Vertical distribution of aeolian sand transport on beaches

Sand transport studies indicate that, among the three processes of wind-blown sand drift, saltation is the principal mode of movement, representing three quarters of the transport. The total distribution of transport rates is a function of height. Our understanding of vertical flux profiles thanks to wind tunnel studies is improving, and we know that the sand flux over a sandy surface increases with height in the very near surface layer, but then decays exponentially. Several theoretical models of saltation have been published, in particular on the higher portion of the sand trajectory, but none of them have proven to be applicable at a wide range of sites. We do not have much data on field measurements of the distribution of transport with height above the bed. More experimental work is needed if we are to refine our predictions of total sediment transport rates. This study reports on the results of the measurement of vertical aeolian transport in the field. We analyze the temporal and spatial variability of the saltating cloud over several wind events, along the line of the main wind direction. A tower of Safires, properly calibrated and distributed at specific heighs, is located at different points on the beach. The data is combined with the measurements of total sand transport and wind characteristics. Results allow us to critically assess the measurements of saltating grains taken with Safires, and the convenience of locating them at certain heights in order to obtain a better representation of the saltating cloud.