After more than 85 years, the iconic Afsluitdijk is in need of a reinforcement. During the latest safety assessment of Rijkswaterstaat the dike did not meet the standards at two components; the amount of wave overtopping (>10 l/m/s) and armour stability. This research goes into detail about the overtopping on the Afsluitdijk. In the new design a lot a of different factors influence the amount of wave overtopping: the roughness of several elements and a berm. The combination of these different factors makes it difficult to make a reliable estimation of the amount of wave overtopping. In the design new materials are used of which the effect on wave overtopping is unknown. The band width of the design is very narrow so an accurate prediction of the amount of overtopping in the prototype is necessary. Physical model tests of two different dike section are used in this research. These dike sections are tested on different scales (small to large) to validate the final design on prototype scale. Not much is known about the possible scale effects on wave overtopping so this research goes into more detail on this issue.

Witteveen+Bos as part of construction consortium Nautilus, has prepared the design of a sea defence system in Middelkerke. The very shallow water conditions (h/Hm0 = 0.3) and complex geometry of the structure, i.e. a high berm and stepped revetment, caused uncertainties in the usage of the empirical equations from the EurOtop Manual (2018) for wave overtopping discharges. Therefore, small-scale experiments have been performed to asses the overtopping discharges. Physical model experiments can be used to determine wave overtopping discharges, but can be expensive and time consuming. Recent studies show promising results for the use of SWASH as tool to predict overtopping discharges for relative simple geometries, but SWASH is suspected to be less accurate for more complex cross-sections. Two methods (SWASH, EurOtop) are used to predict wave overtopping discharges for the new boulevard Middelkerke and the results are compared with measurements from small-scale experiments conducted in Ghent. The goal is to asses the feasibility of using both methods for this complex structure with stepped revetment in shallow water conditions. The EurOtop Manual (2018) uses influence factors to account for roughness at the slope and the presence of a berm in the structure. To use the empirical formula to determine the average overtopping discharge for this specific complex cross-section, a berm influence factor was added to the equation for shallow water conditions developed by Altomare et al. (2016). Recent studies of Schoonees et al. (2021) found that the influence of the roughness of a stepped revetment on overtopping discharge mainly depends on: a characteristic step height, relative overtopping discharge and the wave period at the toe of the structure. Using their research as guideline, a roughness influence factor of γf = 0.75-0.9 was estimated for the stepped revetment for this case study. Although not validated for this specific configuration, using the (adjusted) equation resulted in very comparable average overtopping discharges compared to the physical experiments in Ghent. In this case study, the usability of SWASH to predict the average wave overtopping discharges has been evaluated. First, the SWASH model was calibrated based on the incident wave conditions at the toe of the structure (Hm0, Tm-1,0) with the data the physical experiment in Ghent. This were the target wave conditions of this study since they are generally used to determine the average wave overtopping discharges (e.g. EurOtop) and to exclude the wave-structure interactions. Thereafter, the structure was added to the bathymetry with a smooth slope and local friction was added to represent the stepped revetment, as resolving the small steps would require an overly fine grid. SWASH was able to reproduce the target incident wave conditions of the physical experiment very well (Hm0<3%,Tm-1,0<5%). However, when the structure was added to the bathymetry, larger differences were seen for the wave conditions at the toe compared to the physical experiment, for which no explicit explanation was found. Contrarily, Hm0 and Tm-1,0 include the full wave field, primary waves and infragravity waves, and the limited number of overtopping waves made it difficult to asses the influence of the difference in wave spectrum on the overtopping discharges. The overtopping reduction due the added roughness/friction compared to a smooth slope reference test, was eventually related to a Nikuradse roughness height for the stepped revetment. A Nikuradse roughness of 1-1.5 times the characteristic step height of the stepped revetment, resulted in very similar average overtopping discharges compared to measurements from the Ghent experiment. Both the EurOtop Manual (2018) and SWASH were able to reproduce the average wave overtopping discharges from physical experiments, but the results need a wide confidence band since the number of overtopping waves were limited and discharges small (q < 1 l/s/m). Each method has their own benefits and limitations. The EurOtop Manual (2018) is easy to use, but the validity of the empirical equations are uncertain for more complex geometries. SWASH gives more detailed information than only an average q: spatially and temporarily varying surface elevations and velocities along the domain, by which direct attack on the slope and structures (extreme values of u and F) can be calculated. SWASH could also be used as a ’numerical laboratory’ to further parameterize the influence of roughness on wave overtopping for a wide range of boundary conditions and structural configurations.

Wind energy from the North Sea is one of the solutions to achieve the climate goals of the Paris agreement. The Dogger Bank, a North Sea sandbank, has a lot of potential for wind energy due to the relatively shallow location and good wind conditions. An artificial island creates even more opportunities, because alternating energy can be converted here into direct current. An island will also make the construction and maintenance of the windmills cost-effective. The Dogger Bank, however, is part of Natura2000 area, for which strict legislation applies. To design a stable island coastal defence, which contributes to the North Sea ecology, it is researched how natural value could be added to make the island licensable. The flat oyster (Ostrea edulis) has been chosen as an umbrella species, a species that creates an environment in which a large group of other species can benefit. The disappearance of the present ecology by building an island can be counteracted by restoring an oyster habitat. To obtain the boundary conditions for a successful oyster bed, research was done into the relationship between the bed shear stress and the historic presence of oyster beds. The shear stress boundary condition for the highest significant waves was 119.8 N/m2 while the shear stress due to the average significant wave climate must stay between 2.5 and 10.3 N/m2. The orientation of the coastal protection, the depth, the profiles (as the presence of a reef or foreshore) and the chosen material are decisive factors for success of oyster beds. Concluded is that opportunities are available in the coastal defence. In typical cross-section are only few areas suitable. For the most exposed side (330-360ºN), it is opportune for oyster beds to grow around the toe and foreshore when located in water deeper than -25.0 m MSL. At the least exposed side (120-150ºN) this is -18.0 m MSL. Reefs and prolonged foreshores are expected to be efficient for creating larger nature enhancing surfaces. The design and three-dimensional consequences of the suggested measures are recommended to study into detail. In addition, the biotic factors and the method of initiation of oyster beds will have to be further investigated to obtain more information about successfully creating oyster beds around an island on the Dogger Bank.

