Xi Feng

Tidal asymmetry (TA) is a key physical process governing residual sediment transport and morphological evolution in coastal environments. As nature-based shoreline restoration gains increasing attention, understanding how restoration configurations affect TA is essential for effective project planning. Focusing on the western Yellow Sea (WYS), this study investigates the response of TA to the implementation of Operational Landscape Units (OLUs). Based on the realistic WYS coastline, 18 independent OLU restoration scenarios were simulated using a high-resolution FVCOM model. In parallel, an idealized rectangular domain was constructed to examine OLU-induced tidal responses under a progressive tidal-wave regime. The effects of restoration location, length, spatial connectivity, bottom friction, and inner-slope geometry on TA were systematically investigated. The results reveal two geographically distinct response patterns: Type I, characterized by localized TA changes, and Type II, characterized by far-field responses. OLUs implemented along the Shandong coast and near the Changjiang Estuary generate primarily localized responses, whereas restoration along the central WYS coast, particularly from Lianyungang to Rudong, induces far-field changes across the WYS shelf, with tidal skewness varying by up to approximately 0.27. For Type I responses, OLUs redistribute tidal energy flux and modify energy partitioning between the shallow-water constituents and their parent constituents, thereby controlling TA within and near the OLU entrances. For Type II responses, OLU implementation shifts the amphidromic points of the WYS Kelvin-wave system, resulting in spatially extensive TA changes across the shelf. Restoration length is the primary control on the magnitude of TA change and is more influential than spatial connectivity, whereas bottom friction and inner-slope geometry mainly affect TA within the restored areas. The idealized experiments further show that the M2 and M4 constituents exhibit quasi-standing-wave behavior within the OLUs, with phase lags of 50°–80°. Tidal energy flux is redistributed toward the OLU entrances, and the relative M2–M4 phase difference outside the entrances decreases by up to 30°, promoting a transition of M2 toward progressive-wave behavior and contributing to a shift from ebb to flood dominance within the OLUs. These findings demonstrate that restoration location and total length should be prioritized in OLU-based shoreline planning, while bottom friction and inner-slope design should be optimized to regulate local tidal responses and minimize unintended ecological impacts.

This study employed physical model experiments based on a practical engineering project to investigate the wave attenuation performance of a floating breakwater under oblique irregular wave and wave–current interaction conditions. The effects of key controlling parameters, including wave incident angle, relative water depth, wave steepness, relative width, and relative current velocity, on the transmission coefficient ( K _t ) were systematically analyzed. The results indicate that the floating breakwater used in this engineering project exhibits satisfactory wave attenuation performance under oblique irregular wave conditions, with both transmitted wave heights and the occurrence probability of high wave crest events on the lee side being significantly reduced. The transmission coefficient K _t exhibits pronounced nonlinear responses to the governing parameters. As the relative water depth increases, K _t shows an overall increasing trend, with an inflection point occurring at a relative water depth of 4.5, beyond which the growth rate increases markedly. With increasing wave steepness, K _t rises significantly. In contrast, increasing relative width leads to a pronounced reduction in K _t , with an accelerated decreasing trend. Meanwhile, K _t generally decreases with increasing wave incident angle, and the most favorable wave attenuation performance is observed under the 45°condition. Under wave–current interaction, K _t exhibits an overall decreasing trend with increasing relative current velocity. Relative contribution analysis based on the investigated experimental parameter ranges reveals that relative width is the dominant controlling factor, contributing 42.9% to the variation in K _t , followed by relative current velocity and wave incident angle, whereas relative water depth has the smallest influence. This study elucidates the dominant control mechanisms and governing factors affecting the wave attenuation performance of floating breakwaters under oblique irregular wave and wave–current interaction conditions through physical model experiments, and provides a quantitative basis for parameter optimization and layout design in practical engineering applications.

Introduction: High-tide flooding (HTF) is becoming an increasingly frequent coastal hazard under accelerating sea-level rise (SLR), yet the combined influences of tidal evolution and non-tidal hydrodynamic processes on future HTF remain insufficiently quantified along the Chinese coast. This study investigates future HTF evolution at six tide gauge stations along the coasts of Jiangsu and Shanghai, spanning the western Yellow Sea and the Yangtze Estuary. Methods: A multi-factor statistical prediction framework was developed by decomposing historical water levels into multiple physical components and constructing four nested HTF prediction models. These models were used to quantify the individual and combined effects of SLR, tidal-amplitude amplification (TA), and non-tidal residuals (NTR) under different emission scenarios. Results: The results show that SLR is the dominant long-term driver of increasing HTF frequency, with the most rapid increase occurring under SSP5-8.5. However, TA and NTR exert strong regional modulation on HTF evolution. Tidal amplification is most pronounced at Lianyungang and Yanwei due to the convergent morphology of Haizhou Bay, with tidal amplification alone contributing up to 124 additional HTF days/year at Lianyungang by 2100. In contrast, tidal amplification at Wusong remains weak because of runoff regulation and frictional dissipation in the Yangtze Estuary. NTR contributions are strongest along the central Jiangsu coast, particularly at Sheyang, where NTR contributes up to 137.9 additional HTF days/year under SSP5-8.5. When all three factors are combined, HTF risk exhibits strong spatial heterogeneity, with Lianyungang emerging as the highest-risk hotspot and Wusong remaining comparatively less sensitive. These findings indicate that future HTF evolution along the Jiangsu–Shanghai coast is controlled not only by regional SLR but also by local geomorphology, tidal dynamics, and estuarine hydrodynamics. By explicitly incorporating tidal-amplitude evolution and quantitatively separating the relative contributions of SLR, TA, and NTR, this study provides scientific support for regionally differentiated coastal adaptation, flood-risk management, and dynamic resilience planning under future climate change.