The seasonal variations in the textural parameters and Principal Component Analysis (PCA) of beach sediments were collected along the Purangad to Gaonkhadi coast of the Ratnagiri district, Maharashtra, India. A total of 56 samples (28 samples from each season i.e. pre-monsoon and post-monsoon) were collected from multiple beach locations, encompassing diverse geomorphological features. The foreshore sediments show symmetrical to strongly fine skewed whereas, backshore sediments are fine skewed to strongly fine skewed. During post-monsoon (POM) season, foreshore and backshore sediments are coarse-grained sand, whereas raised beach and foredune sediments show fine-grained sand. The foreshore sediments are poorly sorted to very poorly sorted, while the backshore and raised beach sediments are moderately sorted to poorly sorted. The linear discriminant analysis (LDA) plots of sediments fall in a shallow marine environment, while few sediments fall in a shallow beach environment. PCA revealed distinct clusters corresponding to different beach environments, highlighting the influence of local geological sources and human activities on sand composition. The first two principal components explained approximately 78% of the total variance, with grain size and mineralogy being the most significant factors. This analysis underscores the utility of PCA in environmental geosciences, providing insights into sediment dynamics and the ecological implications of coastal processes. The findings contribute to a deeper understanding of coastal sedimentology and offer a framework for future beach system resilience and management studies.
How to cite: Bagul, P. and Herlekar, M.: Sediment characterization of beach sediment along a part of the West Coast of India:Implications for the Climate change., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-602, https://doi.org/10.5194/egusphere-egu25-602, 2025.
Quantifying sediment transport is crucial for thoroughly understanding coastal systems and accurately designing coastal management interventions (e.g., sand nourishments). Lagrangian particle tracking models are valuable tools for investigating sediment transport, as modelling in a Lagrangian framework provides complete records of particle transport sources, sinks, and the pathways between them. Here we present two examples of application of Lagrangian sediment tracking modelling in coastal settings. Both studies are conducted using SedTRAILS [1], a Lagrangian particle tracking model that derives particles position from flow velocity fields generated from hydrodynamic models.
In the first application we simulate the dispersal of a nourishment on the ebb-tidal delta of Ameland Inlet (Wadden Sea, Netherlands). The flow velocity fields employed by the SedTRAILS simulation are generated from a Delft3D simulation of Ameland Inlet. The nourishment is modelled as a sample of representative sand parcels randomly sourced within the nourishment area and its gradual erosion is modelled by continuously releasing the parcels at regular intervals for the duration of the simulation. The accuracy of the Lagrangian simulation results are validated by comparing maps of particles position generated at different time steps of the SedTRAILS simulation with maps of sand spatial distribution derived from the Delft3D simulation at the same time steps. Ultimately, we are able to model the pathways of individual nourishment particles up to six months after its displacement.
In the second application we couple SedTRAILS with measurements of sand grains luminescence (i.e., the ability of a mineral grain to store energy when buried and release it upon exposure to sunlight) to reconstruct sand transport history in coastal settings. In order to do so, we combine SedTRAILS with a model that quantifies sunlight exposure of a given sand particle as a function of turbidity and its position in the water column [2], allowing to compute the cumulative sunlight exposure of such particle during its transport history. Since luminescence signals produce evidence of how long a sand particle was buried for, we are able to infer and simulate the forcings that the particle was exposed to before burial (i.e., during its transport history). As luminescence signals also yield information on how much sunlight the sand particle was exposed to before being buried, we can eventually combine the modelled cumulative sunlight exposure with evidence on resetting of luminescence signals as a function of light exposure [3] to infer, for the first time, coastal sand transport history from luminescence measurements.
Overall, the two studies provide an overview of how Lagrangian particle tracking modelling can (on its own and in combination with other techniques) provide unique insights on where, when and how sand is transported across coastal systems, which can advance our understanding of coastal systems and be exploited for accurately designing coastal management interventions.
References
[1] Pearson S.G. et al. (2023). Proceedings of the Coastal Sediments 2023, 1212-1221.
[2] Storlazzi C.D. et al. (2015). Coral Reefs, 34 (3), 967-975.
[3] de Boer A.-M. et al. (2024). Netherlands Journal of Geosciences, 103, 22.
How to cite: Pannozzo, N., Pearson, S., Meijer, M., de Boer, A.-M., de Wilde, T., Elias, E., Kooistra, T., Wallinga, J., and Van Prooijen, B.: Tracing sand transport pathways using a Lagrangian sediment tracking model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4879, https://doi.org/10.5194/egusphere-egu25-4879, 2025.
The Guiana coastline, stretching for 1500 km along the northeastern coastline of South America between the Amazon and Orinoco Rivers, is one of the most dynamic shorelines in the world. The frontage is characterised by a series of alongshore migratory, shore-attached mudbanks, with shoreline accretion and seaward expansion of mangrove vegetation during in-bank periods, followed by significant shoreline erosion during inter-bank phases. These coastal dynamics are of great concern to the nation states of Guyana and Suriname and the French overseas department of French Guyana where > 90% of the urban population live within the low elevation coastal zone.
Whilst considerable research has been undertaken along the Guiana coastline over the last four decades, the full determination of the dynamics of this long coastline remains challenging. Not all analyses have used sufficiently long temporal sequences of imagery to track at least one complete accretion-erosion cycle. Where high temporal resolution has been achieved, analysis has often been limited to one, and often only part, of the regional administrations.
This presentation provides the first ever analysis of rates of shoreline change across the entire Guiana coastline annually over a 35-year period (1987-2023). The seaward extent of mangrove forest or other coastal vegetation was selected as the shoreline proxy. This was extracted from Landsat multispectral 30 m resolution imagery using machine learning and image thresholding techniques. Annual shoreline change rates were measured at 200 m intervals over the 1500 km frontage, providing unprecedented insight into how the entire shoreline system has evolved.
This analysis discovered differences in the position, size, and speed of alongshore migration of nine mudbanks along the Guiana coastline, with mudbanks exhibiting either a graded or abrupt form of alongshore migration. Contrary to previous research, this analysis identified no evidence of a 30-year cycle in shoreline accretion – erosion across two extensive regions of the Guiana coastline: Saramacca, Suriname and Guyana. In both these locations, three other categories of landform were identified as affecting shoreline position: naturally migrating headlands, the presence of emplaced polders and sites of rapid accretion along anthropogenically modified coastlines. In addition, correlation analysis was conducted between shoreline change metrics, wave metrics derived from ERA5 reanalysis data, and climate indices including the North Atlantic Oscillation (NAO) and the El-Niño Southern Oscillation (ENSO). This analysis identified a statistically significant relationship between pan-Guiana shoreline position and the 18.6-year nodal cycle. However, at the landform scale, significant wave height and direction had the strongest statistical relationship with shoreline change. This analysis is supported with the release of a comprehensive pan-Guiana shoreline change dataset, facilitating future holistic research and management of the Guiana coastline.
How to cite: Rogers, M. and Spencer, T.: Holistic analysis of shoreline change and mudbank dynamics across the Guiana coastline, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7311, https://doi.org/10.5194/egusphere-egu25-7311, 2025.
Gravel barriers play an important role in protecting coastal communities and infrastructure along mid- to high-latitude shorelines. However, their ability to adapt and fulfil their protective role in the context of a global sea level rise and intensifying storm events remain uncertain. One the major obstacles to the creation of modelling tools for predicting the evolution of these coastal features is the diversity of their morpho-sedimentary character. Although gravel beaches are all characterized by a predominance of coarse-grained particles (> 2 mm), they are often mixed with varying amounts of finer sand particles, resulting in different beach sub-categories (e.g. pure gravel, composite, mixed sand-and-gravel). In addition to sediment variability (which links to sediment availability and supply), gravel beaches, like their sandy counterparts, organise themselves into various barrier landforms, such as spits, barrier beaches or beach ridge plains. It is commonly accepted that the morphodynamics of coastal barriers over several decades or centuries is closely tied to their geomorphological heritage that controls both accommodation space and sediment supply. The analysis of the environments surrounding the barrier is therefore just as important as the characterization of the barrier itself. Systemic approaches are usually considered at a local scale and rarely applied beyond the immediate sedimentary cell. To enhance consistency and gain a more comprehensive understanding of coastal barrier contexts and controls across the broader range of geomorphic contexts, a new approach of analysing these coastal features is needed.
An inventory of over 250 sites has identified gravelly shorelines around the UK, which have been subdivided according to beach and barrier types. Here, we demonstrate a framework for systematic morphometric analysis of gravel beach-barrier systems at the national scale. Barrier metrics (e.g. width, height, volume), inland topography, nearshore bathymetry and habitat mapping are extracted at a system scale that is divided into multiple segments to facilitate categorisation. The results represent a step forward towards a typology classification of gravel barrier systems. They also allow to highlight the importance of the various data sets when considering this approach, as well as identifying important gaps in data availability.
How to cite: Pancrazzi, L. and Burningham, H.: Evaluation of the morpho-sedimentary diversity and multi-annual to multi-decadal dynamics of gravel barrier systems around the UK, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17923, https://doi.org/10.5194/egusphere-egu25-17923, 2025.
Low-lying coastal areas are vital hubs, hosting invaluable ecosystems and supporting large human populations for centuries. Nonetheless, these regions face growing threats from climate change, sea-level rise, and intensifying extreme weather events, negatively affecting the quality of life in coastal communities. In response, storm-surge barriers have been widely adopted as a global solution to mitigate coastal flooding risks, with numerous projects proposed and implemented over the past two decades, although questions arise on the long-term ecological response.
