The Netherlands are prone to flooding, with 30% of the country lying below sea level. To protect its densely populated and economically important coastal zone, Rijkswaterstaat (RWS) applies a maintenance strategy based on regular sand nourishments. These nourishments involve the placement of large volumes of sand, typically dredged from the North Sea seabed, to compensate for structural erosion. While this process is effective for maintaining coastal safety, it is resource-intensive and increasingly unsustainable in light of climate change, sea-level rise, and stricter environmental ambitions. With national coastal programmes such as Kustgenese 2.0 and the Dutch Coastline Challenge calling for more sustainable and adaptive maintenance strategies, complementary alternative concepts are under consideration. One such concept is sand recirculation: the artificial redistribution of sand within the coastal system, without the need for additional offshore extraction. Internationally, this principle is already applied through various forms such as sand bypass systems, which transport sediment along the natural littoral drift to counteract obstructions like jetties; sand backpass systems, which move sediment against the dominant transport direction to replenish eroding areas; and periodic dredging campaigns, where accumulated sediment is relocated within the same littoral cell. These systems respond to sediment imbalances caused by human interventions and offer a sustainable alternative in settings where offshore resources are limited or environmental impacts must be reduced. This thesis explores whether such a recirculation strategy can be a technically feasible addition to the nourishment policy at Maasvlakte 2. This protruding coastline, located on the western boundary of the port of Rotterdam, experiences a structural morphological imbalance: persistent erosion in the westfacing bend and visible accretion in the southern section (in the form of a spit), primarily due to strong gradients in alongshore sediment transport. Currently, large-scale nourishments from offshore sand sources are periodically used to reinforce the eroding zones. However, the simultaneous accumulation of sand in the south offers potential for a circular approach to sediment management. This study aims to evaluate whether this locally available sediment can be redistributed to erosion-prone areas through artificial means, thereby reducing the demand for traditional offshore sand sources. The research begins with a morphodynamic analysis of Maasvlakte 2, using various datasets including bathymetric surveys, coastal profile data, and shoreline extractions. Accretion and erosion patterns were quantified and compared to predictions made using the one-line ShorelineS model, which simulates coastal evolution based on alongshore transport driven by transformed offshore wave conditions. This comparison confirmed that the largest erosion hotspot coincides with the western bend of the coastline, while the southern section consistently accumulates sediment. An additional finding, which was not initially anticipated, is the identification of a secondary accretion hotspot that may serve as a viable source area for sand recirculation. This results in the presence of both a southern source (the spit) and a northern source, each subjected to distinctly different hydrodynamic conditions and therefore requiring a distinct approach to extract sediment from these respective hotspots. Annual redistribution volumes between 300,000 and 415,000 m³ were identified as potentially technically recoverable, equating to a reduction of approximately 42-59% in the need for offshore-originating sand nourishments. Several operational strategies were explored, including the use of trailing suction hopper dredgers (TSHDs), cutter suction dredgers (CSDs), and sand backpass systems, in which sediment is transported continuously through pipelines. For each strategy, design parameters such as dredging volume, frequency, location, and required vessel or system dimensions were assessed. A Multi-Criteria Analysis (MCA) was used to evaluate each option based on technical feasibility. The evaluation revealed that a TSHD is the most suitable option for the northern source, while a CSD is preferred for the southern source. This distinction arises from the deeper location and greater flexibility requirements in the north, which suit the mobile operation of a TSHD. In contrast, the southern site allows for more precise, ii iii stationary excavation nearshore, favouring a CSD in combination with barge transport. In a subsequent multi-criteria analysis that considered operational feasibility, costs, and other relevant factors, the TSHD and the sand backpass system emerged as the most favourable options for their respective locations. The greatest technical complexity lies in the redistribution of sediment within the western bend of Maasvlakte 2, where bi-directional sediment transport dominates. This area requires nourishments to be placed across a wide spatial range and over varying water depths, posing significant operational and morphological challenges for any recirculation strategy. Although the research is limited to a pre-feasibility level, the results indicate that artificial sand recirculation could reduce reliance on offshore resources while maintaining coastal safety at the Second Maasvlakte. However, legal and regulatory barriers remain, as current Dutch legislation restricts the reuse of dredged material in water depths smaller than 20 meters for nourishment purposes. Moreover, the influence of cross-shore processes and seasonal transport variability, especially under tidal forcing, remains uncertain and would require further investigation. This thesis concludes that sand recirculation at the Second Maasvlakte is potentially technically feasible under the studied conditions and has the potential to serve as a sustainable addition to the Dutch coastal maintenance strategy. Its implementation depends on careful system design, regulatory reform, and alignment with broader environmental goals. Further research is recommended to optimise operational parameters and develop integrated system concepts that satisfy the demands of both coastal managers and other stakeholders.

