Many regions around the world are prone to tsunami risk, and their populations are expected to increase. Moreover, past events like the 2011 Great Eastern Japan Earthquake and Tsunami resulted in numerous fatalities and the failure of many coastal protection structures. These events underscore the urgent need for further research in tsunami engineering and the mitigation of tsunami risk. In fact, the capability of coastal protection structures, such as breakwaters, to withstand tsunami loads is not yet fully understood. Additionally, these structures are typically designed to resist wind waves loads rather than the longer waves produced by tsunamis. This research provides further insight into the interaction between tsunamis and composite breakwaters by analyzing experimental results where a unique technique capable of accurately reproducing tsunamis as scaled N and E-waves was used. The experiments employed a 2-dimensional flume where waves were generated with a tsunami simulator and propagated until they impacted a composite breakwater model, inspired by the world-record breakwater in the Kamaishi bay in Japan. This research thoroughly analyzed the results of one of the experiments conducted at the HR Wallingford research center in the UK, with the objective of understanding the response of a composite breakwater when impacted by a tsunami, focusing particularly on the caisson on top of the structure and its stability. Another objective was the development of a numerical model based on the coupling of the two software OceanWave3D and OpenFOAM, aiming to reproduce physical experiments on tsunami-structure interaction and provide further insights beyond the capabilities of physical tests. The results of this research indicate that the pressures and forces induced by a tsunami on the caisson of a composite breakwater have a dominant hydrostatic contribution. The absence of wave breaking as the tsunami approaches the breakwater and shoals on its rubble mound prevents the generation of impulsive forces on the structure. The analysis also shows that, for the considered tsunami at prototype scale, the caisson would be unstable and fail due to sliding, primarily because of the water level and pressure differences on the two sides of the structure. The model developed in this research demonstrated a good accuracy in representing the physical experiment, as evidenced by elevation and pressure time series, with minor limitations on the lee side of the structure and on its rubble mound. With further validation using additional experimental results, this model can serve as a starting point for future studies on tsunami-structure interaction. It overcomes some limitations of physical testing, potentially provides more accurate results for caisson stability analysis, and offers a cost-effective alternative to physical experiments.

In 2008, a new concept to extract tidal energy was introduced called Dynamic Tidal Power (DTP). In this concept, the natural tidal wave propagating along a coastline is blocked using a long dam, inducing a water level difference between both sides of the dam. This water level difference, called the hydraulic head, can be exploited by placing turbines inside the dam. This is a promising concept, but the feasibility and suitable locations for DTP are largely unknown yet.

This study aimed to identify locations that have the highest potential to implement the DTP concept. By investigating the feasibility criteria and their influence and translating these criteria to spatial analysis, geographic regions with high potential were identified. Additionally, linkage opportunities were assessed and identified to possibly improve the feasibility of DTP.

Based on a sustainable feasibility study framework, the key aspects can be categorized into three main categories; technical, economic and social-ecological feasibility. These aspects were translated into criteria, whose influence was investigated using a hydraulic model. Considering the technical criteria, the tidal flow velocity proved to be more influential on the feasibility than the depth, finding weighting factors of 0.87 and 0.13, respectively. In order to define a threshold of the feasibility of DTP, the technical and economic criteria were combined by assessing the upper threshold of the Levelized Costs Of Energy (LCOE) of 0.1 €/kWh to find a minimum required average flow speed of 0.63 m/s. This threshold was used in the spatial model. The island linkage opportunity proved to be highly valuable. Connecting an island increases the effective blockage length, resulting in a hydraulic head and power output increase with approximately the same dam construction costs. This lowers the mean tidal current speed required for feasibility to 0.39 - 0.57 m/s.

