Coupled sandbar patterns and obliquely incident waves

Price, Timothy; Castelle, Bruno; Ranasinghe, Roshanka; Ruessink, Gerben

doi:10.1002/jgrf.20103

Cited by 14 publications

(21 citation statements)

References 54 publications

(105 reference statements)

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“…The initial beach morphology corresponds to a post storm, alongshore uniform, single‐barred beach. The morphological characteristics are similar to the observations in Price et al [] on the Gold Coast, consisting of a Dean profile that extends offshore to 15.7 m water depth with a superimposed bar located 150 m from the mean sea level shoreline with its crest in 2 m water depth. The computational grid covers a cross‐shore distance L x =780 m and an alongshore distance L y =2000 m, with a regular grid mesh composed of 10 × 10 m cells with periodic lateral boundary conditions.…”

Section: Model and Simulation Setupmentioning

confidence: 99%

“…The influence of tide is disregarded. A spatially constant d 50 of 200 μm was used in agreement with the beach sediment at the Gold Coast from which the initial Dean profile is derived [ Price et al , ]. Preliminary simulations were performed to address the sensitivity of the sandbar response after one morphological time step for a large

{scriptC}_{c} - {scriptC}_{w} - {scriptC}_{g}

space.…”

Section: Model and Simulation Setupmentioning

confidence: 99%

“…Using such a modeling approach, regularly spaced rip‐channeled morphologies were found to be nearshore morphodynamic instabilities developing as a result of the positive feedback between waves, flow, sediment transport, and the evolving bathymetry [ Falqués et al , ]. A variety of such morphodynamic models were subsequently developed and allowed investigating, for instance, the role of preexisting morphologies, wave conditions, or morphological coupling with other bed forms on the nonlinear evolution of surf zone sandbars [e.g., Garnier et al , , ; Tiessen et al , ; Smit et al , ; Castelle et al , ; Price et al , ]. However, the common characteristic of all these models is that they do not properly account for cross‐shore sediment transport processes.…”

Section: Introductionmentioning

confidence: 99%

“…Although such approach allows the saturation of the growth of the 3‐D patterns and, as a result, the detailed investigation of their nonlinear behavior, it has a number of drawbacks. The basic state approach is not compatible with time‐varying tide and wave conditions, therefore limiting the applicability of such models to real beaches [ Price et al , ]. In addition, such models can simulate the downstate LBT‐TBR or LBT‐RBB sequence but cannot simulate the LBT‐RBB‐TBR sequence as the onshore sandbar migration is inhibited.…”

Section: Introductionmentioning

confidence: 99%

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Mechanisms controlling the complete accretionary beach state sequence

Dubarbier

Castelle

Ruessink

et al. 2017

Geophysical Research Letters

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Accretionary downstate beach sequence is a key element of observed nearshore morphological variability along sandy coasts. We present and analyze the first numerical simulation of such a sequence using a process‐based morphodynamic model that solves the coupling between waves, depth‐integrated currents, and sediment transport. The simulation evolves from an alongshore uniform barred beach (storm profile) to an almost featureless shore‐welded terrace (summer profile) through the highly alongshore variable detached crescentic bar and transverse bar/rip system states. A global analysis of the full sequence allows determining the varying contributions of the different hydro‐sedimentary processes. Sediment transport driven by orbital velocity skewness is critical to the overall onshore sandbar migration, while gravitational downslope sediment transport acts as a damping term inhibiting further channel growth enforced by rip flow circulation. Accurate morphological diffusivity and inclusion of orbital velocity skewness opens new perspectives in terms of morphodynamic modeling of real beaches.

