Shoreline-Sandbar Dynamics at a High-Energy Embayed and Structurally-Engineered Sandy Beach: Anglet, SW France

Huguet, Jean-Rémy; Castelle, Bruno; Marieu, Vincent; Morichon, Denis; Santiago, Iñaki de

doi:10.2112/si75-079.1

Cited by 5 publications

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“…The alongshore standard deviation of the shoreline position was also computed to give a measure of the alongshore variability of the cross-shore position. During the winter period of 2013/2014, high-energy wave conditions (H s > 5 m) drove important changes in Anglet Beach shoreline dynamics [5]. Part of the seasonal erosion cycle is captured in Figure 11, where the shoreline position varied within a range of 30 m. The mean shoreline apparent position was also affected by an approximately 10-20 m bias, showing that incorrect tilt may bias positions of features by condensing or stretching the image in the cross-shore direction.…”

Section: Discussionmentioning

confidence: 99%

“…The beach is delimited by a prominent headland in the South and extends over 4 km up to a 1 km long jetty protecting the entrance of the river mouth. According to the classification of Wright and Short [46], Anglet Beach is an intermediate-reflective beach composed of medium to coarse sand, with a steep beach-face slope (tan β ≈ 0.1) characterized by a mostly double bar system [5,47]. Given the west-northwest (WNW) beach orientation, the coast is predominantly exposed to North Atlantic high-energy swells coming from the WNW direction with an average annual significant offshore wave height H s = 1.57 m (occasional wave heights >10 m during winter storms) and average peak period T p = 10 s [47,48].…”

Section: Study Site and Video Datamentioning

confidence: 99%

“…Over the past decades, the use of shore-based video systems has become a very popular and accessible low-cost tool for coastal monitoring, given their capability to deliver continuous, high-frequency (e.g., daily) data over large enough spatial scales [1,2]. Among the many applications using video-based remote sensing are shoreline and sandbar position tracking [3][4][5], nearshore bathymetry estimation [6][7][8], determination of intertidal beach slopes [9,10], rip channel formation and evolution, [11][12][13][14], estimation of longshore currents [15,16], wave celerity, period and direction [6,17,18], and breaking wave height [19].…”

Section: Introductionmentioning

confidence: 99%

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A Simple and Efficient Image Stabilization Method for Coastal Monitoring Video Systems

et al. 2019

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Fixed video camera systems are consistently prone to importune motions over time due to either thermal effects or mechanical factors. Even subtle displacements are mostly overlooked or ignored, although they can lead to large geo-rectification errors. This paper describes a simple and efficient method to stabilize an either continuous or sub-sampled image sequence based on feature matching and sub-pixel cross-correlation techniques. The method requires the presence and identification of different land-sub-image regions containing static recognizable features, such as corners or salient points, referred to as keypoints. A Canny edge detector ( C E D ) is used to locate and extract the boundaries of the features. Keypoints are matched against themselves after computing their two-dimensional displacement with respect to a reference frame. Pairs of keypoints are subsequently used as control points to fit a geometric transformation in order to align the whole frame with the reference image. The stabilization method is applied to five years of daily images collected from a three-camera permanent video system located at Anglet Beach in southwestern France. Azimuth, tilt, and roll deviations are computed for each camera. The three cameras showed motions on a wide range of time scales, with a prominent annual signal in azimuth and tilt deviation. Camera movement amplitude reached up to 10 pixels in azimuth, 30 pixels in tilt, and 0.4° in roll, together with a quasi-steady counter-clockwise trend over the five-year time series. Moreover, camera viewing angle deviations were found to induce large rectification errors of up to 400 m at a distance of 2.5 km from the camera. The mean shoreline apparent position was also affected by an approximately 10–20 m bias during the 2013/2014 outstanding winter period. The stabilization semi-automatic method successfully corrects camera geometry for fixed video monitoring systems and is able to process at least 90% of the frames without user assistance. The use of the C E D greatly improves the performance of the cross-correlation algorithm by making it more robust against contrast and brightness variations between frames. The method appears as a promising tool for other coastal imaging applications such as removal of undesired high-frequency movements of cameras equipped in unmanned aerial vehicles (UAVs).

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Section: Discussionmentioning

confidence: 99%

Section: Study Site and Video Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Simple and Efficient Image Stabilization Method for Coastal Monitoring Video Systems

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“…The morphology of PCA beach is seasonally modulated and is mostly double‐barred. For more information on Anglet beach setting and beach morphodynamics, the reader should refer to Huguet et al (2016). The beach is composed of medium to coarse (D50 ∼ 2 mm) sand with a steep beach face (∼1/10) and a more gentle sloped surf zone (∼1/50).…”

Section: Field Experimentsmentioning

confidence: 99%

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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“…PCA beach is composed of medium to coarse (D50 ≈ 2 mm) sand with a steep beach face (≈1/10). For more information on Anglet beach setting and beach morphodynamics, the reader is referred to Huguet et al [38], Rodriguez-Padilla et al [39].…”

Section: Field Sitementioning

confidence: 99%

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

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Mouragues

et al. 2020

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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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Shoreline-Sandbar Dynamics at a High-Energy Embayed and Structurally-Engineered Sandy Beach: Anglet, SW France

Cited by 5 publications

References 0 publications

A Simple and Efficient Image Stabilization Method for Coastal Monitoring Video Systems

A Simple and Efficient Image Stabilization Method for Coastal Monitoring Video Systems

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

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