Session GM9.1

GM9.1 | Coastal morphodynamics: nearshore, beach and dunes

Coastal morphodynamics: nearshore, beach and dunes

Co-sponsored by IGU-CCS

Convener: Irene Delgado-Fernandez | Co-conveners: Derek Jackson, Emilia Guisado-Pintado, Susana Costas, Melanie Biausque

Orals

| Fri, 19 Apr, 14:00–15:45 (CEST)

Room G1

Posters on site

| Attendance Fri, 19 Apr, 16:15–18:00 (CEST) | Display Fri, 19 Apr, 14:00–18:00

Hall X1

Examining the morphodynamics of coasts from the nearshore through to inland dune systems is a fundamental requirement in understanding their short- to long-term behavior. Operating across large spatial and temporal scales, examination of their resulting landforms is both difficult and complex. Recent methodological advances, however, now enable traditionally isolated coastal disciplines to be examined across various zones, promoting integration along multiple time and space scales, helping to couple processes with landform responses.

At the coast, dunes provide a physical barrier to flooding during high-energy storms, while beaches and nearshore areas help dissipate storm impact through a series of dynamic interactions involving sediment transfers and sometimes rapid morphological changes. Examination of complex interactions between these three interconnected systems has become essential for understanding, analyzing, and ultimately managing our coasts.
This session welcomes contributions from coastal scientists interested in measuring and modelling physical processes and responses within the three sub-units over various spatial and temporal scales. It will highlight the latest scientific developments in our understanding of this part of the planet's geomorphic system and will facilitate knowledge exchange between the submerged (e.g., nearshore waves, currents, and sediment transport) and sub-aerial (e.g., beach and aeolian dune dynamics) zones.

This session is sponsored by the Commission on Coastal Systems (CCS) of the International Geographical Union (www.igu-ccs.org) and by the IGCP Project 725 ‘Forecasting coastal change’ (https://www.sfu.ca/igcp-725.html).

This year's solicited speaker is Dr Mitchell Harley, UNSW, Australia.

Orals: Fri, 19 Apr | Room G1

Chairpersons: Irene Delgado-Fernandez, Emilia Guisado-Pintado, Melanie Biausque

14:00–14:05

5-minute convener introduction

14:05–14:10

Nearshore and Beach

14:10–14:20

EGU24-13785

solicited

Highlight

On-site presentation

Ninety years of shoreline change at Narrabeen Beach (Australia) from sub-daily to decadal time scales

Mitchell Harley, Raimundo Ibaceta, Kristen Splinter, and Ian Turner

Narrabeen Beach is 3.6 km-long embayed sandy beach located in southeast Australia on the northern beaches of Sydney. It is well known in the coastal research community for its long-term beach monitoring program, that was commenced in 1976 by Prof. Andy Short and has continued uninterrupted until the present day. This program has led to a number of groundbreaking research advances, including the Wright and Short morphodynamic beach state model, embayed beach rotation and links to climate cycles like the El Niño/Southern Oscillation.

This presentation will present a significant extension of this monitoring program through the inclusion of advanced shoreline monitoring techniques. These techniques include: historical aerial photographs, airborne and fixed Lidar, UAV, satellite-derived shorelines (CoastSat), Argus coastal imaging and CoastSnap citizen science. This large dataset (comprising over 1 million data points) enables an unprecedented look at shoreline change in dynamic, wave-dominated environments on time scales from sub-daily to decadal. The talk will showcase new research derived from this dataset, including data-driven forecast models of shoreline erosion and insights on long-term coastal change. Finally, links to accessing this open-source dataset will be described.

How to cite: Harley, M., Ibaceta, R., Splinter, K., and Turner, I.: Ninety years of shoreline change at Narrabeen Beach (Australia) from sub-daily to decadal time scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13785, https://doi.org/10.5194/egusphere-egu24-13785, 2024.

