To limit global warming to 2 °C or below, the IPCC emphasizes the need for large-scale carbon dioxide removal (CDR) alongside emissions reductions. There is a growing recognition of ocean-based CDR techniques and expanded research is needed. This thesis investigated the long-term (>100 years) carbon sequestration potential of enhancing the biological carbon pump by ocean nitrogen fertilization, a research domain which so far has received little attention. The objective was to make an initial rough quantification of the (cumulative) CDR potential of one-off ocean nitrogen fertilization achieved within 5 years after the fertilization, to evaluate its potential as a global CDR technique and for commercial implementation.
An idealized one-dimensional vertical (1DV) model framework, coupling a marine ecosystem model with a vertical eddy diffusion physical model, was established to simulate ocean nitrogen fertilization, incorporating essential processes of ocean productivity and the biological carbon pump. Half of the ocean was excluded from the framework since these regions are incompatible with 1DV modelling. Additionally, regions where nitrogen is not the first limiting nutrient were excluded. Various fertilization simulations were performed in which the nitrogen limitation in the mixed layer of the remaining ocean areas was replenished by a one-off addition. Long-term carbon sequestration resulting from fertilization was assessed by comparing these simulations with baseline simulations of the biological carbon pump. An aggregated global outcome, forming the basis for feasibility assessment, was derived by averaging over simulations, while excluding hexagons with low sequestration efficiency as they contribute insignificantly to CDR.
In principle, the one-off nitrogen fertilization shows an effective carbon sequestration efficiency (2.95 kg CO2 per kg N). However, the high and challenging-to-reduce carbon footprint of current urea production, coupled with challenges in collecting manure and the priority of utilising it in agriculture rather than directing it for carbon removal, leads to a low overall global carbon sequestration potential. Nevertheless, it is demonstrated that implementing one-off nitrogen fertilization at a location with high sequestration efficiency using manure can be commercially viable. The cost per net tonne of CO2 sequestered is lower than the current market price of a carbon credit, considering the transportation is conducted with vessels that would have navigated the route regardless.
Based on the findings of this study, it is concluded that nitrogen fertilization has very limited potential to serve as a large-scale global carbon dioxide removal strategy, but can be effectively employed on company-level using surplus manure without agricultural purpose. The initial quantification, despite inherent limitations such as the use of a 1DV modelling approach, serves as a valuable addition to the scarcity of research in the domain of ocean nitrogen fertilization. Further more detailed research into strategic nitrogen fertilization for company-level CDR is justified, with this study providing valuable guidance on optimal research locations.

Some of the sediment which is eroded from the Dutch coast ends up in the Wadden Sea. Because of this the morphological development of the Wadden Sea is important, not only for the Wadden Sea itself but also for the maintenance programs of the adjacent coastlines. This is one of the reasons that the morphological development of the Wadden Sea is extensively studied. Some of these studies use the ASMITA model to make predictions of the morphological development with accelerating sea level rise. The Groningerwad is a part of the Wadden Sea consisting of a number of smaller tidal basins which has not been modelled with ASMITA. It has not yet been necessary to structurally nourish the coastlines surrounding the Groningerwad. However, as sea level rise increases it might well be possible that the coastal profiles surrounding the Groningerwad require nourishment. Therefore this thesis aims to study the Groningerwad with ASMITA to make a prediction of how the area will develop with accelerating sea level rise. To do this a morphological study is performed to determine the current morphological developments. This morphological study, based on available literature and bathymetry measurements of the area, finds that the Groningerwad is a highly dynamic area. It also determined the area and characterizing volume of each of the tidal basins, which have been used to set up the ASMITA model. For each basin in the Groningerwad an ASMITA model is set up using the information from the morphological study. The ASMITA model is used to make predictions for the development of the intertidal, channel and delta volumes of each of the Groningerwad its basins. The required parameters for the model have been derived from relevant formulas and the assumption that the Groningerwad is currently in a morphodynamic equilibrium. This was done because the time period for which bathymetrical measurements are available are to short to allow for a proper calibration procedure for these parameters. With this setup the ASMITA models show that all basins will lose intertidal sediment volume with rising sea levels. The larger basins of the Groningerwad also will not reach a new dynamic equilibrium state with large levels of sea level rise rate increase. When comparing these results to other basins in the Wadden Sea, it appears that the basins in the Groningerwad respond a lot slower than other Wadden Sea basins. Given the difference between the Groningerwad and the Wadden Sea and the fact that the time period over which bathymetrical data is available was to short to fully calibrate the model the recommendation is made to revisit this study when more data is available and it is possible to calibrate the relevant parameters.

