Hydrodynamic effects induced by constructed oyster reefs on a slope

Shell-based constructed oyster reefs (CORs) serve as nature-based coastal stabilization structures in living shoreline applications. This study investigates oyster colonization effects on the interactions of currents and waves with CORs on a slope. Using the computational fluid dynamics framework OpenFOAM®, a validated numerical model simulates the hydrodynamic performance over CORs with simple geometric surrogates for the oysters. Simulations are conducted considering: (1) unidirectional currents and regular wave conditions, (2) different oyster rugosities (R), and (3) still water depth variations on the flat seabed. Oyster colonization alters water velocity and turbulence distribution patterns. Under unidirectional currents, oysters expand wake regions and amplify upstream-propagating waves. Under pure waves, turbulent kinetic energy exhibits uneven distribution above oyster-colonized CORs, with maxima near wave-breaking zones. Oysters enhance wave nonlinearity, driving energy transfer from the primary harmonic to higher harmonics. Oyster-colonized CORs induce more wave height attenuation than bare CORs, though they produce an increase in wave shoaling and local energy. Along the slope, wave height attenuation varies significantly, with differences between R = 0 and R = 1.61 reaching up to 34% downstream of the landward COR. Lower oyster density may optimize wave dissipation through edge vortex formation and undertow intensification. Furthermore, increased still water depth reduces wave height attenuation by oyster-colonized CORs but enhances oyster-induced energy dissipation. These findings offer critical insights for designing oyster reef restoration strategies that balance ecological and coastal protection goals.