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Floeculation settling characteristics of mud: sand mixtures

机译：泥沙混合的絮凝沉降特性

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摘要

When natural muds become mixed with sandy sediments in estuaries, it has a direct effect on the flocculation process and resultant sediment transport regime. Much research has been completed on the erosion and consolidation of mud/sand mixtures, but very little is known quantitatively about how mixed sediments interact whilst in suspension, particularly in terms of flocculation. This paper presents the settling velocity findings from a recent laboratory study which examined the floeculation dynamics for three different mud/sand mixtures at different concentrations (0.2-5 g.l~(-1)) and turbulent shear stresses (0.06-0.9 Pa) in a mini-annular flume. The low intrusive video-based Laboratory Spectral Floeculation Characteristics instrument was used to determine floc/aggregate properties (e.g., size, settling velocity, density and mass) for each population. Settling data was assessed in terms of macrofloc (> 160 μm) and microfloc (< 160 μm) settling parameters: Ws_(macro) and Ws_(micro), respectively. For pure muds, the macroflocs are regarded as the most dominant contributors to the total depositional flux. The parameter-ised settling data indicates that by adding more sand to a mud/sand mixture, the fall velocity of the macrofloc fraction slows and the settling velocity of microflocsrnquickens. Generally, a mainly sandy suspension comprising 25% mud and 75% sand (25M:75S), will produce resultant Ws_(macro) which are slower than Ws_(micro). The quickest Ws_(micro) appears to consistently occur at a higher level of turbulent shear stress (τ～0.6 Pa) than both the macrofloc and microfloc fractions from suspensions of pure natural muds. Floeculation within a more cohesively dominant muddy-sand suspension (I.e., 75M:25S) produced macroflocs which fell at similar speeds (±10%) to pure mud suspensions at both low (200 mg l~(-1)) and intermediate (1 g l~(-1)) concentrations at all shear stress increments. Also, low sand content suspensions produced Ws_(macro) values that were faster than the Ws_(micro) rates. In summary, the experimental results of the macrofloc and microfloc settling velocities have demonstrated that floeculation is an extremely important factor with regards to the depositional behaviour of mud/sand mixtures, and these factors must be considered when modelling mixed sediment transport in the estuarine or marine environment.
机译：当天然泥浆在河口中混入沙质沉积物时，会直接影响絮凝过程和由此产生的泥沙输送方式。关于泥浆/砂混合物的侵蚀和固结，已经完成了许多研究，但是关于混合沉积物在悬浮过程中如何相互作用的定量研究很少，尤其是在絮凝方面。本文介绍了最近一项实验室研究的沉降速度发现，该研究研究了三种不同泥浆/砂混合物在不同浓度（0.2-5 gl〜（-1））和湍流剪切应力（0.06-0.9 Pa）下的絮凝动力学。微型环形水槽。基于低侵入性视频的实验室光谱絮凝特性仪器用于确定每个种群的絮凝物/聚集体特性（例如大小，沉降速度，密度和质量）。沉降数据根据大絮凝物（> 160μm）和微絮凝物（<160μm）沉降参数评估：分别为Ws_（macro）和Ws_（micro）。对于纯泥浆，大絮凝物被认为是总沉积通量的最主要贡献者。参数化沉降数据表明，通过向泥浆/砂混合物中添加更多的沙子，大絮凝物馏分的下落速度会减慢，微絮凝物的沉降速度会降低。通常，主要是含25％的泥和75％的砂（25M：75S）的沙质悬浮液会产生比Ws_（micro）慢的合成Ws_（macro）。最快的Ws_（micro）似乎始终在比纯天然泥浆悬浮液中的大絮凝物和微絮凝物分数更高的湍流剪应力（τ〜0.6 Pa）处发生。在凝聚力更强的主导性泥沙悬浮液（即75M：25S）中的絮凝产生了大絮凝物，在低（200 mg l〜（-1））和中度（1）时，其絮凝速度与纯泥悬浮液相似（±10％）。在所有剪应力增量下都达到gl〜（-1））的浓度。同样，低含沙量的悬浮液产生的Ws_（宏观）值比Ws_（微）速率快。总之，宏观絮凝物和微絮凝物沉降速度的实验结果表明，絮凝是影响泥浆/砂混合物沉积行为的极其重要的因素，在模拟河口或海洋中的混合沉积物运移时必须考虑这些因素。环境。

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  • 来源
    《Ocean Dynamics》 |2010年第2期|p.237-253|共17页
  • 作者

    Andrew J. Manning; John V. Baugh; Jeremy R. Spearman; Richard J. S. Whitehouse;

  • 作者单位

    Coasts & Estuaries Group, HR Wallingford, Howbery Park, Wallingford, Oxfordshire OX10 8BA, UK School of Marine Science & Engineering, University of Plymouth, Portland Square Building (A410), Plymouth, Devon PL4 8AA, UK;

    Coasts & Estuaries Group, HR Wallingford, Howbery Park, Wallingford, Oxfordshire OX10 8BA, UK;

    Coasts & Estuaries Group, HR Wallingford, Howbery Park, Wallingford, Oxfordshire OX10 8BA, UK;

    Coasts & Estuaries Group, HR Wallingford, Howbery Park, Wallingford, Oxfordshire OX10 8BA, UK;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    mixed sediment; floeculation; settling velocity; laboratory simulation;

    机译：混合沉积物絮凝沉降速度实验室模拟;

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