Investigation of detached breakwaters. Part I—hydrodynamics

This paper examines the hydrodynamic processes associated with detached breakwater schemes. It is based on a physical model study of the Elmer breakwater scheme, undertaken in the UK Coastal Research Facility. The main objectives were to investigate the influences on the hydrodynamics of wave directionality and directional spread, irregular bathymetry and breakwater permeability. In contrast to previous studies, it was found that one circulation cell was dominant across the middle of the bays for both random and monochromatic waves. Refraction due to the irregular bathymetry had a significant influence on the wave-induced currents behind the breakwaters. In addition, transmission through and overtopping of the breakwaters were responsible for the observed current patterns. Long-period waves were formed in the near-shore for multidirectional waves, resulting in long period oscillations of the currents. These complex hydrodynamic processes are not included in most current numerical models used in the design of offshore breakwater schemes. The paper concludes that a new generation of models is needed to incorporate these processes, but recommends the most appropriate techniques to use in the meantime.