Relationship between eddy viscosity of seawater and eddy diffusivity of suspended particles

Lees, B.J.

doi:10.1007/bf02462442

Cited by 27 publications

(18 citation statements)

References 8 publications

(5 reference statements)

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“…The second columns of Figures and show the eddy viscosity,

ν_{t} = - \overset{u' w'}{true} \cdot {(\partial \overset{true¯}{u} / ∂z)}^{- 1}

(Trowbridge & Madsen, ), which is a measure of the effectiveness of vertical turbulent mixing of momentum and is a fundamental parameter used in modeling the mean flow. Furthermore, the turbulent diffusivity, which can be used to model sediment suspension and mixing of ecologically significant chemicals, is expected to be comparable to the eddy viscosity (Lees, ). A few negative eddy viscosities were observed.…”

Section: Resultsmentioning

confidence: 99%

Turbulence Within Natural Mangrove Pneumatophore Canopies

et al. 2019

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High‐resolution velocity measurements were collected within and above two dense canopies of mangrove pneumatophore roots in a wave‐exposed mangrove forest. In both canopies, root density decreased steadily with height above bed owing to the variability in root heights and the tapered shape of the roots. Within the canopies, we consider turbulence within three zones: near the bed above the wave boundary layer, around the mean canopy height, and above the canopy. The near‐bed turbulence was particularly intense (up to 6.5 × 10−4 W/kg), likely owing to oscillatory wave‐driven currents flowing past dense vegetation. Near the bed and around the mean canopy height, peaks in horizontal velocity power spectra at frequencies corresponding to Strouhal numbers of ~0.2 may indicate Von Kármán wake shedding in the lee of the pneumatophores. Furthermore, a recirculation zone was observed immediately behind a cluster of pneumatophores at intermediate heights. These coherent flow structures were associated with zones of enhanced Reynolds stresses (up to 5.3 × 10−3 m2/s2) and eddy viscosities (up to 1.9 × 10−3 m2/s). Large near‐bed stresses were associated with near‐bed drag coefficients that are up to an order of magnitude larger than those expected in the absence of vegetation. Observed eddy viscosities are consistent with theoretical expectations, derived from scaling arguments using a standard mixing‐length model. These results suggest that pneumatophore roots can contribute greatly to turbulent mixing (e.g., eddy viscosities were on average O(10−4–10−3 m2/s) and therefore may enhance the sediment transport occurring in mangrove forest fringes.

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“…The second columns of Figures and show the eddy viscosity,

ν_{t} = - \overset{u' w'}{true} \cdot {(\partial \overset{true¯}{u} / ∂z)}^{- 1}

Section: Resultsmentioning

confidence: 99%

Turbulence Within Natural Mangrove Pneumatophore Canopies

et al. 2019

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“…1 < p < 0.5. Van Rijn (1985) presented evidence that P increases from values less than 1 to values greater than 1 with increasing (u*!ws)' Lees (1981) made measurements of profiles of velocity and concentration in the sea from which she obtained values of p generally in the range 1 < P < 10. The value increased with grain size and decreased with concentration.…”

Section: Constantmentioning

confidence: 97%

Sand Transport on the Continental Shelf

Dyer¹,

Soulsby²

1988

Annu. Rev. Fluid Mech.

140

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“…Swart (1976) cites workers who have found /l to be less than one, and others with p greater than one. This stage of the interpretation is considered in more detail in Lees (1982). The method of computation assumes, of course, that the Karman-Prandtl and Rouse equations are the best representatives of the velocity and concentration profiles.…”

Section: Tidally Dominated Sediment Transportmentioning

confidence: 98%

The relationship of sediment transport rates and paths to sandbanks in a tidally dominated area off the coast of East Anglia, U.K.

Lees

1983

Sedimentology

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Sand transport measurements of bedload and suspended load in the Sizewell‐Dunwich Banks area, East Anglia have shown that the suspended mode is dominant. The depth‐integrated spring tidal residual is 5.66 g cm−1 sec−1, although the neap rate is only one‐fifth of this. The calculated bedload transport rates also vary, from 0.012 to 0.040 g cm−1 sec−1, correlating with changing meteorological conditions. In order to predict the bedload sediment circulation pattern from midwater current meter measurements, five sediment transport equations were calibrated, using fluorescent dyed sand. Yalin's relationship gave the best estimates. The bed shear stress was determined by extrapolating the velocity profile as a power law relationship, with an exponent equal to 0.1, from midwater down to 2 m and as a lognormal profile from 2 m to the sea‐bed. Roughness length values appropriate to the substrate were used. Although bedload transport residuals are mainly to the south, the banks trend northwards from the coast and have also elongated in this direction. This is thought to be in response to the dominance of the suspended sediment transport. It is suggested that a tidal residual eddy mechanism is responsible for the banks’maintenance, similar to the process operating in Start Bay, Devon. The well‐documented westward movement of the banks is likely to be related to wave processes.

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Relationship between eddy viscosity of seawater and eddy diffusivity of suspended particles

Cited by 27 publications

References 8 publications

Turbulence Within Natural Mangrove Pneumatophore Canopies

Turbulence Within Natural Mangrove Pneumatophore Canopies

Sand Transport on the Continental Shelf

The relationship of sediment transport rates and paths to sandbanks in a tidally dominated area off the coast of East Anglia, U.K.

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