Figure 1 - uploaded by Tristan B Guest
Content may be subject to copyright.
(a) Map of the Maritimes region of Canada and the northeastern United States. The location of Advocate Beach is indicated by the red box in the map inset. (b) Photograph of Advocate Beach at mid-tide, taken from near the high tide level facing westward. Northwest is alongshore to the right, as indicated by the arrow at the bottom right of the photo. (c) The mean profile of the beach, averaged over the duration of the 2018 field experiment. Mean High Water (MHW) and Mean Low Water (MLW) are both indicated, also as averages over the experiment's duration. The location of a pressure transducer (PT) used to obtain wave and tide data is indicated by the green dot. The inset plot shows the difference in each tide's profile from the mean profile, highlighting the upper beach profile near the high water line as the region of greatest morphological change.

(a) Map of the Maritimes region of Canada and the northeastern United States. The location of Advocate Beach is indicated by the red box in the map inset. (b) Photograph of Advocate Beach at mid-tide, taken from near the high tide level facing westward. Northwest is alongshore to the right, as indicated by the arrow at the bottom right of the photo. (c) The mean profile of the beach, averaged over the duration of the 2018 field experiment. Mean High Water (MHW) and Mean Low Water (MLW) are both indicated, also as averages over the experiment's duration. The location of a pressure transducer (PT) used to obtain wave and tide data is indicated by the green dot. The inset plot shows the difference in each tide's profile from the mean profile, highlighting the upper beach profile near the high water line as the region of greatest morphological change.

Source publication
Article
Full-text available
On mixed sand–gravel beaches, impacts from gravel- and cobble-sized grains—mobilized by the energetic shorebreak—limit the utility of in situ instrumentation for measuring the small-scale response of the beach face on wave period time scales. We present field observations of swash zone morpho-sedimentary dynamics at a steep, megatidal mixed sand–gr...

Contexts in source publication

Context 1
... Beach is a mixed sand-gravel-cobble barrier beach located near the head of the Bay of Fundy in Nova Scotia, Canada (Figure 1). Based on the 8-12 m tidal range, Advocate beach can be classed as megatidal rather than macrotidal [28]. ...
Context 2
... the southwest, the beach is exposed to the full 500 km fetch of the Bay of Fundy and adjacent Gulf of Maine, but from other directions is more fetch-limited. At low tide, the beach is uniformly planar with crest to low water distance as much as 100 m in spring tides (see Figure 1c, and [29,30]). The large tidal range results in high rates of change in the shoreline position; during maximum flood or ebb, the rate of change of water level is as much as 3 m h −1 , or roughly 0.5 m min −1 across-shore. ...
Context 3
... frames were positioned immediately shoreward of the high water line during periods of low to moderate energy forcing conditions such that the instruments were suspended over the swash zone. Wave and tide data were obtained using a pressure transducer located on the lower beach face between the mid-tide and mean low water levels (see Figure 1c). The pressure transducer housing was secured to a heavily weighted frame such that the sensing element was ca. 10 cm above bed level. ...
Context 4
... longshore (x) and cross-shore (y) coordinates reported in this paper are relative to the intersection of the mean high water shoreline, computed for the tides encompassed by the 2018 experiment, and the fixed across-shore line along which the beach profile was surveyed each tide. Vertical coordinates are reported as orthometric elevations referenced to the vertical datum used by the RTK GPS ( Figure 1c). ...
Context 5
... distribution of bed level changes (Figure 10) shows that the majority of changes between swash events were near zero. The larger changes-both positive and negativeare loosely approximated by a Gaussian distribution, though with higher kurtosis values (kurtosis of 5.1 and 5.4 for tides 19 and 27, respectively, relative to a value of 3 for a Gaussian distribution). ...
Context 6
... joint probability distributions of the swash height and bed level change associated with each swash event indicate that bed level change and swash height are largely uncorrelated. Figure 11 shows time series of swash height, bed elevation, and the change in bed elevation during the high tide for tide 27. The magnitude of bed elevation change is largest when bed elevation was higher (i.e., near the beginning and end of the time series). ...
Context 7
... net and cumulative transport statistics for the four stations are summarised in Figure 12. The net cobble transport was shoreward at S1 and S2, where the substrate consisted mostly of coarse-grained berm material. ...
Context 8
... inspection of the transport characteristics within each station reinforces the finding of low cumulative transport and net onshore transport of cobbles in the presence of the coarse-grained berm material. For example, data from S1 are shown in Figure 13. At the more seaward stations, a trend of divergence of the cobbles away from the midswash zone is observed: shoreward transport above the mid-swash level, and seaward transport below. ...
Context 9
... was particularly the case at S2 and S3, for which the camera's field of view was well-centred in the swash zone, and the surficial sediments were predominantly fine-grained. Data from S3 illustrating this divergence are shown in Figure 14. ...
Context 10
... beach step has been demonstrated elsewhere to play an important role in controlling wave breaking on steep beaches, and has also been shown to migrate with the translating swash zone [15]. The net shoreward transport of cobbles in the vicinity of the berm (Figure 12, stations 1 and 2) suggests that the beach profile at high tide was in disequilibrium with the forcing in this case. ...
Context 11
... the validation analysis, x values in the range of 0.5 through 1.5 were tested. RMS errors associated with all the x values tested are summarized in Table A1, and results for a subset of the values are plotted in Figures A1 and A2 for the sieve and point count method comparisons, respectively. The best result in a minimised root mean square error sense was obtained using x = 0.8 (RMSE = 3.35 mm). ...
Context 12
... best result in a minimised root mean square error sense was obtained using x = 0.8 (RMSE = 3.35 mm). Though the higher values for x arguably lead to a more linear (though positively offset) relationship (see x = 1.5 in Figure A1), this comes at the expense of the ability to differentiate grain sizes in the low-to mid range-i.e., the 10-20 mm mean grain size range-which accounts for a large proportion of the grain size distribution. Other parameter values were held constant. ...

