Rising sea levels and increasing storm intensity are driving the implementation of large-scale storm surge barriers globally to protect coastal communities and critical infrastructure. As these structures are increasingly located within major maritime access routes, their design introduces new navigational challenges that directly affect nautical safety. While extensive experience exists in the hydraulic and structural design of storm surge barriers, the navigational implications of alternative barrier configurations have received comparatively limited quantitative attention. Existing studies often focus on single configurations or rely on qualitative assessments conducted late in the design process, leaving a gap in systematic, configuration-specific methods that support early-stage design decisions.

The objective of this thesis is to develop and apply a quantitative assessment framework that enables systematic evaluation of the nautical safety performance of alternative storm surge barrier configurations during early design stages. The framework is grounded in the premise that, at this stage of design, nautical safety performance is most directly reflected in vessel maneuverability under constrained geometric and environmental conditions. Rather than attempting to predict accident probabilities or prescribe absolute safety classifications, the method focuses on configuration-dependent maneuvering demand and available control margins as necessary preconditions for safe navigation.

A structured assessment framework is developed that integrates spatial schematization of the navigational environment, critical environmental forcing scenarios, representative design vessels, fast-time ship maneuvering simulation, and quantitative nautical safety assessment metrics. These metrics describe maneuvering performance in terms of spatial, temporal, and control margins, enabling reproducible and configuration-specific comparison. Fast-time simulation is employed to ensure computational efficiency and repeatability, making the framework suitable for iterative application during early design phases.

The practical applicability of the framework is demonstrated through a case study of the proposed Bolivar Roads storm surge barrier in Texas. Multiple alternative barrier configurations are evaluated using the fast-time simulation model SHIPMA. Simulations are conducted for a set of representative design vessels under selected flood and ebb tidal conditions, using consistent spatial schematization and environmental assumptions across configurations. Simulation outputs are post-processed to derive the values of the quantitative safety metrics for each configuration.

The results show that nautical safety performance is highly sensitive to barrier geometry. Configurations featuring wider gate openings and more favorable alignment and siting consistently exhibit larger spatial and temporal maneuvering margins, reduced control effort, and more stable vessel behavior. Conversely, configurations with constrained openings or unfavorable alignment impose increased maneuvering demand and reduced controllability. These findings demonstrate that geometric design choices can substantially influence navigational safety performance and that such effects can be captured quantitatively using the developed framework. While the absolute values of the assessment metrics are subject to modeling assumptions and simplifications, the relative differences between configurations provide meaningful insight for comparative evaluation. As such, the results are not intended to replace expert judgment but to serve as structured input for pilot and stakeholder discussions, supporting transparent and informed interpretation of navigational safety implications.

This research contributes a systematic, maneuvering-based framework that bridges the gap between hydraulic design and nautical safety assessment in storm surge barrier projects. By enabling early-stage, quantitative comparison of alternative configurations, the framework provides capabilities that were previously unavailable in design practice. The case study illustrates the framework’s practical value and transferability to other navigation-constrained barrier locations. Future research should prioritize integration of configuration-specific hydrodynamic modeling, enhanced representation of human factors, and further refinement of assessment metrics to improve physical realism and decision relevance. ... Read more

Flooding is one of the most frequent and destructive natural hazards, accounting for significant human and economic losses every year. Flood hazard mapping allows to identify vulnerable areas by estimating water depth, extent, and intensity under specific scenarios. These maps are created via numerical models as they provide accurate flood simulations. However, they are computationally expensive, particularly for overland flow at high resolution. Data-driven methods based on neural networks offer a promising alternative, delivering faster predictions while maintaining high accuracy.

To provide a comprehensive perspective on deep learning for flood mapping, we first reviewed the state of the art across different applications, considering a range of flood types, spatial scales, and deep learning architectures. Our analysis shows that deep learning methods generally outperform both traditional numerical approaches and conventional machine learning in terms of speed and accuracy. However, most existing models are tailored to individual case studies, neglect the dynamic evolution of flood waves, and cannot transfer to new topographic settings and boundary conditions not seen during training. Furthermore, current approaches struggle to incorporate physical principles, represent hydraulic structures, and provide physically consistent methods for validating outputs, particularly in the context of uncertainty quantification. Finally, we highlight that dike-breach floods remain largely under-represented in the literature, despite their high uncertainty stemming from flood defence failures.

