The University of Southampton
University of Southampton Institutional Repository

Estuarine mud flocculation properties determined using an annular mini-flume and the LabSFLOC system

Estuarine mud flocculation properties determined using an annular mini-flume and the LabSFLOC system
Estuarine mud flocculation properties determined using an annular mini-flume and the LabSFLOC system
Most entrained estuarine sediment mass occurs as flocs. Parameterising flocculation has proven difficult as it is a dynamically active process dependent on a set of complex interactions between the sediment, fluid and the flow. However the natural variability in an estuary makes it difficult to study the factors that influence the behaviour of flocculation in a systematic manner. This paper presents preliminary results from a laboratory study that examined how floc properties of a natural estuarine mud from the Medway (UK), evolved in response to varying levels of suspended sediment concentration and induced turbulent shearing. The experiments utilised the LabSFLOC floc video camera system, in combination with an annular mini-flume to shear the suspended sediment slurries. The flows created in the mini-flume produced average shear stresses, at the floc sampling height, ranging from 0.01 N m?2 to a peak of 1.03 N m?2. Nominal suspended particulate matter concentrations of 100, 600 and 2000 mg l?1 were introduced into the flume. The experimental runs produced individual flocs ranging in size from microflocs of 22.2 ?m to macroflocs 583.7 ?m in diameter. Average settling velocities ranged from 0.01 to 26.1 mm s?1, whilst floc effective densities varied from 3.5 up to 2000 kg m?3. Low concentration and low shear stress were seen to produce an even distribution of floc mass between the macrofloc (>160 ?m) and microfloc (<160 ?m) fractions. As both concentration and stress rose, the proportion of macrofloc mass increased, until they represented over 80% of the suspended matter. A maximum average macrofloc settling velocity of 3.3 mm s?1 was attained at a shear stress of 0.45 N m?2. Peak turbulence conditions resulted in deflocculation, limiting the macrofloc fall velocity to only 1.1 mm s?1 and placing over 60% of the mass in the microfloc size range. A statistical analysis of the data suggests that the combined influence of both suspended concentration and turbulent shear controls the settling velocity of the fragile, low density macroflocs.
Flocculation, Settling velocity, Cohesive sediment, Annular mini-flume, LabSFLOC
0278-4343
1080-1095
Manning, A.J.
a6c7da76-5ac7-4a6d-a341-861d69c9ae90
Friend, P.L.
600afae0-5185-4e55-8322-34bb8e0ae1f4
Prowse, N.
e0e3f736-5a6c-428b-8922-4e9cdba5a8bd
Amos, C.L.
d0a18a13-bccd-4fdc-8901-aea595d4ed5c
Manning, A.J.
a6c7da76-5ac7-4a6d-a341-861d69c9ae90
Friend, P.L.
600afae0-5185-4e55-8322-34bb8e0ae1f4
Prowse, N.
e0e3f736-5a6c-428b-8922-4e9cdba5a8bd
Amos, C.L.
d0a18a13-bccd-4fdc-8901-aea595d4ed5c

Manning, A.J., Friend, P.L., Prowse, N. and Amos, C.L. (2007) Estuarine mud flocculation properties determined using an annular mini-flume and the LabSFLOC system. Continental Shelf Research, 27 (8), 1080-1095. (doi:10.1016/j.csr.2006.04.011).

Record type: Article

Abstract

Most entrained estuarine sediment mass occurs as flocs. Parameterising flocculation has proven difficult as it is a dynamically active process dependent on a set of complex interactions between the sediment, fluid and the flow. However the natural variability in an estuary makes it difficult to study the factors that influence the behaviour of flocculation in a systematic manner. This paper presents preliminary results from a laboratory study that examined how floc properties of a natural estuarine mud from the Medway (UK), evolved in response to varying levels of suspended sediment concentration and induced turbulent shearing. The experiments utilised the LabSFLOC floc video camera system, in combination with an annular mini-flume to shear the suspended sediment slurries. The flows created in the mini-flume produced average shear stresses, at the floc sampling height, ranging from 0.01 N m?2 to a peak of 1.03 N m?2. Nominal suspended particulate matter concentrations of 100, 600 and 2000 mg l?1 were introduced into the flume. The experimental runs produced individual flocs ranging in size from microflocs of 22.2 ?m to macroflocs 583.7 ?m in diameter. Average settling velocities ranged from 0.01 to 26.1 mm s?1, whilst floc effective densities varied from 3.5 up to 2000 kg m?3. Low concentration and low shear stress were seen to produce an even distribution of floc mass between the macrofloc (>160 ?m) and microfloc (<160 ?m) fractions. As both concentration and stress rose, the proportion of macrofloc mass increased, until they represented over 80% of the suspended matter. A maximum average macrofloc settling velocity of 3.3 mm s?1 was attained at a shear stress of 0.45 N m?2. Peak turbulence conditions resulted in deflocculation, limiting the macrofloc fall velocity to only 1.1 mm s?1 and placing over 60% of the mass in the microfloc size range. A statistical analysis of the data suggests that the combined influence of both suspended concentration and turbulent shear controls the settling velocity of the fragile, low density macroflocs.

This record has no associated files available for download.

More information

Published date: 1 May 2007
Keywords: Flocculation, Settling velocity, Cohesive sediment, Annular mini-flume, LabSFLOC

Identifiers

Local EPrints ID: 49688
URI: http://eprints.soton.ac.uk/id/eprint/49688
ISSN: 0278-4343
PURE UUID: 8d29a15f-de4c-4813-8e53-49b3bcaa7a59

Catalogue record

Date deposited: 22 Nov 2007
Last modified: 15 Mar 2024 09:58

Export record

Altmetrics

Contributors

Author: A.J. Manning
Author: P.L. Friend
Author: N. Prowse
Author: C.L. Amos

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×