A comparison of in situ techniques for estuarine floc settling velocity measurements

Dyer, K.R.; Cornelisse, John M.; Dearnaley, M.P.; Fennessy, M. J.; Jones, Sarah E.; Kappenberg, J.; McCave, I Nick; Pejrup, Morten; Puls, W.; Leussen, Wim van; Wolfstein, K.

doi:10.1016/s1385-1101(96)90766-2

Cited by 126 publications

(24 citation statements)

References 14 publications

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“…Flocs are fragile [Hunt, 1986] and their presumed breakup near the bed in the buffer layer ( Figure 4) appears to be borne out by some recent measurements in shallow water where particle size in suspension decreases toward the bed in the bottom $1.0 m of the flow (Figure 7) [Fugate and Friedrichs, 2003]. This is still far above the buffer layer, but is much closer to the bed than the regions of flow in which large flocs are usually measured [Dyer et al, 1996]. It has been argued that the floc size in the buffer layer is proportional to the Kolmogorov microscale l k = (n/G) 1 = 2 where n is the kinematic viscosity and G is the shear rate (e/n) 1 = 2 in which e is the turbulent kinetic energy dissipation rate.…”

Section: Particle Aggregates Breakup and Sorting By Selective Deposmentioning

confidence: 94%

Size sorting in marine muds: Processes, pitfalls, and prospects for paleoflow‐speed proxies

McCave

Hall

2006

Geochem Geophys Geosyst

302

309

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[1] The basis for, and use of, fine grain size parameters for inference of paleoflow speeds is reviewed here. The basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field, experimental data on suspended sediment transport and deposition, and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed. In the deep sea, sorting events occur under resuspension/deposition events in benthic storms. At flow speeds below 10-15 cm s À1 , size in the noncohesive ''sortable silt'' (10-63 mm) range is controlled by selective deposition, whereas above that range, removal of finer material by winnowing also plays a role. The best particle size instruments to measure a flow speed-related grain size employ the settling velocity method, while laser diffraction sizers can yield misleading results because of particle shape effects. Potential problems, including source effects, downslope supply on continental margins, spatial variability of flow over bedforms, and influence of ice-rafted detritus, are examined. A number of studies using the sortable silt flow speed proxy are reviewed, and inverse modeling of grain size distributions is examined. Outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed.

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Section: Particle Aggregates Breakup and Sorting By Selective Deposmentioning

confidence: 94%

Size sorting in marine muds: Processes, pitfalls, and prospects for paleoflow‐speed proxies

McCave

Hall

2006

Geochem Geophys Geosyst

302

309

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“…Flocs are sufficiently close together to interact and trigger many processes such as breakage, reflocculation and cloud settling effects. For high concentrations, the mean sediment settling flux is usually deduced from SSC measurements with Owen tubes or using similar techniques based on the application of mass conservation [see, e.g., Dyer et al, 1996]. In any case, these systems do not operate in turbulent flow.…”

Section: Cohesive Sediment Settling Flux Measured In a Fluid At Restmentioning

confidence: 99%

On the determination of the settling flux of cohesive sediments in a turbulent fluid

Gratiot¹

2005

J. Geophys. Res.

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[1] In this paper we compare the settling flux of a cohesive sediment mixture measured in a quiescent fluid with that achieved in a turbulent flow. Experiments were performed in a mixing tank. The turbulence produced mechanically by an oscillating grid maintains a stationary, highly concentrated fluid mud layer in which the concentration is almost uniform. In this layer the turbulence decay with increasing distance from the grid is similar to that obtained in clear water. For steady conditions the settling flux of the fluid mud mixture is balanced by the upward turbulent flux, and its value can be determined from the measured depth of the fluid mud layer. At high concentrations (10-200 g L À1 ), we show that the settling flux in a turbulent fluid is much larger than estimated in a quiescent fluid (up to two orders of magnitude). Hindering effects in the settling process of cohesive sediments may thus be considerably reduced by turbulence.

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“…Dyer et al (1996) tested nine methods (including Owen tubes, video systems and settling boxes) for estimating the settling velocity of particles at the same location in an estuary. The mean settling velocity from all the methods was Lee, Lick & Kang (1981) Laboratory 38.0 Bloesch & Sturm (1986) Sediment trap (freshwater) 1.9 Rosa (1985) Sediment trap (freshwater) 0.8 Eadie et al (1990) Sediment trap (freshwater) 0.5 Hill et al (1998) Video technology (marine) 86.0 Dyer et al (1996) Various methods (marine) 47.5 Table 1 Settling velocity of particles measured in this study and values estimated using laboratory, sediment trap and video technology methods 47.5 m day )1 with a SD of ±34.6 m day )1 . The calculated settling velocity in lakes is less well researched and this may be the result of the design of previous trapping experiments being unable to distinguish between sedimentation processes because of the lack of time series traps and the use of WML theory.…”

Section: Discussionmentioning

confidence: 99%

“…The accurate determination of in-situ settling rates of particles and resuspended particles has been a challenging objective in the marine and freshwater sciences for many years (Dyer et al, 1996). There is evidence that sediment resuspension can influence the concentrations of metals, phosphorus and phytoplankton in the sediment and water column of lakes Tessier et al, 1996).…”

Section: Introductionmentioning

confidence: 99%

“…One of the major problems of these estimates is that the sedimentation rate is assumed to be constant over the period of sampling, whereas in many lakes it can be highly variable throughout the year, for instance, because of wind driven resuspension, algal blooms and peripheral wave action (Weyhenmeyer, Håkanson & Meili, 1997;Douglas & Rippey, 2000). Video imaging and photography have been used to provide more accurate values for the marine environment, and these are much higher than the values estimated for freshwaters (Dyer et al, 1996;Hill et al, 1998). Laboratory-based methods are complex, and will invariably give inaccurate in-situ estimates, because of problems in recreating the turbulence, floc formation and chemical characteristics in the lake.…”

Section: Introductionmentioning

confidence: 99%

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Estimation of the in‐situ settling velocity of particles in lakes using a time series sediment trap

2003

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SUMMARY 1. We outline a simple method for estimating the in‐situ settling velocity of particles in wind disturbed lakes. The total sedimentation rate (primary and secondary sedimentation) was measured during storm events in two lakes using a time series sediment trap. 2. The sediment trap had 12 sample bottles which were programmed to open for periods of 3–4 h, giving total deployment times ranging from 36 to 48 h. 3. Wave mixed layer theory was used to infer if and when sediment resuspension occurred and the first order rate equation was used to estimate the settling velocity of resuspended particles. 4. The settling velocity during three resuspension events in Lough Neagh and one in Lough Macnean were 34.3, 29.5, 24.1 and 77.3 m day−1, respectively. These are similar to values obtained using recent in‐situ video imaging in marine environments, but much larger than previous lake sediment trap studies.

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A comparison of in situ techniques for estuarine floc settling velocity measurements

Cited by 126 publications

References 14 publications

Size sorting in marine muds: Processes, pitfalls, and prospects for paleoflow‐speed proxies

Size sorting in marine muds: Processes, pitfalls, and prospects for paleoflow‐speed proxies

On the determination of the settling flux of cohesive sediments in a turbulent fluid

Estimation of the in‐situ settling velocity of particles in lakes using a time series sediment trap

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