Transport mass of creeping sand grains and their movement velocities

Aeolian sand transport is an important component of material circulation above terrestrial surfaces and can include processes of creep, saltation, and suspension. The complex movement of material and energy during aeolian transport has meant that these processes have previously been examined in isolation. Although a significant amount of research has been conducted on aeolian sand transport, this focused primarily on saltation. As a result, there are few data available on sand grain creep, primarily due to a lack of theoretical models and the difficulty of direct measurements. In this study, we present novel methods and instrumentations to accurately measure the transport mass and the velocity of creeping sand grains. Using data collected with above instrumentations and a ladder sampler at four friction velocities (u* = 0.26, 0.35, 0.47, and 0.56 m s−1) in a wind tunnel, we studied the transport mass of creeping sand grains and their movement velocities, as well as other key parameters of aeolian sand transport. Four major conclusions can be drawn from this study: (1) The transport mass (q0) of creeping sand grains increases with increasing frictional wind velocity (u*). The relationship between these variables is represented by the power function q0 = −0.053 + 9.195u*2.800. (2) The contribution of creep to total aeolian sand transport decreases with increasing frictional wind velocity. Creep contributed 57% of total aeolian transport at the lowest frictional wind velocity but only 19% at the highest velocity. (3) The threshold frictional wind velocity for entrainment was 0.158 m s−1. (4) The movement velocity of creeping sand grains ranged from 0 to 0.14 m s−1, but more than 70% of recorded velocities were less than 0.02 m s−1. Although the results of this study require further validation, they provide a strong basis for future research and help deepen our understanding of aeolian sand transport.