Aeolian structure formation in a laboratory wind tunnel

Sand dunes and ripples result from the interaction between topography, hydrodynamics and sediment transport and exhibit self-organization on multiple scales. In this thesis, we show the formation of aeolian viscous bedload barchan-ripples in a laboratory wind tunnel. These bedforms are subject to the same longitudinal instability and transverse instability as subaqueous ripples and aeolian dunes and share the same transport mechanism as subaqueous ripples, thus making our bedforms the aeolian counterpart of subaqueous ripples. To realize such an experiment, we carefully select a particle system with small particle diameters at low densities. We follow the evolution of barchan-ripples from onset to their steady state form and show that they arise from both a flat particle bed and a particle heap. We study the transport mechanism at the particle level and demonstrate that the aeolian viscous bedload transport regime is responsible for the formation of the barchan-ripples. We measure and derive the saturation length from equations given by calibrated numerical and theoretical models and show that the order of magnitude is in the millimeter range. Access to this previously unexplored area in parameter space gives us a deeper understanding of the mechanisms that govern sedimentary bedform formation on controllable time and length scales