Wind Erosion in Western Queensland Australia

Chapter 2 – Land Erodibility Controls2.2.5 Soil Moisture EffectsSoil moisture increases inter-particle cohesion and induces soil aggregate and crustformation. Moisture binds soil particles by adhesion and capillary effects (Cornelis andGabriels, 2003). The increase in particle binding causes a reduction in the availability ofloose erodible sediment and an increase in the energy required to mobilize grains on a soilsurface (u *t ). Soil moisture content therefore plays a critical role in determining thesusceptibility of a soil surface to mobilization.Numerous experimental studies have been carried out to quantify the relationship betweensoil moisture content and u *t. Early reports on the effect of moisture include those by Chepil(1956), Belly (1964) and Bisal and Hsieh (1966). The research demonstrated a non-linearresponse of increasing u *t and decreasing soil particle movement with slight increases in soilmoisture content for a range of desert soils in North America. Chepil (1956) established anempirical relationship accounting for the increasing bed resistance to shear stress due to soilmoisture by the expression:u=u+2 c* tw * t(2.13)awhere ρa is the air density (kgm -3 ), and γc is the resistance against shear stress due tocohesion between particles (due to the presence of water films between grains), andexpressed as:2 w 0.6c=(2.14) w1.5where w is the gravimetric moisture content (kgkg -1 ), and w 1.5 is the gravimetric moisturecontent at -1.5 MPa (kgkg -1 ). Subsequent research has demonstrated that u *tw valuescalculated by equation (2.14) tend to be higher than those computed using more recentlyderived expressions. Like Chepil, Belly (1964) used wind tunnel experiments to derive anempirical function for the computation of u *t adjusted for percent soil moisture content (w).44