BEACH DRAINAGE AS A FORM OF SHORELINE STABILIZATION: CASE STUDIES IN ITALY Ciavola Paolo 1 , Vicinanza Diego 2 , Fontana Elisa 1 Abstract This paper reports the performance of a number of Beach Drainage Systems installed around Italian coastlines. With the exception of one experimental site (Lido Adriano) where a 3 year record of morphological monitoring undertaken by the authors was available, on other sites surveys were not frequent enough to ultimately express a positive judgment on the performance of the system. It is concluded that so far there is not enough confidence in design procedures to ensure the success of this type of soft protection schemes. INTRODUCTION TO BEACH DEWATERING SYSTEMS Beach drainage systems are considered by many as a soft-engineering solution to beach erosion, on the basis that they should decrease the offshore sediment transport from the swash area to the submerged beach. The loss of potential energy due to infiltration decreases the energy of the back-swash (Grant, 1948), as when the beach water table is high due to wave set-up there is an increase in the role of the back-swash in generating shoreface erosion (Duncan, 1964). The process is related to the fact that the beach face in this condition may be saturated and therefore the surface friction may be decreased. Laboratory studies have indeed observed that artificially lowering the groundwater it is possible to enhance the sediment stability. Although Machemehl et al. (1975) were the first to propose a role of beach dewatering in coastal stabilization, the first field test was conducted by Chappell et al. (1979) in Australia, while it was only 10 years later that the first prototype installation was finalized in Hirtshals, on the north-eastern coast of Denmark. The first patent of a commercial drainage system corresponds to what is normally called the Beach Management System (BMS) or Beach Drainage System (BDS). This was registered by the Danish Geotechnical Institute in 1985 (see also Vesterby, 1991; 1994) and is based on the simple principle of the role of a granular drain located just below the shoreline in communication with the free-surface aquifer (Fig. 1). Obviously a crucial point is where to locate the drain and at which depth, as this must influence the performance of the system. So far there are no published design guidelines in this sense, therefore a "rule- of-thumb" is the approach that installers prefer, which is clearly not satisfactory 1 Dipartimento di Scienze delta Terra, Universita di Ferrara, Ferrara, Italy, cvp@unife.it 2 Dipartimento di Ingegneria Civile, CIRIAM, Seconda Universita di Napoli, Aversa, Italy, diegovic@unina2. it 2646