Local scour around offshore wind turbine foundations is a common engineering challenge. It changes the hydrodynamic loads and affects the foundation’s load-bearing capacity. This study investigates the field scour characteristics and wave–current force characteristics under local scour effects using field data, physical modeling, and numerical simulations. The results show that the field scour hole slope is more gradual than that observed in laboratory settings, and Zhang’s scour depth equation proves more accurate for practical engineering. In addition, under wave–current conditions (Keulegan–Carpenter number, 2 < KC ≤ 15), the relative maximum post-scour wave–current force increases with the relative post-scour water depth but decreases as the KC rises. An equation is developed to predict the relative maximum post-scour wave–current force. This provides key insights for improving load assessments of offshore wind foundations on scoured seabeds.

Local scour at composite bridge foundations in macrotidal estuaries is governed by both foundation geometry and reversing-flow history, whereas most design equations assume steady unidirectional flow. A 1:80 undistorted movable-bed model was used to investigate three foundation configurations of the Qianjiang Third Bridge with two prototype-derived fast-flood, slow-ebb hydrographs per configuration. Pointwise scour evolution was measured using an optoelectronic interface probe, and post-test bed surveys provided global maximum scour depths. Most erosion occurred during the short flood phase; the weaker ebb phase produced limited backfilling, and pointwise scour approached dynamic equilibrium after approximately three complete tidal cycles. Prototype-scale global maximum scour depths were 11.8–12.2 m for Model 1, 9.5–9.9 m for Model 2, and 8.0–8.4 m for Model 3. Inverse calibration of steady-current tests yielded geometry coefficients of 0.72, 1.08, and 0.88 relative to HEC-18 equivalent obstruction widths. An exploratory tidal-asymmetry relation, $K_{\eta }=K_b{\eta }^{\beta }$, was calibrated using nine cases with a common Oh-type baseline. The fitted $\beta$ was 0.329, and the in-sample mean absolute percentage error decreased from 29.0% for $K_b$ alone to 13.6%. Because the dataset is small and the relation did not transfer consistently to HEC-18-based cases, local recalibration remains necessary. The results provide a traceable experimental basis for site-specific scour assessment of complex foundations with strongly asymmetric tides.

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