Lake Bardawil is a hypersaline, shallow coastal lagoon located along the coast of the northern Sinai Peninsula in Egypt. Coastal systems are understood to be hypersaline when the salinity exceeds values of 30 parts per thousand throughout the year.
Being located in the arid climate region of North Africa the lagoon is subject to year-round extreme weather conditions which are dominated by high air temperatures, extreme evaporation rates, and limited precipitation. All the above in combination with the lagoon’s shallow bathymetry and restricted freshwater input causes Lake Bardawil to inhibit hypersaline conditions throughout the whole year. For Lake Bardawil this means average salinity values in the order of 42 – 51 parts per thousand.
The here conducted study is the first in the line of five successive studies focusing on three-dimensional hydrodynamics. Making use of the three-dimensional hydrodynamics, the movement of the water and salt through the lagoon is considered. Here the response of the system to the extreme meteorological conditions around Lake Bardawil is investigated. The meteorological forcing causes subtidal flows in coastal waters which are responsible for the propagation of waterborne materials such as salt and pollutants.
The results show that during periods of extreme meteorological forcing the response of the lagoon and its inlets is in line with expectations one might have from literature. During periods and events of high evaporation, the lagoon shows an overall increase in top and bottom layer salinity. Furthermore, the largest compensation flow due to evaporative losses of approximately 34 m3/s from the Mediterranean Sea into the lagoon is observed. While the lagoon waters act rather inert as shown for the average conditions during the month of April, it is the wind that initiates the motion. Successively the phenomenon of gravitational circulation in the deeper areas around the inlets can be observed with more saline waters propagating towards the inlets, along the bottom layer. At times, these processes cause subtidal velocities up to 0.15 m/s, which were computed in the inlets.
Crucial for the overall response of Lake Bardawil to meteorological forcing is the complex lagoon geometry and shallowness. Here the tidal divide, on the verge of the western bottleneck to the eastern basin is found to be of great importance. At this location very calm flow conditions are present promoting stagnant waters. The eastern basin with its vast areal extent experiences wind-driven circulations, while the western bottleneck is bound by its narrowness and tide dominance. As a consequence, the western inlet Boughaz 1 can be described as continuously well-mixed, while its eastern counterpart, Boughaz 2, experiences periodic stratification.
The application of system adaptations as proposed by The Weather Makers (TWM) proves to increase the exchange flow with the Mediterranean Sea. Here the dredging of two new inlets as well as dedicated tidal gullies through the lagoon established a more dynamic system where the inner lagoon connectivity is significantly enhanced. This is evident by the widespread presence of Mediterranean waters and the decreased salinity in a broad stretch along the barrier island as well as on the full lagoon scale. However, the lagoon waters in remote locations along the fringes of the large eastern basin remain of high salinity and show still little interaction with the tidal flow.