This study focuses on the flood-regulated Venice Lagoon (Italy), a pilot example of an artificially controlled estuarine system, to explore the future of urban coastal environments as they navigate the challenges of balancing wetland conservation with the resilience of coastal communities—two goals that are often interdependent yet conflicting. Using a custom-built two-dimensional numerical model, we investigate four years of floodgate operations (2020–2023) to compare different flood regulation scenarios and their effects on urban flooding risk and ecosystem health. Specifically, we simulated tidal and wind-wave-induced circulations across the Venice Lagoon and compared the results of the real-case flood-regulated condition with those of a hypothetically non-regulated scenario. Additionally, we examined a third, hypothetical, flood-regulated scenario in which floodgate closures are managed using an optimized approach to minimize their frequency and duration.
Our analysis shows that the current operational strategy, while effectively protecting Venice and surrounding urban settlements from flooding, significantly disrupts the submersion dynamics of salt marshes, thereby reducing sediment deposition and fostering ecosystem degradation. However, this study demonstrates the feasibility of adaptive, sustainable management strategies that balance the competing demands of mitigating flood risk while preserving valuable coastal ecosystems, enhancing their resilience to climate change as a whole.
How to cite: Michielotto, A., Finotello, A., Tognin, D., Mel, R. A., Carniello, L., and D'Alpaos, A.: A window to the future: balancing urban protection and ecosystem preservation in flood-regulated shallow coastal areas, insights from the Lagoon of Venice, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18006, https://doi.org/10.5194/egusphere-egu25-18006, 2025.
Estuaries and lagoons have historically served as sheltered areas for navigation and harbours, fostering settlement and trade. Over centuries, human interventions such as channel dredging and canal excavation have reshaped these environments to accommodate increasingly larger vessels and facilitate harbour access. While these modifications offer immediate benefits for navigation purposes, they alter the delicate hydro-morphodynamic balance of shallow tidal systems, potentially intensifying erosion and vulnerability to sea level rise. Therefore, understanding the side effects and long-term consequences of dredging and excavation is essential for developing informed management strategies for back-barrier lagoons.
Here we examine the effects of canal excavation and dredging on the hydrodynamics of two back-barrier lagoon systems in the northern Adriatic Sea: the Venice and the Marano-Grado Lagoons. In the Venice Lagoon, the Malamocco-Marghera canal, excavated in 1970, is periodically dredged to a minimum depth of -10 m along its 16-km path connecting the Marghera harbour to the open sea through the Malamocco inlet. In the Marano-Grado Lagoon, a 5-km canal completed in 1969, is dredged to -6 m to connect the industrial harbours on the Corno and Ausa rivers to the Porto Buso inlet. We constructed computational grids for the pre- and post-intervention scenarios, as well as for the present-day configurations, based on available bathymetric surveys for both lagoons. Using a 2-D finite element hydrodynamic model, we simulated tidal flows in the considered configurations, setting as boundary conditions a sinusoidal tidal wave with a 0.50 m amplitude and a 12-hour period, typical of the northern Adriatic Sea.
Despite differences in morphology and intervention scale between the two cases, consistent trends emerged. Comparisons of pre- and post-intervention scenarios reveal an increase in the water discharge through the inlet connected to the excavated channel. This increased water exchange leads also to a different subdivision of the sub-basin connected to each inlet. Moreover, the increase in the ebb-phase discharge is more pronounced than that in the flood phase, indicating that channel dredging promotes a shift toward ebb-dominant conditions, with implications for water and sediment dynamics.
These findings highlight the potential long-term consequences of excavation and dredging in shallow tidal systems and emphasize the need for management strategies that reconcile navigational needs with the preservation of the morphological integrity of back-barrier lagoon ecosystems.
How to cite: Tognin, D., Piazza, A., and Carniello, L.: Canal excavation impacts on the hydrodynamics of shallow back-barrier lagoons, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2568, https://doi.org/10.5194/egusphere-egu25-2568, 2025.
Wetlands are among the most unique and biologically diverse ecosystems on the planet, playing critical roles in water filtration, carbon sequestration, and supporting rich biodiversity. However, these ecosystems are increasingly under threat from a combination of climate change and anthropogenic pressures. To safeguard these vital systems and ensure their sustainable functioning, the Ramsar Convention, an international treaty for wetland conservation, was adopted by 172 countries. The Anzali Wetland, situated in northern Iran, is one such Ramsar site and represents a significant ecological and hydrological resource. This wetland receives freshwater inputs from over 11 rivers and maintains a dynamic connection with the Caspian Sea. However, a confluence of challenges, including climate change-induced flooding, agricultural and wastewater runoff, declining Caspian Sea levels, and accelerated sediment deposition, has severely threatened the wetland’s integrity and functionality.
Addressing these challenges requires comprehensive management strategies informed by robust scientific understanding. Decision-makers and stakeholders need accurate tools to predict the outcomes of various interventions and develop targeted restoration plans. Hydrological and hydraulic models have become essential tools in this context, providing insights into complex ecosystem dynamics and helping evaluate the effectiveness of proposed management measures before their implementation.
In this study, the HEC-RAS (Hydrologic Engineering Center's River Analysis System) model, a computational fluid dynamics (CFD)-based software, was employed to simulate the hydraulic behavior of the rivers flowing into the Anzali Wetland. This model is particularly well-suited for assessing open-channel hydraulics and has been tailored to represent the unique characteristics of the Anzali Wetland. Given that the wetland’s water levels are predominantly influenced by seasonal river inflows rather than Caspian Sea fluctuations, the model emphasizes the critical role of river hydrology in sustaining wetland productivity, including vegetation health and biodiversity.
The HEC-RAS model was calibrated and validated to cover the vast region and major inflows of the Anzali Wetland. It aimed to assess the effectiveness of existing flood control infrastructure, analyze contamination pathways and their impacts on water quality, and identify areas within the wetland prone to excessive sediment deposition. The model results also provide valuable insights into the interplay between hydrology, sediment transport, and water quality within the wetland. For example, the model highlights areas with severe sediment accumulation, threatening to disrupt aquatic habitats and navigation. Additionally, it identifies critical zones where agricultural and urban runoff introduce contaminants, adversely affecting water quality and wetland health.
The outcomes of this modeling effort serve as a vital decision-support tool for wetland managers and policymakers. By simulating different restoration scenarios, such as improved flood control measures, sediment management strategies, and contamination mitigation efforts, the model enables stakeholders to prioritize actions that will have the most significant impact on preserving and restoring the Anzali Wetland. This study underscores the importance of integrating advanced hydraulic modeling with ecosystem management to safeguard vulnerable wetlands like Anzali, ensuring their ecological, cultural, and economic functions for future generations.
How to cite: Fatheenia, A., Farhadi Cheshmeh Morvari, B., Hasanabadi, M., and Alizad, K.: Developing a Hydraulic Model for Sustainable Restoration and Management of Anzali Wetland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7216, https://doi.org/10.5194/egusphere-egu25-7216, 2025.
Coastal ecosystems are shaped by the dynamic interaction of freshwater and saltwater, governed by both oceanic and terrestrial hydrological processes. However, anthropogenic development and climate change are disrupting these processes, necessitating targeted conservation strategies to sustain ecosystem functions. This study examines the hydrogeological processes influencing water levels and salinities in a coastal wetland near Avoca Lagoon (NSW, Australia), an intermittently open and closed system that is manually breached when water levels exceed a threshold to prevent urban flooding. The wetland was specifically designed to support the breeding of the endangered Green and Golden Bell Frog (GGBF), whose eggs and tadpoles require a narrow range of low-salinity conditions for survival. We established two surface water and three groundwater piezometers at depths of 3.5 to 5.5 m to monitor water levels and salinity. Additionally, multiple electrical resistivity tomography transects were acquired near the wetland, and the lagoon's depth and salinity profile were surveyed using a kayak. The results reveal that lagoon levels rise rapidly after rainfall and decrease gradually through evapotranspiration and water loss to the ocean during dry periods. The wetland’s water levels closely follow those of the lagoon, indicating hydraulic connectivity through the subsurface. Manual breaching of the lagoon’s berm prevents flooding of low-lying areas but leaves the lagoon level too low to sustain wetland water, causing it to dry out. Salinity within the lagoon is stratified, with brackish water overlaying seawater. While these saline conditions are unsuitable for frog breeding, the wetland is surrounded by fresh groundwater, which can discharge into the wetland under lower lagoon levels to create favourable breeding conditions. High lagoon levels, however, breach the barrier between the lagoon and wetland, causing salinisation and compromising habitat suitability. Our investigation reveals the delicate balance of water level and salinity conditions required for GGBF breeding, requiring a critical "goldilocks zone". Effective habitat conservation strategies must address a complex interplay of hydrogeological processes to enable breeding conditions, including challenges posed by climate change-induced shifts in rainfall patterns and future sea level rise. These findings underscore the broader challenges coastal areas face under increasing anthropogenic and climatic pressures, highlighting the critical need for improved management approaches that integrate surface and groundwater processes to protect frog habitats and maintain broader ecosystem functionality.
How to cite: Rau, G. C., Palombi, B. R., Reinhard, P., Brown, W., Power, H., and Callen, A.: Hydrogeological controls on endangered frog breeding habitat in an urban coastal wetland: Insights for conservation strategies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5273, https://doi.org/10.5194/egusphere-egu25-5273, 2025.
