A Digital twin, a digital replica of a physical entity or system, encapsulated in a software model, represents a promising technology that has demonstrated its effectiveness for asset management in various industries. Rijkswaterstaat has gained interest in investigating the possibilities for digital twin integration in the asset management of storm surge barriers. Therefore, in this Engineering Doctorate (EngD) research, the application and development of a digital twin for a storm surge barrier is investigated, with the Maeslant barrier serving as the case study. Storm surge barriers are technically complex systems that fulfil a vital role in the flood protection of the Netherlands. A strict form of risk based asset management (ProBO) is applied to keep the barrier operational. However, the complexity and infrequent use of the barrier makes this form of asset management highly knowledge intensive. Currently it is a large asset management challenge for Rijkswaterstaat (the organization responsible for operation and maintenance of the storm surge barriers in the Netherlands) to maintain the necessary expertise at the right level. The goal is therefore to explore the following question: “How can a prototype digital twin support in investigating the application of a full-scale digital twin for storm surge barriers, to strengthen the knowledge and information in support of their maintenance and operations?” A prototype of a digital twin for the Maeslant barrier has been designed and constructed by the writer of this report, with a particular focus on the barrier’s retaining walls. For the design of this prototype (see Figure 1), knowledge from three fields had to be integrated: 1) organizational & user needs; 2) functioning of the barrier (civil and mechanical engineering); 3) ICT architecture design. As a first design step the user needs were investigated by conducting interviews with Rijkswaterstaat employees. These were translated into four applications the digital twin should fulfil to provide added value: 1. Enhancing efficiency in knowledge and information management 2. Avoiding unnecessary costs through better barrier status monitoring 3. Improving risk management with models and data analysis 4. Providing insights into barrier behaviour The user requirements were translated into design requirements to build the digital twin prototype, which is developed using Unity and Python scripts. The scripts are used for data calibration purposes and to make a connection between the digital twin model and existing models. For this prototype, a connection is made with a hydrostatic force model, a failure probability model and a pump discharge model. The Unity model acts as the user interface for the digital twin model in which a 3D data animation model of the barrier is integrated combined with data visualization panels. The functional application of the prototype is illustrated by means of three use cases: • Case 1 - Analysis of closing procedures based on observations. Quickly accessible and direct available data put users in the position to analyse the barrier closures and monitor its status by means of data visualisation, animation and model calculations. • Case 2 - Knowledge conservation and transfer: hydrostatic forces example. Increasing knowledge transfer, illustrated by an example in which hydrostatic forces acting on the barrier are animated and supplemented with visualized data that can be analysed. • Case 3 - Observing abnormal behaviour and including risk management. Using the digital twin to observe abnormal pump performances and directly calculate the impact of possible measures on the failure probability, to avoid unnecessary quick and costly decisions. The prototype is tested among 14 potential users within Rijkswaterstaat to investigate the perceived added value and the organizational feasibility of a full implementation. The results of the tests demonstrate that digital twin users recognize clear value to enhance knowledge and information management. The current prototype exhibits potential in this regard, especially for the sake of information sharing and education, suggesting significant possibilities for a full-scale (i.e. of the entire barrier) digital twin. In the long term, it is expected that the digital twin could add value in increasing the barrier’s asset management. An important notification, however, is that the reactions of respondents was diverse. The respondents with a more practical role at the barrier (e.g., the operational technical specialists) were less enthusiastic about the prototype for direct use for asset management than the higher management. The development of the prototype demonstrated the feasibility of a small-scale digital twin of the barrier. However, it does not guarantee a successful implementation of a full-scale digital twin within the Rijkswaterstaat organization. Therefore, the challenges and obstacles in implementation have been further investigated through a technical, economic, and organizational feasibility study. The prototype indicates that the available technology in the market, both at hardware and software level, is sufficient to develop a full-scale digital twin for the Maeslant barrier. However, the current state of hard- and software within Rijkswaterstaat is insufficient for full-scale implementation. Especially on cyber security, challenges need to be overcome to be able to use the maximum capacity of a full-scale digital twin. A full-scale digital twin is expected to be financially feasible: a business case study indicates that a digital twin could be cost effective within five years. The economic added value of the digital twin is estimated based on expected savings in time and maintenance cost for Rijkswaterstaat. The costs are estimated by extrapolating the development cost of the prototype. The Maeslant barrier organization is, resulting from the questionnaire, enthusiastic about implementation of a full-scale digital twin. However, achieving a digital twin with added value to the entire organization necessitates further development of the existing prototype, and a better connection to the user needs of the respondents that rated the prototype less positive. Subsequently, for successful implementation, the technically oriented Rijkswaterstaat employees need to be heavily included in the development process and must be given time to support in the implementation. All points considered it is concluded that a full-scale digital twin is, under reasonable assumption of several surmountable challenges, feasible to implement for the Maeslant barrier. @en

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.

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.

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.

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.

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.

The Hollandsche IJssel storm surge barrier is expected to last another 40 years, but replacement or renovation may be needed sooner than anticipated due to factors such as climate change and societal developments. Yet, there is relatively little known about what factors and how these factors influence the remaining life, and methods that can be used to estimate the remaining life of the barrier are lacking. This thesis aims to identify the dominant factors and associated uncertainties affecting the remaining life and to provide a method for the estimation of the remaining life of the Hollandsche IJssel storm surge barrier. The focus of the study is on the functional and technical life of the barrier.

First, the functions and structural components of the storm surge barrier were identified. For each function, requirements were formulated to support the evaluation of the impact of the external drivers. The physical decomposition of the storm surge barrier was needed to identify the dominant deterioration mechanisms. This analysis revealed that the technical life is not governing for the total remaining life of the barrier. Therefore, the focus should mainly be on the functional life of the storm surge barrier. Next, the impact of external drivers on the functional performance or technical state of the barrier was evaluated by a semi-quantitative analysis in which scenarios with the projected changes were used. The study identified sea level rise as the dominant (physical) driver affecting the remaining life of the storm surge barrier because of the potentially large future changes and far-reaching consequences.

By combining the required performance levels expressed as critical amounts of sea level rise with various sea level rise projections, estimates of the remaining life of the Hollandsche IJssel barrier were obtained. It was found that even for moderate sea level rise scenarios, there is a significant probability that the end of life of the barrier could be reached within 20 years. The estimates of the remaining life of the barrier are, however, uncertain, and a considerably longer lifespan cannot be ruled out. Accordingly, it is recommended to investigate possible measures to lengthen the lifespan and determine the best moment in time to implement these measures. The decision to implement specific measures will be dependent on the costs and benefits. Economic considerations should therefore be included as well. Furthermore, a more system-oriented approach is recommended for this kind of analysis since modifications to a certain object could impact other elements within the system, e.g. dike reinforcements affect the required closure reliability of the storm surge barrier. Finally, a more general recommendation is to perform similar studies for other critical structures as the remaining life of those structures may also be reached sooner than anticipated if, for example, functional aspects are taken into account.