GM9.4 | River Deltas, Estuaries, and Coastal Wetlands
EDI
River Deltas, Estuaries, and Coastal Wetlands
Convener: Alvise FinotelloECSECS | Co-conveners: Anne BaarECSECS, Lisanne BraatECSECS, Jana Cox, Alice PuppinECSECS, Christian Schwarz, Davide TogninECSECS
Orals
| Fri, 19 Apr, 16:15–18:00 (CEST)
 
Room G1
Posters on site
| Attendance Fri, 19 Apr, 10:45–12:30 (CEST) | Display Fri, 19 Apr, 08:30–12:30
 
Hall X1
Posters virtual
| Attendance Fri, 19 Apr, 14:00–15:45 (CEST) | Display Fri, 19 Apr, 08:30–18:00
 
vHall X1
Orals |
Fri, 16:15
Fri, 10:45
Fri, 14:00
River deltas, estuaries, and coastal wetlands are critical transitional environments at the interface between land and sea. Ranking among the most valuable ecosystems on Earth, they provide important ecological functions and numerous ecosystem services such as coastal protection against storm impacts, biodiversity support, and climate change mitigation through carbon sequestration and storage.
However, these highly valuable coastal ecosystems face imminent threats from global climate change, land loss, and human activities, placing their long-term sustainability at risk. Unfortunately, predicting the fate of these environments remains challenging due to complex feedback between physical, biological, biogeochemical, and human-driven processes that drive morphodynamic adjustments to both natural and anthropogenically induced changes in relative mean sea level, sediment supply rate, and hydrodynamic forcings such as waves and tides.
This session aims to foster the required collaborative cross-disciplinary effort by bringing together a broad representation of the scientific communities focused on the study of fluvial and tidal estuarine landscapes. This includes, but is not limited to, research on hydrodynamics, hydrology, sediment properties and dynamics, geomorphology, bio-morphodynamics, ecology, biogeochemistry, impacts of climate change and global sea level rise, as well as implications for management and restoration.
We invite presenters to share recent scientific advancements in our understanding of the fluvial to marine transition zone through new theories, field studies, data-driven approaches, remote sensing analyses, geological reconstructions, laboratory experiments, and numerical modeling applied to coastal environments found on Earth as well as potentially on other planets. Furthermore, we welcome studies that focus on coastal environment adaptation, restoration, and management under projected climate changes.
By leveraging these tools and approaches, we aim to gain deeper insights into the ecomorphodynamics of critical coastal ecosystems, ultimately enhancing our ability to predict and improve their resilience at local, regional, and global scales.

Orals: Fri, 19 Apr | Room G1

Chairpersons: Alvise Finotello, Lisanne Braat, Jana Cox
16:15–16:20
16:20–16:30
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EGU24-17209
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ECS
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On-site presentation
Claudia Zoccarato, Pietro Teatini, Giulia Meneghini, Massimo Fabris, Andrea Menin, Michele Monego, Philip Minderhoud, Alessandro Gasparotto, and Jane Da Mosto

In recent decades, numerous projects aimed at restoring tidal morphologies have been planned and implemented. These initiatives are driven by the objective of reestablishing the vital services provided by these ecosystems. A key parameter for the ecological functionality of restored tidal ecosystems is the elevation of the landforms with respect to mean sea level. Non-optimal elevations can result in permanently submerged areas by the sea only a few years after their construction (i.e. when elevation is too low), and/or vegetation cover remains more patchy and less biodiverse than on natural marshes (i.e. when elevation is too high). In this contribution, we present recent work conducted between 2021 and 2023 to study a nourishment project realized in the central basin of the Venice Lagoon (Italy) to restore a 6.1-ha salt marsh. The marsh area was enclosed by wooden poles connected by geotextile and subsequently filled by dredged sediments using a nourishment pipe. The area was partially nourished in October 2021 and 2022 after the establishment of a specific monitoring network aimed at measuring the consolidation of the pristine lagoon bottom and the new infilled sediments. The network consists of 10 Nourishment Elevation Change (NEC) stations by which vertical movements were monitored with a topographic intersection technique at millimeter accuracy. Additionally, drone photogrammetry was employed to monitor the nourishment landform and elevation evolution through time. Additionally, a bathymetric survey and a 10-m deep core were carried out before the restoration activities to characterize the local morpho-geological setting of the lagoon platform. The data obtained by the campaign surveys provided detailed spatio-temporal evolution of nourishment infilling and consequential post-depositional sediment compaction. To simulate the evolutional process, the data has been integrated into a numerical simulator which couples groundwater flow and sediment consolidation equations in a 3D setting under the hypothesis of large deformations. Using Finite Elements, the numerical model describes sedimentation and compaction in an evolving domain where new elements are incorporated into the original domain when sedimentation takes place, and these elements undergo deformation as consolidation occurs. The model enables us to successfully reproduce the subsurface sediment beneath the salt marsh (based on the 10-m coring) and the marsh nourishment itself in 3D with appropriate sediment lithology characterization. This preliminary marsh reconstruction is fundamental for a comprehensive assessment of the salt marsh's ability to cope with future sea-level rise while also accounting for autocompaction of both the newly infilled sediments and the pre-existing, underlying deposits, which significantly contributes to lowering the marsh platform. Moreover, the model is used to quantify post-depositional compaction and provides a valuable tool to estimate required nourishments to eventually achieve the optimal marsh elevation for ecological functioning.

How to cite: Zoccarato, C., Teatini, P., Meneghini, G., Fabris, M., Menin, A., Monego, M., Minderhoud, P., Gasparotto, A., and Da Mosto, J.: Managing Marsh Nourishment Projects: An Integrated Measuring and Modeling Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17209, https://doi.org/10.5194/egusphere-egu24-17209, 2024.

16:30–16:40
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EGU24-9168
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ECS
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Highlight
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On-site presentation
Reinier Schrijvershof, Bas van Maren, Mick van der Wegen, and Ton Hoitink

The morphological configuration of estuaries and tidal basins influences future development because the channel-flat pattern and geometry control tidal dynamics and, as a result, residual sediment transport patterns. Large-scale human alteration of estuarine plan-form and channel dimensions, as a result of land reclamation, influences long-term evolution, because the existing balance of sediment import versus export is disrupted. The morphodynamic response to land reclamation is, however, slow, impacting the system for decades to centuries. Consequently, there are usually multiple human interventions cumulatively impacting the system. Our understanding of the cumulative effects of land reclamation and other anthropogenic interference is limited because observations usually do not span the complete morphological adaptation time. The Ems estuary (bordering The Netherlands and Germany) provides an unique site to study the effects of the cumulative impact of land reclamations and 20th-century human interference. Extensive storm surge-formed basins have been gradually reclaimed over a period of 500 years in this well-documented estuary, and dredging works dominated in the past century. Our objective is to quantify the effects of land reclamations and channel dredging on the historic evolution of the Ems estuary from century-scale observations combined with numerical morphodynamic modelling.