In this thesis, we introduce Graph Neural Networks (GNNs) as hydraulics-inspired Surrogate models for simulating the spatio-temporal evolution of floods. While applicable to different flood types, our focus is on dike-breach floods due to their high uncertainty and particular relevance in the Netherlands and other low-lying areas. We build GNNs that are conceptually analogous to finite-volume methods used to solve the shallow water equations: finite-volume cells are treated as graph nodes, and flux exchanges are learned between adjacent cells by the model. The flood propagation in the proposed SWE-GNN model resembles hydraulics principles and enforces water to propagate only from cells with water. The model works in the same fashion as numerical solvers, auto-regressively predicting the evolution of the hydraulic states over time. By stacking multiple GNN layers, the model captures wider spatial dependencies without requiring small numerical time steps, theoretically needed for stability conditions. We also develop a multi-step ahead loss function combined with curriculum learning that further stabilizes long-term predictions.

We propose a multi-scale GNN formulation that models flood dynamics across different spatial resolutions, enabling the capture of both local and large-scale propagation processes. Time-varying boundary conditions are incorporated through ghost cells, removing the need for separate numerical solvers to initialize simulations. To enhance generalization across unseen unstructured meshes and reduce training data demands, we enforce invariance principles, ensuring the model is independent of coordinate rotations. This multi-scale approach proves both faster and more accurate than its single-scale counterpart. Our methods are validated on a suite of two-dimensional synthetic dike-breach simulations generated with a high-fidelity numerical solver. These datasets progressively increase in complexity by varying initial conditions, location of boundary conditions, size of the domain, computational mesh, and time-varying hydrographs used as boundary condition. Results demonstrate that the GNN generalizes well to unseen topographies, boundary configurations, and mesh configurations, without relying on inputs from numerical simulations. The models achieve a testing critical success index consistently higher than 70% in all datasets. The model also shows generalization to a real case study, dike ring 15 in the Netherlands, with only one fine-tuning simulation.

Finally, we extend the model to explicitly include hydraulic structures and to quantify uncertainty in flood hazard mapping of another real-world case study, dike ring 41 in the Netherlands. The framework is tested for large-scale uncertainty analysis with 10,000 scenarios. All simulations are completed in under 10 hours on a single GPU, corresponding to a speed-up of approximately 10,000 times with respect to the numerical solver, with over half of the scenarios maintaining plausible mass conservation. The combined scenarios are then used to produce probabilistic flood hazard maps, which assume equal likelihood of occurrence for each event. We also analyse the flood uncertainty for a given breach location and return period, showing that the model ensemble can provide better flooding estimates than the deterministic scenario.

This thesis highlights the potential of GNN-based surrogates for time-sensitive flood risk assessments under uncertainty. By demonstrating both accuracy and computational efficiency, it contributes to bridging the gap between complex hydraulic modelling and large-scale flood risk analysis. Despite being applied on dike-breach floods, the framework introduced in this thesis can readily be applied to fluvial and coastal floods without modifications. This open pathways for integrating surrogates into operational decision making and future flood resilience planning.
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Flood risk is of key interest to societies in low-lying areas such as the Netherlands, where a wide variety of dikes protect people and property from flooding. This thesis focuses on canal dikes, located along drainage canals in polders, mainly in the northern and western regions of the Netherlands. Safety assessment outcomes and recent dike failures indicate that inner-slope instability is a key failure mechanism affecting canal-dike safety, occurring under both very dry and very wet conditions. Assessing inner-slope instability remains challenging due to large uncertainties in geotechnical and geohydrological parameters. The aim of this thesis is to enhance the geohydrological understanding of canal dikes through monitoring and observation-based analysis, thereby improving the assessment of their stability and the safety of dike systems as a whole. Two unique datasets were established: a multiyear detailed monitoring series of soil moisture levels and hydraulic heads at ten canal dikes, and a nationwide collection of over one hundred hydraulic head time series from about 50 monitoring sites.

The detailed monitoring series included two extremely dry summers (2020 and 2022). Hydraulic heads at inner-slope and toe monitoring points showed strong seasonal variation. During winter, conditions were near saturation, while during dry summers heads dropped down to nearly 2 m, despite outside water levels remaining nearly constant. Non-hydrostatic hydraulic head levels were observed within dike bodies, conditions often not accounted for in safety assessments for drought situations. The precipitation deficit proved the most reliable meteorological drought indicator, outperforming the standardised drought indicators (SPEI and SPI).

