Undertow over a barred beach

Faria, A. F. Garcez; Thornton, E. B.; Lippmann, Thomas; Stanton, Timothy P.

doi:10.1029/2000jc900084

Cited by 127 publications

(33 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…From the new non‐dimensional ϵ scaling , the non‐dimensional eddy diffusivity K is

\frac{K (z)}{h {((), d F / d x)}^{1 / 3}} = δ^{4 / 3} A^{1 / 3} e x p (\frac{α}{3} \frac{z}{h}),

a different vertical structure than the commonly assumed constant [ Faria et al , 2000] or log‐profile [ Beach and Sternberg , 1988; Denny and Shibata , 1989] based ≈ u * κz (where u * is the bed friction velocity). The dimensional K depends on wave breaking (d F /d x ) analogous to earlier dimensional analysis [ Battjes , 1975].…”

Section: Discussionmentioning

confidence: 99%

Scaling surf zone turbulence

Feddersen

2012

Geophysical Research Letters

View full text Add to dashboard Cite

[1] Turbulence in the surf zone, the shallow region adjacent to the shoreline, has a key role in beach erosion, fertilization, dispersal, and larval settlement of marine invertebrates, and microbial contamination dilution in beach waters. Breakingwave generated (the dominant source) surf zone turbulence is understood poorly. A new surf zone turbulent dissipation rate scaling is derived, that collapses new field surf zone observations with relatively high skill compared to other scalings. The vertically-uniform length-scale is 1/6 the water depth, and 15% of the wave-energy flux gradient is dissipated below the mean surface. Field and laboratory surf zone turbulence observations are shown to be consistent using the scaling. The non-dimensional surf zone diffusivity and suspended sediment profile can be applied to sediment transport and a range of biological processes including microbial pathogen contamination of beach waters.

show abstract

“…From the new non‐dimensional ϵ scaling , the non‐dimensional eddy diffusivity K is

\frac{K (z)}{h {((), d F / d x)}^{1 / 3}} = δ^{4 / 3} A^{1 / 3} e x p (\frac{α}{3} \frac{z}{h}),

Section: Discussionmentioning

confidence: 99%

Scaling surf zone turbulence

Feddersen

2012

Geophysical Research Letters

View full text Add to dashboard Cite

show abstract

“…At each frame, the friction velocity u * is estimated from the alongshore bottom stress (6) as u 2 * 5 c d hjujyi, where the best-fit c d 5 2.3 3 10 23 (section 4a). Although the crossshore bottom stress can also contribute to the total bottom stress and thus u * , because of the strong vertical structure of the mean cross-shore current (Faria et al 2000), it is unclear whether a quadratic drag law is applicable for the cross-shore bottom stress t b…”

Section: Bbl Scalingmentioning

confidence: 99%

Observations of the Surf-Zone Turbulent Dissipation Rate

Feddersen

2012

Journal of Physical Oceanography

View full text Add to dashboard Cite

The contributions of surface (breaking wave) boundary layer (SBL) and bottom (velocity shear) boundary layer (BBL) processes to surf-zone turbulence is studied here. The turbulent dissipation rate , estimated on a 160-m-long cross-shore instrumented array, was an order of magnitude larger within the surf zone relative to seaward of the surf zone. The observed covaried across the array with changing incident wave height, tide level, and alongshore current. The cross-shore-integrated depth times was correlated with, but was only 1% of, the incident wave energy flux, indicating that surf-zone water-column turbulence is driven directly (turbulence injected by wave breaking) or indirectly (by forcing alongshore currents) by waves and that the bulk of occurs in the upper water column. This small fraction is consistent with laboratory studies. The surf-zonescaled (or Froude-scaled) is similar to previous field observations, albeit somewhat smaller than laboratory observations. A breaking-wave scaling is applicable in the midwater column at certain locations, indicating a vertical diffusion of turbulence and balance. However, observations at different cross-shore locations do not collapse, which is consistent with a cross-shore lag between wave energy gradients and the surface turbulence flux. With strong alongshore currents, a BBL-scaled indicates that shear production is a significant turbulence source within the surf zone, particularly in the lower water column. Similarly for large currents at one location, the dissipation to shear production ratio approaches one. Both dissipation scalings depend upon wave energy flux gradients. The ratio of BBL to SBL has complex dependencies but is larger for a deeper part of the surf zone and more obliquely incident waves.

show abstract

“…In a surf zone characterized by an alongshore homogeneous morphology, the onshore Stokes drift profile is vertically uniform, and the Eulerian undertow flow has a parabolic velocity profile with maximum offshore velocity at middepth or near bottom (Svendsen 1984;Putrevu and Svendsen 1993;Haines and Sallenger 1994;Garcez Faria et al 2000;Reniers et al 2004b), resulting in an imbalance between u St (z) and u E (z) throughout the water column (Fig. 1a).…”

Section: Introductionmentioning

confidence: 99%

“…A compensating wave-driven offshore Eulerian flow u E (z) exists below the wave trough, referred to as undertow. The presence of wave-driven Eulerian undertow inside the surf zone is widely known and has been measured extensively in the field (Haines and Sallenger 1994;Garcez Faria et al 2000;Reniers et al 2004b) and has also been found to extend well offshore on the inner shelf (Lentz et al 2008;Kirincich et al 2009;Ohlmann et al 2012). The summation of u St (z) and u E (z), throughout the water column at a given location, results in a wave-averaged Lagrangian velocity u L (z), where z is the vertical elevation defined as positive upward from the sea surface.…”

Section: Introductionmentioning

confidence: 99%

Field Observations of Surf Zone–Inner Shelf Exchange on a Rip-Channeled Beach

Brown

MacMahan

Reniers

et al. 2015

Journal of Physical Oceanography

View full text Add to dashboard Cite

Cross-shore exchange between the surf zone and the inner shelf is investigated using Lagrangian and Eulerian field measurements of rip current flows on a rip-channeled beach in Sand City, California. Surface drifters released on the inner shelf during weak wind conditions moved seaward due to rip current pulses and then returned shoreward in an arcing pattern, reentering the surf zone over shoals. The cross-shore velocities of the seaward-and shoreward-moving drifters were approximately equal in magnitude and decreased as a function of distance offshore. The drifters carried seaward by the rip current had maximum cross-shore velocities as they exited the surf zone and then decelerated as they moved offshore. The drifters moving shoreward accelerated as they approached the surfzone boundary with maximum cross-shore velocities as they reentered the surf zone over shoals. It was found that Stokes drift was not solely responsible for the onshore transport across the surfzone boundary. The cross-shore diffusivity on the inner shelf was greatest during observations of locally contained cross-shore exchange. These field observations provide evidence that the cross-shore exchange between the surf zone and inner shelf on a rip-channeled beach is due to wave-driven rip current circulations and results in surface material being contained within the nearshore region.

show abstract

Undertow over a barred beach

Cited by 127 publications

References 29 publications

Scaling surf zone turbulence

Scaling surf zone turbulence

Observations of the Surf-Zone Turbulent Dissipation Rate

Field Observations of Surf Zone–Inner Shelf Exchange on a Rip-Channeled Beach

Contact Info

Product

Resources

About