There are very few examples of managed retreat in the coastal zone of the USA. Those that exist are primarily the last, desperate acts for communities with limited financial resources (e.g., Isle de Jean Charles, Louisiana and the Blue Acres Program in New Jersey). The vast majority of retreat in the coastal United States is either completely unmanaged with some government assistance at the household level, or autonomous relocation driven by economic factors like the inability to rebuild following a storm or lack of insurance. Surprisingly, those properties at greatest exposure to storms (those in resort communities along the oceanfront) have almost no history of retreat. Retreat/relocation in the American coastal zone occurs almost entirely inland in working class and underrepresented communities. The explanation for this dichotomy is simple, coastal protection in the USA is funded largely by the public sector and based almost entirely on a cost/benefit analysis that considers only property values. If your property values are high, you are typically offered protection through coastal engineering like beach nourishment. If your property values are modest, you will be left to find your own solution to the hazards you face. If you are lucky, there may be some assistance available to raise or buyout your home, but this happens in a way with very little planning or foresight. 
In the United States, even the suggestion of managed retreat from the oceanfront is typically dismissed as too expensive to implement or too harmful to the economic prosperity of the community. In an effort to argue for the consideration of retreat as a reasonable option for the expenditure of public funds on the oceanfront, we have conducted a fiscal analysis of the cost of buying out highly-exposed, oceanfront investment homes rather than spending those same funds on long-term coastal protection. This analysis has recently been completed for portions of North Topsail Beach and Rodanthe, North Carolina where large-scale, coastal protection is planned. In both cases, the costs of large-scale buyouts are cheaper than the costs of long-term protection and a full consideration of lost tax revenues from the removed/relocated structures. Furthermore, the fiscal analysis does not include many unquantifiable benefits from the proposed targeted acquisition. These are things like transfer of amenity value to other properties, reduced emergency management costs for the municipality, reduced need for consulting engineering fees, improved beach access for all residents and renters, and significant environmental benefits for the beach/dune system. 
Ultimately, it is our hope that funds used in a more efficient manner for investment properties on the oceanfront could result in greater availability of funds to assist those in residential communities that have a far greater need for a well-managed response to rising sea levels and future storms.

How to cite: Young, R., Coburn, A., Peek, K., Tormey, B., and Thompson, H.: A critical review of coastal retreat in the USA , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13579, https://doi.org/10.5194/egusphere-egu24-13579, 2024.

The Curonian Spit is 98 km long, while Lithuania has a 50 km stretch of coastline. The evolution of the Curonian Spit is linked to the alongshore northward sediment transport. However, varying tendencies of coastal dynamics have been observed between the different sections. Hydrodynamic and aeolian processes, generated by the prevailing westerly winds have been identified as the main factors controlling the coastal dynamics. The reasons for inconsistent coastal trends along different sections in a relatively short coast stretch (50 km) remain unclear, despite similar coastal morphology and similar prevailing hydrometeorological conditions.

The previous studies on Curonian Spit coastal development were based on wind, sea level and visual wave observation data collected only in two hydrometeorological (Klaipėda and Nida) stations. The limited spatial distribution of this data allowed only assumptions to be made about the influence of wave regime on the coastal dynamics of the Curonian Spit in different stretches.

The aim of this study was to analyse the spatial variability of the changes in wave regime along the Curonian Spit sea coast and investigate their relationship with the changes in sediment volume. The main goal of this study is to identify the impact of wave regime on the variance of coastal development along the Curonian spit.

The spatial variance of sediment volume was calculated from the 12 cross-shore levelling profiles from the 2003-2019 period. Wave parameters were analysed using Baltic Sea long-term wave reanalysis data, generated with WAM spectral wave model by the Finish Meteorological Institute (FMI). The yearly changes in mean wave parameter values were compared to the sediment volume at the corresponding measurement points using Pearson correlation and regression analysis.

Sediment accumulation in varying magnitude were observed along the entire Lithuanian coast of the Curonian Spit during the study period. The homogeneous changes of wave parameters were established along the entire spit, meaning that the highest and the lowest waves usually occur at the same sites. Significant negative correlation (r= -0.5‒ -0.7; p<0.05) has been found between the changes in wave height and sediment volume, except for the sites at Juodkrantė, Pervalka and Nida. The prevalent accumulative processes along the entire Lithuanian coast may be linked to the right angle of coast exposition relative to the prevailing south-westerly waves. The magnitude of wave influence on coastal development may be dependent on the wave height. This could imply that the spatial variance of mean wave height may be the reason to varying tendencies of coastal development.

This project has received funding from the Research Council of Lithuania (LMTLT), agreement No. P-ST-23-95.

How to cite: Brazdžiūnas, P., Pupienis, D., Jarmalavičius, D., and Žilinskas, G.: New approach to the tendencies of coastal dynamics of the Curonian Spit based on wave reanalysis data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-302, https://doi.org/10.5194/egusphere-egu24-302, 2024.

