Exploring nearshore bed dynamics of a mixed beach using the depth of closure conceptual model.

Mixed sediment beaches are globally commonplace, yet little is understood of the extent and behaviour of their nearshore zones, potentially underestimating total cross-shore change. This paper is the first study to investigate the lateral and vertical extent of the active zone of the gravel-rich mixed beach in Pevensey Bay, a study site on the South East UK coastline. Morphodynamic change in the nearshore zone was studied at a range of timescales (days, months, years) suggesting that the width of the active nearshore zone correlated with the magnitude of the peak morphological change, whilst the depth of closure was influenced by bed slope, grain size and local variation in wave conditions. A conceptual model detailing the physical parameters responsible for local variations in the depth of closure was used to help understand differences between the observed and predicted depths of closure. Finally, ongoing chronic loss of sediment from below Mean Sea Level (MSL) was examined, which was shown to be independent of the depth of closure, but closely linked to the wider geomorphic setting of the bay. • Comparison of observational and predicted depth of closure for a mixed sediment beach • Local variations in the observed depth of closure examined using a conceptual model • Magnitude of subtidal bed elevation change may be controlled by sediment availability. • Loss of nearshore sediments over time reflects the trend in upper beach steepening. [ABSTRACT FROM AUTHOR]