Grain size affects the rates of aeolian sediment transport on beaches.
Sediment in coastal environments typically consists of multiple grain
size fractions and exhibits spatiotemporal variations. Still, conceptual
and numerical aeolian transport models are simplified and often only
include a single fraction that is constant over the model domain. It is
unclear to what extent this simplification is valid and if the inclusion
of multi-fraction transport and spatial grain size variations affects
aeolian sediment transport simulations and predictions of coastal dune
development. This study applies the numerical aeolian sediment transport
model AeoLiS to compare single-fraction to multi-fraction approaches for
a range of grain size distributions and spatial grain size scenarios.
The results show that on timescales of days to years, single-fraction
simulations with the median grain size, D50, often give similar results
to multi-fraction simulations provided the wind is able to mobilize all
fractions within that time frame. On these timescales, vertical
variability in grain size has a limited effect on total transport rates,
but it does influence the simulation results on minute timescales.
Horizontal grain size variability influences both the total transport
rates and the downwind bed grain size composition. The results provide
new insights into the influence of beach sediment composition and
spatial variability on total transport rates towards the dunes. The
findings of this study can guide the implementation of grain size
variability in numerical aeolian sediment transport models.