The study on grain-size distribution of suspended sediment and resuspension process on the Chongming east intertidal and subtidal zones in the Changjiang Estuary in China

On the basis of the measurements of suspended sediment and current velocity at the two measurement stations in the Chongming east intertidal and subtidal zones in the Changjiang Estuary, during spring and neap tides in October 2006, the characteristics of grain-size distributions of suspended sediment and resuspension process are analyzed.The results show that the suspended sediment during spring and neap tides is fine-grained, with a meangrain-size of 6 m.The averaged grain-size of suspended sediment in the intert idalzone is slightly coarser than that in the subtidal zone.Similarly, the meangrain-size in spring tide is coarser than neap tide.The meangrain-size decreases from the bottom to the top within the water column.The relationships between mean grain-size with current velocity and suspended sediment content are insignificant, which is influenced by the factors of spatial variations of seabed sediment, intensity of resuspension, grain-size distributions of resuspended seabed sediments, and resuspension of fluid mud.In response to the complex distribution of seabed sediment, the spatial variation of resuspension is significant in the study area.During the survey period, the resuspension is weak at the places w ere the mean grain-size of seabed sediments is bigger than 60 m, and the seabed sediment transports mainly as bedload.However, at the place where the seabed sediment is fine-grained, with a mean grain-size of 5~11 m, the resuspension is significant and the grain-size distributions of suspended and seabed sediments are almostidentical under strong hydrodynamic condition.The amplitude of resuspension in the spring tide is five to ten factors of neap tide, the mean content of the suspended sediment generated by resuspension is 8%~20% and the content of it is 0.03~0.47 kg/m³ at the bottom layers.