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.

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.