A possible way of generating a stable and predictable base load of renewable energy, supplementing the unpredictable wind and solar energy, is dynamic tidal power (DTP). DTP is generated with the use of large dam, which is built in the sea, under an angle with the propagating tidal wave. A dam of sufficient length can create a phase difference between the propagating tidal waves on either side of the dam, creating head differences over the dam, which can be used to generate renewable energy using large turbines in the dam.
Previous studies considered a DTP dam built perpendicular to the coast and the direction of the propagating tidal wave. However, a structure of this size extending into the North Sea interferes with other functions of the area such as shipping. Instead of a perpendicular dam, an oblique dam off the Dutch delta coast has been proposed to reduce this interference. This design has the additional benefits that it could increase the coastal safety of the surrounding area and potentially increase the sediment budget of the Voordelta area in front of the coast.

In this study, a first-order assessment of an oblique DTP dam has been carried out. This assessment focuses on three aspects: the expected energy yield and how this compares to the expected energy yield of a perpendicular dam under the same conditions; the impact this dam has on the coastal safety of the surrounding area. To this end, an analysis of the change in hydrodynamic and morphological processes in the Voordelta as a result of the construction of such a dam has been carried out.

The propagation of the tidal wave around an oblique DTP dam in the North Sea has been modelled using the FINEL modeling software, applied as a two-dimensional flow model. The reference layout of the DTP dam has been determined beforehand based on several requirements concerning the location and length. Using a turbine module integrated into FINEL, the discharge through each turbine has been determined, base on which the energy output of the DTP dam has been calculated. A comparison was made of the energy output of the oblique dam and that of a perpendicular dam, as used in previous studies. To do this, the same model has been run with a dam positioned perpendicular to the Dutch coast.

A DTP dam with a length of 62.5 km and a southwest orientation starting at the Maasvlakte 2 was found to have a maximum power output in the order of 8 * 10^2 MW and a yearly generated energy yield in the order of 2 TWh. Both of these values were approximately a factor five lower than the power output of the perpendicular dam with the same length also starting at Maasvlakte 2. This is because, in the case of the perpendicular dam, a phase difference in the tidal wave over the dam was created, creating a large head difference over the dam. In the case of the oblique dam, the phase difference was lower, significantly reducing the water head over the dam. As opposed to the perpendicular dam, the head difference was created as a result of amplification of the tidal wave within the estuary.

Subsequently, a SWAN wave model has been coupled to the FINEL flow model. In this coupled model, a design storm with a return period of 10000 years has been simulated. Of this storm, the wave characteristics and water level in the area were compared between the scenarios with and without oblique dam. A large decrease in both significant wave height and peak period behind the dam was found across nearly the whole Voordelta area, with the largest decrease offshore immediately behind the dam. However, the significant wave height increased on the outside of the dam and near Westkapelle. The same result was found for scenarios where 25 cm and 80 cm mean sea level rise has been applied. This is because the incoming waves from a northwestern direction are blocked by the dam, resulting in locally wind-generated waves behind the dam becoming dominant in the area. On the offshore side of the dam, significant wave heights are increased as a result of reflection of incoming waves. The maximum water level during the storm decreases in the nearshore area.

As the area behind the dam is transformed into an area resembling an estuary, the dominant hydrodynamic and, consequently, the morphodynamic processes are changed. The dam blocks all incoming waves from the west and northwest, which are the dominant wave directions in the area. Because of this, the wave energy within the area decreases significantly under storm conditions. At the same time, the tidal amplitude is expected to be amplified within the area. These changes cause the area to become more tide-dominated. As a result, a decrease in the onshore directed sediment transport into the area is expected. The entrance of the estuary is expected to become more flood-dominant, as a result of which more inflow of sediment into the created estuary is expected. Dominant sediment transport mechanisms with the estuary are also changed, but for a more accurate view of the extent to which this happens, a complete morphological model is necessary, which has not been applied in this study.

In summary, a DTP dam oblique to the Dutch coast can provide a substantial amount of energy, although it is significantly less when compared to a perpendicular dam and to previous studies. A further advantage of this dam is that the area behind is sheltered against storm wave conditions and extreme water levels, thus increasing the coastal safety. It is foreseen that the area attracts more sediment by the creation of the dam, but this needs to be confirmed by a future morphological model assessment.

Sint Eustatius is a Caribbean island located in the north of the Lesser Antilles. The coastline west of the capital, Oranjestad Bay, is of vital importance to the island as it is here where tourism, recreation, the harbour and historical ruins are located. On the other hand, Oranjestad Bay has a heavily fluctuating beach, which is undesirable. The Public Entity of St. Eustatius is investigating the possibility of a coastal solution that could preserve and extend this beach. However, there is insufficient knowledge of the hydrodynamic processes and morphology available to design a solution. By analysing the morphological system, this study aims to advise the Public Entity of St. Eustatius on the decision for a coastal solution to create a beach in Oranjestad Bay.

A literature study was performed to obtain basic knowledge of the coastal system of Oranjestad Bay. A two-dimensional numerical Delft3D model was then developed to gain more in-depth knowledge of the wave, current and sediment patterns. The result of both findings is combined in a conceptual model, where the cause of the beach fluctuations along Oranjestad Bay was analysed. Based on the system knowledge and stakeholders’ demands and regulations, three alternatives to create a beach at Oranjestad Bay are proposed. The alternatives are qualitatively verified and evaluated with a multi-criteria analysis and cost-value ratio.

The literature review shows that Oranjestad Bay has the characteristics of a wave-dominated coast. The seasonal wave climate has a strong influence on the beach fluctuations that occur in Oranjestad Bay. The influence of tides and wind on sediment dynamics is expected to be minimal. The modelling study concluded that the wave climate can be described by three main wave conditions, namely a sea condition, a storm condition and a swell condition. The different hydrodynamic and morphodynamic characteristics of these conditions provide a reasonable simulation of the coastal processes in Oranjestad Bay. The model results give an impression of the seasonal wave climate and a net northward sediment transport capacity is found. These results are consistent with the expected coastal morphodynamics found in the literature study. The effect of a storm is less well represented in the modelling study. This limitation is caused by the modelling approach. In addition, there are some uncertainties in the model due to the lack of detailed coastal data in the nearshore. The conceptual model indicates that the coast of Oranjestad Bay may experience seasonal gradients
in alongshore sediment transport leading to beach fluctuations. From April to September, beaches are likely to erode due to net northward sediment transport. In addition, beaches erode due to periodic storm conditions that occur from June to November. It has been found that the recovery of beaches after a storm varies along Oranjestad Bay. Scubaqua beach recovers much faster than the beach at Smoke Alley. This is due to the larger sediment transport capacity in the alongshore direction at Smoke Alley beach, the amount of larger cobbles on the shoreline of Smoke Alley and the lack of sediment north of Smoke Alley...

