Wind Erosion in Western Queensland Australia

Chapter 2 – Land Erodibility ControlsHis expression described the wet threshold friction velocity in terms of the influence ofmoisture content on the dynamic (fluid) threshold friction velocity:[ 1.8 0.6log( w)]u* t= utw+ 100(2.15)Belly’s expression, however, was derived from a single soil type, and did not account for theeffects of grain size, shape or sorting on the effect of moisture content. For this reason, themodel does not perform well in predicting the effects of moisture content on u *t for soiltextures different to that used in the study.Bisal and Hsieh (1966) used a laboratory wind tunnel to determine the effects of moisture onu *t for the entrainment of fine sandy loam, loam, and clay soils. They demonstrated thatsandy soils are least affected by moisture, while loamy and clay soils are more resistant tomobilisation when moist. This is due to the ability of the soils with higher clay content toretain moisture and form aggregates that are less susceptible to mobilization than welldrainedsandy soils.Hotta et al. (1985) developed a linear expression to compute the wet threshold frictionvelocity based on the dry threshold and soil moisture content. Their expression was based onexperimental data for sands with grain sizes ranging form 0.2 to 0.8 mm, although theexpression does not account for soil grain size:u= u 7. w(2.16)* tw * t+ 5where w is the water content in kg kg -1 and w < 0.08 kg kg -1 . Hotta et al. (1985) assumed amodel to describe the presence of soil moisture between soil particles, whereby moisture isconfined to wedges, which can be defined by the contact angle between grains. More recentresearch into the effects of soil moisture on u *t have used or revised this model of moistureretention and grain binding to develop expressions for u *tw . Further research developingnumerical adjustments to u *t as a function of soil moisture have been reported as exponentialrelationships by Azzizov (1977), Hagen (1984), Shao et al. (1996) and Chen et al. (1996).45