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Pile-Rock breakwaters (PRBW) have been constructed as long continuous features in the West Sea of the Mekong Delta. Optimising the gap arrangement and spatial orientation of these continuous breakwaters can result in positive impacts on the velocity field, sediment distribution, and shoreline morphology. In this study, experimental and numerical modelling was performed to investigate the effect of breakwater gaps on bedload sediment transport and nearshore bed morphology. The gap width across various hydrodynamic conditions was found to have a significant impact on bedload sediment transport and nearshore bed morphology. This study found breakwater gaps can result in high current speed and flow due to wave diffraction, which subsequently also accelerates the shoreline and bed erosion process. The gaps also have a positive impact by facilitating sediment supply behind the breakwaters, which enhances the living shoreline. The sediment exchange rate was higher in low water conditions for the emerged breakwater caused by wave circulation stirring up the sediment with higher wave amplitude. During high-water conditions, the results showed a relatively smaller area of sedimentation behind the breakwater. Under high water level conditions, the ability to stir up sediment decreases, resulting in low sediment transport. The findings from this study can be used to optimize the design of pile-rock breakwaters and their performance on the deltaic coast.
•Gap arrangement were investigated by physical and numerical models.•3D wave basin laboratory and 2D Xbeach numerical modelling were applied.•High velocity and flow through the breakwater gaps due to wave diffraction.•The gaps facilitate the sediment supply behind the breakwaters.•The sediment exchange supply is greater in low water conditions and versa.