The morphodynamics of three artificial pebble beaches at Marina di Pisa (Italy): coarse sediment transport and beach profile evolution

This three-year long research involved an insight investigation of the morphodynamics of three artificial coarse-grained beaches at Marina di Pisa, Italy, to best define the processes, such as sediment transport, beach profile evolution, and volume displacement, acting on an environment that is somewhat neglected in the literature. Marina di Pisa is a small, seaside village, located just west of the city of Pisa along the southernmost sector of the Ligurian Sea coast, whose shoreline experienced severe erosion processes during the last 150 years. The previously existing sandy beach was thoroughly wiped out, which prompted the local authorities to set up a long series of protection structures, and eventually gravel and pebble replenishments. The beaches where the fieldworks took place are just the sites of three huge beach fills carried out in 2006. The ensuing artificial coarse-grained beaches (named Cella 6, Cella 7, and Barbarossa) are composed of 30-to-90 mm marble pebbles, and are characterized by a similar project configuration. The twin beaches Cella 6 and Cella 7 differ from Barbarossa in length (240 m as opposed to 110 m) and in the presence of a submerged breakwater 50 m off the coastline, whereas Barbarossa is devoid of any offshore structure. The fieldworks involved primarily the investigation of transport tendencies and pathways of the coarse sediment along these beaches by means of a rapidly developing tracing technology, the Radio Frequency Identification. The RFID technique enables to detect pebbles previously coupled to small, passive transponders. The limit of the technology was constituted by the inefficacy of the underwater detection of the tracers, but this shortcoming has been here overcome by the employment of low frequency radio signals, which allow a fine transmission of the signal even underwater. Along with the sediment transport patterns, the evolution of the beach profile was assessed in a two-year long span of time. The subaerial topographic surveys were performed by means of an accurate RTK-GPS instrument, while the sea floor morphology was investigated by the employment of an echo-sounder Single Beam device. The data collected during these surveys were further processed to obtain reckoning of the sediment volumes that play a major role in the evolution of the beaches relative to the changing sea weather conditions. The results of the research might be spent to expand the comprehension of coarse-grained beaches to begin with. In addition, providing an in-depth definition of the morphodynamic processes governing this kind of beach, they might be useful to improve and optimize coarse replenishments, which are progressively more common as a form of protection from coastal erosion, and to back up studies on ancient gravelly shorelines.