Lake Bardawil is a hypersaline shallow micro-tidal double-inlet lagoon on the northern coast of the Sinai Peninsula in Egypt. The inlets, named Boughaz 1 and Boughaz 2, connect Lake Bardawil to the Mediterranean Sea. The local population relies on the fishing yields from the lagoon, however, in the current situation, the lagoon’s inlets are unstable, needing constant maintenance dredging to stay open. Additionally, due to the hypersaline situation (limiting fish attraction) and high fish catch demand, the current fishing situation is unsustainable. The Weather Makers propose a solution to the problem using dredging interventions. Enlarging the inlets of Lake Bardawil is expected to result in increased fish migration, decreased salinity in the lagoon and increased stability of the inlets. This research aims to investigate the short-term response of Lake Bardawil and specifically its inlets to the dredging interventions proposed. To investigate the response to the interventions, two numerical models are used; a hydrodynamic model in D-flow FM and a coupled morphological model using D-flow FM and D-waves. The model results are analysed in terms of the hydrodynamic tidal response, combined hydrodynamic response to tide and weather and finally the morphological response to tidal and weather effects. From the hydrodynamic model, it can be concluded that the interventions result in a larger tidal prism for the lagoon by a factor of 1.6. This is expected to result in increased fish migration and reduced salinity in the lagoon. As the tidal prism increases, so does the discharge through the inlets. The increased discharge through the inlets results in inlet velocity amplitudes that exceed the theoretical critical value for convergence to a dynamically stable inlet cross-section for both inlets. The interventions affect more than just tidal currents in Lake Bardawil. Weather effects in the lagoon are amplified by the interventions. This is demonstrated by increased interaction between the inlets in terms of net import and export of water. During winter storms, the wind-induced flow from Boughaz 1 to Boughaz 2 is greater in magnitude. The wind waves caused by these winter storms result in sediment resuspension. This results in larger sediment transport from the basin to Boughaz 2. Using the coupled model, the morphological response in both inlets can be predicted. In Boughaz 1, the present sediment-importing character is amplified. Whereas the similar summertime sediment-importing character of Boughaz 2 is reduced substantially. The sediment export of Boughaz 2 during winter is larger in the new situation. The interventions result in increased sedimentation in the dredged channel of Boughaz 1. This does not hinder the increased tidal discharge at Boughaz 1, which is the main intended function of the interventions. This means the increased sedimentation does not influence the intended functioning of the interventions in the short term. Due to the increased sedimentation in the inner dredged channel, there is no indication of increased stability in Boughaz 1. Boughaz 2 shows less morphological activity in the situation after interventions. As is the case with Boughaz 1, there is no hindrance to the functioning of the interventions during the short simulation period. There is reduced deposition of sediment in the inner flood delta region of the inlet and the updrift side of the inlet channel compared to the known unstable situation during both winter and summer simulations. This indicates improved stability for Boughaz 2. The short-term response to the interventions in the inlets of the Lake Bardawil system is as intended, the tidal prism is increased and while there is only an indication of increased stability in Boughaz 2, there are no short-term impediments to the intended primary functioning of the interventions in either of the inlets.

A rise in the global mean temperature induced by climate change is expected to have a large impact on ecosystems in all regions of the world. One of the threats is accelerated sea level rise (SLR). This may induce the loss of intertidal areas in tidal inlet systems. The long-term morphological response of tidal inlet systems can be modelled using reduced complexity model ASMITA (Aggregated Scale Morphological Interaction between Tidal inlets and the Adjacent coast). The ASMITA model simulates morphological development on an aggregated spatial and temporal scale by imposing a morphological equilibrium condition. As such the model is fast, allowing for multiple long-term simulations. The model is physics-based and the parameters can be related to field values.

Currently, salt marshes are not implemented in ASMITA. However, salt marshes could be of importance to the morphological development in tidal inlet systems. Moreover, it is relevant to assess the resilience of the ecologically important salt marshes by themselves. The aim of this research is to implement salt marshes in ASMITA to assess their influence on the rest of the tidal inlet system and to gain insight into the long-term morphological response of salt marshes to accelerated SLR.

Salt marsh development is governed by horizontal and vertical processes. The marsh height increases by capturing mineral sediment and by the accumulation of plant biomass. Autocompaction and deep subsidence lead to a decrease in marsh height. The implementation of salt marshes in ASMITA relies solely on the input of mineral sediment. At the marsh edge, generally, a cyclic behaviour of sedimentation and cliff erosion occurs. Due to the high degree of spatial aggregation, cliff erosion is excluded from the model extension. The governing processes for salt marsh development in the ASMITA model extension are mineral sedimentation, sediment availability and relative SLR.

The spatial and temporal aggregation of governing processes for salt marsh development are included in the aggregated advection-diffusion equation and model parameters for the horizontal & vertical exchange of sediment, and sediment availability. Data analysis on hydrodynamic conditions and salt marsh development was conducted for the derivation and calibration of these model parameters. To verify the salt marsh implementation, three ASMITA models were created. A one-element salt marsh model consisting of only a salt marsh element, and two different multiple elements models, which contain the ebb-tidal delta, channels, tidal flats and salt marshes.

It can be concluded that ASMITA can model the mineral sedimentation on a salt marsh but depicts a large sensitivity to the parameter setting, particularly for the sediment concentration. Based on the chosen parameter configuration, the Oosterkwelder salt marsh is preserved when subjected to SLR rates below 16 mm/year.

The ASMITA salt marsh extension can be employed to obtain an expeditious first impression of long-term morphological salt marsh development. However, due to the lack of incorporation of detailed processes, the model should not be employed for in-depth analyses of salt marsh development. The interaction between the salt marsh element and the remaining tidal inlet system components requires further model improvements.

