Adaptation of the coastal protection system at Marina di Pisa, to extreme sea conditions: experimental analysis of the submerged breakwater and gravel beach

The coast of Marina di Pisa has been subjected to strong erosion for decades. The current protective system comprises a large rubble-mound seawall, 6 emerged rubble-mound breakwaters, and 4 cells made up of a submerged breakwater and an artificial gravel beach framed by two groynes at the extremities. One of these cells experiences large amounts of water and gravel overtop onto the promenade and its two main components are studied through three design parameters: gravel nourishment width, gravel nourishment height, and width of the submerged breakwater crest. Fifteen configurations based on the design parameters were experimentally tested under the same wave motion and sea level. Three main outputs were analyzed: gravel overtopping, water overtopping, and final equilibrium profile which included the height and distance from the promenade of the crest formed due to wave action. The results also showed that an optimization between the increase in gravel nourishment width and breakwater width must be found as a large increase in one minimizes the effectiveness of the other. Additional observations on the amount of gravel added and the classification of gravel beaches are also made.