Morphological development of rip channel systems: Normal and near‐normal wave incidence

Calvete, D.; Dodd, Nicholas; Falqués, Albert; Leeuwen, Sonja M. van

doi:10.1029/2004jc002803

Cited by 94 publications

(193 citation statements)

References 28 publications

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“…This is suggested by the linear stability analysis of Calvete et al (2005) where, in this barred beach, transverse bars at the shore grow from a linear mode which fits with the initial state of our transverse bars evolution described later. Furthermore, previous modelling shows that oblique/transverse bars form in areas where there is significant wave breaking.…”

Section: Equilibrium Beach Profilesupporting

confidence: 75%

Generation and nonlinear evolution of shore-oblique/transverse sand bars

et al. 2006

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The coupling between topography, waves and currents in the surf zone may selforganize to produce the formation of shore-transverse or shore-oblique sand bars on an otherwise alongshore uniform beach. In the absence of shore-parallel bars, this has been shown by previous studies of linear stability analysis, but is now extended to the finite-amplitude regime. To this end, a nonlinear model coupling wave transformation and breaking, a shallow-water equations solver, sediment transport and bed updating is developed. The sediment flux consists of a stirring factor multiplied by the depthaveraged current plus a downslope correction. It is found that the cross-shore profile of the ratio of stirring factor to water depth together with the wave incidence angle primarily determine the shape and the type of bars, either transverse or oblique to the shore. In the latter case, they can open an acute angle against the current (upcurrent oriented) or with the current (down-current oriented). At the initial stages of development, both the intensity of the instability which is responsible for the formation of the bars and the damping due to downslope transport grow at a similar rate with bar amplitude, the former being somewhat stronger. As bars keep on growing, their finite-amplitude shape either enhances downslope transport or weakens the instability mechanism so that an equilibrium between both opposing tendencies occurs, leading to a final saturated amplitude. The overall shape of the saturated bars in plan view is similar to that of the small-amplitude ones. However, the final spacings may be up to a factor of 2 larger and final celerities can also be about a factor of 2 smaller or larger. In the case of alongshore migrating bars, the asymmetry of the longshore sections, the lee being steeper than the stoss, is well reproduced. Complex dynamics with merging and splitting of individual bars sometimes occur. Finally, in the case of shore-normal incidence the rip currents in the troughs between the bars are jet-like while the onshore return flow is wider and weaker as is observed in nature.

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Section: Equilibrium Beach Profilesupporting

confidence: 75%

Generation and nonlinear evolution of shore-oblique/transverse sand bars

et al. 2006

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“…Hoefel and Elgar, 2003;Ruessink et al, 2007bRuessink et al, , 2012 or on alongshore variability (e.g. Reniers et al, 2004;Calvete et al, 2005;Drønen and Deigaard, 2007;Castelle and Coco, 2012) alone, have become quite mature. The key challenge will be to integrate both model concepts into a single model that can adequately simulate the complete dynamics of double sandbar systems.…”

Section: Discussionmentioning

confidence: 99%

Morphological coupling in multiple sandbar systems – a review

Price

Ruessink

Castelle³

2014

Earth Surf. Dynam.

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Abstract. Subtidal sandbars often exhibit alongshore variable patterns, such as crescentic plan shapes and rip channels. While the initial formation of these patterns is reasonably well understood, the morphodynamic mechanisms underlying their subsequent finite-amplitude behaviour have been examined far less extensively. This behaviour concerns, among other aspects, the coupling of alongshore variable patterns in an inner bar to similar patterns in a more seaward bar, and the destruction of crescentic patterns. This review aims to present the current state of knowledge on the finite-amplitude behaviour of crescentic sandbars, with a focus on morphological coupling in double sandbar systems. In this context we include results from our recent study, based on a combination of remote-sensing observations, numerical modelling and data-model integration. Morphological coupling is an inherent property of double sandbar systems, where the inner bar may attain a type of morphology not found in single bar systems. Coupling is governed by water depth variability along the outer-bar crest and by various wave characteristics, including the offshore wave height and angle of incidence. In recent research, the role of the angle of wave incidence for sandbar morphodynamics has received more attention. Numerical modelling results have demonstrated that the angle of wave incidence is crucial to the flow pattern, sediment transport, and thus the emerging morphology of the coupled inner bar. Moreover, crescentic patterns predominantly vanish under highangle wave conditions, highlighting the role of alongshore currents in straightening sandbars and challenging the traditional conception that crescentic patterns vanish under high-energy, erosive wave conditions only.

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“…This mechanism is strongest for shore-normal waves, but it can also model crescentic bar formation for oblique wave incidence. In the latter case, however, the wavelengths and the migration rates are overpredicted by the models (Calvete et al, 2005).…”

Section: Introductionmentioning

confidence: 93%

“…The model employed in the present study is an extension of the model called MORFO60 (Calvete et al, 2005), which describes the feedback between waves, depth-averaged currents, free surface elevation and bed evolution. An extended version of the equations for the roller dynamics has been incorporated, together with the possibility of accounting for wind shear stresses and tide-induced sea surface level slopes.…”

Section: Model Formulationmentioning

confidence: 99%

“…The formation of realistic crescentic bars has been reproduced by many linear (Deigaard et al, 1999;Falqués et al, 2000;Calvete et al, 2005) and nonlinear (Caballeria et al, 2002;Damgaard et al, 2002;Reniers et al, 2004;Garnier et al, 2008) morphodynamic models. A self-organization physical mechanism called 'bed-surf coupling', first described by Falqués et al (2000), explains the formation of crescentic bars in the majority of these models.…”

Section: Introductionmentioning

confidence: 99%

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Modeling waves, currents and sandbars on natural beaches: The effect of surface rollers

Ribas

Swart

Calvete

et al. 2011

Journal of Marine Systems

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A morphodynamic model has been extended to gain more fundamental knowledge about the formation of nearshore sand bars. The model describes feedbacks between waves, rollers, depth-averaged currents and bed evolution, so that self-organized processes can develop. Offshore wave, wind and tide conditions and the bathymetry measured at Egmond site (the Netherlands) are firstly applied to compute the longshore current and wave height profiles. A comparison of the results with field data of that beach reveals that including the roller dynamics and the forcing by wind shear stresses and tide-induced sea level slopes is essential to accurately simulate the longshore current. Several model parameters are calibrated to minimize the rootmean-square errors. Subsequently, the wave and bathymetric conditions measured at Noordwijk site (the Netherlands) are used to compare modeled crescentic bars and up-current oriented finger bars with the nearshore sandbars observed at this site. Positive feedback leading to realistic formation of up-current bars only occurs if a novel term, i.e., the resuspension of sediment due to the turbulence created by the rollers, is included in the model. The modeled wavelength, crest orientation and growth rate agree with those of the observed up-current bars but the model overestimates the migration rate. The wavelength and migration rates of crescentic bars in case of oblique wave incidence are more accurately simulated if the reference longshore current is modeled including the roller dynamics.

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Morphological development of rip channel systems: Normal and near‐normal wave incidence

Cited by 94 publications

References 28 publications

Generation and nonlinear evolution of shore-oblique/transverse sand bars

Generation and nonlinear evolution of shore-oblique/transverse sand bars

Morphological coupling in multiple sandbar systems – a review

Modeling waves, currents and sandbars on natural beaches: The effect of surface rollers

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