Wave overtopping at rubble mound breakwaters: A new method to estimate roughness factor for rock armours under non-breaking waves

Wave overtopping is a relevant threat for rubble mound breakwaters which are designed to protect coastal areas or harbours. Currently, the wave overtopping assessment for such structures is mostly performed by using empirical formulae where hydraulic and geometric variables together with correction factors are included, such as the armour roughness. The predictive overtopping formulae for sloping structures are usually applied by assuming a constant value of this parameter based on the type of armour units, number of layers and type of core. In this paper we present a new methodology to estimate the roughness factor for rubble mound breakwaters as a function of both hydraulic and structural parameters. To this end, new physical model tests and previous results obtained from an existing database (i.e., CLASH) have been used. The new methodology to estimate the roughness factor, depending on a detailed complete geometrical representation, provides an improved prediction of the average overtopping discharge compared to the existing formulae.