Characteristics of Sand Transport on the Surface of Transverse Ridge Microtopography

Through wind tunnel experiments, we measured the surface drifting sand flux structure and sand transport rate at height of 0~70 cm on a bed surface under conditions of ridge microtopography with different height and different spacing. The results show that the percentage of sand transport in 0~10 cm layer above the bed surface is significantly reduced under ridge microtopography condition compared with no ridges condition. Under ridge microtopography condition, the percentage of sand transport in 0~10 cm layer decreases with the increase of ridge height, while it generally increases with the increase of ridge spacing and wind velocity. Under no ridges condition, the sand transport rate decreases in a power function law with the increase of height. The variation of sand transport rate with height under ridge microtopography condition could be divided into two cases: one shows that sand transport rate decreases exponentially with the increase of height, while the other shows that sand transport rate increases with the increase of height under a certain height, and above the certain height it decreases exponentially with the increase of height, known as “elephant nose” effect which seems similar to the structure of drifting sand flux in Gobi desert. For all the ridge heights and spacings, the total sand transport rate at height of 0~70 cm increases with the increase of friction velocity in a power function law, and it increases with the increase of ridge spacing. The simulation of the drifting sand flux structure and the relationship between sand transport rate and height shows that the ridge microtopography reduces the sand transport ratio of near surface air flow compared with no ridges condition. The results will contribute to studies on recognizing the process and mechanism of soil wind erosion in ridge farmland.