Wind Erosion in Western Queensland Australia

Chapter 3 – Modelling Land Erodibility Review3.2.5 Wind Erosion Stochastic Simulator (WESS)The Wind Erosion Stochastic Simulator (WESS) is the wind erosion module of the EPIC(Environmental Policy Integrated Climate) erosion model (Van Pelt et al., 2004). WESS is aprocess-based model that predicts wind erosion on an event or periodic basis. The modelprovides assessments of soil loss at user-specified distances within individual fields. Themodel uses inputs of soil surface data including texture, soil surface moisture and drying rate,erodible soil thickness, surface soil bulk density, and soil roughness parameters for largeaggregates (random roughness), and ridge height and spacing (oriented roughness). This iscoupled with local wind speed data and a stochastic wind speed perturbation factor tosimulate dust emission (Potter et al., 1998). WESS simulates wind erosion based on dailywind speed distributions adjusted by soil, surface roughness, vegetation cover and erodingfield length factors:YW= ( FI )( FR)( FV )( FD)!t0YWRdtWL(3.14)where YW is the wind erosion estimate (kgm -2 ), YWR is the erosion rate (kgm -1 s -1 ), WL is theunsheltered field length (m), FI is the soil erodibility factor, FR is the surface roughnessfactor, FV is the vegetation cover factor, FD is the field length factor (based on WL), and t isthe duration of wind greater than a threshold velocity. YWR is calculated using the approachof Skidmore (1986). The soil erodibility adjustment factor is based on the static WindErodibility Groups (WEGs) reported by Woodruff and Siddoway (1965), and used in theWEQ model:( 0.0001 )IFI = *exp * YW695(3.15)where I is the soil erodibility factor (tha -1 ) with values assigned by soil texture and theWEGs. The effect of oriented surface (cultivated ridge) roughness (FR) is calculated as afunction of wind direction, and the impact angles of saltating grains:RFC FR = 1 exp (3.16) RFB 80