On the variability of near-bed floc size due to complex interactions between turbulence, SSC, settling velocity, effective density and the fractal dimension of flocs

Yang, Yang; Wang, Ya Ping; Li, Chunyan; Gao, Shu; Shi, Benwei; Zhou, Linfeng; Wang, Dandan; Li, Gaocong; Dai, Caili

doi:10.1007/s00367-016-0434-x

Cited by 19 publications

(5 citation statements)

References 88 publications

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“…where v is the molecular kinematic viscosity. According to field observations, the average flocculation settling velocity was in the order of 10 −5 to 10 −3 , similar to other estuarine results [68][69][70][71]. Table 1 lists the parameter values in the sediment model.…”

Section: Sediment Modulesupporting

confidence: 81%

Numerical Simulation and Analysis of Water and Suspended Sediment Transport in Hangzhou Bay, China

Huang

Yuan

Zhu

2022

JMSE

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Hangzhou Bay is a large, high-turbidity shallow bay located on the southern side of the Changjiang Estuary, China. The process and dynamic mechanisms of water and sediment transport in the bay are not yet clear. An improved three-dimensional sediment numerical model that combined various dynamic factors was established to simulate and analyze these mechanisms. The residual current cannot properly represent the net water and sediment transport, and the residual unit width water flux (RUWF) and residual unit width sediment flux (RUSF) were used to explain the water and sediment transport. The results of numerical simulations indicate that in summer, the surface RUWF from the Changjiang Estuary near Nanhui Cape flows westward along the coast, in which the major part flows southward to the Zhenhai area, and the small part flows further westward along the north coast and then turns to the south coast and eastward, forming the water transport pattern of north-landward and south-seaward, which is stronger in the spring tide than in the neap tide. The bottom RUWF near Zhenhai flows northward to Nanhui Cape in the neap tide, which is larger in the neap tide than in the spring tide. In the middle and western parts of the bay, the RUWF has the same pattern as the surface water transport and is stronger in the spring tide than in the neap tide. The pattern of RUSF is roughly similar to the water flux transport. During the spring tide, the water and sediment transport fluxes near Nanhui Cape are from the Changjiang Estuary into Hangzhou Bay, but from Hangzhou Bay into the Changjiang Estuary during the neap tide. In the winter, the distributions of RUWF, RUSF, and suspended sediment concentration (SSC) are similar to those in the summer. In addition, the distance of surface water transport westward along the north coast is shorter than that in the summer, the magnitude of the bottom RUWF is smaller than that in the summer due to the weaker salinity gradient, and the bottom RUSF near Nanhui Cape is weaker than that in the summer during the neap tide. The net transect water flux (NTWF) and the net transect sediment flux (NTSF) near Nanhui Cape are from the Changjiang Estuary into Hangzhou Bay during the spring tide; during the neap tide, the NTWF is still from the Changjiang Estuary into Hangzhou Bay, but the NTSF is from Hangzhou Bay into the Changjiang Estuary because the SSC is much higher in the bottom layer than in the surface layer. The dynamic reason for the temporal and spatial variation in RUWF and RUSF is that the barotropic pressure gradient force is larger than the baroclinic pressure gradient force during the spring tide and is the opposite during the neap tide.

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Section: Sediment Modulesupporting

confidence: 81%

Numerical Simulation and Analysis of Water and Suspended Sediment Transport in Hangzhou Bay, China

Huang

Yuan

Zhu

2022

JMSE

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“…The concentration of C wash was set to the minimum SPM concentration observed during high water slack following Cartwright et al (2013). Recent studies show the applicability of this method throughout different field situations, supporting its relevance for settling velocity estimates in the field (Brand et al, 2010;Wang et al, 2013;Yang et al, 2016). Before calculating turbulent fluctuations, the raw data was preprocessed to remove observational artifacts as follows.…”

Section: Reynolds-flux Methods (Wsadv)mentioning

confidence: 99%

“…We conducted an intensive short-term field campaign investigating flocculation dynamics and testing the applicability of two state of the art methods on providing in-situ estimates of settling velocities in an intertidal channel. Previous applications of these methods by Fugate and Friedrichs (2002), Voulgaris and Meyers (2004), Wang et al (2013) and Yang et al (2016) provided an inspiring first appraisal of the possibilities of these methods in nonstationary intertidal systems. Nevertheless, (1) the influence of along-channel gradients and their associated flux divergence as a cause for violating underlying assumptions of wsADV estimates, (2) and the influence of changing primary particle populations on wsLISST estimates, has not been identified yet.…”

