Sedimentation is a common issue in navigating through channels, berths and anchorages of many ports and harbors. In order to address this issue, maintenance dredging can be done in three different ways; relocating of the sediments, keeping the sediments in place, or dredging with nature and using the natural currents to remove sediment. Trailing Suction Hopper Dredging (TSHD) is currently the preferred method for dredging and relocating sediment, however, this method is both costly and time-consuming. As a result, more nature-based solutions are becoming attractive, like the Water Injection Dredger (WID). The Underwater Plough (UWP) is another commonly used method usually for dealing with irregularities in the seabed. Harwich Haven Authority has recently developed a new dredging technique called the Tiamat, this is a new agitation dredging method and a potential environmentally friendly solution. The Tiamat employs a water injection technique to dredge sediment from the seabed. The system injects water into the seabed to fluidize the sediments and then uses a suction pump to bring the sediment plume higher in the water column, such that it can be carried away by the natural currents.

To ascertain the boundary conditions for the Tiamat, tests were conducted at three locations in the Port of Rotterdam, each with different sediment classifications (cohesive and non-cohesive), current strengths (high and low), and depths. Because the Tiamat was developed by the Harwich Haven Authority, it was expected that the Tiamat would perform optimally in areas with strong currents and cohesive sediment at moderate depths. In order to evaluate the performance of the Tiamat, two other dredging techniques - WID and UWP - were tested alongside the Tiamat in these areas.

The results of the pilots and monitoring indicated that the boundary conditions for the Tiamat are primarily influenced by the depth, currents, and sediment characteristics. The depth is limited by the length of the discharge pipe. The Tiamat has the highest production rate in cohesive sediments, as production rates tend to be lower in coarser sand sediments due to their higher tendency to settle. For non-cohesive sediments, a highly energetic river with strong currents is necessary to achieve a certain sediment transport distance.

In order to estimate the performance of the Tiamat, the dredging technique is compared with the WID and UWP. Different parameters such as turbidity, sediment transport, development of the top sediment layer, depth limitations, the production rate in different grain sizes, fuel consumption and costs are compared and discussed.

To understand the functioning of a river system it is crucial to have information on the sediment transport. Estimates of long-term sediment fluxes in the Rhine at the German-Dutch border are required to understand the morphological evolution of the Dutch Rhine Delta. Especially information about the long-term flux of bed material load is of interest because this flux is morphologically relevant. Bed material load interacts continuously with the river bed and it influences the bed surface texture and river slope and width.

The objective of this research is to gain more insight in the amount of bed material load at Lobith (at the German-Dutch border) and in the free-flowing Rhine, the region upstream from the border. To accomplish this, a literature study on the definitions of wash load and bed material load is carried out and different methods to make a distinction between the two are discussed.

This study shows that the wash load cut-off size – the sediment grain size that marks the boundary between wash load and bed material load – is a dynamic variable that depends on the local flow and/or bed characteristics. Therefore, the wash load cut-off size is different for every river and can also change within a river system. It is suggested to set the cut-off size for a specific location equal to the diameter for which 1% of the river bed grains at that location are smaller (D1).

D1 as a cut-off size and sediment transport data based on direct measurements (Frings et al., 2014a,b) give an average annual flux of bed material load of 0.5 Mt/a or 200,000 m³/a at Lobith for the period 1991-2010. It should be noted that there are large uncertainties in these numbers. First of all there are large uncertainties in the used sediment data. Second, multiple assumptions have been made in the process of distinguishing between wash load and bed material load.

The last part of this research contains a comparison between the results of this study and the sediment transport determined by three existing computer models. The model results did not differ that much from the results of this study. The results of this study were especially close to the results of the model for which the input was almost identical to the conditions under which the measurements – on which the results of this study are based - took place. It can be concluded that at least the order of magnitude of the bed material load estimated at the German-Dutch border is probably correct.

Monitoring of the status of vegetation is required for nature conservation. However, doing this for large areas is a time intensive task. Now the use of aerial data from airplanes has made this task easier. However this data source is dependent on the weather conditions and permission to fly in the busy airspace above the Netherlands. An alternative dataset can be found in the form of optical satellite data, which has become increasingly more suitable due to better spatial resolution and revisit times. For this study the optical satellite data from Superview is combined with the LiDAR elevation data set AHN on a 1-meter raster. With this data available, the goal is to classify vegetation into three different classes: sand, grass and trees. And do this for multiple epochs to analyze class transition patterns. Three classification methods were compared: nearest centroid, random forest and neural network. These methods were tested on 11 epochs on the Meijendel en Berkheide dunal area on the Dutch coast. Both neural network and random forest seemed in good agreement with the aerial imagery data set. Where neural network was faster to process, the random forest produced a more stable result. All the methods are also able to output probabilities, which are used to classify mixed class pixels. The location of these mixed class pixels agree with the transition process that are expected between the classes. This study show that it is possible to use a combination of satellite and LiDAR elevation data for vegetation assessment.

