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United States Department of Agriculture

Agricultural Research Service

Title: On the Effect of Moisture Bonding Forces in Air-Dry Soils on Threshold Friction Velocity of Wind Erosion

Authors
item Ravi, Sujith - UNIVERSITY OF VIRGINIA
item Zobeck, Teddy
item Over, Thomas - EASTERN ILLINOIS UNIVERSI
item Okin, Greg - UNIVERSITY OF VIRGINIA
item D'Ordorico, Paolo - UNIVERSITY OF VIRGINIA

Submitted to: Sedimentology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 5, 2005
Publication Date: March 20, 2006
Citation: Ravi, S., Zobeck, T.M., Over, T.M., Okin, G.S., D'Ordorico, P. 2006. On the effect of moisture bonding forces in air-dry soils on threshold friction velocity of wind erosion. Sedimentology. 53:597-609.

Interpretive Summary: Wind erosion is a dominant geologic process that shapes the landscape in hot dry areas of the world. Wind erosion occurs when the wind speed exceeds a certain level, which depends on a number of factors. Soil moisture is an important factor the affects wind erosion of soils. A better understanding of the effects of soil moisture and relative humidity are needed to improve our understanding of how wind speed affected erosion. In arid regions during the dry season, the atmospheric humidity plays an important role in determining the surface moisture content and the velocity at which soils are moved by the wind, called the threshold wind velocity. In this manuscript, we use a series of wind tunnel studies and develop a theoretical argument to explain how the near surface relative humidity affects the threshold wind velocity. The results show that the threshold shear velocity decreases with increasing values of relative humidity for values of relative humidity between about 40% and 65%, while above and below this range the threshold shear velocity increases with air humidity.

Technical Abstract: Wind erosion is a dominant geomorphological process in arid and semi-arid regions with major impacts on regional climate and desertification. The erosion process occurs when the wind speed exceeds a certain threshold value, which depends on a number of factors including surface soil moisture. The understanding and modeling of aeolian erosion requires a better understanding of the soil erodibility associated with different moisture conditions. In arid regions during the dry season, the atmospheric humidity plays an important role in determining the surface moisture content and the threshold shear velocity. By a series of wind tunnel tests and theoretical analysis, we show this dependence of threshold velocity on near surface air humidity for three soils of different textures: sand, sandy loam, and clay loam. The results show that the threshold shear velocity decreases with increasing values of relative humidity for values of relative humidity between about 40% and 65%, while above and below this range the threshold shear velocity increases with air humidity. A theoretical framework is developed to explain these dependencies assuming an equilibrium between the surface soil moisture and the overlying atmosphere. The conditions under which soil-atmosphere equilibrium occurs were tested experimentally in the laboratory for different soils in order to determine the effect of grain surface area and texture on the time required to reach equilibrium starting from different initial conditions.

Last Modified: 4/20/2014
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