The spatial analysis used a Multi-Criteria Weighted Overlay Analysis (MCWOA) approach, combining datasets and weighting factors for each criterion to find a total Potential Index (PI) score. In total 41 potentially feasible locations for DTP were identified. The geographic regions with the highest potential to implement DTP are the Yellow Sea, the seas in Southeast Asia, and the seas of Oceania. This is due to a combination of high tidal current velocities, relatively modest water depths and a good combination of secondary criteria (energy usage, population size & low shipping disruption). A high share of the island linkage opportunity was found in the locations with the highest potential (44%). It is recommended to investigate whether additional island linkage opportunities can be identified, by lowering the tidal current velocity threshold in the spatial model. Additionally, 233 locations were discarded, mostly due to their remote location. However, since these locations are technically feasible, it is recommended to investigate the possibility of transmitting the energy over long distances using Ultra High Voltage Direct Current transmission lines and study the total feasibility of DTP at these remote locations.

This study assessed the feasibility of DTP and identified that the Yellow Sea, the seas in Southeast Asia, and the seas of Oceania have the highest potential for a DTP project. Additionally, it provided new insights regarding the influence and thresholds of certain influential criteria, and it presents a hydraulic model and GIS tool that can be adjusted based on the preference of the user. These findings could be useful in future research on the DTP concept.

Gates are an essential part of navigational locks, as they are responsible for creating a water barrier and can be repositioned to allow passage for maritime transit. Most lock gates are made of steel but a recent project in Sweden challenged the status quo by constructing the first stainless steel lock gate. The main question of this thesis aims to investigate the possibilities for the application of stainless steel in Dutch mitre gates and how optimisation through implementing a global arch shape can contribute to the material and weld reduction required to do this. To quantitatively assess the hypothesis of this thesis, Lock Veere was chosen as a case study. The finite element method was selected to simulate the operational conditions of a lock gate.
The first part of this thesis aims to define what needs to be taken into account when designing arch-shaped stainless steel mitre gates. The gate can be positioned in three different setups, which each provide different boundary conditions. Eight different load combinations were defined that could possibly be critical based on size, asymmetrical positioning or repetitive loading. In addition to the operational conditions, the requirements and limits of stainless steel in lock gates were considered.
The second part of this thesis investigates the feasibility and optimisation of the global shape. The effectiveness of shape is based on the loading system of a structure. For a lock, this is the water level difference that results in a uniform load over the width of the construction. Arches are relatively more resistant to this load, which allows for material reduction. Mitre gates have another dominant load situation; a point load with asymmetric support during an obstacle situation. Plates alone are not resistant to this load, so a frame around the plate is introduced. Based on the results found in this thesis, both components seem feasible and allow for further material reduction.
The third part of this thesis aims to prove the effectiveness of a complete gate design by simulating the construction with the operational conditions selected in the first part. The aim of the design was to be as simple as possible in order to meet the demands imposed by stainless steel. The final design allowed for 20\% weight reduction and 30\% weld length reduction compared to the traditional design.
Based on the results that were found, an answer to the main question posed by this thesis can be formulated. For the operational conditions found in Dutch mitre gates, an arch shape can be applied in combination with a surrounding frame. This reduces the weight, number of welds and weld length. For these reasons, manufacturing is expected to be less intensive and maintenance is more accessible due to component reduction. Global shape was thus able to contribute to the optimisation of Dutch mitre gate design. This optimisation through global shape adheres to the requirements for stainless steel. However, this result opens up interesting possibilities for further research on using global shape in combination with other materials as well.

The impact of climate change, particularly the rise in sea levels, obstructs the effectiveness of existing coastal structures. Additionally, climate change can also have an amplifying effect on wind speeds (Takagi & Esteban, 2013). Without proper control, the accumulation of changing environmental boundary conditions could lead to disastrous events.
Currently, the design of rubble mound breakwaters is based on the EurOtop (2018) guideline. However, these guidelines may overlook essential influencing factors. Recent studies by Van Gent et al. (2022) and Irias Mata & van Gent (2023) have contributed to new insights that address these limitations. They aimed to identify numerous influencing factors that enhance the accuracy of wave overtopping expressions for rubble mound breakwaters. However, for several factors a more thorough understanding is still required.
Furthermore, recent insights on the influence of wind have proven to be significant. Previous studies indicate that the mean overtopping discharge has the potential to amplify its quantity several times beyond its initial value (de Waal et al., 1996; Wolters & van Gent, 2007; Van Gent et al., 2023 and Dijkstra, 2023). These investigations included tests on vertical sea walls and dikes.