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.

The behaviour of tidal basins has been predicted using a modelling approach in which a morphological equilibrium for an entire basin was used frequently in the past. Because tidal basins have, to an certain extend, a fractal nature, it is expected that this approach could be used with a morphological equilibrium for subbasins as well.

In the first part of this thesis the morphological equilibrium for subbasins is examined. A numerical simulation using tracers is conducted in order to find the watersheds of the Ameland Inlet. The watersheds are used to divide the basin into subbasins of different scales. These subbasins are used to find a morphological equilibrium between the channel volume and tidal prism. The applicability limitations of the morphological equilibrium relation are also investigated in this part of the research.

In the second part of the research the newfound equilibrium is applied in an Asmita model. The modelling exercise is done in order to showcase a proof of concept of the multi element modelling approach. In this modelling approach both a 6 and 10-element model are used to look for the spatial differences in morphological behaviour within a basin.

In the first part of this thesis an equilibrium for the channel volume with respect to the tidal prism of subbasins in the Ameland inlet is found. This equation can be applied to basins (Channel and flat combined) with a minimum area of 40 km². This limitation is for both the equilibrium study as the Asmita modelling. The modelling exercise proofs that the multi element Asmita modelling is possible and gives a good insight into the spatial differences in morphological behaviour within the Ameland Inlet.

The Wadden Sea is a large system of tidal flats and barrier islands. Its individual features have been heavily researched, but sufficient knowledge on the sediment transport patterns on the scale of the Wadden Sea is not yet available. This thesis aims to indicate the dominant sediment transport patterns in the Dutch Wadden Sea and the hydrodynamic forcing mechanism the patterns can be attributed to. The Delft3D-FM model used to indicate these patterns is first adapted by implementing an improved Manning’s roughness field. To assess the patterns for each contributing hydrodynamic forcing mechanism, the tide, wind and waves are added to the model one by one. The results show that the Dutch Wadden Sea is a highly interconnected system, with the influence of each hydrodynamic forcing mechanism depending on the feature and inlet system.

The tidal channels in the Eastern Scheldt basin, are out of equilibrium due to the reduced tidal prism as a consequence of the construction of the Storm Surge Barrier in 1986. An estimated 500 million cubic meters of sediment is required in order to reduce the cross-sectional areas of the tidal channels such that the system reaches a new equilibrium. This phenomenon is referred to as sediment starvation. The sediment starvation has been causing severe erosion of the intertidal areas which are the only available sources of sediment to feed the tidal channels because the storm surge barrier practically blocks sediment import into the estuary. The intertidal areas form the habitats for the benthic commu- nity, foraging ground for wader birds, and rest area for aquatic animals. In addition to their ecological value, the intertidal areas are valuable wave dampers and therefore important for flood protection of the hinterland. Their erosion thus harms the ecosystems as well as the flood safety of the hinterland. Mitigation measures have been carried out in the form of directly nourishing the intertidal areas (Roggen- plaat, Galgenplaat, and Oesterdam). These nourishments have had detrimental effects on the ecology that remained for a period of 5 years after the implementation. Nourishing the channels, hence reduc- ing the cross-sectional area of the channels, can feed the intertidal areas gradually, thus preserving or increasing the ecological value of the intertidal area. Nourishing the channels can succeed according to the theory on channel-shoal interaction and the experience from the Western Scheldt; however, this has not been studied yet for the Eastern Scheldt. In this study, the effects of a nourishment in a tidal channel have been evaluated for different nourishing methods, volumes and locations in the Eastern Scheldt Estuary. The objective of this research is to answer the following research question: Is a tidal channel nourishment in the Eastern Scheldt a feasible way of supplying the channel’s surrounding intertidal areas? To answer this question, we applied a 2DH numerical model (ScalOost) that runs in the Delft 3D soft- ware. For this research, the forcing consists out of tidal elevations as well as a wind climate. For reasons of simplicity and to limit larger computational time, wind waves are excluded from the model’s forcing. The numerical model is capable of simulating the hydrodynamic effects and the morphody- namic evolution of a tidal channel nourishment. For four channels, the effect of nourishing on the velocity magnitude is studied for different ways of nourishing (elevating or narrowing the channel). The model results show that the considered nourishments cause a local increase of the velocity magnitude and an additional flow on the surrounding intertidal area during flood. According to the analyses of the computed hydrodynamics, the Krabbenkreek and the Brabantsche Vaarwater channels show the most potential considering the velocity magnitude increases and velocity direction changes. There- fore, these two cases were analysed separately in form of two case studies with an in-depth hydro- and morphodynamic analysis for various nourishment designs. For the Krabbenkreek, a nourishment of 2 million cubic meters increases the maximal flow velocities in the order of 0.15 m/s, such that the critical velocity for sand transport (0.45 m/s) was exceeded over a larger part of the channel; to approximately 750 meters further landwards. The period in which the critical velocity is exceeded, increased by 15 to 60 minutes per tidal cycle. The results of the morphodynamic simulations indicate that 2.5% of the initial nourishment erodes over the first year, of which 80% settles above the MLW-line. Bearing in mind the model’s limitations, it is concluded that a tidal channel nourishment in the Krabbenkreek feeds the intertidal area at a slow pace such that the ecology is not adversely affected. The Brabantsche Vaarwater and its two main bends were used to study the effect of secondary flow on sediment transport and eventually on the behavior of a nourishment. Historic data, as well as theoretical analysis, indicate that in both bends, the centrifugal effect is dominant over the Coriolis effect for gen- erating secondary flow. Model results confirmed this observation, yet the dominance of the centrifugal effect is larger in the second bend. As outer bends tend to erode and inner bends to accrete, the outer bends were nourished (750 & 920 ∗ 103 cubic meters) in order to use the secondary flow to transport sediment towards the inner bend and eventually onto the intertidal area. The simulation results show that for both bends, 3% of the initial nourishment erodes after the first year of which 80% accreted on both the inner and outer bend. The morphodynamic simulation results do not confirm the dominance of the centrifugal forces on sediment transport, as larger accretion rates than those simulated on the inner bends were expected. Although the results were not as expected, the nourishments did increase the velocities which increased the suspended sediment concentration in the channel and as simulation results show, sedimentation in sheltered areas. A tidal channel nourishment in the Eastern Scheldt has been proven to be a potentially successful way of indirectly nourishing the channel’s surrounding intertidal areas. However, the accretion rates were predicted in the order of 2% per year, whereas this would be 100% if directly nourished. Furthermore, the impact of a tidal channel nourishment on the sediment starvation in the whole basin is small con- sidering the proposed volumes in this research only represent 0.4% of the actual sediment demand. Nourishing a tidal channel should be considered in view of maintaining ecological values.

