The City of Galveston, Texas, has faced repeated hurricane damage, notably from the 1900 Great Galveston Hurricane and Hurricane Ike in 2008. Existing protection, mainly the Galveston Seawall, is insufficient to prevent flooding from storm surge, especially under sea level rise. Along with their plan to raise barrier islands and close off inlets to prevent water coming into the Bay, the U.S. Army Corps of Engineers (USACE) proposed a Ring Barrier consisting of floodwalls and levees to protect Galveston specifically. However, its alignment through developed areas raises concerns over port access, required pump capacity, operational reliability of traffic gates, and future city expansion.
This design study develops three alternative surge protection strategies that seek alleviate the concerns raised for the USACE Ring Barrier, along with protecting the port of Galveston, which is located between Galveston Island and Pelican Island, from storm surge.

Strategy 1 keeps to Galveston Island, placing the road that roughly separates the port terminals from the commercial/residential areas, Harborside Drive, on a levee to avoid the need for traffic gates. Local resilience measures for port terminals, particularly cruise facilities, are proposed to minimize damage and recovery time.
Strategy 2 avoids the developed area on Galveston Island by including the port area inside the protection, reducing required pumping capacity. This would entail two large-scale storm surge barriers at both entrances to the port basin to ensure port accessibility, and a levee around the current development on Pelican Island.
Strategy 3 expands on strategy 2 by including a larger part of Pelican Island, undeveloped as of yet, in preparation for future developments.
The expected reduction in flood risk over structure lifetime and performance on criteria other than cost for strategies 2 and 3 is deemed insufficient when compared to strategy 1. The preferred strategy of the 3 developed is therefore strategy 1, keeping the main protection to Galveston Island, and protecting the port with local measures. ... Read more

The increasing magnitude and frequency of storms driven by climate change have increased global demand for flood protection barriers. Sector gates are one of the barrier types, providing storm surge protection while letting marine traffic pass during normal conditions. However, no dedicated design guidelines currently exist for these structures, and the uniqueness and large scale of sector gates often make conventional design methods suboptimal.

This research investigates a method for determining wave-induced forces on sector gates using three-dimensional computational fluid dynamics (CFD) modelling with OpenFOAM and the Waves2Foam package. Accurate prediction of wave pressure distributions is essential for optimising sector gate design, and CFD offers a high resolution, which is an alternative to traditional physical and empirical approaches. The goal of this study is to evaluate the capability of 3D CFD modelling to analyse the spatial and temporal distribution of wave loads on complex geometries such as sector gates.

The St. Petersburg storm surge barrier was used as a case study. Two 2DV OpenFOAM models, based on Goda's experiments and the St. Petersburg case study, were developed. A 3D model for the St. Petersburg case study was then developed based on these results. The 2DV results showed good agreement with physical test data and confirmed that empirical methods tend to overestimate forces. It was further observed that maximum pressure occurs prior to the peak water elevation at the structure.

The 3D CFD model was simulated under a regular, non-oblique incident wave condition. Due to computational constraints, the model domain was limited to a single gate with a resolution of 12 cells per wave height. The maximum horizontal force obtained from the CFD model was 16.7 MN, falling within the range of 12.2 MN to 17 MN measured in physical model tests. However, minimum force predictions were approximately 50% lower than expected. The model identified critical loading areas, notably, at the junction between gates and at approximately two-thirds of the gate curvature from the junction point. Additionally, a node-antinode pattern in wave pressure along the barrier wall was observed, with extracted phase differences relative to the antinode at the junction between gates, providing further insight.


While significant computational resources are required, as the 3D CFD model took 2.5 weeks to simulate 250 seconds, the results demonstrate this method enhances understanding of wave-structure interactions under extreme conditions. It can be used to complement physical model testing in the detailed refinement phase of the design process. ... Read more

This study explores how storm surge barriers, essential for protecting flood-prone urban regions like the Texas Gulf Coast, can be designed to remain reliable and adaptable over their 100 year lifespans despite unpredictable environmental and socio-economic changes. Traditional flood defenses like dikes are often unfeasible in dense cities, prompting the adoption of movable storm surge barriers. However, fewer than fifty such barriers exist worldwide, and operational knowledge remains fragmented. Once built, barriers must maintain near-perfect reliability despite unpredictable factors such as sea level rise, changing vessel sizes, and institutional shifts, conditions that standard design practices often fail to accommodate.

Focusing on the proposed Bolivar Roads Gate System, the research integrates operational and maintenance needs into early design and planning. It applies the Flexibility in Engineering Design method to identify and evaluate how external drivers, like relative sea level rise and economic development (particularly increased vessel drafts), affect long-term barrier performance. The study maps dependencies between critical system drivers and barrier components, identifying the sill as the most risk-sensitive and costly to modify. As a result, it proposes an innovative, adaptable sill design: a two-stage structure that can be upgraded in the future to accommodate deeper vessel drafts, allowing the barrier to “change” rather than fail under unanticipated pressures.

The study also identifies the importance of designing for maintainability. Barrier components have varying lifespans, electrical (8–15 years), movable (50–100 years), and fixed (100 years), which demand different maintenance intervals. To address this, the research advocates for a maintainability-first design strategy, such as placing short-lived components in easily accessible locations. Maintenance should follow a state-based policy, combining preventive, corrective, and failure-based actions depending on the component’s role and risk level.

From a governance perspective, the study highlights the need for public clients to act as system integrators, balancing in-house oversight with selective outsourcing. The delivery of such complex infrastructure requires differentiated strategies across phases: detailed design should remain tightly managed in-house, while construction and certain maintenance tasks may be outsourced. Operational control, due to high reliability demands, should stay within the public domain. The governance of adaptable components, like the sill, must also remain with public authorities to ensure activation aligns with policy shifts.

