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Modeling flocculation in a hypertidal estuary

机译：模拟潮汐河口的絮凝

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When fine particles are involved, cohesive properties of sediment can result in flocculation and significantly complicate sediment process studies. We combine data from field observations and state-of-the-art modeling to investigate and predict flocculation processes within a hypertidal estuary. The study site is the Welsh Channel located at the entrance of the Dee Estuary in Liverpool Bay. Field data consist of measurements from a fixed site deployment during 12-22 February 2008. Grain size, suspended sediment volume concentration, and current velocity were obtained hourly from moored instruments at 1.5 m above bed. Near-bottom water samples taken every hour from a research vessel are used to convert volume concentrations to mass concentrations for the moored measurements. We use the hydrodynamic model Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) coupled with the turbulence model General Ocean Turbulence Model (GOTM) and a sediment module to obtain three-dimensional distributions of suspended particulate matter (SPM). Flocculation is identified by changes in grain size. Small floes were found during flood and ebb periods- and correlate with strong currents-due to breakup, while coarse floes were present during slack waters because of aggregation. A fractal number of 2.4 is found for the study site. Turbulent stresses and particle settling velocities are estimated and are found to be related via an exponential function. The result is a simple semiempirical formulation for the fall velocity of the particles solely depending on turbulent stresses. The formula is implemented in the full three-dimensional model to represent changes in particle size due to flocculation processes. Predictions from the model are in agreement with observations for both settling velocity and SPM. The SPM fortnight variability was reproduced by the model and the concentration peaks are almost in phase with those from field data.
机译：当涉及到细颗粒时，沉积物的内聚性会导致絮凝并使沉积过程研究变得非常复杂。我们将现场观察和最新模型的数据相结合，以调查和预测潮汐河口内的絮凝过程。研究地点是位于利物浦湾迪伊河口入口处的威尔士海峡。现场数据包括2008年2月12日至22日在固定地点部署的测量结果。每小时从床上方1.5 m的系泊仪器上获得粒度，悬浮沉积物浓度和流速。每小时从研究船上采集的近底部水样用于将体积浓度转换为质量浓度，以进行停泊测量。我们将水动力模型Proudman海洋学实验室沿海海洋建模系统（POLCOMS）与湍流模型，通用海洋湍流模型（GOTM）和泥沙模块结合使用，以获得悬浮颗粒物（SPM）的三维分布。絮凝通过晶粒尺寸的变化来识别。在洪水和退潮期发现小絮凝物，并且由于破裂而与强流相关，而在松散水域由于聚集而存在粗大的絮凝物。研究地点的分形数为2.4。估计了湍流应力和颗粒沉降速度，并发现它们通过指数函数相关。结果是仅取决于湍流应力的颗粒下落速度的简单半经验公式。该公式在完整的三维模型中实现，以表示由于絮凝过程而引起的粒径变化。该模型的预测与沉降速度和SPM的观察结果一致。该模型再现了SPM的两周变化，浓度峰值与现场数据的浓度峰值几乎同相。

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