The Building with Nature approach has been gaining ground in hydraulic engineering, increasing the importance of understanding the cross-shore morphodynamic processes. The intertidal zone, where marine and aeolian processes come together, is an important link in the transport of sediment from the sea towards the dunes. The grain size distribution affects the sediment supply in the intertidal zone. This research investigates the effect of marine processes on the cross-shore variations of the grain size distribution in the intertidal zone by using a one-dimensional non linear shallow water XBeach model.
The intertidal zone is subject to shoaling, surf and swash zone processes. The grain size influences the beach slope, the initiation of motion and settling to the bed. The cross-shore sediment transport is the combination of sediment that is stirred up from the bed and subsequently transported. Breaking induced turbulence enhances stirring of sediment from the bed and keeps sediment in suspension. The amount of stirring and the transport direction depends on the wave conditions.
Input and control data for the model study was provided by the Scanex 2020 fieldwork campaign at Noordwijk, the Netherlands. The ADV velocity data combined with a pressure signal has been used for the tidal and incoming wave signal. Cross-shore profiles have been determined in Matlab based on terrestrial laser scans. Soil samples of the intertidal zone were taken with a sand scraper and analyzed with a sieve tower. For the initial grain size distribution is the average distribution of 14 samples on a transect was used. Based on wave, wind and soil sampling data a model period from 29-2-2020 02:00 to 10-3-2020 13:00 was selected.
The XBeach model used is as described by Reniers et al. (2013), but with a time-averaged turbulent kinetic energy and a different implementation of the Riemann boundary. The model consisted of a 176 x 3 grid with a grid size of dx=1 m and dy=5 m. For the initial bathymetry the laser scan of 29-2-2020 02:00 was used. The initial grain size was imposed on all the model grid cells. Additional to the standard run, runs have been performed to research the effect of a storm, the model sensitivity and the effect of aeolian transport.
The model shows a pattern of cross-shore grain size variations with coarser sediment from x=20 to x=56 m, finer sediment from x=57 to x=105 m and fluctuating grain size from x=106 to x=136 m compared to the initial grainsize. After 24 h a grain size pattern establishes with a clear deposition of fine sediment on the upper beach. The pattern remained stable for nearly the full model period. After 200 hours the fines become less prominent and move onshore. On the intratidal scale sediment becomes coarser when submerged and finer when emerged, except near the high water line where fine sediment is deposited.
The model reproduced the same pattern of grain size variations over the cross-shore as was found in the soil samples of 10-3-2020. As the cross-shore grain size pattern remained stable during the model period, processes on the spring-neap time scale or storm time scale seem to govern the cross-shore variations of the grain size. For the aeolian transport this would imply that for this model period the fine sediment supply is controlled on the same time scales. Nevertheless, considering that aeolian transport could have resulted in coarsening of the fines in the upper intertidal zone, processes over a single tide, could be more important than was visible in the model result.

Infragravity (IG) waves (0.005-0.04 Hz) are surface waves that can dominate the nearshore hydrodynamics and can impact various coastal processes (e.g., run-up, overwash). A proper offshore description of incident IG waves is required for storm impact models, which generally assume a local equilibrium between sea-swell (SS) waves (0.04-0.33 Hz) and the resultant nonlinearly excited bound IG waves. The contribution of free incident IG waves and the directional properties
of the IG wave field are neglected, though they play a critical role in IG wave variations. Various research focuses on IG wave dynamics in shallow waters, but a detailed understanding of IG wave variability in intermediate water depth is lacking. Furthermore, the directional spectra of bound and free IG waves in the field are usually unavailable since bound IG waves do not follow linear dispersion relations, which is assumed by commonly applied directional spectra reconstruction methods.

In-situ observation data (surface elevation, pressure, and velocity) of IG waves from November 2021 to April 2022 at three cross-shore locations in intermediate water depth (∼ 6 − 14 m) off the Dutch coast are analyzed to study generation, propagation, and directional properties of IG waves. The bispectral technique is applied to quantify the contribution of bound IG waves to the total IG wave field. A newly developed method is validated and used on the offshore (∼ 14 m) data to reconstruct directional spectra of bound and free IG waves separately during storms.

The results show that IG wave heights are best predicted (correlation coefficient R² up to 0.94) with an offshore forcing parameter that includes peak period H_ssT_p² , which indicates SS wave energy flux. The growth rate of IG waves is in between the shallow water equilibrium solution (for bound waves) and Green’s Law (for free waves), indicating the total IG wave field consists of bound and free components. The relative contribution of bound IG energy (up to 76%) is correlated to SS wave energy, whereas it decreases dramatically during intense storms when SS waves break. The bound IG waves that are assumed to follow the weakly nonlinear wave theory, have a similar peak direction and broader directional spreading to SS waves. In contrast, the directional spectra of free IG waves are nearly isotropic during calm conditions, but may have diverse peaks during storms, which incident IG waves from remote sources and edge waves can
influence. A better understanding of the complex pattern of free IG waves requires more detailed observations and/ or modeling.