Ultimately, the research proposes a bimodal strategy for barrier management. Mode 1 focuses on maintainability and predictable reliability through conventional design and maintenance practices. Mode 2 embraces uncertainty, embedding flexibility into components to adapt over time. This approach enables barriers to function as dynamic, living systems, built to endure, but also to evolve. By embedding adaptability in the most permanent elements and pairing it with tailored maintenance strategies, public agencies can maintain flood protection, performance, and accountability in the face of long-term uncertainty. ... Read more

This research develops a surrogate modeling framework to efficiently analyze and optimize a proposed pump and gate system designed to mitigate compound flooding in the Clear Lake region, Texas. Traditional numerical hydraulic models are often computationally expensive for large number of simulations. As probabilistic assessments can require $O(10^3)$ to O(10^5) runs, a cheaper alternative would be necessary for robust probabilistic assessment. This study addresses this limitation by developing a deep-learning surrogate to approximate the complex hydrodynamic behavior.

The methodology involved three main stages. First, a 1D HEC-RAS model of the Clear Lake system was adapted to serve as the physics-based "ground truth" generator. Second, this model was used to generate a training dataset of 2,400 simulations. This was achieved by systematically sampling key infrastructure design parameters (gate width $W_g$, number of pumps $n_p$, and activation levels $h_{on}$) alongside a wide range of synthetic compound flood forcings (inflow hydrographs and downstream storm surge boundaries).

Third, three distinct Long Short-Term Memory (LSTM) network architectures (Models A, B, and C) were developed to compare different data encoding strategies. Model A, a direct sequence-to-sequence (seq2seq) model, was provided with all dynamic inputs, including the known pump discharge time series ($Q_{pump}$). Model B tested the model's ability to infer dynamics by replacing the $Q_{pump}$ time series with static design parameters ($n_p$, $h_{on}$). Model C used an autoregressive structure, feeding its own past water level predictions back as inputs to dynamically infer the pump response.

The results demonstrate that the fully-informed LSTM (Model A) can successfully learn and reproduce the governing hydrodynamic processes with very high accuracy. However, models that attempted to infer dynamic behavior from static design parameters (Models B and C) show reduced performance. These models particularly struggled to capture the sharp, transient effects of pump (de)activation, leading to overly smoothed predictions. This study concludes that while LSTMs are capable of learning the physical patterns of the system. The main challenge lies in feature encoding, specifically, enabling the model to capture complex, dynamic responses from static inputs. The framework demonstrates the potential of LSTMs, but emphasizes that how the data is represented is the key factor in developing a surrogate model suitable for design optimization.
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Quay walls are an essential part of port infrastructure, providing diverse functionalities for the quay owner and users. In order to guarantee the structural safety of existing quay walls, owners might want to maintain their quay walls or decide to reassess their safety.

For various reasons, quay wall owners want to lower maintenance costs and postpone investments on their quay walls. Current methods for the reassessment of quay walls are partly depending on stochastic variables, which might lead to a rejection of the quay wall, while it is still safe to use them. Therefore, this research aims to develop an assessment method for existing quay walls based on observations of their real behaviour. This leads to the following research question:

How can existing quay walls in seaports be assessed using real-time data of their deformation behaviour?

In order to answer this question, a method was developed in this research for the assessment of quay walls based on their real behaviour. This method consists of 6 steps: .
1. The first step is the preparation of the data. All data is resampled to hourly values, in order to create a dataset with equal timestamps;
2. In the second step, Bayesian regression is used to create a prediction model of single measurement points on the quay wall;
3. The third step is to prepare the prediction models of the measurement points for the assessments;
4. The fourth step is the short term assessment of the quay wall. Real-time monitoring data is compared to the prediction model to assess if the quay wall shows safe deformation behaviour;
5. The fifth step is the assessment of the difference of the prediction models made for different measurement points on a single quay wall;
6. The sixth step is the assessment of the remaining capacity and the remaining lifetime of a quay wall.

To showcase the method and to verify and validate various aspects of the method, an example case was used. This case consists of four adjacent quay wall sections, that have been rejected by means of load/resistance based calculations. The developed assessment method was used to reassess these quay walls.

The results of this research show that the elastic behaviour of a quay wall is mainly influenced by the air and water temperature, the water level in the port, the groundwater level and direct loading. A prediction model created with Bayesian regression based on these causes was able to predict the quay wall behaviour accurate enough to use it for the assessments of the last three steps of the assessment method.

The application of the assessment method to the quay walls of the example case show that three of the four quay wall sections have enough resistance. One quay wall section shows questionable behaviour, which can be related to an early failure during the construction works.

The differences between the models of the different measurement points on the quay walls of the example case are all explainable by their location on the quay wall and the history of the quay wall. The most important explainer for the difference of the models of the different measurement points was the quay wall section on which the measurement points were located.

During the monitoring project, reinforcing measures were taken to try to reduce the ongoing quay wall deformation. The results of this research show that the measures were successful for most quay wall sections. Only at the section that was already showing questionable behaviour the situation worsened after the application of the reinforcing measures.

The conclusion of this research is that the six-step method explained above can be used to assess the deformation of a quay wall. Recommendations for future research are the broader application of the assessment method, the application of the assessment method with other monitoring techniques and the disentangling of the linear plastic trend in its deterministic causes. ... Read more

In dike safety assessment, failure probabilities are scaled up from the cross-sectional level to the trajectory level. The current Dutch guidelines simplify the upscaling process by relying on rules of thumb. This research introduces a new probabilistic assessment method, named the fragility curve method, which more accurately accounts for the correlation between dike sections and failure mechanisms. The fragility curve method combines fragility curves to transition from the cross-sectional level to the trajectory level. The application of fragility curves allows the water level to be separated from the other variables. Consequently, the correlation of the water level can be regarded independently of the correlation of the remaining variables. In the fragility curve method, the water level is fully positively correlated in space and between failure mechanisms, while the remaining variables are assumed to be independent.
The main objective of this research is to compare the fragility curve method with the current Dutch guidelines for dike safety assessment. To achieve this, both methods are applied to two hypothetical sea dike trajectories. The first trajectory is relatively uniform, comprising dike sections that differ only slightly from one another. The second trajectory contains one dominant dike section. Three failure mechanisms are considered in the assessment, namely: inner slope stability, piping and overtopping. The conclusion of this research is that the fragility curve method is recommended over the current Dutch guidelines to compute the trajectory failure probability of the geotechnical failure mechanisms inner slope stability and piping. The current Dutch guidelines are recommended for computing the trajectory failure probability of the overtopping failure mechanism. Finally, when the failure mechanisms have comparable trajectory failure probabilities, the fragility curve method is recommended for calculating the total trajectory failure probability. ... Read more

