A laboratory study of dynamic sorting of fine, non-cohesive particles by steady, unidirectional currents

Hamm, N. T.; Dade, W. Brian

doi:10.1016/j.margeo.2012.11.014

Cited by 5 publications

(32 citation statements)

References 24 publications

(41 reference statements)

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“…These experiments gave a strong indication of size sorting via selective deposition. However, recent experiments with 13-44 µm silt (mean 30 µm) by Hamm and Dade (2013) found no sorting effect and the deposit size remained the same under a range of shear stresses.…”

Section: Field and Laboratory Previous Workmentioning

confidence: 74%

Relation of sortable silt grain-size to deep-sea current speeds: Calibration of the ‘Mud Current Meter’

McCave

Thornalley

Hall

2017

Deep Sea Research Part I: Oceanographic Research Papers

120

111

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Fine grain-size parameters have been used for inference of palaeoflow speeds of near-bottom currents in the deep-sea. The basic idea stems from observations of varying sediment size parameters on a continental margin with a gradient from slower flow speeds at shallower depths to faster at deeper. In the deep-sea, size-sorting occurs during deposition after benthic storm resuspension events. At flow speeds below 10-15 cm s-1 mean grain-size in the terrigenous non-cohesive 'sortable silt' range (denoted by SS , mean of 10-63 μm) is controlled by selective deposition, whereas above that range removal of finer material by winnowing is also argued to play a role. A calibration of the SS grain-size flow speed proxy based on sediment samples taken adjacent to sites of long-term current meters set within ~100 m of the sea bed for more than a year is presented here. Grain-size has been measured by either Sedigraph or Coulter Counter, in some cases both, between which there is an excellent correlation for SS (r = 0.96). Size-speed data indicate calibration relationships with an overall sensitivity of 1.36 ± 0.19 cm s-1 /μm. A calibration line comprising 12 points including 9 from the Iceland overflow region is well defined, but at least two other smaller groups (Weddell/Scotia Sea and NW Atlantic continental rise/Rockall Trough) are fitted by subparallel lines with a smaller constant. This suggests a possible influence of the calibre of material supplied to the site of deposition (not the initial source supply) which, if depleted in very coarse silt (31-63 μm), would limit SS to smaller values for a given speed than with a broader size-spectrum 2 supply. Local calibrations, or a core-top grain-size and local flow speed, are thus necessary to infer absolute speeds from grain-size. The trend of the calibrations diverges markedly from the slope of experimental critical erosion and deposition flow speeds versus grain-size, making it unlikely that the SS (or any deposit size for that matter) is simply predicted by the deposition threshold. A more probable control is the rate of deposition of the different size fractions under changing flows over several tens of years (the typical averaging period of a centimetre of deposited sediment). This suggestion is supported by a simple depositional model for which the deposited SS is calculated from measured currents with a sizevarying depositional threshold. More surficial sediment samples taken near long-term current meter sites are needed to make calibrations more robust and explore regional differences.

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Section: Field and Laboratory Previous Workmentioning

confidence: 74%

Relation of sortable silt grain-size to deep-sea current speeds: Calibration of the ‘Mud Current Meter’

McCave

Thornalley

Hall

2017

Deep Sea Research Part I: Oceanographic Research Papers

120

111

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“…Studies examining the deposition of sediment

< 63 μ m

in diameter to nonsand beds in the absence of bed forms or biofilms have focused on the deposition of silt‐sized particles to smooth impermeable boundaries (Fries & Trowbridge, ; Hamm & Dade, ; Hamm et al, ) and porous gravel beds (Einstein, ; Fries & Trowbridge, ; Hamm et al, ). A few consistent observations from this body of work are: (1) that sedimentation rates to gravel beds in excess of that predicted by

w_{s} C

are not observed; (2) that net deposition rates to porous beds exceeds the accumulation of sediment on smooth nonporous beds; and (3) that entrainment of sediment from the porous bed is not detectable under steady flow conditions if the sediment deposits into the pore space below the surface‐layer grains.…”

Section: Introductionmentioning

confidence: 99%

Deposition of Suspended Clay to Open and Sand‐Filled Framework Gravel Beds in a Laboratory Flume

Mooneyham

Strom

2018

Water Resources Research

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Pulses of fine sediment composed of sand, silt, and clay can be introduced to gravel bed rivers through runoff from burn‐impacted hillslopes, landslides, bank failure, or the introduction of reservoir sediment as a result of sluicing or dam decommissioning. Here we present a study aimed at quantifying exchange between suspensions of clay and gravel beds. The questions that motivate the work are: how do bed roughness and pore space characteristics, shear velocity ( u∗), and initial concentration (C0) affect clay deposition on or within gravel beds? Where does deposition within these beds occur, and can deposited clay be resuspended while the gravel is immobile? We examine these questions in a laboratory flume using acrylic, open‐framework gravel, and armored sand‐gravel beds under conditions of varying u∗ and C0. Deposition of clay occurred to all beds (even with Rouse numbers ∼ 0.01). We attribute deposition under full suspension conditions to be an outcome of localized protected zones where clay can settle and available pore space in the bed. For smooth wall cases, protection came from the viscous wall region and the development of bed forms; for the rough beds, protection came from separation zones and low‐velocity pore spaces. Bed porosity was the strongest influencer of nondimensional deposition rate; deposition increased with porosity. Deposition was inversely related to u∗ for the acrylic bed runs; no influence of u∗ was found for the porous bed runs. Increases in discharge resulted in resuspension of clay from acrylic beds; no resuspension was observed in the porous bed runs.