Section: Introductionmentioning

confidence: 99%

Field estimates of floc dynamics and settling velocities in a tidal creek with significant along-channel gradients in velocity and SPM

Schwarz

Cox

Engeland

et al. 2017

Estuarine, Coastal and Shelf Science

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A short-term intensive measurement campaign focused on flow, turbulence, suspended particle concentration, floc dynamics and settling velocities were carried out in a brackish intertidal creek draining into the main channel of the Scheldt estuary. We compare in situ estimates of settling velocities between a laser diffraction (LISST) and an acoustic Doppler technique (ADV) at 20 and 40 cm above bottom (cmab). The temporal variation in settling velocity estimated were compared over one tidal cycle, with a maximum flood velocity of 0.46 m s À1 , a maximum horizontal ebb velocity of 0.35 m s À1 and a maximum water depth at high water slack of 2.41 m. Results suggest that flocculation processes play an important role in controlling sediment transport processes in the measured intertidal creek. During high-water slack, particles flocculated to sizes up to 190 mm, whereas at maximum flood and maximum ebb tidal stage floc sizes only reached up to 55 mm and 71 mm respectively. These large differences indicate that flocculation processes are mainly governed by turbulence-induced shear rate. In this study, we specifically recognize the importance of along-channel gradients that places constraints on the application of the acoustic Doppler technique due to conflicts with the underlying assumptions. Along-channel gradients were assessed by additional measurements at a second location and scaling arguments which could be used as an indication whether the Reynolds-flux method is applicable. We further show the potential impact of along-channel advection of flocs out of equilibrium with local hydrodynamics influencing overall floc sizes.

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“…The semidiurnal macro‐tidal regime has an average tidal range of 3.9–5.5 m (e.g., Ren, ; Yang et al, ), with higher tidally averaged current velocity in the middle intertidal mudflat than in the upper mudflat (Wang et al, ). During VSWS, the velocity maximum may last a few minutes or, in some rare cases, just several seconds, but these periods are characterized by large concentrations of suspended sediment that are commonly >1 kg/m 3 (Gao, ).…”

Section: Study Areamentioning

confidence: 99%

Erosion and Accretion on a Mudflat: The Importance of Very Shallow‐Water Effects

et al. 2017

Self Cite

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Understanding erosion and accretion dynamics during an entire tidal cycle is important for assessing their impacts on the habitats of biological communities and the long‐term morphological evolution of intertidal mudflats. However, previous studies often omitted erosion and accretion during very shallow‐water stages (VSWS, water depths < 0.20 m). It is during these VSWS that bottom friction becomes relatively strong and thus erosion and accretion dynamics are likely to differ from those during deeper flows. In this study, we examine the contribution of very shallow‐water effects to erosion and accretion of the entire tidal cycle, based on measured and modeled time‐series of bed‐level changes. Our field experiments revealed that the VSWS accounted for only 11% of the duration of the entire tidal cycle, but erosion and accretion during these stages accounted for 35% of the bed‐level changes of the entire tidal cycle. Predicted cumulative bed‐level changes agree much better with measured results when the entire tidal cycle is modeled than when only the conditions at water depths of >0.2 m (i.e., probe submerged) are considered. These findings suggest that the magnitude of bed‐level changes during VSWS should not be neglected when modeling morphodynamic processes. Our results are useful in understanding the mechanisms of micro‐topography formation and destruction that often occur at VSWS, and also improve our understanding and modeling ability of coastal morphological changes.

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On the variability of near-bed floc size due to complex interactions between turbulence, SSC, settling velocity, effective density and the fractal dimension of flocs

Cited by 19 publications

References 88 publications

Numerical Simulation and Analysis of Water and Suspended Sediment Transport in Hangzhou Bay, China

Numerical Simulation and Analysis of Water and Suspended Sediment Transport in Hangzhou Bay, China

Field estimates of floc dynamics and settling velocities in a tidal creek with significant along-channel gradients in velocity and SPM

Erosion and Accretion on a Mudflat: The Importance of Very Shallow‐Water Effects

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