Tidally induced turbulence and suspended sediment

Souza, Alejandro J.; Alvarez, Luis G.; Dickey, Tommy D.

doi:10.1029/2004gl021186

Cited by 38 publications

(40 citation statements)

References 12 publications

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“…Baumert and Radach (1992) identified the Strouhal number, as a characteristic parameter for the mixing associated with tidal flow. By demonstrating that, apart from bottom and surface roughness lengths, Str is the only parameter defining the dynamics of the well-mixed irrotational pressure gradient driven tidal flow, they could show how the relative time lag of turbulent parameters with respect to the bed stress increases with Str, in a similar way to Simpson et al (2000) and Souza et al (2004). Burchard (2009), Burchard and Hetland (2010) and Souza et al (2013) have used this idea to define the behaviour of tidal and oscillatory flows in shelf seas using turbulent closure models.…”

Section: Use Of the Stokes Number To Describe Tidal Dynamics In Estuasupporting

confidence: 55%

On the use of the Stokes number to explain frictional tidal dynamics and water column structure in shelf seas

Souza

2013

Ocean Sci.

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Abstract. In recent years coastal oceanographers have suggested using the "Strouhal" number or its inverse, the "Stokes" number, to describe the effect of bottom boundary layer turbulence on the vertical structure of both density and currents. These are defined as the ratios of the frictional depth (δ) to the water column depth (h) or vice versa. Although many researchers have mentioned that the effects of the earth's rotation should be important, they have tended to omit it. Rotation may have an important influence on tidal currents, as the frictional depth from a fully cyclonic to a fully anticyclonic tidal ellipse can vary by up to an order of magnitude at mid latitudes. The Stokes number might appear smaller for cyclonic current ellipses (larger for anticyclonic) than it is without rotation, resulting in frictional effects being underestimated (overestimated). Here, a way to calculate a Stokes number is proposed, in which the effect of the earth's rotation is taken into account. The standard Stokes and the rotational Stokes numbers are used as predictors for the position of the tidal mixing fronts in the Irish Sea. Results show that use of the rotational number improves the predictions of fronts in shallow cyclonic areas of the eastern Irish Sea. This suggests that the effect of rotation on the water column structure will be more important in shallow shelf seas and estuaries with strong rotational currents.

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Section: Use Of the Stokes Number To Describe Tidal Dynamics In Estuasupporting

confidence: 55%

On the use of the Stokes number to explain frictional tidal dynamics and water column structure in shelf seas

Souza

2013

Ocean Sci.

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“…The measurements display variable correlation between the two instruments and the observed behaviour is clearly more complicated than simple resuspension. Under this unique process, we would expect SSC peaks to correlate with velocity peaks with a phase lag due to the time needed for vertical transport of suspended particles (e.g., Souza et al, 2004). The ADCP-inferred SSC after 19/20…”

Section: Observed Sediment Dynamicsmentioning

confidence: 99%

“…The ADCP also recorded the acoustic backscatter strength, which can be interpreted into suspended sediment mass concentration via regression against values obtained from the water samples (e.g., Souza et al, 2004 Before 21 February, waves remain small (≤ 0.6 m) and short. During this period, they are unlikely to significantly contribute to sediment transport, and wave-current interactions can be neglected.…”

Section: Field Observations and Environmental Conditionsmentioning

confidence: 99%

Modelling-based assessment of suspended sediment dynamics in a hypertidal estuarine channel