Analysing the nationwide dataset with time-series models, a non-linear model performed best, resulting in 35 reliable time-series models. Four clusters of dikes were identified, differentiated by response times, defined as the time required for 95% of an impulse's influence to dissipate. Longer response times cause peak heads to occur later in the winter. Peak head statistics indicated a that extreme heads are close to yearly occuring heads, with a median decimate height of 15 cm and a range of 5 to 50 cm. By 2100, extreme peak heads are expected to occur between three times less frequently and eight times more frequently, depending on the climate scenario and the type of canal dike.

The time-series models were used to hindcast 60 years of hydraulic head levels and estimate spatial dependencies, quantified using the length-effect factor of peak heads. At the polder scale, variation in head responses can increase the factor by a factor of four to five, whereas spatial weather variability can double it. At the scale of the entire canal-dike system, the length-effect of peak heads is dominated by spatial weather variability, increasing from about 6 for annually occurring heads to around 40 for heads with an exceedance frequency of 1/100 per year.

The impact of small load variations on reliability updating was analysed. The impact of reliability updating increases as load variations decrease, regardless of the prior failure probability. The two canal dikes, with decimate heights below 10 cm, benefited most from reliability updating, whereas updated failure probabilities of the river dikes changed only slightly. A credibility check was introduced: when uncertainty in dike strength is more than 1.5 times larger than the variation in loads, estimated failure probabilities are not credible. Reducing uncertainties in dike strength, through monitoring with reliability updating or more detailed soil strength data, leads to more credible failure probability estimates. ... Read more

This dissertation focuses on validating the Material Point Method (MPM) for analyzing underwater flow slides and slope stability issues to enhance understanding and predictive capabilities. By addressing the complexities of multi-phase, multi-physics, and multi-scale problems, the research aims to establish a reliable numerical solution for simulating these phenomena, which are critical for flood defense systems. The research bridges gaps in knowledge by integrating experimental data, advanced numerical modeling, and validation studies. ... Read more

Singapore’s Long Island project aims to protect the East Coast, meet freshwater demands, and support urban development. It involves constructing a freshwater reservoir by closing off part of the sea using three islands and two barrages. The islands, totaling 850 ha, will be used for urban development. The project is currently in its conceptual design phase. Long Island presents several challenges. Singapore’s flood risk policy focuses on raising the platform level, increasing demand for scarce construction materials. The multifunctional nature of Long Island, providing flood protection, freshwater supply, and urban space, complicates design. Uncertainty in future sea level rise (SLR) further challenges sea defense planning and adaptation. This thesis develops a resilient conceptual design for Long Island’s land reclamation, focusing on platform level optimization and sea defense adaptability. Six reclamation variants are proposed, ranging from polder systems to conventional landfills, combined with a caisson or a dike as sea defenses. Sea defenses are designed to accommodate up to 5 m SLR and are integrated into adaptation pathways. Each variant considers reservoir dike design, effective land area, settlements, and polder pumping requirements. Designs are evaluated through capital cost analysis, lifetime cost assessments using Present Value, Multi-Criteria Analysis (MCA), and sensitivity analyses on design parameters, Social Discount Rates (SDRs) and SLR projections. The most cost-effective design combines a platform level of -4 m SHD with either a dike or caisson. This polder approach is technically feasible and reduces reclamation volumes by 80 million m3 and saves 3 billion SGD compared to a 5.1 m SHD design. Sensitivity analyses confirm its robustness under varying assumptions. Both sea defense types are adaptable and have comparable costs, though further research is needed to determine the optimal choice, including geotechnical design and naturebased integration. The MCA did not yield a clear preference due to close value-cost ratios and a lack of stakeholder validation. While technically and economically promising, the polder system’s societal acceptance and integration into Singapore’s urban context require further assessment. Future design phases should address public perception of flood risk, desirability of polder developments, and nature-inclusive coastal environments, supported by stakeholder engagement. Additional research into flood risk, the polder pumping system, and SDRs is recommended to improve the design and inform decision-makers on platform level selection. This thesis provides a technical foundation for Long Island’s next design stages and supports platform level decision-making. It also offers insights for other regions pursuing land reclamation developments, especially where unit rates are high and/or materials are scarce, demonstrating an integral optimization approach focused on multifunctionality and climate resilience. ... Read more

