Assessment of Flocculation Kinetics of Cohesive Sediments from the Seine and Gironde Estuaries, France, through Laboratory and Field Studies

Mikes, D.; Manning, Andrew J.

doi:10.1061/(asce)ww.1943-5460.0000053

Cited by 26 publications

(18 citation statements)

References 44 publications

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“…Although in Manning and Schoellhamer (), the settling velocities of suspended flocs in San Francisco Bay are not shown to be a strong function of the floc size, for the sake of simplicity, we refer to the suspended sediment of the first size class as microflocs and the second class as macroflocs. This is consistent with the observation that the small microflocs generally settle at less than 1 mm s −1 , while macroflocs settle at

1 - 15

mm s −1 (Mikeš & Manning, ). it is possible to model flocculation and breakup in suspension by including source terms on the right‐hand side of equation to account for transfer of sediment mass between different floc size classes with the population balance approach (Lick et al, ; Sterling et al, ).…”

Section: Modeling Sediment Transport In San Francisco Baysupporting

confidence: 90%

Three‐Dimensional Modeling of Fine Sediment Transport by Waves and Currents in a Shallow Estuary

et al. 2018

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A suspended sediment transport model is implemented in the unstructured‐grid SUNTANS model and applied to study fine‐grained sediment transport in South San Francisco Bay. The model enables calculation of suspension of bottom sediment based on combined forcing of tidal currents and wind waves. We show that accurate results can be obtained by employing two‐size classes which are representative of microflocs and macroflocs in the Bay. A key finding of the paper is that the critical calibration parameter is the ratio of the erosion of the microflocs to macroflocs from the bed. Different values of this erosion ratio are needed on the shallow shoals and deeper channels because of the different nature of the sediment dynamics in these regions. Application of a spatially variable erosion ratio and critical shear stress for erosion is shown to accurately reproduce observed suspended sediment concentration at four‐field sites located along a cross‐channel transect. The results reveal a stark contrast between the behavior of the suspended sediment concentration on the shoals and in the deep channel. Waves are shown to resuspend sediments on the shoals, although tidal and wind‐generated currents are needed to mix the thin wave‐driven suspensions into the water column. The contribution to the suspended sediment concentration in the channel by transport from the shoals is similar in magnitude to that due to local resuspension. However, the local contribution is in phase with strong bottom currents which resuspend the sediments, while the contribution from the shoals peaks during low‐water slack tide.

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Section: Modeling Sediment Transport In San Francisco Baysupporting

confidence: 90%

Three‐Dimensional Modeling of Fine Sediment Transport by Waves and Currents in a Shallow Estuary

et al. 2018

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“…In such environments, conceptual models such as the ones proposed by Dyer () or Droppo (), argue that the aggregated size is mostly controlled by particle concentration, flow shear stress or both. These models are supported by numerous field (Mikeš and Manning, ) and laboratory (Stone and Krishnappan, ; Stone et al ., ) observations. They suggest that while soil particle physical, chemical and biological characteristics will have an effect on aggregate structure, both at detachment and within riverine flow (Walling and Moorehead, ; Ankers et al ., ), the down‐river particle characteristics within the flow will ultimately be determined by in‐channel hydrodynamic processes acting upon the particles.…”

Section: Introductionmentioning

confidence: 64%

From soil aggregates to riverine flocs: a laboratory experiment assessing the respective effects of soil type and flow shear stress on particles characteristics

Grangeon

Droppo

Legoût

et al. 2013

Hydrological Processes

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Abstract:Particles eroded from hillslopes and exported to rivers are recognized to be composite particles of high internal complexity. Their architecture and composition are known to influence their transport behaviour within the water column relative to discrete particles. To-date, hillslope erosion studies consider aggregates to be stable once they are detached from the soil matrix. However, lowland rivers and estuaries studies often suggest that particle structure and dynamics are controlled by flocculation within the water column. In order to improve the understanding of particle dynamics along the continuum from hillslopes to the lowland river environment, soil particle behaviour was tested under controlled laboratory conditions. Seven flume erosion and deposition experiments, designed to simulate a natural erosive event, and five shear cell experiments were performed using three contrasting materials: two of them were poorly developed and as such can not be considered as soils, whilst the third one was a calcareous brown soil. These experiments revealed that soil aggregates were prone to disaggregation within the water column and that flocculation may affect their size distribution during transport. Large differences in effective particle size were found between soil types during the rising limb of the bed shear stress sequence. Indeed, at the maximum applied bed shear stress, the aggregated particles median diameter was found to be three times larger for the well-developed soil than for the two others. Differences were smaller in the falling limb, suggesting that soil aggregates underwent structural changes. However, characterization of particles strength parameters showed that these changes did not fully turn soil aggregates into flocs, but rather into hybrid soil aggregate-floc particles.

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“…Turbulent mixing influences collisions, and therefore the potential for growth, but increases in G also lead to increased stress on the flocs and increases in breakup and erosion rates. Therefore, larger values of G lead to smaller equilibrium floc sizes in both the laboratory [e.g., Mietta et al ., ; Mikeš and Manning , ; Verney et al ., ] and field [e.g., Safak et al ., ; Ramírez‐Mendoza et al ., ], with d fe typically being

\propto η_{k}

[ Tambo and Hozumi , ; Akers et al ., ; van Leussen , ; Verney et al ., ; Kumar et al ., ]. G can also influence floc density.…”

Section: Introductionmentioning

confidence: 99%

Flocculation in a decaying shear field and its implications for mud removal in near‐field river mouth discharges

Strom

Keyvani²

2016

JGR Oceans

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We measure the change in floc size in a decaying shear field that mimics the decay found in a river mouth discharge. The primary questions explored are: (1) how far from equilibrium are the flocs during the decay? And, (2) how significant are the changes in size, and hence settling velocity, brought on by the changes in shear when it comes to predicting settling flux? These questions are examined in the laboratory using a camera system that allows for flocs to be sized within a turbulent suspension. We also examine how inclusion of various approaches to account for flocculation impacts the plume concentration and deposition rates in a simple river mouth discharge model. In the experiments, flocs grew from their initial size of 20–50 μm up to 100–200 μm due only to changes in shear over time scales of decay similar to those in a small river mouth discharge. It is estimated that such growth would lead to fourfold or greater fold increase in the mud settling velocity within the first few kilometers from the river mouth, even though floc sizes were only 0.5–0.8 of their equilibrium values. The plume modeling highlights the strong dependence of the mud deposition rate on the method chosen to account for flocs, and the importance of the settling to entrainment velocity ratio in dictating plume concentrations.

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Assessment of Flocculation Kinetics of Cohesive Sediments from the Seine and Gironde Estuaries, France, through Laboratory and Field Studies

Cited by 26 publications

References 44 publications

Three‐Dimensional Modeling of Fine Sediment Transport by Waves and Currents in a Shallow Estuary

Three‐Dimensional Modeling of Fine Sediment Transport by Waves and Currents in a Shallow Estuary

From soil aggregates to riverine flocs: a laboratory experiment assessing the respective effects of soil type and flow shear stress on particles characteristics

Flocculation in a decaying shear field and its implications for mud removal in near‐field river mouth discharges

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