Chile is heavily dependent on international trade, making its port infrastructure crucial for its economic development. Projections show that container freight demand is growing rapidly. To cope with the growing demand, an expansion for the port of San Antonio has been proposed. However, current expansion plans have faced opposition due to environmental and social impacts. This research investigates current social issues and the technical feasibility of harnessing natural sediment transport to create a Building with Nature port expansion solution.

Many sand spits are morphodynamically complex cases that are hard to quantify. Therefore, most case studies on sand spits in a specific type of environment, are descriptive or even non-existent. As is the case for spits in low-energy lake environments, like the two spits at the Marker Wadden islands. Because quantification is necessary for spits in such complex environments, sedimentation was quantified around both spits using polar coordinates and morphologically simplified elevation levels around the spit-platform. It was found that, sediment rich currents that pass over the spit-platform boundary at a certain direction drive spit-platform growth in that direction. The spit-platform growth in turn dictates the growth of the emerged spit. Spit growth quantification enables a detailed understanding of the Marker Wadden spits, which gives insights in spit behaviour in low-energy lake environments. The quantification of spits in other environments could be a powerful tool for the understanding of spit behaviour.

Nature-based initiatives have emerged as potential solutions to problems caused by saltwater intrusion in deltas found globally, but their successful implementation is enabled partly by a multi-stakeholder approach. The latter involves managing several parallel stakeholder objectives, which usually requires quantitative knowledge to understand possible collisions of interests. On that account, the present work developed a systematic approach (referred to as the `comparison tool') to quantitatively compare the objectives of multiple stakeholders interplaying in a delta. As a first approach, the comparison tool is intended to support decision-making to deal with potential conflicts between freshwater supply and port logistics interests. In particular, the present juncture in the Rhine-Meuse Delta in the Netherlands was used to investigate potential trade-offs generated by the nature-based shallowing (or river bed heightening) of the Rotterdam Waterways. The comparison tool is founded on the objective-based assessment of Building with Nature (BwN) solutions. The effects of a BwN solution are assessed separately for each functional requirement and then are related in a combined assessment. The impact assessment for the shallowing of the Rotterdam Waterways required two numerical modelling studies. First, effects on the hydrodynamics and salt transport in a partially-mixed estuary were modelled with the Operationeel Stromingsmodel Rotterdam (OSR), developed by the Port of Rotterdam Authority. Secondly, changes in meso-scale traffic flows over the port network were modelled with the OpenTNSim developed by TU Delft. Afterwards, the effects on freshwater supply and port performance (capacity and efficiency) were quantified separately and then compared. This research delivered a systematic procedure and demonstrated how a combined assessment could be performed in the context of nature-based solutions to mitigate salt intrusion. The most important outcome entails quantitative trade-offs between port efficiency and freshwater supply over a range of bed level increase from 0.0 m to 3.9 m. In general, results showed that the improvement towards the objective of port logistics always goes to the detriment of the freshwater supply objective while increasing bed level. Also, this study found that a collision of interests between the two types of end-users might worsen for a bed level increase over 2 m. Additional results showed that shallowing could be associated with benefits for freshwater supply through a decrease in the duration of water shortages due to a retreat in salt intrusion. The latter holds for specific environmental conditions of low river discharge and mild wind. Also, this study concluded that shallowing could negatively affect port efficiency due to heavier vessel traffic and more burdensome tidal window restrictions, which can result in an exponential growth of vessels average waiting times if the bed level increases over 2 m. Since the freshwater and port sub-systems were simplified, uncertainty in the results was unavoidably accepted. Despite these simplifications, this research demonstrated the main principles in implementing the comparison tool and lays the groundwork for more comprehensive models. In addition, several recommendations for policy-making are proposed, setting a basis for later discussions between freshwater supply and port-related stakeholders in the Rhine-Meuse Delta.

Since early history, humans have been attracted to coastal areas. This can be related to the economic benefits of these areas due to access of ocean navigation, coastal fisheries, tourism and recreation (Seas and Plans, 2011). Around 40% of the world’s population lives within 100 km of the coast (Seas and Plans, 2011). People are drawn to sandy beaches in particular because of its aesthetics and value for specific economic amenities (Luijendijk et al., 2018). Nevertheless, as these beaches are dynamic both in time and space, proper coastal management is required to prevent loss of land and secure future coastal life.

Up till now, studies into coastal erosion have been conducted locally, resulting in site specific observations. However, the promising results of using satellite imagery in the field of coastal engineering allowed studies to be performed at larger spatial scales. This can lead to the identification of areas with similar characteristics, resulting in methodological standardization of approaching a specific problem. A first step toward this new approach of studying shoreline evolution was taken by Luijendijk et al. (2018) who presented a global dataset of annual shoreline positions for sandy beaches over the period 1984-2016 using satellite derived shorelines
(SDS). However, the drivers (causes) of shoreline evolution on a global scale were still unknown, making it only suitable for identifying areas of structural shoreline change, but less suitable for deriving coastal management solutions. Therefore, the research objective in this study is to identify and characterize drivers of shoreline evolution on a global scale using SDS.

This study focused on dynamic sandy beaches, or hotspots, extracted using a method developed by Kras (2019). In this method, using a 2.5-kilometer moving window, transects showing structural shoreline changes and similar characteristics both in space and time were grouped. The small size of the moving window led to locally created hotspots, 95% of which had a spatial extent of less than 10 kilometers, allowing to study shoreline drivers with small to moderate spatial scales (∼10 kilometer). Therefore, the main focus in this study lies on seasonality as a natural driver of shoreline evolution and three anthropogenic drivers: reclamations, nourishments and littoral drift barriers. As seasonality shows inter-annual variability, the temporal resolution of the SDS is increased from annual to monthly.
Using time series decomposition methods, different parameters are extracted that can be used to link the drivers to the SDS. Besides temporal parameters, also parameters related to spatial characteristics are considered. These parameters can be split into identification parameters, used for identifying a driver, and informative parameters, providing knowledge on the behavior of the driver. These parameters were developed and tested using local case studies. Results from these local case studies showed that the identification parameters showed similar behavior along the case studies. This implies that the identification parameters correctly reflect a driver’s behavior. Next, identification of the drivers was verified on a larger scale, all transects within hotspots on West-European coastlines. Verification was done on hundreds of samples using literature or manual inspection of satellite images. Using precision scores, the fraction of true positives to the total identified cases, optimal settings were derived for identification of the drivers. These settings resulted in a pattern of driver identification and characterization along the West-European coastline that is supported by literature.

