Graduation of Hidde Vader

Assessing the remaining life of the Hollandsche IJssel storm surge barrier

• Professor of graduation: Prof. dr. ir. S.N. Jonkman

• Supervisors: Dr. ir. A. M. R. Bakker (TU Delft), Dr. ir. M. van den Boomen (TU Delft), Ir. E.S. van Baaren (Deltares), Dr. ir. F.L.M Diermanse (Deltares)

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 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 expected if, for example, functional aspects are taken into account.