The Netherlands faces major housing shortages. The total housing shortage is 390 thousand homes and this is expected to increase in the near future because fewer building permits have been issued in recent years. By 2030, the Netherlands will need to have almost a million new houses. To solve this problem, it is essential to build more residential buildings in the near future, but limited space is available. Therefore, the focus shifts to traditionally less conventional spots that potentially can be used to construct residential areas.

One of the proposed solutions is to create residential buildings near dikes, thereby using the dikes not only to combat flood risks but also to relieve pressure on the housing crisis in the Netherlands. To check if buildings can be built on or next to a dike, the assessment method of the Legal Assessment Instrumentation is currently used. However, only a basic assessment is prescribed for this, which is a very conservative approach. This conservative approach often leads to the building not being built or to overdesigning of the dike and thus higher expenses than necessary.

The objective of this thesis is to develop a level I reliability assessment method for multifunctional dikes containing a structure, leading to a less conservative approach than the basic assessment of the Legal Assessment Instrumentation (WBI2017).

First, the possibilities of construction near dikes were studied per water board. The possibilities for building near dikes are prescribed in the water board regulations, previously known as the by-law (Keur). Although the water board regulations vary for each water board, the rules regarding building near dikes are consistent, and almost nothing regarding construction can be done in the profile of free space. Interviews were also held with water boards. During these interviews, the regulations were discussed, including the non-technical obstacles with regards to building near dikes and solutions for them were proposed.

The biggest concern is regarding the management of the houses that would be part of the flood defence. One of the proposed solutions is to use people to regularly send photos to ensure the quality of the parts of the house that will function as flood defence or to use sensors which could measure deformations. This could save much time for the dike managers.

Next, it was determined what failure mechanisms can be affected by the presence of a building on or near a dike. The failure probabilities of macro-stability, piping and overtopping differ when a building is placed on or next to a dike and have been considered in the calculation of the failure probability of the dike. It has been argued by means of an event tree that the absence of a house has a 0.1% probability of occurring.

Subsequently, a case was analysed probabilistically using FORM analyses to demonstrate the difference in failure probability between the current and the proposed schematisation. This showed a 75% reduction in failure probability for the assumed cross-section compared to the current schematisation. The effect of new construction on a standard dike profile can both have positive and negative effects on the failure probability of the dike section depending on the situation. Compensatory measures can be taken to reduce the probability of failure.

Since it is time-consuming to perform probabilistic calculations for every situation, it was decided to create a Level I reliability assessment. Based on the probabilistic calculations, partial safety factors were derived that take the probability of the disappearance of a house into account. These partial factors were calculated per stochastic variable. This allows for a Level I reliability calculation to determine whether a dike cross-section with a house meets the required failure probability of the dike section.

It is concluded that incorporating the proposed level I calculation with adapted partial factors has a different impact for each situation but can, in some cases, have a 75% reduction in failure probability. This is based on the case study, which is elaborated extensively in the report. The developed level I reliability method ensures that existing buildings near houses are assessed more realistically compared to the current WBI assessment, which assumes a gap at the location of the dike. As a result, when this method is used, more dike cross-sections with buildings will meet stability requirements as it is less conservative than the current assessment, which only takes into account the negative aspects of the building. This means that fewer dike sections will be rejected, potentially saving both money and reducing inconveniences. For the design of new structures near a dike, this Level I reliability calculation can provide insight into possible locations for construction in the cross-section of the dike and the potential dimensions of the house. With this method it can quickly be demonstrated whether a multifunctional dike still meets the dike's failure probability requirement, which can also lead to an increase in building possibilities near dikes, as extensive customized assessments are no longer necessary.

In the Netherlands, there are hundreds of operational locks for both recreational and inland shipping. Due to the growing economy, inland shipping is expected to increase in the future. The growing economy causes an increased likelihood of ship collisions with infrastructure, currently estimated at approximately 50 cases per year in the Netherlands. It is necessary to determine the collision energy of a vessel to account for collisions, because this clarifies the potential load. In the context of determining the collision energy for ship collision, the guidelines of the Eurocode, PIANC, and AASHTO involve uncertainties and exhibit variability among them. Therefore, the thesis was initiated to provide more accuracy in the estimation of collision energy in the event of ship-lock collisions. The main objective of this thesis was to enhance the structural design process of lock gates regarding ship-lock collisions. This was done by improving the understanding of the effect of potential loads occurring at a ship-lock collision, and using basic mechanics to estimate the energy absorption capacity of the lock gate.

Making decisions when future conditions are uncertain is a challenging endeavor. This thesis develops a framework to analyse flood risk and create Dynamic Adaptive Policy Pathways, which can provide insights in the behaviour of flood risk protection measures in many future scenarios. The pathways are used to identify robust measures, dead ends and compare measures. The framework is applied to a case study in the Galveston Bay area.

In common practice, quay walls are engineered to fulfil their services for a minimum lifetime. However, in many cases, quay walls are designed stronger than minimally required, which means that the quay wall could be able to serve its purpose over a longer period or endure higher loads. In general, the optimization of quay wall designs or the assessment of the extension load-bearing capabilities, particularly in existing structures, is substantiated through probabilistic design methodologies.

This study investigates the operation of reliability updating with deformation data to enhance the operational lifespan and load-bearing capacity of existing quay walls. Traditionally, quay walls are designed with predetermined probabilities of failure based on preliminary information gathered through desk studies and on-site investigations. Observations of existing structures provide new information on the actual deformation behaviour. This study acknowledges the conservative assumptions in initial designs, potentially resulting in concealed geotechnical and structural capacities. It introduces a novel approach involving reliability updating using monitoring data from 'smart' quay walls equipped with advanced sensors. These sensors, measuring especially lateral deformations, provide input for the updating process in a Bayesian model.

Application of this methodology is demonstrated through a theoretical and an actual case study, including the Sif quay wall in the Port of Rotterdam (Maasvlakte II).

The theoretical case study validated the methodology. This was done by updating two initial (prior) distributions for the friction angles of two soil layers using the observed maximum deformation for a combination of predefined values of the friction angles. The updated (posterior) distributions converged towards the predefined values and the distributions reduced in variation or became more informed. These findings affirmed the overall operation of the intended method and proved the efficiency and accuracy of the addition of metamodelling. However, the success of the metamodel appeared to strongly rely on appropriate settings for the specific situation.

For the case study of the Sif quay wall, its deformation behaviour was analysed for three different load cases accounting for the effect of excavation, the effect of water level fluctuations and the effect of top loading. The most recent deformation measurements, together with the knowledge of past deformation behaviour, have proved most useful for updating as all aspects contributing to the lateral deformation of the quay were present. In the updating process of the Sif quay wall case study, six stochastic variables were analysed: the strength (friction angles) and stiffness parameters (stiffness moduli) of three influential soil layers. Within the scope of this study, an increase in one or both parameter types means that the structure may have a higher functional capacity than expected, in the form of moment or normal force capacity.