Barrier islands cover a large portion of US coasts, support unique ecosystems and beach communities, and protect inland infrastructure from direct storm impacts. Based on their elevation, they can exist in three possible states: relatively protected “high-elevation” barriers with well-developed coastal dunes, vulnerable “low-elevation” barriers without dunes, and “mixed” barriers with scattered dunes separated by overwash fans. We analyzed data from 16 barriers along US coasts and found that the island state is controlled by the barrier ‘elevation capital’, loosely defined as the elevation of the barrier excluding dunes. We find a critical value of the elevation capital, around 0.5m, below which eroded dunes cannot recover and the barrier remains low-elevation, a value consistent with predictions from a recent analytical model of the barrier’s stochastic dynamics. Under the current sand supply, we find that several barriers already reached the tipping point for a potentially permanent “low-elevation” state. We predict this transition to become widespread under expected trends in sea level rise, with important implications for the survival of the whole barrier system.

How to cite: Ramakrishnan, K. A., Rinaldo, T., and Duran Vinent, O.: Critical transition in barrier island’s state and the loss of barrier resiliency, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6594, https://doi.org/10.5194/egusphere-egu24-6594, 2024.

Shoreline erosion presents a significant threat to coastal areas globally, highlighting the need for a thorough understanding of the underlying physical processes to formulate effective mitigation strategies (Luijendijk et al., 2018). Studies on shoreline evolution (Mutagi et al., 2022) often rely on empirical formulations to calculate longshore sediment transport induced solely by waves. However, the extent to which tides contribute to this transport, especially in meso- and macro-tidal coastal environments, remains poorly understood.

This study, conducted as part of a research project (known as MOZES) funded by the Flemish government, aims to quantify the relative effects of tides on longshore sediment transport in the nearshore zone. To achieve this objective, an idealized model (known as Q2Dmorfo, Arriaga et al., 2017) and two complex numerical models (Scaldis-Coast and Flemco, Dujardin et al., 2023) are utilized. In the idealized model, wave- and tide-induced longshore sediment transports are computed using two analytical models inspired by the work of Longuet-Higgins (1970) and Southgate et al. (1989). The two complex models calculate longshore sediment transport by fully resolving the flow field, thereby considering tides, waves, and wind.

Various scenarios are explored, forcing the models with tides and waves independently, as well as in combination. The study area selected for this research is the Belgian coastal zone, which is characterized by meso- to macrotidal conditions.

References

Arriaga, J., Rutten, J., Ribas, F., Falqués, A., & Ruessink, G. (2017). Modeling the longterm diffusion and feeding capability of a mega-nourishment. Coastal Engineering, 121, 1 - 13. doi: 10.1016/j.coastaleng.2016.11.011

Dujardin, A.; Houthuys, R.; Nnafie, A.; Röbke, B.; van der Werf, J.; de Swart, H.E.; Biernaux, V.; De Maerschalck, B.; Dan, S.; Verwaest, T. (2023). MOZES – Research on the Morphological Interaction between the Sea bottom and the Belgian Coastline: Working year 1. Version 4.0. FH Reports, 20_079_1. Flanders Hydraulics: Antwerp

Longuet-Higgins, M. S. (1970). Longshore currents generated by obliquely incident sea waves: 1. Journal of Geophysical Research (1896-1977), 75 (33), 6778-6789. doi: 10.1029/JC075i033p06778.

Luijendijk, A., Hagenaars, G., Ranasinghe, R., Baart, F., Donchyts, G., & Aarninkhof, S. (2018). The state   of the world’s beaches. Scientific reports, 8 (1), 6641.

Mutagi, S., Yadav, A., Hiremath, C.G. (2022). Shoreline Change Model: A Review. In: Nandagiri, L., Narasimhan, M.C., Marathe, S., Dinesh, S. (eds) Sustainability Trends and Challenges in Civil Engineering. Lecture Notes in Civil Engineering, vol 162. Springer, Singapore. https://doi.org/10.1007/978-981-16-2826-9_64

Southgate, H. N. (1989). A nearshore profile model of wave and tidal current interaction. Coastal Engineering, 13 (3), 219-245. doi: 10.1016/0378-3839(89)90050-1. Sedimentary Geology, 33(3), 195–216.

How to cite: Nnafie, A., Verwaest, T., Dujardin, A., and Röbke, B.: Longshore sediment transport in the nearshore zone: role of tides, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12489, https://doi.org/10.5194/egusphere-egu24-12489, 2024.

Coastal cliff erosion affects communities worldwide. In England, cliffs make up approximately 54% of the coastline, a vast proportion of which is of weak to very weak rock resistance. Being able to adequately quantify rates and styles of retreat as well as relating these to their driving forces is key to making informed decisions on future coastal management strategies.