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Section: Model and Simulation Setupmentioning

confidence: 99%

{scriptC}_{c} - {scriptC}_{w} - {scriptC}_{g}

space.…”

Section: Model and Simulation Setupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Mechanisms controlling the complete accretionary beach state sequence

Dubarbier

Castelle

Ruessink

et al. 2017

Geophysical Research Letters

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show abstract

“…Lastly, tides were neglected in our model setup. Morphologic change in the surf zone could be influenced by tide-induced water level variations (Price et al, 2013), tide-driven currents, but also other tide-induced phenomena specific for curved coasts (e.g., tidal flow separation; Radermacher et al, 2017).…”

Section: Comparison With Observations and Model Limitationsmentioning

confidence: 99%

Alongshore Variability in Crescentic Sandbar Patterns at a Strongly Curved Coast

et al. 2019

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Sandbars, submerged ridges of sand parallel to the shoreline, tend to develop crescentic patterns while migrating onshore. At straight coasts, these patterns form preferably under near‐normal waves through the generation of circulation cells in the flow field, whereas they decay under energetic oblique waves with associated intense alongshore currents. Recently, observations at a man‐made convex curved coast showed an alongshore variability in patterning that seems related to a spatiotemporal variability of the local wave angle (Sand Engine). Here, we aim to systematically explore how coastline curvature contributes to alongshore variability in crescentic pattern formation, by introducing local differences in wave angle and the resulting flow field. A nonlinear morphodynamic model was used to simulate the patterns in an initially alongshore uniform sandbar that migrates onshore along the imposed curved coast. The model was forced by a time‐invariant and time‐varying offshore wave angle. Simulations show that the presence of patterns and their growth rate relate to the local breaker angle, depending on the schematization of the offshore angle and the local coastline orientation. Growth rates decrease with increasing obliquity as both refraction‐induced reductions of the wave height as well as alongshore currents increase. Furthermore, simulations of variations in coastline curvature show that patterns may develop faster at strongly curved coasts if this curvature leads to an increase in near‐normal angles. This implies that beaches where the coastline orientation changes substantially, for example, due to km‐scale nourishments, become potentially more dangerous to swimmers due to strong currents that develop with pronounced bar patterns.

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Modelling the response of a double‐barred sandy beach system to time‐varying wave angles

Nnafie

Driessen

Swart

et al. 2021

Earth Surf Processes Landf

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Summary Sandy beaches typically have one or more shore‐parallel bars with superimposed smaller‐scale three‐dimensional (3D) bars. Knowledge of their morphodynamic behaviour under more realistic wave conditions is limited. This study investigates the response of beaches with two shore‐parallel bars to sinusoidally time‐varying angles of incidence, using a non‐linear morphodynamic model. Different periods and amplitudes of this sinusoidal variation are considered, as well as different time‐mean wave angles. For time‐invariant and normally incident waves, results show that alongshore rhythmic 3D bars form in the domains of inner and outer shore‐parallel bars. The 3D bars in the inner domain are coupled at half the outer‐bars wavelength. This phase coupling breaks up when the wave angle varies in time. Initially, regular 3D bars form in the inner domain (free behaviour), which become irregular when 3D bars develop in the outer domain (forced behaviour). The heights of the 3D bars oscillate with time, reaching maximum values when the forcing period is comparable to the system adjustment time scale (∼ 10–20 days). For a time‐varying wave angle around an oblique mean, alongshore migrating 3D bars emerge in both inner and outer domains. In contrast, for an oblique (constant) wave angle, 3D bars only form in the inner domain and they hardly migrate alongshore. For any forcing period, the dominant response period of the oscillating bar heights is at half the forcing period when waves are (on average) normally incident, and it equals the forcing period when waves are on average obliquely incident. Compared with time‐invariant angles, heights of inner and outer 3D bars are (on average) smaller and larger, respectively, when the angle varies with time, particularly for forcing periods in the order of the system adjustment time scale. Increasing the amplitude of the time‐varying wave angle weakens bar growth. Explanations of these results are also provided.

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Coupled sandbar patterns and obliquely incident waves

Cited by 14 publications

References 54 publications

Mechanisms controlling the complete accretionary beach state sequence

Mechanisms controlling the complete accretionary beach state sequence

Alongshore Variability in Crescentic Sandbar Patterns at a Strongly Curved Coast

Modelling the response of a double‐barred sandy beach system to time‐varying wave angles

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