Here, the strength parameters proved more prone to updating than the stiffness parameters and showed a significant increment. The initial parameter uncertainty indicated by the standard deviation was found to have minimal impact, but larger discrepancies between predicted and observed deformations led to more significant updates.
The quay wall at the Sif terminal appeared to have a negligibly small failure probability, even before updating. Therefore, the impact of updating was not measurable in terms of the reliability index, but the outcomes of the limit state function distribution were significantly impacted: their variation was reduced, and the overall distribution moved away from the point of failure.

Regarding cost-effectiveness, the risk mitigation for existing walls after monitoring and reliability updating might be limited. However, the potential for significant steel reduction in new quay wall designs based on updated soil information highlights the value of reliability updating. The approach of this study may lead to more efficient and sustainable quay wall construction practices.

The study also acknowledges limitations in the simplification of the soil model compared to the actual situation and the consideration of one single failure mechanism. Another important factor is the limited level of knowledge on the quay wall deformation conditions, such as loading magnitudes and potential time-dependent effects, compared to the minimized model uncertainties. This aspect should be taken into account when evaluating the results of the update results. Recommendations for further research include:
• To achieve a more realistic representation of quay wall behaviour, it is recommended to incorporate various failure mechanisms, including geotechnical failure, as real-world failures often involve the interplay of multiple mechanisms.
• For a more robust prediction, the model should explore a wider range of stochastic variables, including factors like bed level, water level fluctuations, and top load.
• To enhance the accuracy of the updated parameters, it is recommended to acquire additional measurement data through on-site loading tests or by implementing smart bollards for real-time loading information.
• Investigating the correlation between the stochastic variables is crucial for understanding their combined influence on the model's predictions. This analysis will lead to more accurate results.
• To maximize its practical value, the model should be extended for applications such as berth deepening or designing for increased top loads.

In summary, this research highlights the potential of reliability updating with deformation data, offering more insights into a possible increase of a quay wall's capacity. By understanding a quay wall's reliability, port authorities can optimize its use and extend its service life, reducing environmental impact and bringing economic benefits.

The centre piece of Galveston Bay’s 34 billion dollar flood risk reduction plan is a 3.6 km long storm surge barrier built across the Bay’s main tidal inlet. The barrier, which consists of a series of vertical lift gates and two large floating sector gates, will close when a hurricane approaches in order to reduce the volume of hurricane driven storm surge entering the Bay. However, the rotating wind fields of passing hurricanes can blow offshore directed winds over the Bay which can generate a "reverse head" condition, where water levels on the bay side of the closed surge barrier exceed water levels at the open coast. The resulting reverse load threatens failure of the barrier’s two floating sector gates, which can be pulled from their supporting ball joint sockets. This Master Thesis demonstrates why reverse loading is an important load that must be adequately accounted for in the design of the surge barrier. A model is set up to determine reverse loads generated by a specified hurricane. The model accounts for reverse loading due to reverse head and wave action in the Bay and is comprised of; a parametric hurricane model by Holland (1980), a coupled hydrodynamic flow-wave model by Xu et al. (2023), and load formulations for the reverse heads and wave conditions calculated by the hydrodynamic model. Deterministic application of the model shows that reverse heads/loads are a common occurrence and can be generated by hurricanes landing both West and East of Galveston. Furthermore, hurricanes approaching landfall from oblique Eastern directions can generate a high reverse load before the arrival of a high coastal surge, which threaten more severe consequences as in addition to floating sector gate failure, the following coastal surge can enter Galveston Bay and increase flood risk. Probabilistic application of the model is used to estimate the exceedence probabilities of reverse head/loading magnitudes, for an assumed operation procedure where a decision is made to keep the surge barrier either permanently closed or permanently open depending on assumed surge forecast uncertainties

Sea level rise and land subsidence increasingly put more pressure on Dutch flood protections. Additional to regular dike reinforcements, new, more nature-based, solutions are considered, such as a double dike system (DDS). Such system, consisting of two parallel dikes in combination with an interdike area in the form of a salt marsh, offers the opportunity to adapt via hydro-morphological processes to sea level changes. An increased bed level of the interdike area of a double dike system potentially positively affects wave attenuation. Furthermore, if the second (landward) dike breaches, the elevated salt marsh of the interdike limits breach growth and discharge through the breach. However, previous studies show that it is hard to prove the feasibility and effectiveness regarding flood safety of a DDS relative to a single dike and an in-depth hydraulic engineering substantiation for flood risk reduction is lacking. The objective of this research was to investigate which factors determine the effectiveness of a DDS, with the focus on the dynamic development of the system. This leads to the following research question: Under which circumstances can a double dike system be an effective alternative to a regular dike reinforcement? It is possible to distinguish three distinct systems based on the function of the first (seaward) dike: dynamic open DDS, dynamic closable DDS, and static closed DDS. This distinction is primarily based on the degree to which water is permitted to pass through the first dike under both normal and extreme conditions via an opening in the dike. This interaction between the outerdike area and interdike is unobstructed for a dynamic open DDS and almost nonexistent for a static closed DDS. To achieve a more hybrid approach, dynamic closable DDS utilizes adjustable structures like tidal culverts to regulate the inflow. Under normal tidal conditions, the permitted inflow governs the sediment supply and the potential for accretion of the bed level in the interdike area. Depending on the design of the system, during extreme storm conditions, the first dike can act as primary flood defense or as breakwater that provides shelter for the second (landward) dike. This research focused on an open dynamic DDS system, allowing for maximum potential bed level accretion of the interdike area. In doing so, the first dike functions as a breakwater and failure of the system occurs when the second dike is breached. Due to the unrestricted in- and outflow, the assumption is made that water levels are uniform and equal to the hydraulic conditions outside the system. The double dike systems are analysed with the help of two approaches: failure probability approach and local individual risk (LIR) approach. The first approach compares systems based on equal probability of failure. The second approach compares systems based on an equal LIR of 10−5 per year and includes the expected mortality in case of flooding. Systems have been compared to each other with the help of calculated dike heights and total dike volumes. Dikes were tested for failure due to overtopping or overflow. Therefore, a transmission model was applied to describe the transmission of waves through the system: wave transmission over the first dike, wave propagation in the interdike area and wave overtopping over the second dike. The probabilistic calculation method FORM was used to find the failure probability and design point. For the LIR approach, this model was extended with a 1D flood model to determine the flood characteristics and subsequent mortality fraction if failure of the dike occurs. Firstly, a simplified case study was performed based on conditions in the Western Scheldt. Opening the existing dike in the current hydraulic conditions necessitates the construction of a second dike that is only 1.7 meter lower than the single dike system. A sea level rise (SLR) of 0.4 meter in 2070 and 1.0 meter in 2120 was implemented. In addition, morphology scenarios were applied, ranging from no accretion to maximum accretion. In the scenario with maximum accretion, rapid accretion to Mean High water takes place, after which the bed level accretion follows SLR. Comparing systems based on equal failure probability, a single dike should be raised identically to the SLR. In the case of a double dike system and 1.0 meter SLR, this increase in height of the second dike should be approximately 1.15 meter to maintain equal failure probability. Sedimentation in the interdike area has a negligible impact on failure probabilities due to the dominant influence of water depth, meaning the water depth is too high for waves to be affected by the bottom of the interdike area. However, this comparison changes when based on equal LIR. With 1.0 meter SLR, the additional required height of a single dike increases to 1.7 meters. Applying this approach to a double dike system, the effect of the height of bed level of the interdike area on the breach flow does have significant influence. Analysing the effectiveness of a double dike system in comparison to a single dike system based on volume increase, these differences are magnified. However, generally, it can be noted that the extreme storm surge in the Western Scheldt is dominant and a second dike with substantial dimensions is needed to comply to its retaining function. Secondly, a sensitivity analysis was performed on four different parameters and system configurations: 1) height of the first dike in combination with the length of the interdike area, 2) hydraulic conditions with lower water levels, 3) varying area size of the hinterland and 4) implementation of vegetation. The effect of the first dike on the failure probability is not dominant, since the required increase of the height of the second dike is not proportional to the applied decrease in height of the first dike, increasing its effectiveness in terms of dike volume. This effectiveness increases also for hydraulic conditions with lower extreme water levels. In addition, there is a positive relation between the effectiveness and the area size of the flooded hinterland. Vegetation does not have any influence on the dike height due to the high water depths under design conditions. In conclusion, the following three location specific circumstances are important for an open DDS to be an effective alternative to a regular single dike reinforcement: • Sufficient sediments present to allow for a higher rate of sediment accretion compared to sea level rise. • Hydraulic conditions in which waves are more important than storm surge. • Large hinterland area. It is more advantageous to employ the local individual risk approach in comparative studies assessing the effectiveness of double dike systems. The significant positive impact of bed level accretion on flood impact is disregarded when only considering failure probabilities. It is recommended to improve the flood model, implementing a 2D model and considering the effect of the foreshore on breach growth, to gain a more comprehensive understanding of the potential of an elevated bed level of the interdike area on the flood impact, so it can be effectively incorporated into the Dutch flood risk approach. In addition, it is recommended to consider the implementation of an open dynamic DDS in coastal areas with high sediment concentrations and suitable hydraulic conditions (sufficient tidal range and mild storm surge). Furthermore, the wave damping function of the first dike is not critical for interdike areas with sufficient length and reduced depth. It is more efficient to prioritize the flood safety of the second dike. This allows for more effective design and management decisions concerning the height and safety requirements of the first dike. Finally, it is advisable for areas with high water levels during extreme conditions to consider a closable system. This entails the ability to close the gaps in the first dike under specific conditions, such as utilizing tidal culverts, limiting the hydraulic loads on the second dike. However, implementing a closable system necessitates larger investments in modifications to the first dike. Additionally, the maintenance of the first dike becomes more crucial due to its retaining function first. Therefore, it is recommended to conduct a comprehensive cost-benefit analysis to compare the open dynamic double dike system with the closable double dike system.

