Plume front and suspended sediment dispersal off the Yangtze (Changjiang) River mouth, China during non-flood season

摘要

A sea survey was conducted in May 2001 using CTD together with direct-reading current meter and water sampling to investigate the sediment dynamics off the Yangtze River mouth. Data obtained from five observational sites reveal density flows characterized by the halocline, thermocline and associated sharp current velocity gradients that prevail in the study area, especially at the freshwater plume front. The interaction of the Yangtze freshwater plume, littoral current and tidal current has generated these density flows. Particularly, the anomalous high speed ( ＞ 140 cm s~(-1)) current recorded at the freshwater plume front during the early flood stage leads to the resuspension of the sediment (SSC reaching 0.5 g l~(-1)) off the river mouth during that time period. The suspended sediment flux measured at B2, the ideal site for recording frontal processes in the estuary, indicates the main trend of southward transport of fine-grained sediment up to 60 kg m~(-2) s~(-1) at early flood stage and 1.32 kg m~(-2) s~(-1) as net flux during two tidal periods. It is inferred that the density flow at the plume front plays key roles in dispersing the Yangtze fine suspended sediments southward during the non-flood season.