Safety assessments are taken every five years to examine whether the coast is safe enough. After investigation, it was found that one of the weak spots is the Hondsbossche and Pettemer Sea defence (from hereafter referred to as HPZ) which required reinforcement at this location. Therefore, a mega nourishment was implemented in 2015 to ensure the safety of the hinterland. The implementation of this mega nourishment created the Hondsbossche Dunes (from hereafter referred to as HD). After the implementation of the mega nourishment, it was soon found that the width of the beach decreased. The beach width is defined as the horizontal distance between the waterline and the dune foot position which is defined at elevation NAP + 3.0 m. The decrease in beach width occurred mainly on the edges where there is a stronger curvature, so more change in shoreline orientation, compared to the other parts of the nourishment. As a result of the decrease in beach width, an additional nourishment was implemented in 2018 to meet the requirements. These are not the safety requirements but the beach width is important for recreation so the beach cannot be too narrow.

The aim of this research is to improve understanding of beach width reducing processes at curved coastlines to improve predictions of beach width on a scale of ~5 years after implementing a nourishment at the HD. The relationship between the curved coastline and long waves and its influence on the change in beach width was investigated. Special attention is given to the role of infragravity waves. Hereto the numerical model XBeach is used which can simulate morphodynamics with and without infragravity forcing. From the literature review, it follows that long waves, also called infragravity waves, are formed from small waves. A difference between infragravity waves and short waves is that the processes of the infragravity waves take place mainly in the surf zone and swash zone, while most of the short waves are dissipated in the surf zone and swash zone.

To determine the influence of coastline curvature and infragravity waves on beach width change, two types of models were run. The first model was a schematic model where an alongshore uniform coast is applied in the model to neglect the influence of alongshore variability in cross-shore profiles. In addition, multiple runs were performed varying the strength of the curvature and the mode (stationary mode, so without infragravity waves and groupiness, or surfbeat with infragravity waves) so that the results could be compared. This study showed that including infragravity waves results in a different predicted beach width change. In addition, stronger curvature leads to larger gradients in longshore sediment transport and thus the change in beach width.

The second model run was the HD’s complex model where the conditions as present in reality were applied, i.e., bathymetry and wave conditions. Based on the XBeach model of the HD, it can be concluded that the prediction is reasonably similar for the first year of the simulation. The first year of the simulation is the second year after the nourishment is implemented, i.e. 2016, so initial effects are not included in the result of the measurements. However, the predictions and measurements hardly match in the other years resulting in a very low correlation which follows from the validation.

Coastal areas are highly dynamic systems sensitive to natural and anthropogenic change. The range of social, economic, and environmental functions served by diverse coastal environments makes understanding their geomorphology valuable. Parametric shape functions have historically been used to represent the cross shore profile of specific coastal environments. Geometric (consequential) parameters of these functions are often related to parameters representing key morphological drivers (causal parameters) to provide first order predictive capabilities. Advances in the application of data-driven modelling techniques presents opportunity to develop a unified characterization of cross shore morphology in diverse coastal environments. However, the ability to represent diverse profile geometries using a single parametric representation has not been observed. The aim of this study is therefore to evaluate the ability of parametric expressions to effectively characterize diverse coastal profile geometries. Here, a new parametric function is presented that can effectively represent key geometric attributes of diverse cross shore profiles. This function demonstrated high performance in the representation of both theoretical profile morphotypes (mean SSE = 0.04) and measured profile data from Narrabeen-Collaroy Beach, Australia (mean RMSE = 0.05 m) compared to eight existing parametric functions. Parametric values were effectively applied to group profiles with similar geometry using manual labelling and K-means clustering. The average profile of each cluster (i.e., the cluster centroid) provided a good representation of the grouped profiles, particularly when parametric grouping was used in place of empirical grouping. Correlation analyses between causal and consequential parameters demonstrated an ability to identify expected geomorphological trends using the new parametric function. Application of cluster centroids for correlation analysis provided amplified correlation strengths for expected geomorphological relationships, particularly when clustering with fitted parametric values. These results suggest that a parametric representation of the coastal profile has potential to characterize and group diverse profile geometries, and that causal-consequential parameter relationships have potential to identify geomorphological trends. The application of these results provide a foundation for the development of a predictive coastal profile model. This model could be trained using data from diverse coastal environments to predict coastal profile response to changes in the metocean climate related to human interventions and climate change.

Over the past decades, the majority of research into coastal development has been carried out with a focus on open-sea beaches. However, sheltered beaches make up a larger part of the coastlines in the world. Recent studies have shown that the system of sheltered beaches cannot be approached as an open-sea beach with a lower wave energy climate. Doing so results in an inaccurate coastline development prediction. Understanding sheltered beaches and their coastline development is vital because the stresses on these beaches worldwide will increase due to climate change.
Due to the lower energetic wave climate, bed ripples are expected more often on sheltered beaches than on open-sea beaches. The possible presence of these is not yet incorporated in current models. Bed ripples can affect the sediment transport along the coast and can therefore have a substantial role in the necessary understanding of the different coastline development of sheltered beaches with respect to other beaches. Fieldwork data from the Prins Hendrikzanddijk was used to research the behavior of ripples on sheltered beaches. The research was divided into three categories: the formation and existence of ripples under varying hydrodynamic conditions, the performance of current ripple prediction formulas, and ripple migration-induced sediment transport.
Ripples were present with varying heights of 0.023 to 0.078 meters and wavelengths of 0.091 to 0.275 meters and the ripple dimensions responded to the changes in forcing on the sheltered beach. The parameter that related the best to the ripple dimensions was a mobility number that used the 98th-percentile wave-orbital velocity and not a current-related velocity part.
Three ripple predictors were used, of which the predictor by O’Donoghue et al. (2006) performed the best. This predictor relates hydrodynamic conditions to a representing ripple height and wavelength, allowing for changing dimensions and varying hydrodynamic forcing. However, this suggests a strong relation between the hydrodynamic conditions and the dimensions of the ripples. Overall, no strong correlation was visible between measured ripple dimensions and the mobility parameter. This supports the usage of the ripple predictor by Van Rijn (2007), which uses a constant ripple height until conditions become too energetic. This approach performs similarly to the best-performing predictor and could be more stable during varying conditions.
Lastly, ripple migration was measured and was shown to be driven by wave skewness and asymmetry. Both on- and offshore migrating ripples were measured. The source of either on- or offshore migration was not identified clearly. However, the offshore migrating ripples were accompanied by lower skewness and smaller asymmetry values than the onshore migrating ripples. The order of magnitude of the induced bedload transport by migrating ripples was of the same order as bedload transport predicted by the model XBeach without the inclusion of the existence of ripples.