We compiled a digitized bathymetric dataset, spanning nearly the full reclamation period, from historical maps, nautical charts, and recent sounding observations. The dataset was used to reconstruct the morphological evolution of the estuary over the past 500 years. The centennial-scale morphodynamic trends show that the system responded to land reclamation by subtidal infilling and evolved from a multichannel system separated by shoals to a single channel system flanked by fringing flats. The long-term geometric changes show that the main system-scale morphodynamic adaptation is controlled by the effects of land reclamation. The present-day evolution is additionally influenced by the effects of 20th-century dredging works.

A process-based morphodynamic model (Delft3D-FM), forced with a synthetic spring-neap tidal cycle, was used to investigate the Ems estuary channel evolution in response to historical land reclamations. Simulation results showcase the transformation from an initially flat-bed bathymetry to a system with multiple channels and tidal flats when historic storm surge basins provide extensive intertidal areas. Simulations in which these former storm surge basins are reclaimed result in a single-channel system, confirming the influence of land reclamations on the observed evolution. The results of this study emphasize that, contrary to what is generally assumed, pre-dredging estuarine morphologies are often far from pristine. Ongoing research focuses on quantifying the interplay between natural and human-driven factors in century-scale channel evolution.

How to cite: Schrijvershof, R., van Maren, B., van der Wegen, M., and Hoitink, T.: Land Reclamation Controls on Estuarine Morphological Evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9168, https://doi.org/10.5194/egusphere-egu24-9168, 2024.

16:40–16:50
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EGU24-20007
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Highlight
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On-site presentation
Jose Rodriguez, Patricia Saco, Angelo Breda, and Steven Sandi

A common challenge when modelling long term wetland evolution is the limited amount of information on key ecogeomorphological components of the model. In addition, data integration is often needed due to computational constraints as some variables have an important short-term dynamics and models need to be run for long time periods.  In this work we present a simplified domain model that includes all relevant hydrodynamic, sedimentation and vegetation dynamics mechanisms that affect wetland evolution, and it is efficient enough computationally to allow the simulation of long time periods. We consider the effect of short-term sediment and tidal dynamics, and present methods that extract enough information from the time series that allow for efficient computation with acceptable margins of error. We find that results considering short term sediment and tidal variability display higher values of wetland accretion and resilience to sea-level rise than results using long term averages.

How to cite: Rodriguez, J., Saco, P., Breda, A., and Sandi, S.: How much information do we need for a realistic representation of coastal wetland evolution?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20007, https://doi.org/10.5194/egusphere-egu24-20007, 2024.

16:50–17:00
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EGU24-4787
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ECS
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On-site presentation
Gabriele Barile and Paola Passalacqua

Sediment partitioning at river bifurcations plays a crucial role in determining the morphological evolution of river deltas. However, we still lack a comprehensive understanding of the controlling factors that determine how sediments are partitioned at bifurcations, especially for suspended-load dominated systems such as river deltas. We employed dorado, a Lagrangian reduced-complexity particle tracking model, and a 2D shallow-water hydrodynamic model to investigate this gap. First, we routed sediment particles on calibrated hydrodynamic simulations performed for the Wax Lake Delta. The resulting asymmetries in the sediment partitioning at bifurcations showed good agreement with available field data on sediment concentration and observations of the spatial distribution of sand deposits in the different delta branches. To better interpret our results and extend them to similar deltaic contexts, we developed a simplified model of deltaic bifurcation and analyzed the possible controlling factors on sediment partitioning. We show how different planform controls influence sediment partitioning at the bifurcation node, including channel width, bifurcation angle, and bed elevation differences between the anabranches. Our analysis helps understand preferential pathways for sediment transport in river deltas, with noteworthy implications for delta management.

How to cite: Barile, G. and Passalacqua, P.: Controlling factors on sediment partitioning at deltaic bifurcations: a mixed Eulerian-Lagrangian modelling approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4787, https://doi.org/10.5194/egusphere-egu24-4787, 2024.

17:00–17:10
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EGU24-16273
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ECS
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Highlight
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On-site presentation
Marte Stoorvogel, Stijn Temmerman, Johan van de Koppel, Jaco de Smit, Lauren Wiesebron, Gregory Fivash, Jim van Belzen, Lotte Oosterlee, Ken Schoutens, Lennart van IJzerloo, Tom Maris, Patrick Meire, and Tjeerd Bouma

Tidal marshes can contribute to nature-based coastal protection by reducing both wave loading onto the shore and erosion of the shoreline. To implement such nature-based coastal protection requires knowledge on how to restore or create tidal marshes in such a way that they quickly become highly stable and erosion resistant. Hence, we aimed to identify the drivers controlling the rate by which sediment strength and erosion resistance build up in natural and restored (managed realignment, sand suppletion, and controlled reduced tide) tidal marshes, using three different approaches. That is, we quantified sediment strength and erosion resistance (1) at natural marsh locations of different age, (2) at a restored marsh in sediment layers of different age, and (3) in a controlled experiment with pots filled with sandy or muddy sediment subjected to four different tidal regimes, with pots either left bare or planted with a sparsely or a densely growing marsh pioneer species. Sediment strength and erosion resistance were measured by a broad range of techniques, including shear vane, penetrologger, and flumes.

Our results revealed several important drivers affecting the development of sediment strength and erosion resistance in tidal marshes. Firstly, a densely growing pioneer species (e.g., Spartina anglica) increased sediment strength faster than a sparsely growing pioneer species (e.g., Scirpus maritimus). Secondly, a smaller tidal inundation frequency as well as lower sediment water content  increased sediment strength and erosion resistance. Lastly, lower sedimentation rates led to stronger consolidation, and thus higher sediment strength, in deeper sediment layers. Overall, our research shows that to create erosion resistant sediment beds in future marsh restoration projects, one should ideally aim for densely vegetated tidal marshes with well-drained, cohesive sediments at relatively high intertidal elevation, where sedimentation rates are moderate. These conditions provide the highest chance of resulting in highly erosion resistant tidal marshes that can serve within a reasonable amount of time as a nature-based coastal protection strategy.

