Vertical profiles of longshore currents and related bed shear stress and bottom roughness

Faria, A. F. Garcez; Thornton, Edward B.; Stanton, Tim; Soares, C; Lippmann, T. C.

doi:10.1029/97jc02265

Cited by 115 publications

(26 citation statements)

References 46 publications

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“…Like bed forms in other environments, megaripples affect sand transport through increased suspension by turbulence in their lee, as well as through bulk transport via migration [Gallagher et al, 1998;Ngusaru and Hay, 2004]. They act as hydraulic roughness elements, changing wave energy dissipation and water circulation patterns [Garcez-Faria et al, 1998]. In addition, they are thought to be the source of hummocky cross stratification in sedimentary sequences and therefore are used to interpret ancient environments [Duke et al, 1991].…”

Section: Megaripples In the Nearshorementioning

confidence: 99%

“…Results using the Bailard [1981] sediment transport formulation (not shown) are similar to Figure 2b. Although Average slope = 0, local slope is calculated and constrained to < 17°tan (angle of repose) 0.3 (17°) 0.1-0.8 (∼10°-40°) r w , r s , g 1.0 g/cm 3 , 2.65 g/cm 3 , 980 cm 2 /s constants C f (coefficient of friction) 0.003 [Church and Thornton, 1993] 0.0006-0.012 [Garcez-Faria et al, 1998] " b (bed load efficiency factor) [Bagnold, 1966] 0.135 [Thornton et al, 1996], 0.13 [Bailard, 1981] 0.11-0.14 [Bagnold, 1966] " s (suspended load efficiency factor) [Bagnold, 1966] 0.015 [Thornton et al, 1996], 0.01 [Bailard, 1981] 0.01 [Bagnold, 1966] f w (wave friction factor) 0.01 [following Ribberink, 1998] 0.005-0.04 [Fredsoe and Deigaard, 1992] jf (jump fraction) 0.05 0.1-0.01 (see text) (1) the amplitudes of bed forms from different simulations (Figures 2a and 2b) are slightly different, both types of transport models produce similarly shaped features.…”

Section: Formation and Characteristicsmentioning

confidence: 99%

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Computer simulations of self-organized megaripples in the nearshore

Gallagher

2011

J. Geophys. Res.

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[1] Megaripples are bed forms with heights of 20-50 cm and lengths of 1-10 m that are common in the surf zone of natural beaches. They affect sediment transport, flow energy dissipation, and larger-scale hydro-and morphodynamics. They are thought to be dynamically similar to bed forms in deserts, rivers, and deeper marine environments. Here a self-organization model (similar to models for subaerial bed forms) is used to simulate the formation and development of megaripples in the surf zone. Sediment flux is determined from combined wave and current flows using stream power and bed shear stress formulations as well as a third formulation for transport based on simple rules, which represent sheet flow. Random bed irregularities, either imposed or resulting from small variations in transport representing turbulence, are necessary seeds for bed form development. Feedback between the bed and the flow, in the form of a shadow zone downstream of a bed form and increasing flow acceleration with elevation over the crests of bed forms, alter the transport such that organized bed forms emerge. Modeled bed form morphology (including cross-sectional shape and plan view) and dynamics (including growth and migration) are similar to natural megaripples. The model can be used to extend the field observations of Clarke and Werner (2004), which suggest that, if conditions remain the same, megaripples will continue to grow. Contrary to many bed form models, this model supports the idea that bed form spacing grows continually.

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Section: Megaripples In the Nearshorementioning

confidence: 99%

Section: Formation and Characteristicsmentioning

confidence: 99%

Computer simulations of self-organized megaripples in the nearshore

Gallagher

2011

J. Geophys. Res.

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“…In [27], one can find the data of 22 series of measurements of the parameters of WBBL, including the profiles of currents, the friction velocity u * , and the characteristic sizes of bottom irregularities k. Similar data of three series of measurements are presented in [1]. We use these results for the evaluation the reliability of relations (22) and (23).…”

Section: Experimental Datamentioning

confidence: 98%

“…The results of laboratory and in-situ experiments carried out with an aim of investigation of the structure of nonstationary (fluctuating and wave) bottom boundary layers over smooth and rough bottoms are described in [15,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. Numerous works are devoted to the analysis of the conditions of development of turbulence and its characteristics in bottom boundary layers (see, e.g., [18,36]).…”

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confidence: 99%

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Structure of the Wave Bottom Boundary Layer over Smooth and Rough Bottoms

Kushnir

2005

Phys Oceanogr

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The comparison of six well-known models of the wave bottom boundary layer shows that they are identical in the case of a smooth bottom but exhibit serious differences for the other types of conditions. The thickness of the wave bottom boundary layer and the coefficient of vertical diffusion of momentum are studied by using the relations of the k -ε -model. The validity of these estimates is checked by comparing the measured and computed values of the friction velocity. This comparison demonstrates fairly good agreement between the results characterized by a coefficient of correlation equal to 0.851.

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Depth Dependence of Nearshore Currents and Eddies

et al. 2017

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The three‐dimensional (across‐shore, alongshore, and vertical) structure of hourly mean currents and <0.01 Hz eddies was measured on a natural beach using 12 Acoustic Doppler Profilers. Both eddies and alongshore currents became relatively depth‐uniform inside the surfzone. Eddies showed greater depth dependence than alongshore currents. A two‐layer model, derived by scaling of the wave‐averaged shallow water equations, yielded separate equations for depth‐averaged and depth‐dependent velocity components. Scaling suggests, and observations confirm, only a small role for lateral advection in most surfzone cases, leading to one‐dimensional vertical models for depth dependence. For alongshore currents, depth dependence is generated by opposite forcing on lower and upper layers, respectively by bottom friction (quantified by time scale λb−1) and waves or wind. This generation is balanced by mixing between upper and lower layers (time scale λm−1), so the ratio between depth‐dependent and depth‐averaged alongshore currents equals λb/λm. Established models for bottom friction and breaker‐induced mixing predicted a surfzone reduction in λb/λm consistent with the observed reduction in alongshore current depth dependence. Scatter around trends was considerable. Alongshore variability was significant for depth‐dependence of currents and eddies. Inside (but not outside) the surfzone, the mixing time scale λm−1 was shorter than the eddy period, so a quasi‐steady balance was predicted between forcing and mixing of eddy depth dependence. Observed eddy depth dependence exceeded predictions for barotropic eddies generated by shear production (i.e., shear instabilities), possibly indicating generation of eddies by random breaking waves in the surfzone, or indicating baroclinic effects outside the surfzone.

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Vertical profiles of longshore currents and related bed shear stress and bottom roughness

Cited by 115 publications

References 46 publications

Computer simulations of self-organized megaripples in the nearshore

Computer simulations of self-organized megaripples in the nearshore

Structure of the Wave Bottom Boundary Layer over Smooth and Rough Bottoms

Depth Dependence of Nearshore Currents and Eddies

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