Because of the large uncertainties associated with rising sea levels, present coastal management is inclined towards utilizing soft, nature-inclusive, and adaptive measures over traditional hard protection structures. This shift towards more sustainable and multi-functional solutions is often called Building with Nature. In the coastal zone, these nature-based solutions typically use sand as a building material, have a larger scale than traditional sand nourishments, and serve multiple purposes. The definition of effectiveness of these nature-based solutions can vary for the different project aims. This means that models that predict future states of these interventions must be able to forecast various coastal state indicators (CSIs), such as dune volume, beach width, or habitat area. Using loose-placed sand in coastal protection is intrinsically associated with increased uncertainties of the coastal state compared to more traditional hard protection measures. Therefore, this dissertation examines uncertainty in predicting largescale sandy interventions in the coastal zone and its effect on different CSIs. First, observations of a recent large-scale intervention, the Hondsbosse Dunes, were analyzed to illustrate the evolution of various CSIs in the first years after placement. This 35 million m3 nourishment included a shoreface, beach, and dune and was built in front of a sea dike to serve as flood protection while creating space for nature and recreation. The nourishment created a significant coastline curvature, leading to erosion in the central, most protruding part of the nourishment, bordered by zones with accretion. The artificial cross-shore profile rapidly mimics the surf zone slope and beach width of adjacent beaches. At the same time, the dune volume increased, and the dune foot migrated seaward along the entire nourished site, regardless of whether the subaqueous profile gained or lost sediment. These contrasting trends of different CSIs highlight the need to predict changes in CSIs individually to assess a project’s effectiveness Next, the balance between different sources of uncertainty in predicting the evolution of a large-scale sandy intervention was investigated for the Sand Engine mega-nourishment. The sources of uncertainty in such predictions can be either intrinsic or epistemic. Intrinsic sources are inherent in the system, whereas epistemic sources are related to limitations in knowledge (related to the model). The relative importance of intrinsic and epistemic uncertainty was investigated using a probabilistic framework in which sediment transport is considered a function of random wave forcing (intrinsic) and model (epistemic) uncertainty, calculating transport using a one-line model. The applied wave climate variability was obtained from long-term wave observations, whereas model uncertainty was quantified using Generalized Likelihood Uncertainty Estimation (GLUE) relying on monthly observations. ..

In 1990 the Dutch government passed legislation that dictates the South West Texel coast must be maintained with regard to the 1990 coastline. The coast is currently maintained by applying shoreface and beach nourishments with an interval of approximately 3 years, because it experiences erosion. The problems with this approach are that the mobilization of the dredging vessels is expensive, dredging vessels cause nuisance in the ecological system and moreover, the dredging vessels emit carbon dioxide and therefore contribute to climate change. The first goal of this study was to to investigate if an alternative coastal protection strategy is able to mitigate the drawbacks of the current scheme. Consequently, the application of a mega nourishment was chosen over a cross-shore dam or an outer delta nourishment. To optimally design a mega nourishment, a morphological analysis was executed that focused on elements in the sediment balance of the system. Using Vaklodingen and JARKUS data, volume changes of each transect were identified for 4 parts of the transect: the dune, the beach, the shallow part of the foreshore and the Molengat channel. It was found that dunes started growing from the moment that the nourishments were structurally applied. When nourishments are aborted, it is expected that the shrinking of the dunes will resume, just like the pre-1990 situation. The Molengat in the transects was found to be moving towards shore before the nourishment program started, and its landward movement was not influenced by the implementation of the nourishment program. The Molengat filling rate was projected into the future, leading to a fill date in transects 880-930 by 2035, and in transects 930-1013 by 2055. In transects 1013-1108 and 1108-1210 the Molengat has already been filled. The late projection filling date of transects 930-1013 is a reason to put the mega nourishment at that location, combined with the largest natural erosion occurring at the same location. The application of a mega nourishment is done by putting 20 years worth of sediment at transect range 945-1053 in one construction project. Simultaneously, the mega nourishment aims to diffuse sediment alongshore in the shallow part of the transects, providing sediment to adjacent transects. The sediment supply to other transects could be able to limit the shrinking of the adjacent dunes, or even let them grow. However, this requires further investigation. Delft3D Model results showed that sediment transport in this area is mainly caused by waves on the NUN-shoal, and by the current in the Molengat ebb-tidal channel. The model resolution was not fine enough to accurately describe the accretion and erosion patterns alongshore. Yet, by the use of results of morphological updates it could be determined that the mega nourishment will likely cause accretion south of the nourishment area. This research can be used as a stepping stone for future design steps of a mega nourishment, and also for acquiring knowledge about future behaviour of different parts of the bottom profiles in the South West Texel area.