Tokyo Bay likely faces increasing risks of typhoon-induced flooding as sea level rises and typhoons intensify under climate change. A storm surge barrier (SSB) has been proposed to mitigate this risk, yet little investigated. This study presents initial considerations regarding a potential configuration for a SSB protecting Tokyo. The barrier’s requirements and location are identified through boundary conditions and a criteria analysis, respectively. For dimensioning, typhoon parameters (wind speed, atmospheric pressure, wind direction, and precipitation) are derived through probabilistic analysis. A one-dimensional model evaluates water levels during a typhoon to assess the potential SSB location and dimensions. Finally, key SSB dimensions are derived using rules of thumb. Preliminary results suggest that an effective SSB could be located between Haneda Airport and Disneyland. The concept comprises ungated caisson sections separated by a navigational gate and flow inlets equipped with flap gates, offering both storm surge protection and runoff storage capacity. However, this study represents an initial, system-wide assessment at a relatively coarse level. Despite simplifications, the study finds river-ocean interaction crucial for Tokyo, as the surge could induce river flooding during typhoons. ... Read more

The design of submerged floating tunnels (SFTs) is a challenging task, as it is often seen as a potential alternative water crossing measure for wide and deepwater environments, and the challenge is to find ways to design and construct it economically and reliably. The aim of this thesis is to provide tools for the design and assessment of SFTs. The approach is divided into three parts: first common overarching topics are addressed, to introduce the subject, but also to introduce common theoretical methods and target reliability concepts for structures and specifically for SFT. The second part is the application of probabilistic design and the use of both non-parametric Bayesian Networks and Vine Copulas, the analysis of traffic loads on an SFT and the quantification of the probability of failure due to bending moments, and a dynamic mooring analysis (DMA) is used on a hypothetical SFT model. The results of the research programme will be utilised to translate them into procedures for design and assess SFT in the first place, and also to use them in other fields of application within the industry. Modern numerical modelling tools in combination with experimental work are used to assess the structural behaviour. ... Read more

Storm surge barriers are large movable hydraulic structures that close during a storm surge to prevent coastal floods in bays and estuaries. These barriers are continuously maintained to rely on their operation when needed. Due to rising sea levels and coastal urbanization, coastal flood risk is increasing. Which barrier improvements are needed to cope with this risk increase, is unknown. This thesis presents a systematic method to find, select and evaluate barrier improvements focusing on lowering the probability of a failure to close a barrier. The method is applied to the Maeslant barrier to demonstrate its applicability. ... Read more

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. ... Read more

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. ... Read more

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. ... Read more

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.
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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
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Hospitals are part of the vital and vulnerable infrastructure in the Netherlands. Failure of such infrastructure may have severe consequences on a national scale. The Dutch flood risk management approach aims to prepare hospitals for floods through spatial adaptation. However, the current policy does not prescribe concrete guidelines for consistent decision-making and implementation of flood strategies to increase flood preparedness of hospitals. The engagement of stakeholders in this process is also arbitrary.

The main research question is: “How can flood preparedness of hospitals in the Netherlands be assessed and improved?” The main aim of this research is to quantitatively assess the flood preparedness of hospitals to enable comparison between flood strategies and to make recommendations on which stakeholders should be engaged for the implementation of flood strategies and how this can be achieved.

Six different flood preparedness indicators were selected that together describe flood preparedness of hospitals. Based on these indicators, the impact of several flood scenarios on the Reinier de Graaf Gasthuis (RdGG) and Erasmus Medical Centre (EMC) was quantitatively assessed. The costs per flood strategy are highest for “shelter in place with additional measures”, followed by both “shelter in place without additional measures” and “preventive evacuation”. “Accept” is least expensive. The number of fatalities per flood strategy for the RdGG (0,2 to 2,1 fatalities) is much lower than for the EMC (18,8 to 195,3 fatalities). Furthermore, it was determined which stakeholders should be engaged for the implementation of each flood strategy. Experts who have experience with hospital floods were interviewed to obtain their view on how these stakeholders could be engaged.