Nationwide change analysis, spanning more than 20 years in places, was carried out by comparing the earliest and most recent LiDAR Digital Elevation Models (DEMs) using raster differencing in a GIS environment. Erosion rates over the cliff face were derived by excluding any bias caused by the presence of vegetation from the change analysis. Uncertainty of erosion rates is affected predominantly by the precision of the LiDAR sensors (typically ±15cm in elevation), and was derived at each location by comparison with a network of ground control points. Limitations of a DEM differencing approach are widely discussed in the literature, particularly in areas of high relief where overhanging and undercutting features may be present. Nonetheless, this large-scale assessment provides a consistent approach to estimate erosion rates and was used as a basis for the selection of sites at which more extensive topographic analysis was carried out in 3D, overcoming some of the limitations of a raster differencing approach. Sites were selected to capture the variability in intrinsic (e.g., geology, slope, aspect) and extrinsic (e.g., waves, tides, rainfall) drivers of retreat. An open-source Python workflow was developed by integrating the M3C2 plugin for Cloud Compare to calculate distances between subsequent timesteps of point cloud data, after which the volume of meshed erosion clusters was computed. As a result, an inventory of cliff face erosion scars was compiled, with attributes relating to scar shape, area, volume and elevation relative to cliff top height. A comparison of the two approaches for calculating erosion rates highlighted the ability of the 3D workflow to capture cliff failure in greater detail and with higher accuracy, at the expense of increased computational costs. Findings also indicate spatio-temporal variations in erosion patterns which are related not only to the intrinsic nature of each site, but also to its climatology. It is expected that the broad spatial scale of this research will provide some insights into the main styles and drivers of retreat affecting specific stretches of coastline in England.

How to cite: Coker, C., Javadi, A., Palmer, S., and van Maanen, B.: Rates and Drivers of Coastal Cliff Erosion in England from 2 Decades of Lidar Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9468, https://doi.org/10.5194/egusphere-egu24-9468, 2024.

Gravel berms occur naturally on beaches worldwide, may provide defense against beach erosion and coastal flooding, and have been increasingly built around the world including the U.S. west coast. Recent studies observed longshore transport caused gravel loss from artificially built gravel berms prompting concern about their future stability. However, few observations of long-term gravel-berm behaviors and stability exist. Using historical observations since 1980s combined with modern LiDAR-based observations, this study quantitatively examines multi-decal morphological changes of natural gravel berms in southern California. The morphological observations are compared with wave conditions and local engineering coastal modifications. This contribution provides novel multi-decadal evolution of gravel berm morphology in a relatively urbanized coastal area and useful insights of long-term gravel berm behavior and stability.

How to cite: Matsumoto, H. and Young, A.: Multi-decadal gravel berm observations in southern California, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10836, https://doi.org/10.5194/egusphere-egu24-10836, 2024.

Coastal areas, such as deltas estuaries and lagoons, are highly dynamic environments shaped by the interplay of depositional and erosional forces. While providing a multitude of valuable ecosystem services, spanning from wave-energy dissipation to habitat provision and carbon sequestration, they also serve as important hubs, supporting large populations. 
However, communities living along low-lying coastal environments are currently threatened by rapidly rising sea levels and the intensification of the extreme events, which increase the flooding risk.

To reduce the risk of floods, different engineered structures (e.g., flood-gate barriers) have been adopted worldwide. Here, we present a study delving into the first years of operation of the Mo.S.E. system, the mobile storm-surge barrier system activated in the Venice Lagoon starting from October 2020. The research aims to investigate the impacts of the flood regulations, exploring the potential counter-effects of water level reductions on the lagoonal ecosystems.

During storm surges, floodgte barriers at the three lagoon inlets are raised to temporarily disconnect the lagoon from the open sea, keeping water levels below a prescribed safety threshold to avoid the flooding of the city of Venice. However, the intertwined action of wind waves and reduced water levels may generate an intensification of the eorional processes across the tidal flats. The reduced water levels negatively affect also salt-marsh sedimentation. Although erosion processed can increase the suspended sediment volume within the tidal basin, lower water levels reduce salt-marsh flooding depths and duration, and the sediment deposition over marsh surfaces.

We also explore a hypothetical scenario considering an optimized flood regulation procedure, aimed at reducing the duration of flood-gate closures. Slightly higher water levels, prescribed by the optimized regulation, would allow sediment deposition over salt-marsh surfaces without compromising the preservation of urban areas from flooding.

Our findings offer valuable insights, underscoring the paramount importance of promoting effective defensive intervention policies. Our results might help to identify feasible solutions that better balance the preservation of  coastal urban areas with the protection of natural coastal ecosystems

How to cite: Michielotto, A., Tognin, D., Mel, R. A., Finotello, A., Carniello, L., and D'Alpaos, A.: Navigating the first years of flood regulation in the Venice Lagoon - a delicate balance between humans and nature, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18112, https://doi.org/10.5194/egusphere-egu24-18112, 2024.