14:20–14:30

EGU24-7489

ECS

Highlight

On-site presentation

Spatial characteristics of washovers formed in the coastal zone of the semi-enclosed tideless sea basin, Gulf of Gdańsk, Baltic Sea

Damian Moskalewicz and Felix Bahr

Storm surges lead to coastal erosion but may also leave geomorphological effects that contribute to a positive sediment budget and become a permanent or temporal part of the coastal landscape. We have investigated two study sites in the coastal zone of the Gulf of Gdańsk to examine depositional storm-induced landforms. We have measured and analysed the spatial characteristics of 244 washovers formed between 1979 and 2022. Spatial parameters like length, width, area, and perimeter of individual washovers were derived from orthophoto maps and aerial images with spatial resolution of ~0.2–1m. For the years when DEM was available for two consecutive years, the deposit volume was calculated by subtracting the DEM of the preceding year from the examined DEM. Collected data fills the gap in the knowledge of spatial characteristics of the smallest washovers, commonly forming during the relatively less powerful storms occurring in the Gulf of Gdańsk in comparison to coasts directly exposed to hurricanes or typhoons. Based on our results and data available in the literature, new scaling formulas were delivered for area-to-length, area-to-volume, and length-to-volume washover relationships. The current study indicates that spatial parameters of washover follow most of the relationships described in previous studies. However, it also suggests a more diverse view of different coastal settings impact on the formation of storm-induced landforms. The collected dataset also shows ambiguous data distribution for the smallest mapped features, indicating the influence of acquisition methodology on the data homogeneity and measuring error.

How to cite: Moskalewicz, D. and Bahr, F.: Spatial characteristics of washovers formed in the coastal zone of the semi-enclosed tideless sea basin, Gulf of Gdańsk, Baltic Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7489, https://doi.org/10.5194/egusphere-egu24-7489, 2024.

14:30–14:40

EGU24-15730

ECS

On-site presentation

Effect of cohesive sediments on coastal bar morphology under waves and currents

Anne Baar, Brendan Murphy, Stuart McLelland, and Daniel Parsons

Coastal systems are highly dynamic systems where sand and mud are transported under the complex interactions of bathymetry, currents and waves. A better understanding of the natural dynamics at the scale of individual bars is required for a fundamental understanding of the formation of coastal environments and how they will respond to changes in the future. The current research aims to characterize the relative influence of mud on the morphodynamic change of coastal bars under the combined action of waves and currents. To this end, experiments were conducted in the Total Environment Simulator, a large-scale wave-current flume facility at the University of Hull (6m x 11m, 0.4m deep). The experimental setup consisted of a circular mound of a mixture of sand and clay, placed on top of a flat sand bed in the centre of the flume. The experimental conditions were systematically varied between runs, with 4 different clay percentages of the mound, and 5 different combinations of wave height and current velocity. Flow velocity, water level and bed levels were monitored during each run, providing well-controlled bed development data over time. Preliminary observations of the mound morphology show lateral diffusion due to sediment transport perpendicular to the wave direction under the influence of gravity, and streamwise migration due to sediment transport in the direction of the flow. Increasing the cohesivity altered the relative influence of the waves and currents on the direction of sediment transport and therefore the final shape of the mound. Wave height had a greater control on the morphology with increasing clay content, since higher waves were more effective in winnowing out the clay into suspension and thereby mobilizing the sand fraction. Future analyses will focus on linking the change in direction of sediment transport under combined waves and currents to landscape evolution, to study the larger-scale implications of the observed differences in transport mechanisms.

How to cite: Baar, A., Murphy, B., McLelland, S., and Parsons, D.: Effect of cohesive sediments on coastal bar morphology under waves and currents , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15730, https://doi.org/10.5194/egusphere-egu24-15730, 2024.

14:40–14:50

EGU24-14647

ECS

On-site presentation

Short-term coastal morphodynamics simulation using wave phase-resolving and phase-averaged models.

Gugum Gumbira and Ming Li

Understanding coastal morphodynamics is crucial due to the growing human activity in the coastal regions. This study compared wave phase-averaged and phase-resolving models to simulate short-term morphological changes. Both models were validated against the LIP1C experiment and then applied to simulate bar movement on the microtidal coast of Indonesia. The wave phase-averaged model used in this study was developed based on the FVCOM model, while the phase-resolving model was built by combining FUNWAVE and 1DV models. Both models were modified to take into account the wave skewness and asymmetry effects on the near-bed sediment transport.

In the LIP1C experiment, the models were used to simulate a 201 m long open channel flow with 4.10 m depth. Irregular waves with a height of 0.60 m and an 8 s period were imposed at the offshore boundary, representing calm to moderate conditions. The simulation was conducted for 18 hours to identify model performance in producing onshore bar movement. The wave height, wave set-up/set-down, and currents magnitude produced by both models showed satisfactory results with a Normalised Root Mean Square (NRMS) value less than 0.10 for nine points measurement. Onshore bar movement was reproduced by the wave phase-averaged and phase-resolving models. The former model under-predicted the total transport rate values, while the latter model showed a similar order of magnitude against the experiment, leading to better agreement of bar growth. Two crucial factors in the onshore sediment transport were wave skewness and asymmetry. The wave skewness and asymmetry effects in the phase-averaged model were obtained by using the empirical formula. The phase-resolving model obtained better results because these factors were directly solved in every time step. The Brier Skill Score (BSS) were 0.78 and 0.83 for the wave phase-averaged and phase-resolving models.

