A Morphodynamic Modeling Study on the Formation of the Large-Scale Radial Sand Ridges in the Southern Yellow Sea

The radial sand ridges (denoted as RSRs hereafter) in the Southern Yellow Sea, China, are morphologically striking because of the remarkable size and radial planar orientation, standing out as a unique coastal geomorphology among the worldwide sand ridge systems. The formation of this giant fan-shaped geomorphic feature requires delicate conditions and awaits in-depth investigation. Using an idealized morphodynamic model, this study unravels the governing factors for the formation of the unique large-scale RSRs, in comparison with other types of sand ridge systems over the world. The effects of the M-2 tidal constituent, the Coriolis forcing, the bed resistance, and the initial water depths on the morphodynamic behavior of the RSRs are explored. Numerical results indicate that the tidal regime, characterized by rotational and progressive current action associated with the tidal bulge, is dependent on the eastern coastline of China as well as latitudinal effects. Through the comparison between the simulated and the measured morphology, this tidal regime is demonstrated to be the key driver in forming and maintaining the present-day RSRs. The runs with different parameters further suggest that the asymmetric pattern of the RSRs, which shows larger northern sand ridges than the southern ones, results from both the asymmetric distribution of current activity caused by the tidal bulge and unequal sediment supply. Overall, this study highlights the delicate condition, predominantly represented by the particular currents set up by the tidal wave system and the sediment supply, required to shape the striking large-scale RSRs in the Southern Yellow Sea.