The hydraulic stability of the armour layer of rubble mound breakwaters has been widely discussed in literature and several empirical formulas have been proposed for design purposes. Nevertheless, few studies focused on the armour stability in case of water depth limited water conditions. The aim of the present research is to provide more insights into the stability of the armour layer including extremely shallow water conditions. New 2D physical experiments have been carried out at the EUropean Maritime and Environmental Research (EUMER) laboratory of the University of Salento (Lecce), in presence of a 1:30 foreshore. Tests aimed to investigate both the nearshore hydrodynamics and the hydraulic armour stability under different irregular wave loading. In the present paper the experimental set-up is described together with the main preliminary results. Specifically, the measured damage S after each test in different shallowness conditions is reported and discussed. Experimental results are also compared with the damage evaluated from the empirical formula proposed by Van Gent et al. (2003), in order to investigate the predicted damage level in the shallowness range analysed.

Overtopping wave loads on vertical structures on top of a dike have been investigated in several small scale experiments in the past. A large-scale validation for a mild foreshore situation is still missing. Hence the WALOWA experimental campaign was carried out to address this topic. In the present paper the objectives of the WALOWA project are outlined in detail, the model and measurement set-up described and the test program presented. Furthermore, preliminary results featuring a single 1000 irregular waves test of the test program are highlighted. This includes the study of the mild and sandy foreshore evolution by comparing profiles before and after the test execution. The profile measurements are obtained with a mechanical profiler. The wave parameters offshore and at the dike toe are numerically simulated using a SWASH model. The numerical results are validated against the measurements. Finally, the force and pressure time series of the waves impacting against the wall are processed and filtered. The load cell measurements and the time series of integrated pressures are compared to each other and for each impact event the maximum force is derived.