This study examines the validity of constant failure rates in the reliability assessment of storm surge barriers, with a focus on the Stormvloedkering Oosterschelde (SVKO). Analysing a dataset of 1,501 malfunctions, including 87 critical incidents over six years, we employ Exponential and Weibull statistical models to assess failure rates. The research question—whether the assumption of constant failure rates over time is valid—is addressed with a nuanced perspective. The findings in this study reveal that neither model conclusively fits all failure scenarios, with some data supporting constant rates and other data indicating variability. The Weibull model better describes certain scenarios, suggesting variable failure rates, while in other instances, both models show comparable performance. The p-values from hypothesis testing and visual inspection of component data provide inconclusive evidence, leading to the suggestion that both constant and variable failure rates may exist in storm surge barrier components. The research contributes to the field by challenging the prevailing assumption of constant failure rates, developing a statistical framework, and by suggesting the need for a flexible, scenario-specific approach to modeling failure rates for improved reliability assessments.

Constructing a dam across a tidal basin has alway been a long-term integral solution to many water related problems of the surrounding area such as flooding, river control and fresh water storage. However, immense challenges are accompanied with the closure works of large basins. This research treats the closure strategy to close the Gulf of Khambhat in India. The project is known as "Kalpasar", which aims to create of a fresh water reservoir in the Gulf of Khambhat by constructing a 35 km dam across the estuary. The Kalpasar project has been on the Indian Governments agenda since 1986. Royal Haskoning was involved in the pre-feasibility study, which was presented in 1998. However, due to an alignment change to a more northern position, earlier proposed closure work designs are now considered out of date. To avoid irrelevance of this research through time and assist the Kalpasar development project with optimizing a new design for the closure works, this research treats the development of a fundamental parametric optimization tool to quickly perform a first-order evaluation of possible closure strategies on costs. The tool as a product along with case results are delivered to the Kalpasar development project for further design optimization. Closing the tidal basin involves closing a certain wet cross section along the chosen dam alignment through which large tidal currents penetrate caused by tidal differences up to 11 m. Complexity is caused by increasing tidal flow velocities due to increasing constriction of the wet cross section during the closure. The developed optimization tool can evaluate and compare six pre-programmed strategies to close a multi-sectional wet cross section in time on costs of three fundamental design requirement or "cost factors": Required dam material, bed protection and equipment. Using a multi-sectional storage model to compute the flow velocities in the gap, the channels and tidal flats can be individually modeled after which they are linked as a system. The model reacts as a system to changes in flow area by closing certain cross sections (a channel or a tidal flat). The individual cross sections can be closed strategically by defining their closure method (horizontal, vertical or sudden), execution phase and construction capacity. These are called "strategic input parameters". Defined for all sections, they determine the closure sequence of the system in time. Optimization is achieved when the strategic input parameters define a closing sequence which minimizes the combined cost of all cost factors. Subsequent to the storage model, three computational models are introduced to quantify the required dam material, bed protection and equipment. Based on earlier research, the material model utilizes only quarried rock for gradual closures and sluice caissons for sudden closures. The equipment model utilizes large dump trucks for horizontal closures and ships or a temporary cable-way/bridge system for vertical closures. The construction capacity is linked to material and bed protection models, since both design requirements are time dependent. Increasing construction capacity can therefore decrease these requirements. Since subsequent models largely depend on the flow velocity, an attempt to validate and calibrate the storage model was performed using results from previous research and a 2D-H Delft3D model. Deviations with respect to the Delft3D model were significantly large (factor 2-3), because storage models can only be utilized if the basin size and the remaining gap are small (usability limits). Therefore, calibration was performed by introducing an artificial contraction factor to compensate for the error in the flow velocity. An exponential relation was determined linking the error to the constriction percentage of the gap. With increasing constriction percentage, the error decreased due to increasing validity of the storage model usability limits. The artificial contraction factor can be used to optimize the closure of the Gulf of Khambhat. However, for general use, the model should be calibrated to each specific site. Case study results show that using multiple cross sections to model the bathymetry with respect to a single cross section, the optimal strategy can change from fully vertical to a combination of horizontal and vertical with a specific capacity. Utilizing the developed model for the Kalpasar case is therefore recommendedbecause the complex bathymetry creates many possible strategies and can’t be reliably modeled with single cross-sectional models. The strategy that showed the most potential for further optimization is: First closing the tidal flats horizontally by forward dumping of rocks, while closing the channels up to 40% of their depth with dumping ships after which the remaining gap is closed vertically by a cable-way or bridge system. This strategy is commonly suggested by existing literature, thereby increasing reliability and validity of the optimization model. A second case study showed negative effects of increasing construction capacity on the total cost. However, these case results are based on assumed costs and cost functions for equipment, which should be verified by contractors first. Bed protection requirements did decrease significantly by increasing construction capacity, showing potential for development of high capacity closure equipment to avoid these costs. Further future development should focus on vertical closure equipment to decrease both material and bed protection costs. To conclude the recommendations, more case studies should be performed to quantify influences of parameters already included in the model, such as the permeability of the dam, the presence of a tidal power facility and the use of a sudden caisson closure to relieve the final closure. Secondly, further validation of the storage model is essential to generate more reliable results. Furthermore, research should be performed into cost functions of several existing or new high capacity equipment for vertical closures, relating costs to construction capacity to improve usability of the optimization model.

