CHARACTERIZING THE HEIGHT PROFILE OF THE FLUX OF WIND-ERODED SEDIMENT

Abstract

Wind erosion causes severe environmental problems, such as aeolian desertification and dust storms, in arid and semiarid regions. Reliable prediction of the height profile of the wind-eroded sediment flux is crucial for estimation of transport rates, verification of computer models, understanding of particle-modified wind flows, and control of drifting sand. This study defined the basic height profile for the flux of wind-eroded sediment and the coefficients that characterize its equation. Nine grain-size populations of natural sand at different wind velocities were tested in a wind tunnel to measure the flux of sediment at different heights. The resulting flux profiles resemble a golf club with a small back-turn where the flux increases with increasing height within 20 mm above the surface. If the small back-turns are neglected, the flux profiles can be expressed by an exponential-decay function $ q_{{\text{r}}} (z) = a{\text{e}}^{{ - bz_{r} }} , $ where q r(z) is the dimensionless relative flux of sediment at height z, which follows the exponential-decay law proposed by previous researchers for aeolian saltation. Three coefficients (a creep proportion, a relative decay rate, and an average saltation height) are proposed to characterize the height profile. Coefficients a and b in the above equation represent the creep proportion and relative decay rate as a function of height, respectively. Coefficient a varies widely, depending on grain size and wind velocity, but averages 0.09. It is suggested that the grain size and wind velocity must be specified when discussing creep proportion. Coefficients a and b are nearly linearly correlated and decrease as grain size and wind velocity increase. The average saltation height (the average height sediment particles can reach) was a function of grain size and wind velocity, and was well correlated with coefficients a and b.