Assessment of a gravel nourishment project frontin a seawall at Marina di Pisa, Italy

A gravel beach was created in winter 2001-2002 seaward of a 330-meter-long seawall at Marina di Pisa, Tuscany, Italy.Amonitoring project was performed to evaluate the stability of the new beach and the interaction between the coarse fill and the fine sand comprising the nearshore profile. Bathymetric surveys were conducted in October 2001, before the nourishment operation, in March 2002, two weeks after nourishment, and in January 2003. Topographic surveys were conducted from the backshore to 9 m depth along eleven cross-shore transects spaced every 25 m. Sediment samples were collected on the nearshore surface prior to nourishment and on the nearshore and nourished beach following nourishment. One-meter-deep trenches were dug across the beach in May 2002 and January 2003. Shoreline planform and profile analysis reveals that the beach rotated toward the direction of high energy wave approach, resulting in a narrowing of the berm in one segment that allowed waves to overtop the seawall and deposit gravel landward of it. Sand from the nearshore infiltrated the gravel pore spaces, reducing the permeability and porosity of the gravel beach, and potentially altering its stability. No gravel clasts appeared to move seaward of the beach step during storms. Preliminary results indicate that a gravel beach can protect coastal infrastructure and produce a surface usable for tourist activity.