The Wadden Sea is of great ecological importance. Key elements in the Wadden Sea are the extensive intertidal flats. These contain vast amounts of life, serve as feeding grounds for millions of birds, and provide ecosystem services such as coastal protection. It follows that it is important to be able to understand and predict how these vital elements of the highly dynamic Wadden Sea change over time.

The existence and evolution of intertidal flats rely on the intricate balance between erosion and sedimentation caused by the forcing of wind, waves, and the tide. Exact horizontal flow patterns on intertidal flats are not fully understood, especially under the influence of wind. This study aims to systematically investigate the tidally- and wind-driven horizontal flow patterns on the scale of an intertidal flat in the western Dutch Wadden Sea. To do so, existing literature is assessed and a subgrid-based hydrodynamic model of the Dutch Wadden Sea is created. Most hydrodynamic models require a wetting-and-drying algorithm to resolve the flow patterns near the wet/dry interface. Several types of wetting-and-drying algorithms exist, each with unique advantages and limitations. Subgrid modeling technique does not require a wetting-and-drying algorithm as wetting and drying is automatic. The adequacy of using a subgrid-based hydrodynamic model to achieve the aim of the research is investigated through a comparison of simulations with different settings. Computational grid resolutions are manipulated on the scale of the intertidal flat, along with whether subgrid modeling technique is applied. The tidally and wind-driven horizontal flow patterns are assessed using simulations in which the phase of the spring-neap tidal cycle is manipulated, along with whether wind forcing is applied. These scenarios are applied to two non-fringing intertidal flats with different geometries.

Simulations show that subgrid modeling technique is beneficial for representing the impact of small-scale bathymetric features on the flow pattern while using a coarser computational grid. Subgrid modeling technique offers an increase in how well the flow pattern is represented compared to simulations using interpolated bathymetry and the same computational grid resolution. The automatic wetting and drying is crucial for representing shallow flows, especially at depths where measurements and other hydrodynamic models face difficulties.

Results indicate that the horizontal flow patterns on intertidal flats follow the water level gradient between surrounding channels and are influenced by the intertidal flat geometry (i.e. size, bed elevation, and degree to which the intertidal flat is intersected by tidal channels), hydraulic boundary condition (i.e. phase of the spring-neap tidal cycle, asymmetry of the tidal wave), and wind forcing (which can completely alter hydrodynamics at several scales).

This report contributes to the knowledge on horizontal flow patterns on intertidal flats, benefiting studies into ecology, navigational maintenance, flood protection, and the ability of intertidal flats to keep up with sea level rise. However, the flow pattern is not solely responsible for morphological change. Moving forward, continued research into the drivers of the morphological change of intertidal flats will be crucial for informed management of ecologically valuable estuarine areas like the Wadden Sea.

Thin and large floating structures are increasingly used for a variety of applications, such as floating solar platforms, aquaculture, storage facilities, and even housing. For example, in the Netherlands, where thin plate-shaped floating solar platforms are being deployed in near-shore regions due to their benefits, such as uninterrupted solar irradiance and land conservation. With these deployments, it becomes essential to assess the risk posed to these structures by wave forcing in near-shore environments. Due to the large size of these flexible structures, the potential large impact of long ship-generated waves can be a key scenario of concern.

This thesis explores this scenario using a hybrid model, which couples a weakly nonlinear 2D finite element-based Boussinesq wave-generation model (FEBOUSS) with a 3D linear monolithic fluid-structure interaction (FSI) model. A key contribution of this work is the implementation of a novel, one-way partitioned fluid-fluid coupling algorithm, which efficiently transfers wave-information from the FEBOUSS model to the FSI model. The coupling is achieved by (1) enforcing the normal wave particle velocity from FEBOUSS as a boundary condition at the vertical inlet of the FSI model, and (2) using a damping zone that not only absorbs reflected waves from the membrane but also gradually enforces wave-elevation and normal wave particle velocity at a subsection of the free surface boundary of the FSI model. The accuracy of the coupling algorithm can be adjusted by refining the partition of feeding particles in the overlapping zone while simultaneously controlling the length of the damping zone. This approach ensures both computational efficiency, in terms of total simulation time and data storage requirements, as well as high physical accuracy at the coupling interface. The scenario of ship-induced waves entering a narrow harbour housing a floating structure is demonstrated, focusing on how the velocity of the moving vessel, represented non-dimensionally by the depth-Froude number, influences the hydroelastic response of the membrane. The analysis revealed that for all tested depth-Froude numbers, the membrane initially follows the long ship-induced waves, with subsequent responses that may be either (significantly) amplified or dampened with respect to the incoming waves, depending on the specific case under consideration.

The work presented in this thesis makes a significant contribution to offshore engineering literature by introducing a novel fluid-fluid coupling algorithm that can be extended to even more complex scenarios. Both the FEBOUSS wave-generation model and the FSI model are highly versatile, making them suitable for studying a broad range of fluid-structure interaction problems. Future research could explore the effects of variable bathymetry, irregularly shaped floating structures, and other relevant factors, expanding the scope of this study to include a broader range of physical phenomena.

