Field Observations of Wave-induced Headland Rips

Mouragues, Arthur; Bonneton, Philippe; Castelle, Bruno; Marieu, Vincent; Barrett, Aaron C.; Bonneton, Natalie; Detand, Guillaume; Martins, Kévin; McCarroll, Joshua A.; Morichon, Denis; Poate, Tim; Padilla, Isaac Rodriguez; Scott, Tim; Sous, Damien

doi:10.2112/si95-113.1

Cited by 7 publications

(14 citation statements)

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“…While a few studies have focused on the depth variation of the mean flow (Haas, 2002; Reniers et al, 2004), the vertical structure of VLF motions remains poorly understood. A first inspection at the vertical variation of time‐averaged horizontal velocities at SIG1 and AQ locations (not shown here) indicates that the standard deviation and characteristic periods are relatively depth‐invariant at both low and high tide, as opposed to the associated mean flow (Mouragues et al, 2020; Sous et al, 2020). This suggests a rather weak vertical variation of VLF motions for the studied high‐energy deflection rip that will need to be further explored.…”

Section: Discussionmentioning

confidence: 93%

“…During the high‐energy deflection event (Figure 14a), the depth‐averaged deflection rip intensity reached up to 0.7 m/s at low tide in 12‐m water depth. For the same energetic wave event, Mouragues et al (2020) highlighted the weak vertical variability of this high‐energy deflection rip at low tide. Sous et al (2020) recently analyzed the vertical variability of headland rip flow at PCA under both deflection and shadowed configurations using a current profiler located at the SIG3 position.…”

Section: Discussionmentioning

confidence: 94%

“…Experimental setup of the field campaign (modified from Mouragues et al, 2020). (a) Bathy‐topo map of the field site.…”

Section: Field Experimentsmentioning

confidence: 99%

“…Accordingly, little is known on the relation between incident wave conditions and headland rip activity and, more generally, on the wave‐induced circulation activity occurring along geologically constrained beaches. The present study attempts to bridge this knowledge gap by analyzing dense and high‐frequency wave and current data collected during a comprehensive 3‐week field experiment carried out in one of Anglet beaches (SW France) in October 2018 (Mouragues et al, 2020). After briefly presenting the field experiment in section 2, flow measurements are examined over the entire measurement period in section 3.1.…”

Section: Introductionmentioning

confidence: 99%

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High‐Energy Surf Zone Currents and Headland Rips at a Geologically Constrained Mesotidal Beach

et al. 2020

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We analyze Eulerian and Lagrangian measurements of wave-induced circulation collected during a 3-week field experiment at a high-energy mesotidal barred beach with the presence of a 500-m headland and a submerged reef. Small changes in wave and tide conditions were found to largely impact circulation patterns. Three main regimes were identified depending on offshore wave obliquity: (1) Under shore-normal configuration, the flow was dominated by cross-shore motions, except for moderate waves at low tide, with the presence of a quasi-steady circulation cell on the reef. (2) Under shadowed configuration, an onshore-directed current flowing away from the headland and a weak oscillating eddy were present outside and inside the shadow region, respectively. (3) Under deflection configuration, a deflection rip flowing against the headland and extending well beyond the surf zone was present, with activity maximized around low tide for moderate waves. Under 4-m oblique waves, the deflection rip was active regardless of the tide with mean depth-averaged velocities up to 0.7 m/s 800-m offshore in 12-m depth, with energetic low-frequency fluctuations. Our results emphasize the ability of deflection rips to transport materials far offshore, suggesting that such rips can transport sediment beyond the depth of closure. This study indicates that a wide variety of wave-driven circulation patterns can occur and sometimes coexist on beaches with prominent geological settings. Changes in the dominant driving mechanism can occur as a result of small changes in wave and tide conditions, resulting in more spatially and temporally variable circulation than along open sandy beaches. Plain Language Summary Most field experiments about wave-induced circulation patterns have been conducted along open sandy beaches, while experiments in geologically constrained environments are scarce. We performed intensive field measurements at a high-energy beach with the presence of a 500-m headland and a submerged natural reef. Three main circulation patterns were identified depending on the offshore wave obliquity. For shore-normal waves, cross-shore motions dominated the nearshore region, while oblique wave configurations resulted in more complex horizontal circulation. In particular, under intense headland-directed longshore current, the flow was deflected seaward against the headland. This deflection resulted in an intense seaward flowing jet (deflection rip) extending well beyond the surf zone edge, particularly during storm conditions. Such findings highlight the ability of these deflection rips to dominate water and sediment exchanges between the nearshore and the inner shelf region. Our study further outlines the more spatially and temporally variable circulation patterns occurring along geologically constrained beaches compared to open sandy beaches, ranging from small recirculating cells across the reef to a large deflection rip extending hundreds of meters beyond the surf zone.

