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Eleven-year long time series of monthly beach profile surveys and hourly incident wave conditions are analyzed for a macrotidal Low Tide Terrace beach. The lower intertidal zone of the beach has a pluriannual cycle, whereas the upper beach profile has a predominantly seasonal cycle. An equilibrium model is applied to study the variation of the contour elevation positions in the intertidal zone as a function of the wave energy, wave power, and water level. When forcing the model with wave energy, the predictive ability of the equilibrium model is around 60% in the upper intertidal zone but decreases to 40% in the lower intertidal zone. Using wave power increases the predictive ability up to 70% in both the upper and lower intertidal zones. However, changes around the inflection point are not well predicted. The equilibrium model is then extended to take into account the effects of the tide level. The initial results do not show an increase in the predictive capacity of the model, but do allow the model free parameters to represent more accurately the values expected in a macrotidal environment. This allows comparing the empirical model calibration in different tidal environment. The interpretation of the model free parameter variation across the intertidal zone highlights the behavior of the different zones along the intertidal beach profile. This contributes to a global interpretation of the four model parameters for beaches with different tidal ranges, and therefore to a global model applicable at a wide variety sites.

Long-term datasets documenting the evolution of coastal forms and processes, through the provision of recurring beach as well as shoreface morphological observations and accompanying time-series of environmental controls, remain difficult to collect and are rarely made available. However, they are increasingly needed to further our understanding of coastal change and to improve the models that will help planning what our future coast will be. This data descriptor presents the results of topographic and bathymetric surveys at Porsmilin, a macrotidal embayed beach situated in Brittany, northwest France. The Porsmilin beach survey program was launched in January 2003 by the Institut Universitaire Européen de la Mer (IUEM/Univ. Brest) and is continuing today in the framework of the French coastal observation service SNO-DYNALIT. The dataset contains over 16 years of monthly beach profile surveys and a large collection of repeated high-resolution subtidal and subaerial digital elevation models (DEMs). The dataset is accompanied by time-series of inshore waves and water levels, and enriched metadata, that will facilitate its future reuse in coastal research.Measurement(s)Beach topography • Nearshore bathymetryTechnology Type(s)RTK-GNSS • Terrestrial laser scanning • Digital photogrammetry • Multibeam echosounderFactor Type(s)ElevationSample Characteristic - EnvironmentshoreSample Characteristic - LocationBretagne Region

Wave dynamics contribute significantly to coastal hazards and were thus investigated at Vougot Beach by simulating both historical and projected future waves considering climate change impacts. The historical period included a major storm event. This period was projected to the future using three globally averaged sea level rise (SLR) scenarios for 2100, and combined SLR and wave climate scenarios for A1B, A2, and B1 emissions paths of the IPCC. The B1 wave climate predicts an increase in the occurrence of storm events. The simulated waves in all scenarios showed larger relative changes at the beach than in the nearshore area. The maximum increase of wave energy for the combined SLR and wave scenarios was 95%, while only 50% for the SLR-only scenarios. The effective bed shear stress from waves and currents showed different spatial variability than that of the wave height, emphasizing the importance of interactions between nearshore waves and currents. Increases in the effective bed shear stress (combined scenarios: up to 190%, and SLR-only scenarios: 35%) indicate that the changes in waves and currents will likely have significant impacts on the nearshore sediment transport. This work emphasizes that combined SLR and future wave climate scenarios need to be used to evaluate future changes in local hydrodynamics and their impacts. These results provide preliminary insights into potential future wave dynamics at Vougot Beach under different climate change scenarios. Further studies are necessary to generalize the results by investigating the wave dynamics during storm events with different hydrodynamical conditions and to evaluate potential changes in sediment transport and morphological evolution due to climate change.

Mahabot, M.-M.; Pennober, G.; Suanez, S.; Troadec, R., and Delacourt, C., 2017. Effect of tropical cyclones on short-term evolution of carbonate sandy beaches on Reunion Island, Indian Ocean. Carbonate sandy beaches in Reunion Island show various forms of evidence of erosion. Extreme waves associated with tropical cyclones (TCs) play a major role in beach dynamics. The present study analyzes and quantifies back-reef beach response and recovery from forcing generated by TCs Dumile, Felleng, and Bejisa, which occurred in 2013 and 2014. The study focuses on carbonate beaches of Reunion Island from Cap Champagne to the Passe de Trois-Bassins. Morphological and volumetric changes on beaches were analyzed by comparing 19 beach profiles. The results show that TCs are able to cause significant morphosedimentary change on the back-reef beaches of Reunion Island. These changes affect beach topography and involve longshore and cross-shore sediment transport. An alongshore variation in beach response is observed, which varies according to tropical storm intensity and coastal morphology. The intensity of impact seems to be related to reef width. The most severe erosion occurred at Boucan Canot, where reef is absent with a loss of −24 ± 2 m3 after TC Dumile, −38.7 ± 1.2 m3 after Felleng, and −42.5 ± 1.6 m3 after Bejisa. Elsewhere, the volumetric changes is less than 5 m3 under TC Dumile and vary between 2 and 11 m3 under TC Felleng and between 2 and 23 m3 under TC Bejisa. No significant impact occurred at La Saline where the reef flat is large and provides good protection for the beach; however, relative coastline orientation and prestorm beach-profile morphology also play an essential role in storm impact. Wave height and water level are also determinant factors of storm erosion potential. After storms, the beaches show a relative capacity for recovering because of calm conditions; however, different behaviours are observed along the same beach compartment. This suggests local influence of coastal structure and/or reef geomorphology in sediment transport processes.