Dam failures are rare but highly catastrophic events which can be devastating for both infrastructure and the population living downstream. The recent failures of Abu Mansour dam in Libya (September 2023) and Kakhovka dam in Ukraine (June 2023) have shown that large number of fatalities are associated to these events. It is therefore important to understand the hydrodynamic behaviour of dam break waves to ultimately identify the risk they pose, especially for dams which do not have detailed data information for modelling studies. The objective of the present study is to determine the hydraulic characteristics of the waves and to predict the potential loss of life in case of a dam failure event using a simplified screening method which can be applied to a larger dam dataset. The approach of the research was to utilise the original theory of Ritter (1892) who presented an idealised solution to the Saint-Venant equations. These equations were modified by incorporating the effect of friction which eventually had a reducing effect on the idealized dam break wave celerity. Using this simplified hydraulic model the dam break wave depths and velocities were able to be determined from the required input of dam height. From additional past dam failures, the proposed limits of fatality rates in the curves of Reclamation Consequence Estimation Methodology (RCEM 2014) were validated. To determine the Population at Risk (PAR) the study utilised Geographic Information System (GIS) tools and buffer methods were tested. For a smaller dataset of 22 dams, selected based on range of dam heights from the Global Reservoir and Dam (GRanD) database, the results showed that a buffer with downstream distances determined by one hour travel time and a 1000 m width gave the most consistent estimates of the exposed population when compared to the method incorporating Digital Elevation Models (DEM). When the analysis was extended to the complete dataset of GRanD, a new buffer method was proposed because of the limitation of GIS analysis tool. This buffer method with downstream distance of 25 km was tested against three different inundation widths. Results showed that using a buffer with fixed downstream distance of 25 km and an inundation width of 1000 m gave the most closest estimates when compared with the DEM method. The study was able to highlight the total population at risk on a global scale and also zoomed into the region of Europe. Comparison between the dams allowed identification of high risk dams in terms of the exposed population. Specifically, the total potential fatalities were determined for the top ten PAR dams of Europe. Furthermore, to demonstrate the usability of the risk screening method the analysis was extended to two developing countries, Pakistan and Madagascar, where Multi Hazard Early Warning Systems (MHEWS) do not tend to exist. The results showed the difference in PAR and fatalities for each dam and provides valuable insights to develop preliminary risk management and evacuation plans both at local and national level. Despite its limitations, the study provides a quick risk screening method which can serve as an alternate to the resource intensive numerical modelling approach. Future research might be needed to reduce uncertainties and achieve more accurate estimates. ... Read more

Where water flows, prosperity follows.

Many prosperous areas around the world are situated near large bodies of water such as oceans, seas, and rivers. These bodies of water play a vital role in enhancing the prosperity of societies through various means. They provide convenient access to transportation, food, recreation, and many other benefits. However it is not only prosperity that follows, but also risk. This risk, defined as the product of probabilities and outcomes, is an inherent price that has to be paid to enjoy the social and economic fruits that are provided by these oceans, seas or rivers. As whenever one is close to a body of water, there exists a probability of a devastating outcome: A flood.

In order to effectively minimize and handle risks, the field of Flood Risk Management has naturally evolved. Within this field numerous decisions need to be made, such as determining an acceptable probability of flooding for a particular area or deciding when to evacuate if a flood is imminent. These decisions involve individuals who process information and make judgments under risk. However, it has been observed that the decision-making process is vulnerable to the influence of risk preferences. The St. Petersburg Paradox provides an illustrative example of how risk preferences can affect behavior, as individuals are only willing to pay a limited amount of money for an expected outcome of an infinite sum. By considering risk preferences, researchers were able to explain the observed mismatch between the expected value and the willingness-to-pay. This example raises the question of whether similar discrepancies between willingness to pay and expected outcomes can also arise in flood risk management, and whether the inclusion of these risk preferences can aid in the decision-making process under risk.


This research looks at ways of incorporating risk preferences into the field of Flood Risk Management. A stated preferences method is used to uncover the risk preferences of individuals for flood risk related problems, consisting of a series of flood related choice problems. The subsequent results are fitted to several commonly used risk preference models, which consist of a utility- and probability weighting function. A modified version of Prospect Theory by Tversky and Kahneman (1992) is found to best describe the risk preferences of individuals towards flood risk related problems. This research shows that individuals have similar risk preferences for flood risk related choice problems as for general (behavioural) economic choice problems. The found utility function shows that individuals have a diminishing sensitivity for outcomes that are larger in magnitude, with a greater diminishing effect for positive outcomes than for negative outcomes. Additionally, it became apparent that individuals experience flood-related losses around 1.5 times more intensely than equal gains, aligning with the current understanding of behavioural economics. The identified probability weighting function indicates that individuals overestimate small probabilities, perceiving them as greater than their actual value, while simultaneously underestimating large probabilities. The point where overestimation switches to underestimation occurs around probabilities of 0.3, in line with the results found in behavioural economics. Special attention was given to probabilities between one in a hundred thousand and one in a hundred where, instead of assuming a functional form for the probability weighting function, an additional elicitation was performed. This elicitation revealed that individuals perceive probabilities below one in a hundred as largely the same. Suggesting that people are unable to distinguish between very small probabilities, such as one in a thousand and one in ten thousand. This finding carries significant implications for the perceived level of safety in flood risk management, considering that flood safety standards typically fall below one in a hundred.