This work describes the main evolutionary stages of the Sacalin barrier island developed in the last 125 years in relation to storminess variability, river supply, accommodation space, and the establishment of the morphodynamic feedbacks operating in association with the occurrence of extensive breaches. This deltaic barrier is highly mobile due to its low elevation and high wave and currents exposure, recording a continuous elongation (of ca. 150 m/yr) and progradation in the downdrift sector (South Sacalin) but rapid retreat (20-70 m/yr) of the updrift sectors (North and South Sacalin). We found a contrasting behavior of the barrier characterized by fast shoreline retreat and small elongation during high storminess intervals but slight retreat and rapid elongation during low storminess. The occurrence of a vast breach (ca. 2.5 km long) at the end of the 1976-1981 stormy interval changed the evolution of the central barrier by the onset of a cyclic pattern of the barrier retreat and (large) breaching triggered mainly by barrier width but a pace influenced by storminess. The overall barrier coastline evolution is highly correlated with storminess, but the (alongshore) inter-sector analysis also highlights the influence of i) the river supply, which large oscillations (i.e. floods) are transmitted via mouth bar morphometric amplitudes to the North Sacalin and of ii) the significant breaches and related feedbacks for the Central and South Sacalin.

How to cite: Vespremeanu-Stroe, A., Zainescu, F., Tatui, F., Pirvan, M., Verga, M., and Preoteasa, L.: Long-term evolution of Danube delta barrier islands under the influence of storms, floods and big breaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18215, https://doi.org/10.5194/egusphere-egu24-18215, 2024.

Along the coastal stretch of the Phlegraean Fields, an active volcanic district near Naples (Italy), significant erosion processes affect a large part of the coastal cliffs, being the latter mainly composed of fractured volcanic tuff and pyroclastic deposits. Assessing processes related to cliff instability, factors contributing to cliff failures, and evaluation of retreat rates, is essential for effective coastal hazard assessment and management.

In view of this, this research aims to identify the main predisposing factor to rockfall/rockslide phenomena in tuffaceous coastal cliffs in this coastal area assessing any relationships between meteorological factors (rain, temperature, wind, etc.), weathering, and structural and geomechanical characteristics of rocks.

This was made by using, as an example, the large landslide that affected the Capo Miseno cliff on March 25, 2015, when approximately 87.000 m³ of material detached from the slope, reshaping the morphology of the coastline.

In order to determine the triggering factors of this landslide, a database of meteorological measurement time series taken over ∼ 2 years (January 2013–March 2015) was used coupled with a geomechanical survey carried out on the contiguous cliff known as 'Spiaggetta Verde' in 2014, which shares broad characteristics with the considered cliff.

This survey shows the presence of several sets of long and deep discontinuities identifying rockfall and rockslide as potential landslide kinematics. In addition, the meteorological analysis demonstrated that several diurnal and seasonal cycles of heating and cooling may lead to deformation and crack opening and propagation. Both increasing temperature and temperature fluctuations may enhance fracturing.

However, the predisposing factors identified by the field analyses are not sufficient to make hazard assessments if sea condition factors are not considered in detail. The analysis of the relationships between structural characteristics and meteo-marine forcing factors may be very useful in the perspective of hazard assessment being this study site located in a densely urbanized area.

How to cite: Tursi, M. F., Matano, F., Sacchi, M., and Aucelli, P. P. C.: Rockfall/Rockslide hazard analysis in tuffaceous coastal cliffs: The case of Miseno cliff, Phlegraean Fields, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18607, https://doi.org/10.5194/egusphere-egu24-18607, 2024.

Coastal environments undergo continuous changes due to the complex interactions of geological, oceanographic, climatic, and anthropic processes. In the last centuries, human activities have deeply altered the natural balance of coastal areas, making coastal evolution studies crucial for planning strategies related to prevention, preservation, and restoration, particularly in areas with a relevant role in biodiversity conservation.
The aim of this research is the evaluation of recent morphological and environmental changes that occurred since the second half of the 20th century along the sandy stretch belonging to the Site of Community Importance (SCI) “Spiaggia del Mingardo e Scoglio di Cala del Cefalo” in the Campania region (Southern Italy), near the mouth of the Mingardo River. Through an integrated GIS analysis of topographic maps, aerial and satellite photos, and high-resolution data (a photogrammetric survey carried out with an aerial drone in April 2023), a retreating trend of both the shoreline and the dune system was observed. In particular, a decrease in the retreating trend of the shoreline has been detected since 2004, while the mean erosion rate is equal to -0.354m/y for the period between 2011 and2016, approximately 12 cm more than the previous time span. On the other hand, the retreat of the dune system over the whole period amounted to 40 m, 35 m, and 27 min the northern, middle, and southern areas respectively, while the highest retreat has been detected for the period between 2012-2016. This coincides with the results obtained for the shoreline between 2011 and 2016. Since one of the strongest storm surges occurred in 2014, this result demonstrates the great influence of storm surges on the state of conservation of the coast, as testified by detected wash-over fans and strong degradation of the vegetation cover. Therefore, the resulting forcing factors acting in the area are the winter wave regime, which can cause flooding and consequent dragging of sediment offshore, and the draining of the Mingardo River. Another relevant aspect is the intense anthropization of the area, especially during the summer season.
To conclude, this work provides evidence of the high impact of storm surges on beach and dune environments, showing the importance of an integrated approach for the analysis of coastal dynamics in a fast-evolving world, where human presence could strongly interfere with natural processes. The potential erosion risk is crucial information for sustainable management of the coast, also taking into account the expected increase in storm surge frequency and magnitude strictly related to climate change.

