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Scour around a circular monopile in coastal regions has been investigated extensively over the past decades, but the time development of scour depth around an offshore-wind monopile under large current–wave ratio still lacks a predictive model. By considering the conservation of sand volume and adopting the conventional exponential law for temporal variation, a semi-empirical model, which has three parameters, i.e., an equilibrium scour depth, a shape coefficient and a scour characteristic time scale, is developed for predicting the time development of scour depth around a monopile under live-bed conditions of combined wave–current flows. A series of laboratory experiments was conducted in current-only and wave–current flows to obtain data for model calibration and validation. Experimental results indicate that adding weak waves on current accelerates scour development, which is successfully captured by the proposed model through using the far-field bottom shear stress as a key model input. The overall model inaccuracy is within 25%, and the model's applicability is further confirmed by field measurements from an offshore wind farm in east China. This model can help to determine the timing of installing scour protection around offshore monopiles, especially for the circumstances with very strong local sediment transport (live-bed). • A new model for scour time development around a circular pile is proposed. • A set of scour tests was conducted in live-bed conditions for calibration and validation. • A field study was carried out for an offshore monopile wind farm in eastern China. [ABSTRACT FROM AUTHOR]

The effects of sea level rise (SLR) are relevant to the future evolution of coasts and estuaries. This study analyses the importance of different SLR trends on the morphological evolution of a mixed-energy fine-sediment coast (the Caofeidian Sea in Bohai Bay, China) using a validated numerical model. Results show that SLR produces spatially non-uniform relative morphodynamic responses, depending on the local coastline (uninterrupted or inlet-interrupted) and wave exposure. In the Caofeidian Sea, the uninterrupted coast is exposed to waves and tidal currents, and SLR reduces the accretion of tidal flats via heightening waves. On the inlet-interrupted coast, the morphological response to SLR is dominated by changes in tidal asymmetry and current velocity. In low SLR scenarios, the enhanced flood tidal asymmetry makes the system initially resilient to SLR. For high SLR scenarios, tidal sediment transport capacity is dampened by the reduction in current velocities, which accelerates the degradation of tidal flats along the inlet-interrupted coast. Differences among results with eight theoretical SLR trends show that the magnitude of SLR-induced morphological change is influenced by the target value (0.5 and 1.0 m) and rising mode (abrupt growth, linear growth, parabolic growth, and exponential growth) of the SLR. A newly-introduced parameter (equivalent SLR, E SLR), which reflects the time-weighted average value of an SLR trend for a period of time, shows a strong linear relationship with SLR-induced morphological change. Results suggest that the morphological response to other SLR scenarios for the Caofeidian Sea is expected to be interpolated from the E SLR ratios without performing extra time-consuming simulations. • SLR triggers erosion of tidal flats on the uninterrupted coast via heightening waves rather than enhancing currents. • Morphological response of inlet-interrupted coast is subject to net sediment flux controlled by tidal asymmetry and currents. • Morphodynamic modelling that neglects the SLR trends has a limited predictive capacity of SLR effects on the coasts. [ABSTRACT FROM AUTHOR]