Résumé
The hydraulic stability of the armour layer has been widely discussed in literature, and several formulas have been proposed for design purpose. Nevertheless, few studies focused on the armour behaviour in case of limited water depths. The objective of the present research is to provide more insights on the stability of the armour layer till extremely shallow water conditions. New physical experiments have been carried out in the wave flume at the Environmental European Maritime and Environmental Research Laboratory (EUMER) of the University of Salento (Lecce), in presence of a 1 to 30 foreshore. Tests aimed to investigate both the nearshore hydrodynamics and the hydraulic stability under different irregular wave attacks. Four water depths were adopted and in order to produce a significant damage to the structure, the rock size was scaled down accordingly. After each test, the erosion area (Ae) has been quantified by a laser bed profiling system, and the structure damage (S= Ae÷Dn50²), where Dn50 is the rock nominal diameter, has been determined to investigate it in a range between 0 and 12, useful for design purposes. Moreover, both statistical and spectral wave characteristics, have been retrieved from resistive wave gauges located along the flume and at the structure toe. The latter have been evaluated even without the breakwater, since no reflection analysis is suitable in shallow water conditions (Van Gent, 1999). In the full paper the experimental set-up will be described together with the main preliminary results. Specifically, the measured damage S calculated after each test in different shallowness conditions will be reported and discussed. Experimental results will be also compared to the damage computed by applying the widespread formulas of Van der Meer (1988) and Van Gent et al. (2004), in order to understand if the formulations are able to predict the level of damage when the breaker parameter ξm is larger than 10