Experimental observation of saline underflows and turbidity currents, flowing over rough beds

Varjavand, Peyman; Ghomeshi, Mehdi; Dalir, A Hosseinzadeh; Farsadizadeh, D; Gorgij, Alireza Docheshmeh

doi:10.1139/cjce-2014-0537

Cited by 14 publications

(6 citation statements)

References 21 publications

(26 reference statements)

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“…They used conical-and cylindrical-shaped roughness along the bed. They observe that, for the same gradient Richardson number Ri g , entrainment rate increases as roughness increases (Figure 12a in Varjavand et al, 2015). With increasing roughness, the velocity peak moves away from the bed (Sequeiros et al, 2010) and with homogenized mixing in the near-wall region the velocity profile is observed to shift toward a subcritical-like character.…”

Section: Discussionmentioning

confidence: 93%

“…As in a turbulent boundary layer, smooth‐wall, fully rough, and transitional regimes can also be identified in the case of a turbidity current. For example, Varjavand et al () study experimentally the effect of bed roughness on entrainment. They used conical‐ and cylindrical‐shaped roughness along the bed.…”

Section: Discussionmentioning

confidence: 99%

“…Several experimental investigations of turbidity currents have proposed empirical relations for the functional dependence e w ( Ri ) (Fukushima, ; Parker et al, , ). Additional dependence of entrainment coefficient on Reynolds number of the current (Cenedese & Adduce, ), basal drag coefficient (Dallimore et al, ; Fernandez & Imberger, ), flux coefficient (Wells et al, ), and bed roughness (Varjavand et al, ) have also been advanced.…”

Section: Introductionmentioning

confidence: 99%

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Properties of the Body of a Turbidity Current at Near‐Normal Conditions: 1. Effect of Bed Slope

et al. 2019

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We study the body of turbidity currents in normal flow conditions by means of highly resolved direct numerical simulations of a homogeneous model. We focus on turbidity currents where the net amount of sediment is held fixed. We consider the sediment to be fine enough that their settling effect is neglected, and in the companion work we consider the effect of settling velocity. We consider five different shear Richardson numbers from 5 to 80. Under normal condition, basal drag and entrainment at the interface precisely balance the momentum supplied to the current from the excess weight of the sediment. The normal flow properties of a turbidity current can be fully characterized in terms of bulk Richardson number Ri and bulk Reynolds number Re. The velocity, concentration, and turbulent kinetic energy profiles take a self-similar shape when the current is at near-normal conditions. We observe the flow to display supercritical features for Ri ⪅ 0.4 and to display subcritical features for Ri ⪆ 0.7. From the behavior at intermediate Richardson numbers it appears that the transition between subcritical to supercritical behavior is not sharp. We observe good agreement between experimental and simulation results in both regimes. The entrainment coefficient as a function of bulk Richardson number at normal condition is in good agreement with the empirical relation and with available experimental results. We present a simple model for drag coefficient as a function of bulk Reynolds and Richardson numbers.

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Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Properties of the Body of a Turbidity Current at Near‐Normal Conditions: 1. Effect of Bed Slope

et al. 2019

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“…Where turbidity currents are able to erode the seabed and generate scours, these scours should work to slow the eroding current as would be predicted by hydraulic relationships showing that average flow velocities and bed roughness are inversely related ( 92 ). However, given that turbidity current velocity is related to sediment volume, this relationship may break down if sufficient volume is eroded despite the bed roughness increase ( 92 – 95 ). This relationship is further complicated during the passage of the flow as the body and tail may be less erosive and thus interacting with the bed roughness surface generated by the more erosive head of the flow ( 23 ).…”

Section: Methodsmentioning

confidence: 99%

First source-to-sink monitoring shows dense head controls sediment flux and runout in turbidity currents

et al. 2022

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Until recently, despite being one of the most important sediment transport phenomena on Earth, few direct measurements of turbidity currents existed. Consequently, their structure and evolution were poorly understood, particularly whether they are dense or dilute. Here, we analyze the largest number of turbidity currents monitored to date from source to sink. We show sediment transport and internal flow characteristic evolution as they runout. Observed frontal regions (heads) are fast (>1.5 m/s), thin (<10 m), dense (depth averaged concentrations up to 38% vol ), strongly stratified, and dominated by grain-to-grain interactions, or slower (<1 m/s), dilute (<0.01% vol ), and well mixed with turbulence supporting sediment. Between these end-members, a transitional flow head exists. Flow bodies are typically thick, slow, dilute, and well mixed. Flows with dense heads stretch and bulk up with dense heads transporting up to 1000 times more sediment than the dilute body. Dense heads can therefore control turbidity current sediment transport and runout into the deep sea.

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“…The initially reduced gravity g′ is generally used to describe this density difference (Eggenhuisen et al, 2019;Gray et al, 2005;Meiburg & Kneller, 2010), defined as g′ = (ρ 0 − ρ 1 )g/ρ 1 , where ρ 0 and ρ 1 are the densities of the heavy current and ambient fluid, respectively (see Figure 1), and g is the gravitational acceleration. The hydrodynamics of turbidity currents can be characterized by the bulk Reynolds number Re d and Froude number Fr d (Varjavand et al, 2015), which are calculated as,…”

Section: Experimental Parametersmentioning

confidence: 99%

Hydrodynamics and Sediment Transport of Downslope Turbidity Current Through Rigid Vegetation

Han

Lin

et al. 2023

Water Resources Research

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Systematical downslope‐turbidity‐current experiments were performed to clarify the relationship between sediment‐transport modes and current propagation patterns caused by rigid vegetation, as well as adjustments in turbulence characteristics of current. The equations for predicting the front velocities of downslope turbidity currents with emergent vegetation were proposed and validated via experimental data. Experimental results reveal that sediment deposition causes the lower turbulent kinetic energy (TKE) peaks of turbidity currents to decrease or even disappear without affecting their upper TKE peaks, while the rigid vegetation has the opposite effect. Vegetation stems destroy the longitudinal low‐high speed streaks associated with the quasi‐streamwise eddies in the near‐bed region and increase the proportions of the outward and inward interactions. In addition, sediment deposition severely suppresses the turbulent bursting events within turbidity currents but does not influence the relative proportions of the four bursting types. Rigid vegetation and sediment deposition both degrade the absolute values of the third‐order moments of velocity fluctuations without changing their signs to reduce the generation frequency of sweep events. Emergent rigid vegetation accelerates the formation of the reflected bore to provide energy for the deposited sediment to move downstream continuously. On the other hand, the dense submerged vegetation makes turbidity currents easily form the two‐head propagating mode, which allows part of the sediments carried by the upper current head to be transported downstream rather than deposited within or upstream of the vegetation region. Furthermore, the sloping boundary provides favorable conditions to initiate these specific modes for sediment transport adjusted by rigid vegetation.

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Experimental observation of saline underflows and turbidity currents, flowing over rough beds

Cited by 14 publications

References 21 publications

Properties of the Body of a Turbidity Current at Near‐Normal Conditions: 1. Effect of Bed Slope

Properties of the Body of a Turbidity Current at Near‐Normal Conditions: 1. Effect of Bed Slope

First source-to-sink monitoring shows dense head controls sediment flux and runout in turbidity currents

Hydrodynamics and Sediment Transport of Downslope Turbidity Current Through Rigid Vegetation

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