Wind Erosion in Western Queensland Australia

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Chapter 3 – Modelling Land Erodibility ReviewThe WEPS erosion model operates with a scheme that computes entrainment when the windfriction velocity over a field surface (u * ) exceeds a threshold friction velocity (u *t ) for particlemobilisation (after Bagnold, 1941; Chapter 2). A static threshold is computed for fieldsurfaces and employs factors to adjust for flat biomass cover, soil wetness, and aggregate sizeand density. The effects of standing biomass are used to adjust the wind friction velocityrather than the threshold velocity of the surface (Visser et al., 2005). The model allows forsoil conditions to be updated during erosion events through changes to the aggregatedistribution and crust factors.First, a static threshold friction velocity WUB *ts (ms -1 ) is computed for a bare soil surface as afunction of the fraction of the surface that can/cannot erode:( 1.35) exp[ ( b ) ]WUB = 2(3.5)* ts1.7 SF cvwhere b2 is a coefficient computed as a function of the aerodynamic roughness height, andSF cv is the fraction of bare soil that is not erodible. SF cv is computed using an empiricalrelationship between the soil erodible fraction, rock cover, and clod and crust cover. Increasesin the static threshold friction velocity WUC *tx due to flat biomass are computed by:WUC +* ts= 0. 02 SFC cv(3.6)Further adjustments can then be made to adjust for soil moisture effects WUCW *tx :WUCWHR0wc* ts= 0.48(3.7)HR15wcwhere WUCW *ts is the increase in u *t due to surface wetness, HR0 wc is the surface watercontent (kgkg -1 ), and HR15 wc is the surface water content at 1.5 MPa (kgkg -1 ). The staticthreshold friction velocity is computed as an amalgam of Equations 3.5, 3.6 and 3.7:WU* tsWUB*ts+ WUC*ts+ WUCW*ts= (3.8)76
Chapter 3 – Modelling Land Erodibility ReviewWEPS uses a series of empirical relationships to compute changes in soil erodibility withinthe soil sub-model. The soil sub-model accounts for surface crusting through a linearrelationship with cumulative precipitation. It then computes the amount of loose erodiblematerial on the crust as a function of soil textural properties, organic matter, carbonatecontent (after Zobeck and Popham, 1992). As for surface crusting, the loose erodible fractionof soil can be adjusted within the model by accommodating precipitation effects (Hagen,1991). Additional soil properties that affect soil erodibility such as dry aggregate sizedistribution and stability are also derived within the soil sub-model. Like RWEQ, WEPS hasa relatively small spatial application, with the model simulation region being confined to asingle field, or a few adjacent fields. The model accommodates land surface heterogeneity bydividing non-homogeneous regions into smaller homogeneous sub-regions, and runningsimulations for each (Hagen, 1991).WEPS has been applied to simulate field conditions (crop residue roughness effects) andwind erosion on cultivated fields in North America and Europe (Van Donk and Skidmore,2003; Funk et al., 2004; Hagen, 2004). Hagen (2004) compared WEPS predictions tomeasured data from 46 wind erosion events across North America. Across the sites, WEPStended to under-predict soil loss, but reproduced the field data reasonably well (r 2 = 0.71). Ina similar comparison, Funk et al. (2004) found a better match between WEPS predictions andfield measured erosion rates (r 2 = 0.91) for a series of erosion events in Germany. Coen et al.(2004) used WEPS to map wind erosion risk of soils in Alberta, Canada. However, the modelwas run at a coarse (field scale) resolution, and did not provide information on high spatialand temporal resolution changes in soil erodibility.3.2.4 Texas Erosion Analysis Model (TEAM)The Texas Erosion Analysis Model (TEAM) was developed to have a low dependence onfield-measured inputs and empirical relationships as used in WEQ, RWEQ and WEPS.TEAM simulates the detachment, maximum transport rate and emission of dust particles(Singh et al., 1999). Like WEPS, the model erosion scheme operates on the principle thatentrainment occurs when u * exceeds u *t . The schemes used to compute land surfaceconditions draw upon external studies of the effects of land surface processes on u *t . LikeWEPS, TEAM computes both a static threshold friction velocity required for the initiation ofentrainment, and a dynamic threshold for sustained sediment transport.77
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Modelling Land Susceptibility toWin
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AUSLEM was developed as a Geographi
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who joined me on many trips, shared
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Conference Presentations by the Aut
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2.2.5 Soil Moisture Effects........
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Chapter 6: Assessing Land Susceptib
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List of FiguresChapter 1: Introduct
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Figure 2.11 Conceptual model of lan
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hand column) presents trajectories
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Chapter 1 - Introduction• The abi
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Beadle, N.C.W., 1945. Dust storms.
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Bryan, R.B., Govers, G., Poesen, J.
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Chepil, W.S., 1965. Transport of so
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Fryrear, D.W., Sutherland, P.L., Da
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Gregory, J.M., 1984. Prediction of
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Hugenholtz, C.H., Wolfe, S.A., 2005
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Littleboy, M., McKeon, G.M., 1997.
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Marshall, J.K., 1973. Drought, land
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Assessment Report of the Intergover
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Penner, J.E., et al. , 2001. Climat
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Rickert, K.G., McKeon, G.M., 1982.
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Stokes, C., J., McAllister, R.R.J.,
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Williams, W.J., Eldridge, D.J., Alc
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Wind Erosion in Western Queensland Australia

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