Short Term Pebble Displacement On A Mixed Sand And Gravel Beach On The Adriatic Sea (Portonovo, Italy)

The transport of marked pebbles on a mixed sand and gravel beach has been addressed by means of tracers using radio frequency identification tracing technique, which proved to be efficient in terms of recovery rate also in the underwater environment. The aim of the research was to evaluate the displacement rates of marked pebbles at short time spans and under low energy wave conditions. The experiment was carried out at Portonovo beach, central Adriatic Sea (Italy), on 29-30 March 2012. Two recovery campaigns were carried out respectively 6 and 24 hours after the injection.. During the time frame of the experiment wave motion was minimum (wave height never exceeded 0.2 m). The results showed that pebbles of about 30 to 90 mm diameter did move significantly (more than 0.5 m) already 6 hours after the injection (17%). After 24 hours pebble significant displacements reached 39% and pebble loss increased to 7%. The large majority of tracers moved seaward, pointing out that coarse sediments move under low-energy conditions mainly because the beachface slope controls swash processes on coarse-clastic beaches. Backswash action contributes to generate not negligible rate of offshore pebble displacement also under low-energy conditions. In conclusion, the results of this research confirm that coarse sediment transport during short, fair-weather spans of time, is considerable and it is mostly directed downslope