Many Dutch infrastructure assets were constructed in the first half of the 20th century and by considering an average design life time of roughly 100 years, a lot of these structures will reach the end of their designed life in the upcoming decades. This results in a large replacement and renovation challenge in the nearby future. Assessing the end of life of individual critical hydraulic structures (case studies) and prolonging their lifetime by suggesting adaptive measures is of importance to better define and solve this challenge. In this research, the Haringvliet sluices are used as a case study.

The focus of this research is to apply two existing methods, the framework of Vader et al. (2023) and the Adaptation Pathway Approach of Haasnoot (2013), to the Haringvliet sluices, to make an estimate of the remaining life time and to propose suitable measures to elongate it. Next to this, this research aims to connect both methods mentioned above to create a new integral method. This full method aims to qualitatively and quantitatively analyse hydraulic structures and map out possible paths to elongate its remaining life time. The results of this thesis provide valuable insights in assessing the remaining lifetime of different hydraulic structures in the future. The Haringvliet sluices are an interesting candidate for this research due to the many functions it has to fulfil and the complexity of its interactions within the water system.

The first part of the analysis on the Haringvliet sluices describes the functional analysis as well as the technical decomposition performed on the Haringvliet sluices. The goal of the functional analysis is to define requirements for each of the functions. The goal of the structural decomposition is to identify the most important deterioration mechanisms of the structural elements, which in turn are important in estimating the remaining technical life. The next step in the analysis aims to either qualitatively or quantitatively describe the external drivers which influence the functional performance and technical state of the Haringvliet sluices. The external drivers to consider for the Haringvliet sluices, or hydraulic structures in general, can be subdivided into physical external drivers and economic, political and societal drivers. From this analysis, the drivers which are expected to have the most severe influence on the Haringvliet sluices are defined. For the Tipping Point analysis in the next part of the analysis, existing models are evaluated and used to quantify Tipping Points due to the expected most dominant driver and function combination. A Tipping Point is reached if the system fails to meets its technical or functional requirements due to changes caused by the external drivers. The dominant combination investigated in the analysis is the effect of sea level rise on the flood protection function. The Tipping Point analysis shows that there is a large dependence of the Tipping Points on the evaluation criteria. The analysis gives insight in how other evaluation criteria, like accepting more overflow discharge over a dike section, could impact the Tipping Point. Even though Tipping Points are sensitive to decisions on evaluation criteria and chosen climate scenarios, it does provide valuable insights in the response of the system to sea level rise when investigating different decision criteria. In the last part of the analysis an Adaptation Pathway for the remaining lifetime of the Haringvliet sluices is presented by proposing life elongating measures. Life elongating measures for the Haringvliet sluices can be split into two different categories: Strategies for the bigger water system, i.e. future visions for the Dutch Delta, which could have either a positive or negative effect on the remaining life and life elongating measures focussed on the object or direct system. It is chosen to only investigate mitigation measures focused on the Haringvliet sluices and its direct system.

Each sub-analysis in the total research design has its individual results and therefore its individual assumptions, limitations and critical remarks. The assumptions and limitations of previous steps could have a significant impact on other steps in the analysis. One of the biggest uncertainties in the results of the remaining life time of the Haringvliet sluices is that there is a possibility that other critical combinations found from the driver analysis would reach a potential Tipping Point sooner than the one investigated in this research. Also, the impact of the proposed mitigation actions for the Adaptive Pathways needs to be revaluated on their impact on other function or technical requirements, i.e. an extra feedback loop is needed. The full analysis must be run through several times to create a more complete overview of the most critical ways a structure could reach its end of life and to indicate which measures could be best applied at what time.

By applying the methodology proposed by this research to other case studies and by conducting more research on assessing the remaining life time of critical hydraulic structures, key insights can be found in how to manage our critical hydraulic infrastructure in an adaptive way to elongate their life time.

The world is heating up quickly. Since 1901, the temperature in the Netherlands has risen about twice as fast as the global average and the effects of climate change seem clearly noticeable. With sea levels rising and peak river discharges increasing an enormous pressure is mounting on the current Flood Protection Programme in the Netherlands and measures to prepare for an uncertain future are being developed. Although expensive, the most commonly used strategy as in the current Flood Protection Programme is to increase the retaining heights of the existing dikes. A new method to improve the flood defence system in the South West Delta of the Netherlands is the Delta21 concept. With discharging instead of raising the dikes in mind, Delta21 poses an alternative strategy to reinforcing dike sections for the downstream area of the Rhine and Meuse. The idea of Delta21 is a future-proof solution for the Southwestern Delta of the Netherlands. A solution for not only flood risk management, but energy transition and nature restoration as well.