Embankments are one of the key aspects of flood protection programs. As the sea levels are expected to rise the coming decades coastal protection is becoming increasingly important. To better prepare for the future, increased understanding of embankment breaching is desired. An area of embankment breaching that has been relatively left untouched is the impact of a foreland during a breaching event. This study examines the different effects caused by the presence of a foreland, namely reduced flow rate through the breach, limited breach growth and an elliptical erosion pattern in the foreland.
Embankments are generally more erodible than forelands, and erosion of the foreland occurs after the adjacent embankment has been breached to its base level. As water continuous to flow over the foreland, a plunging jet will form, falling from the high foreland into the breach bottom. This causes undermining in the foreland and subsequent headcut erosion. A distinction is made between cohesive and non-cohesive forelands. Cohesive soil layers experience rotational failure and non-cohesive layers experience sliding failure.
A model is presented that calculates headcut erosion in a foreland, flow characteristics over the foreland and erosion shape of the foreland. The erosion shape of the foreland affects the discharge through the breach and is captured in the non-dimensional constant m. The presented model is implemented as a module into the existing breaching model BRES. The added functionality will increase the accuracy BRES model results.
Two experiments were performed to verify the model. The first experiment examined soil failure of a foreland in dry conditions by pushing an extracted foreland soil layer from a table to observe the failure type and the effects of vegetation on the strength of the soil. The second experiment was performed in collaboration with the University of Antwerp. A soil layer was extracted from a foreland and placed in a large flume. The foreland was subjected to a plunging jet to simulate a breaching event. The outcomes of the model were in line with observations made during both experiments.
The presented model serves as a significant first step towards implementing forelands in flood protection programs, but further research is suggested. The uncertainties stemming from assumptions in the model and the underlying sediment transport relations are significant. Most importantly uniformity of the soil is assumed, whereas in reality root systems in fertile forelands can lead to significant local strengthening. The assumptions in this model are conservative, but additional studies can further increase the accuracy of the foreland- and BRES model.

The main objective of this thesis is to increase the understanding of the effect of shellfish presence on the stability of loose rock revetments and to investigate the possibilities in the design. Pacific oyster (Crassostrea gigas) and blue mussel (Mytilus edulis) presence on loose rock revetments was quantified. C. gigas and M. edulis are common shellfish species in the port area and act as ecosystem
engineers. They require a certain salinity level, water temperature, phytoplankton ratio, and sufficient submersion time for daily feeding and respiration. The current presence of shellfish in the port area was predicted based on salinity levels generated by an OSR model. Outcomes were compared to qualitative measurements of C. gigas and M. edulis presence performed in the port area. C. gigas is present on revetments where salinity levels exceed 16‰, which is the case at Maasvlakte 2, Beerkanaal, and Calandkanaal. M. edulis were hardly observed in the port area on revetments. M. edulis can move relatively easily and detach from the surface after mortality occurs in contrast to C. gigas. They are, therefore, not considered a reliable structural addition, so only the effect from C. gigas was studied. C. gigas presence leads to binding of stones in revetments. This binding of stones will increase the stability of stones in the revetment. The relationship between the presence of oysters and stability upgrading is described using a connectivity model. The relationship between the presence of oysters and binding of stones is measured in the port area, these measurements are used to validate the model. Measurements showed that the cumulative coverage ratio of dead and living C. gigas decreases as one moves up to the intertidal zone from the mean low water level (MLW). The binding of stones increases when the coverage ratio of C. gigas is larger. This shows that there is a relationship between the coverage ratio of oysters and the binding of stones, and this assumes that there is a relationship between the coverage ratio of oysters and stability upgrading. The presence of oysters comes with structural, environmental, and ecological impacts. The conditions in the Port of Rotterdam as a system itself can pose various opportunities and threats for oyster coverage, such as global warming, pollution, and future port plans. Complementary measures can be implemented to mitigate the limitations and threats. The maintenance demand, and associated costs, decreases when oysters are present. Oysters are usually present naturally; their presence can be stimulated by enhancing C. gigas populations at locations with conditions that would allow potential oyster growth. Enhancement strategies depend on local conditions. Application is most promising when bow thruster or ship wave impact is normative because oysters are mainly found up to NAP +0.5 m. Additional enhancement costs are approximately equal to the expected reduction in maintenance costs. Possible ways of application in the Port of Rotterdam are summarized in a flowchart.

