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DIVISION S-1—SOIL PHYSICS

A Conceptual Model to Predict the Deflation Threshold Shear Velocity as Affected by Near-Surface Soil Water

I. Theory

Ghent University, Dep. Soil Management and Soil Care, International Centre for Eremology, Coupure links 653, B-9000 Gent, Belgium

^* Corresponding author (wim.cornelis{at}UGent.be).

A crucial parameter in predicting wind erosion is the deflation threshold shear velocity, which is highly dependent on near-surface soil water. The empirical and theoretical models to predict the deflation threshold as affected by near-surface water that have been reported in literature all suffer from a weak physical background and very large differences between the predicted results can be observed. The present study was conducted to develop a new conceptual model to predict the deflation threshold as affected by near-surface wetness and to contribute to a better understanding of the role of the latter on deflation of sediment. The model was developed by solving the moment balance equation for entrainment of soil particles by wind, including the moments associated with drag forces, lift forces, aerodynamic moment forces, gravitational forces, and interparticle forces due to dry and wet bonding. The wet bonding force, which represents the effect of near-surface soil water, is due to liquid bridge bonding or capillary forces, and adsorbed layer bonding or adhesive forces. It was related to the particle diameter squared, surface tension squared and the inverse of matric potential. The latter was then converted to water content by assuming a logarithmic relationship, which was shown to be valid between oven dryness and a matric potential of –1.5 MPa, a range that is of interest in the light of deflation of soil particles by wind. The conceptual model presented in this paper is relatively simple and predicts, for a given particle diameter and surface tension, the deflation threshold shear velocity as a function of the ratio between water content and the water content at a matric potential of –1.5 MPa.

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