CHANGE IN THE AERODYNAMIC ROUGHNESS HEIGHT BY SALTATING GRAINS - EXPERIMENTAL ASSESSMENT, TEST OF THEORY, AND OPERATIONAL PARAMETERIZATION

Data from an experiment at Owens Lake provided an opportunity to verif y the validity of Raupach's formula that predicts the apparent roughne ss height at equilibrium with saltation during wind erosion episodes. In addition to that verification, a simplification of Raupach's formul a is presented which allows the computation of the wind friction veloc ity affected by saltating sand grains without the need to measure the threshold wind friction velocity and to do iterative calculations. Thi s method estimates the increase of the wind friction velocity Delta u , above the nonsaltating wind friction velocity caused by the saltatin g grains: Delta u = 0.3 [U -U-t](2) where U and U-t are the wind spee d and the threshold wind speed, respectively, at 10 m.