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Texas Tech University (2013)

A wind tunnel investigation to examine the role of air humidity in controlling the threshold shear velocity of a surface and in controlling the mass flux of material from a surface

Massey, Joe

Titre : A wind tunnel investigation to examine the role of air humidity in controlling the threshold shear velocity of a surface and in controlling the mass flux of material from a surface

Auteur : Massey, Joe

Université de soutenance : Texas Tech University

Grade : Master of Science 2013

Résumé partiel
Aeolian erosion, the wind-forced movement of soil particles, is a dominant process in arid regions. The impacts of wind-driven dust emissions are numerous and can have both localized effects and far reaching impacts. The susceptibility of a soil surface to wind erosion is gauged using the threshold friction velocity (u*t), which is related to the wind speed needed for the erosion of surface material to commence. This threshold varies for every surface and depends on numerous variables, including surface soil moisture. In arid regions, which contain air-dry soils, soil moisture is the driving factor controlling changes in the threshold shear velocity of a surface at short, diurnal timescales (Ravi and D’Odorico, 2005). Therefore, an understanding of these varying moisture conditions, and the associated changes in soil erodibility, is vital in understanding and modeling aeolian soil erosion (Ravi et al., 2006). In such regions, where rainless periods are common and there is a lack of moisture provided by precipitation or capillary rise, the humidity of the overlying air is particularly influential in controlling soil moisture content at the surface (Ravi and D’Odorico, 2005). Through wind tunnel tests, this study analysed the control relative humidity had on the threshold shear velocity for three soils : a loamy fine sand, a clay loam and a sandy muck. The loamy fine sand and the clay loam material were previously studied and the results found here agreed with those from other studies (e.g., Ravi et al., 2006). The relationship found is made up of a high and low section of humidity, where the threshold shear velocity increases with humidity, and a mid-range section of humidity, where the threshold shear velocity decreases with increased humidity. The previously unstudied sandy muck also showed this relationship. The results were explained using the theory of equilibrium between the surface soil moisture and the humidity of the overlying atmosphere. In such studies, an accurate measurement of the threshold shear velocity is vital and this study compared the sensitivity of two particles sensors (Wenglor YH03PCT8 and Sensit model H10) in determining the threshold shear velocity of a soil surface. It was found that the newer Wenglor sensor recorded the threshold at considerably lower wind speeds throughout the test and for each soil. This, however, did not significantly change the relationship seen between the threshold shear velocity and relative humidity.

Mots clés : Threshold shear velocity ; humidity ; mass flux ; wind erosion ; soil moisture.

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Page publiée le 18 juin 2013, mise à jour le 9 novembre 2018