How to cite: Fasciglione, G., Sorrentino, A., Mattei, G., Pappone, G., and Aucelli, P. P. C.: Multitechnical approach for the reconstruction of coastal changes: the case of Cala del Cefalo (southern Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19690, https://doi.org/10.5194/egusphere-egu24-19690, 2024.

Ireland has made a commitment under the newly developed Marine Strategy Framework Directive Programme of Measures to develop Nature-based Solutions to conserve and restore estuarine, coastal and marine habitats. Existing evidence show that a large number of coastal communities, environmental NGO’s, EU-funded research programmes and local government bodies are already engaged with the transition towards NbS to defend or conserve coastlines with varying degrees of success. This research first provides an overview of over fifty NbS projects in Ireland in different coastal habitats (dunes; machair; saltmarshes; seagrass meadows; oyster reefs; kelp forests) being led by different organizations with different motivations, services delivered, biodiversity value, beneficiaries, and resources. We then present multiple dune-based NbS case studies along urban and rural coastlines to illustrate how these projects are successfully building coastal resilience. It is obvious to NbS practitioners that many of these projects are not sustainable in the long-term and overly rely on the selfless work of volunteer groups who continuously face institutional (governance; legal responsibility; stakeholder forum; tourism) and technical barriers (climate adaptation; funding; environmental designation; lexicon of climate resilience and sustainability; erosion and flooding control; seasonal tourism) in their attempts to build resilience to climate change and anthropogenic pressures. To unlock the full potential of dune-based NbS, Ireland urgently requires (1) new government policies and planning structures to organize the planning, implementation and maintenance of NbS, including a coastal community engagement mechanism to coordinate working partnerships and funding between local government bodies, coastal communities, and landowners at every stage in the process; (2) appropriate and expert staffing resources (e.g., climate and biodiversity officers) within local government authorities and the National Parks and Wildlife Service, the state agency responsible for Ireland’s nature conservation; (3) a standardized NbS indicator framework to measure the ‘impact’ of NbS projects; and (4) a valid financial mechanism to facilitate significant future investment in NbS as ‘new assets’ and biodiversity credits (measurability, monitoring, verification, and certification of the NbS process). 

How to cite: Farrell, E. and Lynch, K.: Dune-based Nature-based Solutions in Ireland: unlocking their full potential to build coastal resilience , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17924, https://doi.org/10.5194/egusphere-egu24-17924, 2024.

Coastal foredunes serve as a natural defense against rising sea levels and storm floods, support important Natura2000 biodiversity and habitats, and offer areas for human recreational activities. Along urbanized coasts, a large proportion of dune systems have been replaced with hard infrastructures such as dikes and sea walls. Over the past decade, the limitations of these traditional grey infrastructures (their static character and high maintenance costs) were recognized. This caused scientists across many disciplines to explore coastal dunes as nature-based solutions for sustainable and cost-effective long-term coastal protection.

Coastal dunes develop from ecological interactions between sand fluxes and vegetation development. Plant-sand feedbacks are the basis for the unique dynamic and self-organizing properties of coastal dunes. These properties are anticipated to make them resilient and responsive to tidal and wave conditions, and hence future climate change impacts. The construction of hybrid dune-dike systems, where dunes are built in front of the dike, emerges as a promising solution to secure coastal regions against floods and storms.

To allow the design, the creation but also the natural development of such dune-dike hybrid nature-based solutions in the most optimal way, we have to understand the responses of plants to changes in environmental conditions, as well as their effects on the environment.

First, to be able to predict where natural dune development is possible, I constructed an ecological niche model for embryo dune plants on the Belgian coast. These embryo dune plants are the pioneer plants responsible for the natural initiation of dune development on the high beach. They consist of (rare) annual species that lay the foundation for further dune development and are subject to both human and environmental stressors. I built a spatio-temporal regression model, based on annual sand dynamics and flooding potential, to deduce and demonstrate that the establishment of embryo dunes is feasible along the entire Belgian coast, but is mainly constrained by mechanical beach cleaning and beach management.