Due to climate change, low river discharges are expected more frequently. As a result, salt intrusion in the Rotterdam Waterway will be critical at least five times more frequently, negatively impacting freshwater availability. A possible new measure to reduce salt intrusion is providing additional mixing by internal wave generation, which reduces the estuarine circulation. The potential to reduce salt intrusion in the Rotterdam Waterway by internal wave generation is investigated. To determine this the irreversible mixing generated by internal waves is quantified and related to salt intrusion length. Numerical 2DV simulations of a decelerating flow over an undular bed were executed for an idealized section of the Rotterdam Waterway. The mixing was quantified by determining the background potential energy in a chosen control volume. This method can be applied if disturbances in the velocity or density profile do not reach the boundaries of the control volume. The mixing observed in the control volume is related to salt intrusion by the buoyancy frequency of the background state. The net salt flux imported by estuarine circulation was found to be proportional to the squared buoyancy frequency. Estuarine circulation is the main forcing mechanism of salt intrusion in the seaward part of the Rotterdam Waterway. For the small idealized section of the Rotterdam Waterway, internal waves generated over geometrical features are capable of reducing the salt intrusion caused by estuarine circulation by approximately 1.7% of the initial value, if bed waves are present over 27.5% of the control volume.

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

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

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

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

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

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

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

Placed block revetments on dikes are used for the protection of the structure against wave loading. The dimensions of the revetment are determined with empirical relations and design tools. The stability of the design solution needs to be checked by physical flume tests to ensure the safety of the structure. However, these tests can be costly and time-consuming. Research has to show whether computational fluid dynamics (CFD) can be used to improve the design process of the revetment and reduce the number of required physical flume tests. The most important load on a placed block revetment is an uplifting force that results from a (porous media) flow through the top and filter layer of the structure during wave-structure interaction. This study aimed to determine whether CFD modelling can accurately predict the uplift of the top layer of a placed block revetment and identify the optimal approach for modelling this type of revetment.

In order to reach this goal, an existing CFD model is used and validated with a physical test performed in the Delta Flume. First, the data from the physical test is extensively analysed to check how the results relate to the physical processes described in the literature. Next, a two-dimensional CFD model has been set up with the open-source software package OpenFOAM. To mimic the physical test, the model is created in 1:1 scale with all the structure dimensions similar to the Delta Flume set-up. The top layer in the physical test consisted of C-star blocks that have been schematized in order to model the structure as a two-dimensional model. Two different schematizations are proposed and tested on their performance. In the first schematization, the top layer is modelled as a continuum in which the resistance is determined by the Darcy-Forchheimer equations, just as in the filter layer. In the second schematization, the top layer is modelled by rectangular blocks alternated by small gaps. The CFD model results and the physical test are compared based on trends and statistics.

The model performance has been evaluated for three consecutive processes. First, the wave generation and propagation are analysed by comparing the wave spectra of the incoming waves and monitoring the wave conditions along the numerical flume. The model could reproduce a wave spectrum accurately, and the wave properties remained constant during propagation. The second process that has been evaluated is the wave-breaking that results in wave loads on the slope. It has been shown that the quasi-static wave loads are predicted with reasonable accuracy (i.e. measured values deviate less than 10%) while the dynamic wave loads deviate up to 35% from the physical test results. It is concluded that there is room for improvement in modelling the wave-breaking. The last evaluated process is the porous media flow that leads to pressure differences over the top layer. The optimal schematization of the top layer was the rectangular blocks alternated with gaps. Just as in the physical test, only the dynamic wave loads lead to upward forces. These predicted forces deviate less than 20%.

To model the flow through the top layer, the local inertia, advective inertia and resistance terms are important in the conservation of momentum equation. For the top layer schematized with a continuum layer, the advective inertia term is underestimated by orders of magnitude leading to inaccurate results. The top layer schematized with rectangular blocks led to load predictions with reasonable accuracy. The resistance term was underestimated because no shear stress in the gaps between the blocks was included. However, the resistance term is small compared to the local inertia and advective inertia.

In future research, additional attention should be given to determining the optimal grid resolution. Results have shown that decreasing the grid sizes leads to increased predicted pressures. It could also be beneficial to further investigate the modelling strategy of the top layer. Schematization 2 has led to the most accurate model results. However, this model requires a fine grid resolution to resolve the flow through the gaps, leading to high computational times. A CFD model in which the top layer is schematized as a continuum would be beneficial in terms of computational times. Increasing the fictional porosity and grain size increase the contribution of the inertia term in the momentum balance, leading to better results. Investigating a method for obtaining these values may be of added value.