The awareness of climate change has grown worldwide in the past years. Possible consequences of climate change are sea level rise, heavier storms and high river discharges, but also prolonged drought. For a country such as the Netherlands, these water level variations, high discharges and droughts could have a great impact. Therefore, solutions of flood protection and water management are required to cope with these possible consequences.

The Delta21 project proposes a solution for flood protection of the Southwest delta in the Netherlands, while contributing to energy storage and nature preservation. The Delta21 project is a dam structure located in the Haringvliet mouth and, when constructed, results in a large change of the environment in the Haringvliet mouth. The remaining area of the Haringvliet mouth becomes the tidal lake. The important functions of the tidal lake are to be navigable and to have the capacity for extreme discharges to flow through the lake, without posing threats to safety. The functions are fulfilled by a channel through the tidal lake. The current channel (Slijkgat) requires highly frequent maintenance to allow for navigability and contains bottlenecks to meet the discharge capacity function. Hence, the objective of this research is to determine a suitable channel configuration in the tidal lake of Delta21, considering navigability and discharge capacity.

A suitable channel configuration is determined by designing a channel, accompanied by a morphological modelling study. The functional requirements and criteria for the design are defined based on the stakeholders interests. The requirements and the expected hydrodynamic and morphodynamic conditions in the tidal lake have resulted in three channel concepts that are considered for the design process. One of the concepts is the current bathymetry of the Slijkgat. The other concepts are Channel Concept 1 and Channel Concept 2, which are the same in cross-sectional area but different in orientation and location. The orientation of Channel Concept 1 is a small adjustment from the current Slijkgat, where the bend is slightly straightened. Channel Concept 2 is an almost straight channel and has the shortest length through the tidal lake.
The numerical modelling study is applied on the design in order to determine the morphological response of the system to the concepts and indicate the influence on the navigability, discharge capacity and maintainability. A Delft3D-FLOW model is applied for two simulation periods; normal conditions of one year of morphological modelling and extreme conditions for one week. The normative hydrodynamic drivers for normal conditions are the tide and the river discharge and for the extreme conditions only (extreme) river discharge.

The hydrodynamic and morphological results from the modelling study are processed in order to evaluate the three concepts in a qualitative and quantitative manner. The evaluation criteria are based on navigability, maintenance and nature preservation. Based on the results, Channel Concept 2 is most suitable in terms of navigability and maintenance with respect to the other concepts. Therefore, evaluation has led to the selection of Channel Concept 2 as the most suitable channel configuration. Additionally, an optimisation is proposed for the selected channel concept in order to improve the fulfilment of the maintainability criteria. A dam around the north western end of the channel is proposed in order to decrease the sedimentation volume in the channel. Modelling computations including the dam resulted in a significant decrease of sedimentation in the channel. Hence, the dam is an improvement to the selected channel concept.

Concluding, Channel Concept 2 is considered the most suitable channel configuration in the tidal lake with respect to the other concepts. Implementing the dam in the tidal lake further improves the channel concept in terms of maintainability and navigability.

Wave surfing is a water sport in which a surfer uses a board to ride a wave towards the shore. It is done in the coastal areas around the globe. Each surf spot has its own wave quality depending on the wave climate and the type of coast. Some spots have year-round perfect waves and other surf spots only work ’when the stars are aligned.’ The search for the perfect spot and conditions makes the sport unique and interesting. On the other hand, it makes the sport exclusive. Only people that are able to access surf spots during the right conditions have the chance to surf.

Wave surfing is becoming an increasingly popular sport. Therefore, the demand for year-round good quality waves increases as well. Since a few decades, the sport has found itself a new opportunity: the wavepool. In a wavepool the surfer rides a man-made wave. These artificial waves can be adjusted to ones preferences, can be generated whenever you want and are independent of natural circumstances. Various types of wavepools exist, each with their own technology. Engineers have the ambition to continuously improve technology and efficiency.

Area X is a water recreation area in the Weerd near Roermond. Area X is planning to construct a wavepool in the lake environment of the Noorderplas. To realize the wavepool, Area X has consulted 24/7Waves. 24/7Waves is a company that is researching, developing and operating scalable wavepool concepts. The project ambition is to create waves for beginner, intermediate and advanced surfers.
The wavemaker should generate 150 waves per hour with a ride of 11 to 15 seconds per wave with a wave height up to 2 meters.

So far, no wavepools exist in open water environments. It is unclear in what way the wavepool system and the lake system will interact. On the one hand, it is unknown what the hydrodynamic and morphodynamic impact will be from the wavepool on the lake system. Wave induced bed bank and shore erosion or deteriorated water quality are for example undesired. On the other hand, it is unknown in what way the natural varying conditions of the lake system will affect the performance of the wave. Water level differences or local generated wind waves may not influence the quality of the generated wave.