Sea level rise will increase the risk of flooding in coastal areas. This poses a risk to the coastal protection as well as rivers and lakes close to the coast. Solutions are needed to cope with this threat. The past decade, nature based solutions have gained significant interest. One of these solutions could be sandy foreshores. Due to the use of natural materials, sandy foreshores are a ‘nature-based solution’ opposed to a more traditional approach of dike reinforcement. For sandy foreshores to be a viable alternative to regular dike reinforcements, the order of magnitude of construction and maintenance costs need to be known. For this reason, it is necessary to be able to calculate a failure probability of a dike with sandy foreshore, to predict the required maintenance and to optimize the design based on life-cycle costs.

To improve the calculation method, a step-wise calculation of the failure probability for wave overtopping of a hybrid structure was developed. The calculation included an iterative process. The calculation methods consists out of calculating the failure probability for wave overtopping in Riskeer and a dune erosion calculation in Xbeach. In this research, overtopping was considered as the dominant failuremechanism. For the assessment, the dike was seen as an impermeable hard layer and the foreshore as a beach. Therefore, dune erosion could not erode the main structure and is considered a sub-mechanism of overtopping.

Next, a calculation was performed to predict the longshore transport along the beach in Almere Duin. The occurrence of different wind directions, together with a Delft3D model of the Markermeer, was combined to find the longshore transport. The LST was calculated with transport formula calibrated for coastal areas. The life cycle costs (LCC), including design and maintenance costs, were calculated for different strategies. The calculated alongshore transport together with cost estimates were used to calculate the LCC. Subsequently, the net present value of the maintenance costs was calculated to determine the LCC for each maintenance strategy. At the end the uncertainty and sensitivity of each strategy were analysed.

The time-varying protection level can be optimized by calculating the failure probability due to wave overtopping, with Riskeer and calculating the erosion of the foreshore, with Xbeach. To use this method, Riskeer and Xbeach should have the same design point and if the design point shifts, an extra iteration is necessary. For a 1/10 profile, only a 0.25 m lowering of the foreshore height was found and one extra iterative step was required to carry out the calculation. A maintenance strategy with a 100 year maintenance interval period was found to be optimal in this thesis and a Monte Carlo simulation, which included uncertainties, led to similar results. However, the total LCC were 21% to 34% higher, when uncertainties were included in the calculation. These findings suggest that it is not necessary, to carry out a probabilistic calculation, to find the optimal maintenance strategy. However, the models used, aswell as the local boundary conditions, such as the longshore transport and the cost of sand, were found to influence the life cycle costs significantly. For this reason, it is concluded that a location specific analysis is important to optimize the maintenance strategy.

Estimating wave runup is of crucial importance during a coastal risk assessment. Currently, runup levels are usually calculated using empirical formula derived from experiments conducted at beaches all over the world, and during different beach states. During this research, conditions are analyzed where runup reaches the dune toe and above. The main objective of this research is to examine the changes in the runup characteristics, which are the wave setup, the infragravity swash motions (low frequency wave motion) and the incident swash motions (high frequency wave motion). In order to examine these conditions, a fieldwork experiment has be conducted at the Sand engine near Kijkduin (South Holland). a dune of 150 (m) in width and 5.5 (m) above NAP (Nieuw Amsterdams Peil) have be constructed near the waterline. Instruments have been installed which have monitored the incoming wave conditions and the behavior of the hydrodynamic conditions at the waterline. One of these instruments was an instrument new to measurements conducted at the coast. This was a LLC (Line scanning Low Cost) LiDAR, which was used to track the runup during extreme wave conditions.
The LLC LiDAR was evaluated in terms of measuring the nearshore hydrodynamics by comparing the water level measured by the LLC LiDAR to the water level measured by a pressure sensor. The water levels from both instruments compared well with an 𝑅2 ranging from 𝑅2 = −0.86. The match in the peaks of the water levels were lower, showing 𝑅2 in the range of 0.34 − 0.78.
Data from the Fieldwork Experiment showed an increase in incident swash wave height during collision conditions when compared to swash conditions. Although the nearshore wave field showed similar conditions between the swash and collision conditions, the swash height showed an increase. Several parameters have been investigated to find the dependence of runup height to the offshore wave or beach characteristics. A best fit is found between runup and the beach slope (𝑅2 = 0.86), also indicating that swash motions are significant. Runup heights during these conditions are also compared to an empirical runup formula. This comparison indicated that runup elevations could still be predicted during conditions where runup reaches above the dune toe elevation.