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Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 94%

“…Experimental setup of the field campaign (modified from Mouragues et al, 2020). (a) Bathy‐topo map of the field site.…”

Section: Field Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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High‐Energy Surf Zone Currents and Headland Rips at a Geologically Constrained Mesotidal Beach

et al. 2020

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“…However, the relationships with an offshore wave and tide conditions were not systematically addressed, and the time-averaging of the velocities was unclear. The second exception is a field experiment that was recently conducted in October 2018 at Anglet beach, southwest France, described in [31] and from which some of the data presented here builds on.…”

Section: Introductionmentioning

confidence: 99%

Field Measurements of a High-Energy Headland Deflection Rip Current: Tidal Modulation, Very Low Frequency Pulsation and Vertical Structure

Sous

Castelle

Mouragues

et al. 2020

JMSE

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Headland rips, sometimes referred to as boundary rips, are rip currents flowing against natural or artificial obstructions extending seaward from the beach, such as headland or groynes. They can be driven either by the deflection of the longshore current against the obstacle or by alongshore variation in breaking wave height due to wave shadowing in the lee of the obstacle. The driving mechanism therefore essentially depends on the angle of wave incidence with respect to the natural or artificial obstruction. We analyze 42 days of velocity profile measurements against a natural headland at the high-energy meso-macrotidal beach of Anglet, southwest France. Measurements were collected in 6.5–10.5-m depth as tide elevation varied, during the autumn–winter period with offshore significant wave height and period ranging 0.9–6 m and 8–16 s, respectively, and the angle of wave incidence ranging from −20 ∘ to 20 ∘ . Here we analyze deflection rip configurations, corresponding to approximately 24 days of measurements, for which the current meter was alternatively located in the rip neck, rip head or away from the rip as wave and tide conditions changed. Deflection rips were associated with large offshore-directed velocities (up to 0.6 m/s depth-averaged velocities) and tide modulation for low- to moderate-energy waves. The vertical profile of deflection rips was found to vary from depth-uniform in the rip neck to strongly depth-varying further offshore in the rip head with maximum velocities near the surface. Very low frequency motions of the rip were dramatic, ranging 10–60 min with a dominant peak period of approximately 40 min, i.e., with longer periods than commonly reported. The strong offshore-directed velocities measured well beyond the surf zone edge provide new insight into deflection rips as a dominant mechanism for water and sediment exchanges between embayed (or structurally-controlled) beaches and the inner-shelf and/or the adjacent embayments.

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Relation between orbital velocities, pressure and surface elevation in non-linear nearshore water waves

Martins

Bonneton

Lannes

et al. 2021

Journal of Physical Oceanography

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The inability of the linear wave dispersion relation to characterize the dispersive properties of non-linear shoaling and breaking waves in the nearshore has long been recognised. Yet, it remains widely used with linear wave theory to convert between sub-surface pressure, wave orbital velocities and the free surface elevation associated with non-linear nearshore waves. Here, we present a non-linear fully dispersive method for reconstructing the free surface elevation from sub-surface hydrodynamic measurements. This reconstruction requires knowledge of the dispersive properties of the wave field through the dominant wavenumbers magnitude κ, representative in an energy-averaged sense of a mixed sea-state composed of both free and forced components. The present approach is effective starting from intermediate water depths - where non-linear interactions between triads intensify - up to the surf zone, where most wave components are forced and travel approximately at the speed of non-dispersive shallow-water waves. In laboratory conditions, where measurements of κ are available, the non-linear fully dispersive method successfully reconstructs sea-surface energy levels at high frequencies in diverse non-linear and dispersive conditions. In the field, we investigate the potential of a reconstruction that uses a Boussinesq approximation of κ, since such measurements are generally lacking. Overall, the proposed approach offers great potential for collecting more accurate measurements under storm conditions, both in terms of sea-surface energy levels at high frequencies and wave-by-wave statistics (e.g. wave extrema). Through its control on the efficiency of non-linear energy transfers between triads, the spectral bandwidth is shown to greatly influence non-linear effects in the transfer functions between sub-surface hydrodynamics and the sea-surface elevation.

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Field Observations of Wave-induced Headland Rips

Cited by 7 publications

References 0 publications

High‐Energy Surf Zone Currents and Headland Rips at a Geologically Constrained Mesotidal Beach

High‐Energy Surf Zone Currents and Headland Rips at a Geologically Constrained Mesotidal Beach

Field Measurements of a High-Energy Headland Deflection Rip Current: Tidal Modulation, Very Low Frequency Pulsation and Vertical Structure

Relation between orbital velocities, pressure and surface elevation in non-linear nearshore water waves

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