Despite being a critical aspect in improving the building stock’s environmental performance and achieving the global environmental goals, the retrofit of traditional historic buildings is hindered by a lack of comprehensive guidelines tailored to their complex building physics and heritage preservation requirements. The conventional retrofit approach – relying on the combined airtightness and insulation improvements – fail to address two decisive aspects of traditional historic buildings:
First, the air leakage is a core contributor to their bioclimatic systems and building physics balance, making its sealing detrimental to their construction durability and their Indoor Environment Quality (IEQ). Second, their heritage protection requirements restrict the conventional retrofit interventions, and particularly hinder the implementation of the mechanical systems needed to mitigate their associated risks on the building and its occupants. Accordingly, there arose an interest in challenging the conventional depiction of the air leakage as an overhead to be eliminated, and in developing a retrofit approach that preserves breathable buildings’ inherent operations by exploiting their air leakage into achieving their optimal post-retrofit performance, accounting for both energy-efficiency and IEQ.
A potential solution to the feasibility of such strategy considered a natural phenomenon characteristic of the diffuse leakage through breathable envelopes – the infiltration heat recovery (IHR) – that is conventionally neglected in building performance assessments. The intentional and efficient exploitation of this effect results in construction elements, referred to as Dynamic Insulations (DI), in which air leakage could act as a heat exchanger, diffuse ventilation source, airborne contaminant filter, and diffusion barrier. Although their original design and operations were not tailored to efficiently harvest the IHR effect, the existing breathable constructions reveal similarities with DI systems. This suggests the potential of retrofitting them to act as an efficient DI system, thus exploiting the air leakage into the building performance improvements. The present research aimed at identifying the envelope and ventilation retrofit variants that would optimize the IHR utilization through the construction, as to provide for performance improvements comparable to (or better than) the conventional approach while preserving the breathability of the construction and minimizing the heritage disruptions.
The study proposes a comprehensive framework for the assessment of the building’s post-retrofit performance, in terms of its energy-efficiency and IEQ, and investigates the relevant retrofit variants to make performance-based decisions in the retrofit design for traditional breathable buildings. This performance was evaluated using a comprehensive building performance simulation (BPS) model.
For a reliable representation of the complex building physics and air leakage dynamics of breathable constructions, the BPS integrates three sub-models: the building energy simulation (BES) model, the air leakage model, and the dynamic insulation (DI) model. Due to a lack of BES tools simulating dynamic construction properties, the well-established analytical Taylor model was adopted and adapted to the dynamic simulation tool. The analysis was implemented in EnergyPlus, for its integral Airflow Network (AFN) and advanced Energy Management System (EMS) capabilities. The model’s validation process revealed significant limitations and highlighted a need for BPS tools capable of more efficiently incorporating the dynamic behavior of building materials and their interaction with dynamic flows, particularly when seeking the tailored, efficient and non-intrusive retrofit of historic traditional buildings...

The natural development of the morphology of rivers in time is important due to the functions rivers fulfil, such as navigability and drinking water supply. Rivers adjust their morphology when there is a change in the river controls, which are mainly the water discharge, sediment discharge and downstream water level. The morphology adjustments continue until a river has reached its equilibrium state (i.e. equilibrium bed slope and equilibrium bed surface sand fraction), which is when all sediment that is supplied upstream of the river can be transported downstream. Even though an assessment of how the river changes towards its equilibrium state is important for the performance of the functions of a river, it is often overlooked. This can for example lead to increased maintenance costs and dangerous situations. A quick method to calculate the equilibrium state of a river can help prevent these negative impacts. The analytical relations by Blom et al. (2017) are a promising method to predict how a river will change, since they give useful and rapid insight in the equilibrium river state. However, the degree of uncertainty of the equilibrium river state as a result of the uncertainty in the input parameters is not yet known. It is recommended to examine this uncertainty before interpreting how a river will change. The aim of this research is therefore to investigate what the range of uncertainty of calculated equilibrium river states is, and to execute a sensitivity analysis to examine which input parameters contribute the most to this uncertainty. The river Waal is chosen as a case study for these analyses. The calculated equilibrium state of the river Waal, including the range of uncertainty, is compared to river state measurements to assess how well an equilibrium state can be identified. A model is created based on the analytical relations, and is used to perform three different analyses; a deterministic analysis that results in a spatially varying equilibrium state without uncertainties, a sensitivity analysis that assesses the influence of each input parameter on the equilibrium state, and an uncertainty analysis that results in a bandwidth of possible equilibrium states. The result of the sensitivity analysis is that the mean gravel content of the total sediment supply and the total sediment supply itself have the largest impact on the uncertainty of the equilibrium state. The result of the uncertainty analysis is that the equilibrium bed slope can be approximately 1.8E-5 smaller or larger than the mean bed slope, with an uncertainty bandwidth of approximately 3.7E-5, and that the equilibrium bed surface sand fraction can be approximately 10% to 20% smaller and 10% to 35% larger than the deterministic bed surface sand fraction, with an uncertainty bandwidth between 20% to 50%, depending on which sediment transport relation has been used. From the comparison between the calculated equilibrium state, including uncertainties, and the measured river state, it follows that the current bed slope is steeper than the equilibrium bed slope, and that the current bed surface sand fraction is either larger than or within the uncertainty bandwidth of the equilibrium bed surface sand fraction. The found milder equilibrium bed slope is as predicted. However, the found equilibrium sand fraction does not match the prediction that the bed surface sand fraction is smaller in the equilibrium state. From the comparison and the results of the uncertainty analysis follows that an equilibrium state cannot yet be identified, because 1) the uncertainty range of the calculated bed surface sand fractions is considered to be too large to predict the equilibrium state of the river Waal, and 2) the equilibrium bed surface sand fraction predictions do not match the expectation. To improve the equilibrium state identification of the river Waal, it is recommended to 1) assess why there is a mismatch between the expected and calculated equilibrium bed surface sand fractions, 2) perform research to reduce the input uncertainty, and 3) validate the equilibrium state predictions.

