Variation characteristics and dynamic mechanism of high suspended sediment concentration in coastal waters of Northern Jiangsu under tidal current action

The coastal waters of northern Jiangsu are one of the areas with relatively high suspended sediment concentration (SSC) in China. Based on bottom boundary layer observations in this region, we processed the current and wave data using phase-space thresholding method, PUV method, and GM79 model to explore the variation characteristics of high suspended sediment concentration (H-SSC) and the mechanisms of its response to tidal dynamics. Results show that the tidal current in the study area is an irregular semi-diurnal tide, and the maximum near-bottom current velocity was 0.87 m/s. During the observation period, the wave height ranged from 0.06 to 0.34 m, and the wave effect was not significant. The SSC increased with decreasing distance from the bottom. The average SSC at 0.4 m and 0.6 m from the bottom was 3.37 g/L and 1.52 g/L, and the maximum SSC was 20.87 g/L and 11.33 g/L, respectively. The peaks of H-SSC occurred after the flood and ebb maxima, and a secondary high-value period appeared during slack water. H-SSC was mainly controlled by sediment resuspension, while it was mainly affected by advection transport during the slack water period. Suspended sediment was mainly transported along the coast, showing a general pattern of southward and onshore transport. This study provided a reference for the research on the sediment dynamic process of H-SSC in the coastal waters.