Modification of a linear bar-trough system by a standing edge wave

Bauer, Bernard O.; Greenwood, Brian

doi:10.1016/0025-3227(90)90003-3

Cited by 40 publications

(19 citation statements)

References 44 publications

(68 reference statements)

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“…Previous studies have confirmed the generation of edge waves by storms both in this particular environment (e.g. Bauer and Greenwood, 1990) and elsewhere (e.g. Huntley.…”

Section: Discussionsupporting

confidence: 54%

Frequency dependent cross-shore suspended sediment transport. 2. A barred shoreface

1992

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Osborne, P.D. and Greenwood, B., 1992. Frequency dependent cross-shore suspended sediment transport. 2. A barred shoreface. Mar. Geol., Field measurements of the local time-varying suspended sediment flux across a barred shoreface demonstrate that sediment transport is a response to high frequency wind wave oscillatory currents, low frequency waves and mean flows. The relative importance of the various transport components varies spatially and temporally in association with variability in the incident wave energy. In contrast to the non-barred shoreface, where variations were strongly depth-dependent, sediment transport across the barred shoreface is constrained by position with respect to the bars.On the lakeward slope of the bar, wind-wave oscillatory currents induce large rates of onshore transport near the bed; low frequency oscillatory currents (< 0.05 Hz) in this region are driven by the group-forced, bound long wave and produce an offshore transport, often equal in magnitude to that induced by the wind waves. The sediment transport attributable to mean currents near the bed is always offshore, resulting in a net offshore sediment flux across the slope. On the bar crest, net sediment transport is seen to be close to zero, owing to a balance between the offshore mean transport and the onshore net oscillatory transport (resulting from interaction between both high and low frequency waves).Landward of the bar crest and in the trough, sediment transport by wind waves decreases owing to dissipation of energy during wave breaking. In contrast, the contribution to suspended sediment transport by low frequency waves increases relatively, and furthermore this transport is now predominantly landward. This transport is probably associated with the release of the group-bound long wave as a free wave and the associated landward sediment flux approximates the offshore transport induced by the mean currents.Local variability in the frequency dependent transport, both in terms of magnitude and direction is closely related to the bedforms present and their variation in response to increasing and decreasing wave energy. Specifically, the oscillatory transport attributable to wind-wave frequencies is predominantly onshore in the presence of steep vortex ripples, but is directed offshore as the flow regime shifts to lower amplitude post-vortex ripples.

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“…Previous studies have confirmed the generation of edge waves by storms both in this particular environment (e.g. Bauer and Greenwood, 1990) and elsewhere (e.g. Huntley.…”

Section: Discussionsupporting

confidence: 54%

Frequency dependent cross-shore suspended sediment transport. 2. A barred shoreface

1992

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“…Thus, there was also a distinct lag in the infragravity wave transport compared to the gravity wave transport. Certainly, infragravity energies became dominant in the wave and current spectra in a manner similar to the lag that had previously been noted by Bauer and Greenwood (1990) in a barred system in Georgian Bay (an arm of Lake Huron).…”

Section: Contributions Au Taux De Transport En Biais Net à 23h15 Le supporting

confidence: 59%

Emergence and Migration of a Nearshore Bar: Sediment Flux and Morphological Change on a Multi-Barred Beach in the Great Lakes

Greenwood

Permanand-Schwartz

Houser

2007

gpq

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Burley Beach (southeastern Lake Huron) exhibits a multi-barred shoreface, the long-term equilibrium morphology characteristic of many low angle, sandy beaches in the Canadian Great Lakes. During a single major storm, a new bar emerged 50-60 m offshore as an irregular trough-crest form, through differential erosion of an existing shore terrace. Emergence, bar growth and offshore migration were associated with: (a) an overall negative sediment balance in the inner surf zone initially (‑2.30 m3>/m beach width), but with a large positive sediment balance (+5.10 m3/m) subsequent to the storm peak and during the storm decay; (b) progradation of the beach step to produce a new shore terrace; and (c) offshore migration of the two outer bars to provide the accommodation space necessary for the new bar. The primary transport mechanisms accounting for emergence of the new bar, its growth and migration were: (a) the mean cross-shore currents (undertow), which always transported suspended sediment offshore; and (b) the onshore transport of suspended sediment by incident gravity wave frequencies early in the storm and subsequently by infragravity waves (at the storm peak and the decay period). The longshore transport of sediment was significant in terms of the gross transport, although the net result was only a small transport to the south-west (historic littoral transport direction). It did not cause bar initiation, but it may have supplied some of the sediment for bar growth. The primary mechanism for bar initiation and growth was the cross-shore displacement of sediment by wave-driven (oscillatory) transport and cross-shore mean currents (undertow).Émersion et migration d’une barre côtière : bilan sédimentaire et changements morphologiques d’une plage à barres multiples des Grands Lacs. La plage de Burley (sud-est du lac Huron) présente une avant-côte à barres multiples, état morphologique caractéristique de l’équilibre à long terme des plages sableuses à pente faible. Au cours d’un seul orage majeur, une nouvelle barre s’est développée à 50-60 m au large de la côte en forme de creux et crête irrégulière, suite à l’érosion d’une terrasse côtière. L’émersion, la croissance et la migration de la barre est attribuable à (a) un bilan sédimentaire négatif dans la zone interne du ressac (‑2,30 m3/m), mais à un bilan sédimentaire positif (+5,10 m3/m) durant l’apogée et la dissipation de l’orage, (b) l’exondation du gradin de plage pour générer une nouvelle terrasse côtière et (c) la migration de deux barres distales au large de la côte, laissant assez d’espace pour la mise en place d’une nouvelle barre. Les mécanismes de l’émersion, de la croissance et de la migration sont : (a) les contre-courants qui transportent les sédiments en suspension au large de la côte et (b) le transport vers la côte via la fréquence des vagues de gravité générées au début de l’orage et par les vagues d’infragravité subséquentes (au maximum de l’orage et durant sa dissipation). Le transport brut des sédiments est important, mais le résultat net correspo...