How to cite: Stoorvogel, M., Temmerman, S., van de Koppel, J., de Smit, J., Wiesebron, L., Fivash, G., van Belzen, J., Oosterlee, L., Schoutens, K., van IJzerloo, L., Maris, T., Meire, P., and Bouma, T.: Identifying the drivers of sediment strength and erosion resistance in natural and restored tidal marshes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16273, https://doi.org/10.5194/egusphere-egu24-16273, 2024.

17:10–17:20
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EGU24-19116
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ECS
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On-site presentation
Ewan Sloan, Nicholas Dodd, and Riccardo Briganti

Around 60% of global rivers do not form deltas, but relatively little attention has been given to the conditions at river mouths at which delta formation is prevented. Here we present an equation for predicting the spread of river-delivered sediments at coastlines subject to combined high energy waves and tidal ranges, for which delta formation is inhibited. This equation is validated against previous numerical modelling work on an idealised coast with a discharging river using Delft3D. The equation is derived from a mass-conserving bottom-evolution equation, reformulated to a partial differential equation, from which the analytical solution is determined using the method of Eigenfunction expansion.

The analytical approach is calibrated against the results of the Delft3D simulations, in order to determine values of two independent variables (downslope diffusion coefficient κ and input width B) controlling the shape of alongshore sediment distribution after a given time. This approach leads to only very small errors in determining alongshore sediment distribution when compared to the computationally expensive Delft3D simulations, and may be calculated in a fraction of the time.

How to cite: Sloan, E., Dodd, N., and Briganti, R.: A 1D analytical approach for predicting alongshore spreading of river-delivered sediments on macro-tidal and high wave-energy coastlines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19116, https://doi.org/10.5194/egusphere-egu24-19116, 2024.

17:20–17:30
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EGU24-19306
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On-site presentation
Sonia Silvestri, Zhicheng Yang, Tegan Blount, Andrea D'Alpaos, A. Brad Murray, and Marco Marani

Coastal wetlands are geomorphic systems highly sensitive to shifts in environmental forcings such as variations in fluvial sediment transport rates, sea level rise, subsidence rates, nutrient concentrations, temperature, and atmospheric CO2 levels. Despite these influences, the presence of vegetation growing on salt marshes significantly enhances their resilience. It mitigates surface and lateral erosion while fostering the accumulation of organic matter, which contributes to marsh soil accretion and the sequestration of organic carbon. Therefore, the characterization of vegetation properties, canopy biomass and species distribution, is crucial to provide a quantitative basis for bio-geomorphic modeling in coastal wetlands.

This study aims to spatially characterize key parameters—such as vegetation species distribution and biomass production—through repeated observations utilizing drone, airborne, and satellite multispectral (MS) imaging. The chosen site for this investigation is North Inlet in South Carolina (USA), renowned for its extensive tidal marshes supporting diverse vegetation species. MS and field data acquisitions were conducted in summer (August 2022 and August 2023), coinciding with the period of maximum biomass, and in winter (February 2023), corresponding to the phase of lowest biomass.

The application of a random forest (RF) approach proved highly effective in the unmixing process of halophytic vegetation species, enabling the retrieval of the percentage cover for each species. To train the algorithm, field observations were employed to classify drone-captured images within a limited section of the marshland. The random forest classification (RFC) algorithm achieves high accuracies in the classification of vegetation species based on the drone image, with a spatial resolution of about 0.02m and the overall accuracy of about 0.99. Based on this classification result, we applied the random forest regression (RFR) algorithm to unmix vegetation species using coarser-resolution WorldView2 data (pansharpened data with pixel of 0.5 × 0.5 m). Our results suggest that RFR achieves high accuracy in the unmixing process (0.80<R2<0.96 and 0.06<RMSE<0.14), enabling us to map the percentage cover of each species or bare soil over the entire North Inlet area. Furthermore, our field observations in August 2023 indicate strong correlations between Vegetation Indexes (VIs) derived from MS data, such as Normalized Difference Vegetation Index (NDVI), Soil Adjusted Vegetation Index (SAVI), Chlorophyll Index Green (CIg), and Chlorophyll Index Red (CIr), and marsh above-ground biomass (AGB). This suggests the potential utility of using multi-sensor MS data at various spatial scales to estimate marsh AGB.

We plan to incorporate field data from summer 2022 and winter 2023 to enhance the relationship between VIs and AGB, facilitating the estimation of AGB distribution over marshes. This analysis will be crucial for informing a spatially explicit bio-geomorphic model for marsh evolution (National Science Foundation Grant No. 2016068, project title: "Coupled Ecological-Geomorphological Response of Coastal Wetlands to Environmental Change").

How to cite: Silvestri, S., Yang, Z., Blount, T., D'Alpaos, A., Murray, A. B., and Marani, M.: Unmixing halophytes in coastal wetlands using a multi-sensor approach at two spatial scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19306, https://doi.org/10.5194/egusphere-egu24-19306, 2024.

17:30–17:40
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EGU24-1661
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ECS
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On-site presentation
Eise Nota, Brechtje van Amstel, Janneke Muller, Lotta Beyaard, Meryem Upson, Menno Wagenaar, Esmee van Amelsfort, Marcel van Maarseveen, and Maarten Kleinhans

Sandy estuaries are characterized by braided channel networks with continuously shifting channels and bars induced by tidal currents. Many estuaries have planforms confined by bedrock or human structures, which can topographically force local morphology by suppressing channel and sandbar migration. To what degree topographic forcing determines channel pattern and mobility is poorly understood, because it is challenging to obtain sufficient temporal and spatial data to completely grasp the timescales at which the morphology changes. In this study, we therefore acquired large temporal datasets through conducting scale experiments of sandy estuaries in the periodically tilting tidal flume, the Metronome. We conducted several experiments with initial flat beds and fixed banks of different configurations using rough sandpaper, with at least one repeat experiment for each configuration, as well as a control run without fixed banks. From our data animations, we observe the formation of topographically forced sandbars as well as channel scours at fixed banks that are consistent between repeat experiments. Moreover, we discovered quasi-periodic formation and disappearance of non-forced sandbars and channels. For one fixed embankment configuration, the channel network rapidly shifted between three stable states, suggesting that aspects of the system morphodynamics may be described by coupled oscillators. Repeat experiments exhibit notable differences in periodicity of this cyclic behaviour, implying sensitivity of the complex system dynamics to initial conditions. These results confirm suspicions based on observations and linear stability analyses that shifting between alternative quasi-stable states can happen in estuaries, which provides a major challenge for field observations and numerical modelling of the dynamics of natural estuaries.

