Cohesive Sediment Flocculation and the Application to Settling Flux Modelling

Manning, Andrew J.; Baugh, John V.; Spearman, J.; Whitehouse, R.J.S.

doi:10.5772/16055

Cited by 8 publications

(6 citation statements)

References 90 publications

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“…4d, e). Including R in the prediction of SSC xs resulted in more normally distributed residuals in the WY 2009-2011and WY 2013-2016.…”

Section: Resultsmentioning

confidence: 99%

“…At the mid-depth sensor, accounting for vertical changes in SSC using Eq. 15 (SSC xs T b ; R; z H À Á ), compared to the typically utilized regression (SSC xs (T b )) that does not account for vertical changes in SSC, changes the sign of ∑Q s from sediment export (i.e., net seaward sediment flux) to sediment import (i.e., net landward sediment flux) for WY 2009-2011and WY 2013-2016). The change in ∑Q s sign at the mid-depth sensor occurs with and without missing data (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Suspended sediment in the San Francisco Estuary is predominantly composed of silt and clay; the sand fraction is greater in Central Bay and increases with landward distance in North Bay (Manning and Schoellhamer 2013). Large low-density fast-settling benthic macroflocs (e.g., Manning et al 2011;Zhang et al 2018), typically formed through flocculation (often referred to as aggregation) of much smaller-sized higherdensity aggregates known as microflocs (e.g., Eisma 1986;Manning 2004b, dominate suspended sediment particle mass in South Bay, while microflocs tend to dominate the suspended sediment particle mass in more marine locations of Central Bay and San Pablo Bay (Manning and Schoellhamer 2013;Manning et al 2010).…”

Section: Study Areamentioning

confidence: 99%

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Suspended Sediment Flux in the San Francisco Estuary: Part I—Changes in the Vertical Distribution of Suspended Sediment and Bias in Estuarine Sediment Flux Measurements

Livsey

Downing-Kunz

Schoellhamer

et al. 2020

Estuaries and Coasts

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In this study, we investigate how changes in the vertical distribution of suspended sediment affect continuous suspended sediment flux measurements at a location in the San Francisco Estuary. Current methods for measuring continuous suspended sediment flux estimates relate continuous estimates of suspended-sediment concentration (SSC) measured at-a-point (SSC pt ) to discrete cross-section measurements of depth-averaged, velocity-weighted SSC (SSC xs ). Regressions that compute SSC xs from continuous estimates of SSC pt require that the slope between SSC pt and SSC xs , controlled by the vertical distribution of SSC, is fixed. However, in tidal systems with suspended cohesive sediment, factors that control the vertical SSC profile-vertical turbulent mixing and downward settling of suspended sediment mediated by flocculation of cohesive sediment-constantly vary through each tide and may exhibit systematic differences between flood and ebb tides (tidal asymmetries in water velocity or particle size). We account for changes in the vertical SSC profile on estimates of SSC xs using time series of the Rouse number of the Rouse-Vanoni-Ippen equation combined with optical turbidity measurements, a surrogate for SSC pt , to predict SSC xs from 2009 to 2011 and 2013. Time series of the Rouse number were estimated by fitting the Rouse-Vanoni-Ippen equation to SSC estimated from optical-turbidity measurements taken at two elevations in the water column. When accounting for changes in the vertical SSC profile, changes in not only the magnitude but also the direction of cumulative sediment-flux measurements were observed. For example, at a mid-depth sensor, sediment flux estimates changed from − 319 kt (± 65 kt, negative indicating net seaward transport) to 482 kt (± 140 kt, positive indicating net landward transport) for 2009-2011 and from − 388 kt (± 140 kt) to 1869 kt (± 406 kt) for 2013-2016. At the study location, estimation of SSC xs solely from SSC pt resulted in sediment flux values that were underestimates on flood tides and overestimates on ebb tides. This asymmetry is driven by covariance between water velocity and particle settling velocity (W s ) with larger W s on flood compared to ebb tides. Results of this study indicate that suspendedsediment-flux measurements estimated from point estimates of SSC may be biased if systematic changes in the vertical distribution of SSC are unaccounted for.