This research focuses on investigating the maximum effect of wind on wave overtopping for a rubble mound breakwater, considering varying slope angles and crest element designs. The key parameter of interest is the maximum wind effect factor, described as a function of the non-dimensional overtopping discharge. Small scale models of rubble mound breakwaters with mild (1:6) slopes, steep (1:2) slopes, and various crest walls are examined to find their influence on the maximum effect of wind.
An extensive experimental programme was carried out within the Pacific Basin at Deltares. In this basin, a flume was constructed in which the breakwater models were built. Various hydraulic conditions, incorporating the water level and the wave characteristics, were systematically tested. All conditions were repeated, both with and without including the maximum wind effect.

A new overtopping expression is developed, taking the form of an exponential function that includes all relevant parameters. The influences corresponding to the crest wall are thoroughly investigated, while the other factors (roughness, obliqueness, and a berm) are only taken into account. The exponents and constant factors were obtained iteratively and were found to accurately predict the overtopping discharges obtained during the experiments.
The relationship between the maximum wind effect and non-dimensional overtopping, as observed in previous research, was confirmed for these measurements. This observation suggests that a maximum effect of wind increases when the non-dimensional overtopping discharge decreases. Only the configuration with a mild slope and the tallest crest wall stood out by showing a notable influence on the maximum wind effect. Moreover, the wind effect is more pronounced for an increasing water level when similar amounts of overtopping discharges are taken into consideration. Based on these findings, new factors for wind were derived.

In conclusion, this research has contributed to a deeper understanding of the influence of wind on wave overtopping. The presented wind factor expressions significantly improved the accuracy of the expression for each measurement, offering broader applicability across different structure types. Moreover, the amplification factors constructed in previous studies and in this study, have proven to be applicable across various structure types. This enhances overtopping predictions initially obtained for this study.

In this research, the influence of the permeability and the porosity of artificial reefs on wave transmission and the sheltered habitat of marine life is investigated. A physical model is used to find the answer to this question.
The main finding of this research is that a hollow, perforated structure can act both as an artificial reef that provides a safe habitat for marine life, and as a breakwater that provides sufficient coastal protection. Moreover, a new empirical relation was derived for a smooth impermeable breakwater, rubble mound breakwater, and a hollow perforated breakwater with an impermeable screen inside.

Climate change affects sea level rise and the safety of the people living behind seadikes. In order to prepare for this, several adaptation measures are available to reduce the overtopping discharge. Wave overtopping can be reduced by including roughness elements or adding a berm. Another possibility is to employ crest elements such as a vertical crest wall, promenade or parapet on the crest wall to reduce wave overtopping discharges.

The overtopping discharge is key when defining the dike dimensions. Moreover, the effect of wind on the overtopping discharge is not included in existing guidelines, whereas wind is complex due to its dynamic behaviour. Also, the knowledge niche regarding the position and height of the vertical crest wall is the reason for performing more research. Physical model tests are conducted to gain more knowledge about the maximum wind effect to obtain a better understanding of how it affects the overtopping discharge and the loading on seadikes.

The following research question is covered in this master thesis: What is the maximum wind effect on wave overtopping at dikes with crest elements? The aim of the present research is to examine this wind effect based on physical model tests, which are performed at Deltares in Delft, the Netherlands. Experiments on a small-scale model of a seadike with a smooth outer slope at an angle of tan⁡(α)=1:3 are conducted. In total, four dike configurations were tested, consisting of a crest wall, which is placed at the seaside of the dike crest in one case and on the land side in another. A paddle wheel is used to simulate the maximum effect of wind, based on the idea that all vertical spray exceeding the dike crest is transported over the crest by onshore wind. The maximum wind effect is determined by comparing the tests with and without the use of the paddle wheel.

The results of this investigation show an optimisation of the existing guidelines, such as TAW (2002), for calculating the overtopping discharge. For non-breaking waves, the wave steepness is not included in the TAW (2002) overtopping formula, but the data show a clear dependency on this parameter.

