Wind Erosion in Western Queensland Australia

Chapter 3 – Modelling Land Erodibility Reviewwhere I’ is the soil and knoll erodibility; C’ is the local wind erosion climatic factor; K’ is thesoil ridge roughness factor; L’ is the field length; and V is the equivalent quantity ofvegetation cover. Table 3.1 provides a description of each of the WEQ model input factors.Table 3.1 Components of the Wind Erosion Equation (after Woodruff and Siddoway, 1965).ControlDescriptionSoil Erodibility, I The potential soil loss (t/acre/annum) from a wide, unsheltered, isolatedKnoll Erodibility, I s field with a bare, smooth, un-crusted surface. Developed from wind tunneland field measures. I s is used to compute erodibility of windward slopes lessSurface CrustStability F sSoil RidgeRoughness K rVelocity of ErosiveWind vSoil SurfaceMoisture MDistance AcrossField D rSheltered DistanceD bQuantity ofVegetative Cover R’Kind of VegetativeCover SOrientation ofVegetative CoverVariable K othan 500 ft long – varies with slope.Considered insignificant as crust breakdown occurs due to aeolian abrasiononce wind erosion has started. This factor is also transitionary and is onlyconsidered significant where the erodibility of a field is to be computed fora given moment in time. Is is usually disregarded.Measure of soil surface roughness (other than clods or vegetation).Mean annual wind velocity corrected to a standard height (30 ft).Moisture is assumed to be proportional to the Thornthwaite P-E Index(Thornthwaite, 1931).Total distance across a given field measured along the prevailing winddirection.Distance along the prevailing wind erosion direction that is sheltered by abarrier, if any, adjoining the field.Surface residue amounts determined by sampling.Factor denoting the cross-sectional area of the cover.A roughness variable. Values vary to describe prostrate to standing cover.Following publication of WEQ, a number of modifications to the model were made byWoodruff and Armbrust (1968), Skidmore and Woodruff (1968), Skidmore et al., (1970),Bondy et al., (1980), Lyles (1988), and Skidmore and Nelson (1992). Bondy et al. (1980)modified WEQ such that the model could provide estimates of erosion rates for periods lessthan one year. While the foundation of WEQ is its soil erodibility factor, defined from fieldmeasured conditions, application of the model outside North America has been limited by itsdependence on the availability of field-measured input conditions, which are expensive toacquire, and the coarse (annual) temporal resolution of its output. The model was designedfor operation in cultivated lands and does not predict short-term or seasonal variations inwind erosion. This means that it does not accurately simulate wind erosion in rangelands, soits application in countries like Australia is further restricted.72