Coastal dunes result from complex interactions between sediment supply, topography and vegetation. However, feedback processes remain uncertain, in part due to the lack of quantitative analyses, integrating plant distribution and morphologic changes. This work seeks to assess how feedback processes are initiated and maintained by analysing the early development stages of a coastal dune, combining data on the evolution of its biotic (plant density and plant communities) and abiotic (morphology) components. For that, we study the establishment and early evolution of a coastal dune (1 ha plot) between 2019 and 2022, using high-resolution images and photogrammetry from Unmanned Aerial Vehicle (UAV) surveys. Results show a gradual plant colonisation with an increasing number of species as the colonised area expanded and plant community composition shifted. Plant distribution appears controlled by environmental conditions (elevation, distance to shoreline and debris presence), explaining three colonisation patterns: 1) over inherited morphological features (ridges) with debris, 2) over nutrient-rich debris lines, and 3) at flat surfaces (platform) with limited sediment supply and debris material. Colonisation initiated along the ridge crests with pioneer and builder species. The ridges also captured and retained most of the aeolian sediment transported under favourable conditions. Plant communities increased their abundance through time and partially shifted to binder plant species. Colonised stranded debris lines displayed greatest plant densities. However, reduced fetch distances inhibited sediment transport and sand accumulation. The platform was the latest area to colonise with pioneer plants shifting to binders and very limited sediment supply. Accumulation of sand was promoted by surface roughness mainly due to changes in slope (3-6°) during the during first months of dune formation, when vegetation was very scarce, and due to the combined influence of slope and plant density at later stages, as plant density increased, gaining relevance. Sand accumulation contributed to reinforce the topography of the inherited morphologies during both phases. Still, low densities (5-20%), more common during early stages, had a higher contribution to the total accumulation of sand in the plot. Builder and perennial pioneer plants were more efficient, while annual pioneer and binders captured less sediment. Interestingly, highly efficient builders colonised areas prone to sand burial, ensuring their success in trapping sand, while binders occupied more protected areas, lacking active sediment supply. Overall, this work elucidates the feedback processes between sediment supply, topography and vegetation during the very early stages of dune formation, with physical feedbacks dominating the onset and biophysical ones dominating a subsequent colonisation stage. The results highlight the relevance of inherited morphologies to the early evolution of a dune and likely to its final configuration, conditioning future responses of the system to disturbances.

This work is supported by FCT – Fundação para a Ciência e a Tecnologia, I.P, through the projects 2022.05392.PTDC, 2021.04286.CEECIND/CP1672/CT0001, UIDP/00350/2020, UIDB/00350/2020 and LA/P/0069/2020.

How to cite: Costas, S., Gallego-Fernández, J. B., Bon de Sousa, L., and Kombiadou, K.: Foredune initiation through plant-topography interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15447, https://doi.org/10.5194/egusphere-egu24-15447, 2024.

Cliff coasts constitute an important geoecosystem of the Southern Baltic coast. The varied geological structure, cliff morphology, and variable hydrometeorological conditions in the annual and multi-annual cycles result in the development of different types of relief, which determine the morphodynamic type of the cliffs. The changes in relief that occur over the annual and multi-annual cycle are good indicators of cliff coastal morphodynamics.

The variation in cliff relief is mainly determined by the lithology, resistance and structure of the sediments. Regardless of the geological structure, the most important factor determining cliff morphodynamics is the morphogenetic activity of the sea. In addition to storm surges, denudational processes associated with mass movements and washout play a very important role. Slopes composed of compact glacial till are mainly modelled by striprockfall and flow processes, while slopes dominated by sandy series are subject to dry ravel processes. In the case of cliffs with a more varied structure conditioning the occurrence of groundwater outflows, the dominant process shaping the relief is landsliding and flow processes. The above conditions, combined with seasonal weathering variability, determine the characteristic types of moraine cliff relief.

A long-term and systematic study of the cliff morphodynamics of Wolin Island and other cliff sections comprising the southern Baltic coast has provided the basis for presenting a morphodynamic classification of moraine cliffs.

The classification was based on two criteria: lithological and morphogenetic. While the lithological criterion takes into account the dominant type of sediment building the cliff slope (clayey, sandy, sandy-clay), the morphogenetic criterion takes into account the genetic type of forms shaping the cliff relief. Based on the criterion of morphogenetic typology, forms related to rockfall, flow, landslide and dry ravel should be distinguished. It should be pointed out that the type of landforms is strictly conditioned by the lithology of the cliff.

Taking into account the assumed classification criteria, the following types were distinguished: rockfall-flow, talus-landslide, rockfall-landslide and landslide-flow. The presented morphodynamic types, in connection with seasonal variability of weathering types, are subject to constant change. Depending on the prevailing hydrometeorological conditions, the presented cliff types may occur in different variants (rockfall, flow, landslide and talus).

In a time of ongoing climate change, the morphogenetic potential of all morphodynamic factors modelling cliff relief is projected to increase systematically. This situation suggests that all the proposed morphodynamic types will be modelled with increasing intensity in the future, and that the process of transition through the various stages of development will accelerate significantly.