To effectively mitigate environmental changes and to manage coastal environments, a good under- standing of nearshore bathymetry and its evolution is required. The coastal zone is expected to be vulnerable in the foreseeable future due to the combined effects of increased coastal impacts and a growing coastal population. The use of spaceborne remote sensing methods has been developed in recent decades to estimate nearshore bathymetry. Compared to traditional methods, spaceborne remote sensing techniques offer a relatively large spatial coverage as well as frequent temporal mon- itoring. The Sentinel-2 mission (EC/ESA) is potentially able to provide regular bathymetry estima- tions, mainly due to its significant revisit time and freely accessible data.

This research focuses on the development of a spatio-temporal cross-correlation model in order to construct a one-minute wave-representing video. The video is used to show the potential for wave- derived bathymetry estimation, exploiting a DMD-based DIA to invert depth. The model is ap- plied to two distinct datasets: a synthetic FUNWAVE dataset and Sentinel-2 imagery. The Sentinel-2 imagery covers research sites in Saint-Louis, Senegal and Capbreton, France. An application frame- work related to the model is furthermore developed by analysing a set of synthetic sinusoidal waves.

Three model requirements are created based on the research objectives. The model should show wave propagation for at least one minute and, moreover, the waves in the video should accurately represent the wave field. Both requirements are demanded by the use of a DMD-based DIA. Lastly, the resulting video should enable an accurate bathymetry estimation. Based on the requirements, the developed spatio-temporal cross-correlation model includes four model parts: pre-processing, image resolution augmentation, wave characteristics estimation and video construction.

The research has led to a range of insights. A discrepancy between the quality of constructed videos and related bathymetry estimations is observed. The videos as constructed by the model generally show a good representation of average wave propagation for a sufficiently long duration, while the bathymetry estimations are less accurate. The low quality of bathymetry estimations is explained by three main error sources: celerity estimation errors, the applied filtering methods and the way in which the video is constructed. These three error sources together lead to videos that lack pixel-wise detail and therefore decrease the bathymetry estimation quality. The developed application frame- work shows that estimating wave characteristics from Sentinel-2 imagery by means of the model is at the edge of possibilities. In temporal sense, relatively large celerity estimation errors are expected for wave periods lower than 5 s and higher than 7 s. The model is less sensitive for spatial parame- ters: as long as wavelengths are larger than circa 150 m the celerity estimation error is acceptable.

All together, the developed model and related video constructions offer added value, although not for the purpose of a bathymetry estimation by means of a DMD-based DIA. The constructed videos represent wave propagation in an average sense and can therefore be exploited for wave-related purposes, e.g. obtaining wave spectra, estimating dominant wave direction and estimating wave climates. In general, the video offers a way to enlarge the temporal range of Sentinel-2 imagery. It is furthermore concluded that the model is probably more suitable for use in combination with other types of imagery, including satellite imagery with larger burst duration and increased spatial resolution as well as standard video imagery.

This research is part of the project "Water Efficiency in Sustainable Cotton-based Production Systems” between Solidaridad Asia and TU Delft. The project aims to increase the livelihood of smallholder farmers in the Maharashtra, India through. A socio-hydrological (SH) model is used extensively in this research as an evaluation tool. However, the baseline research indicates that the lack of stress mechanics in the SH model used in the intervention might cause inaccuracies in yield estimation. Furthermore, it has never been validated at a farmer level before. This research aims to implement the stress mechanics in the SH model, evaluate the overall performance of the model in terms of predicting crop yield, identify potential sources of errors, and give recommendations for future studies. The research uses iterative top-down approach due to the large study area and the varied nature of the 308 farmers surveyed. The research implements the water and temperature stress mechanics based on Food and Agriculture Organization's (FAO) AquaCrop framework. For the performance evaluation process, this research uses four model scores namely Nash-Sutcliffe (NS), log of NS, Mean Absolute Error (MAE), and the coefficient of determination. Furthermore, the sources of uncertainties are divided into two categories namely lack of knowledge (i.e. generated by parameter, input, observation, and structural errors) and variability (i.e. generated by climate variations). The lack of knowledge uncertainty is investigated using Monte Carlo Sampling calibration and the Generalized Likelihood Uncertainty Estimation (GLUE) concept is used to obtain the uncertainty intervals of the model. Going further, the errors are divided into residual and structural error. The latter is explained and quantified through a structural error model using a combination of qualitative analysis, Principal Component Analysis, multiple linear regressions, and projection of the data into kernel space. Then residuals between the model yield + structural error vs. the observed yield is thought to be explained by the residual errors. Lastly, the effects of climate variations to the stability of the model are evaluated.
After the initial calibration, the model scores are NS: -0.343 to -0.996, log of NS: -0.655 to -1.91, MAE: 447.1 to 553.2 kg/ha, and r-squared: 0.003 to 0.008. Because of the poor performance of the model, the uncertainty intervals from GLUE are not enough to capture the total errors of the model. However, after adjustment using the structural error model, the model scores become NS: 0.83, log of NS: 0.56, MAE: 149 kg/ha, and r-squared: 0.859. The adjusted yield calculation has a residual error as Gaussian distribution with standard deviation of 150 kg/ha. The qualitative analysis identified several factors that contribute to the errors viz. farmers' capital, irrigation behavior, and crop production process such as canopy cover growth. Lastly, there is no major instability found through the bootstrap analysis. The physical model is not performing well, especially when it is calculating yield for individual farmers over a large study area. However, the structural error model can adjust the yield prediction so that it is close to the observed yields. This indicates the poor performance is likely to be caused by the prevalence of structural errors in the model instead of the uncertainties regarding parameters, input, or observation values. Therefore, it is recommended for future research to address this first. This can be done by further study and incorporation of more crop production processes, soil water simulation, and exploratory interviews to identify patterns and more factors that can influence the errors.

