Author
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Hagen, Lawrence |
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Submitted to: International Soil Conservation Organization (ISCO)
Publication Type: Proceedings Publication Acceptance Date: 5/24/1999 Publication Date: N/A Citation: In: D.E. Stott, R.H. Mohtar, and G.A. Steinhardt (eds.) Sustaining the Global Farm; 1999 May 24-29; Purdue University, West Layfayette, IN. Interpretive Summary: Wind tunnels are often used to assess the susceptibility of soils to wind erosion and determine the soil protection levels provided by various control measures such as soil clods, residues, and wind barriers. Many of the tunnel tests performed in the past required field-scale measurements of wind erosion to calibrate them for use in erosion prediction models. However, through recent research, most of the individual soil and control measure physical parameters that determine susceptibility to wind erosion have been identified. With careful attention to simulating the atmospheric boundary layer and other experimental details, these parameters now can be directly measured in a wind tunnel. Details of the methodology to measure these individual parameters in laboratory wind tunnels are described in this report. These measurements can then be used directly in field-scale erosion prediction models. Technical 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. Empirical wind erosion prediction models frequently use factors, called soil loss ratios to represent the ratio of soil loss from a proteced 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. Thes parameters include the erosion threshold friction velocity, the saltation/ creep aggregates transport capacity, the emission rate coefficient for loose soil, the abrasion rate coefficients for clods/crust, and the breakage rate coefficient of saltation/creep aggreagates to suspension size. These paramenters, 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. |
