The effects of beach width variability on coastal dune development at decadal scales

A cellular automata model is used to evaluate, over decadal time spans, the effect of beach width changes on the development of coastal dune systems. The model includes the effects of aeolian transport, hydrodynamic erosion and accretion, groundwater and vegetation growth. Simulations using fixed and mobile beach widths scenarios were carried out for a 90-year period. Unlimited and limited sediment supply conditions were regulated by groundwater depth. The final topographies were compared based on morphological characteristics such as dunefoot position and volume increase. Results show that there is a preferential cross-shore position where the foredune tends to be built which is a function of beach width and sediment supply. For narrow beaches, foredunes tend to develop at higher elevations than for wide beaches due to differences in wave dissipation, whereas dune volume is controlled by hydrodynamic erosion and dune recovery potential by sediment supply. Furthermore, if sediment supply is limited, the effect of beach width on dune volume only appears for beach widths greater than 300 m, suggesting that limitation in supply can dominate dune growth on regular beaches whereas on wide systems, such as sand flats and spits, beach width size dominates. These results suggest that for a decadal scale, beach width controls the space available for dune formation, thus the position of the most seaward dune, but the effect of beach width on dune volume can be overruled by other supply limiting conditions such as groundwater depth.