SEDIMENT RESUSPENSION IN THE CHANGJIANG ESTUARY

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SEDIMENT RESUSPENSION IN THE CHANGJIANG ESTUARY

A specific variation pattern of the near bottom suspended sediment concenrtation has been identified the the first time during hydrographic survey of the turbidity maximum in the South Passage of the Changjiang Estuary. Peak values occur in one to three hours later after the reversal of the tidal current in most of monitoring periods (generally exceeding 25 hours).Thereafter the concentration decreases sharply even in full strength ebb or flood current. The origination of those peak values has been analyzed based on the diffusion of suspended sediment.The eddy diffusion coefficients Kz are calculated by using field data. It shows that Kz possesses a periodic variation similar to that of the near bottom concentration due to tidal action and the maximum values occur in midway of the acceleration period of current. This is in fact determined by the tidal variations of the vertical gradient of velocity which has large initial values. It is concluded that peak values of concenrtation occurring soon after the slack water are mainlys caused by strong diffusion of settled suspended materials due to the largest initial gradient of velocity. The resuspension of settled sediment on the bed takes place in relatively short time..