Wind Erosion in Western Queensland Australia

Chapter 4 –Modelling Soil Erodibility Dynamicsin soil erodibility being a spatio-temporally dynamic condition that varies through acontinuum at scales from 10 -1 – 10 6 m over minutes to years (Figure 4.1; Figure 2.10).4.3 The Soil Erodibility ContinuumChepil (1953) demonstrated that soil clay content is a good texture-based predictor of soilerodibility, with clay content up to 15% of the soil weight being extremely important inincreasing aggregation and decreasing soil mobility. The relationship between soil claycontent (percentage clay) and streamwise sediment flux Q (gm -1 s -1 ) was reported as:(% clay)Q = a.(%clay)b . c(4.1)where a, b and c are regression coefficients with the values 63 095, -5.1 and 1.23respectively. An erodibility minimum defined by Equation (4.1) was found to occur in soilswith 15 – 27% clay. The high erodiblilty of soils with 27%) clay content that may suffer from granulation andaggregate breakdown (Chepil, 1953).Leys (1991b) reported on u *t and soil flux rates for selected Australian soils. The study wasextended by Leys et al. (1996) to better detail percentage clay and dry aggregation effects onsediment flux for cultivated and non-cultivated (crusted) soils. The study reported similarpatterns in the relationship between percentage clay and erodibility to those described byChepil (1953). However, a significant difference in the results was evident with the increasederodibility of soils with >27% clay not found in the Australian soils. The elevated erodibilityfor soils with high clay content (modelled by the c(%clay)tail in Equation 4.1) occurs as a resultof a breakdown in soil structure (i.e. crusting and aggregation) induced by freeze-thawprocesses affecting the North American test soils used by Chepil (1953). Without this tail thepercentage clay-Q relationship for Australian soils can be effectively modelled by a powerfunction of the form:104