Between the coastline of the Tweede Maasvlakte and that of the island of Goeree-Overflakkee, the Delta21 project aims to construct a flood defence in the form of a row of dunes, multiple pumping stations and a closable storm surge barrier. Considering protection against flooding, Delta21 strives to limit the water level at Dordrecht to a maximum of NAP + 2.5 m. The flood defence ensures that a lake of about 20 km2 is created in the sea, as it were. By closing off the newly created Tidal Lake by means of a storm surge barrier and opening up a spillway to the Energy Storage Lake, pumping stations are able to pump excess river water from the Energy Storage Lake into the sea. The dunes and the closable storm surge barrier together provide sufficient protection against high seawater levels.

This thesis aims to come up with a preliminary, integral design for the Delta21 storm surge barrier taking into account the new Delta21 landscape design as such that the required functionality of Delta21 is met. This design must fulfil the functional and structural requirements and must fit within the ideology of Delta21. To achieve this, the hydraulic engineering design method is used. The first step in this cycle is to analyse the system with the purpose to better understand the situation in order to formulate the requirements and boundary conditions more accurately. The first design phase is concluded with the basis of design where the processes and functions of the Delta21 system explored
in the system analysis are translated into the requirements and boundary conditions used for the design. The Basis of Design provides mostly "SMART" formulated functional- and structural requirements and boundary conditions. Boundary conditions at sea have been determined using Hydra-NL software.
Climate change plays a vital role in this, as mostly sea level rise influences the boundary conditions significantly. Wishes from stakeholders, which are also explored in the system analysis, are translated either in requirements or evaluation criteria.

In the second step a gate type variant study is conducted. From an inventory of multiple concepts, the vertical lift gate and the segment gate remained after verification. After evaluation of the two remaining concepts using the functional requirements and criteria from stakeholders, the vertical lift gate came out as most suitable for the Delta Barrier. Subsequently, in the second step, a spatial and functional design is presented which satisfies all functional requirements. A new Delta21 flood protection process is proposed in order to more effectively
protect the hinterland from flooding. The reliability of the closure operation has been researched after which is concluded that the closure procedure can be considered reliable until a sea level rise of ca. 1 m. It is verified with a hydrodynamic model that an effective flow area of 6000 m2, defined below NAP,
is to be preferred where mostly the impact on the ecosystem was governing. In order to enable passage of shipping, a location of a separate lock complex is proposed and bridge girders are incorporated into the design in order to enable the passage of road-traffic over the barrier. Furthermore, it is concluded that using tidal turbines to generate electricity with tidal flow behind the Delta Barrier is unfeasible due to the shallow water depth behind the barrier and the relatively low tidal flow velocities through the barrier. Hydraulic cylinders are chosen as driving mechanisms for the gates as it is expected that hydraulic cylinders are less expensive and have a lower failure probability than e.g. a rack and pinion system. Lastly, using a climate adaptive pathway approach, three general strategies are presented to the closure reliability problem of the Delta Barrier after ca. 1 m of sea level rise. Firstly, the barrier could be closed permanently as part of the "protected closed" strategy. Secondly, the dikes in the hinterland
could be strengthened, the bottom protection could be strengthened, the probability that the closure of gates fail could be decreased and the Tidal Lake water level could be increased during a non-closure event. Additionally, the Water Act allows for redistribution of failure probabilities over dike segments
and failure mechanisms. Changes in the closure regime could also prove beneficial. These solutions are part of the "protected open" strategy. Thirdly, inhabitants of the lower lying areas of the Netherlands could be stimulated to move to higher ground in the Netherlands as part of the "move along" strategy.
It should be noted that a combination of either three strategies is very much possible and perhaps to be preferred. The Delta21 project enables the adaptation of any climate adaptive pathway where especially the "protected closed" and "protected open" strategies seem in line with the ideology of Delta21. Whereas the solutions above are presented within the context of the Delta21 flood protection system and the Delta Barrier, the problem is not specific to the Delta Barrier alone and a solution placed within an integral flood protection strategy for the entire (South West) Netherlands might be preferred.

As the third step, a structural design is presented which satisfies all structural requirements. Firstly, it is determined that a prefab construction method suits the construction of the Delta Barrier best, where the piers are to be sunk on to a prepared bed and most of the assembly of the barrier is to take place from the water using specialised vessels and equipment. Secondly, the 40 m long and
10.4 m high steel gates (25 in total) are designed. Thirdly, all main elements of the concrete civil superstructure are designed consisting of the 25 top beams, 25 sill beams and the 26 piers. In general, all concrete elements are restrained from cracking and post-tensioned. Finally, the global stability of the Delta Barrier is verified, taking into account horizontal, vertical and rotational stability, uplift,
scour and internal erosion. A geometrically closed granular bottom protection is designed to tackle the latter two failure mechanisms. In a structural sense, the Delta Barrier is able to withstand a sea level rise of 3.81 m corresponding to the median projection of climate scenario SSP5-8.5 and has a design life of 200 years. The construction of the Delta Barrier will take ca. 5 years, is assumed to be
completed in 2050 and will cost between ca. 2.67 and 3.50 billion euro (price level 2022).

It is recommended to further investigate the ecological impact of the Delta Barrier. Furthermore, a detailed driving mechanisms design and as such a more profound estimate for the probability that the closure of the gates fail is to be recommended.

Besides global warming, climate change is expected to result in (among others) an increased number of extreme precipitation events and a rising sea level. In the future, this can be the cause for an increased number of high river discharge events in combination with high water levels on the North Sea, which goes hand in hand with an increased risk of flooding in the Netherlands. However the rate of change in the future is hard to predict and therefore very uncertain.

One of the projects which seeks to be a (part of the) solution in climate change and flood prevention for the Netherlands is the Delta21 project. By combining a sea defence, energy storage lake, pumping station, overflow structure and storm surge barrier, the Delta21 project increases safety against flooding while providing a sustainable way for temporary energy storage.

In this thesis a design was created for the sea defence of the Delta21 project, during the design process the uncertainty of climate change was taken into account by the use of the adaptive pathway approach.

Three conceptual design variants are created which provide water safety until one meter of sea level rise occurs. When the sea level increases even more, the designs should be altered to the new circumstances. Various adaptation options are put together in the form of adaptive pathways which provide adaptation methods for up to five meters of sea level rise. The pathway schemes are evaluated on 4 evaluation criteria to select the preferred adaptation method for each of the three base design variants.

Using an analysis over the total lifetime of the sea defence measured in meters of sea level rise, the preferred conceptual design for the Delta21 sea defence is selected.

It turns out that the adaptive pathway approach can be used to integrate the uncertainty of climate change into the selection of a conceptual design variant for a sea defence. The use of the approach provides a methodological way of evaluating design options under uncertain circumstances.