Contrary to a breakwater outer slope, rear-slope revetment does not have to withstand breaking waves. However, generally, an equal dimensioned revetment is used on both the inner- and outer slope. Although with low-crested breakwaters severe overtopping occurs, the application of similarly sized armour on both sides still results in an over-dimensioned inner-slope revetment. An (economical) optimisation is possible in this regard. The tests executed by Hellinga (2016) in this topic, showed large scatter in the found stability results of single-layer cube revetment at the rear slope. This scatter was party introduced by the large number of influencing factors in the test scope (Hellinga, 2016). By developing an overtopping simulator, the scope of the model-tests is delimited to solely the breakwater crest and rear slope. Moreover, larger scale tests are feasible in the same flume, reducing scaling errors. The main objective of this thesis is a) determine if the approach of a (semi-) small scale overtopping experiment using an overtopping simulator is increasing the reliability of the test results, and (b) to increase the understanding of failure mechanisms of single-layer cube revetment on the crest and rear side of low-crested breakwaters. To design and construct a simulator that is able to generate realistic waves, the relevant mechanisms of overtopping waves were determined and boundary conditions were composed. The behaviour of the simulator was tested in combination with a ‘mock’ breakwater. Seven types of realistic breakwater models were installed to investigate both the hydraulic behaviour of the overtopping volume and the stability behaviour of the revetment. The determination of the layout of a configuration is every time well substantiated by the results from the former configuration. The water level inside the Wave Overtopping Simulators (WOS) reservoir showed a skewed drop during the release of an overtopping volume. Consequently, the water level measured at one single point was not accurate to determine the volume (change) inside the reservoir, and hence the discharge and velocity. Different test configurations failed, where others remained stable during exposure to simulated waves in the test range. Compared to stability numbers of the theoretical front side, the cubes are relatively stable. The transition of the crest and rear slope showed to be a weak point, and outwash of the rock material filling the gap is a significant possibility. Improvements on the WOS are possible to enhance the ability to simulate the characteristics of a realistic overtopping wave volume and to give a more detailed evaluation of the magnitudes of these overtopping characteristics. The normal forces between the cubes at the slope are more important for the stability than the own weight of the cubes. The lack of interaction between the cubes at the crest results in a significantly lower resistance to hydraulic loads compared to the cubes at the rear slope. The layout of a sharp inner crest-line transition, if well designed, showed a stable alternative for a rounded transition.

Climate change is likely to affect our infrastructures in the Netherlands and seems to accelerate: sooner, faster, stronger. This stresses the need for adaptable infrastructure. Asset owners cannot assume a certain final situation of the infrastructure and the impacts on it due to climate change. This report answers the following research question: How can existing infrastructural asset designs in the Netherlands be adapted to anticipated current and future expected climate change effects? A method is developed to explore what the effects of climate change are on infrastructure and what further steps can be taken to make the infrastructure adaptable. The Afsluitdijk is used as a case study and has five embedded sub-assets: the dam, motorway, outlet sluices, ship locks and bridges. Nine climate change effects are distinguished for the Netherlands in the scenario WH of the KNMI in 2085. The climate change effects are combined with the asset parts and all combinations are assessed separately. An expert reflects on the combination of climate change impacts and asset part and elaborates on how the climate change effect impacts the reliability, safety or maintenance of the asset. This resulted in 21 identified possible problems for the 2020 design of the Afsluitdijk. In this report is looked at foreign situations that are comparable to the Afsluitdijk’s circumstances. Some of the 21 identified problems can easily be solved. A structured approach on how to assess the impact of climate change on infrastructure is lacking so far. The method makes sure all aspects are considered and helps the expert to think of all theoretical problems that have not occurred yet but are in the future a possible problem. Assets that are an integral system are preferred. The Afsluitdijk is interconnected to its environment and hard boundaries are difficult to determine. This makes the Afsluitdijk not an ideal case study, but this interconnectedness is typical for large scale infrastructural projects and those projects are often most interesting. Rijkswaterstaat recognizes the surplus of water problems in the new design. However, drought, heat waves and a low water level are three climate impacts that are not taken into consideration in the new design of 2020. Summer related problems are explored by Rijkswaterstaat but have not yet received the attention it deserves. Rijkswaterstaat is unprepared to a situation where climate change effects are more severe than was estimated in their assumptions. On top of that, Rijkswaterstaat is inclined to address problems of big infrastructural problems by cutting them of in smaller projects and try to solve them. However, in large projects it is better to have an integral solution since all aspects are interconnected and influence one another. The method provides this integral viewpoint and allows the user to make long-term decisions while taking the uncertainties of climate change into account. By using the method, choices in design and management of the infrastructural asset can be made with confidence. This does not guarantee that the outcome of a risky decision will be optimal. But the decision will be rational in the face of uncertainty and that the repeated application of the method will on the long run be more beneficial.

