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Submerged breakwaters have become an appealing alternative for conventional shore protection structures due to their lower impact on the coastal landscape. These structures however cause more complicated wave-induced circulation currents and, as a result, often fail to meet the expected coastal protective functions. Although previous studies have applied two-dimensional-horizontal (2DH) nearshore current models and quasi-three-dimensional (Q3D) models with different wave-breaking and surface roller models for prediction of the circulation currents around submerged breakwaters, most of these models have failed to reproduce the observed circulation current patterns accurately. The objective of this study is therefore to investigate the applicability of multilayer nonlinear dispersive model to predict circulation current patterns under different incident wave conditions. The recently developed SWASH model was applied to a unique set of laboratory experiments, and the effect of the multilayer model was investigated. According to the experimental observations both near-bottom and near-surface mean current patterns are highly sensitive to the incident wavelength. The two-layer mode was able to reasonably capture the variation in current patterns for different wave periods, while the one-layer mode significantly underestimated the current velocities and failed to represent the dependency of the circulation current patterns on incident wavelengths.

Longshore bars are a common site in sandy beaches which is influential on currents, morphology variation and the marine eco system. Longshore bar reacts to the variation of environmental factors and wave properties like wave height, water depth, wave period, wave skewness and it tends to move seaward or shoreward while changing its amplitude. According to Lippmann and Holman, (1990) short term bar migration has been triggered when the wave height or the wave height to water depth ratio are large. Elgar et al. (2001) has shown that short term seaward bar migration was caused by velocity skewness, undertow velocity and acceleration skewness. Influence of the wave breaking on the seaward bar migration has been identified as minimum according to Sallenger and Howd (1989).

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