Sediment variability in a 1-year time span on a mixed beach (Portonovo, Italy)

While sandy beaches tend to have quite constant average grain sizes over time, little is known regarding coarser beaches, especially where mixtures between sand and gravel occur. The study area is located south of the city of Ancona, on the northern edge of the Conero Headland (Adriatic Sea). Portonovo beach is about 500 m long and 15-to-35 m wide; it is bounded by two promontories and characterized by medium-to-coarse sands and by a coarse fraction mainly constituted by gravel and pebbles. Sediment input is limited, mainly by erosion of cliffs constituted by marls and limestones. The aim of this research was to monitor sediment variations throughout 1-year of repeated surface samplings, to define the sedimentological evolution, since it is not clear the direction of the dominant longshore drift and sediment exchange between the submerged and emerged beach both during storm and fair-weather conditions. Six samplings were carried out on the same grid points along 14 even spaced cross-shore transects. Grain-size analyses were performed by dry sieving the samples with 11 sieves of 1 phi mesh interval. The results showed a high variability in grain-size, which is more evident cross-shore rather than along-shore. According to the sand-gravel ratio, this value is higher in winter samplings, implying that the beach is sandier during storms. The study could be useful to sediments management and nourishment activities that are performed by coastal managers using fill from quarries, in order to optimize the best grain size for beach recharge.