Response of tidal asymmetry to coastline changes in radial sand ridges sea area

Based on Delft3D, a two-dimensional flow numerical model of the radial sand ridges sea area was established, and verified with measured tidal level and current velocity to ensure calculation accuracy. Tidal asymmetries of the radial sand ridges sea area under 1984 and 2014 coastal conditions were studied separately. Tidal wave deformations are remarkable and ebb tide duration is longer than that of flooding in most areas. Moreover, tidal wave deformation in the nearshore area has obviously weakened after changes to the coastline. At shoals and deep troughs, the relative magnitudes of current rise and fall velocities differ. Coastline changes have made the flood dominated phenomenon of the radial sand ridges sea area more prominent. Based on the analysis of the tidal asymmetry of the Lanshayang and Xiyang channels, the influence of coastal change characteristics on the two tidal systems is discussed. In the southern part of the radial sand ridges sea area, the influence of coastal change on the progressive wave is mainly reflected in the following: during spring tides, the asymmetry of rise and fall tide height varies greatly before and after coastal change; and skewness increases slightly. In the north, the influence of coastal changes on the rotating tidal wave entering the area is mainly reflected in the following: skewness clearly increases; and the main combination of tidal components that causes tidal asymmetry may change.