Bathymetric surveying of the Netherlands Continental Shelf (NCS) is taken care of, by the Dutch Hydrographic Office and Rijkswaterstaat. The survey frequencies vary from location to location depending on a set of factors defined by the authorities. These are the minimum depth, draught (the difference between seafloor depth and ship’s keel), shipping intensity, human interventions and seafloor dynamics that are taking place in an area. The project is about developing a methodology using the available time-series of bathymetric data to automatically make a well-informed decision on the survey frequency of critical areas of the NCS. This study aims to contribute to the decision-making by performing a risk-based analysis using a probabilistic approach. The main objectives are to estimate and map the risk that the seafloor is changing significantly. Risk severity should be measured and the probability of risk's consequence to occur should be estimated and mapped in temporal and spatial scale indicating if possible, the optimal surveying frequency. Firstly, the accuracy, quality and reliability of the prediction values were defined and computed. This was a necessary step to realize how powerful are the predictions used as an input dataset for the risk assessment of the seafloor to change significantly. As a step further, the risk's impact and probability to occur should be determined. Hence, it was necessary to define quantities related to seabed dynamics that express the evolution of the seafloor. These are mentioned as risk indicators and are the Relative Depth Change (RDC), the Rate of Change (RoC) and the direction of change. The RoC was used for probability estimation and the rest of it as informative variables for the analysis. Finally, an adjustment of the method used here with the Netherlands Hydrographic Office (NLHO) standards was done and conclusions were made regarding the survey frequency of the chosen study areas. The analysis was applied for two study areas: West IJmuiden and West Rotterdam, as these areas according to the NLHO are highly prioritised (should be resurveyed every 2 years) and thus, they are critical areas of the NCS. The method applied and the results can be used as an informative tool in designing a successful, reliable and cost-effective bathymetric survey plan of the NCS.

Coastal dunes are dominant features along much of the world’s sandy coastlines serving as the first line of protection against coastal flooding. Besides this primary purpose, the coastal dunes also provide a variety of other functions such as the supply of drinking water, nature conservation and recreational areas. With the secondary functions in mind, the Dutch coastal management strategy changed in 1990 from erosion control and stabilization of the coastline (reactive) to a policy of dynamic preservation (pro-active) with the introduction of a law called ‘’Dynamic preservation of the Dutch coast’’. This new dynamic strategy naturally induced irregularities in dunes that were completely stabilized before. One of these irregularities is the formation of a blowout. A small depression or hollow in the foredunes formed by wind erosion or wave impact may grow in time as sediment from the beach and foredunes is transported into the back dunes. In several Dutch cases such a blowout feature was artificially initiated as the exchange of sediment from the coastal system into the back dunes enhances the biodiversity significantly. Due to the high importance of the coastal dune performance as flood protection, good understanding and prediction of the (dynamic) coastal dune system is desired. Lately, general interest in this topic increased even more due to new societal challenges, such as decisions on coastal development for longer time scales, more complex management settings and sustainability. Coastal dunes and blowouts are shaped by wind induced sediment transport (aeolian sediment transport), biological - and hydrodynamic processes. To better understand and increase the predictability of dynamic systems, this study focuses on simulating the development of artificially initiated blowout features by including the combination of these relevant processes in the numerical model AeoLiS. This process-based model was originally developed to simulate aeolian sediment transport in supply-limited conditions, such as coastal areas. The study describes simulations of several academic dune formations to validate the applicability of the different (new) processes that were included in the numerical model. Finally, all processes are combined in simulations of a practical case that is used to compare numerical model results to field data on the development of multiple artificially initiated blowout features in the Dutch coast at Meijendel.

