Investigation of detached breakwaters. Part 2—morphodynamics

This paper describes a physical model investigation conducted at the UK Coastal Research Facility into the shoreline response to a detached breakwater scheme. The effect of random unidirectional waves on beach morphology is examined and the influence of wave transmission and choice of sediment and shoreline evolution is also investigated. Little difference is observed in the evolved shoreline between monochromatic and random wave tests. However, a significant difference in morphology occurs below the waterline because of the different wave–current field and accompanying velocity moments. The plan shape is also affected by the choice of material for the mobile bed, and wave transmission through the breakwater. Measurements and empirical predictions of beach evolution behind the breakwaters are compared, and the latter found to be only partially successful. It is recommended that plan shape models continue to be used to predict long-term shoreline change but incorporating a wave refraction/diffraction model. This should be combined with a coastal area numerical model, to investigate beach response during individual storms and recovery after storms. Further research into influence of tides and tidal currents is proposed as well as development of numerical models, which can predict short and long wave interaction and non-linear transformation of multidirectional waves in shallow waters. The application of such models to mixed beaches also requires further research.