Stability of two-class armour berm breakwaters: An experimental study

The recession of a berm breakwater is a key parameter in ensuring its stability, and functionality, to protect coastal areas against wave impacts. Consequently, consideration of the expected recession in structural design is required to ensure the required objectives of the structure. In this study, physical model laboratory experiments were conducted to measure the recession of two-class armour berm breakwaters in response to varying sea state conditions (wave height, wave period, storm duration, and water depth at the structure's toe) and geometrical parameters (berm elevation from still water level, berm width, and rock size). A total of 110 tests were conducted under irregular wave forcing and the results were compared with those of existing formulae, derived specifically for mass armour and Icelandic-type berm breakwaters. Of the existing formulae, the Sigurdarson and Van der Meer (2013) formula that is derived for both mass armour and Icelandic-type berm breakwater outperforms the other formulas. Subsequently, a new empirical formula was developed to estimate the erosion depth based on the dimensionless water depth. The findings from this study could be instrumental for the structural design of two-class armour berm breakwaters under different sea states and geometrical configurations.