Estuarine intertidal flats comprise valuable ecosystems and act as an important sediment source for the adjacent salt marsh systems. However, accelerating sea-level rise threatens the mudflats and associated ecosystems, where the mudflat accretion lag behind sea level rise. A reliable forecast on the morphological developments of the mudflat under sea-level rise scenarios is of vital importance to assess sea level rise impact on the estuarine system.

Different tools exist that can predict the long-term evolution of the mudflats, viz. Delft3D, ASMITA and the hybrid model (Delft3D-ASMITA). Since the hybrid model is newly developed, the comparison among the various approaches has not yet been available. However, it is significant to know if they can produce the same results.

The research aims to compare the three modeling approaches (Delft3D, ASMITA, and the hybrid model) based on a case study in South San Francisco Bay. This comparison will reveal the strengths and weaknesses of the three approaches as well as indications where the approaches may strengthen each other.

The research is conducted in three main phases. Phase 1 consists of the sensitivity analyses in Delft3D for the case of South San Francisco Bay; Phase 2 contains the calibration of one-element and multi-element ASMITA models to reproduce the Delft3D model; Phase 3 focuses on the potential to improve the simulation efficiency of Delft3D in the hybrid model.

Model result comparison shows that, after the calibration, the ASMITA and hybrid model can efficiently simulate the same cases as in Delft3D. However, the upper part (landwards end) of the mudflat is more sensitive to the water level changes in the hybrid model due to the different sediment transport computation modules. The power indicating the relation between the equilibrium and actual morphology as well as the reference level is the important calibration coefficient to adjust the steepness of a mudflat. It can be concluded that the Delft3D model is used as the foundation to calibrate ASMITA and the hybrid model, both of which can improve the simulation efficiency with simplifications, especially in the long-term morphological development.

The study provides clear insights into the comparisons among different modeling approaches in the case of the long-term morphological developments of mudflats by the impacts of sea-level rise. It is recommended to do further research on the configuration of a 2D model and the conduction of the combination of different modeling approaches in other similar cases to confirm the validation.

The Wadden Sea is the largest system of tidal flats and barrier islands in the world extending from the northern Dutch coast to the coast of Denmark. Such a large natural area is ofgreat importance to bothhuman beings and ecosystems. Over 10,000 species of flora and fauna are found in theWadden Sea being a perfect habitat due to the relatively calm environment and high food availability. However, accelerating sea-level rise and human interventions, such as gas extraction, may induce an unwanted morphological change in theWadden Sea posing a threat to the natural habitats. This study investigates the morphological response of the Wadden Sea to SLR and subsidence induced by gas mining. A new hybridmodel whose aggregation level is between a process-based model
(Delft3D) and a aggregatedmodel (ASMITA) is applied in this thesis. The two-dimensional hybrid model applies depth integrated shallow water formulations and the advection diffusion equation for the transport ofsediments like Delft3D, but calculates the exchange ofsediment betweenbed andwater columnbymeans ofan equilibriumbathymetry concept under scenarios disturbing these equilibrium conditions. The Ameland inlet is chosen as the research area because it is a relatively autonomous
and undisturbed basin. The high robustness of the hybrid model makes it possible to apply a high morphological scale factor and a coarser grid compared to the processbased model, which shortens the computation time by orders of magnitude. However, the equilibrium concept also fixes the shoal-channel structure and suppresses channel migrations. Three different scenarios of sea-level rise rate (4, 6, 8 mm/year) are applied over a simulation period of 100 years. The general morphological response simulated by the hybrid model shows that the channels and the ebb-tidal delta erode acting as the main source ofsediment for accretion of the intertidal flats. The erosion/sedimentation is more pronounced with a higher sea-level rise rate. Sensitivity analysis shows a significant influence of the sediment diameter on the
channel erosion and sediment supply to the intertidal flats. Diffusivity plays an important role in the horizontal sediment exchange between the channel and the flat but only slightly influences the sediment import. Global equilibrium concentration and power n are similar to diffusivity in affecting morphological activity. The adaptation time scale is inversely proportional to both of these two parameters. The possibility of using more than one sediment fraction is proved and it can reproduce a more realistic sediment distribution as the observation. The hybrid model is also applied to simulate the morphological response to local
subsidence and the restoration after subsidence stops. The center of the subsidence circle dosen’t lower as much as the subsidence rate, which indicates that sediment is transported to the center. Sediment is supplied to the area ofsubsidence by the adjacent main channel. The result proves the sediment transport principle underlying the hybrid model that sediment is always transported along the gradient of the sediment demand.