The combination of continuous sea level rise, and more frequent extreme river discharges will become a rapidly developing problem for the Rhine-Meuse delta over the course of the next century. The current Dutch delta management policy mostly revolves around the consistent improvement of the existing dikes to account for the increasing water levels in the region. An alternative solution to this problem is the Delta21 project. The Delta21 project proposes the construction of a large scale storage lake, and a high capacity pumping station at the Dutch coast. The project is meant to allow for the simultaneous closure of the storm-surge barriers on the Dutch coast, while actively discharging river water that would normally be pilling up behind the closed barriers. The Delta21 project foresees it will be able to save up to 5billion euros by the end of the century in dike reinforcement costs. In order to enable the flood safety operation of the Delta21 project, the project also requires the construction of a new storm-surge barrier in the Haringvliet ebb-tidal delta, roughly 10km away from the current Haringvlietsluices. The objective of this thesis is the conceptual design of the new Delta21 storm surge barrier, the New Haringvliet barrier. The aim of this design process is to identify critical design components, and requirements that could potentially be hurdles in the development of the New Haringvliet barrier, as well as the overall Delta21 project. For the hydrodynamic design of the barrier, a schematized 1D hydrodynamic model was used to get a first insight into the impact the new barrier will have on the on the tidal range in the tidal delta. As well as how much it could potentially impact the reintroduction of the tide to the Haringvliet. The reopening of the Haringvliet would be a part of Delta21's effort to restore some of the local ecological value to the region as a compensation measure for the project. Additionally, the model was also used to determine the effects of the construction of the barrier on the capability for the system to handle high river discharge rates. The findings of the assessment show that the selection of a small tidal opening in the New Haringvliet barrier will significantly negatively impact the capability for the system to discharge high river water, as well as limit the amount of tidal range that will be available in the system. It was determined that constructing the barrier with a tidal opening with an effective cross-section of 10000m2 will provide the best balance between hydrodynamic performance of the system, and barrier construction costs. An analysis of the possible Delta21 construction sequences was used to determine the preferred construction method for the barrier. In this analysis, an economic construction sequence alternative, and an environmental construction sequence alternative were developed, and consecutively evaluated using a multi-criteria analysis. This MCA revealed that the construction of the New Haringvliet barrier using prefab construction elements and techniques was the desired construction method for the project. The results of hydrodynamic and construction sequence assessment, were used as the basis for the barrier's spatial design. The structure was designed with a total of 20 vertical lift gates, each spanning 80m. This would bring the total tidal opening to 10400m2. Vertical lift gates were chosen for the design due to their great reliability and overall cost effectiveness, which are both important considerations for a barrier of this magnitude. On the southern side of the barrier a shipping lock will be the barrier's primary navigational opening. The final phase of the conceptual design focuses on the design of the gated barrier section, and includes the validation of the transport stability of the caisson, the design of the vertical lift gates, and the design of the scour protection and it's filter layers.

The Kampereiland is an island located at the south eastern part of the IJsselmeer in the middle of the Netherlands. This island serves a purpose to lower water levels in the IJssel- and Vechtdelta during high water, by being inundated. This inundation is meant to result in lower water levels in the IJssel near Kampen. However, the flooding of the Kampereiland is a complex case. There are numerous stochastic variables that are used to determine the water levels, as well as breaching possibilities and a compartment structure which is present on the Kampereiland. All these aspects have influence on inundation of the island. In this thesis research, the flooding of the island is analysed, during multiple different types of high water scenarios, as well as with a variation of breaches or no breaching. This is all done while taking the compartment structure on
the Kampereiland into account.

To analyse how the Kampereiland floods, three main types of highwater scenarios have been analysed. These types are stormdominated scenarios, which are defined by high wind speeds and low discharges. The second type of high water is the discharge dominant scenario. The high water levels in these scenarios are reached by high discharges from the Vecht and the IJssel rivers, in combination with low wind speeds. Lastly, a number of extreme events have been analysed, to give a worst case perspective of the flooding of the Kampereiland. In these scenarios, high wind speeds coincide with high discharges from the two rivers, resulting in extreme water levels in the Ketelmeer, ZwarteMeer and in the Ganzendiep.

Each of the analysed scenarios have outside water levels exceeding the crest height of the flood defenses surrounding the Kampereiland. The scenarios have been analysed for multiple breaching cases. Three different breach locations have been determined. The locations have varying crest heights, type of flood defense (overflow resistant or non overflow resistant), type of high water (storm dominated or discharge dominated) and different hinterland compartments. Each scenarios has then been used to run the model to determine water levels in each compartment. This is done for situations without a breach, a single breach or two breaches at one location. The determination of the water levels is calculated by the use of spillway formulas.

The results show that the Kampereiland mainly floods from west to east. Storm dominated scenarios lead to high water levels in the Ketelmeer, leading to overflow from here. In scenarios up to 32 m/s wind speeds without breaches, the flooding is contained to the compartments to the west of the N50. The entire island floods once water levels increase due to wind speeds of 37 m/s and higher. Adding breaching into the storm dominated scenarios, the results are shifted. Now the evaluated scenarios with 32 m/s also lead to flooding
of the entire island. This case still leads to less high water levels on the Kampereiland than the scenarios of 37m/s without breaching, but every compartment is inundated.

The discharge dominated events are contained in the Willem Meyer- and Stikkenpolder. This is due to the presence of the old flood defense, which contains the flooding in cases with and without breaches.

Finally, the extreme events flood the majority of the Kampereiland, similarly to the stormdominated scenarios. The water levels that occur in the Zwarte Meer and Ganzendiep are higher during the extreme events. They also last longer than in the storm dominated scenarios. This results in a small inflow from the north
and southeast, while the western side of the Kampereiland rapidly fills up. Breaching during these extreme events leads to higher water levels when the breach occurs in the overflow resistant part of flood defense 225. The rising velocities in the west are also the highest in this case. Eastern compartments have higher rising velocities in case of breaching in flood defense 101 (along the northern boundary).