With the optimal settings for identification determined, the methods were deployed on a global scale. The global dataset consisted out of 3033 prograding and 2121 retreating hotspots containing over 58 thousand transects in total. For these hotspots, SDS were generated over the period 1984-2021 with a monthly temporal resolution. This resulted in a global dataset of more than 26 million monthly shoreline positions. Two other processes, in addition to a seasonal change in wave height, were found to be able to generate seasonal variations in coastline positions from this global dataset. At the Red Sea, even though the wave climate is low in energy (Langodan et al., 2017), the coast is characterized by seasonal behavior. However, in this basin, seasonal variations in water levels rather than the wave climate best described this pattern. In addition to varying wave height and water level, seasonal beach morphology can also be caused by a shift in wave direction. This was observed in southern and western parts of Australia. Furthermore, non-seasonal beaches were primarily seen in low-energetic wave regions where neither of these other two processes occurred, as is the case in the Mediterranean. In regions where seasonal shoreline fluctuations are caused by differences in wave energy, minimum shoreline positions were found at the start of the summer. However, the period in which minimal shoreline positions are observed may be observed at a different time of the year in regions where seasonal shoreline behavior is driven by water level variations or a shift in wave direction. The identification of reclamations pointed out that this driver was especially linked to shoreline evolution in the Middle East and East-Asia. Furthermore, while the amount of constructions of reclamations remained
constant on a global level over the period 1987-2017, in these two areas an increase was observed. Opposite behavior was found by the identification of nourishments, as this driver was identified more often in the period 2007-2017 compared to the two decades before that. Moreover, nourishments were mostly observed in Western countries, for example the USA and the Netherlands. Nevertheless, also in Non-Western countries, an increment over time in the amount of nourishments could be detected. This indicates that throughout the entire world the use of nourishments as a measure to prevent coastal erosion is increasing. Shoreline evolution linked to littoral drift barriers was mostly observed in North-America, Europe and Africa. Downdrift (erosive) hotspots were mostly observed in Africa while in North-America and Europe mostly updrift (accreting) hotspots were linked to littoral drift barriers. On a global level, a combination of an updrift and downdrift hotspots (a pair) was observed in only 2% of all hotspots.

The outcomes above can support local-scale studies by identifying the drivers of shoreline evolution, describing their characteristics and even create standardization by analyzing areas with similar behavior. Hence, it can be concluded that spatiotemporal parameters describing the behavior of a driver can be used to identify and characterize drivers on a global scale using SDS. Nevertheless, not all drivers of shoreline evolution were included in this study. Therefore, to include drivers with larger spatial scales, hotspots should be extracted by using a larger moving spatial window. Furthermore, by increasing the spatiotemporal resolution on which this extraction is based, accuracy of the spatial extent of the hotspots is expected to increase. The small proportion of pairs identified for littoral drift barriers can be partly explained by the erroneous spatial extent of some hotspots. Finally, drivers are identified independently from each other neglecting their interactions. Even though interactions might be complex, drivers should not be identified independently as this will rather
require local studies than support them. Still, even though refinement and further development of the methods is required, this research has shown that identifying the drivers of shoreline development on a global scale using SDS has great potential for sustainable coastal management in the face of future challenges

The Oosterschelde has been an area of morphological change for centuries. Both floodings and human influences have caused the Oosterschelde to have its current shape. During the last century before implementation of the Delta plan (1953) the estuary was still expanding as the channels deepened and the tidal flats increased. With the construction of the Delta works the tidal range decreased with 12 % whereas the tidal prism reduced with 31 %. As a consequence of this reduced tidal motion, the tide is not able anymore to counteract the erosion of the tidal flats which is caused by waves/wind. Therefore, the surface area and the height of the tidal flats reduces (‘Zandhonger’). This decrease of tidal area is an undesirable situation as the unique tidal nature of the Oosterschelde provides a lot of functions for both economy (oysters, mussels), ecology and recreation. Furthermore, the Oosterschelde is used as a transport route by cargo vessels.

This research studies the morphological development of a model of the Oosterschelde with two hypothetical interventions: removal of the storm surge barrier (SSB) and applying 2 metre sea level rise (SLR) in 50 years. This is done with four model scenarios: a run with SSB in place, without SLR (1), a run without SSB, without SLR (2), a run without SSB, with SLR (3) and a run with SSB, with SLR (4). This last run was used as sensitivity run in order to see which hypothetical interventions has more impact.

The model results led to conclusions which parts of the model are represented well and which parts of the model need to be improved. The results made clear that current model is promising as the tidal range was modelled correctly for the majority of the Oosterschelde. Also the model represented the tidal prism well compared to the calculated tidal prism (tidal prism = tidal range * wet surface area of the basin – the sediment volume of the tidal flats). It was found too that SLR can be modelled in a correct way by forcing a water level at the boundaries of the model.

It was found that wave activity is an important process with respect to the development of the tidal flats. Therefore, the frequency of the wave computations should be chosen in such way that reliable wave heights are present for each water level during the tidal cycle at all locations in the Oosterschelde. Another key factor which should be improved is the availability of sediment in the model as this determines the (desired) growth of the tidal flats with SLR. Processes/indicators which give information about this availability (ebb/flood dominance, sediment characteristics) can give insight in the development of the tidal flats. With improvement of modelling these two processes it may be possible to improve model capabilities.

Knowledge of nearshore bathymetry is crucial for every aspect of the blue economy. Currently, it is expensive to obtain nearshore bathymetry at regional scales, and therefore this data is not available for many coasts. The data scarcity occurs especially in the global south and big ocean states that are at the highest risk from climate change. Currently the only global bathymetric dataset, GEBCO, provides depth data at approximately a 500 m resolution. This data is of limited accuracy in the nearshore zone because the source data is sparse in nearshore areas. Recent research has found that NASA’s ICESat-2, launched in 2018 to study the cryosphere, can incidentally capture bathymetric data. Some studies have been done in small sites, but the potential for a global product has not yet been investigated. This thesis proposes a method of using GEBCO data as a starting point and incorporating ICESat-2 data via a Kalman filter. This results in a product with a downscaled spatial resolution and improved accuracy without requiring any in-situ data. If other local bathymetry data is available, it can be added as input to the Kalman filter or used for validation of the method. Recent studies in lidar remote sensing have shown that ICESat-2 can capture nearshore bathymetry at depths of up to 20 me in tracks 0–3 km apart, provided atmospheric conditions are good and the water is sufficiently clear. Hence, this data could provide a source of high-resolution bathymetric depth profiles in tropical areas and possibly at higher latitudes. This research project proposes an automated processing chain, written in python, for extracting bathymetry points from the lidar data based on the density of the photon returns in the underwater zone. This method can reliably identify points containing bathymetric signal. To downscale the data using a Kalman filter, first global data from GEBCO is clipped to the area of interest, and then resampled bilinearly to 50 m resolution. Then, the ICESat-2 photon data for the area is processed to generate point estimates of bathymetric depth. To fill in the gaps between these point estimates, the bathymetric points are subsampled and interpolated to the same resolution as the GEBCO data using a universal kriging interpolator. This interpolator results in a raster of the estimated depth, and a raster of the estimated uncertainty. To update the interpolated GEBCO grid, the Kalman gain is calculated for each raster cell and using the Kalman state equation a new bathymetry grid is produced. If other data is available, the process can be applied recursively with other depth and uncertainty grids, allowing the Bayesian combination of any number of bathymetry datasets for the site. To validate the method, the improvement in RMSE is calculated between the resulting bathymetry grid and previously validated, high-accuracy survey data. The validation has been applied at several global test sites to verify that the method is generalizable to other regions. Validation sites are chosen based on the availability of validation data from either USGS survey or survey data from Van Oord projects. The approach was found to improve RMSE compared to validation data by up to 34% in some test sites. However, other sites showed marginal improvement, or increased RMS error. The results of this research could allow easier methods of characterizing nearshore bathymetry in remote areas. It could also be extended to include temporal variation – as more bathymetric data becomes available, it could be used to measure the dynamic changes of coastal systems. However, the method is limited by strict water clarity requirements and missing data due to atmospheric conditions. Despite these limitations, it could potentially be expanded to create a downscaled global bathymetry dataset of clearwater areas.