How to cite: Nota, E., van Amstel, B., Muller, J., Beyaard, L., Upson, M., Wagenaar, M., van Amelsfort, E., van Maarseveen, M., and Kleinhans, M.: Topographic forcing of estuarine channel networks by fixed banks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1661, https://doi.org/10.5194/egusphere-egu24-1661, 2024.

17:40–17:50
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EGU24-17347
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ECS
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On-site presentation
Aron Slabon, Dörthe Holthusen, Lorenzo Rovelli, Annika Fiskal, Andreas Schöl, Ole Rössler, Thomas Hoffmann, and Christine Borgsmüller

The Ems estuary (NW Germany) is characterized by a hyper-turbid state with sediment concentrations ranging from < 1 g/L up to several hundred grams per liter. In summer, when upstream discharge decreases and biomass production increases, substantial fluid mud layers (sediment concentration > 10 g/L) accumulate, particularly during low tides. The thickness of the fluid mud layer reaches a significant fraction of the water column (up to 60%), thus affecting cross-sectional hydrodynamics as well as navigability. Extensive monitoring with high temporal and vertical resolution is required to understand the processes controlling the formation and compaction of the fluid mud layers, given their high temporal and spatial variability.

Between August 2019 and September 2019, two vertical probe arrays were installed in the Lower Ems estuary (km 11.775) equipped with multi-parameter probes (pressure, salinity, oxygen, and current velocity), optical backscatter turbidity sensors, and additional oxygen loggers. The probes/loggers are deployed at three different depths (approx. 1.15m above bed, 1.95m above bed, and attached to a buoy at the surface) measuring continuously every 5 min. Thus, a high-resolution time series with decent vertical resolution over a period of six weeks has been recorded.

Six weeks of monitoring revealed two superimposed cycles of fluid mud occurrence. On a shorter timescale, fluid mud occurrence is separated by distinct stages of formation, entrainment, and stratification throughout a tidal cycle. However, on a longer timescale, fluid mud occurrence is affected by the neap-spring tide. Here, we identify four main stages: buildup, stationary state, breakup, and no presence of fluid mud, each stretching over multiple tidal cycles. Each stage is characterized by distinct differences in, e.g., turbidity, salinity, and oxygen gradients/dynamics. Our approach successfully enables monitoring of fluid mud in the hyper-turbid Ems estuary for a better understanding of the processes of fluid mud formation and breakup. Future research aims to develop predictive models for the occurrence of hyper-turbid conditions and different fluid mud stages in the Ems estuary.

How to cite: Slabon, A., Holthusen, D., Rovelli, L., Fiskal, A., Schöl, A., Rössler, O., Hoffmann, T., and Borgsmüller, C.: Fluid Mud Occurrence in the Hyper-Turbid Ems Estuary: Insights into Tidal Cycle Influence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17347, https://doi.org/10.5194/egusphere-egu24-17347, 2024.

17:50–18:00
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EGU24-20176
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ECS
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On-site presentation
Yizhang Wei, Barend van Maanen, Danghan Xie, Zeng Zhou, and Christian Schwarz

Coastal wetlands, salt marshes and mangroves, fulfil important functions for biodiversity conservation and coastal protection, which are inextricably linked to interactions between hydrodynamics, sediment transport and ecology the so-called eco-geomorphological feedback. However, range expansion patterns of salt marshes and mangroves are changing due to both human influences and global change. Human driven introduction of salt marsh species for erosion mitigation starting in the last century e.g. (Europa and China) are influence natural mangrove habitats and its implications are still unfolding. Conversely, within the last decades, a climate change induced ubiquitous trend of mangrove encroachment on salt marshes has been observed globally in the mangrove-salt marsh transition zones, e.g. the southern USA, South America, Australia, New Zealand and South Africa. Here we present a novel eco-morphodynamic model able to predict species-species interactions, i.e. competition and facilitating, sediment transport on morphodynamics. The aim of our study is to predict competitive outcomes of mangrove-saltmarsh interactions resulting from the interaction of species-specific growth and stress tolerance, and additional natural and climatic factors. First results indicate the competitive outcome to be context dependent on the relative growth properties of the mangrove and salt marsh species in question. Thereby providing highly need to context to interpret implication on shifts in species ranges on morphodynamic wetland development. 

How to cite: Wei, Y., van Maanen, B., Xie, D., Zhou, Z., and Schwarz, C.: Implications of changes in range expansion behavior of salt marshes and mangroves on dominant wetland cover and morphodynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20176, https://doi.org/10.5194/egusphere-egu24-20176, 2024.

Posters on site: Fri, 19 Apr, 10:45–12:30 | Hall X1

Display time: Fri, 19 Apr, 08:30–Fri, 19 Apr, 12:30
Chairpersons: Anne Baar, Alice Puppin, Davide Tognin
X1.100
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EGU24-12648
Ed Garrett, Sönke Dangendorf, Fiona Hibbert, Craig Smeaton, William E.N. Austin, Natasha L.M. Barlow, Martha B. Koot, William Blake, and W. Roland Gehrels

The ability of saltmarshes to accrete sediments and keep pace with sea-level rise is key to their multifaceted role as nature-based solutions to current environmental challenges, including their capacity to accumulate and store ‘blue’ carbon. While saltmarshes can gain elevation through in-situ organic production and trapping of organic and minerogenic sediments, thresholds exist above which rates of sea-level rise outstrip saltmarshes’ vertical accretion capability. Current and future anthropogenically enhanced rates of sea-level rise may therefore pose a significant threat to saltmarsh resilience. A negative accretionary balance (i.e. sea-level rates exceeding sediment accumulation) may result in transgression and potentially erosion, impacting on a range of ecosystem services and threatening stored carbon. Consequently, understanding the relationship between sea-level rise and saltmarsh accretion is critical for projecting future changes to saltmarsh ecosystems. Here, we use age-depth models based on Bayesian analysis of 210Pb, 137Cs and 241Am activities to quantify sediment accumulation rates for 34 cores from 21 saltmarshes distributed around the coastline of England, Scotland, and Wales. These sites were selected to encompass the range of different marsh types found in Great Britain, including large open-coast systems, back barrier, estuarine-fringing, and loch-head marshes. Site average sedimentation rates vary between 0.12 and 1.28 cm yr-1, with a mean of 0.41 ± 0.16 cm yr-1. We compare sedimentation rates at 1 cm depth increments with corresponding site- and time-specific rates of sea-level rise, modelled using estimates of barystatic, sterodynamic and inverse barometric contributions that we benchmark against long tide-gauge records. This comparison enables us to determine the accretionary balance and its development since the start of the 20th century at each core location. We discuss these results in the context of spatially explicit projections of accelerated future sea-level rise around the coast of Great Britain.