et al. 2014

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We investigate the dynamics of suspended sediment transport in a hypertidal estuarine channel which displays a vertically sheared exchange flow. We apply a three-dimensional process-based model coupling hydrodynamics, turbulence, and sediment transport to the Dee Estuary, in the north-west region of the UK. The numerical model is used to reproduce observations of suspended sediment and to assess physical processes responsible for the observed suspended sediment concentration patterns.The study period focuses on a calm period during which wave-current interactions can reasonably be neglected. Good agreement between model and observations has been obtained. A series of numerical experiments aims to isolate specific processes and confirm that the suspended sediment dynamics result primarily from advection of a longitudinal gradient in concentration during our study period, combined with resuspension and vertical exchange processes. Horizontal advection of sediment presents a strong semidiurnal variability, while vertical exchange processes (including time-varying settling as a proxy for flocculation) exhibit a quarter-diurnal variability. Sediment input from the river is found to have very little importance and spatial gradients in suspended concentration are generated by spatial heterogeneity in bed sediment characteristics and spatial variations in turbulence and bed shear stress.

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“…The water depths, tidal current speeds and record durations are listed in Table 2. Site 7 was in the Gulf of California (Souza et al, 2004), site 2 in the northern North Sea, site 3 in the southern North Sea, and the remainder in the Irish Sea-site 1 in Red Wharf Bay, off the east coast of Anglesey (Rippeth et al, 2003), sites 4 and 5 in Liverpool Bay (Souza and Howarth, 2005), site 6 off Holyhead, west of Anglesey (see Fig. 1 for a map of the sites around the UK).…”

Section: Measurementsmentioning

confidence: 99%

Reynolds stress observations in continental shelf seas

Howarth

Souza

2005

Deep Sea Research Part II: Topical Studies in Oceanography

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The three basic observational approaches to estimating turbulence parameters in continental shelf seas are free-fall micro-structure probes from which dissipation is inferred; fast-sample (10-20 Hz) current meters in sea-bed frames measuring turbulence intensity directly; and fast-sample O(1 Hz) high-frequency Acoustic Doppler Current Profilers (ADCPs) where Reynolds stress profiles and hence turbulence production can be estimated from the variance of the along beam data. Uncertainties are associated with each approach since turbulence is a small-scale, high-frequency phenomenon and since estimates can easily be contaminated by the presence of surface waves. This paper concentrates on the latter two approaches, particularly the ADCP method, focussing on the degree of confidence that can be placed on the estimates.Results are presented from nine experiments from six sites in the North and Irish Seas and one in the Gulf of California, involving the deployment of 0.6 and 1.2 MHz standard broadband ADCPs mounted in sea-bed frames. The sites ranged from very tidally energetic, shallow (20 m deep) to low tidal energy, deeper (110 m). The ADCPs recorded data with a variety of sample regimes, from 2 to 0.5 Hz; bin sizes ranged from 0.25 to 1 m. In two of the experiments the ADCP near-bed Reynolds stress estimates were tested against independent estimates from toroidal electro-magnetic current meters measuring the three components of current (vertical and both horizontal) at 8 Hz, deployed on a nearby frame. In all cases the correlation coefficient squared between the two sets of Reynolds stress estimates was 0.7. In a further three recent deployments, an Acoustic Doppler Velocimeter (ADV) was deployed on the bottom frame with the ADV measuring volume located within the first ADCP bin and sampling at 20 or 25 Hz. The ADV measurements also show an explained variance of about 80% and a transfer function of about 1 during periods where waves were not present.One objective of these studies was to test and improve representation of dissipation processes in two-and threedimensional numerical models, including the concept of the constant stress layer. At its very simplest, bottom stress is estimated from the depth-averaged flow via a quadratic drag law. Calculations from these measurements give values for the drag coefficient between 0.0006 and 0.0019, averaging 0.0011, smaller than the value used in most depth-averaged numerical models (0.0025). There is some evidence that the value of the drag coefficient is dependent on the tidal current speed. r

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Tidally induced turbulence and suspended sediment

Cited by 38 publications

References 12 publications

On the use of the Stokes number to explain frictional tidal dynamics and water column structure in shelf seas

On the use of the Stokes number to explain frictional tidal dynamics and water column structure in shelf seas

Modelling-based assessment of suspended sediment dynamics in a hypertidal estuarine channel

Reynolds stress observations in continental shelf seas

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