Spatial layout and wave attenuation efficiency of the muddy coastal protection in Vinh Long, Mekong River Delta

Coastal deltas globally face increasing vulnerability to chronic erosion due to the synergistic effects of sea-level rise and diminished sediment supply, necessitating the development of optimized structural protection strategies for highly dynamic muddy environments. This study utilizes the MIKE 21/3 coupled numerical modeling system to evaluate the morphodynamic performance of two structural interventions under seasonal monsoonal forcing: shore-normal groynes (Option 1) and a detached breakwater system (Option 2). The results show that both interventions successfully transition the nearshore zone from an erosional state (natural retreat exceeding 10.0 cm) to a depositional regime. Option 1 is highly effective for sediment capture, yielding an average accretion of 1.0 cm and a 73% reduction in peak current velocities. In contrast, Option 2 exhibits superior wave attenuation, reducing significant wave heights by an average of 61.9% (approximately 54% more effectively than Option 1) while promoting a more uniform sedimentation pattern. However, both structures induce localized scouring at groyne tips and structural gaps, influenced by fluvial discharge. The study concludes that while detached breakwaters are optimal for wave energy dissipation and uniform morphological stability, groynes are preferable for maximizing total sediment accretion. These findings provide a science-based foundation for sustainable coastal management in climate-vulnerable deltaic regions.