Aeolian Creep Transport: Theory and Experiment

Aeolian sand transport drives geophysical phenomena, such as bedform evolution and desertification. Creep plays a crucial, yet poorly understood, role in this process. We present a model for aeolian creep, making quantitative predictions for creep fluxes, which we verify experimentally. We discover that the creep transport rate scales like the Shields number to the power 5/2, clearly different from the laws known for saltation. We derive this 5/2 power scaling law from our theory and confirm it with meticulous wind tunnel experiments. We calculate the creep flux and layer thickness in steady state exactly and for the first time study the relaxation of the flux toward saturation, obtaining an analytic expression for the relaxation time. Plain Language Summary The sand transport of granular beds under the action of turbulent wind-sheared flows is of major importance for the bedforms evolution and desertification processes. Up to now, the saltation transport is well understood and predictable but not the creep transport and relevant scaling laws. In this study, a theory for the aeolian creep transport is developed and verified through wind tunnel experiments. We propose for the first time a scaling law with the Shields number for the creep transport rate. Our novel model allows predictions of the aeolian creep transport rate and shows that it captures the relaxation process in actual creep transport. Such theoretical model provides key tools for the study of aeolian creep but could not previously be studied in such detail. Our study provides a better understanding for the phenomenon that the bed surface itself appeared to be "fluidized" in aeolian sand transport.