The found risk preferences are subsequently used to reevaluate the Statistical Value of Life (VOSL), previously found to be around €6.7 mln. by by de Blaeij (2003) and Bockarjova et al. (2009). Based on the found risk preferences and answers to the choice problems a new value of €11.8 mln. is found. Adjusted for inflation this value is around 1.18 to 1.33 higher than the previous found values. This research further looked at the influence of the additional risk premium in the Dutch discount rate for infrastructure projects and its effect on the safety standard in flood protections. Including a positive risk premium, which increases the overall discount rate, leads to a decrease in safety standards. This is the logical result of discounting future benefits in the form of reduced risk, while the incurred costs are borne in the present and are therefore not discounted. This decrease in safety standard is indicative of a risk seeking approach, which contradicts the risk-averse nature of the risk premium in the discount rate. To resolve this contradiction and adopt a risk-averse approach, several options for incorporating the risk-averse premium in the discount rate are proposed.

All the previous insights are used in a case study, which consists of the reevaluation of Dutch safety standards for all dike sections along rivers and coasts. The evaluation of optimal flooding probabilities for the Local Individual Risk (LIR) and the Social Cost-Benefit Analysis (SCBA) is modified to include the found risk preferences, along with the adjusted values for the discount rate and VOSL. The resulting criteria are then used to reassess the optimal classified flooding probabilities for various dike sections in the Netherlands. This adjusted evaluation shows that the ratio between the leading principles in the flood safety standards remains largely the same, but the optimal flood probabilities associated with these principles do change. Generally, these probabilities are reduced by approximately one order of magnitude when the best estimates found in this research are included, leading to a stricter safety standard for flooding. An analysis is conducted to examine the sensitivity of the different changes. This analysis demonstrates that the inclusion of risk preferences has the most significant impact on the optimal flooding probability for both the LIR and SCBA, with the probability weighting function exerting the most influence. When the best estimates for the adjusted evaluation are used, the additional costs for each resident of the Netherlands that are the result of risk aversion amount to €37 per year.

This research is concluded with the remark that the insights found in behavioural economics are useable and of value in the field of flood risk management. People tend to show the same degree of risk aversion when presented with an uncertain choice about flooding as they do when they are presented with an uncertain choice about economics, such as the problem posed in the St. Petersburg Paradox. Taking these risk preferences into account can help to better distribute the scarce resources such as time and money to where they are of most utility to society. ... Read more

Between July 12 and 15, 2021, extreme rainfall in Luxembourg, Belgium, Germany, and the Netherlands caused severe flooding. The total damage in the Netherlands is estimated to be between € 350 and € 600 million, with Valkenburg aan de Geul suffering the most damage. The economic and tourist heart of this city is located in the lowest part of the valley, therefore developing a flood reduction measure is challenging due to the limited space and restrictions in this location to protect the culture and nature.

In previous studies, different solutions were proposed for reducing the flood risk such as flood walls in Valkenburg; however, due to the locational difficulties, many options are difficult to implement except for the option of a flood bypass tunnel. A flood bypass tunnel has never been applied in the Netherlands, however; it is applied in mountainous countries. A flood bypass tunnel rapidly conveys floodwaters through densely populated areas. For Valkenburg, a flood bypass tunnel will reduce the flood risk locally while taking up little space and keeping the historic district intact.

Recent research did not look further into the opportunity of a flood bypass tunnel as a flood measure assuming it would be too expensive (Asselman & van Heeringen, 2023). However, different studies concluded that a flood bypass tunnel is a viable option (Van Dijk, 2022; Kallen et al., 2022; Leijser & Nijhof, 2022). Nonetheless, a flood bypass tunnel has never been applied in the Netherlands, and there is no prior research detailing the hydraulic and operational applicability of a flood bypass tunnel for Valkenburg aan de Geul. The main objective of this thesis is therefore to develop a hydraulic flood bypass tunnel design for Valkenburg aan de Geul which should operate to reduce the flood risk.

The objective is reached by combining the design approach for hydraulic structures with a Systems Engineering approach. First, the river system and its environment are analysed. Secondly, the basis of the design is determined. Thirdly, two alternative designs are developed from the two different types of reference projects: a passive and an active flood bypass tunnel.

The first design alternative is based on a passive flood bypass tunnel. It consists of a 2.4-meter-tall and 24.5-meter-wide Ogee weir, two tunnel tubes of 3.5 m diameter, and allows for a maximum discharge capacity of 55 m³/s. Once the tunnel is filled, the flow is pressurised. After a flood, the remaining water will be pumped out. A co-current channel is designed to prevent water from refilling the tunnel from the outlet side in a non-flooding situation.

The second design alternative is based on an active flood bypass tunnel. It consists of four vertical moving flat gates at the inlets and outlets, two tubes of 3.5 m diameter, and allows for a maximum discharge capacity of 58 m³/s. The water level will be controlled by the flat gates using a system for early automatic detection of flood hazards. The tunnel is always filled, thus pressurised. After a flood, the gates at the in- and outlets will close off the tunnel from its environment. The gates are tested twice a year, during which the system is flushed and refreshed.