In conclusion, essential hospital functions can be categorised based on the flood preparedness indicators and flood strategies can be quantitatively compared. For the RdGG and EMC, "shelter in place with additional measures" yield the least amount of fatalities and is therefore the "best" flood strategy. The Executive Board of a hospital, hospital personnel, water boards, municipalities and safety regions should be engaged to realise the implementation of flood strategies. Experts with lived experience recommended to engage stakeholders through legislation or creating awareness.

It is recommended to calibrate the number of fatalities based on historical flood events and to analyse the vulnerability of the regional healthcare system to supplier failure during floods.
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The dissertation focussed on the kind of closure methods used, in the past and at present, to repair breached dikes and to close tidal channels by simple means. By simple means one must think about the application by (mainly) manual labour of local materials and small-scale tools and equipment. The closure of tidal channels is also required in reclamation schemes and to construct dams between islands or from an island to the mainland.
This research was in the first place aimed at Dutch closure methods as practised in the Netherlands, Germany (Schleswig Holstein) and Ghana/Bangladesh (20th century). But it was also considered useful to check the closure methods used in other countries than the ones just mentioned.
Typical topics addressed have been hydraulic features, materials and equipment applied, the importance of manual labour in these closures and their output.
Related topics addressed in this dissertation are the development in time of closure methods and the reasons why sometimes closures failed.
Though flood embankments and sea defences as part of reclamation works have been constructed from the 11th/12th century onward, limited technical information about their construction as well as possible subsequent repairs after breaching, could only be traced for six projects carried out during a period of more than 400 years (1263 – 1675).
More information could be traced about the methods and constructions used in general but not for specific projects.
The closure methods used during the period 1200 – 1700, nearly always started by dumping a horizontal sill of clay clods up to the level of Low tide. Subsequently, the gap was narrowed by dumping clay clods, and the actual closure was, finally, effected by lowering constructions made up of sink-fascines (fascines imprisoning a gravel core or clay clods) and clay clods.. Alternatively, a cofferdam could be constructed across the flow gap.
In case of low tidal ranges, a row of sheet piles or piles, closely placed to each other, was driven across the gap. Sometimes, ships were ballasted and sunk on top of the sill.
At the end of the 17th century floating fascine mattresses were introduced in closure works. They were ballasted and immersed in the breach or tidal channel and functioned as bed protection of the easily erodible soil. Moreover, the aforementioned sill could now be constructed by stacking fascine mattresses on top of each other, again up to the level of Low tide. Subsequently, the closure was performed gradually in a horizontal direction by constructing a bund in sections, comprising fascines, clay clods, stones and wattle work.
From the end of the 19th century up to the middle of the 20th century jetties were constructed across the gap to be closed. A narrow gauge railway track on the jetty enabled the dumping of clay clods or stones in the gap from side tip wagons. Until the Second World war the side tip wagons were loaded by hand and in most cases pushed by manual labour.
During past centuries in many cases simple means were not adequate to close dike breaches and, consequently, the flooded polders could not be reclaimed and had to be given back to the sea.
In the period 1969 – 1985 Dutch closure techniques based on the principles described above were introduced for tidal closures in Ghana and Bangladesh. This required the adaptation of the said closure techniques to locally available construction materials, equipment and skills. Also here, a significant input of manual labour was part of the closure operation.
Closure techniques applied in China, East-Pakistan (which, later became independent as Bangladesh), England and Japan were also studied. It was surprizing to learn that the sink-fascine (having in each country another name, other dimensions and composition) had a major role in closure projects in China and East-Pakistan and, to a lesser extent, in Japan. Moreover, the application of ropes and hawsers (as in the Dutch fascine constructions) turned out to be of vital importance. In China and Japan the closures were required to repair dike breaches along non-tidal rivers. In East-Pakistan and England the closures studied were in the tidal zone.
Finally, a tidal closure performed in Bangladesh (at the Nalian River) by manual labour and simple means in the year 2020, has been studied.
The 75 case histories presented in this dissertation reflect the art of river and tidal closures by simple means over a period of nearly 760 years (1263 – 2020) in six countries. In most cases the area of the tidal basin which could be closed by simple means was less than 2 km2 while the tidal volumes were less than 2 million m3. Production rates in tidal closures varied between 0.26 and 0.62 m3 of fill placed per manhour.
But most of the simple means described can be considered as history. There are, however, countries where cheap manual labour is abundantly available and tidal closures could still be constructed by simple means. Such closures by simple means have been described for the year 1969 (Ghana) and the period 1979 – 2020 (Bangladesh).
The insights from this dissertation will therefore also be useful for future closures constructed by using simple means.
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This dissertation investigates the use of probabilistic models, including copulas, vine-copulas, and Bayesian Networks, to enhance the understanding and reliability of submerged floating tunnels (SFTs). Despite their potential for challenging water crossings, no SFTs have been constructed beyond a prototype in Qingdao Lake, China, highlighting significant uncertainties related to their reliability under complex loading conditions. Through a case study of a hypothetical SFT in the Qiongzhou Strait, China, this research investigates the joint probability distribution of traffic and environmental loads, including wave height, wave period, and current velocities. The study develops methodologies for reliability analysis, focusing on the interactions between traffic loads, metocean conditions, and potential cascading failure scenarios. The findings demonstrate the importance of accounting for complex dependencies among variables to enhance the safety and stability of SFTs. The flexible models proposed in this research can be updated with new data, enabling continuous safety assessments and providing valuable insights for the design and planning of future SFT structures. ... Read more