The Pearl River Delta (PRD) is among the world’s most intricate delta systems, shaped by the dynamic interaction of upstream runoff and downstream tidal dynamics. However, the mechanisms underlying river-tide connectivity within such complex networks remains insufficiently understood, particularly the nonlinear feedback loops and spatiotemporal lag effects governing water level dynamics. This study employs an information-theoretic framework to investigate water level connectivity in the PRD, integrating relative mutual information (RMI) and relative transfer entropy (RTE) to quantify synchrony, causality, and directional information flow among hydrological variables. Results highlight the dominant role of upstream river discharge on water level synchrony in the Xijiang and Beijiang River systems, while downstream tidal dynamics exert greater causal effects in the Pearl River’s mainstream and coastal distributary regions. Since the 1990s, human activities, such as dam construction and channel dredging, have attenuated the influence of river discharge while leaving tidal impacts largely unchanged. Seasonal analysis reveals that that upstream river discharge predominantly governs water level connectivity during the flood season, whereas downstream tidal forcing becomes more prominent in the dry season, with spring tides amplifying these effects across both seasons. The study further shows spatiotemporal heterogeneity in connectivity, highlighting nonlinear feedback mechanisms and lag effects across subsystems. These insights underscore the adaptability and resilience of the PRD under both natural and anthropogenic pressures. By providing a novel perspective on deltaic process dynamics, this study contributes to the theoretical foundation for sustainable management and resilience planning in the PRD.
How to cite: Wang, Y. and Cai, H.: Information-theoretic insights into river-tide connectivity in the Pearl River Delta: Implications for complex network dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6115, https://doi.org/10.5194/egusphere-egu25-6115, 2025.
The Vietnamese Mekong Delta (VMD) is among the vastest low-lying areas in the world and particularly exposed to relative sea-level rise, pluvial, fluvial and coastal flooding. While new studies have shown how the impacts of climate change and land subsidence will further increase the vulnerability of the delta, current flooding characteristics are also shaped by land use and its changes over time, including the distribution of mangroves and urban sprawl. However, the implications of delta-wide land-use changes and the role of coastal habitats for driving flood dynamics in the VMD remain unknown. In addition, there is a lack of analyses that integrate all hydrometeorological forcings in a compound setting (pluvial, riverine and coastal) and use two-dimensional hydrodynamic modelling across the entire delta including the Ho-Chi-Minh-City province.
We address these shortcomings by applying a state-of-the-art two-dimensional hydrodynamic model (SFINCS) across the VMD, and incorporating latest digital elevation models and land-use data from 1985 and 2022. We touch upon difficulties in validating large-scale hydrodynamic models for vast low-lying delta regions and highlight the importance of high-quality digital elevation models (DEMs) for investigating the role of mangroves in nature-based coastal defense schemes by comparing the modelling results obtained for different DEMs (FABDEM vs DeltaDTM). Furthermore, we attribute characteristics of recent flood events to land-use land-cover change since 1985 and sea-level rise, and investigate the role of existing mangrove forests for flood risk mitigation. Preliminary results emphasize the contribution of land use change for compound flood dynamics and point towards the high value of mangroves as a natural surge buffer across the VMD, but specifically in the provinces Ca Mau and Ho-Chi-Minh-City.
How to cite: Kiesel, J., Seeger, K., Minderhoud, P., Couasnon, A., Nguyen, H. Q., Sadana, T., Van Loon, A., and Scussolini, P.: How mangroves and past land-use change have affected compound flood events in the Vietnamese Mekong Delta, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15430, https://doi.org/10.5194/egusphere-egu25-15430, 2025.
Delta plains are vulnerable environments, chiefly due to their low elevation, occurrence of highly dynamic depositional processes, high population density and anthropogenic pressure, and threats coming from climate change, more extreme weather events and accelerating rates of relative sea-level rise. Anthropic activities and interventions, typically aimed at reclaiming deltaic lands for agricultural, urban, and industrial purposes, have significantly modified the hydro-morphodynamic behavior of fluvio-deltaic environments, making the reclaimed land hydrologically disconnected from the river and starving natural wetlands of sediments.
A paradigm change in river-delta management plans is currently underway, from hard infrastructures to new approaches designed to “work with the river”, leading to a broad interest in so-called “nature-based” solutions to restore and create new deltaic lands.
The Po River Delta represents a prominent example of a strongly engineered deltaic system with compromised long-term sustainability. This work focuses on a crevasse delta recently formed in an abandoned and flooded embanked area in the Po Delta, which demonstrates that natural deltaic dynamics can occur also in strongly anthropogenically-modified deltaic plains and effectively build new emerged land. We used field analyses (collection of sediment cores with a hand auger corer) and remotely sensed data to characterize the sedimentary facies and morphosedimentary structure of the crevasse delta.
The study area was reclaimed and used through the 1950s and 1970s for agriculture. In the mid-1970s, levee breaching caused seawater inundation, after which the area was abandoned and partially colonized by reeds. The reclaimed land was hydrologically disconnected from the river and eventually sea level rise and subsidence caused the flooding of the entire area, evidenced in the stratigraphy by a laterally persistent serpulid-rich marker horizon. This situation, with only fine grained sediments deposited from suspension and bioturbation, persisted until 1999-2000, when a fluvial flood caused a natural breaching in the levees and re-establishment of natural deltaic processes and wetlands, with the formation of intertidal and vegetated crevasse delta lobes.
Through the sedimentological analysis of drilled cores, aerial and satellite images and their mutual correlation, this work aims to define and reconstruct the architecture and the morphosedimentary evolution of this crevasse delta, improving our knowledge of natural systems resilience: by reconnecting the river to its wetlands, we can reduce land loss and restore deltaic coasts by harnessing their land-building capacity.
This work is part of the research project “Ensuring resilience of the Po River Delta to rising relative sea levels using nature-based solutions for building land and mitigating subsidence (NatResPoNΔ)”, a PRIN 2022 PNRR project funded by the European Union – NextGenerationEU.
How to cite: Rossi, V., Finotello, A., Ghinassi, M., Irace, A., Zaggia, L., Mandal, A. R., Berton, A., Trifiró, S., Mantovani, M., and Cosma, M.: Nature-based solutions for resilient deltaic coasts: an example from a crevasse delta in the Po River Delta (Italy) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18993, https://doi.org/10.5194/egusphere-egu25-18993, 2025.
The acceleration of sea level rise caused by global warming increases the risk of coastal flooding for people living on river deltas, as well as the erosion of archaeological sites along the Mediterranean coasts. The inhabitants of deltaic areas from the northwestern Mediterranean were exposed to coastal changes during the Holocene, and especially to geomorphic evolution driven by regression and progradation dynamics. Coastal flooding related to transgression can lead to a reduction in terrestrial areas available for human activities, whereas the emergence of new lands during delta progradation can provide opportunities for the development of cities and agriculture, although it can also increase the vulnerability of coastal infrastructures and settlements to sediment accretion.
The archaeological site of Lattara is one of the oldest coastal cities of the northwestern Mediterranean and is particularly interesting to study the impact of flooding on human settlements. This ancient city was built on a delta lobe of the Lez River during the Iron Age in the late 6th century BCE. Already, Middle Neolithic settlements were present in the northern part of the city. However, the absence of human occupations between ca. 3000 and 800 BCE suggests an abandonment of the site over two millennia. Geoarchaeological and environmental studies showed that this period was characterized by high groundwater levels in the Lez delta plain and relatively deeper water in the lagoon south of Lattara. Coastal flooding could thus explain the absence of human settlements at Lattara in the Late Neolithic and most of the Bronze Age, but this hypothesis needs to be investigated further.
Here we present the relation between hydroclimatic changes, sedimentation, coastal flooding and human settlements in the Lez delta plain during the mid-to late Holocene using bioindicators (ostracods, molluscs), geomorphological features (accommodation space, sediment accumulation rates), hydrological parameters (sea level change, water depth, discharge rates), age models based on radiocarbon dating, and archaeological data. Our data points toward the evidence of low sediment accumulation rates in a humid climate from 6 to 3 kyr cal BCE. These low sedimentation rates in a context of continuous sea level rise led to increasing of an accommodation space in the lagoon.
Our new results are compared with multi-millennial environmental records in the northwestern Mediterranean to evaluate the role of hydroclimate changes on coastal flooding. Besides, hydroclimatic parameters from instrumental data were investigated to determine if the relationships between climate change and hydrological processes over the past millennia were similar to those of the last decades.
How to cite: Giaime, M., Degeai, J.-P., Joseph, C., Salel, T., and Piques, G.: Impact of mid-to late Holocene hydroclimatic variability and sediment dynamics on coastal flooding and human settlement in the Lez delta plain, southern France, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10579, https://doi.org/10.5194/egusphere-egu25-10579, 2025.
This study examines the impact of human-induced changes to the lower Brazos-San Bernard delta on sedimentation rates and sediment sources filling the estuarine lakes within its western inland area. The delta began forming in 1929 when the Brazos River mouth was relocated 10 km west of its original position, placing it 5 km from the San Bernard River's mouth. Over time, the wave-dominated Brazos Delta expanded westward, closing the San Bernard River mouth and extending beyond it.
In 1949, the Gulf Coast Intercoastal Waterway (GCIWW) canal was completed, bisecting the Cedar Lakes, a series of five brackish lakes, and enabling sediment transport to these lakes. The San Bernard River drainage basin, situated between the larger Brazos and Colorado Rivers, occasionally receives floodwaters from the Colorado River during high-discharge events like Hurricane Harvey (2017). The geological differences between the Brazos and Colorado Rivers facilitated the development of distinct sediment "fingerprints" using X-ray fluorescence, color spectrometry, imaging, and grain size analysis.
Eighteen vibracores collected across the study area, combined with 137Cs dating, enabled the identification of deposits formed before and after the GCIWW's creation. Findings revealed that prior to the GCIWW and the Brazos River mouth's relocation, Colorado River-derived deposits dominated the region. Following these alterations, the western Cedar Lakes recorded Gulf of Mexico overwash sands and occasional Brazos River flood deposits. The GCIWW acts as both a conduit for Brazos River sediment and a barrier to Colorado River sediment.
