An Italian Experience on BDS: Test Sites in Ostia and Procida

The paper reports on a research work carried out to investigate the effects of BDS (Beach Dewatering System) in reducing beach erosion. The work is part of a larger research program, including both field and laboratory activities, which provided useful results on the hydrodynamic and Morphodynamic effects of the system. As it is well known, the dewatering system is aimed at lowering the water table, thus increasing the extent of the unsaturated beach and enhancing the infiltration flow during the wave run up; thus, on the one hand, the sand in the swash zone becomes more stable under the wave action, and on the other hand the sediment transfer from the near shore zone increases. The dewatering system has been installed so far on five widely different sites along the Italian coastline; the paper deals in particular with the first two locations. The first BDS was installed in February 2001 (Damiani et Al., 2003) on the sandy beach of Ostia (Rome) on the Lazio coastline, which is characterized by a strong in-going erosion process; frequent nourishing actions had previously been attempted, thus deeply modifying the original sand grain size and resulting in a quite coarse granulometry. The drainage system was partially successful in stabilizing the beach, and produced a certain initial increase of the emerged beach. The second Italian BDS system was installed on a beach on the island of Procida, at the northern closure of the Bay of Naples. In this case too, a strong erosion is in progress and some infrastructures are dangerously close to the shoreline; morphology, wave climate and sediment characteristics are however quite different from those in Ostia. The drainage device in this instance brought no significant advance of the shoreline, even though a remarkable accumulation of sediment on the emerged beach was observed.