Scaling laws in aeolian sand transport: Erodible versus non-erodible bed

Abstract

We investigated via wind-tunnel experiments the role of the boundary conditions at the bed in the aeolian sand transport. We analyzed two different bed configurations: one with a sandy erodible bed and the other with a non-erodible bed. By using Particle Tracking Velocimetry technique (PTV), we characterized the saltation layer in both configurations and evidenced contrasting features. We show in particular that over an erodible bed the particle velocity in the saltation layer and the saltation length are almost invariant with the wind strength, whereas over a non-erodible bed these quantities vary significantly with the air friction speed. It results that the particle transport rate over an erodible bed does not exhibit a cubic dependence with the air friction speed, as predicted by Bagnold, but a quadratic one. This contrasts with saltation over nonerodible bed where the cubic Bagnold scaling holds. Our findings emphasize the crucial role of the boundary conditions at the bed and may have important practical consequences for aeolian sand transport in natural environment. © 2013 AIP Publishing LLC.