How to cite: Garrett, E., Dangendorf, S., Hibbert, F., Smeaton, C., Austin, W. E. N., Barlow, N. L. M., Koot, M. B., Blake, W., and Gehrels, W. R.: The accretionary balance of saltmarshes in Great Britain since 1900, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12648, https://doi.org/10.5194/egusphere-egu24-12648, 2024.

X1.101
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EGU24-15885
Jonathan Dale, Gabby Ciappara, Michelle Farrell, Michael Kennedy, and Cai Ladd

Saltmarshes provide important ecosystem services including habitat for wading and migratory birds, nursery grounds for commercial fish species, carbon storage, and flood defence through wave attenuation. Stimulating saltmarsh growth may improve the local level of flood protection, reducing the need for costly engineering works to sea walls and defences, whilst also enhancing the provision of other services. This is particularly important at locations where there is a need to restore and compensate for the loss of saltmarsh due to erosion caused by sea level rise, land claim, and a reduction in sediment supply.  One method of encouraging marsh growth is through the construction of sedimentation fields or polders, typically out of brushwood fencing, to reduce current velocities and wave heights with the aim of increasing sedimentation rates.  However, little is known of the impact polders have on the timing and rate of sediment delivery, or of saltmarsh response to changes in hydrodynamics. This is particularly the case for relatively exposed sites with a large tidal range, with most sedimentation fields constructed in sheltered locations with micro- to meso-tidal ranges such as the Wadden Sea.

Here, we present results from a study of a macro-tidal sedimentation field at Rumney Great Wharf, Severn Estuary, Wales, which was constructed between 1999 and 2005. Field investigations, conducted during May to June and November to December 2023, involved the deployment of sediment traps and measurements of the current velocity and suspended sediment concentration to assess spatial and temporal variations in sediment delivery. Results indicate increased sediment availability in areas of lower elevation, with sediment trap data suggesting a difference of up to 3.7 g / cm2 / day due to elevation differences. Sediment cores were also collected and analysed from both inside and outside of the polders to assess the physical functioning of the marsh that has formed following polder construction.

Findings provide insights into the suitability of sedimentation fields as a form of saltmarsh restoration and coastal flood defence, which are discussed in terms of mitigating against sea level rise and increased storm magnitude and frequency. This study also provides an evaluation of the potential for wider implementation of sedimentation fields as part of shoreline management strategies. It is recommended that further assessment is conducted to evaluate the influence of fence design, including length, height, and orientation, on site evolution to maximise provision of flood defence and wider ecosystem service delivery from these schemes.

How to cite: Dale, J., Ciappara, G., Farrell, M., Kennedy, M., and Ladd, C.: Saltmarsh restoration through construction of sedimentation fields: controls on sediment delivery and hydrodynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15885, https://doi.org/10.5194/egusphere-egu24-15885, 2024.

X1.102
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EGU24-6298
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ECS
Joe Agate, Ray Ward, Chris Joyce, and Niall Burnside

The number of salt marsh restoration schemes is set to increase substantially this decade, driven by three key factors: a) legislative requirements to compensate for losses; b) a transition to a natural approach for coastal management; and c) growing interest in ecosystem services salt marshes provide. Monitoring is key to evaluating the success of restoration projects and can inform future projects. However, many schemes have been found to use ineffective monitoring strategies. A major barrier to developing effective monitoring programmes has been the resources required to carry out frequent, spatially explicit surveys using traditional survey methods, which will become an even greater problem as more schemes are created. Consequently, improvements to survey methods are required.

This project aims to improve our understanding of the role that remote sensing combined with field data can play in assessing the development of salt marsh restoration programmes. To address this aim, monitoring has been carried out at a new restoration site in the Adur estuary, on the south coast of the UK, since its creation in 2019. Field data has been collected, including biannual changes in species cover along transects. These surveys have found positive development at the Adur site, with clear successional changes in vegetation cover. Drone flights have also been carried out at the site to accompany the transect surveys, with machine learning algorithms used to develop models of the observed changes. Preliminary testing has found the machine learning models produce accurate results, demonstrating that remote sensing can be a valuable asset to existing monitoring practices.

How to cite: Agate, J., Ward, R., Joyce, C., and Burnside, N.: Monitoring and Assessment of Salt Marsh Restoration Using Field and Remotely Sensed Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6298, https://doi.org/10.5194/egusphere-egu24-6298, 2024.

X1.103
|
EGU24-7257
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ECS
Xinghua Xu, Xiayang Yu, and Pei Xin

Soil temperature has a marked effect on ecological processes in salt marshes and is significantly affected by tidal fluctuations. Periodic tidal inundation modifies the heat exchange between marsh sediments and the atmosphere, and also induces additional heat exchange between the sediments and tidal water. Tide-driven porewater flow further modulates heat transfer within the sediment, a process complicated by seasonal variations in atmospheric and tidal temperatures. In addition, macropores such as crab burrows are common in salt marsh sediments, and they are expected to regulate heat exchange and temperature distribution within the salt marshes by altering water movements. This study aims to explore how spring-neap tides and atmospheric conditions collectively influence heat exchange and temperature dynamics in salt marshes. We developed a marsh-creek model incorporating sediment-atmosphere/water heat exchange and validated it against laboratory experiments. Extending the model to the field scale, we analyzed temperature dynamics across the marsh and heat fluxes at the sediment-atmosphere/water interfaces over an annual cycle. We also compared simulation outcomes of water and heat dynamics in scenarios with and without macropores. Finally, we discussed the implications of our findings for accurately assessing tidal and atmospheric heat exchange and the associated temperature variations.

How to cite: Xu, X., Yu, X., and Xin, P.: Tidal influence on heat exchange and temperature dynamics in salt marshes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7257, https://doi.org/10.5194/egusphere-egu24-7257, 2024.