In the past decades, beach nourishments have been widely applied along the coast of the Netherlands. Different studies on beach nourishment have been conducted over the years. Most of these studies regard the design, execution method, morpho- and hydrodynamic behaviour, and ecological impact. However, the relationship between the design aspects and the longevity of beach nourishment is not well understood. Here we show with the multiple linear regression (MLR) model that the design aspects volume per metre, height and length of beach nourishment are of interest to analyse the relationship with beach nourishment longevity in the central Holland coast. The storm variables were negligible according to the model since the regression coefficients are insignificant. After numerous reruns of the MLR model, it was noticed that the regression coefficient of design volume per metre is fluctuating. This could indicate a positive, negative, or even no distinct correlation between the design volume per metre and longevity. Therefore, no clear conclusions could be drawn on the design of nourishment volume per metre in order to extend a longer beach nourishment longevity. According to the MLR model, the design length has a positive regression coefficient and design height a negative regression coefficient. These signs suggest that a lower design height elevation and longer design length will result in a longer beach nourishment longevity. The computed beach nourishment longevities of the 7 locations (Julianadorp, Callants-oog, Bergen aan Zee, Egmond aan Zee, Bloemendaal aan Zee, Scheveningen, and Ter Heijde) along the central Holland coast showed that the average longevity of each location could not be interpreted with certainty. This outcome results from the given confidence level of the longevities and the number of beach nourishments used for the computation. Nevertheless, these computed longevities showed that a typical beach nourishment longevity along the central Holland coast is in the range of 3 and 3.5 years. Further, it was observed that computed beach nourishment longevities along the central Holland coast have increased between 1990 and 2020. The increase of beach nourishment longevity coincided with a policy shift in 1999 when shoreface nourishment became a common practice. Therefore, this data suggests that the presence of shoreface nourishment had a positive impact on the longevity of beach nourishments. Despite this result, no certain conclusion could be drawn as the positive contribution can also be caused by increasing nourishment volume through the years. Overall, data-driven research forms the basis of this study and provides a first qualitative insight into the relationship between design aspects and beach nourishment longevity of the central Holland coast.

The Noordstrand of the Marker Wadden has been subject to much more erosion than expected. From our current understanding of this low-energy system we cannot explain what has been the cause of this. The goal of this thesis is to create a better understanding of the different processes responsible for the development of this non-equilibrium beach in a low-energy lake environment. A better understanding of the link between hydrodynamic and morphodynamic processes can be used for the maintenance of the existing Marker Wadden beaches and the design of new sandy protections in this kind of systems. By combining the results of a hydrodynamic and morphodynamic data analysis with the results of the Delft3D Marker Wadden model, it is possible to create a conceptual system description. This can be used to improve our understanding of the Noordstrand development and the responsible processes. In this system description the influence of the general Markermeer system cannot be neglected as the different systems (Markermeer, Marker Wadden and Noordstrand) cannot be regarded separately as the different hydrodynamic processes are linked.

A significant part of the Netherlands lies below sea level. The Dutch have protected their land against seawater since the 10th century. Nowadays, the Netherlands is protected by 3800 km of primary flood defences. Since the Flood Defences Act was included in the Dutch law in 1996, all flood defences are tested against the national safety standards every twelve years. In the latest assessment round, a 47 kilometres long stretch of a Wadden Sea dike in the northern part of the Netherlands dike section, from Koehool to Lauwersmeer, did not meet the requirements. It is rejected to multiple foreshore influenced failure mechanisms. The dike area of Koehool-Lauwersmeer consists of cultural heritage in means of historical dikes and historical land reclamation structures. The (embanked) salt marshes that are present at the foreshores of the dike section, are of great value for both ecology and water safety in the area. The length of the dike section and the unique project location, provide an opportunity to explore alternative solutions for the dike strengthening project. Innovative dike strengthening solutions can potentially minimize the anthropogenic influence of the reinforcement projects, increase the systems adaptability potential to sea level rise and contribute to the ecological values of the area. In this research, an explorative study is conducted to find an alternative dike strengthening design and to assess the morphological developments and ecological opportunities of such a design. Based on the criteria to contribute to both flood safety and ecological value, a slufter alternative is chosen to be studied further. The slufter alternative engages an inland area between two dikes into the Wadden Sea by an artificial dike breach. The area is regularly inundated, creating opportunities for ecosystems to evolve. A depth-averaged (2DH) Delft3D model is used to explore the morphological developments of the slufter area and the potential to add to the ecological value of the area. The project area is characterized by a sediment-rich environment and a flood dominant tide. Higher flood than ebb velocities are present, causing an import of sediment into the slufter area. Model results indicate that the net sediment import of the slufter area mainly depends on the suspended sediment concentration, the critical shear stress and the tidal prism of the slufter area. A geometry that causes an increase in the flow velocity shows higher suspended sediment concentrations that lead to higher amounts of sediment import. Under the influence of a sea level rise (SLR) of +1m, the sediment transport increases with a factor of 2 to 3, depending on the initial geometry. SLR enhances the sediment trapping of the area. The slufter area can potentially keep up with SLR. Assuming an equal distribution of sediment over the slufter area, the average growth rate of the bed level is between 0.22 (minimum sediment import, maximum SLR) and 21.12 (maximum sediment import, minimum SLR) times SLR. Applying the slufter intervention adds 60 ha to the intertidal area of the Wadden Sea. Depending on the applied geometry this results in 30-50ha between MLW and MHW (lower marsh) and 10-30ha above MHW (middle and upper marsh). The slufter alternative creates opportunities for new ecosystems and contributes to the Natura2000 goals to create more gradual transition areas between the Wadden Sea and the surrounding land by creating an area with a gradual wet-dry transition. These potentially add to the biodiversity of the area as they create opportunities for specific plant species and waders. It is concluded that creating a slufter area at the Koehool-Lauwersmeer dike, provides opportunities for sediment trapping due to the flood dominance of the system and the high sediment concentrations. The amount of sediment trapping is influenced by the critical shear stress, the area’s tidal prism, and the suspended sediment concentrations. SLR increases the amount of sediment trapping. Depending on the applied geometry, the bed level growth rate is larger than SLR. Creating a slufter area creates an opportunity to improve both the flood safety and the ecological value in one design.