Second, to be able to optimize the construction of dune-for-dikes through planting strategies of marram grass, I analyzed how the abundance and spatial configuration of marram grass impact the development of established pilot dune-dike hybrids along the Belgian coast. This mechanistic insight on sand burial-plant growth interactions allows for a better prediction of the outcome of different marram grass planting strategies, and the corresponding dune shape and characteristics related to storms and erosion.

In conclusion, my research emphasizes the importance of understanding the ecological dynamics of coastal dunes as essential components to gain a dynamic rather than static understanding of dune-dike hybrid nature-based solutions for effective coastal and biodiversity protection.

How to cite: Taelman, C., Dhondt, M., Batsleer, F., Provoost, S., Van Uytvanck, J., and Bonte, D.: Plant establishment and plant-sand feedbacks as fundaments for dune-for-dike nature-based solutions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2022, https://doi.org/10.5194/egusphere-egu24-2022, 2024.

Coastal dunes are natural landforms formed by complex positive feedbacks between wind driven sediment transport processes, the presence of vegetation, and existing dune morphology. To improve our knowledge of the sand capture efficiency of native and non-native vegetation species found on the Pacific Northwest coast, we designed a 3-day in-situ experiment using four mono-species vegetated plots (20 m by 10 m in size) during strong wind gust conditions on the coast of Oregon, USA. The dune grass species monitored during this experiment were the non-native Ammophila arenaria, Ammophila breviligulata, the new hybrid between A. arenaria x A. breviligulata, and the native Leymus mollis. Wind speed and direction sensors were set upwind and in the center of each plot during the experiment. Multi-directional sand traps were set up at the same position as the wind sensors during a 24-hour period to capture sediment transport coming into and moving through the plots during the stronger wind periods. Lidar surveys were performed before and after the wind event to compute morphological change and to estimate the vegetation cover for each plot. The vegetation cover of the non-native plots ranged between 37% and 47% while the native vegetation cover was 9%. During the wind gust, the plots were exposed to upwind speeds ranging from 3.6 to 4.5 m/s. Between the upwind positions and the plot center, wind speeds decreased by 16% to 28% for the non-native species, while wind speeds increased by 16% within the native species plot. The volume of sand in the A. arenaria plot increased by 6.4% (i.e., +10.8 m³) and the volume of sand withing the plot with A. breviligulata increased by 5.4% (i.e., +4.4 m³). Limited change was observed in the hybrid plot (+1.1% of its volume i.e., +1.3 m³), and the L. mollis (native vegetation) plot lost sand (-4.5% of its volume i.e., -0.1 m³). While the multi-directional sand traps facing the dominant wind direction were saturated during a last hours of overnight windy period, the traps indicate that wind from the south was the dominant transport direction with slightly less transport from the SE and the SW. Lidar and wind data were used in an aeolian sediment transport and dune building process-based model to simulate morphological changes during the wind gust event. The calibrated model will be used to explore the parameter space for drivers of aeolian transport through the vegetated plots. Although further field experiments are needed, this experimental design shows promising results for understanding the effect of different dune grass species on aeolian sand flux and associated morphological changes and encourages further work towards models that capture the magnitudes and relative differences among plots, depending on environmental and ecological boundary conditions.

How to cite: Laporte-Fauret, Q., Wengrove, M., Ruggiero, P., Hacker, S. D., Cohn, N. T., Heminway, S., van IJzendoorn, C., and Ringer, C.: Quantifying the sand capture efficiency of native and non-native dune plants with an in-situ experiment and numerical modeling during wind gust conditions., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12763, https://doi.org/10.5194/egusphere-egu24-12763, 2024.

This study investigates the impact of Hurricane Fiona on sandy beaches and foredunes within Prince Edward Island National Park (PEINP). Fiona was the strongest storm to strike the island in nearly a century, with significant wave heights reaching 8 metres. Its impact on sandy beach-dune systems provides an opportunity to gauge the effectiveness of current PEINP's management policies and practices, and to consider potential changes that enhance the role of foredunes and beaches as natural defences against future storms and rise in relative sea level.

Survey data and ground/UAV photography were used to compare various locations before (October 2021 to July 2022) and after (October 2022 and May 2023) the storm. High dunes experienced stoss slope erosion without significant changes in the height or position of the foredune crest, offering protection to landward areas. Low dunes were substantially eroded, leading to overwash in certain areas, and dunes located on bedrock and till were completely eroded, exposing the underlying surface. Hurricane Fiona's impact highlights the need of reinforcing current management strategies in PEINP that aim at safeguarding the natural biotic and abiotic components of beach-dune systems, and securing the accommodation space needed for their natural inland migration with rising sea level.

How to cite: Delgado-Fernandez, I., Davidson-Arnott, R., Ollerhead, J., George, E., Houser, C., Bauer, B., Hesp, P., Walker, I., and van Proosdij, D.: The impact of Hurricane Fiona on sandy beaches and foredunes in Prince Edward Island National Park: Implications for management., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18705, https://doi.org/10.5194/egusphere-egu24-18705, 2024.