X1.104
|
EGU24-5879
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ECS
Marie Arnaud, Melissa Bakhos, Cornelia Rumpel, Marie-France Dignac, Richard J. Norby, Nicolas Bottinelli, Jonathan Deborde, Philippe Geairon, Pierre Kostyrka, Julien Gernigon, Jean-Christophe Lemesle, and Pierre Polsenaere

Salt marshes are among the most efficient blue carbon (C) sinks in the world, partly due to the slow decomposition of their plant-derived organic matter (OM) in the soil. The fate of this C sink under sea-level rise is still uncertain due to limited knowledge about the processes controlling OM decomposition under different inundation levels. In an in-situ manipulative experiment, we compared salt marsh OM decomposition and quality across simulated sea-level scenarios and litter types (absorptive root, fine transportive root, leave, and rhizome of the shrubby C3 halophyte Halimione Portulacoide) for 170 days. The OM decomposition rate varied only between the longest and shortest inundation treatments, that was lower than the mean inundation of our site. The OM decomposition and C loss rates varied strongly across litter types. Fine absorptive was the slowest to decay, releasing up to 40% less C than the other litter types. Changes in lignin composition varied across litter types, but were unaffected by sea-level rise scenarios. Our study suggests that 1) the assessment of soil C dynamics in salt marshes based on aboveground litter or bulk belowground litter patterns is inadequate because of a marked difference in OM decomposition across litter types; 2) belowground litter lignin quality could be a good proxy for OM decomposition in salt marshes; and 3) sea-level rise is unlikely to decrease OM decomposition under current sea-level rise projections.

How to cite: Arnaud, M., Bakhos, M., Rumpel, C., Dignac, M.-F., Norby, R. J., Bottinelli, N., Deborde, J., Geairon, P., Kostyrka, P., Gernigon, J., Lemesle, J.-C., and Polsenaere, P.: Salt marsh organic matter quality and decomposition under sea-level rise scenarios: from leaves to fine absorptive roots , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5879, https://doi.org/10.5194/egusphere-egu24-5879, 2024.

X1.105
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EGU24-961
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ECS
Angelica Piazza, Davide Tognin, Devis Canesso, and Luca Carniello

Coastal wetlands are important transitional environments, providing several ecosystem services such as carbon sequestration, water filtration and habitat provision for diverse plant and animal species. At the same time, various human activities, such as fishing, aquaculture, tourism and industrial operations, are centred around coastal wetlands. Therefore, the morphological evolution of many coastal transitional systems is not only influenced by natural processes, namely tidal currents and wind waves, but also anthropogenic interventions have been playing a pivotal role in adapting the morphological features to meet the needs of human activities. For instance, extensive areas are usually confined by artificial levees for aquacultural activities, large channels are dredged and inlets are stabilized for navigation purposes. However, the long-term effects of these modifications on the morphological evolution of shallow tidal systems are still unclear and can potentially affect the ecosystem as a whole.

The aim of this work is to investigate the consequences of natural and anthropogenic drivers on two back-barrier lagoons in the northern Adriatic Sea: the Venice Lagoon and Marano-Grado Lagoon. Despite sharing a similar microtidal regime and meteorological conditions, the morphology of these systems exhibits distinct characteristics. The Venice Lagoon is about 550 km2 and it is connected to the Adriatic Sea with three inlets. Its evolution has been strongly affected by human interventions, such as the construction of jetties at the inlets at the beginning of the 20th century, the excavation of navigable channels between 1930 and 1970 and, more recently, the installation of a storm-surge barrier system, named Mo.S.E., to prevent flooding of the city of Venice. Instead, the Marano-Grado Lagoon is smaller, covering an area of 160 km2, and it is relatively more pristine than the Venice Lagoon. It is connected to the Adriatic Sea with six inlets, of which only two were provided with jetties in the 20th century, and it experienced fewer modifications of channels for navigation purposes.

We applied a 2D, finite-element model to describe the hydrodynamic flow field and the wind-wave generation and propagation in these two environments. The computational grids were built upon the most recent bathymetric survey available for each system, that is the 2017 survey for the Venice Lagoon and the 2011 survey for the Marano-Grado Lagoon. We then performed an extensive calibration of the model with water level and discharge data available. Results allowed us to investigate similarities and differences in the hydrodynamics of the two tidal systems, highlighting the effects of specific anthropogenic interventions on the ecosystems.

How to cite: Piazza, A., Tognin, D., Canesso, D., and Carniello, L.: Interplay between natural drivers and human activities in two Northern Adriatic lagoons, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-961, https://doi.org/10.5194/egusphere-egu24-961, 2024.

X1.106
|
EGU24-16633
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ECS
Alvise Finotello, Chao Gao, Eli D. Lazarus, Andrea D'Alpaos, Massimiliano Ghinassi, Alessandro Ielpi, Andrea Rinaldo, Gary Parker, Peng Gao, Ya Ping Wang, and Davide Tognin

The sinuous channels that wind through tidal coastal wetlands resemble meandering rivers. However, features indicative of active meandering over time, such as oxbow lakes and meander cutoffs, are challenging to find in tidal realms. Specifically, while alluvial plains shaped by meandering rivers are filled with scars of meander cutoffs, tidal coastal settings have been perceived by geomorphologists for much of the past century as lacking morphological evidence of cutoff events, even though both environments exhibit similar meander-planform dynamics and width-adjusted migration rates. This led to the broad interpretation that tidal and fluvial meanders differ morphodynamically.
We re-examined this conclusion by identifying, measuring, and compiling examples of meander cutoffs from various tidal coastal wetlands and fluvial floodplains worldwide. We suggest that cutoffs in tidal meanders are far more widespread than previously thought, and the shapes and geometric properties of tidal and river cutoffs are indeed remarkably similar. This indicates that while tidal and fluvial environments differ in many ways, they nevertheless share the same physical mechanism affecting meander morphodynamical evolution.
The perceived scarcity of tidal cutoffs is likely a result of pronounced channel density and hydrological connectivity in coastal wetlands, coupled with the reduced size of most tidal channels and dense vegetation cover. Moreover, despite allegedly similar forming mechanisms, morphodynamic differences arise after meanders have cut off. We observe that tidal meanders remain preferentially connected to the channel from which they originated, preventing the formation of crescent-shaped oxbow lakes and thus making tidal cutoffs more difficult to detect.
While these factors do not erase tidal meander cutoffs, they collectively inhibit oxbow-lake formation and render tidal cutoffs ephemeral, hardly detectable geomorphic features. We thus argue that similar morphodynamic processes drive cutoff formation in tidal and fluvial landscapes, with differences arising only during post-cutoff evolution. This bears important implications for understanding the ecomorphodynamics of coastal wetlands and predicting their long-term evolution.

How to cite: Finotello, A., Gao, C., Lazarus, E. D., D'Alpaos, A., Ghinassi, M., Ielpi, A., Rinaldo, A., Parker, G., Gao, P., Wang, Y. P., and Tognin, D.: Stream Meandering in Coastal Wetlands: Patterns, Processes, and Ecomorphodynamics Implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16633, https://doi.org/10.5194/egusphere-egu24-16633, 2024.

