The role of bathymetry and directional wave conditions on observed crescentic bar dynamics

Swart, Rinse de; Ribas, Francesca; Simarro, Gonzalo; Guillén, Jorge; Calvete, D.

doi:10.1002/esp.5233

Cited by 11 publications

(26 citation statements)

References 69 publications

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“…Planview images in which the alongshore variability of the shoreline decreased (e.g., a clear reduction in amplitude) but the undulations persisted (same horn/bay locations, identical wavelengths) were categorised as partial disappearance moments and added to the dataset with disappearance moments. All these criteria are consistent with those used by De Swart et al (2021) for the detection of crescentic bars. The identified megacusp events were further divided into events with and without crescentic bars by checking whether a crescentic bar was present at some point during each event.…”

Section: Visual Analysis and Data Collectionsupporting

confidence: 83%

“…The study site is a 1 km straight beach section with an east-west alignment (89 with respect to north). Castelldefels beach is composed of sand with a median grain size of 270 μm and the average nearshore bed slope is approximately 0.014 (De Swart et al, 2021).…”

Section: Study Sitementioning

confidence: 99%

“…As explained in Section 3.1, megacusp events in this study were detected visually (analogous to crescentic bar events in De Swart et al, 2021) by two experienced researchers to avoid prejudice and increase accuracy. However, previous studies often used the standard deviation (σ; e.g., Rutten et al, 2018) or sinuosity (Sin; Ojeda et al, 2011) to detect alongshore variability in the barline or shoreline.…”

Section: Accuracy Of Megacusp Detectionmentioning

confidence: 99%

See 2 more Smart Citations

Observations of megacusp dynamics and their coupling with crescentic bars at an open, fetch‐limited beach

Swart

Calvete

Simarro

et al. 2022

Earth Surf Processes Landf

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Alongshore changes in shorelines along sandy beaches are a result of variations in wave conditions and nearshore morphology, which can cause straight shorelines to develop large-scale (100-1000 m wavelength) undulations, called megacusps, which cause local shoreline accretion and erosion. Megacusps are often morphologically coupled to alongshore variability in the nearshore sandbar (crescentic bars). Sandbar rhythmicity has been studied extensively, whilst megacusp dynamics and their coupling with crescentic bars have received less attention. This study uses a long-term dataset of hourly time-exposure video images and detailed propagated wave conditions to investigate megacusp dynamics and the corresponding sandbar-shoreline coupling at the low-energetic, tideless beach of Castelldefels (northwestern Mediterranean Sea, Spain). Megacusps were observed during 24% of the study period. Crescentic bars were present during 91% of the days with megacusps, whilst megacusps were not observed during 50% of the days with crescentic bars. Megacusp wavelengths (100-700 m) were comparable to those of crescentic bars, whilst cross-shore amplitudes (3-8 m) and alongshore migration speeds (0-15 m/day) were smaller than those of crescentic bars. No clear relation was observed between wave conditions and megacusp formation, migration and disappearance. However, megacusp presence was strongly linked to crescentic bar presence, as megacusps mostly developed some days after the formation of a crescentic bar. Coupling between shoreline and inner sandbar was significant during 74% of the time with simultaneous presence of megacusps and crescentic bars. No dominance of one particular coupling pattern was observed, although the pattern depended on the wave height and the wave angle. It is hypothesised that the wave height and angle determine the type of flow pattern over the inner crescentic bar (single or double rip cell circulations versus meandering currents) and thus control the type of coupling.

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Section: Visual Analysis and Data Collectionsupporting

confidence: 83%

Section: Study Sitementioning

confidence: 99%

Section: Accuracy Of Megacusp Detectionmentioning

confidence: 99%

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Observations of megacusp dynamics and their coupling with crescentic bars at an open, fetch‐limited beach

Swart

Calvete

Simarro

et al. 2022

Earth Surf Processes Landf

Self Cite

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“…Generally, larger S bz , W bz , H w, and α w with a steeper nearshore slope are observed in the southern large-scale NBB region than in the northern region (Table 2). It is well-known that oblique wave energy, frequently observed in the southern NBB region, straightens longshore bars [59][60][61]. Therefore, the nearshore morphology results in well-pronounced bars with deeper continuous troughs.…”