Mangrove forests, which serve as a natural sea defence, have been degraded by human action during the last decades. To protect and recover these areas, different types of permeable structures consisting of bamboo have been proposed and applied. However, these structures are currently based on engineering judgement, as design rules are not available. The goal of this research is to make a step forward in the design optimization of permeable structures and gain a better understanding of the processes causing the wave dissipation inside the structure. In this study, scale experiments are conducted in the wave flume at Delft University of Technology. An array of aluminum cylinders is used as a schematization of the structure, with an element diameter of 4 cm and a minimum spacing of 2 cm. The tested wave height is 0.13 m,with a water depth of 0.6 m for the first set of experiments. These experiments evaluated wave transformation through a selected number of configurations. The water depth was 0.55 m for the second set, where the velocities and forces were also measured inside the structure. As the applied wave periods are short (T = 1 − 2 s), the tested wave conditions are in the range of small KC-numbers (4 < KC < 13). The first part of this research focuses on effect of different configurations and arrangements on the amount of energy dissipation, by measuring the incoming and reflected wave heights in front of and behind the structure. For the short waves, the horizontal arrangements dissipate more energy, as energy is dissipated by both the vertical and horizontal drag forces. However, the effect diminishes with increasing wave period. Considering the total dissipation and the amount of dissipation per element, the placement of the elements in rows perpendicular to the direction of wave propagation is found to be the most effective. To study the effect of the element diameter on the dissipation, the results are compared with previous research by Haage (2018) on a model with a diameter and spacing of 2 cm. As with the change in diameter also the structure porosity changed, a direct comparison was not possible and a comparison based on a simplified drag coefficient is done. No direct effect of the diameter is observed, as the obtained drag coefficients show the same trend and magnitude when plotted against an adapted Keulegan-Carpenter number (KC∗), which is based on the element spacing instead of diameter. Small KC∗-numbers result in large drag coefficients,which decrease when KC∗ increases. The second part of this research focuses on the processes inside the structure that cause the energy dissipation. A force and velocity sensor are applied at three locations inside the structure in separate experiments, to determine the relation of the force and velocity inside the structure with the undisturbed values. Two methods are applied for the analysis, based on two different principles. Method 1 is based on the assumption of a constant pair of force coefficients and an increase in velocity inside the structure, method 2 is based on the assumption of a constant velocity and an increase in force coefficients inside the structure.By comparing both methods, it is found that an increase in velocity is the most important factor for the increase in drag force, which is the driving factor for the energy dissipation. It is also found that the amplification factor for the velocity is dependent on both the structure porosity and frontal porosity.

The European energy system is significantly changing to restrict the rise in global average warming. There is a shift from fossil fuels to renewable energy sources, which resulted in an exponential growth of offshore wind energy capacity in the North Sea. However, the North Sea is already one of the most intensively used sea basins in the world and space is limited. Offshore wind farms are therefore increasingly constructed under less favourable conditions. On the one hand the industry is rapidly developing and the cost of offshore wind energy goes down, but on the other hand offshore wind farms are constructed at greater water depths and further from shore. This latter development counteracts the cost reduction achieved by the industry, but countries are forced to construct offshore wind farms under less favourable conditions in order to achieve the climate agreements. In June 2016, Dutch transmission system operator TenneT proposed the Hub and Spoke concept. It is an alternative method to connect offshore wind farms with the onshore grid and makes the parameter distance to shore far less important. Basically, the concept combines offshore wind farms with interconnector cables. An artificial island is created somewhere in the centre of the North Sea which is surrounded by offshore wind farms, thereby being far away from the crowded coastlines while profiting from near shore conditions. The interconnector cables subsequently transport the generated electricity to shore. Dogger Bank is the envisioned location for the Hub and Spoke concept. The area contains strong winds, shallow water conditions and is centrally located. However, the unique characteristics of the shallow sandbank make it also very favourable to a variety of species. The area is therefore appointed Natura 2000 territory and could cause major resistance from environmental organisations. The general consensus amongst environmental organisations is not yet known, but industry experts indicate this as the major reason which could stop the Hub and Spoke concept from being realised on Dogger Bank. The objective of this research is to determine the optimal location for the Hub and Spoke concept in the North Sea. The concept feasibility has never been determined and it is not even certain if Dogger Bank is the most beneficial location, while the location contains a very large risk. Therefore, the site selection model is created. The model contains input data from metocean conditions and electricity markets, which makes it possible to calculate the feasibility of the Hub and Spoke concept for every location in the North Sea. The result is a contour plot with the net present value of the Hub and Spoke concept, which shows the optimal location in the North Sea. The Hub and Spoke concept is divided into five components to determine the influence of certain conditions on cost or revenue and to compare the components between each other. The artificial island and offshore wind turbines are primarily influenced by water depth, while the subsea interconnector cost is mainly influenced by the cable capacity and length of the cable. The optimal location for the island and offshore wind farms with respect to cost is thus along the shallow coastlines or at Dogger Bank, while the optimal location for the subsea interconnector cables is determined by the minimum total cable length. This point is equal to the centre of gravity of the countries surrounding the North Sea and is located just above the Netherlands and Germany. In terms of revenue, the wind conditions are normative for the production and revenue of offshore wind farms and interconnectors derive their congestion rents from electricity price differences between countries. Offshore wind farms generate most electricity in the northeastern part of the North Sea where the wind conditions are strongest. This negatively impacts the generated revenue from subsea interconnectors as the cable is used more often for offshore wind energy. Interconnector revenue of the Hub and Spoke concept is therefore lowest at locations with the strongest wind speed, but in total the highest revenue is generated. A comparison between these components for four various locations is presented in Figure 1. XXX Offshore wind farms are both in cost and revenue the major component in the Hub and Spoke concept. The optimal location is thus expected to be found in areas with shallow water depths and high wind speeds. Finally, each component with its cost and revenue has been determined and can be merged in the site selection model to determine the feasibility of the Hub and Spoke concept in the North Sea. See Figure 2. XXX It can be concluded that the highest net present value for the Hub and Spoke concept is situated along the coastline of Denmark and Germany. However, these locations are known to be very crowded and the reason to investigate alternative locations in the first place. Dogger Bank and the northwest of Denmark are two very interesting alternatives. Dogger Bank is very shallow with depths of 10 m, while the northwest of Denmark is slightly deeper with 20 m but contains roughly 10% higher wind speeds. Both locations are primarily free from other marine uses, although Dogger Bank is protected Natura 2000 territory and therefore contains a very large risk. It is therefore advised to construct the Hub and Spoke concept at the northwest side of Denmark.