X1.107
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EGU24-17274
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ECS
Dawei Wang, Junhong Bai, Chuanhui Gu, Olivier Gourgue, Jean-Philippe Belliard, Liyue Cui, Yinghai Ke, Liming Xue, Lixiang Wen, and Stijn Temmerman

Biogeomorphic interactions between tidal channels and marsh plants play a crucial role in enhancing coastal resilience to climate change. Previous studies linking the channel formation with vegetation dynamics predominantly focused on the early initiation, characterized by local-scale plant-flow feedbacks. However, the influence of rapid changes in landscape-scale vegetation pattern on the channel initiation remains poorly understood, especially in micro-tidal system. In this study, we investigated this relationship through biogeomorphic modeling combined with the analysis of satellite images in a rapidly expanding marsh in China under Spartina alterniflora invasion. The satellite images demonstrated the increase in drainage density and the decrease in unchanneled path length following plant encroachment. Our modeling results showed that local flow acceleration between vegetation patches was insufficient to initiate channels rapidly before the merging of isolated patches under micro-tidal conditions. With plant expansion, the continuous marsh caused landscape flow diversion from homogenous platform flow to concentrated channel flow, which promoted evident tributary channel initiation in the landward marsh zone. The vegetation removal scenarios further highlighted that the flow divergence from adjacent platforms due to the spatial heterogeneity in plant configuration amplified the magnitude of local hydrodynamics and further channel incision. Our findings emphasize that the initiation of tidal channels not only depends on local plant-flow interaction but is largely driven by landscape vegetation configuration under micro-tidal conditions.

How to cite: Wang, D., Bai, J., Gu, C., Gourgue, O., Belliard, J.-P., Cui, L., Ke, Y., Xue, L., Wen, L., and Temmerman, S.: How does landscape vegetation configuration regulate local channel initiation in rapidly expanding marsh?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17274, https://doi.org/10.5194/egusphere-egu24-17274, 2024.

X1.108
|
EGU24-20854
Numerical modeling of the tidal oyster mussel bed interactions with fine sediment in the Ems estuary
(withdrawn after no-show)
Gholamreza Shiravani, Dennis Oberrecht, and Andreas Wurpts
X1.109
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EGU24-5150
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ECS
Sjoukje de Lange, Anne van der Wilk, Claire Chassagne, Waqas Ali, Ton Hoitink, Maximilian Borne, Kristian Brodersen, and Kryss Waldschläger

Flocculated particles, formed by the aggregation of clay particles, are common in rivers. These flocs exhibit a different behaviour than primary particles: they can deform and break apart, and they have greater settling velocities than the particles of which they are composed. The latter allows flocs, unlike primary clay particles, to deposit on the river bed in mildly turbulent conditions, potentially leading to interactions with the bed. Particularly in sand-bedded rivers, where bedforms shape the riverbed, there exists a potential interaction between flocs and the riverbed.

Physical experiments were carried out in an annular flume, using a flocculant to induce flocculation. Different amounts of flocculant and various shear stress conditions were applied, and the resulting floc characteristics and bedform geometry were measured.

Under lower shear conditions, the flocs were larger and transport rates were lower than under high shear conditions. However, under both shear conditions, flocs were transported via saltation and in suspension, and they became integrated within the sediment bed either as individual flocs, clusters, or sheets. Deposition occurred predominantly on the leeward side of the dune, revealing distinct stratigraphy patterns. The presence of flocs had a negligible impact on the actual geometry of the bedforms.

This investigation highlights the active role of flocculated clay particles in sediment transport in riverine systems, contrary to the general assumption that clay particles behave passively as wash load. This finding has the potential to affect sediment transport rates of fines and contaminants and could have far-reaching impacts on the interpretation of mud deposits in the sedimentary rock record. For modelling and predicting the sediment dynamics in river systems a comprehensive understanding of the transport mechanisms of clay flocs is essential and should be taken into account.

How to cite: de Lange, S., van der Wilk, A., Chassagne, C., Ali, W., Hoitink, T., Borne, M., Brodersen, K., and Waldschläger, K.: The capturing of flocs by migrating subaqueous dunes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5150, https://doi.org/10.5194/egusphere-egu24-5150, 2024.

X1.110
|
EGU24-10523
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ECS
Thomas E Nichols, James E Houghton, Richard H Worden, Robert A Duller, Joshua Griffiths, and James E P Utley

Sedimentary cores from the Ravenglass Estuary, NW England, lack some of the sedimentary structures which can be seen in other estuarine sands due to their unconsolidated nature, making it difficult to meaningfully interpret depositional environments using standard sedimentological facies analysis. Here we explore how sediment texture, obtained from laser particle size analysis, and bulk geochemistry, obtained from portable X-ray fluorescence, can be used independently, or in combination, within a machine learning model to automatically classify sub-depositional environment and estuarine zone at the estuary surface to create a model which can be used to classify subsurface sediment samples. Using an adapted an established machine learning workflow we select the most informative geochemical elements to be included in the training set for the classification model.

The most important geochemical elements for modelling represent major elements of the most abundant minerals in the estuary, and minor elements representing trace signals of sulfide mineral deposits present in the hinterland. Models that are trained exclusively on textural data significantly outperform those that use geochemical data when classifying sub-depositional environment but are comparable when classifying estuarine zone. However, the combination of textural and geochemical data in training sets improves model performance in all but one class when compared to separate textural and geochemical models.

Ultimately, we have applied the surface-calibrated combined textural and geochemical model to classify paleo-sub-depositional environment in geotechnical cores obtained from the Ravenglass Estuary. This allows us to interpret their environmental evolution and build scaled correlation panels spanning key areas of the estuary to suggest how the estuary has changed since its formation.

How to cite: Nichols, T. E., Houghton, J. E., Worden, R. H., Duller, R. A., Griffiths, J., and Utley, J. E. P.: Using sediment texture and geochemistry as predictors to automatically classify sub-depositional environments in a modern estuary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10523, https://doi.org/10.5194/egusphere-egu24-10523, 2024.

X1.111
|
EGU24-21037
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ECS
Connor Broaddus and Efi Foufoula-Georgiou

Deltas are among Earth’s most important depositional landforms. They host megacities, serve as ecological hotspots, and control fluxes of water, sediment, and nutrients between terrestrial and marine domains. Nearly all river deltas are subject to some degree of wave-influence, and most river mouths are wave-dominated. These systems exhibit strong spatiotemporal variability across a range of scales and form under hydrodynamic conditions that are highly nonlinear. As a result, the processes involved in the formation and evolution of wave-influenced deltas are poorly understood, limiting our ability to predict how they will respond to future changes.