Section: Factors Determining the Alongshore Variability Of Morphologi...mentioning

confidence: 94%

Analysis of Interannual and Seasonal Nearshore Bar Behaviour Observed from Decadal Optical Satellite Data in the Curonian Spit, Baltic Sea

et al. 2022

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Long-term observations of nearshore bar behaviour are a vital component of coastal monitoring, management, and prediction. Optical satellite remote sensing enables the possibility of such observations over large spatial areas, but its full potential remains unexploited. This study assessed alongshore variability in cross-shore nearshore bar behaviour on a wave-dominated multi-bar coast of the Curonian Spit (south-eastern Baltic Sea) between 2011 and 2021, using satellite-derived bar data. Nearshore bars were extracted from a time series of PlanetScope and RapidEye satellite images with an automated GIS-based algorithm, previously proposed by the study authors. The cross-shore behaviour of a multiple bar system was analysed by adapting traditional bathymetry-based analysis techniques to satellite-derived data that included bar crestlines and images of multi-scale Relative Bathymetric Position Index (RBPI). The analysis was performed on 1071 shore-perpendicular transects. Multi-bar onshore and offshore migration rates were quantified on interannual and seasonal timescales. The results show that, on an interannual timescale, bars migrated offshore at rates up to 9.7 m/month, while the rates of onshore migration reached up to 11 m/month. During the months of low wave energy, bars moved offshore at rates up to 6.2 m/month, and during the months of high wave energy, up to 12.9 m/month. However onshore migration rates, during the months of low and high wave energy, reached up to 7.0 and 13.4 m/month, respectively. A complex empirical orthogonal function (CEOF) analysis was performed on RBPI-derived cross-shore profiles, and cyclic offshore directed bar behaviour was examined. For the first time, the net offshore migration (NOM) cycle with bar cycle return periods of 1.8 to 13.5 years was investigated on the south-eastern Baltic Sea coast. Bar cycle return periods increased and rates of bar cross-shore migration decreased from north to south along the Curonian Spit. Similar nearshore bar behaviour regions were identified using clustering analysis based on quantified temporal and morphological characteristics of the bars. Factors controlling alongshore variability in bar cross-shore behaviour were determined. The study results suggest that small alongshore variations in nearshore hydrodynamics, caused by the local wave climate and its interplay with the shoreline orientation, determine the morphological and temporal variability of the multi-bar system in the Curonian Spit.

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“…This finding triggered the study of sandbar and shoreline dynamics. Tracking breaker lines in multi-year data sets revealed that bars and shorelines respond to incident waves by migrating in onshore and offshore direction (see, e.g., in [9][10][11][12][13]), by developing or straightening out patterns (see, e.g., in [12][13][14][15]), and by rotating clockwise/counterclockwise (see, e.g., in [10,16,17]). Furthermore, images have been used to study dynamics on shorter timescales, including the formation of finger bars [18,19], rip currents [20,21], and groundwater seepage on beaches [22,23].…”

Section: Introductionmentioning

confidence: 99%

Shoreline Detection Accuracy from Video Monitoring Systems

Arriaga

Medellín

Ojeda

et al. 2022

JMSE

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Video monitoring has become an indispensable tool to understand beach processes. However, the measurement accuracy derived from the images has been taken for granted despite its dependence on the calibration process and camera movements. An easy to implement self-fed image stabilization algorithm is proposed to solve the camera movements. Georeferenced images were generated from the stabilized images using only one calibration. To assess the performance of the stabilization algorithm, a second set of georeferenced images was created from unstabilized images following the accepted practice of using several calibrations. Shorelines were extracted from the images and corrected with the measured water level and the computed run-up to the 0 m contour. Image-derived corrected shorelines were validated with one hundred beach profile surveys measured during a period of four years along a 1.1 km beach stretch. The simultaneous high-frequency field data available of images and beach surveys are uncommon and allow assessing seasonal changes and long-term trends accuracy. Errors in shoreline position do not increase in time suggesting that the proposed stabilization algorithm does not propagate errors, despite the ever-evolving vegetation in the images. The image stabilization reduces the error in shoreline position by 40 percent, having a larger impact with increasing distance from the camera. Furthermore, the algorithm improves the accuracy on long-term trends by one degree of magnitude (0.01 m/year vs. 0.25 m/year).

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The role of bathymetry and directional wave conditions on observed crescentic bar dynamics

Cited by 11 publications

References 69 publications

Observations of megacusp dynamics and their coupling with crescentic bars at an open, fetch‐limited beach

Observations of megacusp dynamics and their coupling with crescentic bars at an open, fetch‐limited beach

Analysis of Interannual and Seasonal Nearshore Bar Behaviour Observed from Decadal Optical Satellite Data in the Curonian Spit, Baltic Sea

Shoreline Detection Accuracy from Video Monitoring Systems

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