Physical theory for near-bed turbulent particle suspension capacity

Eggenhuisen, Joris T.; Cartigny, Matthieu; Leeuw, Jan de

doi:10.5194/esurf-5-269-2017

Cited by 24 publications

(22 citation statements)

References 49 publications

(91 reference statements)

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“…It is interesting to contrast these results with recent work on ''hybrid flows'' of Kane et al [2017], who use the turbulence collapse criterion of Eggenhuisen et al [2017] to identify a threshold in a submarine fan (the Skoorsteenberg Formation) beyond which both debris flow or bedload deposits and turbidites are both present. Unfortunately, since the theory of Eggenhuisen et al [2017] determines a threshold that is not strictly a function of Ro and Ri, no direct comparison of their threshold with the K-B threshold is possible. While the results of Kane et al [2017] are suggestive, we believe that it is premature to interpret any particular stratigraphic observations using our two-layer flow hypothesis at this time.…”

Section: 1002/2016jc012635mentioning

confidence: 96%

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Sedimentological regimes for turbidity currents: Depth‐averaged theory

2017

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Turbidity currents are one of the most significant means by which sediment is moved from the continents into the deep ocean; their properties are interesting both as elements of the global sediment cycle and due to their role in contributing to the formation of deep water oil and gas reservoirs. One of the simplest models of the dynamics of turbidity current flow was introduced three decades ago, and is based on depth‐averaging of the fluid mechanical equations governing the turbulent gravity‐driven flow of relatively dilute turbidity currents. We examine the sedimentological regimes of a simplified version of this model, focusing on the role of the Richardson number Ri [dimensionless inertia] and Rouse number Ro [dimensionless sedimentation velocity] in determining whether a current is net depositional or net erosional. We find that for large Rouse numbers, the currents are strongly net depositional due to the disappearance of local equilibria between erosion and deposition. At lower Rouse numbers, the Richardson number also plays a role in determining the degree of erosion versus deposition. The currents become more erosive at lower values of the product Ro × Ri, due to the effect of clear water entrainment. At higher values of this product, the turbulence becomes insufficient to maintain the sediment in suspension, as first pointed out by Knapp and Bagnold. We speculate on the potential for two‐layer solutions in this insufficiently turbulent regime, which would comprise substantial bedload flow with an overlying turbidity current.

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Section: 1002/2016jc012635mentioning

confidence: 96%

“…In this analysis we have used the Knapp-Bagnold criterion for turbulent collapse, equation (71). As remarked above, there are other criteria that have been proposed for turbulent collapse, notably those appearing in Cantero et al [2012ab] and Eggenhuisen et al [2017]. These criteria both depend upon the ''shear Reynolds number,''…”

Section: 1002/2016jc012635mentioning

confidence: 99%

Sedimentological regimes for turbidity currents: Depth‐averaged theory

2017

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“…Recent theoretical work on the transition from competency to capacity driven deposition is linked to the gravitational force acting on the suspended mass exceeding the upward turbulent forces near the bed (Eggenhuisen et al, 2017). Recent theoretical work on the transition from competency to capacity driven deposition is linked to the gravitational force acting on the suspended mass exceeding the upward turbulent forces near the bed (Eggenhuisen et al, 2017).…”

Section: Origin Of Differences Between Model and Experimentsmentioning

confidence: 99%

Turbulent diffusion modelling of sediment in turbidity currents: An experimental validation of the Rouse approach

Eggenhuisen

Tilston

Leeuw

et al. 2019

The Depositional Record

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The margins of submarine channels are characterized by deposits that fine away from the channel thalweg. This grain-size trend is thought to reflect upward fining trends in the currents that formed the channels. This assumption enables reconstruction of turbidity currents from the geologic record, thereby providing insights into the overall sediment load of the system. It is common to assume that the density structure of a turbidity current can be modelled with simple diffusion models, such as the Rouse equation. Yet the Rouse equation was developed to describe how particles should be distributed through the water column in open-channel flows, which fundamentally differ from turbidity currents in terms of their flow structure. Consequently, a rigorous appraisal of the Rouse model in deep-marine settings is needed to validate the aforementioned flow reconstructions. The present study addresses this gap in the literature by providing a robust evaluation of the Rouse model's predictions of vertical particle segregation in two experimental turbidity currents that differ only in terms of their initial bed slopes (4° versus 8°). The concentration profiles of the coarsest sediment, which is suspended predominantly in the lower part of the flow, is accurately reproduced by the Rouse equation. Significant mismatches appear, however, in the concentration of finer grained sediment, especially towards the top of the flow. This problem is caused by the mixing with clear water at the top of turbidity currents.Caution is therefore advised in applying a Rouse model to levee overspill and leveecrest deposits. Nonetheless, the Rouse model shows good agreement with laboratory measurements in the lower regions of the flow and for the coarser grains that are predominantly transported in the lower sections of submarine channels. K E Y W O R D SGrain-size segregation, Rouse modelling, simplified sediment transport modelling, turbidity current reconstruction 204 | EGGENHUISEN Et al.

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“…This aspect of capacity is here called suspension capacity. Secondly, the maximum near-bed concentration goes down with decreasing u* (Smith & Mclean, 1977;van Rijn, 1984;Cantero et al, 2011;Eggenhuisen et al, 2017). This aspect of capacity is here called near-bed capacity.…”

Section: Capacity-driven Depositionmentioning

confidence: 99%

“…15C). The near-bed capacity criterion of Eggenhuisen et al (2017) is used to determine the near-bed concentration at which the flow is saturated:…”

Section: Capacity-driven Depositionmentioning

confidence: 99%

Linking submarine channel–levee facies and architecture to flow structure of turbidity currents: insights from flume tank experiments

2017

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Submarine leveed channels are sculpted by turbidity currents that are commonly highly stratified. Both the concentration and the grain size decrease upward in the flow, and this is a fundamental factor that affects the location and grain size of deposits around a channel. This study presents laboratory experiments that link the morphological evolution of a progressively developing leveed channel to the suspended sediment structure of the turbidity currents. Previously, it was difficult to link turbidity current structure to channel–levee development because observations from natural systems were limited to the depositional products while experiments did not show realistic morphodynamics due to scaling issues related to the sediment transport. This study uses a novel experimental approach to overcome scaling issues, which results in channel inception and evolution on an initially featureless slope. Depth of the channel increased continuously as a result of levee aggradation combined with varying rates of channel floor aggradation and degradation. The resulting levees are fining upward and the grain‐size trend in the levee matches the upward decrease in grain size in the flow. It is shown that such deposit trends can result from internal channel dynamics and do not have to reflect upstream forcing. The suspended sediment structure can also be linked to the lateral transition from sediment bypass in the channel thalweg to sediment deposition on the levees. The transition occurs because the sediment concentration is below the flow capacity in the channel thalweg, while higher up on the channel walls the concentration exceeds capacity resulting in deposition of the inner levee. Thus, a framework is provided to predict the growth pattern and facies of a levee from the suspended sediment structure in a turbidity current.

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Physical theory for near-bed turbulent particle suspension capacity

Cited by 24 publications

References 49 publications

Sedimentological regimes for turbidity currents: Depth‐averaged theory

Sedimentological regimes for turbidity currents: Depth‐averaged theory

Turbulent diffusion modelling of sediment in turbidity currents: An experimental validation of the Rouse approach

Linking submarine channel–levee facies and architecture to flow structure of turbidity currents: insights from flume tank experiments

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