The design of the wavepool in the Binkhorst should be adjusted such that it can perform in harmony with the natural lake environment of the Noorderplas. Figure 1.1 gives an impression of the generated wave that propagates along the natural lake banks of the Noorderplas. Lake bed and banks that are subject to frequent wave impact are likely to erode (Duró et al., 2020). The most important element of the wavepool to prevent lake bed and bank erosion is the edge of the reef and the gutter. The reef edge eliminates the wave from the wavepool basin and the gutter facilitates the discharge of the water that is washed over the edge.

Each year several fatalities due to rip currents are reported in the Netherlands. One of these accidents was during May 11th in 2020 near the Scheveningen harbour, were several surfers lost their lives. During the hydrodynamic and meteorological accident were quite severe, with a significant wave height of 3.0m and wind speeds of 11 m/s, which is likely to have resulted in a boundary rip at the northern mole. On top of that extraordinary amounts of sea foam amassed at the northern harbour mole, disorienting anyone who got trapped in the area. It is likely that due to the wind and wave conditions and the resulting rip current it was near impossible for the surfers to exit the vicinity of the mole, especially with thick layer of foam. The Scheveningen harbour area was modelled in Delft3D and subjected to tide wind and waves. Assessment of the influence of wind, waves and tide on rip current intensity was performed by comparing the model results from a combined run with the rip velocities obtained by superimposing rip velocities per individual forcing condition. Lastly, the model was run with conditions resembling the aforementioned accident as to check whether the model was able hindcast this situation. The main wind and wave directions found to lead to offshore directed rip transport come from 30-70 degrees relative to shore normal. Retentive rips also occur, mainly when the wind-wave forcing comes from -70 to 0 degrees relative to shore normal, although rips occur less frequently in this range.

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.

For the transportation of the produced energy at offshore windfarms to the onshore grid, export cables have to be installed in the sea bed. Usually, at first trenches are dredged, in which approximately one month later the cables are installed. During this period the trench should remain sufficiently open to install the cables, fulfilling the depth requirements. This thesis focusses on the influence of sand wave fields on the sedimentation rate. It is investigated how trench sedimentation can best be assessed: with a simple model in combination with an extensive probabilistic assessment, or with a more complex model in which a less detailed probabilistic assessment is possible. The research is based on a case study at the Borssele Wind Farm Zone, for which the sedimentation rate is determined during the month April.
The sedimentation is primarily caused by a reduction in (the perpendicular-directed) flow velocity. Shifting of shoals or banks does not occur during the short timescale. The same holds for the sand waves, which do not migrate significantly during this time. Under influence of bedload transport however, the largest sedimentation rates are found for trenches around the sand wave crest. Closer to the troughs, less sedimentation can be expected.
During the probabilistic assessment of the trench sedimentation in flat bathymetries, it was found that the uncertainty obtained by Latin Hypercube Sampling (LHS) with an 2DV-model is reduced compared to the Monte Carlo-analysis (MC-analysis) in SedPit: the median is for both cases 0.06m, the 5-95 percentiles are 0.03m-0.09m and 0.04m-0.13m respectively. Including (idealized) sand wave perturbations in the 2DV-model, increases the range of the P05-P95 values for in trench sedimentation to 0.01 and 0.13m.
Based on the results, it is concluded that SedPit can be used as first assessment tool for the trench sedimentation, since it covers the range obtained with the more complex 2DV-model. The main advantage is the limited computation time of around 1.5 hours, compared to around 48 hours with the sand wave model. On the other hand, the 2DV-model is able to produce more accurate results.
The siltation rate in trenches located at sand wave crests is underestimated by SedPit compared to the results obtained from the 2DV-model. The opposite holds for trenches located at sand wave troughs, in which more sedimentation is predicted by SedPit. Adjusting the calibration parameter of sand transport in SedPit within the ranges provided in Van Rijn (2013) (0.5 for a sand wave trough and 1.0 for a sand wave crest), can at most decrease the difference between the models. For trenches located near a sand wave crest or trough, it is therefore advised to use at least the 2DV-model to assess trench sedimentation.
Furthermore, the 2DV-model can only be used in the case of perpendicular flow with respect to the trench-axis. Inclusion of the sand wave processes, which act in the 2DV-direction, for non-perpendicular flows therefore requires 3D modelling.

While waves are propagating towards the shore and are interrupted by an obstacle like a groyne, they will turn around the tip into the sheltered region of the groyne. This sheltered region is called the shadow zone and contains a reduced wave climate. The turning of the waves is based on the lateral transfer of wave energy along the wave crest, caused by a gradient in wave height. This process is called diffraction. Breaking wave heights and angles inside the shadow zone will be influenced significantly because of wave diffraction. Since variations in breaking wave height and/or angle are responsible for gradients in the alongshore sediment transport, should the process of wave diffraction be taken into account while simulating the shoreline evolution in the vicinity of a groyne. Different methods were found to incorporate the effects of wave diffraction inside the coastline model ShorelineS.