The models were used to simulate wave-induced sediment transport on the microtidal coast of Indonesia. It was a semi-enclosed bay in the northern part of Java Island with waves and currents entering from the North. Bathymetry data analysis showed a bar position located around 45 m from the coastline. A bottom-mounted Acoustic Doppler Currents Profiler (ADCP) was placed around 500 m from the coastline. The instrument was used to collect waves and currents data for ten days and to validate model results. Model results, such as significant wave height, surface elevation, and currents magnitude, showed good agreement against measurement. The NRMS values were less than 0.15 and 0.10 for phase-averaged and phase-resolving models. During the ten-day measurement, the hydrodynamics condition at the surface level was dominated by 0.25 m/s south-directed currents that moved sediment materials from offshore to onshore. As a result, the total transport rate was dominated by near-bed transport rather than suspended load transport. The bar moved near the shore, around 35 m from the coastline. The bar movement in this simulation was reproduced by both models, with the phase-resolving model showing better results.

How to cite: Gumbira, G. and Li, M.: Short-term coastal morphodynamics simulation using wave phase-resolving and phase-averaged models., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14647, https://doi.org/10.5194/egusphere-egu24-14647, 2024.

14:50–15:00

EGU24-12232

ECS

On-site presentation

Performance of Satellite-Derived Shoreline algorithms on a beach with banquettes of Posidonia oceanica.

Sabrina Terracciano, Juan Montes Pèrez, Riccardo Brunetta, Paulo Cabrita, Enrico Duo, Stefano Fabbri, Paolo Ciavola, and Clara Armaroli

In recent years, advances in remote sensing sensor resolution and data processing techniques have increased our capability to monitor coastal environments, facilitating a more complete understanding of their dynamics and temporal changes. The development of algorithms able to (semi)automatically detect the shoreline on high spatial and spectral resolution images is particularly noteworthy. However, most of these algorithms have been tested on typical sandy beaches, and the indices used to classify the images often overlook the presence of substantial dark-colored organic material on beaches. This oversight can significantly impact the performance of the algorithms. The presence of casts of dead leaves and rhizomes of Posidonia oceanica (the so-called banquettes) in the swash/intertidal zones, indeed, poses a challenge for the shoreline detection, increasing the inaccuracy of the identified sand-water interface.

The present study includes a comparison of the results obtained using different algorithms for Satellite-Derived Shoreline (SDS) extraction on a beach where large quantities of Posidonia oceanica banquettes are located in the swash area. Specifically, the capability of three available algorithms, developed for multispectral (CoastSat; Vos et al., 2019 - https://doi.org/10.1016/j.envsoft.2019.104528, and SAET; Palomar-Vázquez et al., 2023 - https://doi.org/10.3390/rs15123198) and hyperspectral (HyperSho; Souto-Ceccon et al., 2023 - https://doi.org/10.3390/rs15082117) imagery was tested, using Sentinel-2 and PRISMA satellites.

In order to validate the SDS extracted with the different algorithms and to carry out an accuracy analysis, three RTK-GNSS surveys were performed in September 2022, May and October 2023. The algorithms were tested on the Arborea beach in the Gulf of Oristano, on the western coast of Sardinia (Italy). Arborea beach is characterised by a shallow sloping seafloor that contributes to the accumulation of banks of Posidonia oceanica. Normally, the presence of Posidonia on the beach plays a crucial role in regulating erosional and sedimentological processes and contributes to beach regeneration.

Error analysis revealed that the accuracy obtained is around the spatial resolution of the satellite. Focusing on the multispectral algorithms, we find that SAET obtains better results, considering that the performance of the CoastSat algorithm returns an RMSE of about 25 m, on the three dates studied. The error observed in CoastSat could arise from the misclassification or non-recognition of various classes, particularly the sand class, which is frequently mistaken for buildings or remains unrecognised due to its dark appearance.

