长江口崇明东滩水域悬沙粒径组成和再悬浮作用特征

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

根据2006年10月在崇明东滩潮间带和潮下带两个站位的大小潮水文泥沙观测资料和悬沙水样的室内粒度分析资料,对悬沙粒径的时空分布特征及其与流速等的关系进行了分析,并对再悬浮特点进行了探讨,结果表明,大小潮期间的悬沙颗粒组成较细,平均粒径的均值仅为6μm;大潮时的悬沙粒径略粗于小潮的,潮间带的略粗于潮下带的;由底床向上悬沙粒径趋于减小。悬沙粒径与流速、悬沙含量无明显的统计学关系,底质粒径、再悬浮强度和再悬浮泥沙粒径的空间变化以及浮泥的悬浮作用等是主要的影响因素。由于底质粒径的空间分布复杂,在东滩水域再悬浮具有明显的空间变化。在底质平均粒径大于60μm的粗颗粒沉积区,大小潮的再悬浮作用微小,底质以推移质运动为主。在底质平均粒径介于5-11μm的细颗粒沉积区上,悬沙级配与底质级配基本相同,该区域是再悬浮的主要发生源地;悬沙级配的变化过程揭示,再悬浮对底层悬沙的贡献率平均为8%-20%,大潮时的再悬浮强度是小潮的5-10倍,由底质再悬浮产生的悬沙在底部水层中的平均含量约为0.03-0.47 kg/m3。

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 mean grain-size of 6um. The averaged grain-size of suspended sediment in the intertidal zone is slightly coarser than that in the subtidal zone. Similarly, the mean grain-size in spring tide is coarser than neap tide. The mean grain-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 where the mean grainsize of seabed sediments is bigger than 60 um, 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 5-11um, the resuspension is significant and the grain-size distributions of suspended and seabed sediments are almost identical 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/m^3 at the bottom layers.