Ebb-tidal deltas play a key role in the morphology of barrier coastlines and tidal inlet systems as they serve as a natural source of sediment. They are typified by a dynamic morphology that interacts with the adjacent coastlines and sponsors a unique ecological habitat. Under increasing socio-economic, ecological and climate-induced constraints, it becomes imperative to obtain a better understanding of the evolution of ebb-tidal deltas in order to maintain and preserve these morphological features in the near-future time horizon. An increased interest has therefore been raised to understand, quantify and predict the development of ebb-tidal deltas.

In the context of developing a future-proof coastal management and maintenance strategy, the efficiency of ebb-tidal delta nourishments has been further investigated in research programmes such as Coastal Genesis 2.0. For the Ameland inlet, this entailed the construction of a 5 million m3 pilot nourishment over the course of March 2018 to February 2019 and subsequent monitoring in the years following. This research investigates the impact of this pilot nourishment on the natural behaviour of the Ameland ebb-tidal delta. The second goal is to build further knowledge on the modelling capabilities of present state-of-the-art models for the Ameland ebb-tidal delta.

To this end, a process-based Delft3D model is applied to hindcast the morphological development of the ebb-tidal delta with a particular interest in the evolution of ebb-shields and -chutes over the course of 2005 to 2020. It is identified that the representation of the wave-induced processes is key for capturing the development of ebb-shields and -chutes in the model predictions. Therefore, we applied and experimented with an updated nonlinear wave orbital velocity parameterisation and assessed its contribution to the modelling performance.
This thesis demonstrates that the evolution of ebb-shields and chutes on the outer delta is contingent on its initial presence in the initial bathymetry. Hence, the initiation of ebb-shield development is not inherited in the model response. These insights have been integrated and synthesised to assess the application of the present state-of-the-art model as a forecasting tool for the morphological development of ebb-tidal delta nourishments.

Ultimately, it is shown that a model using schematised boundary conditions and an efficient morphological updating scheme is able the predict the yearly-averaged development of the pilot nourishment on the ebb-tidal delta. It is demonstrated that the 2019 pilot nourishment only locally influences the behaviour of the Ameland ebb-tidal delta. Nourished sediment is likely to be redistributed along the ebb-shields, contributing on the long-term to the sediment exchange process with the downdrift coast of Ameland. The location of the ebb-tidal delta nourishment is thereby important for the sediment exchange process and the development of local features. Placing ebb-tidal delta nourishments to the south of the Westgat invokes a primary sediment exchange between the coast of Terschelling and surrounding morphological features. A secondary readjustment of the Westgat thereby influences the development of the ebb-shields and -chutes. Constructing an ebb-tidal delta nourishment north of the Westgat results in a sediment exchange between the local ebb-shields and the downdrift coast of Ameland. Our results also demonstrate that an increase in the pilot nourishment construction height enhances the redistribution of sediment along the ebb-shields.

Lastly, this study identifies further opportunities for improving medium-term morphodynamic models for the Ameland inlet by incorporating time-dependent boundary conditions including new transport formulations such as SANTOSS.

Burrard Inlet (Vancouver, Canada) has been the home of the Tsleil-Waututh Nation (TWN) for thousands of years. Over the past decades, ongoing erosion has been observed along the shores of Burrard Inlet and the TWN reserve specifically. This leads to loss of land for the TWN community, damage to infrastructure, and exposure of historic sites with cultural value. Currently, there is insufficient knowledge concerning both the governing processes for sediment transport and transport pathways into, within, and out of Burrard Inlet. This knowledge is needed to propose and evaluate effective measures to prevent further erosion. This study aims to investigate the transport pathways in Burrard Inlet and give more insight into the mechanisms governing sediment transport in this inlet.

For this purpose, a Delft3D FM model of the area is set up and calibrated. This model is used to analyze sediment transport in the inlet under various forcing conditions. Transport pathways are visualized using SedTRAILS.

The model shows that flows and sediment transport in Burrard Inlet are tide-dominated and governed by the topography. Flows are strongly accelerated in constricted areas (First Narrows and Second Narrows), which leads to large velocity differences. Following the velocity field, sediment transport patterns are correspondingly dominated by these topographical restrictions. In the wider basins, flows slow down and form eddies. The model results suggest that these eddies act as sediment sinks. Additionally, sediment is lost into Indian Arm, a deep fjord with low flow velocities at the eastern end of Burrard Inlet. The possible pathways for sediment originating from the eroding shorelines at the TWN reserve are visualized. As soon as sediment from these banks is mobilized, it tends to move away from the shore with a final destination either in one of the eddies or in Indian Arm. The impact of wind and waves on the sediment transport patterns is limited.

Since first European contact in 1792, the shoreline of Burrard Inlet has changed significantly due to dredging activities, land developments, and industrial development as the city of Vancouver was built. Reconstructed historic shorelines are implemented in the model to assess the consequences of these shoreline changes on the sediment transport. Model results show that the tidal prism and the velocities in the Narrows have decreased since 1792, while the tidal range has increased. Moreover, sediment mobilized along the eroding shorelines showed greater potential for deposition along these same shores in 1792, compared to the present-day situation.