One of the most significant findings from this study is a quantification of the maximum wind effect. It provides an amplification factor on the overtopping discharge. This maximum wind effect is defined as the ratio q_wind/q, which indicates the overtopping discharge with maximum wind effect due to onshore blowing winds (q_wind) over the overtopping discharges without wind effects (q).

The ramifications of plastic pollution on the environment are becoming increasingly serious in various forms throughout the world. In this context, rivers are the most important suppliers of plastics entering the marine environment. However, rivers that contain high loads of plastic waste also directly harm the livelihoods of people living near these rivers. An example is the flooding of urban areas in Indonesia due to clogging of the hydraulic and drainage systems, which is caused by the blockage of local hydraulic structures by plastic debris.
At this moment, there is a lack of knowledge on this accumulation process and its underlying dynamics, since observational and experimental research is lacking. Numerical modeling has proven to be a great tool for expanding experimental research. However, no suitable numerical method has been identified yet to model the plastic accumulation process, since traditional mesh-based CFD numerical methods are expected to be not a viable option, due to their inability to model the individual interaction between plastic particles, critical during this process. A possible solution could be the SPH-DEM method, which is a two-way coupled numerical approach that simulates fluid and debris as discrete particles and elements.
The objective of this report was to find out if SPH-DEM could be a suitable numerical method to model the dynamic processes of the plastic debris accumulation against hydraulic structures. To accomplish this, the first goal was to realistically model a turbulent open-channel flow and the buoyancy of individual plastic debris, which would be validated by experimental research. The second goal was to investigate which are the most important (numerical) parameters affecting the mentioned plastic debris accumulation.
In this report, experimental research was carried out in the form of buoyancy tests and flume tests, and numerical research was carried out in the form of the design of numerical simulations. In the buoyancy tests, the rising velocities of four plastic fragments that differed in size and density were measured, which were released multiple times in a graduated cylinder filled with water. In the flume tests, first the water elevation was measured along the the flume, after which the passing ratio’s and carpet lengths were measured for the four different released fragments for three different gate configurations. Two types of numerical models were designed that represented both types of experimental tests, for which several design choices had to be made to compensate for several physical phenomena, which can’t be directly represented in the model design.
The numerical buoyancy test was validated with the rising velocities obtained from the experimental equivalent. It was discovered, that for relatively low resolution modeled fragments, the rising velocity is heavily influenced by numerical diffusion. The smoothing length was identified as an important numerical parameter, which can compensate this effect. Furthermore, it was discovered that the degree of numerical diffusion is dependent on the depth of the fragment in the water. The numerical flume test was validated with the water elevation obtained from the experimental equivalent. For uniform flows, by adjusting the boundary viscosity coefficient, smooth turbulent velocity profiles could be simulated throughout the flume corresponding to theoretical values. However, no single value of was found in which the velocity profiles of the uniform flow and the validated water elevation of the gradually varied flows were both in agreement with their theoretical values. After validation, fragments were added to numerical flume model. Per fragment type and gate configuration,
four different numerical scenarios were executed, where each scenario was defined by a combination of a certain density ½s and restitution coefficient e. Finally, the best corresponding scenarios were used to simulate mixed fragments released in the flow. It was found that the gate opening height , density and restitution of the plastic fragments have the largest influence on the passing ratio’s , carpet length , carpet shape and carpet stability. Furthermore, it was confirmed that individual fragment interactions play a crucial role in the accumulation process. However, the model is mainly limited by its low resolution and the absence of suitable turbulence models. This means that many forms of fragment behavior seen in the experimental research such of buoyancy, trajectory and individual interactions, which are heavily influenced by turbulence, cannot be sufficiently represented in the numerical model. However, it is shown that by adjusting the density the buoyancy behavior can be partly replicated and by adjusting the restitution coefficient the turbulent individual interactions can be partly replicated. In conclusion it can be stated that SPH-DEM is an interesting option to model the dynamic processes of the accumulation of plastic debris against a sluice gate; however, further improvements in computational power and turbulence models are needed to be more widely applied.