The report tackles Galveston's flooding challenges, which are currently in development with the US Army Corps of Engineers (USACE) ring barrier. However, the current design, predominantly addressing coastal flooding, falls short in dealing with pluvial flooding, relying heavily on pumps. This top-down approach neglects environmental and stakeholder considerations, resulting in a decoupled response to compound flooding, lacking adaptability, and overlooking the impact of chronic flooding on local businesses. The central research question revolves around reshaping the Galveston ring barrier in The Strand area for enhanced functionality against both coastal and pluvial flooding, sustainable management of catastrophic and chronic flooding, and improved public space value. The methodology consist of a literature review, fieldwork in 'The Strand,' stakeholder engagement in Texas, the design of multiple alternatives that deal with the issue at hand and evaluation through a Multi-Criteria Analysis. Two alternative designs, sensitive to identified issues, are presented for the Strand area. The outcome emphasizes an interdisciplinary approach incorporating the knowledge of the different academic backgrounds of the team, with designs adaptable for broader implementation in Galveston.
The design alternatives centres on measures to counteract flooding, specifically cloudburst roads, retention areas, and a promenade. Caution is advised in interpreting results, emphasizing the need for further investigation into hydraulic conditions. Climate change effects are underscored, considering sea level rise, precipitation rates, and increased hurricanes. The project area, focusing on a 1 km stretch, offers local adaptation measures, with potential extension to larger areas to explore system behaviour on a larger scale. The study notes the uncommon implementation of sustainable drainage systems in the United States,
highlighting the importance of addressing common failure causes such as incomplete knowledge and poor communication. While two measures for pluvial flooding are examined, the report suggests a more detailed design should consider additional factors like green roofs and their impact on runoff speed and drainage capacity.

Low-lying, densely-populated coastal areas across the world are under threat of hurricane-induced floods. This is the case in, among others, the Galveston Bay Area. In response to this threat the USACE (United States Corps of Engineers) recommended a plan to reduce the risk of flooding, through a range of measures to form a resilient coast of Texas. This plan includes a storm surge barrier at Bolivar Roads in Galveston Bay, whilst the other inlet at San Luis Pass remains open for environmental reasons. Leaving the San Luis Pass open still results in a significant rise in the water level of Galveston Bay, so finding a way to close the San Luis Pass is preferred. Therefore, this thesis researches a barrier for the San Luis Pass to contribute to a resilient Texan coast whilst also taking the local natural habitat into account. The methodology combines the concept of 'Building with Nature' and the civil engineering design method. The methodology incorporates the flood safety, ecological values, and socio-economic aspect into the design process. A conventional storm surge barrier does not fulfill all the requirements and criteria for the San Luis Pass. This research thus proposes a new, innovative type of storm surge barrier: The Shade Curtain Barrier. The shade curtain barrier functions by being rolled down in extreme conditions and stored under the bridge under normal conditions. The two main advantages are that no bottom protection is required and the view is hardly disrupted. Concluding, the shade curtain barrier is a promising solution for a storm surge barrier at the San Luis Pass to contribute to a resilient Texas coast.

In this thesis I use a novel approach to estimate the economic impact of the 2021 Limburg flood using high-frequency transaction data from ABN AMRO bank. High- frequency bank transaction data have previously been proven valuable in accessing the economic impact of the COVID-19 pandemic (Neuteboom et al., 2021). To the best of my knowledge, this type of data has not been used to estimate the economic impacts of a natural catastrophe. I focus on a synthetic difference-in-differences methodology to estimate the impact. I find that the economic impact is 18,045 EUR on average of extra spending per inundated individual in Valkenburg aan de Geul, the most heavily hit area. This is very similar to the damage estimate of the ENW (2021) of 18,713 EUR on average per person for the inundated in Valkenburg aan de Geul. Further- more, the duration of the economic impact for the inundated is roughly 35 weeks on average. Finally, I did not find a measurable economic impact to uninundated and evacuated individuals. In summary, high-frequency bank transaction data paired with a synthetic difference-in-differences model is a reliable gauge of the economic impact of a flood and should be used to estimate the economic impact of future natural disasters. Additionally, it can be be the empirical foundation for calibrating existing damage models.

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.

The coastal zone is becoming more vulnerable due to growing concentrations of human population, settlements, and socio-economic activities. The Rhine-Meuse Delta is low-lying land, which makes it vulnerable to flooding. The Maeslant barrier is a storm surge barrier which should prevent flooding in the low-lying land behind the barrier. Various climate models have predicted that sea level rise will occur. The predicted sea level rise is more than what was anticipated during the design stage of the Maeslant barrier. Due to the increasing water levels, the closing frequency of the barrier will increase. This has a negative effect on the reliability of the barrier, as the components are used more often. The Maeslant barrier also needs to discharge river water during a storm closure when the water level on the rear side of the barrier becomes too high due to river inflow. This discharging process is a complex process which contributes greatly to the failure probability of certain components.

Delta21 is a spatial plan to redevelop a part of the Dutch delta to mitigate the effects of climate change which are sea level rise and increased river discharges. Delta21 claims to improve the safety of the entire Rhine-Meuse delta till a sea level rise of 1.1 m. Delta21 pleads for a central approach to focus on improving pump capacity in the main water systems instead of raising and strengthening all the dikes. The main goal of Delta21 is to reduce the flood risk in the downstream area. Due to the large pump capacity available, Delta21 can replace the discharging function from the Maeslant barrier. This simplifies the closure operation of the Maeslant barrier to only retain seawater during storms on the North Sea. The effect of the simplified closure operation has consequences on the reliability of the Maeslant barrier.

Therefore, the main objective of this master thesis is to find out how the failure probability of closure of the Maeslant barrier with the simplified closure operation changes in the Delta21 configuration.

To fulfil the objective, the first step was to find out how the Maeslant barrier itself works and how the discharging procedure impacts the failure probability of closure. Then, a hydraulic system analysis was done to understand how Delta21 impacts the current configuration of the Rhine-Meuse delta. In the next step, the new situation with Delta21 was schematized into a simple hydraulic model which has been verified and validated.
By making the variables in this model probabilistic, a Monte Carlo simulation was done to find out what the probability of a negative head difference larger than 1.5 m was. The simulation was done for the situation without and with 0.6 m sea level rise.
The next step was the failure probability analysis. In the qualitative analysis of the failure probability analysis, different failure mechanisms and failure scenarios are identified for the Maeslant barrier in the current situation, and for the Maeslant barrier in the Delta21 configuration. In the quantitative analysis, the probabilities for the defined failure mechanisms and failure scenarios are calculated according to the upper bound approximation, for the current situation and with Delta21. The probability which was calculated with the Monte Carlo simulation is also used here. Ultimately, a fault tree can be composed on the basis of the qualitative and quantitative analysis for the Maeslant barrier in the current situation and the Delta21 configuration.