How to cite: Winowski, M., Kostrzewski, A., and Zwoliński, Z.: Morphodynamic classification of moraine cliffs of the Southern Baltic Sea coast, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13439, https://doi.org/10.5194/egusphere-egu24-13439, 2024.

The increase in spectral and spatial resolution offered by satellite imagery opens new opportunities in ecosystem monitoring over broader scales. Combined with advances in machine learning algorithms, like the spectral unmixing methods, it is possible to extract information on features smaller than the pixel size, as previously demonstrated for the case of saltmarsh plants. The present study focuses on transferring subpixel classification algorithms to mid-latitude coastal dunes, a significantly more challenging environment in terms of plant size and density, as well as in terms of complexity and heterogeneity of the existing species. To this aim we obtained WorldView2 imagery over the Ria Formosa barrier islands (South Portugal) during May of 2023 and collected data on dune plant distribution over three barrier islands during the same period. A total of 800 m² over the foredune (toe to lee) were photographed during fieldwork, identifying a total of 32 plant species. Plant density distribution was assessed at the level of the pansharpened satellite image pixel and the data were introduced to the Random Forest Soft Classification (RFSC) algorithm for training and validation. The sensing ability of the classifier was tested considering different parameters (number of trees, split criteria) and assessing the performance for increasing number of classes, along with the importance of the 8 spectral bands for each class. The results of the analysis provide insights on the strengths and limitations of the RSFC method for the especially challenging environment of mid-latitude coastal dune habitats and provide a step forward in coastal ecosystem remote sensing and monitoring of these environments.

Acknowledgements: The work was implemented in the framework of the DEVISE project (2022.06615.PTDC), funded by FCT (Fundação para a Ciência e a Tecnologia), Portugal. K. Kombiadou and S. Costas also recognise the financial support of FCT through contracts CEECINST/00146/2018/CP1493/CT0011 and 2021.04286.CEECIND, respectively, and the support of national funds through FCT by projects LA/P/0069/2020, granted to the Associate Laboratory ARNET, and UID/00350/2020, granted to CIMA.

How to cite: Kombiadou, K., Costas, S., Gallego-Fernández, J. B., Yang, Z., and Silvestri, S.: Subpixel classification of high-resolution satellite images to identify dune plants, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17548, https://doi.org/10.5194/egusphere-egu24-17548, 2024.

Coastal dunes systems play an important role as a defensive barrier against erosive and flood processes caused by storms and sea level rise. Delimiting coastal dunes is important for management and analysing local dynamics. Although, it is a complex task due to their inherent variability. This process can be optimized using remote sensing methods, showing to be essential, especially when dealing with extensive and complex systems or when analysing spatio-temporal changes.

This contribution shows a preliminary approach to the automatic segmentation of coastal dunes using the Multiresolution Segmentation (MRS) algorithm. The case of study is located in the Trafalgar Cape (Cádiz), in the southwest of the Iberian Peninsula. This area, that is part of the La Breña and Marismas de Barbate Natural Park, is composed of a combination of cliffs, beaches, dunes, and marshes, creating a diverse ecosystem. Dune vegetation, dominated by species such as stone pine, mastic, coastal juniper, and palmetto, is adapted to the climatic conditions, playing an important role in stabilizing the dunes and soils.

MRS was applied to different data sets i) RGB and NIR reflectances from Sentinel-2 L2 2017 composites at 10 m spatial resolution, ii) NDVI for the same year, and iii) a Digital Terrain Model (MDT). Different combinations of the algorithm hyper-parameters: “image layer weights”, “Scale Parameter”, shape/colour (0-0.9), and compactness/smoothness (0-0.9) were evaluated using the algorithm ESP2.The proportion of different land cover categories in this area (built-up, cropland, barren/sparse vegetation, trees, grassland, open water, herbaceous wetland and shrubland), was compute for every segment, considering the ESA WorldCover map at 10 m spatial resolution. The segments with the highest dune cover were compared to those obtained from a manual interpretation of very high resolution digital orthoimage.

How to cite: Lopez-Nieta, D., Guisado-Pintado, E., Canero, F. M., and Rodriguez-Galiano, V. F.: Supervised segmentation algorithm for coastal dunes delimitation and classification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18560, https://doi.org/10.5194/egusphere-egu24-18560, 2024.

Spits constitute sand-rich, elongated barriers extending laterally through the construction of progradational beach-ridges. Spits are constructed by angular wave approach and longshore currents, which results in the transport of sediment to the spit end and hence their growth. If sediment supply isn’t enough cannibalization can occur causing a narrowing and further breaching of the spit. One of the main controlling factors of sediment supply to spits are waves and particularly high energy events such as storms.

The spit of Punta Rasa, located in the northeast coast of the Buenos Aires province, represents the coastal outer extreme of the Río de La Plata estuary. Towards the north the spit is bordered by the southern extreme of the Samborombón Bay, whereas, to the south, the spit extents along the Oriental Barrier which ends towards the locality of Punta Medanos. The wave-built deposits interact with marshes and tidal channels transgressing the shoreline from the north. Besides, the coastal plain exhibits the interaction between beach-ridge systems, dune fields and sandy beaches.