Stéphan, P.; Blaise, E.; Suanez, S.; Fichaut, B.; Autret, R.; Floc'h, F.; Cuq, V.; Le Dantec, N.; Ammann, J.; David, L.; Jaud, M., and Delacourt, C., 2019. Long, medium, and short-term shoreline dynamics of the Brittany Coast (western France). In: Castelle, B. and Chaumillon, E. (eds.), Coastal Evolution under Climate Change along the Tropical Overseas and Temperate Metropolitan France. Journal of Coastal Research, Special Issue No. 88, pp. 89–109. Coconut Creek (Florida), ISSN 0749-0208. This paper aims to analyze the shoreline changes of coastal accumulations (sandy and gravel beaches/barriers) of Brittany (Western France). Three long, medium, and short term spatio-temporal scale observations are taken into consideration for the assessment of shoreline dynamics at this regional scale. Firstly, the long-term shoreline position evolution is based on a comparison of two sets of aerial orthophotos (1949-1952 and 2006-2009). A total of 652 beaches were analyzed in order to map and quantify erosion (35% of the total studied coastline), stability (38%), and accretion (27%) over the last 60 years. In detail, these percentages vary significantly according to the beach/barrier morphologies (spits vs pocket beaches), sediment composition (sandy vs gravelly), and hydrodynamic context (exposed vs sheltered). Secondly, a pluri-annual (i.e., medium-term) shoreline change analysis based on five representative beaches was conducted. This analysis was also based on image processing using sets of aerial photos taken every five years over the last 60 years (1948-2013). Results show an alternation of significant erosion- and accretion-dominated periods (respectively EDP and ADP), with six main EDP (i.e., periods 1962-1968, 1977-1978, 1980-1985, 1987-1990, 1993-1997, and 2013-2014) related to an increase in the frequency of extreme water levels associated with storm events. Finally, the short-term change analysis based on high-frequency monitoring of 11 sites was carried out over the period 1998-2017. These surveys, based on field topo-morphological measurements, highlight the impact of five morphogenetic events associated with significant storm events: 1998-2000 (storms Lothar and Martin in December 1999), 2008 (storm Johanna on March 10, 2008), the winter of 2013-2014 (a cluster of storms in January, February, and March 2014), 2016 (storm Ruzica/Imogen on February 8, 2016) and 2018 (storm Eleanor on January 2, 2018). A relevant recovery phase, which took place between 2008 and 2012 due to the calm and cold winters, was also recognized. The identification of parameters involved in shoreline variations at these three timescales is important for future management options of the Brittany coast.

Monitoring of dune erosion and accretion on the high-energy macrotidal Vougot beach in North Brittany (France) over the past decade (2004–2014) has revealed significant morphological changes. Dune toe erosion/accretion records have been compared with extreme water level measurements, defined as the sum of (i) astronomic tide; (ii) storm surge; and (iii) vertical wave runup. Runup parameterization was conducted using swash limits, beach profiles, and hydrodynamic (Hm0, Tm0,–1, and high tide water level—HTWL) data sets obtained from high frequency field surveys. The aim was to quantify in-situ environmental conditions and dimensional swash parameters for the best calibration of Battjes [1] runup formula. In addition, an empirical equation based on observed tidal water level and offshore wave height was produced to estimate extreme water levels over the whole period of dune morphological change monitoring. A good correlation between this empirical equation (1.01Hmoξo) and field runup measurements (Rmax) was obtained (R2 85%). The goodness of fit given by the RMSE was about 0.29 m. A good relationship was noticed between dune erosion and high water levels when the water levels exceeded the dune foot elevation. In contrast, when extreme water levels were below the height of the toe of the dune sediment budget increased, inducing foredune recovery. These erosion and accretion phases may be related to the North Atlantic Oscillation Index.

