Coastal morphodynamic responses of a mixed-energy and fine-sediment coast to different sea level rise trends

Abstract

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, ESLR), 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 ESLR ratios without performing extra time-consuming simulations.