In recent years, the interest in integrating shore protection with the local ecosystems has increased. In comparison with the traditional reinforced embankments, integrated shores form a gradual transition from land to water where shore vegetation can establish itself. These nature-friendly shores have a positive impact upon the water quality, flora and fauna and the amenities of the shore. Some of the benefits of vegetation are its capability of reducing the hydrodynamic loads on the shore and its ability to increase the soil strength against erosion. Both effects have been investigated in detail in previous research and have been implemented for coastal protection designs in sandy coastal settings. But a designing tool for cohesive shorelines in lake environments is still missing. In this research, the different aspects important for the erosion of a vegetated cohesive shoreline are studied and the first steps towards a process-based design tool are taken. The model results show that the dominant processes for erosion can be found at the point of wave breaking and at the start of the run-up, as both combinations give the highest induced bed shear stresses. This can be used for a strategic placement of vegetation to dampen the wave impact and reinforce the soil through the roots. There are situations in which a partially vegetated shore is sufficient to withstand the daily wave attack. This allows the vegetation to grow naturally to full strength, which is required in a storm situation. In this way a financial benefit can be reached as well as a healthier vegetated shore, as a large part of the vegetation has grown naturally.

Introduction
San Francisco Bay is one of the largest estuaries of the US Pacific Coast with an area of 4000 km2. It consists of two hydrologically distinctive sub-embayments North Bay and South Bay. South Bay is unique as it does not experience the freshwater flushing typical for estuaries. It experiences the largest freshwater input during a regime of reverse estuarine circulation during Winter, when the entire Bay becomes fresher following peak discharges from the northern rivers. Hence both saline and freshwater enter from Central Bay through the same entrance. South Bay is dealing with increased risk of inundation due to the combination of sea level rise and land subsidence and a deteriorating water quality. Understanding sediment pathways within South Bay and sediment exchange at its entrance can support the development of management strategies dealing with turbidity depended algae blooms and the development of salt marshes as a measure against sea level rise. Additionally, by understanding the current factors controlling fine sediment dynamics, future implications of climate change can be better predicted. Though San Francisco Bay is the topic of much research, a process-based model with a model domain covering the entire Bay is a novel approach to analyse fine sediment dynamics in South Bay. Methods
A Delft3D-DELWAQ buffer layer model was calibrated against a newly available combination of local high-frequency suspended sediment concentration (SSC) measurements and two-monthly, depth varying SSC measurements across the entire 145 km length of the Bay. Subsequently the method of Sediment Connectivity was applied to analyse sediment pathways and net sediment fluxes in South Bay. Sediment Connectivity is an approach that uses network analysis to quantify sediment fluxes based on a schematization of San Francisco Bay into 17 segments. Large data sets of spatial and temporal output were reduced to a 17x17 adjacency matrix permitting a more straightforward analysis and the application of different statistical metrics unavailable in more traditional approaches. Results and implications Calibration enabled the model to better capture seasonal and episodic variations in SSCs across the Bay. Connectivity analysis uniquely revealed key dominant pathways, which agree well with literature. Additionally, it unveiled intra-basin transport pathways, regions of erosion and sedimentation and an indication of the varying controlling forcings during the year. Finally, this study acts as a proof of concept for the Sediment Connectivity method that could be applied in other estuaries.

