Near bed suspended sediment flux by single turbulent events

Amirshahi, Seyed Mohammad; Kwoll, Eva

doi:10.1016/j.csr.2017.11.005

Cited by 12 publications

(4 citation statements)

References 46 publications

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“…8. Current results showed a strong link between turbulent bursting events and suspended sediment concentrations, as previously reported in the field (Amirshahi et al, 2018;Leng et al, 2018).…”

Section: Basic Observationssupporting

confidence: 89%

Turbulence and suspended sediment processes in the Garonne River tidal bore in November 2016

Reungoat

Leng

Chanson

2019

International Journal of Sediment Research

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A tidal bore is a water discontinuity at the leading edge of a flood tide wave in estuaries with a large tidal range and funneling topography. New measurements were done in the Garonne River tidal bore on 14-15 November 2016, at a site previously investigated between 2010 and 2015. The data focused on long, continuous, high-frequency records of instantaneous velocity and suspended sediment concentration (SSC) estimate for several hours during the late ebb, tidal bore passage and flood tide. The bore passage drastically modified the flow field, with very intense turbulent and sediment mixing. This was evidenced with large and rapid fluctuations of both velocity and Reynolds stress, as well as large SSCs during the flood tide. Granulometry data indicated larger grain sizes of suspended sediment in water samples compared to sediment bed material, with a broader distribution, shortly after the tidal bore. The tidal bore induced a sudden suspended sediment flux reversal and a large increase in suspended sediment flux magnitude. The time-variations of turbulent velocity and suspended sediment properties indicated large fluctuations throughout the entire data set. The ratio of integral time scales of SSC to velocity in the x-direction was on

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Section: Basic Observationssupporting

confidence: 89%

Turbulence and suspended sediment processes in the Garonne River tidal bore in November 2016

Reungoat

Leng

Chanson

2019

International Journal of Sediment Research

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“…Understanding the dynamics and spatial distribution of coherent flow structures populating the wake of a bedform is important, as these flow features are hypothesized to produce impulsive, sediment transport events that contribute significantly to bedform evolution (Nelson et al 1995;Diplas et al 2008;Valyrakis, Diplas & Dancey 2013;Shih et al 2017;Amirshahi, Kwoll & Winter 2018;Cameron et al 2020;Schobesberger et al 2020). In the following, the high-frame-rate cross-plane data are used to examine the three-dimensional structure of the flow, using Taylor's hypothesis, to clarify the structural organization of turbulence produced by barchan dunes.…”

Section: Resultsmentioning

confidence: 99%

“…Studies have shown that bedload transport is strongly correlated with Q 4 sweeps (e.g. Williams & Kemp 1971;Grass 1983;Best 1992;Nelson et al 1995), while Q 2 ejections are particularly important for sediment suspension (Jackson 1976;Leeder 1983;Amirshahi et al 2018;Li et al 2019). Moreover, aeolian 'streamers', which are a primary manifestation of saltation transport (Baas & Sherman 2005) are thought to be associated with Q 4 sweeps and are initiated trailing the passage of LSMs .…”

Section: Implications For Barchan Morphodynamicsmentioning

confidence: 99%

Unsteady dynamics of turbulent flow in the wakes of barchan dunes modulated by overlying boundary-layer structure

et al. 2021

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“…During conditions with combined wave and current shear stress well below the threshold of motion, sediment may nevertheless relocate due to avalanching of critical bedform slopes or due to single short-term turbulent events (Amirshahi et al, 2018).…”

Section: Classification Of Reworking Modementioning

confidence: 99%

Relations of physical and biogenic reworking of sandy sediments in the southeastern North Sea

Krämer

Ahmerkamp

Schückel

et al. 2019

Preprint

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Abstract. The reworking of sandy sediments in shallow coastal and shelf seas is mainly driven by physical forcing in the form of wave- and current-induced shear stress. As an important habitat for benthic species seeking shelter and food, the upper seafloor is also marked by intense bioturbation. Although this reworking activity is recognized as an important mechanism for the exchange of particular matter and solutes between sediment and water column, quantifications and assessments of the relative importance of physical and biogenic reworking of subtidal shelf sediments are rare. This work presents in situ measurements of volumetric reworking rates from six different locations in the southeastern North Sea. The investigated sites cover a range of water depths between 23 and 41 m, different magnitudes of physical (wave and current) forcing and sedimentological conditions as well as different habitats and benthic communities. The measured biogenic reworking rates reach up to 14 % of physically driven reworking via bedform migration. Comparisons with physical quantities water depth, median grain size, bottom water temperature and flow velocity reveal good correlations and allow for an approximation of the biogenic reworking rate from a combination of these readily available oceanographic parameters. The diffusive relocation of sediment by benthic fauna also influences the topography of small scale bedforms and may reduce their height by up to 10 % in a few hours during hydrodynamically inactive conditions. The observations show that even in an energetic environment such as the southeastern North Sea, the benthic fauna contributes an important regulating ecosystem service by overturning upper seafloor sediments. This reworking mechanism becomes particularly important in areas and during periods of sub-threshold conditions for physically driven sediment reworking.

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Near bed suspended sediment flux by single turbulent events

Cited by 12 publications

References 46 publications

Turbulence and suspended sediment processes in the Garonne River tidal bore in November 2016

Turbulence and suspended sediment processes in the Garonne River tidal bore in November 2016

Unsteady dynamics of turbulent flow in the wakes of barchan dunes modulated by overlying boundary-layer structure

Relations of physical and biogenic reworking of sandy sediments in the southeastern North Sea

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