Due to the removal of mangrove forests, coastal zones can suffer from severe erosion. One of the proposed solutions is the construction of permeable structures. This study aims to optimise the design of permeable (brushwood) structures in order to restore the sediment balance and encourage mangrove re-establishment on tropical mud coasts. Preferably wave transmission should be low in order to create a calmer climate behind the structure. In that way sediment is able to settle down, which could lead to a recovery of the mud profile. It is also preferred that reflection by the structure is low. High reflection rates cause scour holes that lead to instability of the structure. Furthermore, scour holes could hinder future mangrove re-establishment. Aiming to achieve low reflection and transmission rates, the dissipation inside the structure has to be as high as possible. Experiments were conducted in the 40 meter wave flume at the Environmental Fluid Mechanics Laboratory at TU Delft. The permeable structure was schematized as an array of cylinders. With the physical scale model various effects could be tested, including the porosity, structure width, arrangement, orientation, etc. The tests were done for 5 different wave cases, from which the wave energy distribution over reflection, dissipation and transmission was determined. The existing brushwood structures require intensive maintenance. This is partly due to the sinking of the material into the soft mud. Also, the brushwood material washes away often as it is lighter than water and difficult to constrain in vertical direction. An alternative design that requires less maintenance would be preferred. Therefore, it was interesting to see whether a comparable amount of wave dissipation could be achieved by using vertical elements only. One important finding is that in more shallow water regions, vertical and horizontal orientations have similar dissipation rates. In water regions that go more towards deep water, the horizontal structures have higher dissipation rates. This can be explained by the relative importance of the horizontal and vertical velocities due to the wave motion. In deep water vertical velocities are relatively high. As the horizontal elements have more exposure to this component in comparison to the vertical elements, they provide more dissipation. In shallow water the relative importance of the vertical velocities is lower, which explains the similar dissipation rates of the two orientations. The analytical model of Dalrymple (1984) was used to describe the energy dissipation through the structures. Drag coefficients were derived by using the calibration method. For KC<15 the drag coefficients start increasing. This is possibly due to the relative importance of the inertia force. Comparing the drag coefficients to the ones derived from direct force and velocity measurements in previous studies showed relative high values. This could be due to an underestimation of the horizontal velocity due to the wave motion. The velocity that is used is the undisturbed velocity in front of the structure. However, the velocity inside the structure might be higher as the flow accelerates in between the gaps of the elements. Furthermore, the wave cases in this research are in the Stokes 2nd and 3rd order region, indicating that the waves cannot be fully described by linear wave theory. The inertia, permeability and non-linear effects among other possible effects are not included in the analytical model of Dalrymple. Therefore, the drag coefficients do not only represent drag forces, but also other processes. To gain more insight on the physical mechanisms that affect the wave energy dissipation, it is recommended to test the same scale model with direct force and velocity measurements.

Sea level rise caused by climate change directly affects and threatens low-lying countries. In August of 2021, the report of the IPCC was published, and the findings were disturbing. The sea could rise by a few meters in the coming centuries, causing floods in large parts of West-Europe. Groeskamp and Kjellson proposed a solution to adapt to the effect of extreme sea-level rise, a Northern European Enclosure Dam (NEED). The dam stretched from Bergen in Norway to the north of Scotland and from Ploudalmézeau France to the Lizard Heritage Coast England. The main objective of this thesis is to investigate the technical feasibility of the NEED. To fulfill this objective, the following aspect were studied in more detail: the location and layout of this dam, the favorable cross-section of the dam, and the most likely closure scenarios. The first step was to find out what the optimized location was. The proposed location from Groeskamp was compared to an optimized location based on the boundary conditions. The two alignments are distinguished by their length, depth, and location. An engineering perspective was used to evaluate the alignments. The outcome of the multicriteria analysis (MCA) was that the initial alignment by Groeskamp was most favorable. However, a different perspective can result in a different conclusion, and it is therefore advised to look in further detail to come up with a well-founded decision. For the favorable cross-section, two types of closure dams were investigated to determine the best dam design, the caisson dam, and the earthen dam. Both designs were dimensioned based on safety criteria. These safety criteria were derived from the Dutch guidelines for primary flood defenses, with the top event, inundation of west Europe, given a probability of failure of 1:10 000 per year. A Monte Carlo analysis was constructed to determine the dimensions of both dams. Two failure mechanisms are assessed fully probabilistically as these are considered to be the most relevant. The ULS (ultimate limit state) and SLS (serviceability limit state) conditions are considered per failure mechanisms. The main difference between the resulting designs is the sizes; the earthen dam needs a mild slope to be stable (1:5), requiring a tremendous amount of material. The earthen dam requires seven times more material than the caisson dam. This results in the caisson dam being a more technically feasible design for the NEED than the earthen dam. The caisson is made of concrete filled with sand. Rock protection and concrete foot protection blocks to protect the sill from erosion. The closure procedure depends on the flow velocities inside the closure gap. The occurring flow velocities during the closure determine the feasibility. These velocities were calculated using the shallow water equation. A critical boundary condition for the caissons closure is that the maximum flow velocity in the gap is less than 2.5 m/s. For higher flow velocities, placement of the caissons is impossible. Based on the model, a closure procedure was proposed in which this essential condition is met. The most likely closure scenario is that first, the Southern dam is closed to ensure that the flow velocities do not exceed the critical value. The next step is to fulfill the Northern dam closure. The gap is closed until the maximum velocity is approximately 2m/s. The last part is then closed using sluice caissons. These caissons are placed openly in the gap and closed between 1 tidal cycle, completing the dam. The location of the final gap is at the Norwegian trench. The results from this research are that the NEED is expected to be technically feasible. However, the enormous size of the NEED poses new challenges and effects. Further research is required to comprehensively analyze all impacts of the NEED in order to make it feasible.

