Slope effect on saltation over a climbing sand dune

Results from a three-year study are presented that integrate field work (in Israel), physical modeling (wind-tunnel testing at UC Davis), and numerical solutions of grain trajectories to model and explain sand transport over a climbing dune. Field grain-size analyses of surface- and saltation-trap materials taken along various positions of the slope suggest that only smaller particles (< 230 μm in diameter for a friction speed, u ∗ , equal 30 cm/s) were able to climb a 20 degree slope in an escarpment normal to the prevailing strong wind direction. Numerical solutions of the particle trajectories are in good agreement with field measurements and confirm that particle motion is diminished at the base area of the slope and that the motion of larger-sized particles is completely terminated which causes an accumulation of these particles. The results suggest that the transport of the majority of the larger particles (> 230 μm) is by saltation. The model is numerically extended to a general series of slopes, particle sizes, and friction speeds with similar tends exhibited.