Observation of near-bottom transport of suspended sediment in the offshore area of abandoned Yellow River mouth

In this study, a tripod equipped with an ADV (Acoustic Doppler Velocimeter) and an OBS-3A was deployed to measure water levels, bottom current velocities and suspended sediment concentrations during the spring, moderate and neap tides in the offshore area of the abandoned Yellow River mouth in the Southern Yellow Sea in November 2016 and February 2017. The results show that the tide currents in the study area are significantly affected by coastal topography, and the current direction was roughly parallel to the shore line. The tidal current is in the direction of NNW during flood and SSE during ebb, which suggests that the study area is dominated by a rectilinear current. The ebb is longer than flood in duration. The research area is one of the centers of high suspended sediment concentration (SSC) in the offshore area of the south Yellow Sea, with a high SSC maintained over 500 mg/L from the spring to the neap. In general, the peak SSC is a little lag behind the peak flood or ebb currents. Heavy wind waves may cause a sharp rise in SSC, and its impact on SSC can significantly exceed tidal effects in a short time. The study found that the variations of SSC in a complete tidal cycle can be divided into four stages: the earlier flood, later flood, earlier ebb and later ebb. In the period of mid-ebb tide, neap earlier flood tide and later ebb tide, there was a positive correlation between SSC and tidal current, which indicate that the variations of SSC is dominated by resuspension. The variations in SSC in other stages may be affected by advection. The suspended sediment transport is found to be eastward during the spring, southeastward during the neap, and southwestward between the spring and neap. Generally speaking, the sediment in the abandoned Yellow River mouth is mainly transported southward, indicating that the study area is an important sediment source for the central coastal area of Jiangsu.