Offshore wind farms are being built at an unprecedented pace in the North Sea. The Dutch government is aiming for a CO2 neutral energy supply by 2050 and vast cost reductions have turned (offshore) wind energy into a worthy competitor for other (green) energy sources. Most of the planned wind farms in the Dutch North Sea are located in areas where the seabed is covered with sand waves. In the North Sea these sand waves have lengths of 100-1000 m, heights of 1-8 m and they migrate with rates of up to 10 m/year (Morelissen et al., 2003). Sand wave migration and changes in shape, may cause a significant rise or drop in local bed level. This bed level variation over time could decrease the stability of foundations or bed protections or cause exposure of cables and pipelines.
Various offshore infrastructural projects, like offshore wind farms, thus require long term (30-50 years) predictions of the seabed dynamics. Currently data-driven methods are used to determine the range of expected bed levels. However, the uncertainty in these predictions is significant, with sand waves being the largest source of uncertainty. Furthermore, no real understanding of the systems at hand forms the base of these predictions. Not many attempts have been made to accurately model sand wave dynamics in real-life situations using a process based model. Since sand waves often have steep slopes in migration direction, a need for small numerical grid sizes arises. On the other hand oceanic hydrodynamics are affected by large scale bed forms. To include (the influence of) these bed forms, large model domains are required. This makes numerical modelling of sand wave fields rather difficult due to the balance between grid sizes and computation time. The newly developed Delft3D Flexible Mesh (FM) model may be able to overcome some of these problems.
Through the use of unstructured grids, the desired level of detail can be reached in certain sand wave areas. In combination with the possibility to run simulations in parallel, on multiple cores, computation times can be reduced significantly. However, the Delft3D FM model has not yet been used for the prediction of sand wave dynamics. The aim of this research is to find the opportunities and challenges of the Delft3D FM model for quantitative modelling of sand wave dynamics in the North Sea.

Through two case studies various opportunities and challenges for predicting sand wave dynamics using Delft3D FM are discovered. The Delft3D FM model showed a significant reduction of computation times for a 2DV case using a single core compared to Delft3D-4. For parallel simulations, using multiple cores, an approximately linear further reduction of computation time is observed in a 2DV setting. Furthermore, the possibility of unstructured grids presents a solution for the small grid sizes needed in sand wave areas. Other computational
gains are realized through a morphological scale factor (which is also
ncorporated in Delft3D-4), optimized time-step management and a new type of boundary conditions. This new boundary condition imposes both water level and flow velocity over depth in both horizontal directions. In this way the local flow conditions are accurately represented and the influence of bed forms outside the model domain can easily be incorporated. This potentially eliminates the need for buffer zones.
Challenges for the application of Delft3D FM on sand wave cases are found in amongst others the availability of data. When less data on local hydrodynamics is available the accurate representation of processes driving sand wave dynamics becomes more difficult. Furthermore the inclusion of sub-grid processes, like the growth and migration of megaripples, could be problematic. In the model case studies no calibration was carried out. This calibration could potentially increase the effort needed to apply Delft3D FM to real life sand wave cases.
Furthermore, the Delft3D FM model is still in development and significant differences between the results of different versions of Delft3D FM were observed. Care should be taken when applying a new version of Delft3D
FM. The model is however being developed in collaboration with users which ensures quick feedback and thus stimulates improvement of the results between versions.
Recommended research includes extended exploration of the 3D effects influencing sand wave dynamics. Furthermore, improvement of morphological results and optimization of the model set-up will increase the applicability
of Delft3D FM in an engineering setting. A model run forced by two Riemann boundaries showed improved morphological results, although the hydrodynamics were not well represented. These results might indicate
where differences with reality originate. Examples of such differences are overestimation of peak velocities, exclusion of wind-driven currents and exclusion of processes like suspended sediment transport, free surface waves
and grain size sorting. Further exploration of these factors could enhance the predictive capacities of Delft3D FM. Applying the model at other locations in the North Sea will help determine the overall applicability of the model.
Through this extended research the full potential of the Delft3D FM model can be discovered and prepared for future engineering applications. Insights gained into the processes influencing sand waves dynamics, through the use of Delft3D FM, could pave the way for more nature based solutions, thus reducing the need for dredging. In this way Delft3D FM could contribute to reducing risks, costs and environmental impact of offshore construction projects in sand wave areas.

The lower Ems river suffers from hyper-turbid conditions. These conditions are caused by channel deepening over the last 50 years, resulting in an asymmetrical tidal wave. This asymmetry has resulted in an increased
import of sediment into the Ems river. Recently some effort has gone into determining whether or not the local tidal barrier (Emssperrwerk) can be used to alter the asymmetry of the tidal waves propagating through the Ems estuary. Previous modelling studies, using state-of-the-art models, have been able to reproduce prototype tests involving the same tidal barrier but very little effort has thus far gone into determining what the optimal barrier control regime is and what the restriction imposed on the barrier operation mean for the overall
effectiveness of the barrier. The operation of the tidal barrier was schematised and described using two factors: closure percentage and closure duration. The effectiveness of a broad spectrum of combinations determining the tidal barrier operation is modelled using a simple one-dimensional model which takes only into account the (simplified) hydrodynamics in the lower Ems river. The results of the model indicate that only in part of the Lower Ems the tide can be adjusted to become symmetrical or slightly ebb-dominant. This requires a closure duration longer than approximately 240 minutes. The length of this stretch of river is increase further by increasing the closure percentage. Similarly, increasing the closure percentage also leads to a decrease in the tidal volume and the amplitude of the M4 component. For this reason, the closure percentage should be kept as low as possible, as long as the barrier operation is able to reduce the sediment import into the Lower Ems. The required length of the stretch of the Lower Ems with a symmetric tide is estimated to be around 12 km. Applying restrictions to the barrier operations showed that shorter barrier
operations should be preferred, since short operations allow a larger number of
tidal waves to be altered, increasing the effectiveness in a realistic setting. Based on these considerations an optimal barrier operation consists of a closure duration of approximately 300 minutes and a closure percentage of approximately 60%. The results showed that the method used for evaluating the barrier operation is unable to distinguish between water levels signals consisting of altered and unaltered waves. The effectiveness of the barrier operation is
still estimated by considering the whole water level signal. The impact of the barrier operation in the model interfered with the seaward model boundary. This error increases in magnitude with increasing closure percentages. Making the results for those combinations unreliable. In order to make more reliable conclusions about the effect of the tidal barrier operation, subsequent models should encompass a larger domain and include a more detailed schematisation of the channel geometry, river discharge and the tidal barrier itself.