Here we explore the factors governing wave-influenced delta evolution using a coupled flow-wave-transport model (Delft3D-SWAN). We present the first physics-based simulations to correctly reproduce the morphological attributes commonly observed in wave-influenced deltas (smooth cuspate shorelines, simple distributary networks, systems of barriers and lagoons) and capture the emergent processes that govern their evolution.

We show that wave-influenced deltas grow through a combination of shoreface accretion, crevasse splays, and distributary channel avulsions. Shoreface accretion occurs when fluvial sediment is deposited in the nearshore faster than it can be removed by wave-driven currents, and manifests as spit / barrier growth and migrating sand waves. Splays and avulsions lead to aggradation on the delta top, but also increase the area over which fluvial sediment is distributed, effectively decreasing the deposition rate at each channel mouth and in turn limiting shoreface accretion. We show that for a given wave climate, the relative importance of these processes determines a delta’s morphology and is controlled by the fluvial sediment composition and the receiving basin depth via the distributary channel network. In systems with shallow receiving basins or high sand loads, distributary channels are shallow, wide, and unstable. Network reorganization is frequent, creating deltas with smooth shorelines, many distributaries, and few barrier features. By contrast, a deep receiving basin or an abundance of cohesive fluvial sediment leads to enhanced levee formation, stabilizing distributary channels and reducing network complexity. Simpler networks deliver proportionally more water and sediment to individual distributary mouths, favoring shoreface accretion and leading to deltas with high protrusion angles and an abundance of barrier features.

Our results provide insight into the processes involved in wave-influenced delta growth and the factors governing those processes. This information can be used to improve stratigraphic interpretation of delta deposits and helps inform sediment management practices for improving delta resilience in the face of anthropogenic pressures, such as land use and climate change.

How to cite: Broaddus, C. and Foufoula-Georgiou, E.: Controls on the growth of wave-influenced river deltas: The roles of fluvial sediment composition and basin depth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21037, https://doi.org/10.5194/egusphere-egu24-21037, 2024.

X1.112
|
EGU24-17737
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ECS
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Highlight
Octria Adi Prasojo, Martin D. Hurst, Richard D. Williams, Larissa A. Naylor, and Jaime Toney

Estuaries worldwide are expected to suffer increasing tidal flood risk due to climate change. Climate change is causing sea-level to rise and storm frequency and severity to increase, inducing more frequent tidal floods in estuaries, where most of the world’s largest cities are located. The key to mitigating this flood risk is by reducing tidal propagation from offshore to onshore. Flood alleviation in an estuary requires slowing down the passage of water coming into an estuary, rather than creating space for flood water. There is a nearly infinite supply of water flooding an estuary and thus, in contrast to terrestrial rivers, making space is not an effective solution for flood risk mitigation. To test this hypothesis, we investigate the effectiveness of natural tidal flood interventions for reducing water surface elevations along estuaries by performing sensitivity analyses on a 1D analytical model of tide propagation for estuaries worldwide, considering the impacts of future sea level rise. We find that increasing estuary bed roughness is the most efficient tidal flood intervention, whereas adding space for flood water has minimal impact on water surface elevations. A more focused  2D numerical model experiment simulating the hydrodynamics of the Clyde Estuary, Scotland, also reveals that roughening the estuary bed and banks significantly slows down the passage of water by absorbing tidal wave energy, delaying the tidal wave peak arriving from offshore and consequently reducing water surface elevation and tidal flood extent. However, the 2100 SLR projection consistently reduces the effectiveness of all such interventions, highlighting the challenges of implementing the most effective solutions for alleviating future tidal flood risk.

How to cite: Prasojo, O. A., Hurst, M. D., Williams, R. D., Naylor, L. A., and Toney, J.: Slowing down the tidal flood wave is the key to reducing tidal flood risk in estuaries worldwide, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17737, https://doi.org/10.5194/egusphere-egu24-17737, 2024.

Posters virtual: Fri, 19 Apr, 14:00–15:45 | vHall X1

Display time: Fri, 19 Apr, 08:30–Fri, 19 Apr, 18:00
Chairpersons: Christian Schwarz, Alvise Finotello, Lisanne Braat
vX1.18
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EGU24-19676
Inga Nordhaus, Verena Merk, and Gregor Scheiffarth

Soft sediment coasts are shaped by interactions between sedimentological and biological processes. Intertidal shellfish beds of the World Heritage site ‘Wadden Sea’ are an important habitat with a variety of sedimentological and ecological functions. They are dominated by two ecosystem engineers, the native Blue mussel (Mytilus edulis) and the invasive Pacific oyster (Magallana gigas). Their extents and biomasses are highly variable and are influenced by many environmental factors as well as human interventions. Among the latter, continuous dredging and dumping of sediments for the maintenance of shipping channels and harbours in the large German estuaries and rivers have led to a change in natural sediment dynamics and are suspected to influence the occurrence of mussel beds and seagrass areas in the Wadden Sea National Parks. The outer Ems estuary is a prime example in this context. River deepening and maintenance dredging have been taking place for decades and have led to heavy siltation and lack of oxygen in the lower Ems and an increased water turbidity can also be observed in the outer Ems. In addition, coastal construction measures have caused morphological changes in ​​the Ems estuary.

Within an interdisciplinary project, changes in the morphodynamics, sediment transport and currents are being investigated and methods are developed that allow an assessment of resulting ecological effects on mussel beds, as well as their sedimentological feedbacks in the outer Ems estuary. Investigations on the extent to which sediment shift and deposition affect the occurrence of mussel beds are lacking in the Lower Saxon Wadden Sea. For this purpose, detailed measurements of sedimentation and erosion on selected mussel beds and analyses of the sediment composition were conducted with high spatial and temporal resolution between 2019 and 2023 using sedimentation-erosion-bars and analysis of grain size composition. Mussel beds with different distance to the sediment deposition sites and areas with dense mussel and oyster colonization, gaps in the mussel bank and the tidal flats around the banks were compared. In addition, the extent and biomass of the mussel beds and the condition of Blue mussels were examined and related to sedimentation rates. The results will be presented and discussed against the background of sea level rise in the Wadden Sea and will be provided as a basis for the development of an ecological sediment management for the outer Ems estuary. Within the interdisciplinary project it will be considered how sediments can be sensibly directed to prevent siltation of mussel and seagrass areas on the one hand and to support the natural growth of the seabed where sediments are needed on the other hand, safeguarding the outstanding universal value of the World Heritage site.

How to cite: Nordhaus, I., Merk, V., and Scheiffarth, G.: Influence of river sediment management on the sedimentology and ecology of shellfish beds within the World Heritage site ‘Wadden Sea’, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19676, https://doi.org/10.5194/egusphere-egu24-19676, 2024.