Experimental analysis on a low crested rubble mound breakwater

In the present study, the flow induced by waves around a physical model of a detached low crested rubble mound breakwater is investigated experimentally. The model was designed with a scale factor of 1/30, parallel to the shoreline, along a coast of constant slope 1/15, assuming Froude similarity to be valid. For the design of the rock armour layer, the van der Meer's hydraulic stability formula was applied. Two wave conditions were examined: one with an offshore wave height of 2 m (Case A) and another with the maximum annual characteristic offshore wave height (Case B) calculated in prototype scale. The measurements include surface elevation time series as well as three-dimensional velocity time series of the flow around the model. The results include flow patterns on the seaward and leeward side of the breakwater for both wave conditions as well as transmission and reflection coefficients. Along the leeward side, the current profiles have an offshore direction close to the bottom and a shoreward direction close to the free surface where the reduction of the water depth induced an acceleration of the flow and is influenced by the overtopping. Transmission and reflection coefficient’s data are compared with that from existing literature. The comparison revealed that literature equations tended to underestimate the transmission coefficient due to the critical condition represented by a zero free-board breakwater, whereas it overestimates the reflection coefficient, possibly due to the fact that these formulae were obtained from experiments performed with emerged breakwaters