Short‐term intertidal bar mobility on a ridge‐and‐runnel beach, Merlimont, northern France

Anthony, Edward J.; Levoy, Franck; Monfort, D.; Degryse-Kulkarni, C.

doi:10.1002/esp.1129

Cited by 47 publications

(34 citation statements)

References 12 publications

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“…Significant wave heights vary markedly as waves cross the bar and as a function of the tide-influenced water depths. Wave heights over the bar are at a maximum at high tide and decrease with the water level, in agreement with other studies on macrotidal beaches [Russell et al, 1991;Voulgaris et al, 1996;Levoy et al, 2001;Anthony et al, 2004Anthony et al, , 2005Reichmüth and Anthony, 2007;Sedrati and Anthony, 2007]. Wave attenuation increases as depths decrease until emersion of the crest of the bar.…”

Section: Study Areasupporting

confidence: 91%

Short‐term to decadal‐scale onshore bar migration and shoreline changes in the vicinity of a megatidal ebb delta

Robin¹,

Levoy²,

Monfort³

et al. 2009

J. Geophys. Res.

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[1] Swash bar development has been well documented from coasts with low to moderate tidal ranges, while studies of the effects of these forms on the morphology and dynamics of the adjacent shore in large tide range environments are rare. The analysis of sequential vertical aerial photographs was combined with field work in order to highlight the effects of swash bar development on the adjacent shoreline in the vicinity of a megatidal inlet (mean spring tidal range of 11 m). Swash bars are observed to form on the ebb tidal delta and to migrate landward before welding onto the coast. A close relationship was noticed between the position of the swash bar and shoreline dynamics. The bar protects the shore against wave attack in a sedimentary system controlled by longshore transport. This protective role is, however, modulated by the large tidal range. As the bar migrates upward toward the high-tide level and the subaerial beach, it develops morphologically into a transverse form that acts as a cross-shore obstacle to longshore sediment transport, thus resulting in shoreline accretion updrift and in strong erosion downdrift. This disturbance may persist for years because of the relatively slow speed of movement of the bar at this stage, an aspect characteristic of large tide range environments. This pattern of behavior differs fundamentally from that documented in the literature where the perturbation of the longshore sediment transport occurs over shorter periods. An original conceptual model of swash bar morphodynamics and repercussions on the adjacent shoreline for this megatidal environment is proposed.Citation: Robin, N., F. Levoy, O. Monfort, and E. Anthony (2009), Short-term to decadal-scale onshore bar migration and shoreline changes in the vicinity of a megatidal ebb delta,

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Section: Study Areasupporting

confidence: 91%

Short‐term to decadal‐scale onshore bar migration and shoreline changes in the vicinity of a megatidal ebb delta

Robin¹,

Levoy²,

Monfort³

et al. 2009

J. Geophys. Res.

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“…Field observations show that the effect of these channels on sediment mobility, and, consequently, morphological change, cannot be disentangled from the much more pervasive profile reworking due to wave processes, notably surf and swash bores, which account for much of the cross-shore morphological change on multi-barred macrotidal beaches, even under low wave conditions (Sipka and Anthony, 1999;Kroon and Masselink, 2002;Anthony et al, 2004). However, as stated in the introduction, cross-shore morphological change may also be caused by longshore processes, through the migration of bars dissected by channels, and of large bedforms, notably 3D crescentic dunes, due to high-velocity flows in trough channels (Anthony et al, 2005). Velocities in type 1 channels on Leffrinckoucke beach were too sluggish (<0·2 m s −1 ) to result in the formation and migration of such large bedforms in the troughs.…”

Section: Resultsmentioning

confidence: 99%

“…Sustained near-surface channel longshore velocities of up to 3 m s −1 have been shown to generate and force the longshore migration of large bedforms in trough channels of multi-barred beaches in the eastern English Channel (Anthony et al, 2005) and the Dover Strait (Sedrati and Anthony, in press). These beaches are affected by both more energetic waves and larger tidal ranges than Leffrinckoucke.…”

Section: Discussionmentioning

confidence: 99%

“…While drainage direction in type 1 channels is controlled by topography, the direction of channel meander migration is largely determined by the dominant longshore currents during strong wind events. These currents play a significant role in sand transport over bars (Anthony et al, 2005;Sedrati and Anthony, in press). The mild overall eastward migration of the main type 1 channels (Figures 3 and 4) is in phase with the net eastward longshore residual flow on Leffrinckoucke beach ( Figure 5).…”