The two design alternatives were evaluated according to six weighted criteria and ranked using a multi-criteria analysis in discussion with the municipality (gemeente Valkenburg aan de Geul) and the waterboard (waterschap Limburg), and a cost analysis was conducted. The first design alternative with the passive flood bypass tunnel was selected due to its high reliability and serviceability, which were highly valued, and low maintenance costs, compared to the second design alternative

The flood bypass tunnel reduces the flood risk based on discharge reduction from an estimated once every 19 years to once every 250 years in the current climate. This accounts for uncertainty due to climate change and ensures flood risk reduction in the future. The flood bypass is only active when a flood is impending; hence the water remains to flow through the Geul and does not interfere with the cultural heritage and tourism of Valkenburg aan de Geul. Due to the cost-efficient pipe jacking method, the total construction cost is approximately €40 million with an estimated yearly maintenance cost of €100 k.
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The combination of climate change and increased urbanization has resulted in cities with no historic flooding experience suddenly vulnerable to extreme flood events. Climate change increases the frequency and intensity of rainfalls, whereas urbanization decreases the total porous surface area, resulting in pluvial (rainwater) flooding. One such affected city is Valkenburg, located in South Limburg in the Netherlands. Valkenburg flooded on 14 July 2021 after experiencing an unusually heavy rainfall that deposited 146 mm of rain into the Geul Catchment, causing up to €600 million in damage. In such communities, flood early warning systems (FEWS) are emerging as possible non-structural solutions to minimizing costs of damage and loss of life from flooding. These systems are people-centered, end-to-end networks that predict floods before they are meant to occur to warn people living in vulnerable areas so that they can protect their homes, businesses, and themselves. 
The FEWS network for the Geul uses forecasted precipitation data to predict discharge and water level conditions for the Geul. In the event that the predictions result in an abnormally high water level, warnings can be communicated to the necessary parties and to the population to allow for ample preparation. At the time of the July 2021 flood, the system was offline, with experts familiar with the network believing that it would not have worked even if it was online. This project aimed to analyze the existing FEWS from data collection to communication of warnings to locate existing issues and potential sources of weakness, thereby improving the system to effectively warn for future floods. 
Each step of the FEWS was tested to find and strengthen potential weaknesses. The data inputs were analyzed and compared to the recorded precipitation that occurred in July 2021. Then, this data was inputted into the FEWS prediction models to understand how the system would have calculated the discharge and water level for that event. Both the July 2021 flood event as well as four non-flooding scenarios (summer storm, winter storm, dry season, wet season) were tested. The models were then used to create a flood map, and this flood map was inputted into the Damage and Casualties Model (SSM2017) to estimate how much in damage costs could be saved for the case with FEWS and the case without FEWS. Communication and evacuation were not extensively tested in this research project due to these components being determined by social and political frameworks. 
When inputting the precipitation data associated with the July 2021 flood, it was found that the 1D model overestimated the water level to be 76.5 m+NAP, 6.5 m greater than the expected water level. Implementing a 2D grid reduced this value to 70 m+NAP, which matched the expected water level. It was also found that both HBV and SOBEK produce simulation results that consistently do not align with recorded data, suggesting a need to recalibrate the models to better reflect the behavior of the Geul River. Analyzing the recorded discharge and precipitation data found that using forecasted precipitation data gives Valkenburg enough time to communicate warnings and evacuate if necessary. Cost-benefit analysis that compared the economic impact of warning versus not warning revealed that warning and evacuation is more cost-effective than not not warning and evacuating, even in the case of a false alarm. An evacuation in the event of a false alarm can cost 1/10 of the difference in damage costs with and without evacuation. However, false alarms must still be avoided, as they erode trust in the warning system, thereby reducing its effectiveness in possible cost and loss of life reduction. Analysis of the expected costs of damage with and without the warning system revealed that the inclusion of the warning system has the potential to reduce the total expected damage by more than 50%. 
The insights found in this project can be used to improve the FEWS for the Geul. Future research can be done to create a 2D or quasi-2D model that can predict the discharge and water levels of the Geul in a timely manner (no more than one-two hours’ simulation time). The 2D aspect is important to a warning system as the expected amount of water affects how the community prepares for the disaster. This project can contribute not only to the improvement of the FEWS for the Geul but also for the improvement or creation of FEWS for other river catchments in newly vulnerable cities. ... Read more

The Meuse is a river in West-Europe which rises at the Langres Plateau and flows from France through Belgium and the Netherlands. The river has always been an important shipping route, even though its navigability has been problematic in the Netherlands. To solve this problem seven weirs were constructed in the Dutch part of the Meuse. They are located at Borgharen, Linne, Roermond, Belfeld, Sambeek, Grave and Lith. Weirs are hydraulic structures and mainly control the upstream water level to allow for sufficient depth for shipping. Structures such as weirs generally have a technical life span of 100 years, and because the Meuse weirs were built 100 years ago they are up for replacement. Rijkswaterstaat wishes to have uniformity in the designs of the next Meuse weirs. This decreases the amount of unique components which in turn leads to the reduction of repair and maintenance costs.

The main objective of this thesis is to determine the most cost-efficient maintenance strategy for the next generation Meuse weirs. Part of the objective of this study is also to determine the influence of ship collisions on the availability and costs of weirs. In this thesis a case study is used to set up the analysis. The case study consists of two weir alternatives that were proposed as the replacement for the weir in Grave.

Based on the results for both the availability and costs of both maintenance strategies in this report it seems that the preventive maintenance strategy performs better than the corrective maintenance strategy for both weir alternatives. The availability under preventive maintenance is higher and the total costs (maintenance costs and repair costs) are lower under preventive maintenance. The availability of the weirs are mostly influenced by the failure mechanism of ship collision and the weir component “hydraulic aggregates”. The largest contributor to the maintenance costs are the hydraulic cylinders and for the repair costs the most significant contributor are the hydraulic aggregates. Ship collisions seem to influence the availability greatly, but has limited influence on the repair costs of the weirs.
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Adequate flood protection is important to many countries, but especially so to the Netherlands. With a large share of its population centers located below sea level, in so-called polders, the need for flood protection systems quickly becomes apparent. This need is even more pressing with the rise of sea levels and the increase in river discharge variability due to the onset of climate change. To future proof themselves, the Netherlands needs to maintain and strengthen their flood defences. Especially precar- ious is the situation for polders, which are low-laying areas protected by one or more dikes. From a technical perspective, the feasibility of the polder system has been proven to withstand the expected water level rise as result of climate change for at least 2 to 3 meters sea level rise, shown by Kok et al. (2008). However, research into the economic perspective on the feasibility of the polder concept has been less extensive.

