Wind tunnel experiments on dune sands

Abstract

AbstractThe effect of the dry bulk density, time and the presence of roughness elements at the surface on the wind erodibility of a dry dune sand (D50 = 230–250 μm) were evaluated in a laboratory study.There is no significant correlation between the dry bulk density of the dune sand and the corresponding deflation threshold. During the experiments, a variation of the fluid threshold in time was noticed. It increased to a value 11 per cent higher than the lowest threshold velocity. Selective eroding of the wind cannot be responsible for this time‐effect, for threshold velocities do not work selectively on non‐uniform sands. It can be explained by thinking of a dynamic surface which evolves towards a configuration of lower surface roughness.The size of roughness factors e.g. gravel, marbles, placed on a sand surface, and the density of the cover seem to be important factors influencing the erodibility of the underlying sand surface. Small cover densities are related to values of the deflation threshold, which are below the fluid threshold of the sand surface. Furthermore, dense covers protect the ground against wind erosion by increasing the threshold. The size of the roughness factors determines the inversion point at which a cover becomes protective.