Storm surge barriers are crucial for the flood protection of the Netherlands and other deltas. In the Netherlands, the reliability of flood defenses is typically assessed based on extreme water levels and wave height statistics. Yet, in the case of operated flood defenses, such as storm surge barriers, the temporal clustering of successive events may be just as important. This study investigates the evolution and associated flood risk of clusters of successive storm tide peaks at the Maeslant Storm Surge Barrier in the Netherlands. Two mechanisms are considered. Multi-peak storm surge events, as a consequence of tidal movement on top of the surge, are studied by means of stochastic storm tide events. Clusters of storm tides resulting from different, but related storms are investigated by means of time series analysis of a long sea-level record. We conclude that the tendency of extreme storm tide peaks to cluster is especially related to the seasonality in storm activity. In the current situation, the occurrence of clusters of storm tide peaks have only a minor influence of the flood risk in the area behind the Maeslant Storm Surge Barrier. We envision, however, that this influence is likely to increase with sea-level rise. The numbers are, however, uncertain due to the strong sensitivity to assumptions, model choices and the applied data set. More insight into the statistics of the time evolution of extreme sea water levels is needed to better understand and ultimately to reduce these uncertainties.@en

Sea level rise necessitates the upgrade of coastal flood protection including storm surge barriers. These large movable hydraulic structures are open in normal conditions, but close during a storm surge to prevent coastal floods in bays and estuaries. Barrier improvements lower their susceptibility to operational, structural, or height-related failures. However, there is no method to determine the relative importance of these three barrier failure types. Here, we present a probabilistic method to systematically organize barrier failures and storm conditions to establish exceedance frequencies of extreme water levels behind the barrier. The method is illustrated by an assessment of extreme water level frequencies at Rotterdam (The Netherlands), which is protected by the Maeslant barrier. Four combinations of barrier states and storm conditions were analyzed and prioritized in the following order: (1) an operational failure with 1/100 year storm conditions, (2) a successful closure with an extreme (~1/1000 year) river discharge accumulating behind the barrier, (3) structural failure, and (4) insufficient height both with extreme storm conditions (10^–6 year). The case study confirmed the method's ability to systematically explore promising barrier improvements to adapt to sea level rise, in this case, lowering the susceptibility toward operational failures.

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Coastal flooding events pose a critical risk in delta areas, since they are characterized by population growth and urban expansion. A better understanding of Extreme Water Levels (EWLs), the mechanisms generating them, and their components, i.e., astronomical tide and storm surge is of great importance as they drive the maintenance and design of flood protection systems. Therefore, a statistical investigation of them can provide new insights for more reliable flood risk mitigation infrastructures. In this study, we analyse these components and compare different probabilistic methods i.e., univariate extreme value analysis, copula functions, and Joint Probability Method (JPM) for the better estimation of EWLs. We use Hoek van Holland (NL) as a representative case study, since the dynamic conditions of this deltaic environment with man-made infrastructures render the area of strategic importance. The results indicate that a more accurate estimate of the declustering time between extreme events can be achieved using correlation of high surges and high wind speeds, taking into consideration also the wind direction. In the Southwest Delta this time estimated to be around 4 days. Furthermore, the EWLs components, i.e., surge and astronomical tide, show negative dependence. From the comparison between statistical approaches to model EWLs, results show that EWLs estimated via EVA and JPM do not vary significantly, while copulas’ seems to outperform the other methods. However, the selection of the proper copula to show the dependence is critical. As a conclusion, the analysis of the dependence between tides and storm surges can lead to more robust inferences of EWLs.

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The efficacy of risk models and risk analyses critically hinges on sufficient model evaluation. Nevertheless, the usefulness for the intended purpose is rarely systematically assessed. Poor or even lacking model evaluation of the applied risk models and analyses also troubles the asset management of storm surge barriers in the Netherlands. In practice, obvious flaws, missing failure modes and use that deviates from the original purpose regularly lead to unpleasant surprises, unnecessary costs and avoidable risks. Here, we introduce new guidelines for the quality control during the development, testing, maintenance and usage of risk analyses of critical hydraulic structures. First responses among stakeholders are rather positive since the guidelines help modelers and analysts to better understand critics and independent reviewers to structure their comments. However, the efficacy of the guidelines itself also need rigorous evaluation in the coming years. This may prove challenging as the application of the guidelines may also reveal that the organizations that operation the storm surge barriers are currently insufficiently equipped for the rigorous quality control of risk models and risk analyses. @en

