Near-bed hydrodynamics and incipient sediment response around a detached breakwater: experimental benchmark for advanced depth-integrated models

Predicting sediment dynamics around detached breakwaters remains challenging due to highly three-dimensional hydrodynamics that are often simplified in intermediate-complexity numerical models. This study presents laboratory measurements designed to investigate the performances of advanced-depth-integrated models which can consider non-hydrostatic (NH) pressure and non-equilibrium velocity profiles induced by developing boundary layer and three-dimensional vortex motions. Experiments were conducted with regular waves acting on a fixed slope with a thin layer of coloured sand. A dense grid of Acoustic Doppler Velocimeter (ADV) measurements provided time-averaged near-bed velocity fields, while overhead images documented the movement of the sand layer during the first 6 minutes of wave action. Results show a strong correspondence between circulation patterns, zones of elevated near-bed velocity, and the initial redistribution of the coloured sand, with most changes occurring in the first 2–3 minutes. The dataset isolates the incipient sediment-response stage, offering a controlled benchmark for evaluating how differences in three-dimensional flow effects on the predictions of near-bed flow and erosion/deposition tendencies. Numerical comparisons using the advanced depth integrated models based on Bottom Velocity Calculation (BVC) method are conducted and compared with experiment and the conventional 2-dimentional calculation (2DC) model.