The results obtained from this study demonstrate the advantages of adopting various algorithms, each employing different image processing modes and spectral indices. This approach allows us to assess the accuracy levels of the analysis and emphasise the diverse limitations inherent in each methodology. Additionally, the analysis conducted, underscores the significance of testing shoreline extraction algorithms on beaches characterised by non-standard or uncommon features.

The field data were acquired during fieldwork activities of the OVERSEE project, financed by ASI under contract 2022-14-U.0.

How to cite: Terracciano, S., Montes Pèrez, J., Brunetta, R., Cabrita, P., Duo, E., Fabbri, S., Ciavola, P., and Armaroli, C.: Performance of Satellite-Derived Shoreline algorithms on a beach with banquettes of Posidonia oceanica., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12232, https://doi.org/10.5194/egusphere-egu24-12232, 2024.

15:00–15:05

Dunes and Rocky Coasts

15:05–15:15

EGU24-11826

ECS

Highlight

On-site presentation

Computational Fluid Dynamics Model to Simulate Wind Flow Across a Foredune

Saeb Faraji Gargari, Derek Karssenberg, and Gerben Ruessink

Coastal dunes serve as important protection against water waves, particularly during storms. Therefore, investigating the formation and migration of dunes is imperative for developing hazard management strategies to protect the mainland. The wind flow over dunes plays an important role in sediment transport around dunes, contributing to their formation and shaping over time. The interaction between dune geometry and wind velocity creates a two-way coupling effect. While experimental and field studies have been conducted to examine the impact of wind velocity and dune geometry, they are often constrained by certain limitations. Numerical methods provide a viable approach to simulate wind/air flow by solving the governing equations (Navier-Stokes equations). Computational fluid dynamics (CFD) methods are commonly employed for such simulations. The objective of this contribution is to study spatial changes in near-bed wind speed and direction across a foredune as a function of the wind approach angle and foredune geometry (height and slope of its seaward side) using OpenFOAM, an open-source code that solves the partial differential equations (PDEs) governing physical problems using the finite volume method (FVM). We first tested the model against data collected at the approximately 15-m high foredune (1:2 slope) at Egmond aan Zee, Netherlands. Consistent with the data, the model shows that the speed-up of the wind from the base to the crest of the foredune depends on the wind approach angle. The speed-up varies almost 3 times to 1 when the wind direction changes from 0 to 90 degrees. The error norm of the CFD results, when compared to the measured data, is less than 10 percent, validating the accuracy of the proposed CFD model. The model was then applied to synthetic foredune profiles, in which we varied foredune height between 6 and 25 m, and slope between 1:4 and 1:2. Our results indicate that speed-up is strongest for highest and steepest dunes. Speed-up is barely notable for dunes 6 m in height and 1:4 in slope. The results also show that the speed-up can grow up to 10 times for a dune with a height of 25 m and 1:2 slope.

How to cite: Faraji Gargari, S., Karssenberg, D., and Ruessink, G.: Computational Fluid Dynamics Model to Simulate Wind Flow Across a Foredune, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11826, https://doi.org/10.5194/egusphere-egu24-11826, 2024.

15:15–15:25

EGU24-17322

Highlight

On-site presentation

Assessing the dune system for coastal safety utilizing morphological models

Athita (Emmy) Sukchaiwan

Assessing the dune system for coastal safety utilizing morphological models

Emmy Sukchaiwan¹, Glenn Strypsteen², and Caroline Hallin³

¹SWECO, Malmö²Hydraulics and Geotechnics, Department of Civil Engineering, Bruges Campus, KU Leuven, Bruges, Belgium (glenn.strypsteen@kuleuven.be)³Faculty of Engineering, Lund University, John Ericssonsv 1, 221 00, Lund, Sweden

The Falsterbo Peninsula in Skåne, Sweden, is a low-lying area that provides a home to 7,000 residents. To protect the densely populated area, a dike and the natural dune system are used as safety barriers against storm surges. Despite being part of the protection strategy, the dune system’s capacity to protect the hinterland from storm impacts remains unexplored and requires comprehensive assessment. This study aims to provide a numerical representation of the severity of dune erosion due to historical storm conditions spanning from the period 1959 to 2022. The 1872 storm is the largest storm surge in the study area. Suggesting its potential recurrence, the 1872 storm was included in the analysis.

