Responses of tidal-current-asymmetry to shoreline variation in radial sand ridges in the South Yellow Sea

Tidal-current-asymmetry (TCA) influences sediment transport and geomorphologic changes. It is of paramount importance to understand the current asymmetry in this area in context of a long-term scale with consideration of development and protection of the coastal resources. The radial sand ridges (RSR) in the South Yellow Sea is patterned with strong tidal forcing and complex hydrodynamic environment. This paper simulated tidal current field in the RSR based on the Delft3D model and used combined harmonic analysis and skewness theory to analyze the spatial distribution of the TCA under varied shoreline conditions. The results show that peak-current-asymmetry (PCA) in the RSR is mostly flood-dominant and slack-water-asymmetry (SWA) also shows positive, meaning the flooding duration is shorter than the ebbing duration. Both the positively-dominant PCA and negatively-dominant SWA are mainly affected by the nonlinear interactions between the semidiurnal diurnal tides (M₂, S₂) and shallow water tides (M₄, MS₄). As the shoreline gradually moves towards sea during 1984 to 2014, although the nature of $ {\gamma }_{\mathrm{P}\mathrm{C}\mathrm{A}} $ remains, the magnitude of which increases by up to 25%. Meanwhile,$ {\gamma }_{\mathrm{S}\mathrm{W}\mathrm{A}} $ decreases by up to 20%, which intensifies its shorter-flooding-duration pattern in the core area of the RSR.