Influence of the permeability of submerged breakwaters on surrounding wave and current fields

ABSTRACT While a submerged breakwater has become one of the preferred options of shore protection structures because of its lower impact on the coastal landscape and environment, it causes complicated hydrodynamic characteristics and sometimes fails to meet the expected coastal protection functions. Accurate prediction of wave and current around the structure is therefore essential for appropriate design of a submerged breakwater. This study focused on the influence of the permeability of the submerged breakwater and newly conducted laboratory experiments using permeable and impermeable breakwaters. The model, Simulate WAves till SHore (SWASH), was then applied to these laboratory experiments and the difference of measured and computed wave and current field around the structure was investigated. It was found that the model qualitatively well represented the horizontal distribution of wave heights and phase-averaged current velocities although it overestimated the shoreward volume flux over the impermeable breakwater, but not over the permeable breakwater. Comparison of these contrasting results between permeable and impermeable breakwaters revealed that the phase-averaged bottom shear stress was underestimated on the crest of the impermeable breakwater. This feature highlighted the importance of the bottom friction forces accounting for the wave current coexisting field for better predictions of wave-induced current field around the submerged breakwaters.