To increase the confidence of the prediction of dune erosion, two different morphological models were utilized: the process based XBeach model (Roelvink et al., 2010) and the analytical storm impact model (Larson et al., 2004). Although both models are capable in estimating dune erosion during storm conditions, they differ in their approach and level of complexity. The XBeach model is selected for its comprehensive representation of hydrodynamic and morphodynamic processes, while the storm impact model is chosen for its simplicity. This simplicity makes the storm impact model easier to use, unlike the XBeach model, which can be more computationally intensive. Due to the lack of observational dune erosion data in the study area, model calibrations from other studies were used.

The eroded volume is expressed as a fraction of the available dune volume in that specific transect. The maximum dune erosion under storm conditions in the period 1959 to 2022, estimated by the XBeach and the storm impact model are 7.7% and 32.9%, respectively. These numerical results suggest that the dune system is capable to withstand storm conditions that had occurred during this 63-year timeframe. However, this conclusion is not valid when considering the estimated dune erosion resulting from the 1872 storm. For this event, the XBeach model estimated 67.9% erosion, whereas the storm impact model predicts a dune breach.

A comparative analysis revealed that large difference in the model results can be found in extreme conditions with long storm duration. This divergence is primarily attributed to the incorporation of the negative feedback mechanism in the XBeach model, which is absent in the simplified solution of the storm impact model. The study’s findings highlight the critical role of negative feedback mechanisms in model outcomes.

Roelvink, D., Reniers, A. J. H. M., Van Dongeren, A. P., Van Thiel de Vries, J., Lescinski, J., & McCall, R. (2010). XBeach model description and manual. Unesco-IHE Institute for Water Education, Deltares and Delft University of Tecnhology. Report June, 21, 2010.

Larson, M., Erikson, L., & Hanson, H. (2004). An analytical model to predict dune erosion due to wave impact. Coastal Engineering, 51(8-9), 675-696.

How to cite: Sukchaiwan, A. (.: Assessing the dune system for coastal safety utilizing morphological models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17322, https://doi.org/10.5194/egusphere-egu24-17322, 2024.

15:25–15:35

EGU24-6338

On-site presentation

Towards a theory for the formation of sea stacks

Andrew Fowler, Felix Ng, and Guy Kember

15:35–15:45

EGU24-16635

ECS

On-site presentation

Erosional behaviour of a glacial till cliff coast in Stohl, Baltic Sea, Germany

Jan-Eike Rossius, Tanita Averes, Knut Krämer, and Christian Winter

Erosional processes at an approximately one kilometre long coastal cliff stretch were investigated. The cliff is located at the German Baltic Sea coast and mainly made up of glacial till from the last glaciation. Glacial deposition and folding in multiple advances resulted in complex stratigraphy and locally diverse geology of at least two distinct glacial till complexes and intermediate layers of sand, now eroded by wave action and subaerial processes on the cliff face. To study the changes on the cliff, drone surveys were carried out roughly every month over three years and used to create elevation models with structure from motion. This data was combined with time series of water levels, wave characteristics and precipitation. Three main erosion processes could be identified: marine erosion at the cliff foot, surface runoff and mass movements. 13 marine erosion events are clearly connected to high waves and water levels. Surface runoff creates alluvial fan deposits at the cliff foot and is driven by precipitation. However, the correlation is not clear as the deposition depends on local properties and preconditioning and is very susceptible for marine erosion. The more than 400 detected mass movements cannot clearly be correlated with precipitation, most likely due to the local geology, but they show a distinct negative magnitude-frequency-relation and often follow marine erosion events at the cliff foot.

How to cite: Rossius, J.-E., Averes, T., Krämer, K., and Winter, C.: Erosional behaviour of a glacial till cliff coast in Stohl, Baltic Sea, Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16635, https://doi.org/10.5194/egusphere-egu24-16635, 2024.

Discussion and end of session

Posters on site: Fri, 19 Apr, 16:15–18:00 | Hall X1

Display time: Fri, 19 Apr, 14:00–Fri, 19 Apr, 18:00

Chairpersons: Irene Delgado-Fernandez, Derek Jackson, Susana Costas

X1.130

EGU24-15447

Foredune initiation through plant-topography interactions

Susana Costas, Juan B. Gallego-Fernández, Luisa Bon de Sousa, and Katerina Kombiadou

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.