The Gulf of Mottama, located in the southwest of Myanmar, is home to morphologically interesting processes. An entrance of around 100 km wide narrows into a funnel­shaped bay towards the Sittaung River in the north. The entire estuary region is subject to strong dynamic morphological activity which is alleged to be driven by the large tidal energy and sediment inputs. The dynamics of the tidal channels in the Sittaung estuary have resulted in rapid bank erosion of up to 3 km/y. The Sittaung estuary harbours a unique set of characteristics. This has made the question of which processes and mechanisms cause the bank erosion a complex one for which no clear cut answer is currently available. The knowledge of the main processes and mechanisms is valuable to improve the understanding of morphological functioning in dynamic estuaries. The main research question has thus been formulated as: • What is the effect of the large incoming tide and storm events on the bank erosion of the Sittaung estuary and to what extent can this erosion be simulated with a numerical model? The research objectives have been achieved through a literature analysis, system analysis, satellite analysis and modelling simulations. Main conclusions of the research have been as follows: The satellite analysis has shown little to no correlation between the wet season discharge increase and the bank erosion rates. It also showed large differences between erosion rates at different heights of the estuary. Modelling results indicate a prominent role but cannot substantiate a quantitative impact of the tidal forcing and associated tidal bore. River discharge fluctuations were shown to have little effect on the bank erosion. • The results of both the satellite and numerical modelling analysis have shown no additional implications on the dynamic morphology caused by large incidental storm events. Long­term simulations with respect to the bank erosion resulted in several hindrances. Heightened levels of channel incision occurred through a fault in the numerical schematization. The representation of bank erosion in the model has also been subject to stalling.

A study of five European estuaries by Winterwerp and Wang (2013) showed that tidal ranges increased significantly along with the ongoing narrowing and deepening of these estuaries. In addition to an increase in tidal range, a dramatic increase in suspended sediment concentrations has been observed in the Ems (Germany) and Loire (France) estuaries, often referred to as a regime shift towards hyperturbid state. While it is generally accepted that the increase in tidal range is a consequence of deepening and narrowing, it is not generally true that deepening and narrowing leads to a dramatic increase in sediment concentrations. Whether deepening is a potential cause for the high sediment concentrations observed in the Loire, is still unclear. Although very little observations have been reported over the 20th century, literature clearly shows that sediment concentrations increased drastically over the years. The scarcity of data not only applied for the sediment concentrations over the years but also for bathymetry and hydrodynamics, resulting in uncertainty about the historical states of the estuary. To cope with the large range of uncertainty and variability in the reported observations and model parameters, an idealised model called iFlow has been used. The strength of the iFlow model for this research was twofold. Firstly, iFlow allowed to identify the essential physical processes driving the estuarine sediment dynamics. Secondly, iFlow is computationally efficient, allowing to perform extensive sensitivity studies. In this way, we could determine which processes play a role in the current state of the Loire estuary and how they are affected by deepening. Furthermore, by mapping the effects of the uncertainty on the different physical processes, robust conclusions could be drawn about the effects of deepening despite the given uncertainty. The effects of deepening on the physical processes has been assessed by only varying the depth in the model. Deepening generally resulted in enhanced sediment import or decreased sediment export. Hence, the transport capacity in the Loire became much more favourable for the import of sediment. In order to determine the robustness of these findings, an extensive sensitivity study was performed of 14.157 simulations (1287 conditions for 11 bottom profiles over time) to capture the influence of uncertainties in multiple input parameters. For the bottom profile representing the bathymetry in the year 1900, none of the conditions resulted in a hyperturbid state, whereas independent of the conditions, the likelihood to find a hyperturbid state always increased for increasing depth. From this we can conclude, that the observed regime shift towards high sediment concentrations would not have happened without the deepening of the Loire estuary.

To exploit its socio-economic functions, engineering measures are regularly applied in estuaries. Estuaries are, however, known to be very complex systems. Stemming from this complexity is the generation of a so-called estuarine turbidity maximum (ETM), which poses great siltation problems to the engineering measures. An engineering measure, which is looked upon in this thesis, is a trench accommodating for the construction of a submerged tunnel. Despite the complexity of estuaries, trench siltation rates are predicted in practice by simple empirical engineering tools. However, a lot of uncertainty is associated with the predicted trench siltation rates, as such engineering tools do not capture the complex estuarine mechanisms. These mechanisms are found to dominate the sediment supply to the trench and the subsequent trapping of sediment in the trench. Therefore, in this thesis, it is investigated to which degree of certainty trench siltation rates in estuaries can be predicted, based on a process-oriented and engineering-oriented viewpoint. This is researched according to the implementation of a detailed process-based numerical model, which is considered to be highly accurate. For this purpose, the following case study is adopted: a trench near the ETM of the well-mixed Scheldt Estuary, at Oosterweel, Belgium. The uncertainty of the numerical model is estimated based on a sensitivity analysis, which maps the epistemic uncertainty, and a scenario analysis, which approximates the intrinsic uncertainty. For verification purposes, modelling results are compared with the state-of-the-art theory on trench siltation mechanisms, and estuarine sediment transport and trapping mechanisms. These are thoroughly analyzed in this thesis based on an extensive literature study. Additionally, a link to practice is made by comparison of the degree of certainty and practicality of the numerical model with the engineering tools. It could be estimated, based on the parameter uncertainty, that the epistemic uncertainty of the numerical model equals approximately 1.5 times the expected siltation volumes. A similar uncertainty due to intrinsic uncertainty was estimated, as the trench siltation rates showed a strong dependency on the variation in forcing regarding tide, river and storms at sea. In total, this led to a quantifiable uncertainty in the order of 2.5 times the expected siltation volumes.
Regardless of this uncertainty, great confidence is put in the performance of the numerical model, as in accordance with existing literature of the study area and theory on well-mixed estuary, important mechanisms in the supply of sediment to the trench were found to be: salinity-induced circulation, tidal rectification, Stokes’ drift and river discharge. Additionally, the governing sediment trapping mechanisms of the trench, found by the model, are in line with state-of-the-art literature. In contrast, yet unidentified by literature, the longitudinal salinity gradient over the estuary also seem to dominantly influence the trapping efficiency of the trench, in particular during flood in which it induces a strong decrease in sediment trapping. In comparison, it is believed that engineering tools, applied for trenches in estuaries, are prone to very high epistemic uncertainty caused by model inadequacy. This is because stand-alone application of the engineering tool on the problem gave a significant over-estimation of the siltation volumes, as predicted by the numerical model. Furthermore, the engineering tool was found to behave differently within a tidal cycle, and on changing environmental conditions. Above epistemic uncertainties due to model inadequacy could, however, not be quantifiably supported, as the total quantifiable uncertainty was in the same order of the numerical model. In conclusion, the degree of certainty of the trench siltation rates is believed to be improved significantly using a detailed numerical model instead of engineering tools. However, a huge drawback of the application of detailed numerical models, is the complexity and the impracticality of the numerical model. Therefore, this thesis opts for the development/use of a more sophisticated semi-empirical tool for engineering measures in estuaries. Though, more research is recommended on trenches in both similar and different type of estuaries in order to generalize and confirm the findings of this thesis.