This thesis concerns a hydroelastic analysis of a multi-module very large floating structure (VLFS), analysed in the frequency domain. To this end, the fluid-structure interaction is described by a 2D model, where the VLFS is represented by four floating beams interconnected with rotational springs. The fluid is modelled as an ideal fluid, and the floating beams are modelled by the Euler-Bernoulli beam theory. The finite element method is applied to solve the governing equations of the fluid motion and the motion of the beams, where the model is built using the FE-library Gridap, written in the Julia programming language.
The aim of the study is to investigate the influence of various module and connection stiffness on the behaviour of the system, with the view to obtain more insight in the complex relation between the hydroelastic response and internal loads, when the system is subject to regular waves.

Due to climate change and human interventions, saltwater intrusion is becoming a topic of increasing concern worldwide. Salt water intrudes into the Rotterdam Waterway (RWW) by an exchange flow, where the denser sea water propagates landwards at the bottom. The main competing mechanism for this stratified exchange flow is vertical mixing, which can be realised by internal wave induced shear instabilities or wave breaking. The goal of this study is to investigate whether internal waves generated over undular bottom topography in the RWW can generate additional vertical mixing. The underlying assumption is that a decrease in stratification decreases salt intrusion.   The approach to answer the main research question is a combination of an analytical and a numerical analysis. The analytical study is based on frictionless linear theory. Internal wave behaviour is further analysed with FinLab, a finite element model which includes the non-hydrostatic processes and effects of density differences. FinLab is evaluated for the application of this study by means of a validation case.  In the analytical study, linear theory is applied to obtain a relation between the bed wave parameters and average internal wave energy density E for internal waves generated over sinusoidal bottom topography in a linearly stratified fluid. The derived expression describes that the bottom topography amplitude h0 and bed wave number kT both have a positive quadratic relation with the energy. Additionally, kTkinfluences the resonance conditions.  To validate FinLab for internal wave breaking and mixing an experiment in a wave tank, according to an example from literature, is simulated. The validation case reveals a shortcoming in the turbulent mixing parameterization. However, on scales relevant for the RWW the effect of this will not have the same significance. The validation case offers a suggestion for a subgrid closure of diffusion, where density effects are taken into account.  Numerical simulations of a 2D channel stretch with sinusoidal bottom topography, a linearly stratified fluid and a linearly varying background velocity, show generation of resonant trapped internal waves for the first two resonant modes. These occurrences correspond to the highest values of kinetic energy as function of vertical velocity averaged over the bed wave domain. The vertical buoyancy flux b is downward directed during occurrences of internal waves and becomes upward directed for increasing background flow. Vertical mixing is associated with an increase in average potential energy Ep, which is 17% higher for the base case (containing bed waves) than for a similar case without bed waves. This increase is larger when bottom shear stress increases. Richardson numbers below 0.25, associated with shear instabilities and mixing, are only observed near the bed, mainly when internal waves are present. The effect of variations in bottom topography wavelength LT and amplitude h0 on internal wave energy can be explained by the analytical formulation. The effect of bed wave parameter changes on b and relative increase in Ep can be related to the effect of the changed amount of bed friction rather than the difference in wave energy.   The first resonant mode is the most energetic, however, the average energy density found for these waves is only 0.4% to 6.7% of the potential energy anomaly (PEA); the energy required to fully mix a stratified water column. In the simulations the only mechanism that could transfer internal wave energy to turbulent kinetic energy are shear instabilities near the bed. Over the full simulation, the net vertical buoyancy transport is of negligible magnitude, where Ep shows significant increases between 6% and 99% compared to similar cases without bed waves and is enhanced during the presence of internal waves.  The main discussion point is that the quantification of vertical mixing requires improvement, particularly to determine the importance of mixing by internal wave-induced shear instabilities and by bed shear. Mixing by local shear instabilities (of which the relevant scales cannot be resolved with the current grid resolution) does not have an adequate parameterization, because density effects are not included in the turbulence closure. The bed friction parameter, which greatly influences the behaviour of the system, has to be validated. Furthermore, cases where internal waves might break in practice (e.g. at banks) were not considered. Finally, the observed internal wave energy is of small magnitude, however field measurements by Pietrzak(1991) shows that turbulence production by internal waves was significant.   

When a large ship enters a port the vessel is navigated by the pilots instead of the captain due to safety reasons. The final part of the berthing manoeuver is the most critical and consists of the vessel moving laterally towards the quay wall. At this point the vessel does not use its own propulsion force anymore but is pushed by the tugboats. During this lateral berthing manoeuver a resistance force can be noticed counteracting the lateral manoeuver to the quay which acts as hydraulic damping. A large force is needed to overcome this hydraulic damping which is known as the water cushion effect. There are a handful of circumstances that are suspected to enhance the effect of hydraulic damping, but a substantiated conclusion is not yet drawn. To determine the mechanisms causing the hydraulic damping during ship berthing, field experiments in the Port of Rotterdam are carried out and analysed. In addition, a one-dimensional theoretical model is developed to simulate the field experiments and investigate the flow behaviour around a berthing ship.

