Characteristics of suspended flocs and the combined action of contributing factors in Yangtze Estuary: A case study on the significant differences between the inner estuary and the mouth area
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摘要: 絮凝对河口细颗粒悬沙运动起着极其重要的作用.为深入探讨长江口悬浮絮凝体的特征及其主要影响因子的综合作用，于2014年10月19-23日（长江口径流量、潮差、风浪均接近多年平均值）利用多种仪器在人类活动干扰较小的南支-北港-口外海滨水域进行了综合现场观测和取样，获得了四个潮流特征时刻（涨急、涨憩、落急、落憩）的悬浮絮凝体粒径、分散粒径（即分散悬沙的原始粒径）、悬沙浓度、体积浓度、流速流向、盐度等数据.利用灰色关联度分析方法分析五大影响因子（悬沙浓度、体积浓度、流速、盐度和分散粒径）对絮凝体粒径和有效密度影响程度.结果表明，在相同体积水体中，口门最大浑浊带测点的絮凝体相对口内河槽测点数量多、粒径小，絮凝体内粘土颗粒少、空隙大、自由水多.在口内河槽，絮凝体粒径主要受悬沙浓度、分散粒径和体积浓度控制，有效密度主要受到分散粒径、悬沙浓度和流速控制；在口门最大浑浊带，絮凝体粒径的主控因子是流速，有效密度主要受到盐度、悬沙浓度控制.Abstract: Flocculation plays a vital role in the transport of estuarine fine suspended sediments. To study the natural situation and the main influencing factors of fine suspended sediment flocculation, in-situ observations were carried out along the South Branch to the North Channel of the Yangtze Estuary from 19th to 23th October 2014 (During that time, river discharge, tidal range and wind waves have same value to annual mean value). Floc size, dispersed particle size, volume concentration (VC), suspended sediment concentration (SSC), salinity, temperature and flow velocities were measured at four characteristic moments at four sites. We study the relation between median floc size, as well as effective density, and the five influencing factors with the Grey relational analysis.The results shows that, in the same water volume, flocs in the Turbidity Maximum Zone has more floc numbers and smaller floc size; that floc inside has less clay particles, larger gap and more free water compare to the inner estuary. In the inner estuary, critical factors influencing floc sizes are SSC, dispersed particle size, VC, and critical factors influencing effective density were dispersed particle size, SSC, velocity. In the Turbidity Maximum Zone of the mouth area, the critical factor influencing floc sizes is velocity and the critical factors influencing effective density are salinity and SSC.
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Key words:
- suspended flocs /
- influencing factors /
- grey relational analysis /
- Yangtze Estuary
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图 3 长江口4个测点4个特征时刻时絮凝体中值粒径(a)、分散中值粒径(b)、悬沙浓度(c)、体积浓度(d)、有效密度(e)的剖面平均值
Fig. 3 The vertical average value of the floc median sizes (a), single particle median sizes (b), suspended sediment concentrations (SSC)(c), volume concentrations (VC)(d) and effective densities (e) in the four characteristic moment at the four observation sites in Yangtze Estuary
图 4 长江口分散悬沙的粒度频率分布曲线图
Fig. 4 The frequency distribution versus log diameter of suspended sediments in Yangtze Estuary
图 5 口内河槽与口门最大浑浊带水体中的絮凝体分布模式
Fig. 5 The flocs distribution patternsin the waters between the inner estuary and the Turbidity Maximum Zone of the mouth area
图 6 口内河槽测点与口门最大浑浊带测点关联度比较
注: 观测期间口内河槽盐度无显著变化, 故图中无盐度关联度分析结果
Fig. 6 The relational grade's contrast between the inner estuary and the Turbidity Maximum Zone of the mouth area
图 7 5个影响因子分别与絮凝体粒径和有效密度的关系
注: 图中数据为4个现场观测点在4个特征时刻按照六层法分层的观测结果
Fig. 7 The relation between median flocsize, as well as effective density, and the five influencing factors
表 1 现场观测所用仪器及其观测项目
Tab. 1 Observation instruments and measured parameters
仪器名称 采样频率 观测项目 LISST-100现场激光粒度仪 1Hz 絮凝体粒级分布 OBS-3A光学后向散射浊度计 1Hz 浊度、盐度 Valeport-106自容点式流速仪 1Hz 表层流速 ADCP-300k多普勒流速剖面仪 0.1Hz 剖面流速、流向 
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