The improved model performance of ShorelineS regarding a real-world case study is addressed by using the shoreline of Constanta, Romania. The consequence of incorporating wave diffraction effects onto the shoreline evolution of Constanta is demonstrated in detail. The accretion close to the Southern groyne and erosion near the Northern groyne is visible in the numerical result of the improved model. Therefore, matching the observed anti-clockwise rotation of the coastal cell. Without accounting for diffraction effects, this matching result was not achievable. The transition zone width is found to be an important factor in determining the coastline shape affected by diffraction. After calibration of this parameter, the numerical result demonstrated to be in almost perfect agreement with the observed coastline shape. The root mean square error and bias reduced with factors of 5.5 and 5 compared to the numerical result excluding diffraction effects.

The coastline near Domburg, in the southwest delta of the Netherlands, has been preserved with sand for three decades. Maintenance was conducted on the beach between the low water line and the dune foot every 4 years. To extent this interval, a shoreface nourishment was implemented in 2017 and was supplemented with a beach nourishment in 2019. Such a parallel shoreface bar is not a naturally occurring morphological feature, as the Domburg coast only features transverse bars.
This research investigates the hydrodynamic and morphological effects of different nourishment strategies at the Domburg coast. The study focusses on the application of the shoreface nourishment, as this strategy has not been previously applied at a coast without shore-parallel bars. The study aims at gaining more insight and knowledge on important mechanisms responsible for the spreading of nourished sediment, because this is not fully understood. Additionally, the performance of a numerical model to hindcast erosion and sedimentation in coastal zones is evaluated.
To this end, a morphological analysis based on measurements and a model analysis are conducted for three nourishment scenarios. The morphological analysis uses an extensive dataset of bathymetric surveys to compute volume changes, sediment fluxes, bar migration rates, momentary coastline (MKL) positions and nourishment longevities (defined as the period that the volume in between the dune foot and mean low water level is greater than before nourishment). The numerical model analysis is based on the output of a morphostatic XBeach model with simplified boundary conditions which computes the hydrodynamics and sediment transports.
The longevity of beach nourishments was found to be on average 3.3 years and the MKL regressed 3.9m/yr on average two years after construction. The eroded sediment did not accrete on the shoreface but was likely transported in the direction of the net sediment transport. The model output indicates that a beach nourishment only has a significant local effect on the hydrodynamics and transport rates.
The shoreface nourishment transforms from a landward skewed triangular shape into a more rounded body without the formation of a trough. The bar migrates onshore but not alongshore and the bar volume remains constant. The model shows a contraction of the tidal flow due to the shoreface bar, increasing the seaward velocity and causing a sheltered zone at the leeside and downdrift of the bar. Consequently, the alongshore transport gradients are increased. This causes extra erosion on the shoreface seaward of the bar while accretion is seen at the downdrift shoreface. The shoreface bar contributes little to the offshore dissipation of wave energy. No evidence for a wave-driven salient effect was found at Domburg from the model output.
The longevity of the 2019 beach nourishment is not prolonged by the presence of a shoreface bar, as this was found to be 3.1 years. Likewise, the MKL measured a regression of 4.3m/yr, similar to previous beach nourishments. Positively, the shoreface bar captures eroding beach sediment because accretion was found in the surf zone, as opposed to the 2014 beach nourishment. Therefore, a shoreface nourishment is moderately beneficial on maintaining the MKL but contributes to the sediment balance of the coastal cell.
Additionally, an alternative nourishment strategy was evaluated through the numerical model. A mega nourishment to the west of Domburg is a viable option as it is likely to feed the updrift and downdrift coastlines which have a sediment demand. It is recommended to further evaluate this nourishment strategy with different numerical models.

Recent analysis on measurements in the North Sea has shown a large amount of wave energy ranging in infragravity bands in the North Sea during storm events. To better understand the generation and propagation of free infragravity waves, the SWAN model is used to inspect the infragravity wave pattern, the infragravity wave origins, and the corresponding contribution from different coastlines in the North Sea. The local equilibrium between sea swell wave and infragravity wavebands is applied to parameterize the source infragravity wave along the coastlines bordering the North Sea following the approach of Arduin et. al. (2014). The empirical parameter α1 representing the radiating energy level from each coastline and bottom friction coefficient χ representing the dissipation strength are combined to calibrate the model. 10 storm events with an observed infragravity wave height over 10cm are chosen to gain detailed insight into the evolution of free infragravity waves under extreme conditions in SWAN. A correlation between α1 and χ is found. A relatively good explanation between measured and predicted infragravity wave height can be obtained as long as a large α1 and a large χ are implemented in the model or vice versa, showing an accuracy of up to 75% in the open sea. Based on a proper combination of two variables, the contribution of infragravity energy from each coastline varies spatially in predicted results. The Danish coastline is the dominant region radiating infragravity waves to the open sea and the reflected free infragravity waves could reach the adjacent coastlines such as Netherlands and UK. Behind the peak of an extreme storm event, the excitation of free infragravity energy is observed along the south of the UK coast originating from Denmark. The north of Holland coasts also radiate large amounts of free IG energy but are unable to have a prominent impact in the center of the North Sea due to energy dissipation. These results imply that the radiated infragravity waves can be influential in distant coastlines in the North Sea during storm events and the changes of local coastal dynamics can be attributed to a different generation region due to the storm characteristics.