Phenomena like sea level rise, global warming and erosion together contribute to increasing flood risk in vulnerable coastal areas. As this flood risk increases, initiatives to mitigate the effects of climate change in the coastal zone are also increasingly sought. During recent years, the view that these measures should be circular has gained significant momentum. In line with this, the idea that sediment should not be treated as waste, but as a valuable product in a circular economy has been widely accepted. Within this theme, the sediment uses as resources in circular and in territorial economies (SURICATES) was created to develop and execute eco-innovative solutions for the reuse of sediments in Western Europe. As a part of SURICATES, over the course of a nine week pilot, a total of 500 tonnes of sediment was reallocated in a designated area in the Rotterdam Waterway, with the expectation that this sediment would be transported out of the Rhine-Meuse estuary into the North Sea. The SURICATES project is one of the first real large-scale efforts to reuse sediment for economic as well as ecosystem services. Effective implementation of the SURICATES project, however, requires a thorough understanding of the governing physical processes impacting the distribution of the deposited sediment locally. Furthermore, to assess the feasibility of similar future applications, efficient modelling of the pilot project is necessary. The work presented here aims to elucidate the hydrodynamic processes that are governing in the Rotterdam Waterway, within the framework of the SURICATES pilot project, and assess the reproducibility of these processes by (two) predictive models that are currently operational at the Port of Rotterdam. A special 6-hour monitoring survey was set up to measure salinities, velocities, temperature, and suspended particulate matter (SPM) along a transect crossing the reallocation location. In combination with a literature review, this dataset provides the basis for research into the predictive capabilities of two currently operational hydrodynamic models. Analysis of this dataset reveals the dominant terms in the momentum balance, the influence of Coriolis, the occurrence of internal waves, and the effect that all these mechanisms may have on the SPM distribution around the reallocation location. When the system dynamics are elucidated, the model performance of the two hydrodynamic models is assessed—both quantitatively and qualitatively. It is also investigated whether phase shifts are introduced in the models. It is found that the primary hydrodynamic processes in the Rotterdam Waterway are related to the barotropic tidal asymmetry imposed at the river mouth, the tidal excursion of the salt wedge, baroclinic exchange flow processes, and turbulence damping at the pycnocline. Turbulence damping at the pycnocline generally poses an upper limit to the (re)distribution of SPM over the water column, although field data suggests that this damping may not be sufficient to counteract diffusion processes locally. This effect occurs under certain forcing conditions and during low water slack. Furthermore, an internal Froude number analysis provides evidence for the possible generation of internal waves in one of the river’s bends. The evaluated models, however, are not capable of reproducing all of these hydrodynamic processes adequately. Although both models adequately reproduce water levels and the vertical velocity structure, they have difficulties predicting the pycnocline height. Additionally, it is found that both models introduce a small phase shift in the velocity and salinity prediction. The research presented here is a contribution to the understanding of the governing hydrodynamic processes in the Rotterdam Waterway, and the effect that (in)accurate modelling of these processes may have on future studies. Recommendations following from this research could improve future modelling practices.

