Controls on floc growth in an energetic tidal channel
Controls on floc growth in an energetic tidal channel
复制标题
DOI：
10.1029/2011jc007094
复制
发表时间：
2012-02-14
影响因子：
3.6
通讯作者：
Graham, G. W.
中科院分区：
文献类型：
--
作者：
Braithwaite, K. M.;Bowers, D. G.;Graham, G. W.
在一个浅的、有能量的潮汐通道中连续测量了9个潮汐周期的湍流和悬浮粒子特性。用放置在海床框架上的LISST-100激光衍射仪测量了颗粒大小光谱。利用同一机架的1200 kHz ADCP测量了垂直电流分布，并利用结构函数法确定了湍流动能耗散率。在每个潮汐周期中，观测到中位颗粒大小以3倍或更多的规律变化，其中在退潮时观测到的颗粒最大，在最大洪水和退潮时观测到的颗粒最小。对这种变化最可能的解释是，粒子在低湍流时聚集，在快速流动时分裂。一个包含这些过程的简单动态絮凝模型与观测结果很好地吻合，特别是当考虑到粒径纵向梯度的潮汐平流时。如果颗粒有时间与环境条件达到平衡，该模型预测颗粒大小将与浓度和柯尔莫哥洛夫微尺度的乘积成正比。如果在颗粒大小和柯尔莫哥洛夫尺度测量之间允许一个相位滞后（30-60分钟），观测结果支持大多数潮汐周期的这一预测。这个相位滞后表示絮凝体对湍流变化作出反应的调整时间。中位粒径与Kolmogorov尺度的比例常数随粒径的增大而增大。
Measurements of turbulence and suspended particle characteristics have been made continuously for 9 tidal cycles in a shallow, energetic tidal channel. Particle-size spectra were measured with a LISST-100 laser diffraction instrument placed on a frame on the seabed. A 1200 kHz ADCP in the same frame was used to measure vertical current profiles and from these the turbulent kinetic energy dissipation rate was determined using the structure function method. Median particle size is observed to change in a regular way by a factor of 3 or more over each tidal cycle, with the largest particles observed at slack tide and the smallest at times of maximum flood and ebb. The most likely explanation of this change is that particles are aggregating at times of low turbulence and breaking up during fast flows. A simple dynamical flocculation model that incorporates these processes gives good agreement with observations, particularly if tidal advection of a longitudinal gradient in particle size is allowed for. If particles have time to reach equilibrium with ambient conditions, the model predicts that the particle size will be proportional to the product of concentration and the Kolmogorov microscale. The observations support this prediction on most tidal cycles if a phase lag (of 30-60 min) is allowed between the measurements of particle size and Kolmogorov scale. This phase lag represents the adjustment time for flocs to respond to change in turbulence. The constant of proportionality between median particle size and Kolmogorov scale increases with particle volume.