To more accurately determine the economic viability of the Dutch polder concept, additions to the research of Eijgenraam are proposed that fill in the current knowledge gaps. The result of this research is a mathematical framework for the optimization of dike reinforcements in two dimensions, the lifetime of the structure and the crest height increase of the dike. The framework consist of a discounted Cost-Benefit Analysis with a financial constraint and a constraint on the maximum allowable time before reinforcement is needed. This framework contains stochastic elements in it’s parameters and a stochastic model for the discount rate. The derived framework was subsequently used to analyse two case studies based on regions in the Netherlands. The two case studies were based on the dikering of IJsselmonde (dikering 17) and the dikering of Walcheren (dikering 29). The results were determined for the two climate scenario’s posed by the IPCC and KNMI by means of a Monte Carlo simulation.

This research has opened up the possibility to compare alternatives over different time periods and re- inforcement measures with different constraints and stochastic parameters, adding to the work done by Eijgenraam. As such, a more risk-informed discussion on the general viability of the polderconcept can be had, ultimately resulting in a more informed decision on the future of the polders in the Netherlands. ... Read more

The historic inner-cities in The Netherlands are largely known for their iconic channels and their accompanying quay walls, of which a significant number were constructed over 100 years ago. Due to the limited available space in the sub-surface of the urban environment, a high number of utility lines (i.e. potable water pipes and sewer systems) are situated in the vicinity of these quay walls. In recent years, a number of quay wall collapses have occured in the inner-city of Amsterdam, some of which have been attributed to utility line leakages. However, research into the interaction between inner-city quay walls and utility lines is lacking. Thus, the aim of this report is to answer the following question: "How does utility line leakage relate to deformation and failure of Amsterdam's inner-city quay walls and when does this interaction become significant?". The interaction between utility lines and inner-city quay walls works in both ways, thus the research is split up accordingly. The effects of utility line leakages on quay wall displacement and failure were qualitative studied using a literature study. The effects of quay wall displacement on utility line leakages were quantitatively studied using an analytical model. In this model, the interaction between utility line and surrounding soil was represented using a beam on a Winkler foundation, i.e. a beam supported by a distributed spring. The stiffness of the spring was represented as bi-linear, resulting from the equilibrium bearing capacity of the soil. Quay wall displacements ranging from 20 up to 100 mm were applied to the most common types and outer diameters of utility lines found in the vicinity of quay walls. Utility line leakage is deemed to occur if a predetermined threshold is passed of either maximum angular deflection, maximum allowable bending moment or maximum allowable shear force, each resulting from the utility line displacement. Although the scope of the study is the inner-city of Amsterdam, the study can be used in other cities with inner-city quay walls, given the circumstances are similar.

The literature study showed that quay wall displacement and failure due to utility line leakage follows from internal erosion processes. Two requirements have to be met for instigation of internal erosion: a local head difference between the water level in the channel and the groundwater level in the soil body behind the quay wall, and an open connection in the quay wall structure in the vicinity of the aforementioned local head difference, enabling the flow of soil via water. The rise of the groundwater level can be the result of a potable water pipe leakage, but can also follow from external factors like heavy rainfall. Three forms of open connections were appointed. The first is scour protection screen leakage, which can result in erosion underneath the structure. The second is quay wall floor leakage, which can result in both erosion underneath structure and erosion in the soil body behind the quay wall. The third is sewer leakage, which can result in erosion in the soil body behind the quay wall. In the latter, the aforementioned head difference is not required. This is because the direction of groundwater flow is not towards the channel, but towards the sewer leakage, given that the sewer pipe is located below the groundwater level. Erosion underneath the quay wall floor can result in quay wall displacement towards the channel, while erosion in the soil body behind the structure can result in the formation of a subsidence pit.

Both erosion underneath- as well as behind the structure can result in (further) deformations of utility lines. The former through quay wall displacement towards the channel, resulting in local soil displacement in which said utility line is embedded in. The latter trough local loss of soil, resulting in a local reduction of support. Both have the potential to result in relative utility line displacements, which can result in leakages. This process is can be denoted as a positive feedback loop. Actual failure of the quay wall due to utility line leakage can come in the form of collapse of the quay wall towards the channel or collapse of the road on top of the structure in the formed subsidence pit. Due to the dependence on external factors, quay wall failure resulting from utility line leakage can be described as a second order effect.

It was found that exceedance of the maximum allowable angular deflection of the utility line joints is most likely to result in leakages. Leakage due to exceedance of maximum allowable bending moment is relatively less likely but still significant, while leakage due to exceedance of maximum allowable shear force is unlikely. In all utility lines, a higher bending stiffness resulted in a lower susceptibility to leakage. If utility lines are deemed susceptible to leakage, it is advised that these are monitored intensely. ... Read more

The objective of this research is to design and evaluate a new type of rolling gate for the Western lock (Westsluis) in Terneuzen, for which all sensitive and heavily loaded mechanical parts are both easily accessible and located above water. Having all mechanical parts above water not only makes them easier to inspect and maintain, but it also makes them less prone to fouling or obstruction by debris. In this way, the risk of premature gate failure due to failure of wheels/rails is expected to be lower, increasing the overall availability during the lifetime of the lock.
Six variants are designed and evaluated using a qualitative Multi Criteria Analysis (MCA) and the Cantilever rolling gate is evaluated most feasible. The Cantilever rolling gate concept is a system in which all the rolling supports are located on an extension to the side of the gate. The gate is balanced by a counterweight and in a way 'hangs' in the gate chamber. The carriages are connected to the gate by hinges, which ensure the perpendicular horizontal movement of the gate in closed position to seal the lock against rubber profiles on the sill, gate chamber and recess.