Breakwaters are hydraulic structures used to create calm and steady environments for moored ships in harbors. They dampen the wave by dissipating the energy through wave breaking. Most studies of breakwaters have only been carried out on the seaward slope of the structure. However, few have conducted research on the landward-, inner-, slope of breakwaters. The existing accounts re all empirical design formulae, commonly denoted as applicable for conceptual design. Improvement of the design of the armour layer of the inner slope leads to economical advantages.This research focused on three main goals: (1) Presenting a theoretical methodology for the waves tested, (2) It veried the Wave Overtopping Simulator as built by Rietmeijer (2017) and (3) Performed stability tests for the inner slope by conducting physical model tests in the Fluid Mechanics Laboratory of Delft University of Technology. The first goal of this research has been to develop a theoretical approach to overtopping waves in combination with a simulator. This has been done by linking certain storm characteristics, being the significant wave height Hs and peak period Tp to wave characteristics; water volume, water layer thickness and the front velocity of the water body. These three combined lead to an impinging wave on the rear slope causing damage. Subsequently the storms have been altered to only select the highest percentage of waves, since these were marked as extreme storm conditions. This resulted in dierent signicant wave heights which were tested. To verify the Wave Overtopping Simulator tests have been performed and specic elements have been measured and analyzed. This has resulted in relationships between theoretical wave characteristics and simulator settings. The relationships are the required water level in the reservoir to obtain a certain front velocity of the water body. To adjust the water layer thickness the valve settings have been changed. For a specic volume the overtopping period has been altered. These three elements have been measured using wave gauges and a high speed camera after which the data was carefully analyzed. The stability tests have been executed using a model of a breakwater in the Fluid Mechanics Laboratory of Delft University of Technology. Results of the preparatory calculations together with results obtained from former research have led to the design of the test set-up. A single armour layer of 20 mm cubes with an porosity of nearly 40% was built with an fixed toe. This configuration was tested with increasing storm intensities until failure. Subsequently the damage has been measured using photo camera's and laser technique. This research has successfully verified the wave overtopping simulator by measuring individual waves and their specific discharge, water layer thickness and velocity. These measurements have been compared to an other method, using a high speed camera. The found values have been checked with found literature and it has been concluded that the Wave Overtopping Simulator together with the test set-up as built in the Fluid Mechanics Laboratory is useful for this research. By measuring the displacement of cubes by means of video camera and laser technique, the research has been able to identify damage and failure cases. The horizontal displacement has been divided into several classes ranging from settlement of the armour layer, to instant failure. In addition, this research has presented a possible link between the stability of a single cubic armour layer and the number of rows beneath the waterline.

The Eurocodes are design codes, widely accepted throughout Europe, that provide guidelines on how to deal with loads, resistance, and uncertainty. For most type of structures, loads and materials, the Eurocode has been well developed. However, for the loads on coastal structures, caused by wave, water level and current actions, no such Eurocode exists. Therefore, a new Eurocode is in progress. The preliminary version of this Eurocode is titled prEN1991-1-8, and will describe how to deal with hydraulic loads on coastal structures. The Eurocode has a safety philosophy based upon partial factors and consequence classes, but the extension of this method to hydraulic engineering is not so straightforward. A premature introduction of the new Eurocode could mean that important design aspects related to sea condition parameters, such as extreme value analysis, dependence and wave transformation, are underexposed. In turn, this might give way to unsafe structures. Because of this, it is important to investigate how the semi-probabilistic approach (proposed by prEN1991-1-8) compares to existing design methods, both in terms of safety and in terms of ease of application. The goal of this thesis is to acquire knowledge on how the introduction of the new Eurocode influences the design of coastal structures, and address any inconsistencies and issues in prEN1991-1-8 before the preliminary version is adopted as the definitive version. The main focus of the research is the re-design of a coastal structure following the instructions in prEN1991-1-8. The breakwaters of IJmuiden are used as a case study for this. Three different approaches are adopted for the design: a deterministic approach, a semi-probabilistic approach and a full probabilistic approach. The breakwater elements that have been extensively examined in this thesis are the armour layer, consisting of either rock or artificial units, the crest height and the crown wall. Conclusions have been drawn based on any unclarities that are encountered in the design process, and based on comparisons between the semi-probabilistic approach and the two existing design methods, respectively. The introduction of the new document prEN1991-1-8 should result in more conformity regarding the treatment of sea condition parameters and their accompanying uncertainties in design calculations. However, the new (draft) Eurocode in its current form does not seem to achieve this objective. This conclusion has been drawn based on the practical issues (i.e. room for interpretation in the document and poor descriptions of key concepts) that were encountered in the case study, and because the breakwater design that was arrived at by following the semi-probabilistic approach described in prEN1991-1-8, did not resemble the design outcome obtained with the deterministic and full probabilistic approach. In addition, the semi-probabilistic approach is still a time-consuming method when applied to breakwater elements, while it is relatively easy to set up a full probabilistic calculation. It is recommended to shift (at least part of) the attention towards the full probabilistic approach, and explore the possibilities of making it the default approach for coastal structures, as it raises fewer questions than the semi-probabilistic approach and deals with uncertainties more extensively. Nevertheless, it can be viewed as a positive development that there will be one general document to consult for the design of coastal structures. Most importantly, standardised levels of safety and return periods are now available with the introduction of prEN1991-1-8, even though their interpretations are not always straightforward. It is of course also still possible to improve the semi-probabilistic approach as it is currently proposed by prEN1991-1-8. When this is preferred, it is recommended to include a more systematic explanation of the DA-1 format in EN1991-1-8, describing the characteristic values, partial factors and safety margins to be adopted in design without any ambiguity.

