Enhanced sedimentation beneath particle‐laden flows in lakes and the ocean due to double‐diffusive convection

Jazi, Shahrzad Davarpanah; Wells, Mathew G.

doi:10.1002/2016gl069547

Cited by 36 publications

(33 citation statements)

References 40 publications

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“…Only 9 out of 150 rivers studied by Mulder and Syvitski (1995) have sufficient concentrations to enable plunging hyperpycnal flow. Third, experiments suggest that turbidity currents are generated by dilute river plumes with sediment concentrations as low as 1 kg/m 3 (Figure 1c; Parsons et al, 2001) if the plume locally becomes denser than ambient seawater (by double diffusion or settling-driven convection; Hoyal et al, 1999aHoyal et al, , 1999bJazi & Wells, 2016;Parsons et al, 2001;Sutherland et al, 2018). This 1-kg/m 3 threshold implies that 61 of the 150 studied rivers studied by Mulder and Syvitski (1995) can generate turbidity currents.…”

Section: Introductionmentioning

confidence: 97%

Direct Monitoring Reveals Initiation of Turbidity Currents From Extremely Dilute River Plumes

Hage

Cartigny

Sumner

et al. 2019

Geophysical Research Letters

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Rivers (on land) and turbidity currents (in the ocean) are the most important sediment transport processes on Earth. Yet how rivers generate turbidity currents as they enter the coastal ocean remains poorly understood. The current paradigm, based on laboratory experiments, is that turbidity currents are triggered when river plumes exceed a threshold sediment concentration of ~1 kg/m3. Here we present direct observations of an exceptionally dilute river plume, with sediment concentrations 1 order of magnitude below this threshold (0.07 kg/m3), which generated a fast (1.5 m/s), erosive, short‐lived (6 min) turbidity current. However, no turbidity current occurred during subsequent river plumes. We infer that turbidity currents are generated when fine sediment, accumulating in a tidal turbidity maximum, is released during spring tide. This means that very dilute river plumes can generate turbidity currents more frequently and in a wider range of locations than previously thought.

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Section: Introductionmentioning

confidence: 97%

Direct Monitoring Reveals Initiation of Turbidity Currents From Extremely Dilute River Plumes

Hage

Cartigny

Sumner

et al. 2019

Geophysical Research Letters

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“…In the present work, we aim to understand how the traditional picture of double diffusion is modified if the unstably stratified scalar is a particulate phase with a Stokes settling velocity. A number of laboratory flow visualization experiments (Green 1987;Green & Diez 1995;Carey 1997;Chen 1997;Hoyal, Bursik & Atkinson 1999a,b;Maxworthy 1999;Parsons & García 2000;Parsons, Bush & Syvitski 2001;Manville & Wilson 2004;Carazzo & Jellinek 2013;Manzella et al 2015;Rouhnia & Strom 2015;Davarpanah & Wells 2016) demonstrate that thermal or compositional density gradients can dramatically alter the effective settling velocity of the particles by driving double-diffusive instabilities or settling-driven convection. This mechanism has also been hypothesized to be active in the field observations by Scheu et al (2015), and in the lake measurements of Sánchez & Roget (2007).…”

Section: Introductionmentioning

confidence: 99%

A settling-driven instability in two-component, stably stratified fluids

2017

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We analyse the linear stability of stably stratified fluids whose density depends on two scalar fields where one of the scalar fields is unstably stratified and involves a settling velocity. Such conditions may be found, for example, in flows involving the transport of sediment in addition to heat or salt. A linear stability analysis for constant-gradient base states demonstrates that the settling velocity generates a phase shift between the perturbation fields of the two scalars, which gives rise to a novel, settling-driven instability mode. This instability mechanism favours the growth of waves that are inclined with respect to the horizontal. It is active for all density and diffusivity ratios, including for cases in which the two scalars diffuse at identical rates. If the scalars have unequal diffusivities, it competes with the elevator mode waves of the classical double-diffusive instability. We present detailed linear stability results as a function of the governing dimensionless parameters, including for lateral gradients of the base state density fields that result in predominantly horizontal intrusion instabilities. Highly resolved direct numerical simulation results serve to illustrate the nonlinear competition of the various instabilities for such flows in different parameter regimes.

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“…Because the settling velocity determines the distance into the bay that sediment is transported before it settles, the particle size affects the distribution of sedimentation in the bay. Although the settling speed may be impacted by flocculation and convective sedimentation effects (Fox et al, ; Guo & He, ; Scheu et al, ; Davarpanah and Wells, ), constant settling velocities are used for each sediment size class.…”

Section: Methodsmentioning

confidence: 99%

Modeling Sedimentation Dynamics of Sediment‐Laden River Intrusions in a Rotationally‐Influenced, Stratified Lake

Scheu

Fong

Monismith

et al. 2018

Water Resources Research

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River inflows are often the dominant source of sediment into a lacustrine system and the extent of sediment transport can be an important indicator of the impact of introduced constituents on an ecosystem. Inflow intrusions, which intrude into the middle of the water column at a depth of neutral buoyancy, can be common in deep, stratified lakes and reservoirs. However, the dynamics and associated sediment transport of these flows have received less attention in the literature compared to surface or underflow plumes. A three‐dimensional hydrodynamic and sediment transport model was used to investigate sediment transport due to inflow intrusions in Pallanza Bay, an embayment within Lake Maggiore, Italy. The model was validated using field observations of inflow intrusions over varying conditions and was then used to simulate a range of realistic scenarios to evaluate sediment transport and deposition from inflow intrusions. The extent of sedimentation across the range of simulated scenarios can be estimated using a simple analytical expression with only a priori known parameters. The expression is a function of the intrusion plume speed and thickness, which are governed by the volume flow rate and the ambient stratification. We utilize the first‐mode wave speed to characterize the ambient stratification in the simplified expression, which eliminates the need to characterize near‐field mixing and entrainment to predict the intrusion depth. While the simple expression gives a reasonable estimate of the sedimentation extent, it does not capture lateral variability in the plume due to effects like lateral spreading and the earth's rotation.

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Enhanced sedimentation beneath particle‐laden flows in lakes and the ocean due to double‐diffusive convection

Cited by 36 publications

References 40 publications

Direct Monitoring Reveals Initiation of Turbidity Currents From Extremely Dilute River Plumes

Direct Monitoring Reveals Initiation of Turbidity Currents From Extremely Dilute River Plumes

A settling-driven instability in two-component, stably stratified fluids

Modeling Sedimentation Dynamics of Sediment‐Laden River Intrusions in a Rotationally‐Influenced, Stratified Lake

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