Coastal erosion assessment: experimental analysis of pebbles abrasion to evaluate beach nourishment efficiency in Marina di Pisa (Italy)

In the last decade, coastal erosion has been a phenomenon that particularly affected the Mediterranean shores, generating great interest, especially in scientific studies of the phenomenon. The coastal system is a dynamic environment characterized by continuous evolution due to natural and anthropogenic factors. Among the main precursors of this phenomenon are the reduction of sediment supply from river sources, the increase in subsidence rate, and the sediment transport gradients along the coast due to the presence of coastal structures. To address this issue, various techniques are used, divided into "hard measures" and "soft measures." "Hard measures" include all rigid structures that limit or completely block solid transport and decrease the wave energy acting on the beach. "Soft measures" represent all natural solutions to erosion problems; the fundamental concept involves restoring eroded sediments by introducing new sediments. This technique, known as beach nourishment, allows the natural erosion process to continue, mitigating its impact through the addition of sediments from external sources. The grain size naturally present on a given beach is correlated with the wave energy acting on the coast, but on energetic beaches, to increase the intervention's lifespan, the sediments used for nourishment can be chosen to be larger in size. However, this choice can be subject to other problems related to the abrasion suffered by coarser sediments, making them more unstable and potentially causing a more significant loss of sediment volumes. To evaluate the efficiency of nourishment with coarser material and the consequent reduction of the erosion phenomenon, it is advantageous to study the relationship between wave action and the abrasion suffered by pebbles. In this thesis, the study of some pebbles of different shapes will be addressed through laboratory and in-situ tests. The pebbles of interest were recovered from the nourishment carried out at Marina di Pisa. They were initially marked with an RFID tag inserted into them using a small corer and were subsequently released on the shore of Marina di Pisa at various points on the beach. Once collected, they were carefully weighed and scanned with a 3D device. Other pebbles, also collected from the same beach and uniquely marked with the RFID tag, were subjected to the Los Angeles abrasion test in the laboratory, evaluating their abrasion under different powers. The results obtained in the two campaigns, both in the laboratory and in-situ, were compared to derive a correlation that estimated the extent of coastal erosion considering the abrasion suffered by the pebbles over time.