North of the GCIWW, in lakes isolated from the canal, sediment records show a mixture of Brazos and Colorado River deposits. East of the San Bernard River, deposits include Colorado River material, Gulf of Mexico overwash, or layered deposits from both the Brazos and Colorado Rivers, reflecting simultaneous flooding events. Most Cedar Lake cores exhibit Pleistocene deposits at their base, overlaid by 50–90 cm of pre-GCIWW sediments and 90–130 cm of post-GCIWW deposits. This suggests a significant increase in sedimentation rates after the canal's construction.
In summary, the GCIWW's creation and the Brazos River mouth relocation have significantly altered sediment sources and deposition rates in the Cedar Lakes and adjacent brackish lakes of the Brazos-San Bernard delta. The results of this study are being used by various stakeholders to develop a better management plan for this region.
How to cite: Dellapenna, T., Robbins, C., Majzlik, E., Zhang, Y., and Ahmari, H.: Assessing mixed sediment sources of the brackish lakes of the Brazos-San Bernard River Delta of the northwest Gulf of Mexico and what it can tell us about how anthropogenic alterations have impacted sediment sources and sedimentation rates, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14528, https://doi.org/10.5194/egusphere-egu25-14528, 2025.
Managed realignment, the landward relocation of primary flood defences, is increasingly recognised as a sustainable approach to mitigating tidal flood risk in estuaries. However, the effectiveness of realignment relative to the size and location of intervention, and in relation to estuary size, remains poorly understood. This knowledge gap is critical, especially for urban estuaries where space for large-scale, nature-based interventions is limited. This study explores the scale-dependency of managed realignment using a 2D TUFLOW hydraulic flood model of the Clyde estuary, a large, meso-tidal urban estuary on Scotland’s west coast. Analytical solutions and existing flood models from eight other UK estuaries complement this analysis to facilitate comparisons between estuaries of a range of sizes. Our findings reveal that managed realignment exhibits scale-dependent behaviour: the effectiveness of managed realignment to reduce tidal flood risk is linearly proportional to the ratio of the size of the managed realignment to the estuary size. Larger estuaries, like the Clyde, require significantly more extensive realignment to achieve meaningful tidal flood risk reduction. Conversely, smaller estuaries achieve similar benefits with comparatively smaller interventions as they are more sensitive to geometric changes. Additionally for the Clyde, we also found that reconnecting a previously plugged palaeo-channel is more effective at reducing tidal flood risk than relocating primary flood defences. The results imply that a well-chosen location and size of realignment are needed to have a positive impact on reducing tidal flood risk in an estuary; this can be challenging due to existing land uses in highly urbanised estuaries. Hydrodynamic modelling will provide powerful tools to aid decision-makers and avoid risks of maladaptation, supported by long-term monitoring. Given the growing global adoption of managed realignment, this study offers critical insights into the scale-dependent behaviour of this strategy, helping to refine its implementation in diverse estuarine contexts.
How to cite: Prasojo, O. A., Williams, R. D., Naylor, L. A., Toney, J. L., and Hurst, M. D.: Right size, right place: scale-dependency of managed realignment in an urban estuary, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1524, https://doi.org/10.5194/egusphere-egu25-1524, 2025.
Estuarine dams, built between the estuary mouth and tidal limits, provide freshwater storage and storm surge protection but disrupt natural processes, altering hydrodynamics, sediment transport, and ecosystems. These changes affect freshwater discharge, tidal regimes, stratification, and sedimentation, often degrading water quality and obstructing fish migration. Globally, estuarine dams are found in 10% of 2,396 analyzed estuaries and, along with land reclamation, have caused nearly half of estuarine area loss over 30 years. Their construction peaked in mid-income countries during the 20th century, with limited development in low-income countries due to economic constraints and in high-income nations due to stricter environmental regulations. In a recent study of the Nakdong Estuary in Korea, the morphologic equilibrium following dam construction and subsequent restoration was investigated. Long-term numerical modeling revealed that the estuary achieved equilibrium approximately 15 years after restoration. In contrast, human-altered estuaries stabilized more quickly—within about 9 years—due to hydrodynamic adjustments and sediment redistribution that reduced energy dissipation. Model simulations effectively reproduced key morphological changes, including the transition from barrier island formation under wave-dominated conditions after dam construction to sand shoal development under tide-dominated conditions following restoration. Additionally, the model captured shifts in sediment texture: from sand-dominated under pristine conditions, to mud-dominated during the construction phase, and ultimately returning to sand-dominated post-restoration. This study highlights the value of realistic, long-term numerical simulations in understanding estuarine responses to human interventions and restoration efforts. The findings offer valuable insights for developing sustainable management strategies - conservation in low- and mid-income countries and restoration in high-income countries.
How to cite: Lee, G., Chang, J., and Harris, C.: Global altered estuaries with estuarine dams: Pathways for conservation and restoration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2348, https://doi.org/10.5194/egusphere-egu25-2348, 2025.
The latest IPCC report projects that regardless of the climate scenario, the highest rates of future sea-level rise will occur along the west-central US Gulf Coast. Meanwhile, recent research has shown that coastal wetlands in the Mississippi Delta are unable to survive rates of sea-level rise higher than 3 mm/yr, a number that was exceeded two decades ago. Thus, the 1M+ inhabitants surrounded by marshland will have to adapt to rapidly changing environmental conditions. Here we adopt an interdisciplinary approach to assess this problem.
The archeologic record shows that indigenous people adapted quickly to changing conditions in the rapidly evolving Mississippi Delta, abandoning areas subject to transgression and settling on prograding delta lobes. Present-day populations are much less nimble, yet rapid coastal degradation (notably wetland loss) has been related to the population decline that has already commenced in this region. While catastrophic events (i.e., major hurricane strikes) are commonly thought of as driving population loss, we argue that socio-economic factors (notably a dwindling home insurance industry) may become equally important. One key question is how much continued sea-level rise this region will see.
The last interglacial (LIG, ~125,000 years ago) featured a global average temperature that reached about 0.5-1.5 °C above pre-industrial values. Remnants of a LIG shoreline have been identified in SE Louisiana more than 100 km landward of the present shoreline, with a reconstructed sea level of 3.1 ± 0.8 m higher than present (7.5 ± 1.1 m after correction for fault motion). Since anthropogenic climate change (~1.5 °C in 2024) has already brought us near the upper end of LIG warming, it is plausible that future sea-level rise to such an elevation is already locked in, although the timescale for this to play out remains uncertain. With respect to the LIG shoreline, the New Orleans metropolitan area is located on the “wrong” side.
If future warming is kept well below Paris Agreement levels (2 °C) the shoreline may eventually stabilize at a position comparable to that from the LIG. Conversely, if Paris goals are exceeded, sea level can be expected to rise to an extent that puts other metropolitan areas, farther inland and at slightly higher elevation, in jeopardy as well. The next few decades will be decisive as to whether Paris climate goals are met. As a consequence, the ultimate fate of several million inhabitants, along with trillions in economic and ecologic capital, will likely be determined by mid-century.
How to cite: Törnqvist, T., Keenan, J., Mehta, J., and Shen, Z.: Climate-driven depopulation of a low-elevation coastal zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3718, https://doi.org/10.5194/egusphere-egu25-3718, 2025.
Our study stems from in situ observations of temperature, EC and salinity performed during 2021-2023 along the river Neretva bed within the Republic of Croatia territory. Apart from the local water column profiling performed several times per year, mostly during dry period, continuous observations of EC, and temperature have been performed at fixed locations and for variable depths. As a main driving forces controlling the termohaline stratification of the Neretva water column caused by seawater intrusion, river Neretva discharge and Adriatic Sea level have been observed continuously.
The data sets offer insight to changes in seawater-freshwater interface (SFI) and its shape ranging from typical salt wedge to complete stratification diminishing conditions. Hereby, within the data sets we identify three main scenarios of mechanisms controlling the seawater intrusions and thus the SFI: i) dominant influence of the mean sea level during the dry period with natural discharge kept below 250 m3/s, ii) dominant influence of intermittent discharge events caused by upstream hydropower plant operation and iii) rain period with on average annual duration of app. 25 % when river Neretva natural discharge controls the salinity vanishing from the river bed downstream.
In this way, specific changes in the salinity corresponding to different time scales have been determined. Natural hydrologically induced changes in the salinity are identified to correspond to largest time scales of several days and even weeks, unless intermittent discharge caused changes occur very fast decrease in the salinity, typically less than three hours, with recovery time corresponding to app. three to six hours.
Although the data sets offer the definition of different time scale changes in the river salinity as mentioned above, an improvement in continuous stratification observation has been suggested and implemented as a result of conducted study.
How to cite: Aljinović, I., Srzić, V., and Čarija, J.: Variable time scale changes in the river Neretva salinity regime, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9119, https://doi.org/10.5194/egusphere-egu25-9119, 2025.
More than half a billion people worldwide live in coastal river deltas, which provide critical ecosystem services. However, excess nitrate exported from these systems has led to significant environmental challenges, including hypoxic zones like the Gulf of Mexico's dead zone. Islands near the outlet of river deltas can be important last-ditch effort sites for nitrate processing prior to entering the ocean. Over the past decade, research has begun to numerically quantify nutrient transport through delta systems. These studies have traditionally utilized Eulerian models that are spatially-lumped, and nutrient fluxes are largely determined by catchment land use. Additionally, the potential for nutrients to be removed from channels within the islands or secondary channels in delta systems is typically ignored. This research proposes a distributed, Lagrangian modeling framework that follows individual particles through time and space to better understand the fate of nutrients in deltas (and the potential for removal). We accomplish this goal by adding a nutrient transport component to the open-source Python Package dorado, a Lagrangian model for passive particle transport that requires coupling with hydrodynamic outputs. We use dorado to quantify the hydraulic residence time of simulated nitrate particles in Wax Lake Delta of coastal Louisiana. Instead of only measuring nitrate transport through major distributary channels, we model channel-island connectivity, and the consequential differences in residence time distributions as particles “leak” from the channel into island networks. Deltaic islands have the ideal characteristics for increased nitrate processing capacity (slower water velocities, increased vegetation, etc), so these pathways are important to quantify denitrification potential. We couple modeled hydraulic residence time distributions with a first-order nitrate decay model to simulate the removal pathways of nitrate throughout the delta. Results identify the conditions and/or seasons with higher denitrification potential, offering insights into the role of deltas as sinks for excess nutrients. This work demonstrates the importance of deltaic islands in nutrient cycling and highlights how Lagrangian modeling can improve predictions of coastal nutrient dynamics.