The failure probability of closure has been reduced by a maximum of approximately 10%. This is because many systems and operations were simplified because of the simplified closure operation.
Additionally, the failure probability analysis also provided insight in how the probability of flooding changed for Rotterdam with the Maeslant barrier in the Delta21 configuration. While the failure probability of closure was reduced by a maximum of 10% with Delta21, the probability of flooding for Rotterdam has increased by 53% when using the full pump capacity from Delta21. This increase is not significant since the probability of flooding remains very small. Due to the removal of the discharging function with Delta21, the probability of several flooding scenarios increased drastically which resulted in the increase in the probability of flooding for Rotterdam.
With a sea level rise of 0.6 m, the probability of flooding increased approximately 500% for the current situation (without Delta21). When comparing Delta21 with no sea level rise to Delta21 with 0.6 m sea level rise, the increase was also present with approximately 375%. This is less than 500%, which indicates that Delta21 is effective to mitigate the effects of sea level rise compared to the situation without Delta21.

Flooding is one of the most damaging natural disasters worldwide, and presents a signi_cant risk for a large amount of the global population. For the development of ood disaster management strategies, policy makers make use of ood hazard maps to inform investment strategies to reduce risk. In many current ood hazard mapping methods, the role of embankments is either implicit or completely unaccounted for. However, these defense systems can play a key role in both the _nal extent of the inundation as well as in the development of the inundation. Limitations in available data are often the reason for the lack of explicit implementation of embankments. The goal of this study is the development of a method that can explicitly include the e_ects of ood defenses in a ood hazard map based on limited available data. Next, this has been tested for a low-lying riverine area and the Tisa river basin in Serbia was selected as a case study area for this purpose. First, an idealized approach has been followed to better understand the model behavior using settings resembling this river. Finally, the method has been applied with a more realistic river schematization.
To develop a method for a more explicit inclusion of ood defenses, an understanding of the di_erent current approaches has been generated based on a literature review. On the scale of global ood maps, the failure probabilities of ood defenses are not used. Only with post-processing, certain areas are considered protected by removing inundation from the maps. Many studies of ood hazard mapping use the so-called bathtub approximation. Hereby is assumed that the complete oodplain will ood and that the inundation depth is found by extrapolating the water surface level outside of the embankments to the area inside of the embankments. The inuences of the ood defenses on the inundation are not included. Regional ood hazard maps are still made without ood defenses in many cases. While the improved resolution allows for more detailed maps, the lack of available data still limits the implementation of ood defenses. Flood mapping methods exist that include failure probabilities for ood defenses but these require large amounts of data that is not available everywhere.
An idealized model based on the Tisa river characteristics is used to test a ood mapping method which includes explicitly the presence and potential failure of embankments. Based upon data on the river geometry, hydraulics as well as land-use in the oodplains, a model schematization has been set up with the SOBEK software. The embankments were simpli_ed to a crown height for the purpose of overow and an estimated failure probability. The breaching of the levee is simulated according to the Verheij-vdKnaap breach growth model. The estimation of the failure probabilities was based on historical failure rates of a comparable ood defense system along the Elbe River. The levees were schematized into segments based on the maximum breach width of the breaching model…

The effects of climate change are felt all around the world. An increased sea level goes hand in hand with an increased risk of flooding. To combat this, the coastlines must be reinforced to withstand future sea levels. However, repeatedly reinforcing coastlines to keep up with the sea level rise (SLR) could prove extremely costly. An alternative approach would be to shorten the coastline, as the Netherlands did with the Afsluitdijk to enclose the IJsselmeer. Looking at Europe, Groeskamp and Kjellsson (2020) proposed the construction of the Northern European Enclosure Dam (NEED) — a dam that would disconnect the North and Baltic Seas from the Atlantic Ocean. In this way, it would protect fifteen northern European countries against the accelerated global mean SLR (GMSLR), as it simultaneously shortens the coastline that requires reinforcement. This thesis aims to determine whether the NEED (Adaptation Strategy 2) would be a financially favourable adaptation strategy over raising the coastal defences on a country-by-country basis (Adaptation Strategy 1) around the North Sea to combat future GMSLR, and if so, at which GMSLR.

Through the use of the GLOFRIS model framework it was possible to estimate that by 2080 a total of 15,000 km2 would be inundated, affecting 9.5 million people and resulting in damages up to 1 trillion € for all fifteen countries combined. Reinforcing the regional flood protections (Adaptation Strategy 1) is estimated to have a total cost range of 245 to 335 billion € for a 1-metre GMSLR with an increase in costs between 170 and 235 billion € per metre GMSLR. The construction of the NEED (Adaptation Strategy 2), using an earth-fill dam design with 1:6 slopes on either sides, is estimated to be just under 1.1 trillion €, with an increase in costs of 11 billion € per metre GMSLR.

It was found that the NEED flood protection adaptation strategy will eventually become more financially favourable over the regional strategy. Estimated to be more cost-effective beyond 5.15 metres GMSLR, which is associates with construction costs of roughly 1.15 trillion €. This GMSLR for scenario SSP5-RCP8.5 is expected to occur between 2280 and 2660, approximately. However, as the total costs are greatly contingent upon the core material, modifying slope angles of the NEED design will lead to a significant reduction in volume and, hence, costs. For the alternative designs with a 1:4 and 1:5 slope, the total costs are reduced by 17% and 34%, respectively. For these designs, the NEED will already become favourable at 3.35 and 4.25 metres GMSLR, respectively.

Several cost distributions have been created based on the four aspects that have been investigated, namely (i) coastline reinforcement length, (ii) size of inundated area, (iii) population exposed and (iv) economic damages caused by flooding. Together with the extrapolated regional costs per country, it is possible to determine which distribution is the most and least financially favourable for each country and whether contributing to the NEED is even favourable at all from the perspective of each country.

This research scrutinised the costs, effects and consequences of the most extreme scenario that generated the greatest exposure indicator values (i.e. SSP5-RCP8.5 combined with a return period of 1000 years). Through this
assessment, it was possible to estimate the costs associated with both adaptation strategies, and furthermore, to determine at which GMSLR one strategy surpasses the other in financial attractiveness and when this GMSLR can be expected. However, it should be noted that recent studies have shown that, in reality, the most extreme scenario might, unfortunately, turn out to be even more extreme than the most extreme scenario assumed in this thesis. And as the consequences strongly dependent on how climate change will unfold in the future, the costs to combat and the timing of such GMSLR occuring will differ.

The results retrieved from this research provide insight into when the NEED flood protection adaptation strategy will become a better alternative to regional flood protection reinforcement. However, it should be borne in mind that it is not a matter of ‘either-or’, but rather ‘both-and’, as regional dike reinforcement cannot entirely be omitted when deciding to construct the NEED. Instead, a balance must be found in the extent to which regional dike reinforcement is required to protect the countries while the NEED is under construction. So there are plenty of uncertainties and questions that require additional research to fully comprehend all the effects of this massive operation and making it feasible.

This investigation considers the two floating gates of the Maeslant barrier, which is a storm surge barrier in the Rotterdam area. During the end of each closure operation of the Maeslant barrier, the flow at the barrier may be in seaward direction. Three different effects have been observed in the situation with a flow in seaward direction. The following three effects are considered in this report:

1. A force in the connection between the gate and guide tower
2. A quasi-constant change of the gate orientation
3. A periodic oscillation of the gate orientation

In this report, these three effects are described, and data on these effects and relevant hydraulic conditions is collected. These data are obtained from yearly test closures in the period 2007-2021. Based on the collected data, the three effects and hydraulic conditions are quantified. From a statistical analysis based on the data, a relation with the local discharge is found for each of the three effects.

