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Coastal evolutions are expected to have a significant impact on storm tides, disproportionately aggravating coastal flooding. In this study, we utilize a nested storm tide model to provide an integrated investigation of storm tide responses to changes in coastline and bathymetry along the Zhejiang coasts. We selected coastline and bathymetry data from 1980 and 2016, as well as data from three typical typhoon events (i.e., Winnie, Haikui, and Chan-hom) for simulating the storm surge processes. The results indicate that changes in the coastline and bathymetry from 1980 to 2016 have resulted in an increase in storm tides in the northern part and a decrease in the central part of Zhejiang. Specifically, storm tides in Hangzhou Bay have increased significantly, with an average increase of about 0.3 m in the maximum storm tides primarily attributed to coastline changes. On the contrary, in smaller basins like Sanmen Bay, while reclamation itself has reduced peak storm surges, rapid siltation has consequently exacerbated the storm surge. By decomposing storm tides into astronomical tides and storm surges, we discovered that the change in tidal levels was twice as significant as the surge change. Moreover, the nonlinear tide–surge interaction was nearly four times that of the pure surge, significantly contributing to storm surge variation. Alterations in the momentum balance reveal that the water depth-induced bottom friction and wind stress increase contributes to the local enlargement of storm tides at the bay head, while the coastline changes exaggerate nearshore storm tides through an increase in the advection term. [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]