中文摘要：

根据2005年6月在长江口南支边滩的现场悬沙级配观测数据和悬沙水样的室内粒度分析数据,对分散状态与未分散状态下的悬沙级配的时空分布特征、絮团对悬沙级配的影响及其现场含量等进行了研究。室内粒度分析结果表明,在颗粒分散条件下,悬沙组成较细,以粉砂和粘土为主,悬沙级配的时间和空间变化较小;悬沙级配有明显的垂向分布规律,平均粒径等在垂向上呈线性分布。现场观测结果显示,在颗粒未分散条件下,悬沙组成较粗,粒径大于63μm和4~63μm的颗粒是悬沙的主要成分,悬沙级配在潮周期内变化显著。对比表明,悬沙级配的现场与室内观测结果差异显著,前者明显粗于后者,絮凝作用是造成差异的主因,絮团在现场悬沙中的含量估计超过60%,絮凝作用能够使参加和不参加絮凝作用的泥沙颗粒在絮凝前、后的体积含量发生明显改变。絮团与流速和悬沙浓度的关系复杂,在潮周期内的部分时段里,悬沙平均粒径与流速和悬沙浓度存在较好的线性关系。

英文摘要：

Grain size distribution of suspended sediment on the nearshore zone of the South Branch,Changjiang Estuary,is investigated based on in situ measurements from June 20 to 24,2005,and water samples of the above-seabed layers that were collected on June 22.The study is focused on the spatial and temporal patterns of grain-size distributions of suspended sediment under the condition of flocculation and dispersion,the influence of flocculation process on grain-size distributions,and the in situ content of the flocculation.The results of the water-sample analysis show that：1） the isolated suspended sediment is fine-grained and dominated by silt and clay,with a mean grain size of 6μm;2） while the temporal and vertical variation of the grain-size parameters within a tidal cycle is relatively insignificant,the vertical distribution pattern of grain-size parameters tends to be regular during the most time of a tidal cycle;3） a linear relationship exists between grain-size parameters（e.g.,mean grain size） and above-seabed heights;In situ measurements indicate that the suspended sediment is coarse-grained and dominated by particles larger than 63μm and 4～63μm,and variation in grain-size distributions is significant.A significant difference between grain-size distributions from the in situ and laboratory measurements is thus observed and can be mainly contributed to the flocculation process that increases the volume of the suspended sediment and,therefore,significantly changes the particle content before and after flocculating.The proportion of flocculation in the in situ sediment is estimated to be more than 60%.The analysis suggests that the relationship between mean grain size of suspended sediment,and current velocity and suspended-sediment concentration tends to be linear during part of a tidal cycle.