Field observations of the vertical distribution of sand transport characteristics over fine, medium and coarse sand surfaces

Abstract

AbstractThe vertical distribution of sand transport characteristics is an important issue in aeolian research. Surface characteristics affect sand transport processes, but their effects are not yet fully understood. To provide more data on this subject, we observed sand transport in 16 field experiments above surfaces covered by fine, medium and coarse sand. The sand transport rate over relatively coarser‐grained medium and coarse surfaces could be expressed as a Gaussian peak function: qz = a + b exp (−0.5[(|z – Ch|)/d]e), where qz is the measured sediment transport at height z above the bed and a, b, Ch, d, and e are regression coefficients. The measured sand transport flux peak values (Hh) were linearly related to Ch, and both values were significantly related to the mean surface grain size. However, for the relatively finer‐grained medium and fine sand surfaces, the sediment transport could be expressed as an exponential function. The cumulative sand transport below 0.1 m was directly related to the mean surface grain size, and the relationship could be expressed as the following exponential function: Cz = f + g exp –Mz/i, where Cz is the cumulative sand transport at height z above the bed, Mz is the mean grain size and f, g, and i are regression coefficients. Above 0.1 m, there were no significant relationships between the cumulative sand transport and the mean surface grain size. The mean grain size decreased with increasing height below the peak height and then increased with increasing height. The surface grain size distribution and proportions of the particles in different grain size categories controlled the mean grain size as a function of height. The observed changes in the sand transport rate and grain size with height will provide support for sand disaster mitigation, numerical modelling and studies of dune formation. Copyright © 2016 John Wiley & Sons, Ltd.