Wind Erosion in Western Queensland Australia

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Chapter 4 –Modelling Soil Erodibility Dynamicschanges in the time it takes for a soil to reach a condition of maximum erodibility defined byb max . Parameterisations from (iv) to (vi) demonstrate the effects of varying the modelcomponents M and T that define the time of maximum growth.In reality, temporal changes in soil erodibility are driven by dynamic variations in r, M and T.Therefore, a soil will not move up and down a single growth curve in response to rainfall anddisturbance conditions. Rather, variations in the growth rate and disturbance intensities willinduce an irregular/fluctuating growth pattern, for example (vii). Temporary increases in soilmoisture and changes in aggregation and crust strength due to small rainfall events willinduce additional variations in the growth curve. These effects will be further moderated bysoil properties like organic matter content and climatic factors such as solar radiationintensity and evaporation rates. Soil erodibility dynamics could be modelled using staticgrowth rates based on soil type dependence on drought to erode (e.g. after Gillette, 1978).However, the model output would not display realistic temporal patterns unless the effects ofall dominant controls can be included in the growth rate formulation. The strength of theframework lies in this potential for incorporating a dynamic growth rate model to account forvariations in soil responses to rainfall, drought and disturbance mechanisms.Figure 4.6 demonstrates the model sensitivity to changes in the rainfall thresholds that drivedecreases in erodibility. A hypothetical simulation was run with model parameters set for r =-0.15, M = 0.5, T = 0.5 (Equation 4.11). Rainfall thresholds (Equation 4.15) were set for:(a) ∑r < 3, α = 1; 3 < ∑r < 10, α = -20; 10 < ∑r < 30, α = -40; ∑r > 30, α = -60(b) ∑r < 5, α = 1; 5 < ∑r < 10, α = -20; 10 < ∑r < 30, α = -40; ∑r > 30, α = -60(c) ∑r < 10, α = 1; 10 < ∑r < 20, α = -20; 10 < ∑r < 40, α = -40; ∑r > 40, α = -60Decreasing the model sensitivity to rainfall, from (a) through to (c), results in increases in themagnitude of output erodibility values and in the time for which a soil may have an elevatederodibility. Accurately defining both the model growth rates and rainfall sensitivitythresholds will therefore be essential if the conceptual framework is to be applied to modelsoil erodibility dynamics.118
Chapter 4 –Modelling Soil Erodibility DynamicsFigure 4.6 Graphs illustrating the effect of threshold changes that determine the model sensitivity torainfall events (bars). Parts (a) to (c) illustrate decreasing model sensitivity to small rainfall events andsubsequent increases in soil erodibility.4.4.4 Model LimitationsThe model framework has a number of limitations that are relevant to its future application.The primary limitations include:Limitation 1. The model defines soil erodibility relative to Q, and not the threshold frictionvelocity for grain mobilisation (u *t ). Modern process-driven wind erosion models quantifyland erodibility as a product of soil erodibility and surface roughness in terms of u *t (e.g.119
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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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List of TablesChapter 1: Introducti
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Chapter 1 - Introduction• The abi
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Chapter 1 - IntroductionFigure 1.2
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Chapter 8 - Conclusions• There is
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Chapter 8 - Conclusionsmodels are n
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Chapter 8 - Conclusionsthe opportun
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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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