Continuous sea level rise and growing environmental awareness have led to increasing implementation of nature-based solutions to counter coastal erosion. An example in the Netherlands is the Sand Engine---a mega-scale sand nourishment designed to feed the Dutch coast over a period of 20 years. For such designs to work, a good understanding of the governing natural processes is paramount. The behaviour of the sandy coast, however, is subject to natural variability in future weather and uncertainties in the interactions between sand dynamics and hydrodynamic forcing. To predict the evolution of coastal systems, engineers apply numerical models. Next to uncertainty due to variability in natural forcing, such models introduce a series of model-related uncertainties, which are often not consistently included in predictions. With limited knowledge of the magnitude of these uncertainties, the long-term strategy development and design of projects are impeded. Parameter uncertainty denotes our limited knowledge of the values of free model parameters and is an important source of overall model uncertainty. This study aims to quantify parameter uncertainty in process-based coastal area predictions by analysing uncertainty bounds for morphodynamic predictions of the Sand Engine. The analysis of parameter uncertainty is carried out for a study period of 14 months, from August 2011 (directly after construction of the Sand Engine) until October 2012. Using advanced numerical acceleration techniques, a synthetic dataset of 1024 morphological Delft3D predictions is generated, each with an identical hindcast period but different model parameter settings. First, a sensitivity analysis (elementary effects method) is performed to find the most influential parameters on three morphological indicators: cumulative volume change, shoreline position, and bed level change. Based on the sensitivity analysis, five parameters are selected for an uncertainty analysis. Subsequently, parameter uncertainty is quantified by the Generalised Likelihood Uncertainty Estimation (GLUE). To increase the convergence speed of the samples, quasi-random Sobol sampling is applied. To validate the applied parameter ranges and assess model performance, the predictions are compared to observations. Using GLUE, uncertainty bounds for the morphological indicators and posterior likelihood distributions of the five parameters are derived from the 1024 model runs. Finally, through a simplified uncertainty comparison, the relative influence of parameter uncertainty and wave climate variability is examined. A first key conclusion is that uncertainty in input parameters translates to significant uncertainty in predictions: cumulative erosion volumes for the peninsula show a spread of 1.3 -0.4/+0.7 million m3 after 14 months. Extended to bed level changes in 2D, the uncertainty bounds result in spatial uncertainty maps, which reveal that uncertainty is highest (5--6 $m$ spread) in the northern area of the peninsula, where a sand spit develops. Most uncertainty (90% for volume changes) develops in the first seven months, during which uncertainty growth correlates strongly to periods of high morphological activity (r > 0.95 for volume changes). Further, posterior likelihood distributions of the parameters indicate that, of the five selected parameters based on the sensitivity analysis, only three (f_sus, gamma, and d_50) significantly contribute to parameter induced uncertainty, while the other two (alpha_rol and theta_sd) are considerably less influential. This contrast in results is attributed to a resolution problem in the sensitivity analysis. Optimised parameter sets derived from the posterior likelihood distributions result in similar model skill as the best GLUE simulations (BSS = 0.8), implying that they may be close to the maximum achievable model skill within the examined parameter ranges. Finally, a simplified estimate of the variation due to wave climate variability is in the same order of magnitude as the parameter induced uncertainty bounds, implying that both uncertainty sources form significant contributions to overall prediction uncertainty. The presented results have an impact on two key levels. First, they can be used to communicate and address uncertainty in predictions of coastal change. For example, the spatial uncertainty maps can let stakeholders understand the potential range of outcomes for a certain design. Second, the results, combined with the created dataset, can provide valuable information for future morphodynamic studies. This work contributes to justifying the need for stochastic simulations, which are expected to be increasingly used for many coastal engineering and management purposes in the years to come.

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.

The last couple of years, the interest in large nourishments, that also feed the adjacent coast, has increased. A feeder nourishment is suggested to be cost effective as well as ecological more beneficial than traditional nourishments. However, their behaviour is more complex and the need for better morphological predictions has increased. Earlier research has given insight in the morphological behaviour and the driving forces of a feeder nourishment in the Netherlands (the Sand Engine). A new feeder nourishment was constructed in October 2019 at the coast of Bacton (UK). This provides a new opportunity to evaluate the feeder nourishment behaviour outside the Netherlands. This thesis describes the results of a numerical morphological model of this feeder nourishment called Bacton Sandscaping (hereafter: BSS) A full bathymetric survey was conducted three times with echo-sounder, LiDAR scanner and photogrammetry during the first half year of the BSS. The surveys showed that the erosion of the first two months is four times higher than the erosion volumes of the months following, indicating a strong initial response. Moreover, a clear link between the morphological response of the sub-aerial beach and submerged beach was found. The numerical model has been calibrated and validated extensively with the bathymetric data of the first half year of this nourishment. The model is very well capable of representing beach volume changes and scores excellent on the Brier skill score. To obtain this excellent score, similar calibration parameters for waves were used as in the Sand Engine case in the Netherlands. The strength of this model was then used to evaluate the effect of offshore wave heights on the erosion volumes of the nourishment and showed that significant wave heights lower than 1 meter are causing 57% of the observed erosion. As the model is well capable of simulating the first half year it is then assumed that the model is also capable of simulating beach volume changes for a different grain size as well as different wave event intensities. The model predicted that sediment grain size and wave event intensities do not have a significant effect on the morphological behaviour of the BSS, therefore the initial state of the nourishment is more important in how the nourishment will evolve. The BSS model is a step forward in the understanding of the morphological behaviour of feeder nourishments and can be used for future modelling purposes of the BSS.
For future feeder nourishments it is advised to focus more on the design shape of the nourishment and not so much on the wave event intensity and grain size of the nourishment. In addition, future calibration of feeder nourishments can further point out if feeder nourishments can use similar calibration parameters for waves.

