The Influence of a Crown Wall on Wave Overtopping over Breakwaters

This paper investigates the influence of a crown wall on wave overtopping on rubble mound breakwaters. Existing data is used to modify the EurOtop overtopping formula updated by Eldrup et al. (2022) to cover the influence of the crown wall. The effect of raising the wall above the armour crest (elevated wall) or lowering the wall below the armour crest (lowered wall) is investigated. A crown wall at the armour crest level is considered as the reference case. By increasing the elevation of either the armour crest or the crown wall, overtopping is reduced and by lowering either of them, overtopping increases. The influence of the crown wall height, elevated or lowered compared to the armour crest, is not considered accurately in the present design guidelines and thus corrections are suggested. For an elevated wall, a modified crest width has been defined, to better describe the presence of the armour crest in front of the wall. For the lowered wall the effective freeboard might be taken as the average of the wall and armour freeboards. The improvement compared to existing methods is significant, especially for breakwaters with a large elevated wall. The proposed modifications to the EurOtop Manual increase the range of applicability with respect to the wall configuration.