In this study, the effects of extreme flood events on vegetation and morphological patterns in a natural river were investigated. For this purpose a new vegetation-development model was introduced and linked to a hydro-morphodynamic Delft3D Flexible Mesh model. Based on the results in this study it can be concluded that the direct effects of an extreme flood are relatively low, with almost no vegetation removed during a flood event. However, the extreme floods lead to an increased area suitable for seedling colonization within the river floodplain, which is partly caused by the formation of a secondary channel in the extreme flood scenarios. This causes an increase in the seedling recruitment rate in the years directly after an extreme flood and in a higher vegetation coverage.

Estuaries are dynamic partially enclosed water bodies that are constantly or periodically influenced by the ocean and at least occasionally impacted by river discharge. This creates unique but fragile ecosystems that have to be managed with care in order to be recreationally, economically and ecologically valuable. One of the management issues is water quality, which is mainly influenced by hydrodynamic processes and other processes affecting the transport of dissolved or suspended materials. The understanding of the hydrodynamic processes of an estuary and its physical drivers is crucial for management. One of these fragile ecosystems that have been prone to many human interventions in the past, is the Leschenault Estuary. In this thesis, a 3D-numerical model is developed in D-Flow FM to unravel the governing hydrodynamics of the Leschenault Estuary. Besides, field measurements provided data used as input for the numerical model and more information about the dynamics of the Leschenault Estuary. Most importantly, a methodology is proposed to improve the efficiency in drawing relevant conclusions from observed and modelled data. Efficient and easy-to-apply classification methods are therefore considered that could be powerful management tools. To validate this methodology, a scenario has been considered where the Preston River is aligned to the Bunbury Port. The governing hydrodynamic processes in the Leschenault Estuary are internal circulation, stratification and turbulence, which are predominantly driven by the freshwater discharge and the tides. However, the dominant physical processes are highly dependent on the seasonal conditions and the specific locations. In general, three different seasonal conditions were distinguished: normal summer, normal winter and peak river discharge conditions. In summer, freshwater discharge is reduced, which increased the impact of tidal stirring and vertical mixing. In winter, the high river flow generated more stratified flows and under peak discharge conditions some areas of the estuary presented salt-wedge regimes. The Leschenault Estuary can be spatially subdivided in four distinct regions (southern, central, northern and riverine basin), based on the governing hydrodynamic processes. The southern basin is the most dynamic and can not be specified by a single regime due to the influence of the ocean, the Preston River, the Collie River and the northern regions. The central and northern basins were classified as partially-mixed throughout the year and showed weakly to strongly stratified water bodies, depending on the seasonal conditions. Furthermore, a classical estuarine circulation develops under normal winter conditions. In summer, the northern regions become hypersaline, generating an inverse circulation in the central and northern basins. The Collie River is characterized by a partially-mixed water body, with high stratification. Under peak discharge conditions, the salt wedge can be temporally forced out of the river and partially out of the estuary. Winds, waves and Coriolis have a significant influence on the hydrodynamics of the central and northern basin, due to their shallow and stagnant waters. The driving forces of the salt transport were obtained by the decomposition of the salt flux. The main physical processes affecting the salt transport between the estuary and the ocean along the transect of the 'Cut' over the whole year and in winter were freshwater discharge, topographic trapping and Stokes drift. Stokes drift was dominant in summer, followed by freshwater discharge and topographic trapping. This indicates that regardless the season the advective terms were dominant drivers of the salt transport. It also indicates the seasonality of the salt flux at the 'Cut'. The dominant salt flux components at the central basin was the Stokes drift, followed by freshwater discharge and topographic trapping. The Preston River alignment was compared with its current location to provide useful information for management and to evaluate the efficacy of the adopted classification methods. The scenario results were significantly different than the initial model results and the Preston River alignment had a substantial impact on the hydrodynamics of the Bunbury Port and the southern basin. Bunbury Port circulation became more stratified and its seasonal variation was increased, while the southern basin became less dynamic and partially-mixed, with low to high stratification. The Collie River and central and northern basins however remained almost unaffected. Further, the physical drivers of the salt transport did not vary much but the role of the Stokes drift became relatively more pronounced at the `Cut', due to the decreased influence of freshwater discharge and topographic trapping. At the central basin, the Preston River alignment had a negligible effect on the physical drivers of the salt transport. However, larger spatial and temporal variability of salinity and temperature distributions were observed. It is therefore recommended to conduct an additional ecological valuation of this intervention. Valuable insights were presented in this thesis that have been critically validated. The used methods have proven to be efficient and valuable tools for management.