Breakwaters used to protect harbours and coastal areas worldwide are one of the most common coastal structures. The complexity of the physical processes associated with the design has led to the development of many empirical formulas while a standardized method for the selection of breakwaters’ design parameters in the EU does not yet exist. The most common approach to design such a structure nowadays entails using information and recommendations from design manuals and guidelines such as PIANC and the Eurotop Manual. A new Eurocode 1 which includes specific considerations for coastal structures such as breakwaters is in the development process. This study aims to compare the PIANC method with the method to derive actions/loads included in the Eurocode proposal prEN1991-1-8. To do so the following research question has been formulated: “What differences between the PIANC method and the method proposed by the new EUROCODE in the design of a vertical wall breakwater can be identified, using the new breakwater at the Port of Genoa as a case study?“ As mentioned in the question, a case study is used. The Port of Genoa, one of the biggest ports in Italy plans to construct a new vertical wall breakwater. An initial design is openly available along with wave and water level data. This design is assessed using both methods and is further optimized. The aim is to gain insights into the differences between the PIANC and the new method. At first, the failure mechanisms of such a structure are defined along with the safety factors and parameters. The data required to perform such an assessment is also an important aspect of the exercise. Most of the data are openly available during the consulting phase for the new breakwater in Genoa. In cases where extra data were necessary, they were based on the literature or on reasonable assumptions. Based on the failure mechanisms and the retrieved data, the initial breakwater cross-section was assessed. The assessment both with the PIANC method and the new Eurocode proved that this design is sufficient and can be further optimized to decrease its costs. A high-level optimization is also conducted as part of this study in order to better understand the differences between the two methods. It can be concluded that the differences lay more in the method than in the actual result. For example, the proposed Eurocode creates a stable theoretical framework of how to choose a return period. The actual number may be very similar to the one that one would have used either way, but the choice can be argued in a better way. On the other hand, the use of the new Eurocode revealed some problems and inconsistencies in the document which is confusing in certain parts. In addition, the new Eurocode which among others aims at standardizing the design process. However, parts like the combination of wave and water level actions and the choice of return period for the two main limit state functions are relatively clearer providing a solid base.

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.

Geotextiles are permeable fabrics used in various civil engineering and construction applications for the protection against erosion and scour. Geotextiles have predominantly been manufactured using synthetic materials due to their durability and precise design pore sizes. However, the environmental concerns associated with synthetic geotextiles have led to the exploration of sustainable alternatives, including natural fibers and biodegradable thermoplastic polymers. This study addresses the problem of designing stable geotextile filters. The problem statement resolves around the assumption that geotextiles of natural fibers are considered "open" filters. Existing design criteria for open filters do not directly account for load conditions or the use of fibers in the fabric. Instead, they rely on the relationship of the geometrical properties of the base and filter material. To address this gap, a new approach is proposed based on hydraulic pressure gradients. This approach considers the actual gradient and critical gradient at the geotextile interface. To achieve this, the geotextile will be evaluated within the context of an open channel with uniform flow conditions. The main research objective is to formulate a design method for geotextiles based on the principles of an open filter structures under a single granular filter layer. A comprehensive literature review has been conducted to investigate the hydrodynamic processes that define the actual gradient at the filter/base interface where the geotextile is positioned. The framework of linear wave theory proved to be a valuable tool for investigating and modeling these hydrodynamic processes. To define the actual gradient, the following hypothesis is proposed: The actual gradient can be defined by adding the average gradient to a turbulent component derived from measured turbulent wall pressure spectra at the top of the filter layer. Based on spectral approach and linear damping, it is hypothesized that these turbulent components undergo damping within the filter layer, resulting in a diminished turbulent component at the filter/base interface. From the literature review, it can be inferred that the dimensionless turbulent rough wall pressure spectra developed by Blake (1970) offer the most appropriate representation for the relevant hydraulic conditions (rough horizontal bed, uniform open channel flow). In a turbulent wall pressure spectrum, outer scaling variables and inner variables relate to different length scales within the flow, representing large-scale and small-scale fluctuations, respectively. In this hypothesis, it is assumed that the low-frequency region is scaled by the average velocity and water depth, while the scaling variables for the high-frequency region are presented in terms of the shear velocity and nominal diameter of the filter material. By combining both spectra, converting the pressure spectrum to the gradient spectrum, and transforming the spectral domain to the spatial record, the fluctuating gradient can be determined. The hypothesis was verified using measured data from experiments conducted by Van de Sande (2012) and Wolters & Van Gent (2012). By incorporating Van de Sande's measured dataset into the scaling parameters of the dimensionless pressure spectra and determining the stability parameter for open filters, it was concluded that qualitatively the results align with Van de Sande's findings, indicating stability or instability of the filter layer. However, in some test cases, the hypothesis suggested instability while the experiments indicated stability. This discrepancy may be due to the fact that while the stability parameter may indicate an unstable filter, it does not necessarily correlate with significant base material transport through the filter layer. In a quantitative analysis, the amount of dimensionless transport of base material was compared to the stability parameter. According to the data presented in figure 4.12, it can be observed that the stability parameter exhibits a value that is three times larger then the stability parameter defined by Schiereck (2012), while not inducing any significant transport of base material. This finding aligns with previous experimental investigations, such as the study conducted by Wolters & Van Gent (2012), which similarly demonstrated that the stability parameter could reach values that are two to three times larger, while still not resulting in notable base material transport. A direct quantitative comparison was conducted between the measured dataset of Wolters & Van Gent (2012) and the calculated gradients obtained from the hypothesis. The results revealed that the calculated gradients exhibited a comparable magnitude, ranging from 0.25 smaller to 1.50 larger in comparison to the measured gradients reported by Wolters & Van Gent (2012). This indicates a reasonably close agreement between the calculated and measured gradients. In conclusion, the research objective in this study was to formulate a design method for open geotextiles under a single granular filter layer. To achieve this, it was necessary to take some steps back and define the actual gradients, as well as identifying a suitable method for calculating these gradients. The actual gradient is calculated with the sum of the average gradient and the fluctuating gradient. The fluctuating gradient can be characterized by the turbulent wall pressures, which are derived from the pressure spectrum measured at the top of the filter layer, as described in Blake (1970). Assuming linear damping of the pressures within the filter layer, the actual gradient can be computed at the interface of the geotextile. Consequently, the assessment of stability entails a comparison between this calculated actual gradient and the critical gradient measured by Lemmens (1996). With a clearer understanding of how to calculate the actual gradients at the geotextile interface, the same approach employed in the hypothesis is applied to address the design of a stable open geotextile under a single granular filter layer. This has been demonstrated through a case study, where the thickness of the filter layer was determined to create a stable filter structure. Several recommendations can be made to improve the understanding and design methodologies in relation to the hypothesis. Firstly, there is a need for a better understanding of the spectral density of wall pressure fluctuations in open channel flow. This understanding will enable more accurate estimations of fluctuating gradients. Secondly, further research is necessary to incorporate the distribution of pressure at the filter/base interface for non-linear damping. Thirdly, it is advised to conduct tests using modern natural geotextile materials to refine the critical gradient determination and explore alternative approaches, such as considering critical filter velocities. Lastly, it is recommended to extend the design method to encompass wave conditions. Verifying the effectiveness of the design approach under wave conditions through comparison with measured data will ensure its applicability and reliability in practical scenarios. While further investigations are needed, it still offers a fresh perspective on evaluating the stability of open filter structures. If successfully refined, the design method could become a valuable tool in geotextile design and potentially find applications in other contexts involving "open" structures.