Subsequently the Cantilever rolling gate is further elaborated at the case study location by means of structural calculations. The focus of the design calculations is on the load balance of the gate and supports in the longitudinal direction. To minimise the required extension of the gate chamber, the added cantilever length is kept as short as possible. To find the most optimal cantilever length, limits are defined regarding the minimum required force acting downwards on the carriages to maintain equilibrium and the maximum design capacities of the wheels and rails with respect to strength and fatigue.
Based on the performed calculations, the most optimal Cantilever rolling gate design for the Western lock in Terneuzen has the following properties; an added cantilever part with a length of 16.6 meters; a cantilever truss structure constructed of Circular Hollow Sections (69 t); a counterweight directly below the back carriage (1083 t); an 8-wheel front carriage and a 4-wheel back carriage.
The added cantilever structure of 16.6 m extends the gate part of 44.6 m by 37%. The designed cantilever rolling gate fits at the location of the case study, but the lock chamber and rails should be lengthened by 16.6 m to fit the extended gate.
Based on this research it is expected that the concept of a Cantilever rolling gate is technically possible. However, it is not yet certain whether the Cantilever rolling gate will also be feasible in practice. Some additional development is still required before the design can be considered fully technically feasible. For example, it is important that the horizontal force transmission and guidance is further evaluated. It is also recommended to calculate the actual availability and determine whether the difference in availability between the Cantilever rolling gate and the conventional rolling gate outweighs the cost.
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Because of the fortunate absence of great flood events in The Netherlands during the second half of the twentieth century, no physical data was added to the structural understanding of flood fragility on walls. Considering that during the same period the cavity wall became standard in the construction of houses, a certain inconsistency can be recognized between the expected and observed (structural) behaviour of a modern wall during flood events. Nevertheless, failure, or collapse, of residential buildings is included in the Dutch flood protection standards as an important cause of damage and one of the main reasons for loss of life. It is generally believed that the developments in terms of building materials translate to a safer residence i.e. less prone to flood actions. This consensus is also found in the trade-off for certain mitigation measures, especially in areas where horizontal evacuation is difficult. An improved understanding of the flood fragility of a modern cavity wall is thus needed to prove the general consensus or to adjust the current mitigation measures to comply with the allowed fatality risks.

A window-featured cavity wall section was constructed at the Flood Proof Holland facility, using calcium silicate bricks, fired clay bricks, and a weaker mortar to partly account for the virgin effect of any newly-built wall. Both inner and outer walls were connected with adequate wall ties. The wall section was subjected to several hydrostatic pressures at both sides. These experiments were performed to physically grasp the deformations corresponding to certain flood scenarios affecting cavity wall sections from ordinary terraced houses. Additionally, the effect of the window was investigated; both on the stability and its contribution to the water height inside a residence.

Computations showed that the cavity wall in a one-way bending configuration starts to show significant cracks between 1.3 and 1.6 meters of outside water level. Because of the brittleness of the masonry, this would imply failure. It was further found that the non-linear deformations would reach 4 millimeters. Considering that for these water levels the internal moments were still far from their maximum capacity, the results suggest that failure occurred due to cracks that were forced to form because of the deformations. This indicates that modern cavity walls are still quite vulnerable for floods and their flood actions. The influence of the hydrostatic pressure, however, can be decreased considerably by a water level inside the residence that acts as a counter force. Contrary to what was expected, the window does not contribute to this inside water level, since its leakages turn out to be negligible. To keep the damages to a minimum and preserve the overall stability, it is advised to seal the residence to a height of 1.0 meter; floods that exceed this sealing should not be countered anymore and rather be allowed to enter the residence.
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Coastal flood risk is expected to increase over the 21st century as a result of climate change and economic growth, which makes low-lying regions especially vulnerable. Global screening techniques are needed for a more widespread use of NBS in these flood prone coastal regions. This research expands on the current assessments done by developing a quantitative global screening method that evaluates the costs and benefits for two defence approaches; 1) increasing the dike height, 2) a hybrid solution that includes increasing of the dike height in combination with restoring mangroves and/or corals. The screening method is based on Van Oord’s Climate Risk Overview tool, in which, globally, coastal hotspots are indicated that have a predefined risk of flooding in the 21st century. The steps added by my screening method include; 1) determining which
NBS can be applied depending on the local physical conditions, 2) determining the costs for both NBS and conventional hard solutions, 3) determining the increase/decrease in flood risk of the different interventions for current and future conditions, 4) monetizing additional benefits that NBS provide, 5) assessing the benefits and costs to determine if NBS are the most optimal solution. The results of this global method are inherently limited by several simplifying assumptions and by the lack of high resolution local data, which influences the cost/risk estimates and corresponding site identification. For 2.6-3.3% of the coastal hotspots, NBS can reduce the investment costs in addition to being cost-beneficial. There is potential for expanding this work by adding sea grasses, salt marshes and oyster reefs as vegetated foreshore systems, and by including more thresholds to make the criterion for potential sites to apply NBS more strict.
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The Segment barrier is a conceptual design for a storm surge barrier consisting of individual concrete segments which can be combined to form a barrier. The structure is designed with the ability to expand in size to deal with the uncertainties of global mean sea level rise by stacking the individual segments into various configurations. At its core, the Segment barrier is a temporary structure that can be assembled before the advent of a storm surge and dismantled afterwards with the intent of mitigating the long-term environmental and ecological impact associated with permanently fixed hydraulic structures. However, the Segment barrier is equally able to function as a typical structure with a long design life if necessary. Long Island Sound served as a case study for the development of this concept. The severity and frequency of annual hurricanes is expected to increase within this century and recent examples of hurricanes have already shown the devastating impact to New York City and the wider coastal region. The area of Long Island Sound is expected to have a crucial role in providing protection for millions of people through the development of flood protection measures. The development of this concept involved analyses on the structure’s overall stability, local wave climate, structural design of prestressed concrete elements and the applicability of the barrier for this region. An important aspect of this concept is optimization for which a number of suggestions are provided to inspire further research and design efforts. This thesis establishes the foundation for a new type of storm surge barrier and aims to convey the potential of this concept for wider applicability around the world. ... Read more