The port of Rotterdam is located within the Rhine-Meuse estuary where a substantial amount of fine sediment transport takes place. Therefore, the port of Rotterdam is subject to significant siltation, requiring maintenance dredging to guarantee a sufficient nautical depth of fairways and harbour basins. To optimise the dredging strategy in the port of Rotterdam, a pilot study has been carried out wherein sediment is reallocated in the Rotterdam Waterway, during ebb, instead of offshore in the North Sea. Between May and November 2019, 210,000 tons of sediment has been reallocated. This pilot study has been carried out in the context of the larger EU-Interreg Sediment Uses as Resources in Circular and Territorial Economies (SURICATES) project. The main goals are to re-use the sediment as a resource and to reduce the sailing time of the dredging vessels. Both ideas comply with the Building with Nature philosophy; a concept gaining popularity over recent years in The Netherlands focusing on, amongst others the optimisation of dredging strategies. It is expected that the reallocated sediment is mainly transported offshore, while at the same time some of the sediment will nourish the river banks of the Rotterdam Waterway enhancing its flood resilience. This thesis focuses on understanding the fine sediment behaviour of the SURICATES pilot project on two different scales. This is done by analysing measurements and model hindcasts. The measurement campaign is set-up by Deltares and the Port of Rotterdam. For the model hindcasts an operational hydrodynamic and sediment model is used. On the small scale this is done by focusing on the behaviour of a single disposal over a tidal cycle. The large scale focuses on the cumulative long term behaviour of all sediment reallocations. For the small scale two measurement surveys are analysed. In both surveys it is found that a sediment reallocation executed by bow coupling is subject to mixing up to halfway the water column. Subsequently, the sediment plume is advected around and below the pycnocline. Further measurements in the mid field are lacking, but it is hypothesised that the majority of the sediment settles during subsequent low water slack. For the other execution method, drawing the bottom doors, which is used to reallocate the majority of the sediment, useful measurements are absent. It is hypothesised that the majority of this reallocated sediment is confined in the salt wedge and therefore mainly transported upstream over time. To assess the long term behaviour of the cumulative behaviour of all sediment reallocations, a different measurement campaign is set-up. In this measurement campaign, bed samples are collected prior to and during the pilot study to determine the change of the bed composition. In this campaign an indication for increased sedimentation related to the pilot study is found for nearly all the sample locations. The short term model study is set-up to enhance the understanding of the short term behaviour of a sediment plume, to derive an accurate source term for the sediment disposals and to carry out a sensitivity analysis. This sensitivity analysis is executed to derive the influence of differences in disposal method, timing of disposal, and uncertainties in the model. It is found that the execution method has the largest influence on the critical sediment fluxes on the short term, followed by the timing of disposal. From the long term model hindcast, in which the entire pilot study is hindcasted, it is found that 27% of the total amount of reallocated sediment flows downstream from the location of disposal and 73% upstream. These estimations are in line with the hypothesis and long term measurement results, but a thorough calibration of the results is lacking. To conclude, in this thesis a pilot study utilising a different sediment reallocation strategy in the port of Rotterdam has been investigated. This study shows that majority of the sediment disposed, in the current set-up of the pilot study, is estimated to flow upstream. In the sensitivity analysis, it is predicted that this might be caused by the timing of disposal or method of execution. It is also found that the initial behaviour of the sediment plume and the long term measurement contain a large amount of uncertainties. As most important recommendation for future work an expansion of the current measurement survey is proposed with at least two fixed locations: one downstream and one upstream of the location of disposal. In this way sediment fluxes can be established, which can also be used to verify and calibrate the sediment model.

Sand ripples are small (10 cm height) bed forms which occur in the nearshore and surf zone under the impact of both waves and currents. They impact the roughness of the bed used in models of this zone, and contribute to sediment transport. Predictions of their geometry are important to properly model roughness, so correlations between the waves and ripples need to be established. In this project, data about the instantaneous bed level and wave conditions at two point locations in the surf zone was used to analyze the relationship between wave conditions and ripples on the bed. Values for significant wave height, peak period, skewness, ripple height and ripple period were found over bins of 15 minutes in length. It was found that there are relationships between ripple height and wave height, wave skewness and ripple height. These correlations are strongest for a zero shift in the signals, meaning the ripple height can adjust to the wave height and/or skewness within 15 minutes. These results can be used with further research, which includes local current measurements, to make more accurate estimates of the ripple height.