Over the recent years, the Dutch Continental Shelf has seen the erection of various wind farms in an effort to counter climate change by replacing fossil-based power plants. Since the majority of these sites use scour protections which have a substantial impact on the surroundings, the Dutch government increasingly stimulates and requires ecological enhancement of such structures in order to restore the natural habitat and maintain the marine ecosystem of the North Sea. Oyster enhancement has been one of the methods used for the ecological enhancement of offshore wind farm scour protections. However, studies report that a successful structure for the harbouring of an oyster population is yet to be developed. Existing structures were found to be unstable or unable to provide a suitable habitat for the oysters (Bouma, Belze, et al., 2013; Stokes et al., 2012). The study at hand aims to develop a successful design for oyster broodstock structures for nature enhancement in offshore wind farms. It was conducted for Van Oord as part of project Ecoscour. To establish design criteria for the oyster broodstock structures, oyster habitats and the Borssele V site were analysed and a brainstorm session with partners from project Ecoscour was set up. The final criteria concerned: ecology; structural integrity; commissioning & construction; and monitoring. The design criteria were used to develop several viable structure designs. In order to rapidly assess the strength and stability of potential designs, a Python-based open source tool was built named Econstruct. With this tool, geometries can easily be evaluated under various influences, accounting for the effect of marine fouling. This could be used for quick investigations of loads, stability and structural integrity. The Econstruct tool was validated and analysed for sensitivity for the input parameters, of which the input radius and current velocity had the highest influence on stability. Using the environmental input parameters that hold for the Borssele V wind farm, a terraced design was proposed. After consultation with the manufacturer of the structure, D & M engineers, this proposal was altered to account for manufacturing limitations. The definitive design was evaluated using the Econstruct tool and found to be stable. It was then manufactured, and ultimately placed in Borssele V in October 2020. Several recommendations are made for future research and the design of ecological enhancement structures for offshore wind farms. Most importantly, the Econstruct open source tool can be used in the future for the design of structures for other ecological enhancement projects such as coral reef restorations.

Degrading mangrove forests and coinciding erosive coastlines is an urgent global concern. Mangroves are essential for their interaction with hydrodynamic and sediment processes at mangrove-mud coasts. Earlier on, solutions were sought in building ’hard’ structures, such as concrete sea walls, to lower incoming wave energy and enhance sedimentation to restabilize erosive coastlines and bring back mangroves. As these approaches proved to be counterproductive and even accelerate destabilization of the coastline, nature-based solutions might provide a new path to a durable solution. A pilot project was initiated in Demak, Indonesia, where several permeable brushwood and bamboo dams were constructed near the receding coastline. The open structure of the dams allows sediment to flow through, while they decrease wave heights by dissipation. This creates calmer conditions behind the dams and allows mud to settle. The deposition of fine sediments enhances a rise in nearshore bedlevel and provides nursery ground for mangroves to reestablish, realizing a first step towards rehabilitation of the mangrove ecosystem and restabilizing the coastline. A conceptual 2DH process-based model, using Delft3D FM, was created to analyse the effect of permeable structures under changing boundary conditions at various shorelines. Three boundary conditions were varied to see the influence on dam performance: wave height, wave direction and suspended sediment concentration. A decrease or increase in wave height resulted in similar rise in bedlevel elevation behind the dams. Without the dams, an increase in wave height increased the tidal flat elevation and steepened the foreshore, inducing a concave profile shape. Placing the dams on the tidal flat induces extra rise in elevation, but won’t mitigate the erosion of the foreshore. Smaller wave heights tend to reshape the profile towards a more convex profile. When dams are implemented on, an increase in bedlevel behind the dams occurs. The waves stir up sediment at the tidal flat boundary which are redistributed by the tidal currents forming a more convex profile. The dams could be placed best close to the shoreline to allow for the natural redistribution of the sediment when at the same time induce a rise in bedlevel for mangroves to reestablish. Altering the nearshore sediment supply affects the dam performance significantly. The dam performance increases for lower sediment supplies. Dams reduce erosion due to decreased sediment input, but it is likely a short-term solution. For higher sediment supplies, the coastline can more effectively restore by itself and the dams reduce in efficacy. The model results show an increase in dam performance for increasing wave angles (shore-normal to shore-parallel). The bed shear stress is decreased more effectively for smaller wave angles, but also reduce the sediment concentration behind the dams. With the many distinctive boundary conditions at mangrove-mud coasts in mind, the simplified model setup is made easily adaptable to enable future use of the model. Based on the model setup for Demak and the model results in this research, an improvement on the computational grid is suggested before applying the model to other coastal sites.