Over the course of the last century, storm surge barriers have been built in several countries and proven to be successful in preventing flooding. However, the operation, reliability, and remaining life of these structures have come under increased pressure due to changing demands, intensified utilisation, and climate change. Yet, there is relatively little known about how these factors affect the remaining life of storm surge barriers. To address this issue, a framework is presented to assess the impacts of external drivers on the remaining life in a systematic manner. The framework considers both the technical state and functional performance and uses scenarios to evaluate the impact of external drivers. The application of the framework is demonstrated for the Hollandsche IJssel barrier (the Netherlands). The results indicate that sea level rise (SLR) is the dominant physical driver. Even in moderate SLR scenarios, the lifespan of the barrier may end in the 2040s if the functional performance with respect to flood protection and navigation cannot be improved. Ultimately, the study demonstrates how the remaining life of storm surge barriers could be assessed systematically and the impact of external drivers on the remaining life could be evaluated.@en

Next decades, many hydraulic structures in the Netherlands will reach their end of life. Timely mitigation requires accurate estimates of the end of life. This appears however hard since many external drivers and multiple functions may lead in many plausible combinations to insufficient technical or functional performance. As a consequence, a complete integrated assessment is rather labour intensive and time consuming. This study shows a quick-scan of the end of life of five storm surge barriers and three other critical hydraulic structures in the Netherlands. The quick-scan reveals that sea-level rise is the major driver for the end of life of most coastal hydraulic structures since it impacts both the free discharge capacity and the flood protection function. Yet, the strategy to adapt the river delta to climate change may be even more important. Future developments are however such uncertain that the life time assessments may prove especially useful for the exploration of adaptive asset management strategies and to a lesser extent as an accurate planning tool.@en

Storm surge barriers are large movable hydraulic structures which close during a storm surge to prevent coastal floods. In the regions they protect, a failure to close the barrier is often the most likely cause for a catastrophic flood. Nevertheless, flood risk assessments usually only focus on raising flood defences behind the barrier. Despite its importance, there is no general method to assess the costs and benefits of improving the closure reliability. This paper presents a model that optimises investments considering both closure reliability improvements and raising flood defences behind the barrier, using the region protected by the Maeslant barrier as a case. We substantiate that constructing the Maeslant barrier was an optimal economic decision. Moreover, we demonstrate large investments such as a redundant barrier already being economically sound with a few decimetres of sea level rise. Based on our experience with this case study, we expect the model is useful in finding strategies to adapt to rising sea levels and other developments that cause coastal flood risk to rise worldwide.

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Coastal defenses must be upgraded to combat increasing flood risk due to climate change and other factors. Storm surge barriers, large movable hydraulic structures that close temporarily during storm surges to prevent coastal floods, play a vital role in protecting estuaries. Due to the complexity of their risk analyses, important improvements are sometimes overseen. Our objective is to develop a systematic approach which is more likely to find these important improvements. We tested the method to three historic cases where important improvements were initially overlooked. We anticipate that our method can be applied to other safety systems with a large number of failure modes as well. @en

In the coming decades, the storm surge barriers in the Netherlands will reach their end of the designed life time of 100 years. Therefore, the Dutch storm surge barriers are preparing for major renovations. Next to this, as a result of the expected sea level rise, the hydraulic loads and the number of necessary closures will exceed the original design requirements. This gives urgency to look further than an one-to-one replacement or conservation and it a good moment to include changes in functional requirements. The functional end of life is, however, typically surrounded by large uncertainties. Since storm surge barriers bear multiple functions (e.g. hydraulic safety, the environment, shipping and road traffic infrastructure connection), changes in conditions can lead in several ways to the functional end of life. In this paper we explore what aspects should be added to current asset management strategy to include the functional performance of our hydraulic structures.@en

The pumping-weir complex at IJmuiden plays an important role in the drainage of excess water in the Western Netherlands. Multiple pumps need replacing as 4 out of 6 pumps near their end-of-life term. The optimal replacement strategy critically hinges on the future required pumping capacity. Yet, currently available models are not suited to assess the effect of sea level rise or extremer precipitation events as they ignore certain complexities of the water system. Preliminary data analysis in this paper showed the sensitivities of the system. The required pumping capacity is sensitive to the ability of free discharging during extreme water events. Yet, it is less susceptible to extremer precipitation events. Further research will aim at including more of the water system’s complexity in the model. Due to the node-like structure and high availability of data, a neural network modelling approach will probably be suitable.@en