Aeolian Creep Transport: Theory and Experiment
GEOPHYSICAL RESEARCH LETTERS, (2020)DOI: 10.1029/2020GL088644
Abstract
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.