Within the Rijkswaterstaat asset management strategy ProBO (Probabilistic Operations and Maintenance), quantitative reliability models are used to demonstrate compliance with legal safety standards of storm surge barriers and to support risk-based operations and maintenance (O&M) decisions. However, asset managers have raised concerns regarding the accuracy of current models and have experienced difficulties when addressing exploratory questions related to maintenance strategies and system changes.

To address these concerns, the internal review and support department for ProBO within Rijkswaterstaat (CSK) proposed an alternative reliability modelling process specifically intended for the development of new reliability models for complex storm surge barriers. In this process, modelling choices are explicitly guided by predefined model values, intended objectives, and progressive refinement. For this research, the selected model values were accuracy, usability, and transparency.

The suitability of this modelling process was investigated through a case study of the Haringvliet Sluices. A conceptual reliability model was developed and verified through expert sessions. The model itself was not the primary objective of the research, but rather served as a means to evaluate the modelling process in practice.

The results demonstrate that explicitly guiding modelling choices through predefined model values and intended objectives can support the development of reliability models that are better aligned with the needs of asset managers. Experts considered the resulting conceptual model capable of achieving its intended objectives. In addition, the iterative refinement approach, in which the model was progressively developed from a coarse to a more detailed level, proved valuable in maintaining transparency and supporting well-founded modelling decisions throughout the process. At the same time, the study shows that inherent trade-offs between the selected model values remain unavoidable.

The research further highlights the importance of extending the modelling process with a governance structure that supports both the reliability model and its users. This includes clearly defining modelling objectives, maintaining iterative review sessions between model developers and a predefined review body of stakeholders, and safeguarding model quality during the operational phase through disciplined documentation procedures.

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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.
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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. ... Read more

The projected increase in sea level is expected to increase the intensity of coastal flooding threatening communities living along the coast. This, in combination with population growth and urban expansion, calls for a better understanding of Extreme Water Levels (EWLs), the mechanisms generating them, and their components, i.e., astronomical tide and storm surge, since they drive the maintenance and design of flood protection systems. Netherlands' flood defense is crucial in facing the risk of flooding given its particular geographical configuration, its large number of inhabitants, and its high value of assets. For this, a better understanding of EWLs and their components is essential to assessing the quality of current structures and developing new adaptation strategies since they drive design and risk assessment procedures. Hence, in this paper, we investigate EWLs in Hook of Holland which represents a strategic location due to the inlet of the port of Rotterdam and the Maeslant storm surge barrier. Here, we present a stepwise procedure that starts by defining EWLs, assessing drivers of storm surges on observed sea levels via spectral analysis and coherence, and ends in estimating the statistics of EWLs based on multiple approaches, i.e., univariate extreme value analysis, copula functions, and Joint Probability Method (JPM). The results show that storms in the Southwest Delta have a duration of about 4 days and that EWLs components, i.e., surge and astronomical tide, present negative dependence (the Kendall's tau $\tau = -0.50$). From the comparison between statistical approaches to model EWLs and infer design values, results show that copulas and JPM lead to an overestimation of EWL. However, EWLs modeled via copulas fit better low quantiles. ... Read more

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

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

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

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

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