Double bar beach dynamics on the high-energy meso-macrotidal French Aquitanian Coast: A review

Castelle, Bruno; Bonneton, Philippe; Dupuis, Hélène; Sénéchal, Nadia

doi:10.1016/j.margeo.2007.06.001

Cited by 164 publications

(166 citation statements)

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“…A similar configuration was found by Price and Ruessink (2011) along the double-barred Gold Coast in Australia and is attributed to the dominance of parallel wave approach (Castelle et al, 2010a, b). Compared to other beaches described in the literature, Perranporth is most similar to Truc Vert (Castelle et al, 2007;Senechal et al, 2009;Coco et al, 2014), although the latter beach is characterised by more energetic wave conditions and a smaller tide range. There is no obvious effect of geological control on the beach morphology (cf., Jackson et al, 2005;Loureiro et al, 2012;van de Lageweg et al, 2013); however, the beach is quite long (c. 3.5 km; Figure 1) and can be considered uninterrupted, despite being embayed.…”

Section: Discussionsupporting

confidence: 65%

“…Upstate transition of the outer bar (W → CA → C → L/MR), characterised by offshore migration and straightening of the outer bar, requires an extended period of energetic wave action (e.g., a sequence of storms); a downstate transition represents the opposite sequence and occurs following an extended period of calm wave conditions (cf., Poate et al, 2014; Figure 11). Such upstate and downstate sequences have been reported previously for double-barred beaches in micro-and mesotidal settings (e.g., Castelle et al, 2007;Coco et al, 2014), but have not been identified previously for macrotidal beaches. On many sites characterised with multiple bar morphology, bar systems exhibit a bar-cycle, with time scale O(5-10 years), characterised by formation at the shoreline followed by intermittent offshore migration, and finally disappearance of the outer bar (e.g., .…”

Section: Discussionmentioning

confidence: 43%

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Role of wave forcing, storms and NAO in outer bar dynamics on a high-energy, macro-tidal beach

et al. 2014

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Outer sand bar dynamics on a high-energy macro-tidal beach were investigated using long-term (multi-year) field datasets of intertidal morphology and offshore bathymetry. Utilising a 15-year time-series of Argus video images, five distinct outer bar types were identified: Mega Rip, Longshore, Crescentic, Crescentic Attached and Welded. The most common classification was Crescentic Attached, with the outer bar oscillations being out of phase with the inner bar oscillations, as would be expected for the shore-normal wave approach at this site. The outer bar had a typical amplitude of 0.5-1 m and a longshore wavelength of 600 m. Changes in outer bar morphology were related to measured and modelled nearshore wave data. However, the outer bar morphology changed over a much longer time scale (monthly-to-annual) than the daily-to-weekly variations in wave height and period. An extended duration of energetic wave action was required to bring about an upstate bar transition to the Longshore or Mega Rip state, where the bar then remained arrested for a significant amount of time, requiring several months of low wave conditions to induce a down state transition through Crescentic to Welded. This slow morphological response is explained by extended relaxation times attributed to the large tidal range at the study site where the outer bar morphology is only active for part of the tidal cycle (several hours around low tide). The configuration and position of the outer bar were related: the more upstate (downstate) bar types being associated with a more offshore (onshore) bar position. The detrended outer bar position was significantly related to a forcing term based on wave power and disequilibrium of the dimensionless fall velocity with offshore (onshore) bar migration occurring when wave conditions were more (less) energetic that the antecedent conditions. The upstate end member (Longshore or Mega Rip) was attained sometime during the winter months for 14 out of the 16 years of monitoring; the outer bar remained attached to the low tide shoreline over the winter 2005/2006 and 2010/2011. These two winters with incomplete upstate cycles were characterised by the lowest winter wave conditions and negative winter North Atlantic Oscillation (NAO) indices, suggesting that the winter NAO is correlated with both beach state and nearshore bar configuration. KEYWORDS

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Section: Discussionsupporting

confidence: 65%

Section: Discussionmentioning

confidence: 43%

Role of wave forcing, storms and NAO in outer bar dynamics on a high-energy, macro-tidal beach

et al. 2014

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“…Truc Vert beach is characterized by the presence of two sandbars, one subtidal and one intertidal, whose shape ranges from linear to the more commonly-observed crescentic shape. The inner sandbar is usually more dynamic with the presence of well-formed rip channels (Castelle et al, 2007). The mean grain-size of the beachface is 0.35 mm.…”

Section: Field Sitementioning

confidence: 99%

Beach response to a sequence of extreme storms

Coco¹,

Sénéchal²,

Rejas³

et al. 2014

Geomorphology

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“…Van Enckevort et al, 2004;Ruessink et al, 2007a), spatially limited to (an alongshore transect of) the inner bar (e.g. Lippmann and Holman, 1990;Shand et al, 2003;Sénéchal et al, 2009) or based on data acquired at different locations or at irregular intervals (Short and Aagaard, 1993;Castelle et al, 2007). Furthermore, the large relaxation times of outer bars, in relation to the offshore wave forcing, have often prevented an abundance of state transitions of the outer bar to occur during the studied periods (see e.g.…”

Section: Alongshore Sandbar Variabilitymentioning

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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Double bar beach dynamics on the high-energy meso-macrotidal French Aquitanian Coast: A review

Cited by 164 publications

References 50 publications

Role of wave forcing, storms and NAO in outer bar dynamics on a high-energy, macro-tidal beach

Role of wave forcing, storms and NAO in outer bar dynamics on a high-energy, macro-tidal beach

Beach response to a sequence of extreme storms

Morphological coupling in multiple sandbar systems – a review

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