There is a lot of uncertainty in climate change developments, and therefore in its consequences. For the flood defence system of the Netherlands, an important consequence of climate change is the sea level rise. Marine locks are large, rigid, and intricate structures, with a required lifespan of at least 100 years, for which often design decisions have to be made for many decades, which is not made easy by the uncertainty of sea level rise. In this thesis, it is first analysed by means of a probabilistic model how sea level rise alters the failure probability of a marine lock, and at what degree of sea level rise the safety norm is reached. This analysis also results in knowledge on the critical lock characteristics which are required to be improved once the safety norm is reached. Once the safety norm of a lock has been reached, the lock can either be adapted, or completely replaced. Adaptation concepts were developed to improve the critical lock characteristics. To compare these adaptations to the lock replacement, an adaptive pathways map was drafted, which visualises the implementation of adaptations and replacement in regard to the sea level rise development. It was found that the application of a minor adaptation is always preferable over a replacement, but that the benefits of a drastic adaptation depends on the functional and structural state of a lock. When a lock eventually has to be replaced, because of sea level rise or any other reason, the question still remains how to implement the uncertainty of sea level rise into the design. Instead of designing for a conservative sea level rise scenario, one can create an adaptive design. This is a structure which can be adapted over time, meaning costs are saved in case of a mild sea level rise scenario, but the lock can still be made sufficient in case of a severe scenario. Again, an adaptive pathways map was drafted to compare the application of a conservative lock to several adaptive lock alternatives. Unfortunately, no general recommendation can be made for adaptive lock designs, as the advantages and disadvantages of the alternatives depend on the specifics of a lock. ... Read more

Immersed tunnels, located in waterways, could be a limiting factor in the dredging in waterways. This dredging is required since cargo vessels draught increased the past decades. In this thesis a new method is defined for temporarily, effectively, re-floating immersed tunnels. With this method extra risks arise, for these risks’ measures are given. The validity of this method is proven by applying the method a relevant case study. This case tunnel is the Wijkertunnel, consisting of six elements and a total immersed length of 600 meters. It showed that the maximum deepening available is 6.60 meters. It is concluded that the impact of the risk measures is limited. Finally other immersed tunnels are compared to the Wijkertunnel. For these tunnels the different types are described, and the impact of these differences are discussed. It showed that for all the immersed tunnels the method is viable, except for immersed tunnels with a very few elements. ... Read more

The number of fatalities due to a potential flood event is traditionally determined utilizing 'mortality functions’. Data of recent large-scale flooding in the Netherlands are not available since the Netherlands was successful in flood prevention. Therefore, only data from the last coastal flood event in 1953 with 1795 direct fatalities are available. The mortality functions are empirical relationships to provide mortality as a function of three explicit flood characteristics, namely water depth, flow velocity, and water level rise rate. Many more factors are included implicitly since the functions were derived from 1953 data. These underlying factors are thus based on the circumstances of the coastal flooding in 1953 and might not be representative anymore for future flood events elsewhere in the Netherlands. The three flood characteristics in current flood risk assessments are determined by means of coarse flood simulations. Since modern software is becoming more advanced, more detailed flood simulations are becoming possible. Therefore, the applicability of the mortality functions needs to be studied if finer model resolutions are used. This report presents the case study of river area the Bommelerwaard in which the validity of the 1953-based functions, possibilities for alternative functions, and finer model resolutions in hydrodynamic models are tested and analyzed with regards to their impact on flood fatality risk. A hydrodynamic model is developed using the new software program D-Flow Flexible Mesh which is able to apply finer resolutions at locations that require more detail. The different model resolutions that are tested are 100m and 25m, and 5m for the area close to the breach. The flood simulations with these model resolutions resulted in similar outcomes for the number of estimated fatalities in this case study. Overall, the 100m model is preferred because it is sufficiently able to indicate the dangerous locations, provide the order of magnitude of the flood characteristics, while it demands short computation times and matches the level of detail of the data of 1953. However, it is recommended to model the area around the breach (‘breach zone’) with finer model resolutions because the resulting higher local peak velocities are relevant for potential building collapse. For the areas around obstacles and underpasses, it is also recommended to use finer resolutions or to make use of 1D objects or fixed weirs. This study concluded that finer model resolutions at dangerous locations have an impact on the individual risk value of the neighbourhood, and this can have consequences for the maximum individual risk value and thus the overall safety standard of a large dike ring. Furthermore, the case study illustrated that compartment dikes have a significant impact on the local mortality because of the high water level rise rates just upstream. It is recommended to look into possibilities to reduce this high local mortality rate and hence, individual risk, for example by optimizing the location and number of compartment dikes or exploring the effects of openings in the dikes. Moreover, this study identified the discussion points in the current Dutch loss of life approach by a literature study, knowledge of recent flood events abroad, and loss of life approaches internationally. Alternative mortality functions are proposed based on the literature and analyzed through sensitivity analyses in the case study. It is recommended to substantiate and take into account the factors water arrival time, improved building characteristics, and age in the loss of life approach. Preventive evacuation is already taken into account in this approach, but in addition, water arrival time can be included by means of fleeing. This study shows that water arrival time has a great effect on the number of fatalities because some areas have relatively large arrival times and this enables inhabitants to flee the area. Emergency response is thereby of crucial importance. Also in 1953 this factor proved to be relevant. The improved building characteristics compared to 1953 are shown to have a limited impact on the absolute number of fatalities in this case study but it reduced the maximum value of the individual risk and is thus of relevance, especially for dike ring areas with large water depths (>2.1m) and high rise rates (>0.5m/h). Moreover, this study underlines the vulnerability of the elderly during flood events. Since the age distribution has shifted since 1953 and significantly more elderly are present in society nowadays, it is relevant to take this explicitly into account. This case study shows that correcting for age can have a significant impact on the number of fatalities. The impact on the individual risk is limited, but this depends on the spatial distribution of the elderly and should be further analyzed. Finally, the individual risk is sensitive to the configuration of the neighbourhoods. It is therefore also recommended to look into more robust approaches to determine the individual risk. ... Read more