ABSTRACT

Low-crested (LC) rubble mound breakwaters, whose crest level is at the still water level (SWL), represent an environmentally friendly method for shore protection. Numerical simulations of the flow field induced by wave overtopping over these structures were performed. Three different cases of breakwaters were examined with crest width equal to d, 2d and 3d, where d is the depth at the seaward toe of the structures. From the results, which include reflection and transmission coefficients and velocity and vorticity fields, it is revealed that the crest width affects the wave and flow behavior in the leeward side of LC breakwaters.

INTRODUCTION

LC rubble mound breakwaters, which are characterized by frequent overtopping, are widely used for coastal protection. The main advantage of these structures is their mild aesthetic impact on the natural environment. As the waves approach and transmit over these structures, significant hydrodynamic processes occur in their proximal area. In the seaward side, the most important processes are wave breaking and reflection, while in the leeward side wave overtopping and transmission (Garcia et al., 2004). Many researchers have studied the hydrodynamics of flow in the vicinity of such structures, as well as the influence of their geometrical characteristics on the flow field. However, most of these structures are either emerged or submerged, while the case in which the crest level of the breakwaters is at the still water level has to be further investigated.

Losada et al. (1996) examined the effect of the incident wave obliqueness of a non-breaking wave on a porous breakwater, placed on a sloped bottom, as well as the effect of the geometrical characteristics of the breakwater and porosity on the kinematic and dynamic characteristics of the flow around the breakwater. More specifically, they studied the influence of the above parameters on wave reflection, transmission and energy dissipation, assuming ideal flow. From their results, it was indicated that wave reflection was significantly affected by the obliqueness of the incident waves, while wave transmission was not. Regarding the geometry of the structures, it was found that the crest width influences the processes of reflection and transmission of waves, while the effect of the sloped bottom (where the breakwater is placed) is negligible. It is important to note that this behavior might change under the influence of breaking waves. Finally, it was also found that porosity affects wave transmission significantly.

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