Within the KustGenese 2.0 research project a 5Mm3 pilot nourishment is created on the ebb-tidal delta of Ameland. For this thesis I was involved in the parties; Van den Herik, the contractor who executed the work, Deltares and Rijkswaterstaat. A tool is created to quickly analyse new surveys in combination with the ships deposit data. The tool is applicable for any other dredging project.
The tool is applied on the 4-6 weekly surveys during the execution of the pilot nourishment. An analyse with the tool gives insight into the morphodynamics of the ebb tidal delta and the location of the pilot nourishment. The sediment transport on the nourishment location is wave dominated, as the sediment transport is limited during calm wave conditions. The sediment transport on the second ebb shield is however tide dominated. During the January 2019 storms an increase in sediment transport is seen on both tidal and wave dominated parts.

Estuarine shoals are valuable areas with functions of nature, safety and navigation. It is of utmost importance to understand their underlying physical processes and long-term evolution to achieve protection. The first aim of this report is to determine the impact of wind-waves on long-term morphological development of estuarine shoals. The rapid sea level rise requires a valid model prediction of esturine shoal evolution in the future. Whether waves should be included for forecast needs to be evaluated. This rises the second aim to investigate wind-waves impact on estuarine shoals evolution under the sea level rise. A 2-D, process-based numerical model (Delft3D) is applied. This study sets up a large scale realistic model covering the whole Western Scheldt geometry and focuses on shoal Van Ossenisse by constructing high resolution grids and imposing wind-waves. Simulations are compared on a timescale of 50 years, with and without wave effects. Results revels that waves tend to slightly migrate shoals along their propagation direction. Waves erode sediment in the intertidal area, resulting in a lowering elevation of the shoal and high suspended sediment concentrations in water column. On the one hand, high SSC combined with wave asymmetry and wind-driven flow enhance sediment transport rate along wave propagation direction over top of the shoal, causing more sediment appearing in the lee side of the shoal. On the other hand, wave-induced suspended sediment follows tidal currents and transport to shoal edges where low bed shear stress exists. These cause shoal widening at lower intertidal area and upper subtidal area. Channel velocity hence increases with response to channel area reduction. This leads to erosion in the channel and channel deepening. In a longer timescale, waves impact do not lead to fundamental difference on estuarine autonomous behaviors. It reveals that waves impact may be sensitive to some parameters (eg. sediment grain size, tidal range, type of boundary conditions), especially in the inner channel. It is recommended to do more investigations. Sea level rise scenarios are carried out by imposing gradually sea level rise at the seaward boundary. Its timescale is 100 years. Both in wave and no wave case, sea level rise leads to elevation of shoal height and area lose in shoal edges, resulting in steeper slope in the intertidal area. Larger channel area and volume are presented with sea level rise. Waves maintain their function under the sea level rise. It lowers and widens the shoal, resulting in the increase of intertidal area and volume. Sea level rise does not change the tendency of waves impact.

Considering scenarios of sea level rise, the sediment budget of the Wadden Sea is of interest for both coastal safety and for the maintenance of values of this unique environment. Sand nourishments are foreseen on the ebb-tidal deltas of the Wadden Sea to increase the sediment budget, which requires us to predict the fate of the nourishment. This study focusses on the exchange of water and sediment between the North Sea and the Wadden Sea through Ameland Inlet. Based on a combination of field observations from the extensive 40 days Kustgenese2.0/SEAWAD field campaign in fall 2017 and Delft3D modelling results, the flow conditions are explained and the contribution of different forcing mechanisms is unravelled. Residual flows and sediment transport at the ebb-tidal delta were found nonstationary due to the action of waves, but also due to local wind-shear stresses. The wind-driven exchange with neighbouring basins over the tidal watersheds leads to significant residual flows through Ameland Inlet, which increases the importance of wind for the system functioning. The many shallow areas and the orientation of the system in relation to the prevailing wind direction for strong winds are believed to make wind forcing as important as observed around Ameland Inlet.

Tidal basins are highly dynamic environments with a complex behavior that is often disturbed by human activities. Considering that tidal dynamics have a direct impact on surrounding engineering infrastructures, adjacent coastlines, nature environment and socio-economic human activities, it is crucial to know the impact of human interventions on these dynamics. This research focuses on the closure of the Gulf of Khambhat in India, which aims at the creation of a fresh water reservoir in the gulf by partly closing the current estuary with the Kalpasar dam. The most recent design of the closure concerns a 30 km dam from the eastern bank near Aladar to the western bank near Bhavnagar. This closure will significantly reduce the total basin area. Consequently, major and morphodynamic changes are expected in the basin. The Kalpasar project has been on the Indian Government's agenda since 1986. Royal HaskoningDHV was involved in the pre-feasibility study, which was presented in the late 1990s. Since then, the existence of a detailed report study has not been confirmed and the status of the announced feasibility studies by the Indian government is unknown. The main objective of this research is to investigate the morphodynamic response at the seaward side of the dam after the closure. A process-based morphodynamic model has been developed to study this response. Deltares and NIOT have provided a two-dimensional (2DH) numerical model of the Gulf of Khambhat to study the tidal propagation in the basin. After calibration and validation of the hydrodynamic predictions, the model has been extended to a morphodynamic model in order to perform morphological calculations. Several adaptations have been made to improve the hydrodynamic simulations of the model; the main contributing factor was the new initial bathymetry. An extensive spin-up simulation has been performed to gather this. To deal with introduced model artefacts, the model results are compared to the reference case. Therefore, two almost identical simulations are performed: the only difference is that one run contains the Kalpasar dam while the other does not. This way, the relative effect of the dam is determined. Moreover, the morphological results have to be interpreted qualitatively, since the predictive skill of the model has not yet been determined. Model results show an overall increase of the tidal range in the basin after the closure, which will have effect up to 100 km from the dam. Close to the dam, the range will initially increase from 7.88 to 10.25 m, and up to 10.50 m after 96 years. Besides, the tidal signal switches from being ebb-dominant to flood-dominant. The velocities around the dam become negligible and the velocities at the main western channel significantly decrease. The eastern channel remains the main channel of the gulf, although its maximum flood- and ebb-velocities also decrease. As a consequence of the hydrodynamic changes, the basin will start importing sediment, directly becoming a sink. On the long term, the area up to 40 km southward of the dam partly fills in. The eastern side of the main channel will also accrete, although its western side will erode over the years. The implementation of the dam will have negative impacts on several locations at the study area. Four vulnerable locations are identified, namely Dahej (India's largest LNG-terminal), Hazira (container terminal), Surat (> 6 million inhabitants) and Alang (largest ship wrecking worldwide). All of these locations will become prone to flooding because of the increased maximum water levels. Moreover, sedimentation at the approach channels of the ports of Dahej and Hazira may hinder their accessibility. The increased water levels at Alang may lead to the suspension of heavily contaminated sediments from these beaches. Furthermore, coastal erosion might be a problem for the entire study area, if the ebb-tidal delta is not large enough to balance the sand hunger of the basin. Relocating the dam is not an effective measure to prevent the negative impacts. Maintenance dredging activities will probably be required to maintain the accessibility of the ports. Moreover, major infrastructural changes will be needed to prevent floods. It is recommended to execute follow up studies with more detailed tools to determine the exact response at these locations. More accurate and up-to-date hydraulic and bathymetric data is required to develop these tools. To this end, it is highly recommended to partner with local parties like the Government of Gujarat, the EAG and local universities.

