Impact of tropical cyclones on the hydrodynamics and sediment dynamics of the radial sand ridge system in the southern Yellow Sea

Abstract

The large radial sand ridge (RSR) system located in the southern Yellow Sea near the Jiangsu coast, China, is highly impacted by tropical cyclones (TCs). However, the temporal and spatial variations of sediment dynamics and associated morphodynamics in this region under the influence of TCs have been little explored due to the difficulty of implementing direct observation during these extreme events. Taking typhoon Lekima in August 2019 (No. 1909) as an example, this study simulated and comprehensively investigated the dynamic processes in the RSR area under the impacts of TCs based on the Finite Volume Coastal Ocean Model (FVCOM). During the passage of Lekima, the spatial patterns of residual flow (RF), sediment flux (SF) and morphology changes in the RSR area were totally different from that during the pre- and post-Lekima periods, especially in the offshore areas (the seaward edge of sand ridges). This is because TC Lekima can generate strong wind-driven currents and waves, increasing the bottom stress and influencing the sediment transport. Due to the shallow water depth of RSRs, wave height decreased significantly towards the coast, and tidal effects gradually dominated the nearshore sedimentary dynamic processes instead of wave effects. Furthermore, the effects of TCs with different tracks and intensities were discussed in this study, and we found that TCs passing the west/east side of the study domain can induce opposite directions of sediment transport and lead to the spatial asymmetry of geomorphological evolution. This research can contribute to an improved understanding of sedimentary dynamic processes during extreme events and indicates the importance of exploring sediment dynamics response to TCs with different characteristics for reducing TC-induced coastal risks in future climate change scenarios.