Citations

... L'étendue de cette section est dépendante de la hauteur de la plateforme sédimentaire (si celle-ci est présente) ( très mauvais tri granulométrique (e.g. Montes et al., 2018;Guest, 2020;Pancrazzi et al., 2022 Figure IV.5). Bennett et al., 2009;Montes et al., 2018). ...
Thesis
Full-text available
L'objectif de la thèse est d'approfondir les connaissances existantes sur le comportement morphodynamique et l'enregistrement sédimentaire des barrières littorales sablo-graveleuses en environnement hypertidal. Ces systèmes complexes présentent une forte variabilité granulométrique, des sources sédimentaires généralement restreintes, et une dynamique de houle variable et intermittente, liée à la translation rapide du niveau d'eau sur le profil de plage sous l’action de la marée. Les approches expérimentale et in-situ mises en œuvre permettent d'aborder la dynamique de ces barrières à différentes échelles spatio-temporelles, depuis les processus instantanés opérant sur le profil de plage, jusqu'à l'évolution pluri-décennale à centennale de systèmes de barrières complexes. La modélisation d’une plage de galets par des sédiments plastiques de faible densité a permis de montrer la réponse du profil de plage à divers scénarios de houle et de niveau d’eau, ainsi qu’au caractère bimodal du sédiment. Les données géoradar acquises sur différents types de barrière littorales dans les embouchures hypertidales de la Baie de Somme (France) et de l'estuaire du Santa Cruz (Argentine), ont permis de caractériser en détail leur architecture. La signature tidale est difficilement identifiable dans l'architecture des barrières mais certains indicateurs, comme la présence de bermes à des altitudes variables dans les beach ridges, ont pu être révélés. Une attention particulière a été portée sur les flèches littorales avec la réalisation d'un modèle de dépôt incluant la formation des crochons sédimentaires. L'analyse combinée de la stratigraphie et de l'évolution morphologique d'une flèche littorale s'est avérée utile pour en étudier les facteurs de contrôle, d’origine naturelle ou anthropique.
... These insights remain limited by availability in time and quality of data. Indeed, wave breaking and swash were specifically shown to be linked with morphological processes especially for gravel beaches (Guest and Hay, 2021) although their variability is expected to be more significant at longer time scales (Almeida et al., 2014;Buscombe and Masselink, 2006;Karunarathna et al., 2012;Poate et al., 2013;Ratliff and Murray, 2014). ...
... Position, orientation, size, shape, and composition of assemblages are the result of antecedent conditions of sediment supply availability, and sediment sorting processes (Buscombe and Masselink, 2006). Their temporal variability could potentially be used as a proxy of surface sediment transport processes, as was demonstrated by Guest and Hay (2021) using remote sensing techniques applied on 14 days of high frequency video images, over a 2.7 m longshore span. ...
Article
Full-text available
This article aims to investigate the 3D morpho-sedimentary dynamics of two gravel beaches in relation to hydrodynamic forcing, using a multi-sensor approach. Study sites, namely Etretat and Hautot-sur-Mer, are both located in Normandy, France. Thus, they face similar wave conditions of the English channel's eastern side, with megatidal ranges and channelized wave orientations. However, they differ in gravel size (D50 Etretat = 5.2 cm; D50 Hautot-sur-Mer = 7.0 cm), vertical composition (Etretat is a purely gravel beach, Hautot-sur-Mer is a composite one with a low tide terrace) and wave exposure (Etretat is an embayed beach, oriented 47°N, Hautot-sur-Mer is a semi-open beach, oriented 71°N). Used data include shoreline positions automatically extracted from coastal Video Monitoring Systems (VMS) images between 2018 and 2020, wave data provided by the WaveWatch 3 model, and gravel size maps derived from UAV-imagery at different dates (one in Etretat, three in Hautot-sur-Mer). First, an Empirical Orthogonal Function (EOF) analysis was performed on the shoreline position data to extract the Principal Components (PC) describing mechanisms of morphological changes in the shoreline shape at different elevations (−2 to +3 m in Etretat and + 1 to +3 m in Hautot-sur-Mer). Four mechanisms spread within five PCs were found in Etretat: cross-shore translation (PC1), rollover (PC2), scale/elevation dependent rotation (PC3 and PC4) and breathing (PC5). Four PCs describing three mechanisms were identified in Hautot-sur-Mer: right-centered beach cell rotation (PC1), left-centered beach cell rotation (PC2), large scale rotation (PC3) and rollover (PC4). Interpretation of the PCs were supported by significant correlations with morphological parameters such as average beach width (BW), beach orientation angle (BOA) and beach slope (BS). The main mid-term morphological periods of variability include 2, 3, 5 and 8+ months in Etretat and 2, 3 and 6 months in Hautot-sur-Mer (all parameters included), which essentially corresponds to the variability of the wave energy. Finally, the analysis of surface grain size spatial variability revealed the presence of textural patterns with spatial and temporal variations in sorting and average grain size up to 1 cm in two months.