Assessment of Wind Erosion Parameters Using Wind Tunnels

*Lawrence J. Hagen, USDA-ARS, Wind Erosion Research Unit, Throckmorton Hall 2004, Kansas State University, Manhattan, KS 66506. *Corresponding author: [email protected]. Contribution from USDA-ARS in cooperation with Kansas Agric. Exp. Sta., Contribution No. 99-389-A. ABSTRACT Assessment of wind erosion parameters applicable to the field scale using wind tunnels requires attention to both scaling laws and matching of nondimensional parameters. Proper upwind development of the boundary layer flow and meeting the Froude number criterion are especially important in studies involving saltation of aggregates in the wind stream. Empirical wind erosion prediction models frequently use factors, called soil loss ratios, to represent the ratio of soil loss from a protected surface and a defined reference (usually highly erodible) surface. These ratios often are determined in wind tunnel tests but must be correlated to field wind erosion measurements before application. In addition, the ratios also are highly dependent on the tunnel wind speed used in the tests. Recent research has identified most of the critical physical parameters that control field-scale wind erosion. An alternative to measurement of soil loss ratios is to use wind tunnels to directly measure these physical parameters and apply them in physically based models. These parameters include the erosion threshold friction velocity, the saltation/creep transport capacity, the emission rate coefficient for loose soil, the abrasion rate coefficients for clods/crust, and the breakage rate coefficient of saltation/creep aggregates to suspension size. These parameters, along with the aggregates size distribution created by various processes, determine the downwind soil discharge in the saltation/creep and suspension transport modes. In general, one needs a relatively long wind tunnel, an upwind abrader feeder, wind speed measuring transducers, various surface materials, and specialized soil catchers to obtain downwind mass and size distribution of the soil discharge.