Shore-Parallel Flows in a Barred Nearshore

Greenwood, Brian; Sherman, Douglas J.

doi:10.9753/icce.v18.101

Cited by 2 publications

(1 citation statement)

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“…All sensors were hardwired to a shore-based power supply and computercontrolled data acquisition system (Greenwood, 1983;Greenwood and Sherman, 1983). Sensors were scanned every 0.42 s for twenty-one minutes during each sample period, to give data records of approximately 3000 values.…”

Section: Data Acquisitionmentioning

confidence: 99%

Vertical and horizontal structure in cross-shore flows: An example of undertow and wave set-up on a barred beach

Greenwood

Osborne

1990

Coastal Engineering

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Greenwood, B. and Osborne, P.D., 1990. Vertical and horizontal structure in cross-shore flows: An example of undertow and wave set-up on a barred beach. Coastal Eng., 14: 543-580. Eulerian measurements of the horizontal, cross-shore velocity field in the lowermost meter of the water column, in association with measurements of waves and the mean elevation of the water surface, across a nontidal, low relief, barred surf-zone reveal: (a) spatially coherent patterns of the timeaveraged first, second and third moments of the velocity field, which vary temporally in direct response to the incident waves; (b) large asymmetries in the flow field, with offshore-directed mean flows upto ~ 0.20 m s-a and onshore-directed velocity skewness (the third moment normalized by the standard deviation) upto ~ + 0.60; (c) mean flows decrease and oscillatory flows (measured by the standard deviation of the velocity field) increase towards the water surface; (d) a fourth-order polynomial provides the best fit to the cross-shore set-up, reflecting the influence of variable energy dissipation due to topographic controls on wave breaking; (e) significant linear correlations exist between the cross-shore mean velocities and the maximum set-up of the still-water surface near to the shoreline (upto 82% of the observed variability in the former can be accounted for by linear regressions ); (f) set-up is highly correlated with the incident wave height (86% of the observed variability in the former can be accounted for by a linear regression); (g) gradients in the mean water surface are significantly less than those predicted by a linear function of beach slope as originally proposed by Bowen et al. ~ even using an appropriate breaking criterion (0.4-0.6) for the spilling breakers recorded.Cross-shore circulation over the low relief, barred nearshore slope is predominantly two-dimensional over the outer bar in this case study. The near-bed mean flow is an undertow responding to the balance between the wave-generated, depth-dependent momentum flux directed onshore, the stress induced by the onshore mass transport under waves and wind, and the hydraulic pressure gradient induced by set-up of the mean water.level.~Bowen et al. (1968).0378-3839/90/$03.50

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Section: Data Acquisitionmentioning

confidence: 99%

Vertical and horizontal structure in cross-shore flows: An example of undertow and wave set-up on a barred beach

Greenwood

Osborne

1990

Coastal Engineering

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Hummocky cross‐stratification in the surf zone: flow parameters and bedding genesis

1986

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Primary sedimentary structures exhibiting the diagnostic criteria for single sets of hummocky cross‐stratification (Harms et al.) have been found in the surf zone of a storm‐wave dominated coastline in the Canadian Great Lakes. Epoxy peels of box cores (0.45 m × 0.30 m) reveal hummocky stratification in well‐sorted, fine‐grained sands in water depths less than 2 m under conditions of wave breaking and strong longshore currents. The wavelengths of the hummocks (0.3–0.6 m) are somewhat smaller than the norm for their ancient analogues, but the ratios of length to height (8–12) are comparable. Depth of activity rods have been used to identify those hummocks that formed during sediment transport events when the near‐bed currents were recorded directly using electromagnetic flowmeters. Results from such experiments clearly identify the hummocky stratification as being produced by an actively growing bedform with little or no lateral migration. Hummocks occur under conditions close to that expected for the upper flat bed. In one vertical sequence, the hummocky cross‐stratification is underlain by subhorizontal, planar lamination and overlain by undulatory lamination which grades upward into small‐scale, trough cross‐lamination of wave ripple origin. This sequence was associated with a single storm and would appear to represent a combined‐flow regime sequence with the hummocky structure representing a post‐vortex (?) ripple bedform. At the inferred time of hummock formation, near‐bed oscillatory flows were dominant and reached maxima of 1.1 m s −1 with a superimposed longshore current of 0.27 m s−1. Rapid sedimentation associated with vertical growth of the hummocky bedform was triggered by a significant reduction in the orbital currents (by 19%) and'steady'currents (by 67%) while the total bed shear remained high.

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Shore-Parallel Flows in a Barred Nearshore

Cited by 2 publications

References 10 publications

Vertical and horizontal structure in cross-shore flows: An example of undertow and wave set-up on a barred beach

Vertical and horizontal structure in cross-shore flows: An example of undertow and wave set-up on a barred beach

Hummocky cross‐stratification in the surf zone: flow parameters and bedding genesis

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