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Title: AIRBORNE HORIZONTAL MASS FLUX CALCULATED WITH DIFFERENT EQUATIONS

Authors
 Buschiazzo, Daniel - INTA Zobeck, Teddy

 Submitted to: ASAE Annual International Meeting Publication Type: Proceedings Publication Acceptance Date: July 17, 2005 Publication Date: July 20, 2005 Citation: Buschiazzo, D., Zobeck, T.M. 2005. Airborne horizontal mass flux calculated with different equations[abstract]. ASAE Annual International Meeting. Paper No. 052049. Interpretive Summary: Accurate field measurements of wind erosion are needed to verify estimates made my computer models and to evaluate practices used to reduce erosion. Field measurements are usually made with dust samplers placed at various heights above the soil surface. The amount captured versus the height of the sampler is plotted on a graph and an equation is used to describe the relationship. The total amount of erosion is estimated by integrating the equation throughout the height of interest. In this study, we test two commonly used equations. We evaluated measurements when only three samplers and when nine samplers were used. The tests showed that the amount of erosion predicted by the equations was not the same. Equation 1 predicted from 40 to 55 percent less erosion than equation 1. The amount of erosion predicted with equation 1 was highly dependent on sampling height. The amount of erosion predicted with equation 2 produced similar results when three or nine samplers were used. Technical Abstract: The quantification of airborne material passing by a vertical plane as a function of height, the horizontal mass flux (HMF), is essential in measuring field wind erosion. Two commonly used equations to calculate HMF are : Q = a Z-b [1], where Q is the amount of dust collected, Z the height, and a and b are regression coefficients: and Q = fo(1 + (Z/ ') –ß [2] where fo = is the movement of the soil at the soil surface, ' and ß are regression coefficients. Different HMF estimates are expected when comparing equations, as the integration of the eroded material as a function of height can be performed from 0 (surface) with equation [2] but not with equation [1]. Calculations were made for 28 storms using dust samplers placed at heights of a) 13.5, 50 and 150 cm (Q3) and b) 0.15, 0.7, 1.5, 7, 12, 22.5, 13.5, 50 and 150 cm (Q9). HMF calculated with equations [1] and [2] correlated well but HMF of equation [1] were 40 to 55% lower than those of equation [2]. The averaged fitting of the amount of transported material with height was lower and more variable when using equation [1] than when using equation [2]. These results showed that HFM obtained with equation [1] are highly dependent on sampling height, and need to be corrected on the basis of data obtained closer to the surface before they can be used to test wind erosion prediction models, unlike HMF obtained using equation [2].