Key points:- Pre-closure salinity intrusion into Haringvliet-Hollands Diep is known to have reached Biesbosch National Park at flood tide. Post-Delta21 salinity intrusion is projected to be less extensive than pre-closure. Maximum intrusion is estimated to reach the westernmost Moerdijk ports mainly due to diminished tidal flow at the estuary mouth.- Freshwater intake in the Haringvliet is projected to be compromised for the majority of the year whereas freshwater intake in Hollands Diep is compromised during prolonged drought.- Salinity outwash from the Haringvliet on ebb tide is projected to be poor under both drought and normal conditions due to widespread salinity diffusion in lateral and vertical directions on flood tide. The Delta21 framework, in which this study is positioned, aims at increased flood safety and ecological restoration of the Haringvliet, a former estuary in the Dutch southwestern delta that has been closed as part of the Delta works. To achieve this, Delta21 proposes to reopen the Haringvliet freshwater basin to tidal effects in an attempt to restore its estuarine character. Implementation of Delta21 introduces the risk of compromising agricultural and industrial activities around the Haringvliet-Hollands Diep by reintroducing salinity and tidal movement in the basin. The central problem lies in quantifying the extent and stability of the expected periodic salt intrusion post-Delta21. This has been done by projecting a geographical bandwidth of salinity intrusion patterns depending on the severity of SLR (2020-2100) and low-to-mean Rhine-Meuse discharges (in 2100 CE) using a numerical model. Mitigation strategies are then recommended based on these numerical results. The OSR-HV model (owner: Port of Rotterdam) is used to run predictive scenarios of salinity intrusion for the lower reaches of the Rhine-Meuse basin. OSR-HV runs in TRIWAQ (Rijkswaterstaat), which is 3D numerical modelling software that employs coupled hydrodynamics and constituent transport thereby resolving salinity transport. An upper-end critical scenario consists of a Rhine (Lobith) discharge averaging 1000 m3/s for 31 days combined with 85cm SLR in 2100. This resulted in an intrusion pattern reaching the westernmost port of Moerdijk in Hollands Diep. Results show that the basin geometry, possibly nudged by Coriolis deflection, initially causes a preferential path of salinity intrusion along the southern bank of the Haringvliet. Lateral and vertical mixing is extensive in the western part of Haringvliet which is thought to be a combined effect of weakened tidal flow at the estuary mouth and robust and erratic geometry of the basin. Further up-estuary, the historical flood-ebb tidal channel structures is the main transporter of salinity. The Haringvliet shows distinctly different estuarine behaviour compared to the neighbouring Rotterdam Waterways where stratification is more stable, causing less up-estuary diffusion. The relative robustness of the Haringvliet and mild freshwater forcing give rise to extensive 3D mixing which subsequently limits the maximum horizontal excursion of salinity. Salinity intrusion into the Old Meuse is observed to aggravate upon opening of the Haringvliet sluices due to flow reversal in Spui which connects Haringvliet with the Rotterdam Waterways. This effect can even result in salt intrusion from the Rotterdam Waterways via Old Meuse and Spui back into the Haringvliet, causing a secondary spike in salinity on ebb tide there. Finally, height-limitation of the Haringvliet sluice gates is somewhat effective in countering horizontal excursion of salinity but runaway diffusion in the Haringvliet results in similar salinity profiles compared to full opening of the sluice gates. A shipping channel that crosses the current Haringvliet front delta is included in Delta21. This deep feature promotes advection of salt through the Haringvliet sluices. Subsequent diffusion patterns cause for poor washout of salinity from the basin upon ebb tide. Limiting the depth of this channel is recommended if salt intrusion is to be reduced. Full opening of the Haringvliet sluices furthermore causes approx. 0.50m lowering of Mean Low Water (MLW) near Moerdijk which affects busy shipping routes between Rotterdam-Moerdijk-Scheldt. Partial reduction of the conveying area of the Haringvliet sluices may be used to suppress the tidal wave penetration into Haringvliet-Hollands Diep. Significant gain in ecological value is likely post-Delta21 due to addition of approx. 1900 ha of intertidal areas and a 40 km salinity gradient (excl. front delta). Ample recommendations on further research have been made in this exploratory study. It is recommended to further study the effects of Delta21 interventions on macro hydrodynamics of the Dutch coastal shelf. The interconnected nature of the region requires a larger modelling domain to prevent the occurrence of non-physical effects obtained from the current numerical schematization. Furthermore, hydrological relations and bathymetry were generated from 2020 data. It is therefore recommended to precede the assessment of salinity intrusion into the Haringvliet with numerical projections on change to these environmental factors. Lastly, significant gain in accuracy may be obtained from applying spatially varying temperature and wind to the domain to better replicate baroclinic flows and turbulent mixing.

The coastal area provides important services such as valuable habitats for wildlife, resources for regional development, and buffer zones for the land against natural disasters such as storm surges. But these narrow coastal areas experience pressure from both land and ocean side. In order to regulate sustainable coastal development, protect coastal areas from natural forces, implement ecosystem protection strategies and mitigate the impacts of climate change on coastlines, it is crucial to observe and quantify the changes along coastlines that are vulnerable to these pressures. Among the various coastal environments, the focus of this master thesis is on muddy coasts. A muddy coast is defined as a coastal depositional environment that is usually formed along an unsheltered coastline exposed to low energy conditions and that consists mainly of fine sediments, which are smaller than 63 micrometres in diameter. So far, few methods have been developed to detect sandy coasts and the rate of change of sandy coastlines at global scale, but little is known about the detection and behaviour of muddy coasts. The main objective of this thesis is to develop an automated classification method to identify muddy coasts along all the coastlines of the world. The main objective can be translated into the following research question: How can a reliable global mud classification be obtained by analysing the characteristics of muddy coasts using publicly available satellite remote sensing techniques and globally available coastal datasets? To obtain a reliable global mud classification, a method based on the spectral properties of individual mud patches and on the physical geographical characteristics of muddy coasts is proposed.
The spectral properties of individual mud patches are studied at pixel level using multispectral satellite images and the physical geographical characteristics of a muddy coastal system are studied using seven globally available coastal datasets. The information from the multispectral images and the information from the coastal datasets are used as the input of the development of a hybrid coastal transect classification model, in order to obtain a more reliable and robust classification model that can detect muddy coasts at global scale. With supervised machine learning the hybrid coastal transect classification model is developed, which can classify global coastlines into five coastal types: plain beaches, muddy coasts, coastal cliffs, vegetated coasts and other. 85 percent of the muddy coasts are correctly recognised by the hybrid classification model. The accuracy of the hybrid model is still increasing significantly, meaning that the model could perform even better if more training data is added to train the model. The large amount of training and validation data at both pixel and transect level resulted in a reliable, robust global mud classification model. With the addition of the coastal datasets, the model performs better than when only the multispectral satellite images are used for classifying muddy coasts. The hybrid classification model is used to classify 100000 global coastal transects from which 12 percent are classified as muddy coasts; 60 percent of the classified muddy coasts are in the tropics.