TheAmazon-Orinoco river plume is a buoyant freshwater lens of 1.2 × 10⁶km², which has been traced over 2000 km from the Amazon river mouthinto the Caribbean Sea and along the Lesser Antilles. The river plume iswarmer than the surrounding open-ocean waters, with temperaturedifferences up to 1.5 ∘C caused by a stratification-induced barrier layerinhibiting vertical mixing and coloured matter increasing solar energyabsorption. Due to its magnitude, the river plume affects thehydrodynamics and the oceanic conditions in the Western Tropical NorthAtlantic (WTNA) substantially, but its variations on interannual time scales andthe corresponding relation to local sea-surface temperature (SST) are notwell understood. The Caribbean Sea is a region of high ecological value as itis home to extensive coral reefs, which are especially sensitive topersistent high SST. Therefore, this study investigates the interannualvariability of the Amazon-Orinoco river plume and its relationship to SSTsin the Caribbean Sea and the WTNA. It is hypothesised that fresh anomaliesof the river plume salinity pattern are indicative of a more extensivetransportation of the heat contained in the river plume. As a result, itis expected that interannual variations of dominant river plume pathwaysaffect the magnitude and location of anomalous SSTs. To test thishypothesis, model reanalysis fields of oceanic conditions from 1993 to 2017are used to conduct statistical analyses. In this context, the river plumevariability is determined using specific regions of freshwater influenceestablished using Empirical Orthogonal Function (EOF) analysis ofanomalous sea-surface salinity (SSS). Cross-correlations analysis relatingthese EOF modes of with atmospheric processes show that the interannualvariability of the river plume is dominated by wind-inducedadvective transport and -mixing. Strong winds along the Brazilian shelfare related locally increased SSS, while a weak southward component makesfor extensive spreading of the low-salinity plume waters. Additionally, weshow that high river discharge affects SSS east of the Lesser Antillesafter a lag of three months. Through its modulation of these atmosphericprocesses, there is a strong indication that the El Niño-SouthernOscillation affects SSS variability in the main along-shelf northwestplume pathway, with low SSS 1–9 months after a La Niña event. DecreasedSSS are found in phases 2 and 3 of the Madden-Julian Oscillation, whileincreased SSS was observed in phases 6 and 7. However, the evidence forthis relation is weak and should be investigated in further research.
The results show that, opposed to the hypothesis,a more extensive river plume is not associated with higher SSTs in theCaribbean Sea. However, strong correlations are found between river plumesurface area and SSTs at a lag of 1 year. Based upon results of previousstudies, we argue that the river plume has the ability to pre-heat themixed layer in the WTNA leading to extreme temperatures in the followingyear. It is wise to conduct a Lagrangian parcel back-tracking experimentto verify this mechanism.