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“…Distribution D3 covers the size range for 'sortable silts' which have received considerable research attention (see Hamm & Dade, 2013). These are thought to be silt-sized grains that travel close to the bed under relatively low shear stress (McCave et al, 1995b;Chang et al, 2007;Johnson & McCave, 2008;Law et al, 2008;Molinaroli et al, 2009;Hamm & Dade, 2013). Turbulence in the bed boundary layer keeps these particles in suspension, and they undergo progressive sorting as flow decelerates (Middleton, 1976;McCave et al, 1995b).…”

Section: Alberta Lake E Grain-size Populationsinterpretation Of Procementioning

confidence: 99%

“…Process-based studies indicate that the finestgrained bedload population is generally related to saltation processes (Middleton, 1976;Ashley, 1978;Singer & Anderson, 1984;Sheridan et al, 1987;Chang et al, 2006;Law et al, 2008;Barusseau, 2011;Hamm & Dade, 2013). Distributions D3 and D4 have significant positive correlations between their position and shape parameters (mode and FWHH; Table 2C and D), suggesting that the sedimentological processes controlling these two populations are related; this is consistent with both being related to benthic boundary layer turbulence, which strongly controls the transport and progressive sorting of both sortable silt and saltating particles (Singer & Anderson, 1984;Hamm & Dade, 2013). Singer & Anderson (1984) documented four populations within bedload transport that in order of increasing grain size were: (i) 'intermittent suspension' (equivalent to what nowadays would be considered suspended load sortable silt rather than bedload); (ii) saltation; (iii) finergrained traction population; and (iv) coarsergrained traction population.…”

Section: Alberta Lake E Grain-size Populationsinterpretation Of Procementioning

confidence: 99%

A log‐normal spectral analysis of inorganic grain‐size distributions from a Canadian boreal lake core: Towards refining depositional process proxy data from high latitude lakes

et al. 2017

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Better methods for interpreting grain‐size spectra will enhance current understanding of past transport–depositional processes. A high‐resolution inorganic grain‐size dataset has been measured from a freeze core extracted from ‘Alberta Lake E’ a boreal fresh water lake 40 km east of the Athabasca Oil Sands in north‐eastern Alberta, Canada. The grain‐size spectra are remarkably consistent throughout the core, exhibiting a structure comprising six persistent grain‐size distributions below ca 250 μm, plus a rare medium‐sand distribution. Automated deconvolution of the grain‐size spectra produced poor results. Constraining the modes of two of the distributions produced deconvolution solutions that were statistically excellent and consistent with the structure of each spectrum. Statistical analysis of the ‘constrained’ solutions indicates that deconvolution successfully extracted independent grain‐size populations. Conversely, the multimodal spectra generate traditional measures (for example, mean grain size) that are inconsistent combinations of different individual populations and thus are poor proxies of transport–depositional processes. Alberta Lake E is situated in a boreal wetland landscape where sediment delivery is dominated by overland flow transport during spring melt. This context means that the Alberta Lake E grain‐size spectra can be interpreted to reflect: (i) a bedload component transported during short‐duration high discharge events that reflect the intensity of the melt; and (ii) a finer suspended load component representing material whose magnitude is controlled by the volume of the spring melt. Stratigraphically, bedload and suspended load populations demonstrate different short‐wavelength and long‐wavelength cyclicity, suggesting that spring melt is likely to be driven by cyclic external forcing factors. The links between the grain‐size spectra and spring melt have potential for generating proxy records that better capture the external controls over spring melt in boreal systems and the risks associated with these energetic hydrodynamics. This is exemplified by the coarsest Alberta Lake E distributions, which indicate that more intense spring‐melt dynamics occurred in pre‐historical times.

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A laboratory study of dynamic sorting of fine, non-cohesive particles by steady, unidirectional currents

Cited by 5 publications

References 24 publications

Relation of sortable silt grain-size to deep-sea current speeds: Calibration of the ‘Mud Current Meter’

Relation of sortable silt grain-size to deep-sea current speeds: Calibration of the ‘Mud Current Meter’

Deposition of Suspended Clay to Open and Sand‐Filled Framework Gravel Beds in a Laboratory Flume

A log‐normal spectral analysis of inorganic grain‐size distributions from a Canadian boreal lake core: Towards refining depositional process proxy data from high latitude lakes

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