How to cite: Henson, E. and Passalacqua, P.: Denitrification Hotspots or Nutrient Highways? Modeling the Fate of Nutrients in Coastal River Deltas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13802, https://doi.org/10.5194/egusphere-egu25-13802, 2025.
Delta ecosystems are critical zones connecting terrestrial and marine environments, with delta sediments preserving long-term records of land-sea interactions and environmental changes. The Pearl River Delta (PRD) is characterized by elevated ammonium levels in groundwater, posing risks to water quality and environmental health. This study investigates the microbial processes driving ammonium generation and accumulation across distinct depositional zones (terrestrial-dominated, transitional, and marine-dominated) in Holocene sediments of the PRD. Microbial communities exhibit stratification along environmental gradients. Bacterial communities (dominated by Pseudomonadota) reflect influences from both terrestrial and marine environments, while archaeal communities (led by Bathyarchaeia) resemble those in marine anaerobic ecosystems. Fermentation is the primary process driving ammonium production across all zones, with negligible ammonium consumption via nitrification and anammox. Secondary processes include nitrate reduction in terrestrial-dominated zones and dissimilatory nitrate reduction to ammonium (DNRA) in transitional and marine-dominated zones. Sulfate reduction predominating over nitrate reduction in marine-dominated zones. Brevirhabdus, a key bacterial contributor to fermentation and DNRA, links early marine deposition to ammonium dynamics in deltaic sediments. Environmental factors such as electrical conductivity (EC), carbon isotope composition (δ13C), and sediment depth strongly influence microbial community structure and function, emphasizing the critical role of geochemical processes in shaping microbial adaptation. Purifying selection dominates metabolic gene evolution, with functional genes related to sulfate and nitrate reduction highly conserved in marine-dominated zones, while fermentation genes exhibit depth-dependent. These findings reveal the interplay among depositional history, microbial adaptation, and biogeochemical processes, linking ammonium dynamics to climate-driven environmental changes, thus providing a framework to address groundwater quality risks in deltaic systems.
How to cite: Lu, M., Jiao, J. J., Luo, X., Feng, X., Liang, W., Yu, S., Qi, Y., Li, H., and Li, M.: Microbial Drivers of Ammonium Accumulation in Holocene Sediments of the Pearl River Delta, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14159, https://doi.org/10.5194/egusphere-egu25-14159, 2025.
Damage caused by land subsidence due to excess pumping has become a serious problem in coastal major cities and landscapes around the world. To prevent this damage, it is necessary to predict local deformation in the ground and design the appropriate pumping amount. To verify the predicted deformation from land subsidence modeling, experimental methods with visualizing deformation distribution is of importance.
A visualization method using transparent synthetic soil (TSS) as a physical model of soil behavior has been developed in the field of soil mechanics. This experimental method simulates the geotechnical properties of natural soil using a transparent surrogate containing a transparent porous medium and pore fluid. In this study, the authors performed a tank experiment using a TSS made of polymers which is inexpensive and easy to control.
In the previous experimental study by the authors, a pumping test was carried out in an acrylic tank measuring 300 mm wide x 250 mm long x 249 mm high, filled with a transparent hydrated polymer to represent an aquitard (clay layer) above an aquifer (saturated silica sand). Using the target racking method, 100 particles with a diameter of 3 mm were submerged in the synthetic clay layer, and the subsidence in the synthetic clay layer caused by the pumping of pore water in the silica sand was constantly monitored.
In this study, an AI-based object detection method was used to more quantitatively visualize the spatiotemporal distribution of deformation inside the TSS caused by the propagation of pore water pressure change in the TSS after pumping was stopped. It successfully revealed the three dimensional elastoplastic deformation distribution. The developed methods and the obtained results are expected to contribute to a better understanding of land subsidence mechanisms and verify the numerical land subsidence modeling.
How to cite: Tabe, K. and Aichi, M.: Visualization technique for the deformation distributions in transparent synthetic soil with object detection, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3389, https://doi.org/10.5194/egusphere-egu25-3389, 2025.
Land subsidence is a slowly progressing phenomenon that often goes unnoticed due to its gradual nature, yet it can significantly compromise long-term sustainability if left unaddressed. This challenge is particularly pronounced in coastal and deltaic regions with limited fluvial sediment input – e.g. the Netherlands, the Po River Basin, the Mekong Delta, the Mississippi Delta – where anthropogenic activities altered water tables, sediment dynamics and ecosystem health, and further such impacts with climate change and sea-level rise are expected. Any robust, future-proof adaptation strategy and spatial planning must therefore account for ongoing land subsidence, if human presence is to be viable.
In the Netherlands, the situation is already severe: approximately 50% of its coastal-deltaic plain now lies below mean sea level (Koster et al., 2018) owing to soft soil consolidation, peat oxidation and mining, accumulated over centuries and never technologically halted. Even more, progressive subsidence has increasing economic costs (Van den Born et. al., 2016). Recognizing the urgency of this problem, the Dutch government and related authorities pay attention and resources at regional and national scale (e.g. platforms, knowledge centres, incentives, directives, regional deals), and several cross-disciplinary research programs have been prompted (e.g. NWA-LOSS, NOBV, DeepNL). Within NWA-LOSS (nwa-loss.nl) our work focuses on the numerical modelling. With partners, we develop and operate the land subsidence model Atlantis (Bootsma et al., 2020) that captures the interplay of soft soil consolidation, peat oxidation, climate change, and human interventions (e.g. agricultural drainage) to predict future spatial and temporal evolution of the Dutch landscape. Employing global sensitivity analyses (Morris screening and Sobol’ indices), we identify the most influential parameters and processes and integrate uncertainty quantification to ensure robust subsidence predictions.
Our results reveal how shallow subsidence evolves under various climate scenarios, pinpointing ‘hotspots’ for targeted adaptation and nature based solutions (e.g. peat regeneration). Critically, our findings underscore the role of subsidence in shaping relative sea-level rise, a driver of coastal vulnerability that can profoundly influence coastal and deltaic biogeochemistry, biomorphodynamics, and hydrodynamics. Incorporating land subsidence into long-term adaptation measures is therefore essential for mitigating climate change impacts and improving the resilience of coastal and estuarine environments worldwide.
References:
Bootsma, H., Kooi, H., Erkens, G. (2020). Atlantis, a tool for producing national predictive land subsidence maps of the Netherlands. Proceedings of the International Association of Hydrological Sciences, 382, 415-420.
Koster K., Stafleu J., Stouthamer E. (2018). Differential subsidence in the urbanised coastal-deltaic plain of the Netherlands. Netherlands Journal of Geosciences. 2018;97(4):215-227. doi:10.1017/njg.2018.11
Van den Born, G. J., Kragt, F., Henkens, D., Rijken, B., Van Bemmel, B., Van der Sluis, S. (2016). Dalende bodems, Stijgende kosten, Report Planning Agency for the Environment (PBL), report nr. 1064, 93 pp., 2016.
How to cite: Kılıç, D., Erkens, G., Cohen, K. M., and Stouthamer, E.: A Process-Based Modelling Approach to Evaluate Alternative Sustainable Land Subsidence Adaptation Pathways in the Netherlands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11383, https://doi.org/10.5194/egusphere-egu25-11383, 2025.
In tourism-oriented coastal regions, beaches provide significant economic value alongside vital ecosystem services, such as habitats for benthic organisms, recreational spaces for local communities, and natural wave energy dissipation. However, these environments face increasing hazards due to anthropogenic influences, compounded by climate change. Developing robust and cost-effective monitoring and modelling plans is essential to ensure the sustainability and resilience of these valuable ecosystems.
This study, conducted within a transboundary cooperation project focused on beach vulnerability and resilience improvement across the eastern Adriatic coast (Croatia, Bosnia and Herzegovina, and Montenegro), explores the application of publicly available data as a baseline for monitoring and modelling efforts at twelve pilot beach sites. Spatially dispersed meteorological data from platforms like Visual Crossing and oceanographic data derived from CMEMS hindcast models and EMODnet bathymetry are assessed for their temporal and spatial coverage, reliability, and limitations. These datasets serve as a foundation for identifying site-specific conditions and knowledge gaps that will be addressed through project-specific monitoring, including photogrammetry campaigns, numerical sediment transport modelling, and physical laboratory experiments on erosion countermeasures.
By leveraging publicly available resources, this study develops practical guidelines for organizing monitoring activities and integrating modelling efforts tailored to the south-eastern Adriatic context. While the approach is specific to this region, it provides insights into balancing resource constraints with the need for detailed environmental data in other coastal settings under similar pressures.
How to cite: Rumenović, R., Galešić Divić, M., Kekez, T., and Srzić, V.: Leveraging public data for beach monitoring plan development in coastal regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9335, https://doi.org/10.5194/egusphere-egu25-9335, 2025.