Section: Discussionmentioning

confidence: 99%

“…Since much of the water discharge affecting multi-barred macrotidal beaches during both rising and falling tides is routed through these channel systems, they may redistribute sand over the intertidal beach and thus affect the beach morphology. Anthony et al (2005) argued that channel mobility may induce significant beach profile change through the longshore migration of 2D to 3D crescentic dunes in high-velocity channels. However, although channels are commonly evoked as components of the intertidal bar-trough systems on many beaches, their position and potential variability in this intertidal beach morphodynamic framework have not been explored thus far.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of intertidal drainage channels on a multi‐barred macrotidal beach

Reichmüth

Anthony

2007

Earth Surf Processes Landf

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The intertidal drainage channels on a macrotidal bar-trough (ridge-and-runnel) beach were monitored during a 17-day survey. Type 1 channels were persistent, dominantly longshore systems essentially limited to the wide intertidal zone between mean high and low water neap tidal levels. The cumulative length of this channel type fluctuated as a function of topographically controlled through-flow or flow impedance in troughs, and showed no correlation with the semi-lunar tidal cycle. Smaller, ephemeral type 2 channels appeared as dominantly cross-shore systems incising bars on the narrower upper and lower beach zones during spring tides. They disappeared during neap tides through infill by waves and aeolian activity. The only significant phase of type 1 channel mobility occurred during a brief moderate-energy storm at the start of the survey. The effect of this mobility on beach morphology was inextricably linked to that of waves and currents. Meander bend migration, forced by wave-and longshore-current-induced migration of a bar during the storm, resulted in important but highly localized morphological change that was only a minor part of an irregular saw-tooth pattern of change that affected the entire beach profile, and that was largely controlled by wave processes and longshore currents. The flow velocities in channels on this beach are too weak to generate the formation and longshore migration of high-energy bedforms. Channel mobility and impact on beach morphology are expected to increase under storm conditions.

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Characteristics and dynamics of multiple intertidal bars, north Lincolnshire, England

Houwelingen

Masselink

Bullard

2005

Earth Surf Processes Landf

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Multiple intertidal bars and troughs, often referred to as 'ridges and runnels', are significant features on many macrotidal sandy beaches. Along the coastline of England and Wales, they are particularly prevalent in the vicinity of estuaries, where the nearshore gradient is gentle and a large surplus of sediment is generally present. This paper examines the dynamics of such bar systems along the north Lincolnshire coast.A digital elevation model of the intertidal morphology obtained using LIDAR demonstrates that three to five intertidal bars are consistently present with a spacing of approximately 100 m. The largest and most pronounced bars (height = = = = = 0·5-0·8 m) are found around mean sea level, whereas the least developed bars (height = = = = = 0·2-0·5 m) occur in the lower intertidal zone. Annual aerial photographs of the intertidal bar morphology were inspected to try to track individual bars from year to year to derive bar migration rates; however, there is little resemblance between concurrent photographs, and 'resetting' of the intertidal profile occurs on an annual basis. Three-dimensional beach surveys were conducted monthly at three locations along the north Lincolnshire coast over a one-year period. The intertidal bar morphology responds strongly to the seasonal variation in the forcing conditions, and bars are least numerous and flattest during the more energetic winter months. Morphological changes over the monthly time scale are strongly affected by longshore sediment transport processes and the intertidal bar morphology can migrate along the beach at rates of up to 30 m per month.The behaviour of intertidal bars is complex and varies over a range of spatial and temporal scales in response to a combination of forcing factors (e.g. incident wave energy, different types of wave processes, longshore and cross-shore sediment transport), relaxation time and morphodynamic feedback.

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Short‐term intertidal bar mobility on a ridge‐and‐runnel beach, Merlimont, northern France

Cited by 47 publications

References 12 publications

Short‐term to decadal‐scale onshore bar migration and shoreline changes in the vicinity of a megatidal ebb delta

Short‐term to decadal‐scale onshore bar migration and shoreline changes in the vicinity of a megatidal ebb delta

Dynamics of intertidal drainage channels on a multi‐barred macrotidal beach

Characteristics and dynamics of multiple intertidal bars, north Lincolnshire, England

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