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

Abstract

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.