Wave overtopping at two-class armour berm breakwaters: an experimental study

Abstract

This study investigates the overtopping behaviour of two-class armour berm breakwaters by conducting 110 small-scale physical model tests. The investigation focuses on the influence of key parameters, such as wave steepness, dimensionless crest height, stability number, berm height, and the reshaped profile of the berm, on mean overtopping discharge. Among these, the dimensionless crest height emerged as the most influential factor. Furthermore, the results indicate a noticeable increase in overtopping discharge with decreasing wave steepness and increasing degree of reshaping. The results show that the EurOtop (2018) mode underestimates overtopping rates, with more scatter compared to the other formulas. In contrast, the formulas by Lykke Andersen (2006), Pillai et al. (2017), and Sigurdarson and Van der Meer (2012) provide more accurate predictions, though slight underestimations remain, except in the case of the Lykke Andersen (2006) one. The observed underprediction for the conducted tests highlights the need for modifying existing formulas to more accurately reflect the specific characteristics of two-class armour berm breakwaters. Recalibrating these formulas with the new dataset improved prediction accuracy, with the modified Lykke Andersen (2006) and Sigurdarson and Van der Meer (2012) models performing the best. Accuracy metrics such as BIAS, RMSE, R², and Discrepancy Ratio (DR) further confirmed the improvements, showing reduced BIAS and RMSE values compared to the original formulations. The findings emphasize the need for more refined formulas to predict overtopping for two-class armour berm breakwaters, particularly those with reshaped berms, under varying wave conditions.