Coastal regions are at risk of flooding because of their natural layout. Evidence of a changing climate, like sea levels rise and more extreme weather events, along with growing populations and cities, can make the impact of floods on society even greater. Additionally, estuary regions are threatened by compound floods, i.e., flood events generated when multiple physical drivers, e.g., the water level and river discharge, interact, even if each driver on its own might not seem threatening.

Along the Chinese coastline, particularly in the south, cities like Shanghai and Haikou are prone to flood, especially during the typhoon season. When typhoons hit the coast, high storm surges and heavy rainfall can interact leading to severe impacts. Characterizing compound flooding in coastal regions poses different challenges, including identifying the physical drivers that potentially generate a flood event, selecting an appropriate numerical model to describe the interaction between these drivers in terms of frequency and magnitude, and ensuring the quality and representativity of the available observations.

This thesis aims to tackle these challenges using cities along the Chinese coast as case studies. It seeks to (i) provide a probabilistic characterization of the physical drivers of compound floods, considering the effect of sea level rise, and (ii) integrate this quantification with a hydrodynamic model to assess the extent and depth of compound flood impacts in inundated areas. This approach can lay a solid foundation for developing flood-resilient strategies and mitigating potential impacts.

Chapter 2 introduces a design approach via conditional probability for quantifying compound flood hazards in coastal regions and its implication for infrastructure design considering the seasonal variation in surge peak occurrence. We found that along the southern coast of China, the severity of the expected rainfall events in case of a storm surge peak is larger compared to the expected severity inferred from the probability distribution of annual maxima of precipitation. Consequently, from a design perspective, implementing rainwater storage systems and facilities to mitigate hydrograph peaks is crucial for these regions.

Chapter 3 focuses on Shanghai and investigates how relative sea level rise (RSLR) affects design values for flood protection systems. We employed the D-Flow FM ocean storm surge model to reconstruct 210 historical typhoon storm surge events in Shanghai to overcome the constraint of unavailable water level records. We then applied a copula-based approach to calculate the joint probability and design value of peak water level and accumulated rainfall with the impact of RSLR. This research improves our understanding of how storm surges, rainfall, and RSLR interact, revealing how they collectively contribute to the risk of flood in coastal areas. Thus, it is crucial to monitor and predict the interplay of these factors for developing future design standards for better flood preparedness.

Chapter 4 reveals distinct patterns in the relationship between flooded areas and volume for both single-driven and multi-driven flood scenarios at the coastal city of Haikou by implementing an ocean storm surge generator and urban overland hydrodynamic model. The results highlighted storm tide (a combination of surge and astronomical tide) as the predominant factor contributing to compound flooding in Haikou. Only examining single-driven factors would underestimate flood hazard.

Chapter 5 investigates the sensitivity of inundated areas to the relative timing between the occurrence of the rainfall peak and the storm surge peak in Shanghai and provides a characterization of the consequent inundated areas based on the main flood driver(s). This is achieved by inferring from the probabilistic model the severity of the expected pairs of storm surges and rainfall events. They are then used as forcing of a hydrodynamic model to generate flood extent. We showed that the relative time between the peak of flood drivers affects the extent and depth of the flood and the flood zone classification. This can better suggest potential strategies for dealing with different types of compound flooding for coastal cities. ... Read more

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. ... Read more

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.
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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.
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