The dynamic nature of coastal hazards has drawn interest in developing, holistic, nature-based, sea defence strategies. Composite beaches are a type of mixed sand-gravel beach regarded as excellent natural coastal defence due to their dynamic stability in changing hydrodynamic conditions (Blenkinsopp et al., 2022a; Bayle et al., 2021).These beaches are distinguished by a dissipative sandy lower foreshore which is backed by a reflective gravel or cobble berm close to the mean high-water level. Wave energy is dissipated along the sandy foreshore, and the steep, porous cobble berm drives swash asymmetry, stabilizing the upper beach and protecting the hinterland by minimizing overtopping (Bayle et al., 2021). Essentially, composite beaches embody the two most stable end-members of the morphodynamic continuum (Blenkinsopp et al., 2022). Recent developments have sought to exploit the morphodynamic stability composite beaches offer by installing a ‘dynamic cobble berm revetment’. These revetments are intended to mimic the cobble berm found naturally on a composite beach. Prototype-scale flume experiments and trial installations along vulnerable sections of the US West Coast have shown promising results in the face of rising sea levels and energetic wave conditions (Blenkinsopp et al., 2022b; Bayle et al., 2021). However, our understanding of composite beach behaviour (processes, responses to storms and longer-term evolution) is distinctly lacking due to the absence of dedicated studies. Therefore, our current definition of composite beaches may not adequately encapsulate the range of sub-morphotypes of composite beaches.
This research tackles our lack of knowledge by conducting one of the first detailed studies of composite beach behaviour on a regional scale. Currently, the term ‘composite beach’ covers a broad variety of different sand-gravel beach morphologies. By analysing a wide range of different composite beach types in a range of locations we will develop a more robust definition of composite beaches and their sub-types. Analysing historic topographic data of UK composite beaches enables us to gain new insights into the general behaviour of these beaches. Initial results indicate that natural cobble berms demonstrate morphological variations in constituting cobble size ranges, crest elevations, slope angles and berm width. These berms undergo relatively minor morphological changes when runup is confined to the seaward slope. In energetic conditions, when overtopping happens, larger changes can occur, but the berm remains dynamically stable rarely losing cobble volume.
- References
Bayle, P.M., Kaminsky, G.M., Blenkinsopp, C.E., Weiner, H.M. and Cottrell, D., 2021. Behaviour and performance of a dynamic cobble berm revetment during a spring tidal cycle in North Cove, Washington State, USA. Coastal Engineering [Online], 167, p.103898. Available from: https://doi.org/10.1016/j.coastaleng.2021.103898
Blenkinsopp, C.E., Bayle, P.M., Martins, K., Foss, O.W., Almeida, L.-P., Kaminsky, G.M., Schimmels, S. and Matsumoto, H., 2022b. Wave runup on composite beaches and dynamic cobble berm revetments. Coastal Engineering [Online], 176, p.104148. Available from: https://doi.org/10.1016/j.coastaleng.2022.104148.
Casamayor, M., Alonso, I., Valiente, N.G. and Sánchez-García, M.J., 2022. Seasonal response of a composite beach in relation to wave climate. Geomorphology [Online], 408, p.108245. Available from: https://doi.org/10.1016/j.geomorph.2022.108245.
Jennings, R. and Shulmeister, J., 2002. A field based classification scheme for gravel beaches. Marine Geology [Online], 186(3–4), pp.211–228. Available from: https://doi.org/10.1016/S0025-3227(02)00314-6
How to cite: minnigin, A., Blenkinsopp, C., and Marrero, S.: Chasing Cobbles: A Regional Exploration of Composite Beach Morphodynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13783, https://doi.org/10.5194/egusphere-egu25-13783, 2025.
This study analyses sediment accretion, river discharge, and wind dynamics in coastal wetlands combining data from the Delta-X project, the United States Geological Survey (USGS), and the National Oceanic and Atmospheric Administration (NOAA). Data covers the period from 2020 to 2023. Sediment accretion data from feldspar marker horizons in the Wax Lake Delta were processed to evaluate organic carbon content and bulk density variations across different hydrogeomorphic zones. Discharge measurements were obtained from USGS monitoring sites, while wind speed data came from NOAA stations. Wind data were filtered using speed and direction thresholds to isolate storm conditions significantly affecting sediment transport processes. All data were processed with MATLAB, aligning all datasets for time-series analysis and exploring interactions between hydrodynamic and atmospheric factors. Statistical and computational analyses explored seasonal sedimentation patterns and the effects of storm events. The results show significant spatial variability, with sediment accretion rates ranging from approximately 17 to 115 mm/year. Storm events with wind speeds exceeding 10 m/s blowing from the sea with prevailing directions between 90° and 270° strongly influence sediment deposition, driven by wind-induced water level changes. Intertidal zones, where accretion is vital for wetland resilience, exhibited elevated sensitivity to discharge peaks and wind-driven dynamics. Sedimentation patterns reveal that seasonal high-flow events are key to sediment supply, particularly during spring and fall. These findings advance our understanding of sediment transport mechanisms in dynamic wetland systems and could suggest strategies for sustainable sediment management. Insights are particularly relevant also for flood-regulated systems, such as the Venice Lagoon (Italy), where altered sediment transport dynamics are challenging for wetland survival and critical ecosystem service maintenance.
How to cite: Ruffini, A., Tognin, D., Carniello, L., and Tambroni, N.: Sediment Accretion Dynamics and Environmental Drivers in CoastalWetlands: Insights from the Wax Lake Delta, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19052, https://doi.org/10.5194/egusphere-egu25-19052, 2025.
Salt marshes and mangrove wetlands provide crucial ecosystem services to deltaic areas. They also significantly modulate hydrological conditions (e.g., currents, tides, and waves), thereby altering sediment dynamics and morphology. However, how these vegetation types shape morphology at the delta scale remains a largely unresolved question.
In this presentation we will compare the hydro-morphodynamic impacts of salt marshes and mangroves in river deltas, using field observations of the Changjiang (Yangtze) River Estuary and Beibu Gulf in China, respectively. Additionally, numerical modeling using Delft3D is employed to analyze the interactions between vegetation and hydro-sedimentary processes.
Preliminary results from fieldwork reveal that both salt marshes and mangroves effectively attenuate waves and currents, promoting sediment deposition, particularly at the interface between bare flats and vegetated zones. In calm weather, salt marshes tend to accumulate sediment more readily than mangroves. However, during storm events, salt marshes are more susceptible to erosion, resulting in greater variability in sediment dynamics. There are also seasonal differences. In salt marshes, wave and current attenuation is more pronounced during summer than winter, whereas such seasonal variation is less significant in mangroves. Multi-year variability, on the other hand, may be greater in mangroves.
In ongoing numerical simulations, we find a strong nonlinear sedimentation effect as mangroves transition from small saplings to mature individuals. Future work will include modeling the role of salt marshes, with comparisons across different temporal scales (e.g., tidal cycles, seasons, years, and decades) and in direct competition with mangroves. Broadly, these findings will help us to explore potential river delta change as mangroves encroach on salt marshes in our warming planet.
Acknowledgements: This research has been supported by the National Key R&D Program of China (2023YFE0121200) and the National Natural Science Key Foundation of China (NSFC) (42430406).
How to cite: Luo, J., Dai, Z., and Nienhuis, J.: Comparing the effects of mangroves versus salt marshes on delta morphodynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2865, https://doi.org/10.5194/egusphere-egu25-2865, 2025.
Intertidal areas are considered critical ecosystems as they serve as dynamic zones of interaction between land, ocean, and atmosphere; influencing sediment transport, coastal erosion, and habitat formation. Intertidal areas can also influence larger-scale hydro-morphodynamics and perhaps explain delta instability. However, intertidal areas are notoriously difficult to monitor. Here we present on work on multispectral remote sensing in combination of non-stationary harmonic analysis (NHSA) to explore time changes in the size and elevation of intertidal areas in the Ganges-Brahmaputra delta. Using Unified Tidal Analysis and Prediction (UTide) and earth engine platform in python programming, we analyzed tidal variations, reconstructed water levels, and quantified changes in intertidal geometry over multiple decades . We find a long-term decline in intertidal area across the delta, and we also find that only a small fraction of intertidal areas remains stable, with an average lifespan of only 2–3 years. This short time is likely the combined effect of cyclones, tidal range amplification downstream, and channel migration, which collectively drive sediment reworking and result in significant spatiotemporal variability in intertidal extents and elevations. The processes thus highlight the dynamic and transient nature of intertidal zones in abruptly changing planform. This research provides critical insights into potential geophysical processes and their impacts on intertidal habitats, emphasizing the need for further studies and monitoring that can help in adaptive management strategies in response to the rapid geomorphological changes occurring in unstable deltaic systems.
How to cite: Tahsin, N., Nienhuis, J., and Hoitink, A. (.: Intertidal Area Dynamics in an Unstable Delta, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6772, https://doi.org/10.5194/egusphere-egu25-6772, 2025.
The lagoon landscape is characterized by a diversity of tidal morphologies, such as salt marshes, tidal flats and subtidal platforms, playing an essential role for the ecosystem services these areas provide. The existence of these low-lying morphologies depends on the delicate balance between site-specific bio-geo-morphodynamic processes and relative SLR. Tidal morphologies are at risk of survival since they must keep pace with sea level rise and land subsidence. Given the expected climate change scenario, it is important to identify the most threatened areas, where effective measures are urgently needed. This work presents a novel assessment of the vulnerability of tidal morphologies to relative sea-level rise, using as a study case the Venice Lagoon: the largest wetland in Italy and one of the most important coastal ecosystems of the Adriatic Sea, where the natural hydro-morphological setting is strongly influenced by anthropogenic interventions. Vulnerability is assessed for past, ongoing and future relative SLR conditions through an index-based approach that combines sensitivity and hazard maps generated using a series of indicators such as SLR, land subsidence, morphological setting, and stratigraphic characteristics of Holocene deposits. Results indicate that most of the lagoon area will be at moderate to severe vulnerability in the future, representing a significant worsening of conditions compared to the past. Although the expansion of subtidal areas is anticipated, this will be at the expense of intertidal areas, which will experience a significant and alarming decline. This change contributes to the flattening and deepening of the lagoon's topography, which in turn threatens the diversity of the landscape and is likely to lead to a decline in the ecosystem services provided by these tidal morphologies. The vulnerability maps provide a valuable tool to highlight the areas that need more attention, which can assist policymakers in developing restoration, conservation and mitigation plans. This work is part of the research program RESTORE (REconstruct subsurface heterogeneities and quantify sediment needs TO improve the REsilience of Venice saltmarshes), a PRIN 2022 PNRR project funded by the European Union – NextGenerationEU.