The XblocPlus is a new type of single layer armour unit for breakwaters. The key difference between earlier single layer armour units is that the unit is not only placed in a regular grid, but also with a regular orientation. The main benefit of this is that it can directly be seen whether the unit is placed correctly. Additionally, the placement always takes place with the same repetitive movement, as is preferred by crane drivers. The benefits to the placement procedure would however be reduced when the requirements for the under layer become very tight. Since the time that is saved during placement of the armour units, then would be lost during the profiling of the under layer. This has led this study to focus on the influence of irregularities in the under layer on the stability of the XblocPlus and the allowed tolerances for the placement of the under layer. In the process of obtaining a stable armour unit, multiple researches have been conducted. The final shape has been further optimised by adding a hole in the middle of the unit and increasing the interlocking capacity. Better interlocking increased the connection between the units and thereby improved the resistance. The hole increased the porosity and thereby reduced the overpressure underneath the armour layer. Which is a result of a difference in water level inside and outside of the breakwater. The increase in stability due to the enlargement of porosity, validated earlier findings that the acting failure mechanism is extraction due to the overpressure. The stability was expected to be mainly effected by the amount of interlocking. Subsequently, the amount of interlocking is determined by the relative angle between the armour units. For this research physical model tests have been performed to check that hypothesis. Multiple tests have been conducted with different radii of convex and concave shapes in both long shore and cross shore direction. The goal was to find the critical relative angles of each combination of shape and direction. The convex shape in cross shore direction was the only irregularity that caused failure and proved to be critical. The relation between the relative angle and the stability number resulted to be linear, instead of the expected drop of stability at a certain critical value. The relation showed signicant spreading, for which tests with small deviations from the design profile seem to form the upper bound and large deviations the lower bound. Thereby indicating that the level of stability is not only determined by the relative angle but also by the deviation from the design profile. In succession of the tests with specific shapes and directions, more realistic tests have been performed with micro irregularities and S-proles. The convex shape in cross shore direction proved to be critical for these congurations as well. Furthermore it was found that for large S-proles, sudden failure could occur without previous indication of loss of interlocking. Further analysis of the divergent failure behaviour of large S-profiles indicated that the arched shape of the profile enabled the lifting of the armour layer. A mechanism similar to the buckling of beams. The pressure inside the breakwater, the drag of the down-rush and the weight of the upper part of the slope, cause the initial distortion of the profile to be enlarged. The differences between the measurements of the profile before and after the tests, showed that the same movements occur for smaller S-proles and the tested convex shapes in cross shore direction. The movement could even be seen in tests that have not failed. Which implies that the arching mechanism that causes sudden failure for large S-proles, also induces the loss of interlocking for other convex shapes. A simplied model of the forces on the convex sections in the profile indicates that the enforcing of the arching mechanism mainly depends on the length and steepness of the downward part of the convex section and the  atness of the upward part of the convex section. These findings correspond with the test results and explain why the stability performance is the highest for the short length scale micro irregularities and lowest for the large scale S-proles with large deviations from the design profile. Evaluation of the effect of irregularities is performed with the tolerances of the regular Xbloc, which are also intended to be used on the XblocPlus. To prevent differences in stability due to the size of the under layer, the tolerances are expressed in the unit size (Dn) instead of the under layer grain size (Dn50). The resulting tolerances are maximum 0.25 Dn for the deviation from the design profile and maximum 0.1 Dn deviation between subsequent measurements along the profile. The profile is measured every 10m of the breakwater and subsequent measurements along the profile have a distance of 0.3 Dn. The requirements are a little more liberal than the tolerances of the regular Xbloc since the tolerances of the largest under layer grain size are taken as a starting point. The test results indicate that the tolerances are sufficiently safe, with potential for more liberal requirements.