In this work, coastline changes and recent evolution of the system of spits in Punta Rasa are analyzed using sedimentalogical profiles and aerial photographs. Results show an evolution marked by periods of erosion and significant changes in its morphology. Firther a general trend (since approx. 500 years) of the spit to curve towards the internal part of Bay is also found which could indicate a deficit in the contribution of sediment among with increasing mean sea level.

How to cite: Guisado-Pintado, E. and Isla, M.: Morphosedimentary evolution of a beach spit system (Punta Rasa, Argentina), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19712, https://doi.org/10.5194/egusphere-egu24-19712, 2024.

First described by King and Williams in 1949, multiple intertidal barred (MITB) features are characterised by a succession of intertidal sandbars, comprising a complex system subject to variable hydrodynamics. Relatively stable under macrotidal conditions and low to moderate wave energy, MITB systems can however, display cross-shore migrations and morphological changes under energetic and extreme events. Storm Barra occurred in December 2021, and crossed the east coast of Northern Ireland. It was the second highest energetic storm to have occurred there in the last 25 years, with waves reaching a maximum significant wave height (H_s) of 5.5m for a peak period (T_p) of 10s and, from a southeasterly direction on the 7^th December. To examine the morphological impact on Dundrum Bay and its MITB system, DGPS surveys were conducted, before and after storm Barre, at two adjacent sites, Murlough and Ballykinler beaches, on the 6^th and 9^th of December respectively. Topographic beach surveys showed distinct alongshore variability at both sites. Despite onshore waves, the Ballykinler site (eastern side of the bay) presented linear post-storm Barra profiles due to a complete flattening of the bar crests and sediment in-filling within the runnels. In contrast, the western end of the bay displayed an elevation of the beach profiles, with the central zone a more transitional area associated with onshore bars’ migrations to no significant changes, eastward. Additionally, nearshore wave modelling (SWAN), including adjustments for surge, was conducted to better understand the wave dissipation patterns and local interactions with sandbars’ morphology. Preliminary wave model results show a significant role of the bars during the event. At the peak of the storm, which corresponded to a falling tide period, the maximum wave dissipation was focussed on the offshore-most bar, just outside the intertidal area and thus limiting impacts on the beach and nearshore MITB system. The following rising tide period however, coupled with decreasing wave height and energy, corresponded with much less intense energy dissipation at the site. During the final phases of the storm, maximum values of wave energy dissipation concentrated closer to the shore and were primarily induced by the MITB system in the intertidal beach area. It therefore appears that the offshore-most bar of the MITB features plays a significant role dissipating extreme events energy and limiting morphological changes, while the other bars are more effective during less energetic conditions and at low tide. SWAN simulations help explain the relatively low coastal impact detected at both Ballykinler and Murlough beaches from storm Barra, although further investigation of sediment transport patterns and (antecedent) storm chronologies throughout the winter 2020/2021 season are still required to fully understand the alongshore variability observed. 

How to cite: Biausque, M., Guisado-Pintado, E., Grotolli, E., Jackson, D., and Cooper, A.: The role of a multiple intertidal barred (MITB) system in dissipating extreme storm wave energy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21383, https://doi.org/10.5194/egusphere-egu24-21383, 2024.

This study examines the impact of individual storm events, the recovery, and the effect of successive events on pebble beaches. As a first step, storm events in the Normandy region (France) were identified and classified according to their energy content using a 42-year wave height time series. Of the total number of identified storms, 187 were classified as Weak. 74 storms fell under the Moderate category, 25 storms were classified as Significant, 9 storms were labeled as Severe, and 2 storms were characterized as Extreme. A close examination of storm characteristics was done for the 2018-2019 and 2019-2020 winter seasons, where two Severe storms took place in each season. During these periods, the response of the beach was characterized through i) an evaluation of the intertidal beach volume using Digital Elevation Models (DEMs) generated through a video camera platform, and ii) an examination of shoreline change using Sentinel-2 satellite imagery. The analysis revealed distinctive differences between the two winter seasons. The 2018-2019 contained half the storm energy content compared to the 2019-2020 season. During the first winter season, the Severe storm took place by the end of the winter period and encountered an eroded beach. Subsequently, there was a slight volume increase during the summer season which did not fully recover the pre-
winter beach volume. As the 2019-2020 winter season commenced, there was further erosion, notably following the impact of the Severe storm (Ciara), which stood out as the most energetic storm during the study period. This event caused the beach to reach its minimum volume in the study, the posterior series of moderate and weak storms arriving at the beach assisted to the partial recovery of the beach volume. By July 2020, the beach volume had reached the pre-winter 2018-2019 values. The assessment of shoreline change using satellite images was used to complement the partial beach coverage of the cameras. Although, this approach was limited by the resolution of satellite images, evidence of shoreline retreat and beach rotation developments were associated to certain storm events, assisting in the evaluation of the beach response to storms.

How to cite: Mendoza, E. T., Soloy, A., Turki, I., Ojeda, E., Salameh, E., Lecoq, N., and Deloffre, J.: Storm impact and recovery on pebble beaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21984, https://doi.org/10.5194/egusphere-egu24-21984, 2024.