M. Teixeira,1*, E.M. Horstman1, K.M. Wijnberg1
1 University of Twente
Aeolian sediment transport plays a crucial role in the growth of foredunes. The cellular automata model DuBeVeg (Keijsers et al., 2016) provides a powerful tool for simulating bio-geomorphological evolution of sandy beach-dune systems, as it captures the key elements and interactions of aeolian, hydrodynamic and vegetation dynamics in a simple and efficient manner. The model has successfully been applied to beach-dune systems along the Dutch coast, providing useful predictions of beach-dune evolution over decadal time scales, generally focussing on final states rather than the transient path towards that state. Currently, sand transport in DuBeVeg is predominantly represented as bedload transport, or ripple migration. When we consider shorter time spans and very wide beaches, this representation seems to misrepresent the timing of embryo-dune and foredune development as well as the rate at which sand is transported over longer distances. This study explores a different representation of the aeolian transport in DuBeVeg to reflect transport by saltation rather than ripple migration.
DuBeVeg simulates sediment transport through the stochastic movement of slabs of sand, which are picked up by the wind and moved across the domain in the downwind direction over a fixed distance, the jumping length L. This allows for the self-organization of the slabs resulting in the emergence of new dunes. At the same time the movement of slabs represents, in an aggregated manner, the transport of grains of sand. Consequently, the slab size and the jumping length must agree with the actual volume and mode of the sand transport. Previous modelling studies applied a unit jumping length of L = 1 m which can be interpreted as the migration of bed ripples. An increased jumping length of L = 5 m is more representative of saltation transport (Werner, 1995). In this study, we implement different jumping lengths in DuBeVeg and compare the resulting dune development predicted for two idealized beach profiles (narrow and wide) and for a real-case scenario (the southern part of the Sand Motor).
An increase in the jumping length results in striking differences in the predicted 50-year morphological development of a beach-dune system as well as its intermediate states (e.g. at 10 years), producing fewer but taller dune ridges, especially for wide beaches (Figure 1) similar to the central part of the Sand Motor.
Figure 1: Comparison of the cross-shore profile development obtained when running DuBeVeg with different jumping lengths (L) for an idealized wide beach after (a) 10 years and (b) 50 years.
Keijsers, J.G.S., Groot, A.V. De, Riksen, M.J.P.M. (2016). Modeling the biogeomorphic evolution of coastal dunes in response to climate change. Journal of Geophysical Research: Earth Surface, 121, 1161–1181. https://doi.org/10.1002/2015JF003815.
Werner, B.T. (1995). Eolian dunes: computer simulations and attractor interpretation, Geology, 23, 1107–1110. https://doi.org/10.1130/0091-7613(1995)023<1107:EDCSAA>2.3.CO;2