Many coastlines feature a sediment transport in a dominant direction, possibly burying a traditional breakwater in sand in several years. The sandbar breakwater concept uses this sediment supply to its benefit to make the use of vast amounts of rocks abundant. During this research the morphological development of the worlds first sandbar breakwater built in Lekki, Nigeria, is analysed: The minimal amount of sand used for construction of the Lekki breakwater is placed such that the combination of the adaptation of the initial
profile and the natural supply of sediment results in a smooth coastline at the end of the first year. This development is in turn used to setup a calibrated model to study the influence of the wave climate on the development of the sandbar breakwater concept. The wave climate at Lekki is characterised by a single dominant wave direction (called unidirectional) and has a narrow direction bandwidth (yearly standard deviation of the wave direction is about 5 degrees). This ideal wave climate is altered to research the influence of the mean wave direction, directional variation and the sequence of waves (seasonality). The study showed the sandbar breakwater concept to be mainly influenced by the mean wave direction and to lesser extent by the directional variation and the seasonality. These results can be used to make a first assessment on the possibility of applying a sandbar breakwater for a wave climate somewhere around the world.

Siltation affects navigation in harbors and waterways by reducing the water depth. To regain depth and safeguard navigation, dredging is required. Water Injection Dredging (WID) is one of the available hydrodynamic dredging techniques, in which pumps on a vessel inject water at high flow velocities and low pressure into the bed and fluidize the bed material into a mixture of water and suspended sediment. The fluidized material travels as a turbidity current to deeper areas, driven by natural processes. Sediment transport is then less controlled and the final destination of the dredged material is more difficult to estimate than for other dredging techniques. The passage of a WID-induced turbidity current produces an increase in suspended sediment concentration (SSC) in the water column that increases turbidity. Turbidity increase may have a negative environmental impact. Therefore, to evaluate and mitigate the environmental impact of WID, the increase in SSC should be estimated. Additionally, from an operational perspective, the sedimentation footprint of the turbidity current should be determined. Deltares developed with Boskalis a numerical tool named “Lagrangian 1DV model” (Deltares, 2019). The Lagrangian 1DV model can calculate the thickness and density of the WID-induced turbidity current at a distance from the dredger, as well as the deposition rate. It provides the information to estimate the increase in SSC in the water column and the sedimentation footprint. The tool was defined to be a rapid assessment tool, as it is necessary at the early stages of WID projects when there is usually a limitation of time and available data. Such a tool is useful to analyze different dredging strategies and different solutions to mitigate environmental impact.
As its name indicates, it follows a Lagrangian 1DV (1-Dimensional Vertical) approach. This approach follows the turbidity current in space as it moves away from the dredger. It is an innovative approach that requires less computational effort than a 3D or a 2DV (2-Dimensions in the Vertical plane) approach.
Three main steps were followed by Deltares (2019) for conceptual and mathematical modelling: - Step 1: assume that the turbidity current is a 2DV process, thus neglecting lateral gradients - Step 2: schematize the 2DV process as a Lagrangian 1DV approach. - Step 3: select the 1DV Point Model (Uittenbogaard and Winterwerp, 1997) as the basis to solve velocity and concentration profiles over the vertical. In order to schematize the 2DV process as a Lagrangian 1DV approach (Step 2), two main points were assumed:
- Uniformity of the 1DV Point Model (in the Eulerian frame of reference) was assumed as stationarity in the Lagrangian frame of reference - The Lagrangian velocity was defined as a concentration-weighted velocity over the water column, expressed as the ratio between the mass flux and sediment load.
The validity of these assumptions to estimate sediment transport was analyzed in this report. For that purpose, the Lagrangian 1DV model (Lagrangian 1DV approach) was compared to a 2DV computation in Delft3D-FLOW (called Delft3D model) in four sets of numerical experiments. The validity of the Lagrangian 1DV approach for uniform flow was confirmed with the first set of numerical experiments. Experiment Set 2 showed that the Lagrangian 1DV approach is as valid as the Eulerian 2DV approach to represent sediment transport in non-uniform flow when density differences are negligible. Differences between the Lagrangian 1DV model and the Delft3D model in velocity, concentration and, consequently, in the concentration-weighted velocity (calculated in the Delft3D model as the ratio between mass flux and sediment load), arose in non-uniform flow for the cases in which density differences became significant. The results suggest that the origin of the differences between the Lagrangian 1DV model and the Delft3D model in the concentration-weighted velocity relies on the expression of the advective transport term of the sediment transport equation.
In Experiments Set 3 and Set 4, the numerical models were based on laboratory experiments on turbidity currents by Parker et al. (1987) and van Kessel and Kranenburg (1996), respectively. The baroclinic pressure gradient was higher for these sets experiments. Thus, differences in the baroclinic pressure gradient between the models produced important differences in velocity.
In the case of Experiments Set 3, based on Run 13 of Parker et al. (1987), the concentration-weighted velocity was lower for the Lagrangian 1DV model along the analyzed reach. Experiments Set 4, based on Run 2 of van Kessel and Kranenburg (1996), presented the opposite behavior: a higher value for the concentration-weighted velocity for the Lagrangian 1DV model. A possible explanation for these results was found, based on the variation of the sediment load along the channel in the Delft3D model and the magnitude of the baroclinic pressure gradient. In order to analyze possible implications of the observed differences when the model parameters are in the range of the WID application, the variation of the concentration-weighted velocity was calculated in the Lagrangian 1DV model for a typical case of WID. The trend of the variation along the reach was similar to the case of Experiments Set 3. Then, the results suggest that the estimated concentration-weighted velocity in the Lagrangian 1DV model may be lower than the result for the 2DV approach. As a consequence, the travelling distance of the turbidity current may be shorter. More specific cases can be addressed by comparing the Lagrangian 1DV model and the Delft3D model, following the methodology presented in this report.