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“…4d, e). Including R in the prediction of SSC xs resulted in more normally distributed residuals in the WY 2009-2011and WY 2013-2016.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Study Areamentioning

confidence: 99%

See 1 more Smart Citation

Suspended Sediment Flux in the San Francisco Estuary: Part I—Changes in the Vertical Distribution of Suspended Sediment and Bias in Estuarine Sediment Flux Measurements

Livsey

Downing-Kunz

Schoellhamer

et al. 2020

Estuaries and Coasts

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“…9). As Manning et al (2011) noted, flocculation plays a major role in mud sedimentation processes within estuaries. Below the flocculent layer is a denser, muddy sand with abundant ovoid faecal pellets with a mean length of 400 mm and, in places, fine to medium quartz.…”

Section: Comparison To Modern Estuarine Trochammina Known From Elsewhere In Australiamentioning

confidence: 87%

Invasive Japanese foraminifera in a south-west Australian estuary

Tremblin

Holzmann

Parker

et al. 2021

Mar. Freshwater Res.

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An invasive foraminiferan is recorded for the first time in an Australian estuary. Trochammina hadai, originally described as endemic from Japan and subsequently found to be alien in coastal waters of California and Brazil, has been identified in estuarine sediment in the vicinity of Bunbury Port in Western Australia. Species determination is based on morphological, molecular and ecological similarities to the Japanese type. The species has not been recorded in other estuaries in Australia. Bunbury Port is a major exporter of woodchip to Japan and the introduction of T. hadai may have come from ballast water out of shallow-draught woodchip vessels. Small sediment samples of estuarine mud obtained at water depths of ~5 m contain abundant T. hadai (on average ~0.4 mm in adult diameter) that are easily recognised in microscopic view of the sediment surface by their bright reddish-brown colour. The collection of sediment samples from the estuarine floor and ballast water, and the examination of these for foraminifers, may provide a useful indicator in estuaries for the possible presence of other exotic species, particularly in the vicinity of ports.

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“…Cohesive individual particles in suspension are attracted to one another to form flocculi, which themselves can join together to form microflocs which join to form macroflocs; this is the basis of Krone's (1963) classic hierarchical order of aggregation theory. Biogenic cohesion allows silt and even fine sand particles to form flocs with these cohesive flocs (Manning et al 2010, Manning et al 2011aSpearman et al 2011). For example, epipsammic diatoms can attach to sand grains using their mucilage stalks (Harper and Harper 1967), and Little (2000) found that sticky EPS can efficiently bind to fine sand grains.…”

Section: Cohesive Particlesmentioning

confidence: 99%

On the hindered settling of sand-mud suspensions

Spearman

Manning

2017

Ocean Dynamics

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Hindered settling, the process by which the settling of sediment particles becomes impeded due to the proximity of other sediment particles, can be an important process for the coastal modeller, especially in highly muddy environments. It is also a significant process in other disciplines such as chemical engineering, the modelling of debris flow, the study of turbidites, piping of slurries and the understanding of processes occurring within a dredger hopper. This study first examines the hindered settling behaviour of monodisperse suspensions in order to create a framework for polydisperse hindered settling that works for both non-cohesive and cohesive suspensions. The Richardson-Zaki equation is adapted to make it compatible with the changes with viscosity that occur near the point at which suspensions become solid. The modified monodisperse settling equation is then compared to data for hindered settling of cohesive suspensions and shown to be consistent with the transition between hindered settling and the initial permeability phase of consolidation. Based on the monodisperse framework developed initially, this paper proposes a hindered settling model for sand/mud mixtures which is based on a modification of the Masliyah (1979) and Lockett and Bassoon (1979) hindered settling equation. The model is shown to reproduce the hindered settling of a variety of different sediment mixtures whilst reducing the extent of empiricism often associated with the modelling of polydisperse hindered settling of mud/sand mixtures.

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Cohesive Sediment Flocculation and the Application to Settling Flux Modelling

Cited by 8 publications

References 90 publications

Suspended Sediment Flux in the San Francisco Estuary: Part I—Changes in the Vertical Distribution of Suspended Sediment and Bias in Estuarine Sediment Flux Measurements

Suspended Sediment Flux in the San Francisco Estuary: Part I—Changes in the Vertical Distribution of Suspended Sediment and Bias in Estuarine Sediment Flux Measurements

Invasive Japanese foraminifera in a south-west Australian estuary

On the hindered settling of sand-mud suspensions

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