Parametric tropical cyclone models are widely used to generate large wind field ensembles for assessing extreme storm tides and wave heights. The radius of maximum wind (RMW) is a key model parameter and is commonly estimated using empirical formulas. This study shows that uncertainty introduced by the choice of RMW formulas has been largely overlooked in tropical cyclone risk assessments. Using the Pearl River Estuary as a case study, historical wind fields (1981–2024) were generated with a parametric tropical cyclone model combined with eight empirical RMW formulas. Storm tides and wave heights during tropical cyclone events were simulated using a coupled wave–current model (ROMS–SWAN) and analyzed with extreme value theory. The results indicate that, for estuarine nearshore zones, the 100-year return period of water level and significant wave height vary by up to 1.26 m and 1.54 m, respectively, across all the selected RMW formulas. Joint probability analysis further shows that RMW uncertainty can shift the joint return period of the same compound storm tide and wave event from 100 years to 10 years. For an individual extreme event, differences in the RMW formula alone can produce deviations up to 2.11 m in peak storm tide levels and 3.8 m in significant wave heights. Such differences can also change the duration of extreme sea states by 13 h. These results highlight that RMW formula selection is a critical uncertainty factor, and related uncertainty should be considered in large-sample tropical cyclone hazard assessment and engineering design.

Local scour around submerged piles in currents are common in coastal and offshore engineering. This paper studies the influences of the submergence ratio (flow depth to pile height) on local scour around a square pile in steady flow. Submergence ratio ranging from 1–4, as well as two unsubmerged tests, were tested with a 10 × 10 square pile of 20 cm height. The three-dimensional profiles were measured to study the scour and deposition characteristics. Results show that the maximum scour depth was always at the upstream corner points rather than at the symmetry center point of the pile. The temporal maximum scour depth achieved its equilibrium sate in less than 4 h for each test. The equilibrium scour depths at the upstream corner points were independent of the submergence ratio when the latter was larger than 1.5. These findings give meaningful reference to the numerical simulations and local scour depth protections in the submerged pile cases deeper than which the flow depth does not affect the equilibrium scour depth.

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.

Local scour threatens monopile foundations, while the construction-stage washout and post-curing stability of fluidized solidified slurry remain insufficiently quantified. This laboratory study evaluates slurry diffusion and fragmentation at upstream, side, and downstream grouting positions and assesses the protection provided by a cured slurry layer. A 1:100 recirculating-flume model representing an offshore wind farm in eastern Zhejiang Province was tested at flow-intensity ratios V/Vc of 0.31 and 0.60; an unprotected scour test and a protected live-bed test up to V/Vc = 1.65 were also conducted. At V/Vc = 0.31, the slurry showed no flow-induced fragmentation at any grouting position. At V/Vc = 0.60, fragments from upstream and side grouting travelled up to 10.7D and 14.9D downstream, respectively, whereas the downstream-grouted mass remained largely stable. The side-grouting response coincided with an amplified bed-shear-stress zone extending approximately 1.2D transversely and 1.1D streamwise. The unprotected test produced a maximum scour depth of approximately 0.35D and a horizontal extent of about 2D. Under live-bed conditions at V/Vc = 1.65, the cured 2D-radius protection layer lost 0.88% of its mass and retained its structural integrity. By linking grouting position to pile-induced hydrodynamics and evaluating both construction and post-curing stages, the study provides site-bounded evidence for grouting-position selection and protection-extent design under steady-current conditions.