Suanez, S.; Blaise E.; Cancouët R., and Floc'h F., 2016. Empirical Parameterization of Wave Runup and Dune Erosion during Storm Conditions on a Natural Macrotidal Beach. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 932–936. Coconut Creek (Florida), ISSN 0749-0208. An experimental study based on field measurements for runup parameterization was conducted on a high energy macrotidal beach located on North Brittany (Vougot Beach). The approach was based on morphological and hydrodynamic high frequency monitoring collected between 2008 and 2013. The aim was to quantify in-situ environmental conditions and dimensional swash parameters for the best calibration of Battjes (1971) runup formula. In addition, an empirical equation based on observed tidal water level and offshore wave height was produced to estimate extreme water levels defined as the sum of (i) astronomic tide, (ii) storm surge, and (iii) vertical wave runup. A good correlation between this empirical equation (1.01Hmoξ;o) and field runup measurements (Rmax) was obtained (R2 85%). The goodness of fit given by the RMSE was about 0.29 m. Extreme water levels were then used to explain dune erosion processes that occured during the winter storms 2013–2014. A good relationship was noted between dune erosion and high water levels when they exceed the dune foot elevation.

Floc'h, F.; Le Dantec, N.; Lemos, C.; Concouët, R.; Sous, D.; Petitjean, L.; Bouchette, F.; Ardhuin, F; Suanez, S., and Delacourt, C., 2016. Morphological Response of a Macrotidal Embayed Beach, Porsmilin, France. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 373–377. Coconut Creek (Florida), ISSN 0749-0208. Morphodynamics of sandy, macrotidal, embayed beaches is complex because of the numerous physical processes interacting at the same location over a wide range of temporal scales. As most of these processes are controlled by beach morphology, dynamic feedbacks are generally observed between hydro- and morphodynamics. Investigating short-term processes is essential in order to improve long term morphological prediction. A key question is to understand how beach slope reacts to forcing conditions, in particular the response time of the beach profile, how long the transient state lasts. This study deals with the spatial and temporal responses of beach morphology to varying incident conditions. Here we report main observations, preliminary results and on-going investigations on the DYNATREZ1 field campaign, which was conducted in the framework of the National Observation Service Dynalit. Beach profiles are shown to adapt rapidly to forcing conditions, within two days, with more intense variations observed in the high tide swash zone. The presence of infragravity waves and their dissipation on the beach is highlighted. It is likely that the very large variability in beach slope observed over a single neap-spring cycle is responsible for the accordingly large variability in wave skewness, asymmetry and breaking processes, and thus in sediment fluxes and morphological changes.

Suanez, S.; Stéphan, P.; Fichaut, B.; Ammann, J., and Accensi, M., 2020. Medium-term morphological changes of a gravel spit driving by storm events (Sillon de Talbert, Brittany, France). In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 669-673. Coconut Creek (Florida), ISSN 0749-0208. The Sillon de Talbert (Northern coast of Brittany) is a large 3.5 km-long swash-aligned gravel spit comprising a volume of sediment of 1.23x106 m3. Since 2002, a morphodynamic survey based on annual DEMs, and waves and water level measurements and/or modeling, has been carried out. The 17-year (2002-2019) monitoring program shows that cross-shore sediment transfers reaching 430,000 m3 are dominant, while the longshore sediment transfer -through cannibalization process- is about 52,000 m3. The maximum landward displacement of the spit due to rollover processes reaches –4 m.yr-1. Storm events control more than 95% of this retreat due to catastrophic overwash/inundation processes that led to the opening of a breach in March 2018. The morphological evolution of the Sillon de Talbert is driven by anthropogenic forcing (i.e., impact of coastal defence structures, cutting off of longshore sediment transport), and natural forcing such as the depletion of the supply of sediment from the platform.

Coastal boulder deposits provide vital information on extreme wave events. They are crucial for understanding storm and tsunami impacts on rocky coasts, and for understanding long-term hazard histories. But study of these deposits is still a young field, and growth in investigation has been rapid, without much contact between research groups. Therefore, inconsistencies in field data collection among different studies hinder cross-site comparisons and limit the applicability of findings across disciplines. This paper analyses field methodologies for coastal boulder deposit measurement based using an integrated database (ISROC-DB), and demonstrates inconsistencies in current approaches. We use the analysis as a basis for outlining protocols to improve data comparability and utility for geoscientists, engineers, and coastal planners. Using standardised and comprehensive data reporting with due attention to precision and reproducibility – including site characteristics, boulder dimensions, complete positional data, tide characteristics, and geodetic and local topographic datum information – will help ensure complete data retrieval in the field. Applying these approaches will further ensure that data collected at different times and/or locations, and by different groups, is useful not just for the study being undertaken, but for other researchers to analyse and reuse. We hope to foster development of the large, internally consistent datasets that are the basis for fruitful meta-analysis. This is particularly important given increasing focus on long-term monitoring of coastal change. By recommending a common set of measurements, adaptable to available equipment and personnel, this work aims to support accurate and thorough coastal boulder deposit documentation, enabling broader applicability and future-proofed datasets. Field protocols described and recommended here also apply as best practices for coastal geomorphology field work in general.