A total of 52 variables, organized into six groups, were assessed and categorized into a locally adapted coastal dune vulnerability index. This study took into consideration socio-ecological aspects and incorporated local factors into the vulnerability index, along with adaptation strategies. This index has been tested in the Caota Sand Dunes, one of the largest sand dune systems in Taiwan, that has been developed into a geopark. The study area was divided into three zones according to access facilities, visitor pressure and degree of of exposure of the dunes, which are pre-defined within the boundaries of the geopark. Results revealed that main vulnerabilities in the dune landscape lead back to human disturbance, dune fragmentation and coastal erosion. Geomorphologically, the dune landscape displays high fragmentation and steep slopes due sand fences and the presence of landfill sites, while the absence of vegetation on frontal dunes is prevalent across many regions. Adaptation strategies could therefore focus on reducing the vulnerability by promoting natural dune formation and enhancing biodiversity of sand binding species. Adaptive management, involving community participation and regular monitoring, can balance conservation with recreation, ensuring resilience through strategic adjustments. The dataset established in this study could serve as an initial foundation for monitoring future variations in coastal dune systems using DVI parameters as indicators of environmental changes.

Keywords: CDVI, coastal management, geopark, sand dunes, adaptive capacity.

How to cite: van Onselen, V. and Lin, T.-Y.: Coastal Dune Vulnerability Assessment of Caota dunes, Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2988, https://doi.org/10.5194/egusphere-egu24-2988, 2024.

In the face of increasing anthropogenic pressures on the Earth's surface, exploring ancient agricultural methods holds promise for innovative approaches, especially in traditionally considered less fertile landscapes like sandy landforms. The earliest documented instances of agricultural utilization on aeolian sand landforms are found in the form of Plot-and-Berm (P&B) agroecosystems along the present-day coastal plain dunefields of Israel.  The close to pristine state of a P&B agroecosystem in the hinterland of ancient Caesarea appears to have exhibited exceptional resilience. Here, following a survey, three excavation seasons (2020-2022) were conducted. The primary objectives of this study are : (1) Defining its spatial extent; (2) Explaining its agrotechnological innovation; (3) Providing a high-resolution, luminescence-based chronological analysis; and (4) Interpreting the motives for its development. Portable Optically Stimulated Luminescence (port-OSL) profiling was applied for chrono-stratigraphic analysis, discrete sample selection for OSL dating and a novel type of spatial analysis to determine development stages of the agroecosystem  

Covering 1.5 km², the Caesarea P&B agroecosystem features a checkerboard-like array of agricultural plots sunken between 3-10 meters high berms. The agroecosystem is neatly situated in the Caesarea dunefield lowlands between the shoreline and base of an aeolianite ridge, stream mouth brackish water in the south, and the ruins of Caesarea in the north. The agroecosystem ingeniously utilized refuse to stabilize loose aeolian sand and harness groundwater. Dark grey anthropogenic sedimentary units were enriched with fine-grained limekiln additives, reducing the infiltration rate of natural sand by filling the pores between sand grains. These morphological and sedimentological modifications sustained innovative annual irrigation methods in a Mediterranean climate.

Primary construction and agricultural activities were dated to the later part of the Early Islamic period, particularly the Fatimid caliphate (late 10th-late 11th centuries). The existence of the entire agroecosystem spanned ~200 years. This immense effort for cultivation indicates that the region flourished as the caliphate center relocated to Cairo. Additionally, this innovative agrotechnology was likely part of the large-scale "Islamic Green Revolution". Intermittent activity was noted during the subsequent early Crusader period (first half of the 12th century). Local evidence of reworking of anthropogenic sediments and aeolian sand deposits dating to Mamluk and Ottoman periods, is interpreted as periods of neglect.

Roman activity at the base of the berms suggested utilization of the dunefield during that era. Interestingly, during the Byzantine period, when Caesarea was at its peak, no activity was found, despite documented Byzantine utilization of sandy landforms in other areas like the Negev. This may suggest that during the Byzantine period, the aeolian system was active.

In summary, our investigation of the P&B agroecosystem at Caesarea reveals a pioneering approach to sustainable agriculture, marked by the ingenious use of refuse and limekiln fine-grain additives for groundwater and rainfall harnessing. Through coupled absolute and relative luminescence analyses, we trace its evolution from Roman times to the peak of the Fatimid caliphate, offering insights into resilient agricultural practices in less-fertile landscapes, pertinent to modern land-use challenges.

How to cite: Robins, L., Roskin, J., Grono, E., Porat, N., Ostrowski, A., Bookman, R., and Taxel, I.: Sands of Time - Relative and Absolute Luminescence Chronologies of the Early Islamic Plot-and-Berm Agroecosystem, Caesarea dunefield, Israel, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-245, https://doi.org/10.5194/egusphere-egu24-245, 2024.