To further explain the effects, simple conceptual models are derived for each of the effects. The conceptual models yield the most relevant results for the observed force, which is appropriately modelled based on a momentum balance over the barrier. For the other two effects, the conceptual models presented in this report do not adequately model the gate behaviour, however suggestions are provided for further improved models.

Lastly, based on the most relevant statistical and conceptual models, an extrapolation of the three effects is performed to assess the magnitude of the three effects in extreme situations.

Sea level variations and storm surges are expected to increase as a result of climate change. 570 cities and some 800 million people are by 2050 estimated to be exposed to these phenomena when emissions do not decrease (UCCRN, 2018). It is, however, deeply uncertain if and to what extent emissions will decrease. Additionally, the effects of climate change are not fully understood due to its complexity, resulting in a wide range of uncertainty. Flood risk measures can be implemented to reduce flood risk. The economic evaluation of such measures is affected by other factors of uncertain nature such as economic growth. The Dynamic Adaptive Policy Pathways (DAPP) approach has been identified as an approach capable of identifying and implementing effective flood risk strategies under uncertain conditions (Haasnoot et al., 2013). This approach aims to provide decision-makers with insight into what action to take when. Simultaneously, the approach focuses on ensuring flexibility which facilitates adjustments to unforeseen conditions. Within this approach, so-called adaptation pathways need to be developed. These pathways describe a sequence of actions over time required to ensure a minimum level of flood safety. The DAPP approach has been applied to simplified cases in previous research, but not yet to more detailed master-planning for which the creation and economic evaluation of pathways is a not straightforward process. This results in the main research question of this thesis:

How can the Dynamic Adaptive Policy Pathways (DAPP) approach be used to create and select effective flood risk strategies under highly uncertain conditions?

This research question has been addressed by developing a framework capable of creating adaptation pathways and evaluating them with an incorporated scenario-based economic evaluation. This framework is supplemented with a probabilistic assessment that evaluates the performance of pathways in the full range of possible but uncertain futures. The use of these tools has afterwards been validated by applying them to a fictive case and a case study along the South East Coast of Singapore. The framework can be used to assess the sensitivity of uncertainties. Additionally, it can be used to obtain the conditions for which a different pathway turns out to be more effective. Damages corresponding to certain water levels are required as input and are used to build the damage function of a specific project area. These damages can be modelled with damage modules like the Global Flood Risk Tool (GFRT). The damage function and other basic information like dimensions and characteristics of the project area are used to perform an economic optimisation of individual measures. A selection of adaptation pathways (consisting of combinations of measures over time) is made based on prerequisites and a scenario-based evaluation. The scenario-based evaluation is supplemented with a probabilistic assessment as the use of scenarios might lead to cognitive biases and does not cover the full range of future possibilities (Hoffmann, 2017). This probabilistic assessment is conducted by means of a Monte Carlo simulation and can be used to evaluate the robustness of pathways in the full range of possible futures. A pathway can afterwards be selected and trigger values that should initiate the implementation of subsequent measures can be obtained via the framework.

The developed method has first been applied to a fictive case. A small area with a standard damage function was assumed for this. After the framework had been validated, the input-conditions were altered to assess the individual influence of each uncertain input value. The outcome turned out to be dependent on the characteristics of the project area and the assumed conditions. An increased area resulted in a pathway with a flood wall instead of a landfill as first measure being most effective. Out of the uncertainties, the discount rate and socio-economic growth rate turned out to most significantly affect the Net Present Value (NPV) and Cost-Benefit Ratio (CBR) of flood risk strategies. Especially, low discount rates and high socio-economic growth rates resulted in pathways built up of individual measures with lifetimes exceeding the technical lifetime of measures. To prevent this, and to ensure a flexible approach, the lifetimes of individual measures were restricted. A flexible approach enables one to adjust to conditions other than those that have been assumed. Measures with a long lifetime ahead lead to bigger investment costs and these are irreversible when the conditions turn out to be less severe than anticipated. The contrary also turned out to be possible. These short lifetimes corresponding to measures with practically infeasible low heights were prevented by setting a minimum height at which the linear relationship between the height and costs of measures starts. The probabilistic assessment was conducted after a pathway was selected. Increasing the range of uncertainty for this pathway logically led to a wider range of possible outcomes. This wider range of outcomes can be a reason not to select a certain pathway as the probability of a low NPV is higher. The fact that this difference could not be observed in the outcome of the framework underlines the need for this probabilistic assessment. Finally, trigger values were set for the selected pathway of the fictive case. The trigger values were initially set for the planned subsequent measures. However, it could be observed that the obtained trigger value for the planned subsequent flood wall increment did not result in sufficient time to implement a storm surge barrier without dropping below the required minimum level of flood safety. Therefore, trigger values corresponding to the next planned subsequent measure could potentially lead to the exclusion of other possible subsequent measures. Instead of setting trigger values for the planned subsequent measures, trigger values should provide enough time for all possible subsequent measures to forestall the exclusion of possible measures and ensure flexibility.

The findings from the fictive case led to adjustments of the framework to ensure practical feasibility and flexibility. The adjusted framework was afterwards applied to a real-life case along the South East Coast of Singapore characterised by a narrow water level distribution, i.e. a relatively small difference (∼15 centimeters) between water levels that differ a factor of 10 in return period. A storm surge barrier turned out to be a factor of 10 more costly than alternative solutions, irrespective of the assumed sea level rise scenario. Therefore, it was concluded that the storm surge barrier was not the desired flood risk reduction measure for the project area and the area was subdivided into smaller areas to further optimise the flood risk reduction strategy. The framework was used to create flood risk reduction strategies. No measures turned out to be required until 2092 for the assumed conditions. The sensitivity analysis of this case study showed that assuming a more severe sea level rise scenario (an additional 58 centimeters in 2100) and accounting for additional storm surge caused by climate change, could result in measures being required over 50 years earlier. Without taking this into account, two pathways turned out to satisfy the safety standards until 2200 for the assumed conditions. One pathway solely consists of a flood wall and subsequently flood wall increments (AP10) while dryproofing is the first measure of the other pathway and subsequently a flood wall and a flood wall increment are implemented (AP33). The costs of AP10 turned out to be slightly higher in the full range of futures than that of AP33 but the probability of obtaining a higher NPV than obtained from the framework was also higher (58% vs. 51% of the outcomes higher than the NPV of AP10 obtained in the framework). As the differences between the probabilistic assessments of the pathways are not substantial, the preferences of local stakeholders are even more important. Dryproofing can lead to inundation of the land for high water events with a return period lower than the safety standard while Singapore has set the goal to protect its coastlines and prevent inundation of the land. Therefore, the pathway consisting of a flood wall and flood wall increments turns out to be the most suitable solution for the project area.