Shallow jet flows are often coupled to high flow velocities and complex flow patterns. To properly ensure the stability of the barrier between both water bodies surrounding the jet, a scour analysis is often a necessity. Such analyses are inevitably coupled to the hydrodynamic processes occurring in jet flows, either in the form of loads on potential bed protections or equilibrium scour hole depths. Numerical models could assist in the design of bed protections by supplying accurate hydrodynamic input parameters for the design formulae or by predicting the hydrodynamic processes at play. Due to the limited computational power available, simplifications must be made within the numerical model to ensure reasonable computational costs. One of these simplifications is to resolve the flow in depth-averaged sense to create a 2DH model. To allow this simplification to be made, the performance of a 2DH model compared to a fully 3D model needs to be researched. By comparing simulations of a controlled environment and of a prototype scenario, insight in the predictive capabilities of the numerical models for possible other projects can be gained. This work aims to research the performance of 2DH and 3D numerical models regarding the reproduction of the hydrodynamic processes in shallow jets. First, it was investigated which hydrodynamic processes thrive at a prototype shallow jet by analysing measurement data available at Waterdunen. Afterwards, we systematically determine the performance of both a 2DH and 3D numerical model by setting up FINEL models both for a laboratory experiment of a shallow jet and for the shallow jet at Waterdunen. Insight in the predictive capabilities of 2DH and 3D numerical models for shallow jets can contribute to future design problems surrounding shallow jets. Information regarding the shallow jet at the seaside of the culvert at Waterdunen was obtained by Svasek Hydraulics, commissioned by the public government Waterschap Scheldestromen and the province of Zeeland, during a measurement campaign split into six individual measurement scenarios. Immediately at outflow from the culvert, the jet is subject to a 1:6 slope in streamwise direction. The geometry of the seaside channel is asymmetric, with 1:4 lateral slopes at either side of the channel. Furthermore, morphological changes as a result of the jet flow introduce an asymmetric topography in the channel. Visual observations during the measurement campaign indicated the flow can be characterized by an horizontal contraction over the longitudinal slope and an asymmetric flow profile depending on which casings were active within the culvert. The analysis of the measurement data shows the jet concentrates on the eastern side of the channel during all six scenarios. As a result, the recirculation zones on either side of the jet can be characterized as a small, non-dominant recirculation zone on the east side of the jet and a large, dominant recirculation zone on the west side of the jet. The streamlines show a continuous horizontal contraction until the flow hits the eastern side of the channel. Over the longitudinal slope, the flow seems to remain attached to the bottom rather than separating. However, due to a relatively large clearance of the ADCP measurements with respect to the bottom, this cannot be proven directly. It was decided to simulate the shallow jet of experiment 2.4.1 of van de Zande (2018) to investigate the performance of a 2DH and 3D numerical model for a laboratory simulation. In this experiment, the behaviour of an asymmetric shallow jet over a longitudinal slope at the point of the horizontal expansion was investigated. It was shown that both the 2DH and 3D numerical model were capable of reproducing the most dominant hydrodynamic processes within the jet. However, the accuracy with which the processes were reproduced differed significantly. The 2DH model reproduced too much curvature of the flow towards the lower wall of the flume compared to both the 3D model and the measurement data. As a result, the high flow velocities in the jet center were located further down in the channel. The flow velocities in the jet center were modelled with a maximum error of 12.4% in the 2DH model and 3.02% in the 3D model. The lower accuracy of the 2DH model is caused by the comparison between depth-averaged velocities and surface PIV velocities. Due to the additional curvature the recirculating velocities in the non-dominant recirculation zone were modelled too high by the 2DH model, with an error of up to 56.6% relative to the jet center velocity. In the 3D model, this error decreased to 18.9%. However, it was remarked the recirculating flow velocities in the PIV data were subject to clumping of tracer particles. The horizontal streamline contraction was simulated in the 2DH model, but can only be directly related to the changes in water depth. In both the 3D model and the measurements, this horizontal streamline contraction was shown to continue further downstream of the slope. It was concluded the horizontal streamline contraction is directly related to the vertical velocity profile, which was observed to differ from the standard log-profile both on the slope and downstream thereof. The 3D model was capable of reproducing the vertical velocity profile with a maximum relative error of 10%. In the numerical simulations at Waterdunen, both the 2DH and 3D models were shown to behave similarly. Both the 2DH and 3D numerical models were capable of reproducing the eastern concentration of the flow. However, the curvature of the jet further downstream was modelled more accurate in the 3D model. The better reproduction of the flow curvature in the 2DH model compared to the laboratory simulations is the result of the asymmetric inflow boundary, which allows the 2DH model to more easily resolve the flow curvature. Both models underestimate the flow velocities throughout the entire DOI. It was concluded this was caused by errors in the model input. Similar to the laboratory simulations, the 2DH model reproduced the horizontal streamline contraction over the slope but failed to reproduce the contraction further downstream. The 3D model was capable of reproducing the continuing streamline contraction. Furthermore, the 3D model reproduced vertical flow attachment over the slope, which complies well with the measurement data. It was concluded that a 3D numerical model can better reproduce the flow curvature in case of asymmetrical flows. Furthermore, the recirculating flow is better reproduced by a 3D model compared to a 2DH model. Finally, a 3D model is capable of accurately reproducing the vertical velocity profile, which supplies additional information of accurate flow velocities at the bed. However, on a prototype scale the differences between a 2DH and 3D numerical model are small. In channels with symmetrical boundaries, it is suggested to use a 3D numerical model in case the flow is subject to the Coanda-like effect. However, if the inflow into the channel is already asymmetrical, a 2DH numerical model can be considered to save computational effort. Nevertheless, when employing a 2DH model one should be wary of geometric and topographic asymmetries, as the effect of both factors on the flow symmetry is still unclear.

Velocities derived from X-band radar were compared to depth averaged ADCP measurements in a complex tidal inlet system at Ameland, the Netherlands. Inclusion of depth assimilation and ensemble averaging in radar calculations led to smaller differences between ADCP and radar. The observed differences were clustered and related to water level elevations, wind velocities, wave periods, wave heights, spatial coherence in radar output and error metrics of the radar fitting procedure. Larger waves and higher wind velocities were observed to benefit radar agreement with ADCP results. Rising water levels benefitted agreement in east west direction. Falling water levels benefitted agreement in north south direction. Confidence intervals of the fitting procedure were observed to coincide with differences between ADCP and radar and potential for filtering based on them was shown. Nevertheless, an unclarified tendency towards northwestern bias, which may be specific to the comparison locations, remains. The radar at Ameland monitors the whole inlet system and provides current velocities everywhere in its range. This study shows that its currents are in good agreement with ADCP depth averaged currents throughout most of the tidal cycle. Furthermore, it stresses radar’s potential for better monitoring of the coast and for cost effective coastal field measurements to obtain large datasets, even in hydrodynamically very complex regions.