Coastal bays in the Caribbean accommodate different marine ecosystems, including seagrass meadows and coral reefs, which provide important ecosystem services. However, these marine ecosystems are endangered. Seagrass ecosystems have a key role in coastal bays, but despite their alarming rates of loss, they receive little attention compared to other marine ecosystems. This study aims to provide a better understanding of the role of seagrass ecosystems in coastal bays by assessing their impact on the morphodynamic behavior. In order to achieve this, an existing hydrodynamic model has been extended to include morphodynamics. Two different bays have been investigated: Baie Orientale and Baie de l’Embouchure (St. Martin). These bays represent a partially exposed and fully sheltered bay, respectively. Both regular wave conditions, as well as extreme storm conditions, have been investigated to understand the consequences of seagrass loss on coastal erosion for different environmental climates. The coastal erosion has been found to be more prominent in the exposed region, whereas the more sheltered areas are more resilient. The erosion takes place in shallow waters but remains limited under regular swell conditions. The increased wave energy, during the extreme storm event, increases the erosion rates considerably. However, the regular swell conditions are normative in shaping the morphological development of these coastal bays when longer timescales are considered. The seagrass counters erosion most effectively in the foreshore and much less in deeper regions. Removal of seagrass in the foreshore (between 1-3m) halves the sediment stabilization. In contrast, the sediment stabilization increases if the meadows are able to spread especially towards the shore. In addition, the wave energy and waveform have a significant impact on the sediment stabilization. The stabilization typically decreases for higher and shorter (storm) waves, whereas it increases for smaller and longer (swell) waves. The long-distance interactions between seagrass meadows and coral reefs have led to their mutual coexistence, which is also found to be beneficial for the erosion control of the coastal bays. The dissipation of wave energy on top of the reefs fosters the sediment stabilization by seagrass. Moreover, the impact of the reefs on sediment stabilization also increases in the presence of seagrass meadows due to the additional drag exerted by the seagrass. The seagrass meadows are typically more effective under swell waves, whereas the reefs are more dominant in the dissipation of storm waves. Seagrass meadows and coral reefs form thus a synergy, in which the stabilization of sediments provided by the individual ecosystems is facilitated, reinforced, and complemented by the proximate presence of the other ecosystem. Finally, the role of seagrass on sediment stabilization has been explored under climate change. The coastal erosion increases for the considered sea-level rise scenarios. The impact of the seagrass on sediment stabilization decreases when the bays, seagrass and reef ecosystems are not able to keep up with sea-level rise. The synergy between seagrass and reefs emphasizes that the responses of both ecosystems are of importance for the future of tropical sheltered bays and should therefore not be managed in isolation.

Intertidal flats and salt marshes can protect hinterland against wave energy and flooding by tides or storm surges. Thus, the development of tidal flats is important to foresee. The presence of specific small scale features could indicate a certain development and large scale morphological shape. The shape is a predictor for development and it is expected to influence small scale feature formation. Tidal flat management could benefit from technological process, e.g. in drones, if these indicators can be used. Hence, the aim of this research is to find indicators and gather sufficient knowledge to make them applicable.

The main research question is: "Can small scale morphological features on estuarine tidal flats be used as indicators for large scale morphological shape and development?”. The main question contains two aspects. The first facet is whether the small scale morphological features are indicators for large scale morphological shape and development. It focuses on detecting indicators. The second part is about gathering knowledge to properly use the indicators. It is investigated which mechanisms explain the found indicator roles of the small scale morphological features. The focus is on the identification of the mechanisms. Two sub-questions can be extracted from the above:
1. Are the small scale morphological features on estuarine tidal flats indicators for large scale morphological shape and development?
2. Which mechanisms explain the found indicator roles of small scale morphological features?

Indicators are detected with the analysis of aerial photographs and elevation measurements at transects in the Eastern and Western Scheldt. New and already in literature known features are identified and classified in this process. The mechanism that form and erase the small scale morphological features and their dependence on large scale morphological shape are investigated to explain the found indicators. The mechanisms are determined in various ways: Two 1D models are created, a field campaign is conducted, (subsequent) aerial photographs are looked into, elevation measurements are analyzed in detail and literature research is done.

Small scale morphological features on estuarine tidal flats can be used as indicators in the Western Scheldt. This research detects and explains features that indicate large scale morphological shape, development, hydrodynamic conditions and ecological activity of an area. However, the applicability of the indicators in other systems should be proven by extending this research to other situations. A specific sequence of small scale morphological feature categories between salt marsh and waterfront, a build-up, has been identified as indicator for convex large scale morphological shape and indirectly for accreting behavior. All the features in the build-up are indicators on their own. Megaripples, seen within build-up, indicate (future) convex profiles. Furthermore, all of the features indicate a certain relative height and slope when they are seen within the build-up. These individual indicator roles are clarified by elaborating on the hydrodynamic conditions that form and erase the features. Therefore, the prevailing conditions can also be determined with the indicators.