This research contributes to the existing knowledge related to the DAPP approach as it smooths the not straightforward process of creating and evaluating adaptation pathways under uncertain conditions. It showed how to economically optimise individual flood risk reduction measures and build adaptation pathways out of those measures. A framework has been developed to automate this process and instantly evaluate the effectiveness of such pathways for set conditions. This study also showed how a probabilistic assessment of these adaptation pathways could be used to select a robust flood risk strategy. This developed method can further be fine-tuned by including transfer costs that reflect the costs of maintaining flexibility in the face of deep uncertainty. Additionally, flexibility can be incorporated within the probabilistic assessment to enable alteration of type and/or height of subsequent measures for conditions different than assumed. This would result in a more accurate assessment. Automating the integration of the probabilistic assessment within the framework can eventually lead to one complete tool which enhances the applicability and allows for the probabilistic assessment of all pathways instead of just a selection of pathways.

The geographical features in the Southern part of Limburg forces precipitation from upstream located areas to flow through a bottleneck, which is exactly located at the city centre of Valkenburg. This makes increasing the safety level more complicated than in other areas. The safety level of Valkenburg has a lower standard in comparison to the rest of the country, namely 1 in 25 years. The combination of those two characteristics is not desirable. Official documents
state that this lower standard is based on detailed (societal) Cost-Benefit Analyses. In reality however, the safety standard is based on simple back of the envelope calculations. The Limburg Waterboard has indeed developed a Cost-Benefit tool which they could use to find out whether the implementation of safety measures are cost effective, however they have not been able to
implement it until now. Additional safety measures to increase the safety level are assumed too costly based on the same brief calculations. It is doubtful whether individual risk laws are met, since the Limburg Waterboard assumes no casualties in the Geul area. The 2021 flood however showed that this might be false for future floods which get more severe over time due to climate change.

The citizens and entrepreneurs in Valkenburg were not completely aware of the risks they were exposed to and their sense of safety related to flooding decreased after the flood. Most of the people questioned in a survey demanded a higher safety level than the current standard. They would even be open for an increase in tax to realise this improvement. Raising the quay walls would be a cost-effective solution according to some of the citizens. However, the entrepreneurs who rely on tourist based income, do not prefer this option due to loss in aesthetic value.

Hydraulic, structural, and non-technical solutions which are investigated in this report, have the aim to increase the safety level or make the safety level more acceptable for citizens. The hydraulic, and structural solutions focus on four main aspects. The first aspect is related to the redesign of bridges in the city centre. This is mainly done by applying a flat bridges design, which is further elaborated with a case study for the collapsed Emmalaan bridge, and a liftable bridge design. The second aspect is related to closing the gaps in the quay walls, and increasing the height of the quay walls. The third aspect is related to the implementation of water tunnel concepts with six different design concepts. The fourth aspect is related to implementing parts of Meerssen’s 4-step approach. The first three aspects of the hydraulic and structural solutions are focused on increasing the discharge capacity of the Geul, while the latter aspect focuses on retaining, delaying, and storing the precipitation. Non- technical solution are also proposed
that focus on making people more aware of the risk they are exposed to. This could eventually lead to more acceptance and thus more pleased citizens.

The first order estimations for investment costs and safety level for the hydraulic, and structural solutions are graphically displayed in order to provide an overview of possible interventions to the municipality of Valkenburg and the Limburg waterboard. Although preliminary, and based on limited available data, these results should encourage both stakeholders, and other relevant parties, to reconsider safety standards and search for measures that could increase the safety level of Valkenburg when desired.

Two types of calculations are currently used to assess dikes for macro stability. These are the semi-probabilistic calculation and the probabilistic calculation. In practice, the semi-probabilistic calculation is currently mostly used. However, the probabilistic calculation is the most accurate calculation of the two methods resulting in the most realistic results. Performing a probabilistic calculation is on the other hand less simple and a lot more time consuming. Therefore it would be more efficient to still regularly apply the semi-probabilistic calculation to save time and also find a way to make this calculation more accurate. Although the probabilistic calculation results directly in a reliability index, this is not the case with the semi-probabilistic calculation. To link the target reliability index to the factor of safety of the semi-probabilistic calculation, a calibration formula is used. This formula was made using a set of probabilistic calculations from the calibration study. The formula is designed in such a way that in reality 80% of dike profiles are calculated too conservatively with the semi-probabilistic calculation and 20% not strict enough. This means that this formula results in a lower reliability index for the majority of dike profiles than what the realistic value would be. The result of this conservative formula is that in some cases actual reliability of the dike profile can deviate reasonably from the probabilistic reliability index. Some profiles can therefore be made far too robust, while a few others may be approved unfairly. There could be a lot of profit to be made in both safety and in the amount of reinforcement required if the existing calibration formula can be further elaborated. This leads to the main question of this report: “How can the current calibration equation for the assessment of a dike on macro stability be elaborated by using the results of probabilistic calculations from the calibration study and SAFE?” As emerges in the research question, the probabilistic calculations of two projects are used for the research; the calibration study and the project SAFE. The calibration study is the project from Deltares on which the current calibration formula is based. The set of dikes in this project consists of a mix of local and regional dike profiles around the Netherlands. The set is arranged in such a way that almost every type of dike in the Netherlands appears in it so that it can be applied as widely as possible. In contrast to the dataset from the calibration study, the dataset from SAFE consists of dike profiles of only two dike sections at the Lek. The dike profiles belonging to SAFE have been compiled by the water authority and calculated probabilistically by Sweco and Arcadis. The data set from safe is composed in such a way that the critical dike locations of these 2 sections on the Lek are included. Several ways to see if the current calibration formula can be made more accurate are investigated. Initially, SAFE's location-specific set is compared to the calibration formula. It is checked to which extent SAFE corresponds to this and what the reasons can be for existing differences. It is also examined whether the current calibration formula can be improved on the basis of different dike characteristics. A distinction is made of several general , soil and geometric characteristics. The research shows that SAFE's dike profiles require a slightly different calibration line than the line from the calibration study. Instead of 80%, only 64% of the dike profiles lie below the calibration line of the calibration study from Deltares. Especially at the lower reliability indexes, the profiles from SAFE are not calculated safely enough. It is not demonstrable that the profiles from SAFE lead to different results due to the fairly similar type of dikes from the project or the specific location. The difference will therefore mainly be due to the different calculation methods of both projects. In addition, there were also two dike cases/characteristics that has an influence on the difference in reliability index; the design profiles and the berm. With Both, it seems useful to draw up a special calibration line that takes this into account. Especially a calibration line for only the design profiles produces a much more accurate result. This new calibration line results in 30% more accurate reliability indexes. The conclusion of the report is therefore that it would be effective to apply a separate calibration line for SAFE and for the design profiles. For SAFE, the difference with the current calibration line could also be solved with a better calibrated schematization factor, using frequently probabilistic calculations or by renewing the existing calibration study because the difference that occurs seems to be mainly due to the calculation method. Moreover, a separate calibration line for the design profiles thus produces a lot more accurate results. However, the consequence of these more accurate results is that fewer profiles will be on the positive side of the calibration line. The separate calibration line for the dike profiles without designs is 20% less accurate but resulted in safer calculations. When both formulas for designs and normal profiles are used, the complete data set gets a little more accurate with 8% and also even safer than the current calibration formula. So there is certainly something to be improved from the current calibration formula by distinguishing between dike profiles without design and with design.