How to cite: Cosma, M., Da Lio, C., Donnici, S., and Tosi, L.: Mapping the vulnerability of tidal morphologies to Sea Level Rise through an index-based approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9183, https://doi.org/10.5194/egusphere-egu25-9183, 2025.
The spatio-temporal development of a meandering river is controlled by its channel morphodynamics. In regions of rapid channel evolution, understanding the driving factors of meandering migration is crucial in forecasting the rate and extent of morphological change. Sediment supply and fluvial discharge are the primary influences on migration rate, however climate oscillations are also integral in indirectly regulating migration rate through their control of regional precipitation, as well as the monsoon season of sub-tropical Asia. Despite this, an in-depth investigation into the impact of climate oscillations on meander bend migration remains undocumented. This study presents a satellite-based analysis of multi-decadal climatic forcing on the migration rate of the Sittaung River in Myanmar, through interpretation of the El Nino Southern Oscillation (ENSO). The mode of ENSO exerts significant climate control on the migration rate of the meandering channels of the Sittaung River, with low-to-average migration rates recorded during dry El Nino events and peak migration rates observed during wet La Nina events. However, this climatic signal may have been obscured by certain local environmental conditions. In cases where meanders faced geological basement, the basement rock inhibited their migration through extension, forcing more rapid migration by way of seaward translation. Consequently, these translating meanders developed to be more elongate, with lower curvatures. Meanders downstream of the approximate tidal limit were less downstream skewed, indicative of tidal modulation, potentially obscuring the impact of fluvially driven climate forcing. Additionally, downstream of a major confluence, the input of sediment and fluvial discharge may have been regulated by upstream anthropogenic activities such as mining and dam construction, leading to greater variability in migration rate downstream of this confluence and further obfuscation of the climate signal.
How to cite: Bisson, L. and Choi, K.: Climate control on the channel morphodynamics of the Sittaung River, Myanmar, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12372, https://doi.org/10.5194/egusphere-egu25-12372, 2025.
Deltas are unique landforms that develop where rivers debouch into standing bodies of water such as oceans or lakes. Characterized by intricate networks of interconnected channels, they evolve in response to dynamic environmental factors, including sediment particle size, sediment supply, vegetation growth, waves, tides, and climate change. Among these factors, tidal currents play a significant role by continually modifying delta morpholodynamics. However, quantitative measures for assessing tidal influence on delta morphology remain challenging and are poorly understood. Here, we conducted hydro-morphodynamic modeling using Delft3D, varying tidal amplitude and the ratio of mud and sand supply to capture changes over a broad range of timescales. Furthermore, we measured bifurcation lengths, the distances between two adjacent bifurcation points along the channel centerlines in deltaic channel networks, and analyzed the spatial pattern of these lengths. The results indicate that higher tidal amplitude leads to a spatial increase in bifurcation length with bifurcation orders and that a higher proportion of muddy composition responds more sensitively to the tidal effects. Channel geometry, governed by fluid flow properties and sediment compositions, and the evolution of mouth bars collectively explain the observations in this study. We propose that stronger tidal currents and cohesive sediment composition facilitate channel deepening and narrowing, ultimately increasing the advection length and thus bifurcation length. Our study aims to elucidate the spatial pattern of branching channel networks, providing a quantitative measure compared to conventional methods for predicting delta morphology. Building on these findings, we can further enhance our understanding of how channel networks evolve across global scales under a variety of coastal processes.
How to cite: Lee, J. and Kim, W.: Investigating and quantifying tidal effects on the formation of bifurcated channel networks in modern river deltas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15368, https://doi.org/10.5194/egusphere-egu25-15368, 2025.
In recent decades, sand extraction from rivers has accelerated to meet the needs of economic development. Locally, this results in river bed and bank erosion, but it is unknown how these local disturbances affect the larger scale morphodynamic feedback and whether sustainable sand-mining strategies can be designed to minimise impacts. Our objective is to test dredging strategies in a river-estuary Delft3D model and to quantify the resulting morphodynamic response of the system. We systematically varied the number and intensity of dredging sites along the river, relative to the sediment supply from upstream. The results show that the system equilibrium is disturbed when the amount of mined sediment exceeds the sediment supply from the river. We found that when intensive sand mining occurs at a small number of sites, the dredged area is able to recover over time after mining ceases, while the downstream estuary continues to erode as a result of upstream sand extraction. In contrast, less intensive sand mining, spread over a larger number of sites, results in an overall lower river bed that continues to erode and export sediment after sand mining ceases, while the non-dredged estuary is relatively stable. With our results, we aim to describe guidelines for more sustainable sand mining.
How to cite: Baar, A. and Hackney, C.: Morphodynamic impacts of sand mining in river deltas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14975, https://doi.org/10.5194/egusphere-egu25-14975, 2025.
The purpose of this study is to investigate the depositional history of Kuwait Bay (KB) for the past millennium based on sediment cores. Kuwait Bay is in the northwest corner of the Arabian (Persian) Gulf, encompasses 720 km2, is semi-enclosed, elliptically shaped, and is an inverse estuary that opens to the east. Kuwait is extremely arid, receiving rainfall typically ranging from 100-120 mm y-1, and KB has no direct fluvial input within its interior. However, KB does receive sediment from the Tigres-Euphrates River, which empties into the Gulf adjacent to the mouth of KB. KB also receives sediment from dust storms and through direct precipitation of carbonates from the water column. Although sedimentation rates and age dates have yet to be generated, if we assume as a rough estimation that sedimentation kept pace with average global sea level rise, which averaged approximately 2 mm y-1 for the past millennium, then 2 m long cores roughly represent millennium time scales. A total of 28 submersible vibracores, ranging in length from 1-2.5 m, were collected in 2021. By using X-ray fluorescence (XRF) core scanning, elemental abundances were analyzed at 1 cm increments. Color spectrophotometry and grain size analysis were also conducted downcore. For all cores, the upper 10-25 cm have elemental abundances and colors that differ from the down core portions, and it is assumed this upper portion represents the Anthropocene. When considering the pre-Anthropocene portions of the cores, the XRF elemental abundance ratio of Si/Ca was used to differentiate calcium carbonate from siliceous sediment. The bay was subdivided into the eastern portion proximal to the mouth of the bay, the central portion, distal from either the mouth or the western shore, and the western portion, proximal to the western shoreline. Although all Si/Ca abundance profiles are “spikey,” there are significant overall trends. Cores from the bay’s interior have overall lower Si/Ca ratios, indicating the cores have a greater abundance of calcium carbonate. This may potentially indicate either higher auto-precipitation in the bay’s interior or less dilution of the auto-precipitated carbonate. Cores around the interior western side of the bay have, overall, the highest Si/Ca ratios, suggesting a greater abundance of siliceous minerals. Much of the dust derived from dust storms from this region is siliceous and probably explains this higher abundance of Si. Si/Ca profiles from cores from near the mouth of the bay have the broadest range of ratios but overall have higher ratios than from the interior, potentially indicating a variability in advection of Tigres-Euphrates sediment into KB. Overall, the depositional history suggests a mix of autochthonous sediment sourced from dust storms and the advection of Tigres-Euphrates suspended sediment and the auto-precipitation of allochthonous carbonates. These are preliminary results of what will become a much larger investigation into the paleoclimate history of the region.
How to cite: Cerv, J., Dellapenna, T., Al Mukaimi, M., Alaskar, H., Dasti, J., and Esmaeil, A.: Preliminary results of the depositional history of Kuwait Bay for the past millennium suggest a spatially and temporally variable mix of autochthonous and allochthonous sediment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13956, https://doi.org/10.5194/egusphere-egu25-13956, 2025.
Continued increases in climate extremes, population growth, natural and human-induced subsidence present a significant threat to the sustainability of many of the world’s river deltas. Hard engineering solutions, such as dikes and river embankments designed to prevent flooding in reclaimed deltaic regions, are proving increasingly unsustainable and may undermine the long-term resilience of deltaic ecosystems.
This challenge is particularly pressing in highly human-modified river deltas, where vast expanses of land have been reclaimed in the past. The combined impact of subsidence, climate change-driven sea-level rise, and intensified storm surge events is exposing reclaimed areas to a growing risk of flooding, saltwater intrusion and soil salinization. These processes will ultimately lead to a devaluation of reclaimed lands, making the continuous maintenance of levees and pumping systems, required to keep these areas dry, economically unfeasible. As a result, when the cost of sustaining reclaimed land outweighs its economic value, abandonment becomes the more likely outcome. Once these low-lying areas are abandoned, they become increasingly vulnerable to dike and levee failure, re-exposing them to natural fluvio-deltaic morphodynamic processes.
In this study, we use Italy’s heavily modified Po River Delta as a case study to illustrate these dynamics. We focus specifically on the seaward-most portion of the subaerial delta topset, where the failure of dikes protecting a previously reclaimed area known as “Isola della Batteria” led to the rapid infill of the area by river-borne sediment and to the formation of approximately 30 hectares of new emergent wetlands within just 30 years.
