Spatial and temporal variations of sediment size on a mixed sand and gravel beach

Mixed sand and gravel beaches have been the subject of comparatively few studies in the UK. This paper describes the sediment distribution before, during and after a programme of beach nourishment along a section of mixed sand and gravel beach forming part of the Pevensey Bay Coastal Defences, in East Sussex, UK. The beach was recharged in September 2002, and beach profiles were measured along three cross-shore transects from August 2002 to February 2003. Sediment samples were taken along the transects between August and November 2002, and a total of 147 sediment samples were analysed, 40 before nourishment and 107 after nourishment. The majority of the sediment samples were strongly bimodal, with mean sizes varying between a minimum of 0.18 mm (2.48 ϕ) for the sand fraction and a maximum of 27 mm (− 4.74 ϕ) for the gravel. The recharge material was also bimodal but contained more fine sediment than the natural beach material, particularly on the upper beach. The recharge sediment had grain sizes and sorting similar to some of the natural material but lower bimodality parameters than any of the natural sediment. The sediment distributions after recharge contained significantly more fine sediment, particularly on the upper beach. Over time, the beach profile lowered and fine sediment appeared to be selectively transported seawards from the beachface.