The coast of Galicia (NW Spain), about 1,700 km long, is formed by cliffs and deep estuaries (Rias) flooded during the Late Holocene and the most characteristic sediments are sand and gravel deposits. Sandy sediments (aeolianites) are the most widespread along the entire coast and they are due to a massive aeolian accumulation that began at the end of MIS3 with an initial sea-level from -60 m (below the present one) to -120 m at the end of MIS2. This involved a coastline displaced up to 40 km from its present position and the subaerial exposure of a continental shelf covered with sand, which was mobilised by the strong coastal winds as dunes. In turn, these dunes advanced towards the continental edge, filling in the valleys and covering reliefs of more than 250 m high at the time. For instance, the current Cies Islands were linked to each other and to the mainland, as the current Ría de Vigo was a densely vegetated fluvial valley. Dunes of 40 to 17 ky are observed on these islands, as well as a 35 m thick flooded dune similar to the 13 to 6 ky old flooded dunes identified in the nearby Ría de Arousa. All these aeolian formations are in physical continuity with the (relict) dunes that only remain in this coast, most of them powered by wind up to 2.5 ky ago. The sea-level rise during the Early and Middle Holocene enhanced the mobilization of sand, as also occurred on the Atlantic coast of Portugal, France and the United Kingdom. This caused both the collapse of the coastal ecosystems (forests and freshwater lagoons) that were buried under the dunes and the accumulation of sand against the rocky cliffs, as demonstrated by the climbing dunes that rise to more than +160 m (apsl); under this blanket of sand, archaeological remains and fossils of vertebrates more than 6,000 years old have been found. This aeolian transgression stopped at the Late Holocene, when rising sea-level sealed the sands' source area by marine flooding. From this point onwards, the coastal wind became mainly erosive and gradually destroyed the dunes. This was coupled with the erosive effects of waves, leading to the current situation in which it is extremely difficult to preserve the remains of the coastal dunes that have endured the Holocene transgression. To prevent this degradation of the coast, none of the measures adopted so far have been effective, from physical barriers (including the replanting of trees) or the continuous deposits of sand that are systematically destroyed during storms. Dating of other fossil dunes in the study area using optically stimulated luminescence (OSL) or infrared luminescence (IRSL) indicates that it is still possible to distinguish older aeolian accretion events that took place during the pre-Eemian regressive episode (MIS6). Therefore, the formation of coastal dunes in northwest Spain is strongly related to glacioeustatic fluctuations, corresponding specifically to the Upper Pleistocene.

How to cite: Arce Chamorro, C., Sanjurjo Sánchez, J., Guérin, G., Menier, D., Grandal d´Anglade, A., and Vidal Romaní, J. R.: 40.000 years of Aeolian Accretion in the Coast of NW Spain: Evolution of Coastal Dunes from MIS3-MIS2 transition to Late Holocene and Present-day Management., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3092, https://doi.org/10.5194/egusphere-egu24-3092, 2024.

Coastal sand dunes are a key feature of coastlines worldwide, performing a number of functions in the landscape. They act as important coastal defences, reduce beach erosion, and provide habitats for a number of endangered species. Dune morphology and location are controlled by deposition and erosion by aeolian (wind) processes, and these processes are of great interest to geomorphologists, ecologists, and land managers.

In dune sand transport models, sand grain density is assumed to be a constant 2.65 g cm^-3, the density of quartz, as this is the most common sand-forming mineral in most beaches. However, many beach sands also include a proportion of denser minerals such as ilmenite (~4.7 g cm^-3) or magnetite (~5.17 g cm^-3). Although such minerals generally form a relatively small proportion of the overall composition, they may become concentrated at the surface, leading to local regions with a substantially higher proportion of heavier grains. The effect of this on wind threshold speeds required to erode dune surfaces is unknown.

We sampled transects of dune surfaces with higher concentrations of heavy minerals at the Ainsdale National Nature Reserve in Formby, Northwest England. Samples were scanned using a Nikon MCT X-ray CT at a resolution of ~5.7 microns voxel size. Density distributions of grains at the surface of the samples were compared with deeper levels within the sample, with a control sample and with other samples in the transects. Several transect samples were found to have denser grains at and near the surface compared with the overall distribution and with the control, as well as dense layers within the sample perhaps representing inactive buried dune surfaces. Characterisation of the mineralogy of the sand and correlation with the CT scans will allow us to quantify the density variation at the surface in different locations and provide more realistic input parameters for sand transport modelling. 

How to cite: Fox, B., Tawfik, A., Armitage, O., Einsle, J., and Smyth, T.: X-ray CT characterisation of dune sands to inform geomorphological models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8052, https://doi.org/10.5194/egusphere-egu24-8052, 2024.