In submerged conditions groynes add resistance to a river, thereby increasing the water levels for a particular discharge. Groynes are modelled in two ways, either they are included in the bed topography when the grid resolution is sufficiently high or with a sub-grid parametrisation when the grid cell-size is larger than the geometry of the groyne. To investigate the flow patterns over and around groynes, data from a groyne flume experiment, as carried out by the BAW, is analysed. This to investigate to what extent a groyne behaves as a weir. The experiment is modelled in 2DH and in 3D to compare the performance of the sub-grid parametrisation with full 3D non-hydrostatic simulations.

River discharge is an essential parameter in morphodynamic modelling. It proves to be highly variable in both time and space. In this thesis the impact of the schematisation of time-dependent discharge series on morphodynamic change is studied. The impact is governed by several factors such as the long-term discharge statistics, and both short- and long-term sequences of discharge stages. A variable river discharge itself does not necessarily result in morphodynamic change. Changes in conveyance area and roughness are dominant sources of bed fluctuations and bed waves. Moreover, backwater dominated segments are subject to mild fluctuations in the river bed. The combination of natural variation of hydrological processes in the upstream river catchment and the absence of a significant correlation among statistical characteristics of subsequent years makes it hard for river engineers to construct discharge time series for river models that simulate morphodynamic development. The limited predictability of future discharge time series is an important source of uncertainty in model predictions. A way to estimate this uncertainty is by means of a time-consuming Monte Carlo approach, resulting in a mean long-term morphodynamic trend and the associated uncertainty. An alternative method is the application of a deterministic series for which the long-term discharge statistics are translated into a cycled annual hydrograph (CAH). It is expected to yield similar morphodynamic changes with respect to the mean trend from the Monte Carlo approach without the need for a large number of computations. However, as is demonstrated in this study, the CAH-method lacks in performance in simulating average long-term development and the amplitude of fluctuations in the river bed, especially at locations where strong sediment transport gradients are experienced. Using a simplified two-dimensional model that represents a locally widened floodplain, the impact of the included bandwidth, short-term and long-term sequences on morphodynamic change is investigated. The aim is to improve the deterministic hydrograph schematisation and to find a more convenient way to get insight into uncertainty in simulated morphodynamics. These findings result in a set of recommendations for future schematisations of discharge time series in morphodynamic river models. An improved deterministic approach is proposed. Using historical measurements of daily discharge data, years with a similar statistical maximum, mean and standard deviation can be classified. The classified years are translated into multiple cycled annual hydrographs (MCAH). By using these hydrographs, synthetic time series are constructed. Compared to the CAH-approach, the proposed MCAH-method yields a significant reduction of the root mean square error with respect to the long-term average morphodynamic trend from the Monte Carlo simulations. Moreover, the MCAH-series result in amplitudes of bed fluctuations that are closer to the response to natural discharge time series. Finally, the MCAH-series can be used to give a rough indication of the uncertainty in future morphodynamics.

At the edge of Vancouver and the Strait of Georgia the Point Grey cliffs experience marine and subaerial erosion. The retreat of the cliffs will eventually result in losing university assets, infrastructure and archaeological treasures. Wave-induced sediment transports are supposed to be the main marine erosion mechanism. This report presents other potential marine erosion mechanisms (e.g. direct wave attack, sediment budget deficits, sea-level rise and increased storm intensity) over different time scales and studies the sediment transport and budgets in more detail. The study is performed with the help of a numerical hydrodynamic model with representative scenarios of the hydrodynamic conditions. The model and scenarios are set-up by means of a site visit, literature, water level records, wind and wave records and sediment samples. The resulting scenarios and results provide an hydrodynamical overview of flow- and wave conditions. Subsequently, the sediment transports, indeed, seem to be initiated by waves. Results also opened up a new potential sediment transport path not yet mentioned by sources. However, the sediment transports does not seem to be the only erosion mechanism. A potential human-induced sediment budget deficit is likely as well. Additionally the direct wave attack and the combined sea-level rise and intensified storms are also either present or becoming more relevant in the future. The contents of this report forms a basis for developing design criteria for a coastal solution to the marine erosion of the Point Grey cliffs. An engineered beach, together with a foreshore nourishment, out of locally dredged material seems like the most logical option. By further improving the numerical model and the overall study with presented recommendations, this study can inspire further design steps for a solution to save the Point Grey cliffs.