In the upcoming decades, the Netherlands is going to face challenges regarding the protection against flooding. The reason for this is the expected rapid change in climate around the world. As a result of the changing climate, the sea levels rise and the peak river discharges increase. These changes lead to higher water levels in the Dutch rivers. To deal with this increase, the current flood defence system has to be improved. A new method for Southwest Delta of the Netherlands is the Delta21 concept. 
The focus of the Delta21 concept is on the Southwest Delta, the region around Rotterdam and the Haringvliet. The idea is to create a lake, the Energy Storage Lake, next to Maasvlakte II in the North Sea. During high discharge conditions in the rivers of the Southwest Delta, the Rhine and the Meuse, the lake can be used to store excess river water. From the Energy Storage Lake, the water can be pumped into the sea. In combination with a closed storm surge barrier next to the Energy Storage Lake, the water level in the rivers upstream of the lake can be lowered. To achieve the lowering of the water levels in the upstream rivers, a spillway is required to let the water flow into the Energy Storage Lake. 
This thesis aims to come up with a conceptual design for the spillway discharging the water from the Tidal Lake towards the Energy Storage Lake. This design must fulfil the functional and structural requirements, must be affordable, constructible and must fit within the ideology of Delta21. To achieve this, the hydraulic engineering design method is used. The first step in this method is to analyse the problem, in which climate change plays a vital role. In the second step, the basis of design is elaborated, including the boundary conditions and the requirements. The main requirements for the spillway are the discharge capacity of 20 000 m3/s and that the water level near Dordrecht may not exceed NAP + 2.5 m.
In the third step, the location of the spillway is first decided upon. After this, four different concepts are generated that differ in, among other things, the type of flow and the way the structure is part of the surrounding flood defence structures. The different concepts are concept Siphon, concept Underflow, concept Caisson and concept Ogee.
The fourth step is the verification of the concepts. The concepts are verified on the functional requirements and the stability requirements. This results in the main dimensions of the concepts. After this step, the concept Ogee is rejected due to stability issues and a large flow velocity at the end of the spillway.
In the next step, the remaining three concepts are evaluated by a multi criteria-analysis and a cost estimation. This evaluation shows that the best concept is the concept Caisson. After the selection of the best concept, the strength verification is performed for this concept and the scour protection is designed.

Two control structures in the form of compound weirs were built near Pannerden and in the Hondsbroeksche Pleij. These compound weirs consist of multiple adjacent gates with individually configurable weir heights. To make optimal use of the flexibility of the structures, research must be done into how different compound weir configurations affect the stage-discharge relationship. Both perfect and imperfect flow are researched.
This thesis has the following research question: “How is the flow over a compound weir affected by the configuration of the individual weirs?”
The research on imperfect weirs was caried out by constructing two analytical models based on a combination of momentum- and energy conservation, and a combination of Carnot losses and energy conservation. This was done for two cases, one case in which the equations were solved explicitly by using the average weir height, and the second case in which the equations were solved by solving a system of equations (one for each gate). The research on perfect weirs was caried out by making use of the Rehbock formulation, again for both the individual weir heights and the average weir height. To validate the models and to research interaction between adjacent gates, experiments were carried out in a 3-meter-wide flume with a scale model of the control structure near Pannerden.
In the experiments it was found that in the case of perfect weir flow, the discharge coefficients hardly change for different configurations with the same average weir height. The recorded maximum change was 1.9%. The best performing model for perfect flow was the model based on the average weir height. In the case of imperfect flow, it was found that the discharge coefficient can vary up to 13%, so the configuration influences the discharge coefficient significantly. No unambiguous results were found on how certain configurations affect the discharge coefficient. The models for imperfect flow performed well for an average weir height of 10 cm, but not for an average weir height of 7.5 cm. The least performing model was the model based on individual gates with the momentum equation.
With PIV (Particle Image Velocimetry) it was found that lateral flow starts at a greater distance from the weir if the lateral travelling distance is bigger. Furthermore, the streamlines hit the weir at an increased angle if the transition between high and low weir heights was sudden instead of gradual.
Further research should focus on adding more forms of energy head loss to the analytical model. Focus should be on one specific average weir height and more data should be collected on fewer configurations to get more insight into the behaviour caused by specific properties of a configuration.