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A study of the temporal variability in particle size in a high-energy regime

机译：高能条件下粒径随时间变化的研究

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The variation in sediment particle size and concentration has been measured over a tidal cycle in an area of strong tidal energy and on the fringe of a turbidity maximum in the Irish Sea. Laser In-Situ Scattering and Transmissometry (LISST 100) particle size data were collected and subjected to harmonic analysis. The results show a classical 'twin-peaked' signal consisting of a quarter-diurnal cycle superimposed on a semi-diurnal one. In previous studies this has been interpreted as a combination of resuspension and settling (producing the quarter-diurnal cycle) and advection of a horizontal gradient (producing the semi-diurnal one). However, analysis of the quarter-diurnal signal for different particle sizes shows that it is in phase with a likely resuspension signal for small particles, but out of phase for the larger particles. An explanation of this, proposed here, is that the larger particles become disaggregated by the strong shear at maximum flow speeds, producing a maximum in the concentration of fine particles and a minimum in the large particle concentration. The reverse is seen to occur at slack water. We estimate that this aggregation/disaggregation process accounts for approximately 1/4 of the quarter-diurnal signal. The conclusion is that previous studies may have considerably over-estimated the resuspension of suspended sediments by tidal streams.
机译：在爱尔兰海中，在一个潮汐周期内，在潮汐能强的地区和最大浑浊度的边缘测量了沉积物粒径和浓度的变化。收集激光原位散射和透射法（LISST 100）粒度数据并进行谐波分析。结果显示了一个经典的“双峰”信号，该信号由一个四分之一的昼夜周期叠加在一个半昼夜周期上。在以前的研究中，这被解释为重悬和沉降（产生四分之一日循环）和水平梯度的平流（产生半日数）的组合。但是，对不同粒径的四分之一昼夜信号的分析表明，对于小颗粒，该信号与可能的重悬浮信号同相，但对于大颗粒，其信号却异相。这里提出的一个解释是，较大的颗粒在最大流速下由于强剪切力而分解，从而产生最大的细颗粒浓度和最小的大颗粒浓度。看到相反的情况发生在松弛的水中。我们估计此聚集/分解过程大约占四分之一昼夜信号的1/4。结论是先前的研究可能大大高估了潮汐流对悬浮沉积物的重悬浮。

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