Effect of transverse ridge microtopography on the surface shear stress distribution and soil wind erosion

Abstract

Through wind tunnel experiments, we measured the surface shear stress (τs) on a bed surface that contained widely but uniformly spaced non-erodible ridges. We found that when the ridge spacing is larger than 10 times the height (H), the τs between two adjacent ridges could be divided into two sections. In each section, shear stress gradually increases and then decreases. The first section appears to be produced by the reverse-flow vortex that develops close behind upwind ridges and the second appears to result from airflow recovery followed by blockage by the downwind ridge. The mean surface shear stress (τs¯) of the total bed increases with increasing ridge spacing and friction velocity, and decreases with increasing ridge density. The spatial differences in τs lead to a non-uniform distribution of wind erosion between the ridges. Based on the threshold shear stress (τt) of the tested soil, we revealed a regular distribution of effective shear stress (τeff) on the sand bed, and established quantitative relationships among mean effective shear stress (τeff¯), H, ridge spacing (L), friction velocity (u*), and the threshold friction velocity (u*t) for sand entrainment: τeff¯=aLHu*-u*t2.