Coastal flood risk is expected to increase over the 21st century as a result of climate change and economic growth, which makes low-lying regions especially vulnerable. Global screening techniques are needed for a more widespread use of NBS in these flood prone coastal regions. This research expands on the current assessments done by developing a quantitative global screening method that evaluates the costs and benefits for two defence approaches; 1) increasing the dike height, 2) a hybrid solution that includes increasing of the dike height in combination with restoring mangroves and/or corals. The screening method is based on Van Oord’s Climate Risk Overview tool, in which, globally, coastal hotspots are indicated that have a predefined risk of flooding in the 21st century. The steps added by my screening method include; 1) determining which
NBS can be applied depending on the local physical conditions, 2) determining the costs for both NBS and conventional hard solutions, 3) determining the increase/decrease in flood risk of the different interventions for current and future conditions, 4) monetizing additional benefits that NBS provide, 5) assessing the benefits and costs to determine if NBS are the most optimal solution. The results of this global method are inherently limited by several simplifying assumptions and by the lack of high resolution local data, which influences the cost/risk estimates and corresponding site identification. For 2.6-3.3% of the coastal hotspots, NBS can reduce the investment costs in addition to being cost-beneficial. There is potential for expanding this work by adding sea grasses, salt marshes and oyster reefs as vegetated foreshore systems, and by including more thresholds to make the criterion for potential sites to apply NBS more strict.

In recent years, nature-based solutions have gained recognition for their capacity to reduce flood hazard on coastal communities. These coastal threats range from waves and tides, to future storm variability and predicted sea level rise. Vegetated foreshores are one of the measures that fall under this palette of solutions, and are the focus of this thesis. While vegetated foreshores can be colonized by several plant species (mainly mangroves or marshes), this thesis presents the study of phenomena occurring at salt marshes in an attempt to determine which are relevant indicators that can predict the presence or absence of this ecosystem at a given location. Moreover, the wave height attenuation capacity of such vegetated foreshores under different conditions is also assessed for different effectiveness indicators, in a way that provides insight into whether this habitat is not just feasible, but also effective as a coastal protection measure, with respect to wave height attenuation.

Results suggest that within a water system with similar sediment composition, inundation-free period and daily-occurring hydrodynamics can explain the presence/absence of vegetation at most sites, while storm conditions can the determining condition for vegetation absence in other locations. For comparison between systems, the dimensionless wave-induced excess bed-shear stress factor may serve as a relevnat proxy. These conclusions indicate the occurrence of sediment re-suspension during approximately 20% of the assessed time, at the most.

From the wave attenuation effectiveness assessment, considerations for tidal regime, surge height, and type of wave forcing were used to determine the degree of effectiveness of salt marshes in the studied water systems, while defining effectiveness in terms relative to a mudflat located at MSL. Results suggest that salt marshes located in macro tidal sites, like in the Western Scheldt, can dissipate more wave energy than habitats located in micro or meso tidal areas, such as the Wadden Sea. On the other hand, results treating the different wave loads further indicates that greater attenuation may be achieved in sheltered coastal locations such as the Western Scheldt estuary, indicating that this system may be more effective in sheltered than in exposed coastal areas.

Finally, the set of conclusions provided by both sections may serve to determine whether an arbitrary location is capable of hosting salt marsh vegetation, as well as the effectiveness of such nature-based solution with respect to wave height attenuation. The elaboration of an assessment tool was not achieved in this thesis; however, in order to perform a quick check for salt marsh introduction as an effective flood defense measure at a given site, results indicate the gathering of necessary data such as bed level elevations - for inundation-free period analysis - as well as occurring hydrodynamic forcing and sediment properties at such arbitrary site (excess bed shear stress determination, evaluated with the previously proposed limits). With respect to the degree of wave height reduction effectiveness, the determination of the occurring tidal regime, design surge heights, and considerations of sheltered/exposed coastal conditions may serve as a first estimate for this purpose.

To improve the socioeconomic situation in the Republic of Nicaragua, the government has decided to strengthen the country’s transport infrastructure by building a port on the Caribbean coast. The future port will be in Bluefields Bay, which can be characterised as a lagoon-shaped estuary. The inner basin is connected to the sea by two tidal inlets, located north and south of a barrier island. This study assesses the hydrodynamics and morphodynamics of the area; in addition, it analyses the influence of the port structures on these natural processes. A qualitative analysis of the hydrodynamics and sediment transport in the area is conducted, and sedimentation rates in the navigation channel and the erosion rates of the coast are calculated. The area is analysed with the help of a conceptual model that is supported by the process-based model Delft3D. Large parts of the area consist of shallow depths of around 1.5 m below mean sea level (MSL). The bed of these shallow parts consists mainly of mud. In those areas with a depth of more than 5 m below MSL, which are the river channel and the tidal channels at the inlets, the flow velocity increases, and a more substantial fraction of sand can be observed. In the data analysis, distinct wet and dry seasons can be observed; these seasons change the hydrodynamic influences over the course of the year. The river discharge increases by a factor of 10 during the wet season. In addition, the river delivers large quantities of mud, particularly during the wet period. When the tidal flow enters the lagoon, it influences sediment transport. As the dominant hydrodynamics change throughout the year, the sediment fluxes change with them. Beyond the hydrodynamics within the lagoon, the adjacent coast is under the influence of a swell wave climate. As the waves mainly come from the east-northeast at a height of 1 m, a moderate southward longshore transport is initiated year-round. The Delft3D model is used to analyse the hydrodynamics and sediment transport of the area in more detail. The model is used to analyse the flow magnitudes and directions. This approach allows the dominant hydrodynamic components to be identified. The most relevant hydrodynamic components are considered in the Delft3D model. These include tide, river discharge, waves, and wind. The 2D mode is sufficient to model these hydraulic components. Because of the hydrodynamic climate changes that occur throughout the year due to changes in the meteorological climate, the simulation period is one representative year. The model is calibrated and validated by means of phenomenological calibration and expert judgement, as field data is scarce.

