Hydrodynamic and Sediment Response to Oyster Castles Under Wave Forcing: Insights From Laboratory Flume Experiments

Nature‐based shoreline protection strategies, such as engineered oyster reefs and living shorelines, offer sustainable alternatives to hard infrastructure. In this controlled laboratory study, we evaluate relative hydrodynamic and sediment‐response differences among interlocking oyster‐castle configurations under monochromatic wave forcing. Using two‐dimensional Particle Image Velocimetry, image‐derived surface‐elevation diagnostics, and suspended‐sediment visualization, we quantify phase‐averaged velocities, turbulent kinetic energy, Reynolds stresses, bed shear stresses, wave quality, reflection, and sediment‐mobility diagnostics across low‐ and high‐energy conditions. Comparisons between scaled‐down 3D‐printed models of bare and oyster‐populated castles show that oyster population suppresses onshore near‐bed turbulence and reduces sediment mobilization potential under the tested laboratory conditions. Geometry also modulates the near‐bed response, with smoother onshore profiles producing lower shear‐stress and turbulence metrics. The offshore, no‐structure mobility diagnostic was approximately one order of magnitude below the wave‐adjusted model‐sediment threshold under low‐energy forcing and of the same order of magnitude, but below the threshold, under high‐energy forcing. The results are therefore interpreted as comparative mechanistic evidence for oyster‐castle performance under a laterally confined laboratory configuration, rather than as direct predictions of absolute field‐scale sediment transport rates.