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“…Many studies have linked the coastal morphology, in particular the positions and shape of bars, to the spatial scales of lf waves. The length scale of standing waves measured in field conditions has been shown to fit well to the cross-shore spacing of bars (Aagaard, 1990;Bauer and Greenwood, 1990;Aagaard and Greenwood, 1994; among others). This has been interpreted as a sediment particle movement from standing long wave nodes to antinodes when the dominant sediment transport mode was suspended load (Bowen, 1980;Holman and Bowen, 1982).…”

mentioning

confidence: 81%

“…This has been interpreted as a sediment particle movement from standing long wave nodes to antinodes when the dominant sediment transport mode was suspended load (Bowen, 1980;Holman and Bowen, 1982). Bauer and Greenwood (1990) and Aagaard and Greenwood (1994) have shown experimental evidence of such a mechanism. However drift velocities in the bottom boundary layer beneath standing waves are generally assumed to be small compared to lf and hf wave orbital motions and mean currents (Aagaard and Greenwood, 2008).…”

Section: -Introductionmentioning

confidence: 99%

Sediment transport and beach profile evolution induced by bi-chromatic wave groups with different group periods

Alsina

Padilla

Caceres

2016

Coastal Engineering

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In this paper, large-scale experimental data are presented showing the beach profile morphological evolution induced by four different bi-chromatic wave conditions characterized by very similar energy content between them but varying the modulation period. Important differences were observed in the resultant beach profiles as a function of the wave group periods. Larger variability in the profile evolution is generally observed for larger wave group periods and, more importantly, as the wave group period increases the distance between the generated breaker bar and the shoreline increases. The measured primary wave height to depth ratio () increases with the wave group period, which is consistent with the observed larger wave height at the breaking location. The primary wave 2 breaking location is also observed at increasing distances with respect to the initial shoreline as the wave group period increases. The variation in  with wave group period is related to the selective energy dissipation of the higher primary frequency component (f1) during the wave group shoaling. Broad bandwith conditions (reduced wave group period) lead to larger dissipation of wave heights at the f1 component relative to f2 resulting in a reduction in the wave modulation and primary wave height at the breaking location. Suspended sediment fluxes obtained from collocated velocity and sediment concentration measurements in the surf zone showed a consistently larger contribution of the mean return flow to the suspended sediment fluxes compared with the wave group and primary wave components. The distinct beach profile evolution in terms of bar location is interpreted from an increasing distance of the mean breakpoint location and the location of maximum return flow with respect to the shoreline as the wave group period increases.Keywords: bi-chromatic wave groups, bar morphology, sediment transport, suspended sediment concentration, large scale experiments, morphodynamics. -IntroductionHigh frequency (hf) wave groups and the associated low frequency (lf) waves are natural characteristics of random waves propagating to coastal areas. Wave grouping has important implications in coastal sediment transport and in the evolution of the coastal morphology.Measured sediment transport rates in surf zone conditions suggest a larger influence of mean components and short-scale wind and swell waves in the net cross-shore sediment transport (Ruessink et al., 1998). However, the relative importance of long waves has been showed to increase within the surf zone, as short wave dissipation occurs via wave breaking, and has 3 been reported to dominate the suspended sediment transport in the inner surf zone (Aagaard and Greenwood, 2008).Moreover, beach evolution is the result of sediment transport gradients that may vary at the time-scales of long waves and wave groups. Wave groups also introduce further intermittency into the short-wave scale hydrodynamics (i.e. wave breaking, slow modulation of the water depth and wave height to water depth ratio...

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Modification of a linear bar-trough system by a standing edge wave

Cited by 40 publications

References 44 publications

Frequency dependent cross-shore suspended sediment transport. 2. A barred shoreface

Frequency dependent cross-shore suspended sediment transport. 2. A barred shoreface

Emergence and Migration of a Nearshore Bar: Sediment Flux and Morphological Change on a Multi-Barred Beach in the Great Lakes

Sediment transport and beach profile evolution induced by bi-chromatic wave groups with different group periods

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