WAVE RUN UP OBSERVATION AND 2DV NUMERICAL INVESTIGATION ON BEACHES PROTECTED BY STRUCTURES

1. INTRODUCTION The main parameter for the assessment of coastal vulnerability is the wave run up on the beach, defining the limit of maximum flooding, but also hydrodynamic properties in the Swash Zone (SZ) are trivial for the comprehension of hydro-morphodynamic processes. Several studies have been carried out on the SZ but few literatures are still available on the run up and on SZ flows on beaches protected by Low Crested Structures (LCSs), where flow motion is driven by a combination of low frequency infra-gravity waves and incident waves. In presence of breakwaters, swash incident waves are transmitted through the structure. In the transmission area behind the structures, wave energy is shifted to higher frequencies with respect to the incident wave spectrum and in general its mean period considerably decreases with respect to the incident one (van der Meer, 2000). The 2% of exceedance level derived from the PDF of run-up time series is a useful measure of inundation hazard during storms. The parameter, usually called R2%, is the standard definition of the wave run up, commonly used for instance by the American Flood Insurance Program. Therefore, collecting in situ run-up measurements during storms is essential to understand the SZ processes and properly calibrate both empirical and numerical models, but measuring extreme run up is difficult, due to the severe sea conditions and due to unexpected nature of storms. One of the most innovative and appropriate techniques to measure wave run up on the beach is based on video image analysis (Stockdon et al., 2006). 2. OBJECTIVE The aim of the present paper is the numerical and experimental analysis of the wave run up and of the flow properties on a beach: the study will show the different behavior of unprotected and protected beach, subjected to the same wave conditions.