In dit onderzoek zal antwoord worden gegeven op de vraag: Moet het falen van gemalen mee worden genomen in de watersysteemtoets? In de 6-jaarlijkse toetsing van de waterschappen wordt bepaald of het watersysteem voldoet aan de door de provincie opgestelde eisen voor wateroverlast. Op dit moment wordt er in deze toetsing geen rekening gehouden met het feit dat gemalen kunnen falen en dit falen invloed kan hebben op de wateroverlast. In dit onderzoek zijn de onbeschikbaarheid van gemalen en de gevolgen van deze onbeschikbaarheid in kaart gebracht. Met deze gegevens is het risico dat gemalen vormen voor het watersysteem bepaald.

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

Climate change is adding more and more pressure to the water systems. The area which is protected by the storm surge barrier of Ramspol have high probability of flooding for climate projections in 2050 and 2100. Nowadays, the development of the technology is providing with numerous tools and analytical models for the engineers. However, in the early stages of assessment is important to have in hand a decision making method capable to fast and reliably highlight the most promising solutions. In this thesis an assessment method of multiple flood protection improvements have been developed in order to highlight the most promising ones. The assessment method is based on three decision making parameters, the decrease of water level maximum, the cost and the ecological impact. To handle the first aspect, the wind set-up formula, a lake level formula, the normal flow depth formula and the probabilistic model Hydra-NL have been used for the water level calculations. The implementation cost has been calculated using rough dimensioning and characteristic unit values. To qualitatively assess the aspect of the ecological impact, the concept of the ecological sign has been developed. The qualified improvements can be then handled from a second detailed assessment. In this thesis the second assessment stage is only a recomendation and have not been applied. The method which developed have been applied for the case of Ramspol Barrier. From the 20 designed improvements, 5 have been qualified as the most promising and those are the construction of a breakwater in IJssel Lake, the construction of an outflow channel at Ketelbrug, the sizing-up of Zwarte Lake, the raising of the height of the dikes and the construction of flood plains.

The coastal zone is becoming more vulnerable due to growing concentrations of human population, settlements, and socio-economic activities. The Rhine-Meuse Delta is low-lying land, which makes it vulnerable to flooding. The Maeslant barrier is a storm surge barrier which should prevent flooding in the low-lying land behind the barrier. Various climate models have predicted that sea level rise will occur. The predicted sea level rise is more than what was anticipated during the design stage of the Maeslant barrier. Due to the increasing water levels, the closing frequency of the barrier will increase. This has a negative effect on the reliability of the barrier, as the components are used more often. The Maeslant barrier also needs to discharge river water during a storm closure when the water level on the rear side of the barrier becomes too high due to river inflow. This discharging process is a complex process which contributes greatly to the failure probability of certain components. Delta21 is a spatial plan to redevelop a part of the Dutch delta to mitigate the effects of climate change which are sea level rise and increased river discharges. Delta21 claims to improve the safety of the entire Rhine-Meuse delta till a sea level rise of 1.1 m. Delta21 pleads for a central approach to focus on improving pump capacity in the main water systems instead of raising and strengthening all the dikes. The main goal of Delta21 is to reduce the flood risk in the downstream area. Due to the large pump capacity available, Delta21 can replace the discharging function from the Maeslant barrier. This simplifies the closure operation of the Maeslant barrier to only retain seawater during storms on the North Sea. The effect of the simplified closure operation has consequences on the reliability of the Maeslant barrier. Therefore, the main objective of this master thesis is to find out how the failure probability of closure of the Maeslant barrier with the simplified closure operation changes in the Delta21 configuration. To fulfil the objective, the first step was to find out how the Maeslant barrier itself works and how the discharging procedure impacts the failure probability of closure. Then, a hydraulic system analysis was done to understand how Delta21 impacts the current configuration of the Rhine-Meuse delta. In the next step, the new situation with Delta21 was schematized into a simple hydraulic model which has been verified and validated. By making the variables in this model probabilistic, a Monte Carlo simulation was done to find out what the probability of a negative head difference larger than 1.5 m was. The simulation was done for the situation without and with 0.6 m sea level rise. The next step was the failure probability analysis. In the qualitative analysis of the failure probability analysis, different failure mechanisms and failure scenarios are identified for the Maeslant barrier in the current situation, and for the Maeslant barrier in the Delta21 configuration. In the quantitative analysis, the probabilities for the defined failure mechanisms and failure scenarios are calculated according to the upper bound approximation, for the current situation and with Delta21. The probability which was calculated with the Monte Carlo simulation is also used here. Ultimately, a fault tree can be composed on the basis of the qualitative and quantitative analysis for the Maeslant barrier in the current situation and the Delta21 configuration. The failure probability of closure has been reduced by a maximum of approximately 10%. This is because many systems and operations were simplified because of the simplified closure operation. Additionally, the failure probability analysis also provided insight in how the probability of flooding changed for Rotterdam with the Maeslant barrier in the Delta21 configuration. While the failure probability of closure was reduced by a maximum of 10% with Delta21, the probability of flooding for Rotterdam has increased by 53% when using the full pump capacity from Delta21. This increase is not significant since the probability of flooding remains very small. Due to the removal of the discharging function with Delta21, the probability of several flooding scenarios increased drastically which resulted in the increase in the probability of flooding for Rotterdam. With a sea level rise of 0.6 m, the probability of flooding increased approximately 500% for the current situation (without Delta21). When comparing Delta21 with no sea level rise to Delta21 with 0.6 m sea level rise, the increase was also present with approximately 375%. This is less than 500%, which indicates that Delta21 is effective to mitigate the effects of sea level rise compared to the situation without Delta21.