity (obtained by fitting a logarithmic wind profile law to a wind profile measured in the tunnel). An average over 10 replicate plots for each surface type was necessary to smooth the large scatter in Q and the smaller scatter in u*. The Q values spanned three decades of magnitude, from the highly erodible sand, through the weakly erodible sandy clay loam to the basically nonerodible clay. Cultivation increased the erodibility of the sand and the sandy clay loam by about a factor of 10, but slightly decreased the erodibility of the clay. The function Q(u*) is well described by the Owen (1964) soil flux equation (J. Fluid Mech. 20, 225-42) but the threshold friction velocity is not well described by existing simple models.