KEY POINTS:
• While the formation of the intertidal shoal Hinderplaat was a direct consequence of a human intervention, its degradation was a natural response of the system to frequent hydrodynamic forcing conditions.

• Tidal currents push the Hinderplaat in offshore direction, but this is counteracted by waves: these generate cross-shore and longshore currents on the shoal, inducing its landward migration and southward spreading.

• Extreme discharge events provide a significant contribution to channel formation on the Hinderplaat by generating initial local breaches that are enhanced by regular tidal flows.
EXECUTIVE SUMMARY:Ebb-tidal deltas (ETDs) evolve constantly under the influence of natural processes and anthropogenic activities. The Haringvliet ETD in the Southwest of the Netherlands is an extreme example of the latter: closing off the estuary in 1970 triggered a regime shift, completely altering the evolution of the ETD. Initially, the coastnormal sandy shoals evolved towards a narrow coast-parallel intertidal spit: the Hinderplaat. Subsequently, this tidal flat breached around 1995. Thereafter, the flat eroded continuously while sediment was transported from the flat towards the coast.
Previous research with the aim to understand the morphological development of the Haringvliet ETD has provided insights into the processes that are responsible for the large morphological changes directly after the construction of the Haringvliet Barrier. The processes driving the observed ongoing erosion and flattening of the Hinderplaat are however still poorly studied and understood. Therefore in this research, the underlying mechanisms are investigated and linked with anthropogenic interferences and meteorologicalevents.
To this end, a combination of data analysis and numerical simulations is applied. In an analysis of singlebeam bathymetry measurements (gathered in the Vaklodingen dataset), the development of the subtidal shoreface and the intertidal area of the Hinderplaat was explored. In general, the degradation of the Hinderplaat can be divided into three developments: (1) a landward migration since its formation, (2) a lowering since 1992 after a period of significant heightening and (3) a breach and channel formation in 1995, after which the shoal spread and merged with other shoals.
A depth-averaged (2DH) Delft3D model is used to explore the mechanisms behind these developments and to reveal the relative importance of the tidal-, river discharge-, wind-, surge- and wave-forcing driving the flow and sediment transport in the ETD. The first two developments (landward migration and lowering) occurred gradually, hence they were possibly a response of the system to the regular hydrodynamic forcing. Various simulations with a wide range of forcing-scenarios are performed to evaluate this. The third development(breaching) was observed in the same year an extreme discharge had occurred. A morphodynamic hindcast is performed to study the link between the two.
Model results indicate that the landward migration of the Hinderplaat was induced by regular wave action from WNW to NNE direction. Such wave conditions generate cross-shore transport over the shoal in eastern direction. This counteracts the effect of the tide, that enhances (much smaller) residual transport rates in seaward direction. Furthermore, breaking waves generate longshore transport along the Hinderplaat, with the highest transport rates at its southern end. This resulted in its spreading in southern direction and lowering of the highest part of the shoal. In addition, a correlation is found between the sudden increase in height of the Hinderplaat before the degradation and the construction of the Slufter. Considering the abundant transport rates from the Slufterdam towards the shoal, it is concluded that the port extension served as an important sediment source directly after construction. However, the sediment supply might have decreased in subsequent years. The hindcast simulation confirms that breaching of the shoal was a direct consequence of the high discharge event of February 1995: the strong offshore directed currents created an initial channel which was later on maintained by the tide.
Wind-driven currents are very effective in generating residual flow patterns at the shoreface in front of the Hinderplaat. Besides, both the wind and surge act as important amplifiers for the sediment transport rates on top of the shoal. However, waves are indispensable for the morphological changes of the study area as the other hydrodynamic drivers are hardly capable of generating sediment transport by themselves.
Concluding, it is undoubted that the formation and thereby existence of the Hinderplaat is a direct consequence of the man-made closure of the Haringvliet estuary. However, its degradation (lowering, landward migration, breaching and further spreading) is a response of the system to the natural hydrodynamic forcing. Therefore, this evolution can be considered as part of the intrinsic behaviour of the shoal that is independent of human interventions in the former estuary.