Sand flux and wind profiles in the saltation layer above a rounded dune top

ZHANG ChunLai, ZHOU Na & ZHANG JiaQiong

State Key Laboratory of Earth Surface Processes and Resource Ecology, MOE Engineering Research Centre of Desertification and Blown-sand Control, Beijing Normal University, Beijing 100875, China.

Abstract: The near-bed airflow and the movement of sand dune sediments by wind are fundamental dune geomorphological processes. This research measured the wind profiles and sand mass flux on the rounded top of a transverse dune at the southern edge of the Tengger Desert to examine how to best predict the vertical profile of sand flux. This work also tested the accuracy of previously developed models in predicting the apparent roughness length during saltation. Results show that mass flux vertical distribution over the dune top is underestimated by an exponential function, overestimated by a power function, but closely matches the predictions made using the LgstcDoseRsp function. Given suitable values of α, β and γ according to the grain size composition, Sørensen equation with the peaked shape of the mass transport curve will well predict the dimensionless mass flux qg/ρu_* ³ against dimensionless shear velocity u_*/u_*t. The modified Charnock model works best of the previously published models tested, with an R² of 0.783 in predicting the enhanced roughness over the moving sand surface, as opposed to an R² of 0.758 for the Owen model and an R² of 0.547 for the Raupach model. For the rounded dune top in this study, C_m=0.446±0.016.

Keywords: sand mass flux; roughness length; shear velocity; modified Charnock constant.