Worldwide, coastal regions are pressured due to sea-level rise and the increased likelihood of extreme events. Traditionally, hard engineering techniques were used for shoreline protection. However, due to the negative side effects at adjacent beaches, a switch was made to more sustainable soft solutions, such as nearshore berm nourishments. Although several manuals are available describing the preliminary design of nearshore berm nourishments, most of them are based on expert judgment and not on quantitative predictions, which potentially leads to design flaws and, therefore, to unnecessary costs. To overcome this problem, this research aims to increase the understanding of the development of nearshore berm nourishments in relation with the corresponding shoreline evolution by analyzing a shallow concentrated placement at New Smyrna Beach. It is found that the theoretical Feeder and Leeside effects played an important role in shoreline dynamics. The Feeding effect is characterized by shoreward propagating accretionary waves (SPAWs) while the Leeside effect is depicted by shoreline erosion patters downdrift of the nourishment induced shadow zone. Contrary
to most nearshore berm nourishments, the placement at New Smyrna Beach resulted in a significant increase of 45.000 m2 of the sub-aerial beach. Although not validated in this study, it is hypothesized to be a result of
the high cross-shore density of the nourishment, ¼ 875 m3/m, and shallow placement location of 4-5 meters.

About 80-90% of U.S. East Coast barrier beaches have experienced erosion in the last 100 years. South Carolina’s coastline forms no exception, a third of its developed shoreline experiences erosion. Among these eroding shorelines is Hilton Head Island, the second largest barrier island on the U.S. East Coast. Until now, erosion here has been addressed through traditional local beach nourishments. An alternative approach to the traditional nourishment method, are so-called feeder nourishments or feeder beaches. The potential advantages of the feeder nourishment concept over the traditional method are reduction of the nourishment frequency, containment of the ecological stress in a relatively small area, and a short to medium term increase of local available space for recreation and the environment. Given the potential advantages above, the residents of Hilton Head Island asked TU Delft to investigate the possibility of applying a feeder nourishment at their shoreline. Currently, a pilot project known as “The Sand Engine” is examined along the Dutch coast. Several studies into its morphological behaviour show that this feeder nourishment can be beneficial to the sediment budget of a larger coastal cell. Because of the promising results at the Sand Engine pilot project, it is tempting to state that a feeder-nourishment could also be applied at Hilton Head Island. The problem, however, is that the conditions at Hilton Head Island and the Sand Engine are different. There are two main differences between Hilton Head Island and the Sand Engine. First, Hilton Head is subjected to a relative calm wave climate in comparison to the Sand Engine. Second, the presence of two tidal inlets at Hilton Head, compared to a relative straight and uninterrupted coastline at the Sand Engine. As a result, the conclusions drawn from the Sand Engine pilot project do not necessarily hold for Hilton Head Island as well. The main objective of this thesis is to analyse the morphological behaviour of a feeder nourishment located at Hilton Head Island. First, to study its potential as a measure against erosion at Hilton Head. Second, to compare its morphological behaviour to that of the Sand Engine. And third, to be able to examine the potential of the concept for the Atlantic southeast coast of the U.S. in general. The morphological development of a feeder nourishment at Hilton Head Island was simulated with Delft3D over the course of 1 year for different model scenarios, with varying forcing conditions and varying bathymetric features. The effect of the relative calm wave climate at Hilton Head Island in comparison to the Sand Engine is twofold. First, the contribution of wave forcing to the total erosional volume of the feeder nourishment after 1 year is smaller as compared to the Sand Engine. Eliminating all driving forces besides wave forcing reduces the total erosional volume to 58% at Hilton Head, in comparison to 75% at the Sand Engine. Second, the contribution of storm events to the total erosional volume after 1 year from the feeder nourishment is smaller at Hilton Head compared to the Sand Engine. It measures 23% at Hilton Head, in comparison to 60% at the Sand Engine. To assess the impact of the two tidal inlets on the feeder nourishment, they were closed off. Closing of the tidal inlets eliminates any (potential) residual currents. This reduces the total amount of sediment that is eroded from the feeder nourishment by 7% compared to a reference scenario with open tidal inlets. Before construction of the feeder nourishment the coastline south of the nourishment experienced a net sediment outflux of approximately 4000 m3/year. After construction of the feeder nourishment, the southern section experiences a net import of sediment of approximately 100.000 m3/year. Meaning that the southern section, on average, has transitioned from being erosive to accreting. Up to 500 meter away from the nourishment the cross-shore profile shows a seaward movement of the shoreline position of approximately 25 m compared to the original situation without nourishment. Before construction of the feeder nourishment the coastline north of the nourishment experienced a net sediment outflux of approximately 40.000 m3/year. After construction of the feeder nourishment, this net outflux of sediment has decreased to approximately 25.000 m3/year. This shows that the feeder nourishment is feeding sediment to the northern section, but at a rate that is not sufficient to keep up with the underlying erosion rate. The northern domain, on average, still experiences a sediment outflux and stays erosive. Roughly 50 m of coastline directly north of the feeder nourishment experiences a seaward movement of the shoreline position. However, moving further away from the nourishment, the shoreline remains erosive. The Atlantic southeast coast of the United States is made up of North Carolina, South Carolina, Georgia and Florida’s east coast. The South Carolina and Georgia coastline are comparable in both hydrodynamic conditions and geomorphological setting. They are mixed-energy coasts, broken up by numerous tidal inlets, and home to short barrier islands with complex sediment transport patterns. North Carolina’s and Florida’s east coast are wave-dominated, with relative straight shorelines. Which is distinctly differences from the conditions found at Hilton Head Island. Therefore, the potential of the feeder nourishment concept is only analysed for South Carolina’s and Georgia’s coastline. The presence of numerous tidal inlets leads to strongly varying conditions along the coastlines of both states. The developed locations along South Carolina’s coastline that require erosion mitigating measures are south Debidue beach, North Island, Hunting Island and Daufuskie Island. Along Georgia’s coastline there are only some erosion hotspots along Sea Island’s coastline that require erosion mitigation measures. The wave climate at all the above mentioned location is similar to Hilton Head. A southeast swell, with a narrow range of directions and an annual wave height of roughly 1,0 m. The same goes for the tidal range. The results at Hilton Head show that erosion on adjacent coastal sections can be lessened and/or prevented by constructing a feeder nourishment. Given that these locations are subjected to similar conditions, the construction of a feeder nourishment could potentially be an effective measure to prevent or lessen the occurring erosion.