The thesis presents a numerical study on dredging induced undrained instability and subsequent static liquefaction of submarine landslides. For the study, a pre-existing hydro-dynamic uncoupled submarine slope numerical model, developed by Molenkamp (1999), has been modified to incorporate a fully hydro-dynamic coupled interaction between submerging water mass and submarine slope. The modified model is able to simulate transient quasi-static and dynamic phenomena up-till and including the immediate post-liquefaction behavior of submerged slopes of loose undrained homogenous fine sands in a 2 dimensional Updated Lagrangian (UL) finite element (FE) frame of work. To simulate soil behavior under dredge loading applications the model incorporates a Monot soil constitutive model and for submerging water behavior a Lagrangian expression of Navier stokes for nearly-incompressible visco-elastic, irrotational, fluid model.
The study primarily addresses the effect of dynamics of submerging water on the liquefying submerged slope. The research findings suggest that the dynamic motion of submerging water barely affects the occurrence of instability. However, it may decrease the rate of post-instability liquefied flow as compared to the commonly sorted uncoupled scenario, where dynamics of submerging water mass is ignored and only constant hydrostatic pressure heads due to water level is considered at the slope interface. Moreover, the findings suggest that about 50% of the loss in the potential energy of soil is consumed by the potential energy of the submerging water at the very initial stages of post-instability and that the contribution of kinetic energy of water amounts to mere 3.4%.
Next, as a secondary issue, the study also provides a valuable insight into the effect of the liquefying slope on the motion of the submerging water mass. The findings show a surface impulse wave formation post-instability, moving along the direction of landslide. Moreover, it shows a development of a distinct circular motion of fluid along the slope interface. Other than this, the thesis also attempts to provide some similarities and differences between the current findings and the published conventional research studies which make use of basic slide shapes such as viscous or rigid sliding wedge blocks.
Finally, the thesis also addresses some numerical shortcomings such as the hour-glass effect, the shake-down by the procedure to define the “initial state” effect etc., and thereby providing necessary recommendations useful for future computational modelling work.

In this report, an experimental investigation of the influence of currents on submarine slope stability is presented for the Eastern Scheldt storm surge barrier case. Slope instabilities, including liquefaction failures, have been observed in the scour hole slopes near this barrier. The currents above the sloping bed are expected to initiate the liquefaction slope failures. The effects of the excess pore water pressure increase, that is generated by the currents, on the soil response are investigated by triaxial tests. Multiple excess pore water pressure rates are applied on a loose soil sample. The triaxial tests show that higher excess pore water pressure rates result in earlier developments of strains at lower stress ratios. This research is intended as a step towards a better understanding of the initiation mechanism of the liquefaction slope failures near the barrier.

In 2003 certain areas of the Dutch coast were found not to meet contemporary safety standards, as a result of erosion that occurred over the last century. One of these 'weak links' stretches from Camperduin to Petten and is known as the Hondsebossche Pettemer Zeewering; a former 'hard' sea dyke with a stone revetment. To fortify this 12 kilometres coastal area construction of a dune, beach and shoreface nourishment began in 2014.

A 2DH model, FINEL2D, was used to predict the development of the zone for twenty years to estimate the maintenance. However, significant deviations in sand volume losses were found when comparing measurements and model predictions. These differences may affect maintenance budgets. Especially in the Nature Zone of the HD, where the contractor must pay a fine if maintenance is needed within the first ten years after construction.

To evaluate the consequences of the deviations on the maintenance prognosis of the coming years, a model is required which predicts the volume losses of the Hondsbossche Dunes with sufficient accuracy. The goal of this research is to evaluate the applicability 2DH models to simulate volume losses of a mega nourishments such as the Hondsbossche Dunes.

An analysis of the data available for the first and second year after construction is performed to provide insight into the causes of the deviations between the measured and modelled volume losses. It focusses on finding the effect of initial processes. Furthermore, it aims to define the relative importance of cross and longshore transport. Afterwards, the model performance is evaluated by means of a hindcast, using brute forcing. Together with the data analysis this information is used to improve future predictions of 2DH models.

From the data analysis it can be concluded that volume losses occurring in the first year are significantly larger than those in the second year. This difference cannot be explained by the difference in occurring wave climate and coastline orientation alone, it can have multiple other explanations; winnowing, settlement of nourished sediment, settlement of the subsoil, sediment losses beyond the dunes, and losses to deeper water. The significant reduction of the volume losses in the second year indicate that initial effects are less pronounced in this year. This indicates that the losses in longshore direction of second year after construction should be predictable. It is also found that aeolian transport is an important process in both years.

The evaluation of the model performance showed higher model accuracy for the second year after construction than for the first year. The modelled volume losses are compared to the losses in longshore direction based on measurements. The second year models the volume losses reasonably well, especially when looking at the Nature Zone, dominated by erosion.

Some aspects that could further improve the model are analysed using a strongly simplified model. Those aspects are assumed to increase the sediment transport and thereby the sediment available for sedimentation in the recreation zone north. Only using a smaller grid size around the bars seems to strongly enhance higher sediment transport. The other aspects considered are the interpolation between SWAN and FINEL2D, the amount of swan calculation per tidal cycle, the change in the cross-shore profile due to lack of 3D processes in 2DH models, and the morphological acceleration factor, none of which significantly affected total sediment transport.

It is found that a 2DH model is applicable in a situation where initial effects are no longer present. In case of a first year after construction, a factor could be applied to account for initial effects. For the second year, the model accuracy is quite good when comparing it to measured losses assumed in longshore direction. Yet an important factor to the losses is aeolian transport which is not accounted for in a 2DH model.

For future projects, it is important to realise that initial effects can significantly affect volume losses, and should be accounted for in some way. Another aspect that is important to take into account when designing a mega nourishment is the contribution of aeolian transport, which is quite constant during the first and second year after construction. A third aspect to keep in mind is the way the model results are interpreted.