GRAIN-SIZE ANALYSIS OF SURFACE MATERIAL UNDER WIND EROSION USING THE EFFECTIVE SURFACE CONCEPT

The grain mobility and roughness of a surface exposed to wind are depe ndent on the grain size of the surface particles. This paper deals wit h the temporal variation in the grain size of surface material using a n analytical method based on the effective surface concept. The analys is of grain size data obtained from a wind tunnel experiment indicated that, above the threshold wind friction velocity for all surface part icles, the grain-size distribution of surface particles was very simil ar to that of the parent material over a time period of 10 to 15 minut es. However, the mean grain size of surface particles apparently decre ased over the initial time period of 2 to 3 minutes. We therefore conf irm earlier studies that on a nonuniform grain bed a larger particle c ould be more mobile than a smaller particle if the wind friction veloc ity was higher than the threshold for the larger particle. However, th is does not imply that the largest particle is most mobile due to the nonlinear dynamics of aeolian sediment transport processes. (C) 1997 b y John Wiley & Sons, Ltd.