Starting in the 1930’s, many research projects have been performed with the intent to establish rules, which can be used to design granular, geometrically closed filter structures for hydraulic structures. However, for the vast majority of these research projects, the filter structure was loaded by uniform flow, either in the parallel or perpendicular direction. This means that, while for filters under flow loading multiple design options and diagrams are available, the knowledge on design rules for sloped, closed filters under wave loading remained limited. These knowledge gaps mean that, in design practice, often the design criteria for closed filters under flow loading, for instance the original criterion by Terzaghi, are used for the design of closed filters under wave loading, while these have not yet been experimentally verified for this use case. This thesis combines model test results from two historically performed experiment programs on sloped, closed granular filters under wave loading with new experiments, which were conducted especially for this thesis. By analyzing the results from these three research projects, it was found that commonly used interface stability criteria for closed granular filters under flow loading are not valid for use in the case of a sloped, closed granular filter under wave loading. Based on the test results from the three test programs that were analyzed, a new interface stability criterion for sloped, closed granular filters under wave loading is proposed.

On the seabed in front of coastal structures sediment movement takes place due to incoming waves. The erosion of sediments creates a scour hole at the toe of structures such as embankments, breakwaters and dikes. This scour hole may lead to instabilities in the main structure due to material sliding into this hole. A common method of protecting against scour is the placement of a rubble mound toe structure and bed protection. The goal of this study is to better understand the background and main parameters that leads to scour, to predict the (location of the) maximum scour depth and how this is influenced by the bed protection. Consequently, the main research question of this thesis is: What is the expected, wave induced, scour depth over time in front of a sloped embankment, and what is the effect of a scour protection on the (location of the) maximum scour depth?

Downstream of hydraulic structures, the flow is normally of turbulence. This will cause considerable erosions on the gravel bed. To prevent this, block mattress is preferable in many cases. Its effective stabilization and feasibility on construction make it commonly used against scouring problems, protecting underwater pipelines and cables. The currently widely used design formula with dedicated parameters for block mattresses was derived by Pilarczyk. However, it is observed to be partly functioning under non-uniform flow condition, since the turbulence parameter is rather empirical. Therefore the main purpose of this thesis is to optimize the current design formula (Pilarczyk’s) for non-uniform flow condition. In this flow regime, turbulence is of importance for bed material entrainment. Thus this research focused on how to introduce turbulence effect into formula explicitly. To predict the failure of block mattress better, a detailed study on failure mechanism and impact of flow condition over the block mattress edge is necessary.

This research focuses on the estimation the failure probability of Shanghai sea-dikes system, taking into account several failure mechanisms. This method follows fully probabilistic approach, in which all relevant parameters for the resistances and the hydraulic loads vary according to specific distributions.

Nowadays, the use of concrete armour units on rubble mound breakwaters designs has become a common practice. Concrete armour units can be placed in a single layer system or in a double layer system and can its placement can be either random or uniform. Recently, Delta Marine Consultants have designed a new armour unit called Xbloc+. This new block is applied as a one layer system and has a regular placement. As Xbloc+ is still under development, preliminary guidance on the performance of this new armour unit is required. This led this research to investigate how Xbloc+ behaves concerning wave overtopping. To analyse wave overtopping, small scale tests were performed in a 2D wave flume. Wave overtopping was measured at a 3Dn distance from the seaward edge of the crest, which is made of rock. In front of the slope there is a flat transition of 0.3m followed by a sloping foreshore of 1/30. In total, 10 series of tests were conducted. In this research, three wave steepness (Sop) were tested (0.02, 0.04 and 0.06) to see the effect of wind waves and swell conditions on the armour layer and tests were performed in two different slope angles (1/2 and 3/4). Each series is formed by several sub tests conducted with increasing wave heights (and wave period in order to maintain a constant wave steepness). Tests were carried out until the failure of the armour slope was reached. Besides, a smooth slope was tested in a 1/2 slope angle to be able to compare smooth and rough results and determine the roughness coefficient of the armour unit more accurately. The test results showed that wave overtopping rates increase exponentially with wave height (Hm0) and wave period (Tm-1,0). Moreover, waves with lower wave steepness (swell conditions) induce higher overtopping discharges as compared to larger wave steepness. Steeper slopes also lead to higher overtopping rates. Therefore, the larger the breaker parameter is, the larger the overtopping discharge results. The influence of the armour roughness and armour permeability is also analysed and it is observed that swell conditions are less affected by these properties. This can be explained by means of the breaker type. Swell conditions are characterized by large surging waves. These waves have a thicker water tongue as compared with other type of breaking (e.g. spilling or plunging) and therefore, they tend to feel the top layer “smoother”. This fact is supported by the analysis of the influence of the roughness coefficient since higher values are obtained for surging waves. In fact, the roughness coefficient ranges between 0.34 and 0.68 showing that, although empirical prediction consider this parameter as a constant, it is dependent on the wave conditions. Concerning the comparison of dimensionless overtopping rate over Xbloc+ armour between test results and empirical prediction, it was found that the present formulae does not give a good estimation due its simplicity. In order to improve the representation of some parameters such as slope angle and wave steepness, correction factors are introduced in the empirical formulae leading to a better fit between prediction and measured data.