X1.131

EGU24-12478

Eco-Geomorphological mapping of the Camposoto Barrier System in Cadiz Bay, S Spain

(withdrawn)

Irene Delgado-Fernandez, Pilar Martín-Gallego, Cristina Montes, Javier Benavente, Laura del Río, Theocharis A. Plomaritis, Susana Costas, Javier Gracia, Luis Barbero, Tomás Fernández-Montblanc, and Christopher Marston

X1.132

EGU24-13439

Morphodynamic classification of moraine cliffs of the Southern Baltic Sea coast

Marcin Winowski, Andrzej Kostrzewski, and Zbigniew Zwoliński

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.

X1.133

EGU24-14178

Highlight

Resuspension of intertidal cohesive sediment during the passage of extreme typhoons

(withdrawn after no-show)

Ho Kyung Ha, Seong Woon Jeong, Hun Jun Ha, and Jong Seong Khim

X1.134

EGU24-14671

ECS

Dynamic Insights: Advanced Techniques for Assessing Coastal Sediment Budgets Using DSAS and ArcGIS Spatial Analysis in the Kozhikode Sector along the SW Coast of India

(withdrawn)

Rafeeque Mk and Sheela Nair L.

X1.135

EGU24-17548

Subpixel classification of high-resolution satellite images to identify dune plants

Katerina Kombiadou, Susana Costas, Juan B. Gallego-Fernández, Zhicheng Yang, and Sonia Silvestri

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.

X1.136

EGU24-18560

ECS

Supervised segmentation algorithm for coastal dunes delimitation and classification

Diego Lopez-Nieta, Emilia Guisado-Pintado, Francisco M Canero, and Víctor F Rodriguez-Galiano

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.

X1.137

EGU24-19644

ECS

Highlight

Linking headland bypassing to the evolution of a spit and beach ridge system - Slocums River Embayment, Buzzards Bay, Massachusetts, USA

Silke Tas, Zoe Hughes, Duncan FitzGerald, Danghan Xie, Tansir Asik Zaman, and Sergio Fagherazzi

The northwestern Buzzards Bay shoreline in Massachusetts, USA is a complex system consisting of multiple headlands, dividing the coastline into several coastal cells containing tidal inlets and mixed-sediment beaches. While these compartments form (mostly) closed sediment cells during regular wave conditions, high energy events can generate sediment pulses past headlands. As a result, infrequent extreme events, like hurricanes, play a major role in the long-term evolution of this shoreline. The inlet of Slocums River is situated near the mouth of Buzzards Bay, between the two headlands of Barneys Joy Point and Mishaum Point. The western side of the inlet is characterized by a mixed sand-gravel beach, a sandy spit and a series of beach ridges. This study aims to link headland bypassing volumes and frequencies to the spit and beach ridge evolution near Slocums River inlet, closing the gap between the time scales of headland bypassing (storm-induced, hours to days) and spit and beach ridge evolution (years to centuries). We developed two numerical models in Delft3D, a large-scale grid to model the headland bypassing on shorter time scales, and a finer grid to model the longer term morphodynamic evolution inside the embayment, using a morphological acceleration factor. The long-term spit and beach ridge evolution was studied using aerial and LIDAR images.

How to cite: Tas, S., Hughes, Z., FitzGerald, D., Xie, D., Asik Zaman, T., and Fagherazzi, S.: Linking headland bypassing to the evolution of a spit and beach ridge system - Slocums River Embayment, Buzzards Bay, Massachusetts, USA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19644, https://doi.org/10.5194/egusphere-egu24-19644, 2024.

X1.138

EGU24-19712

Morphosedimentary evolution of a beach spit system (Punta Rasa, Argentina)

Emilia Guisado-Pintado and Manuel Isla

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.

X1.139

EGU24-21352

Highlight

Multi-annual nearshore evolution of a mega-nourishment in the southern coast of Namibia

(withdrawn)

Carlos Loureiro

X1.140

EGU24-21361

Long-term shoreline change trends over the last 191 years in Northern Ireland

(withdrawn after no-show)

Edoardo Grottoli, Derek Jackson, Andrew Cooper, and Melanie Biausque

X1.141

EGU24-21383

The role of a multiple intertidal barred (MITB) system in dissipating extreme storm wave energy

Melanie Biausque, Emilia Guisado-Pintado, Eduardo Grotolli, Derek Jackson, and Andrew Cooper

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.

X1.142

EGU24-21984

Storm impact and recovery on pebble beaches

E. Tonatiuh Mendoza, Antoine Soloy, Imen Turki, Elena Ojeda, Edward Salameh, Nicolas Lecoq, and Julien Deloffre

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.