Modelling the vertical grain size sorting process in aeolian sediment transport using the discrete element method

We present a model study of the aeolian saltation process where sediment samples are studied for the size selective transport processes. The discrete element method is used to simulate the sediment particles of different sizes, coupled with a fluid boundary layer model to capture the driving wind forces. Sediment samples with identical median grain size, but with systematically varying size distributions were simulated to investigate under various wind shear rates which sediment fractions are transported. The presented model results show - well in line with other research - that the median grain size is an appropriate sediment sample parameter to quantify the total rate of sediment transport. However, our results show that this does not determine what fractions of sediment are in transport. The larger the standard deviation in the sediment size distribution the smaller the median grain size becomes of the sediment that is in transport compared to the median grain size present at the bed.