The beach recovery process determines the resilience of a sandy coast and is an important aspect of the coastal safety. Sediment stored underwater due to storms is transported onshore by the migration of subtidal and intertidal bars under mild wave conditions. The intertidal zone is an im-portant interface, connecting the marine and aeolian zone and facilitating the transition of hydro-dynamic to aeolian sediment transport. The aim of this study is to investigate the cross-shore mor-phodynamics of intertidal sandbars. The dominant cross-shore sediment transport processes can mainly be divided into surf zone and swash zone processes. The surf zone processes are primarily determined by the balance of wave nonlinearities, undertow and infra-gravity waves. In the swash zone, the cross-shore sediment transport is determined by the balance between the turbulent uprush and the gravity induced backwash. A recent terrestrial laser scanning (TLS) measuring campaign conducted at Kijkduin, the Nether-lands, provided new insight in the intertidal bar behavior. The results of one cross section are ana-lyzed. In a period of 6 weeks, two distinctive intertidal bars formed, grew and migrated onshore during mild wave conditions and eventually eroded again during a storm. Within 5 days, the upper intertidal bar migrated onshore over a distance of 25m and grew with a height of 0.3m, attributed to swash zone processes. Onshore sediment transport fluxes reached values of nearly 2 m3 per meter width in one tidal cycle.
The findings are compared with two XBeach models (surf beat model and hydrostatic swash model) which are used to reproduce the observed morphological behavior of the upper intertidal bar. Both models partly reproduce the onshore migration but show deviating results regarding the final growth of the intertidal bar. In contrast to the surf beat model, the morphological changes in the hydrostatic swash model are primarily induced by swash zone processes, which is comparable to the processes in the TLS measurements. Finally, a conceptual model is developed in which four intertidal bar regimes are classified based on the tidal water level. The distinction determines the dominant cross-shore processes for the for-mation, migration, growth and destruction of intertidal bars. The model shows that the swash zone processes are dominant for the onshore migration and growth of intertidal bars in the overwash regime, while the surf zone processes are dominant in the submersion regime. The findings presented in this study provide a better understanding of the intertidal bar behavior. Although the XBeach models did not reproduce the observed behavior completely, there are some pronounced similarities. Further research is required to increase the knowledge of intertidal bar behavior at a variety of sandy coasts and to improve the performance of rocesses-based models like XBeach.

The Hondsbossche Dunes is a seven-kilometre-long dune, beach and shoreface nourishment that serves as a primary flood defence since 2015. In addition to its protective function, the Hondsbossche Dunes stimulate ecological habitat development in the coastal area, in line with Ecoshape's 'Building with Nature'-approach. Its morphologic development is monitored to simulate the morphological response to marine processes and aeolian sediment transport, and to determine the optimal profile for dune growth and nature development.The monitoring program of Ecoshape studied the volume change of the beach and the dunes. The decrease of sediment volume on the beach is not equal to the increase of sediment volume on the dunes. The hypothesis is that the remaining sediment must stem from the intertidal zone and the shoreface. The research objective of this study is to investigate the contribution of sediment supply and marine processes in the intertidal zone to changes in morphology and bed composition in the beach and dune. The results of this data analysis show that sediment is transported from the intertidal zone to the shoreface in the north and south of the Hondsbossche Dunes. This behaviour is different from the middle of the domain, where sediment is transported from the shoreface to the intertidal zone. The direction of cross-shore sediment transport between the shoreface and the intertidal zone may depend on the crest level of sandbars in the shoreface: The sandbars in the middle of the Hondsbossche Dunes break more short waves than those in the north and south, which causes 'freeing' of long waves and net landward sediment transport. The modelling study suggests that wave runup and the presence of soil moisture reduce aeolian sediment transport from the intertidal zone to the beach, because grains in the intertidal zone are immobile when they are moist. This reduction results in increased erosion at the dry part of the beach, because the wind picks up sediment from the beach instead of the intertidal zone. The soil moisture content also significantly coarsens the bed composition in the intertidal zone, because the difference in threshold for aeolian transport between fine and coarse grains becomes larger. Hydraulic mixing does not contribute to significant morphological changes in the intertidal zone, but redistributes grains on the bed of the intertidal zone toward its initial distribution by stirring up the bed of the intertidal zone. These marine processes only affect dune growth if aeolian sediment transport is supply limited, which is mainly the case for Profile 2 north and Profile 4. Aeolian sediment transport in Profile 3 south is mainly transport limited, because the dune growth volume in most simulations is equal to the dune growth capacity following the formulation of Bagnold (1941). It seems that dune growth in this profile is less affected by marine processes. These results are likely to be related to the finer bed composition and wider beach at Profile 3 south.