By integrating field data and remote sensing techniques—including sediment core analyses, UAV LiDAR surveys, ground-based topographic measurements, satellite-derived subsidence rates, historical aerial imagery and topo-bathymetric maps—we reconstruct the morphological evolution of the area over the past 50 years. We then use these data to calibrate a morphodynamic numerical model, which we apply at multiple locations within the Po River Delta to assess the feasibility of managed realignment strategies aimed at creating new wetland habitats of significant ecological and socio-economic value.
Our findings highlight the potentials of controlled dyke-breaching interventions in highly human-modified delta systems characterized by extensive reclaimed land. Such strategies enhance sediment retention on delta plains, promoting vertical accretion at rates that easily exceed projected relative sea-level rise. This process supports the rapid formation of new deltaic wetlands, ultimately strengthening the resilience of deltaic ecosystems as a whole.
This work is part of the research project “Ensuring resilience of the Po River Delta to rising relative sea levels using nature-based solutions for building land and mitigating subsidence (NatResPoNΔ)”, a PRIN 2022 PNRR project funded by the European Union – NextGenerationEU.
How to cite: Finotello, A., Rossi, V. M., Ghinassi, M., Viero, D. P., Carniello, L., D'Alpaos, A., Shamsnia, S., Irace, A., Mandal, A. R., Berton, A., Trifirò, S., Mantovani, M., and Cosma, M.: Harnessing Natural Land-Building Processes in Human-Dominated River Deltas: Lessons from the Po River Delta (Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13631, https://doi.org/10.5194/egusphere-egu25-13631, 2025.
Delta plains are crucial landscapes in many respects. They serve as hotspots for biodiversity, provide fertile land for agricultural practices, and act as natural buffers against coastal storms. However, they face greatly increased risks due to climate change and anthropogenic activities. Previous human interventions based on hard engineering solutions to remediate these coastal systems have largely failed in the long run. Besides being expensive, these measures have disrupted the land-building processes of natural wetlands, compromising the sustainability of these coastal ecosystems and making them more vulnerable to flood risks. This underscores the urgent need for more sustainable, nature-based approaches to realign and restore these vital ecosystems.
River diversion has emerged as an effective strategy for restoring wetlands in river-dominated deltas. This approach involves breaching river levees to restore water flow and sediment deposition in low-lying inundated areas of the deltaic system. The process generates new landforms, such as crevasse splays and crevasse deltas, which provide a foundation for wetland plants to thrive, fostering the development of new wetland ecosystems.
This work focuses on a crevasse delta in the "Isola della Batteria" region, located in the northeastern part of the Po River delta (Italy). The morphological evolution of the area is studied through the analysis of aerial photographs and satellite imagery from Sentinel-2 (2016–2024), Landsat-8 (2013–2016), and Landsat-7 (2009–2013) using QGIS, complemented by sedimentary core and LiDAR data. The study area was previously reclaimed for agricultural purposes but later succumbed to subsidence and became inundated, leading to its abandonment. Between 1999 and 2000, a fluvial flood caused a breach in the levee, initiating the formation of a crevasse delta. By around 2011, the crevasse delta emerged as a subaerial feature and has continued to grow, with vegetation (reeds) progressively colonizing the area and contributing to its development. The newly formed wetland area is approximately 30 hectares.
The results of this work help to characterize the morphodynamic and depositional elements evolution of a crevasse delta developed in a highly anthropized river delta systems, thereby informing cost-effective strategies for nature-based restoration projects in deltaic wetlands.
This work is part of the research project “Ensuring resilience of the Po River Delta to rising relative sea levels using nature-based solutions for building land and mitigating subsidence (NatResPoNΔ) ”, a PRIN 2022 PNRR project funded by the European Union – NextGenerationEU.
How to cite: Mandal, A. R., Rossi, V. M., Finotello, A., Ghinassi, M., Irace, A., Zaggia, L., Berton, A., Trifiró, S., Mantovani, M., and Cosma, M.: Understanding Crevasse Splay Evolution in Po River Delta (Italy) via Satellite Imagery: Implications for Coastal Resilience, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18769, https://doi.org/10.5194/egusphere-egu25-18769, 2025.
Posters virtual: Mon, 28 Apr, 14:00–15:45 | vPoster spot 2
EGU25-770 | ECS | Posters virtual | VPS25
Alongshore Varying Dune Retreat at a Barrier IslandMon, 28 Apr, 14:00–15:45 (CEST) | vP2.10
This research investigates the alongshore variability of shoreline and dune line responses to storm events and long-term changes on Culatra Island, located in the Algarve region of Portugal utilizing a combination of LiDAR data, satellite imagery, and numerical models (ShorelineS and SnapWave). Using a dune model based on Larson et al. (2016), integrated within the ShorelineS framework, to analyze the dynamic interactions between dune erosion, overwash by waves, and dune growth driven by aeolian (wind) transport. These interactions are critical in understanding the long-term and storm-induced changes in shoreline positions.
The calibrated ShorelineS model, supported by SnapWave's wave data, reveals that longshore transport gradients are the predominant drivers of shoreline change, significantly influenced by southeast prevailing waves, shallow active heights at the ebb delta, and the presence of the western breakwater.
By simplifying these processes into a 1D sand balance equation, where dune interactions are treated as source and sink terms, the model effectively captures several key dynamics of coastal morphology. However, certain idealizations, such as the assumed dune vegetation lines and simplified coastal profiles, result in some processes, like overwash, not being fully represented.
To ensure the accuracy and reliability of the model outputs, extensive sensitivity analyses were conducted with parameters such as impact coefficient Cs, median grain size d50, wave output points distances, and sediment transport factor (qscal). Validation of the ShorelineS model against 2011 DEM data and satellite trends reveals varying degrees of accuracy. For shoreline positions, the model demonstrates a strong positive correlation with DEM data (R² = 0.78) and even better alignment with satellite trends (R² = 0.85). However, the model's predictions for dune positions exhibit higher variability and weaker correlations with DEM data (R² = 0.47), indicating significant discrepancies. Interestingly, the model shows a stronger positive correlation with satellite trends for dunes (slope = 0.96).
The research identifies several key factors contributing to alongshore variability in dune and shoreline responses during storm events, including initial berm width, storm duration, wave height, and cumulative sediment transport due to dune erosion. Notably, dune responses exhibit higher sensitivity to these coastal parameters compared to shoreline responses, with cumulative sediment transport being a significant driver of dune change (Corr: -0.86).
Overall, this study highlights the critical need for integrating comprehensive modeling approaches with empirical data to inform coastal management practices. It offers a robust framework for future research aimed at enhancing the sustainability and resilience of coastal environments.
How to cite: Dabu, R., Roelvink, D., van Dongeren, A., and Garzon, J.: Alongshore Varying Dune Retreat at a Barrier Island, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-770, https://doi.org/10.5194/egusphere-egu25-770, 2025.
EGU25-8615 | Posters virtual | VPS25
Assessing Long-Term Water Dynamics in the Danube Delta Lakes using Sentinel-1 Radar ImageryMon, 28 Apr, 14:00–15:45 (CEST) | vP2.11
The EcoDaLLi project is an integrative initiative designed to contribute to the European Green Deal’s freshwater objectives by supporting the restoration, protection, and sustainable management of the Danube River Basin and its delta. As part of the broader mission "Restore Our Ocean, Seas & Waters by 2030," the project employs a systemic approach to ecosystem restoration through the implementation of innovative solutions and improved governance frameworks. By focusing on the Danube Basin, one of Europe’s most ecologically significant areas, EcoDaLLi aims to strengthen climate resilience, enhance biodiversity conservation, and promote sustainable water resource management. Additionally, Unitatea Executivă pentru Finanțarea Învățământului Superior, a Cercetării, Dezvoltării și Inovării (UEFISCDI) from Romania has awarded a special funding grant to support the present research.
A core scientific objective of the project is to document and analyze the dynamic behavior of the water surfaces in the Danube Basin. The present research relies on satellite radar imagery from the Sentinel-1 constellation, made available through the Copernicus Program. The radar data’s ability to penetrate cloud cover and record consistent surface reflections makes it highly suitable for long-term multi-temporal monitoring of water bodies, especially in a complex and variable environment such as the Danube Delta.
The initial phase involves the systematic collection of radar imagery, focusing on the VV polarization channel, which offers superior water isolation characteristics compared to other channels. In the second phase, a rigorous preprocessing workflow is applied to the raw imagery, including orbital corrections, radiometric normalization, and noise reduction. These steps are critical for ensuring data consistency and enabling precise extraction of water body extents. The processed data is then subjected to detailed geospatial analysis using advanced GIS tools, enabling the derivation of key hydrological metrics. These metrics include maximum and minimum water extent, presence and recurrence of water bodies, and seasonal variations.
The analysis will employ methodologies such as Continuous Change Detection and Classification (CCDC) to track and quantify spatial and temporal changes across the monitored lakes. Statistical models will further be used to correlate observed hydrological changes with climatic and environmental factors. The resulting datasets will provide a robust foundation for understanding the long-term hydrological dynamics of the Danube Delta’s lakes and their role in regional ecosystem functioning. Moreover, the results will offer guidelines for local and regional stakeholders, supporting evidence-based policy-making and adaptive management strategies.
Acknowledgments
This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI - UEFISCDI, project number PN-IV-P8-8.1-PRE-HE-ORG-2023-0089, within PNCDI IV.
How to cite: Toma, A. and Scrieciu, A.: Assessing Long-Term Water Dynamics in the Danube Delta Lakes using Sentinel-1 Radar Imagery, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8615, https://doi.org/10.5194/egusphere-egu25-8615, 2025.
