Initial damage, caused by previous wave loading or other events, might affect the hydraulic stability of pattern-placed revetments. Three common types of damage are considered in this study. The effect of this assumed initial damage on the hydraulic stability and failure probability of revetments is quantified using a FEM model. This model is developed using data from large-scale flume and field experiments. Using results from the FEM model, surrogate models are created to predict the effect of each type of initial damage on the hydraulic stability and failure probability. Through the use of these surrogate models, it is demonstrated that S-shaped deformation caused by filter migration around the wave impact zone has the largest effect on the hydraulic stability decreasing up to 30%, and failure probability per year increasing up to 10,000 times. When the granular filling between the joints of the columns is washed-out, the stability decreases up to 29% and the failure probability increases up to 700 times. A missing column has a limited effect on the hydraulic stability and failure probability when there is no other (structural) damage. However, if it originates from underlying damage, it might be an initial sign of total failure of the revetment. This study demonstrates the effectiveness of finite element modeling for studying (damaged) revetments, which can be used to complement flume experiments. The results can be used to prioritize maintenance efforts in risk-based maintenance of pattern-placed revetments.

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The condition of flood defence revetments is influenced by many different degradation processes such as animal burrowing, rutting and growth of weeds. Many of these processes are shock-based rather than progressive continuous. As shocks can cause a drop in performance, this means that the condition of a revetment can suddenly decrease, meaning that revetments can have significant initial damage at the beginning of a storm. Combined with the limited detection probability of common visual inspections of flood defences, this can have a significant influence on the reliability of flood defence systems, something typically not considered in reliability analysis. In this paper we study the reliability of a flood defence system subject to shock-based degradation. Various maintenance concepts are compared for a case study of a riverine flood defence of 20 kilometres length. This demonstrates that the current maintenance concept is insufficient to satisfy the reliability requirements for failure of the revetment. Overall, the joint influence of degradation and the existing maintenance concept leads to a 20 times higher failure probability estimate compared to a typical assessment without these aspects. Next, we demonstrate that both additional inspections, and targeted interventions to reduce the impact of for instance animal burrowing, can significantly reduce total cost and improve robustness of the considered flood defence system.

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Many countries rely on flood defence systems to prevent economic damage and loss-of-life due to catastrophic floods. Asset managers of flood defence systems need to cope with the consequences of structural degradation, and changing societal and environmental conditions, in order to satisfy performance requirements and optimize societal value of flood defence assets. This is a continuous effort of planning, executing and evaluating a variety of different system interventions. These can be aimed at both reducing the uncertainty on (e.g., inspection or monitoring), or improving the performance of a flood defence system (e.g., reinforcement). Performance is typically expressed as the reliability on a system level, which in this thesis is interpreted as the life-cycle reliability: the estimated reliability with all foreseen interventions in time. The key objective of this thesis is to improve decisions on life-cycle reliability of flood defence systems. This is elaborated for three key topics, with a focus on earthen flood defences (also known as levees or dikes)...@en

EU Member States invest some €2.5 billion per year in flood protection, yet flood damages continue to increase. A new approach to the planning, design and management of flood protection assets is needed to ensure risks are better managed and asset management is aligned with broader socio-economic policies and supporting governance systems. This paper sets out a policy framework to enable this transition. The framework results from a collaboration of researchers and practitioners from around the North Sea. The findings highlight common challenges and identify four priority Policy Recommendations in response to these: ‘Break free of the silo’ by aligning planning processes; ‘Mind the gap’ between strategic and operational choices; ‘Prepare for change’ by developing multi-functional and flexible plans; and ‘Make space for innovation’ by seeking to manage risk rather than avoiding it.

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Prioritisation of flood defence maintenance is typically based on visual inspection. However, literature shows that the Probability of Detection (PoD) of visual inspection can vary significantly. Here we investigate the PoD for visual inspections of flood defence structures, the consistency of damage classification, and the influence of different variables on the PoD, such as past experience. Four flood defence sections were inspected by 22 different inspectors for a variety of damage types, such as animal burrowing and damage to block revetments. It is found that the PoD varies significantly both per damage type and inspector. Additionally, the estimated severity of damages varies significantly in comparison to the reference situation: over half of the registered damages is assigned a different severity compared to the reference, which potentially leads to incorrect maintenance measures. A likely explanation for the variation in results is the complexity of inspection guidelines and task definitions. Therefore it is advised to simplify inspection guidelines and use more focussed inspections for the most important types of damage. This likely leads to both a reduction of the number of false negatives associated with an increase in flood risk, and better risk-based asset management and maintenance prioritisation in general.

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Climate change and deterioration require a continuous effort to reinforce flood defences and meet reliability requirements. To efficiently upgrade flood defence systems, insight in costs and benefits of measures at a system level is required throughout the process of planning and design. Due to the size of flood defence systems the number of possible decisions is large, which hampers system optimization. We describe a greedy search algorithm that can find (near-)optimal combinations of reinforcement measures for dike segments. The algorithm has been validated by comparing results for 2800 different dike segments to an integer programming implementation. The difference in objective value (Total Cost) is only 0.04% on average, which is small compared to other uncertainties in assessment and design of dike segments. The algorithm is applied to a reinforcement project for a dike segment of 41 independent sections, and compared to the common design practice which uses reliability-based requirements on a section level. It is found that the resulting reinforced dike segment is 42% cheaper to construct than the one obtained from the common approach, based on the same input information. This illustrates the practical and societal value of the design approach using a greedy search algorithm in this context.

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Spatial variability and limited measurements often result in low reliability estimates of geotechnical failure modes of dikes (i.e., earthen flood defences). Required dike reinforcements are usually not executed within a few years after inception, which enables efforts to improve reliability estimates by reducing uncertainty. Often decision makers are unclear on whether uncertainty reduction is worth investing, and which (combination of) methods yields the highest Value of Information (VoI). This paper presents a framework to assess the VoI of two uncertainty reduction methods (proof loading and pore pressure monitoring) for a case study of a typical river dike with an insufficiently stable inner slope, using a decision tree. In all cases, a positive VoI was found for at least one strategy consisting of a proof load test, monitoring or both. The optimal strategy of proof loading and monitoring has a VoI of 4.0 M€, being a reduction in total cost of 25% compared to a conventional dike reinforcement. It was also found that sometimes proof loading enhances the VoI of pore pressure monitoring, which demonstrates the benefits of jointly considering different methods in a single decision tree. The decision framework yields insight in total cost and VoI of risk reduction strategies, which enables decision makers to determine where proof loading and/or pore pressure monitoring are efficient, leading to more efficient flood defence asset management.

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Uncertainties about climate change consequences, changing societal requirements and system complexity require flood protection asset managers to continuously evaluate their asset management policies and practice to manage risk and improve the resilience of their assets. However, there are many challenges in doing this, with asset operators often facing conflicting interests and major uncertainties about the future needs for asset performance. In the EU Interreg IV FAIR project, flood protection asset owners and operators, with scientific partners from the North Sea Region of Europe collaborated to develop practical guidance for adaptive asset management of flood protection infrastructure. The central component of this guidance is the FAIR framework, presented here. The framework combines insights and principles from ISO 55000 on asset management and ISO 14090 on climate adaptation with asset operator experiences to provide a practical guide for integration of asset management considerations within both strategic and operational contexts via a tactical handshake. This is a means to avoid the common lack of connection between strategic plans and operational practice. The applicability of the framework is illustrated with examples from Pilot Cases within the FAIR project, in which its value in terms of improved asset management and reduced costs has been demonstrated.

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This paper provides an overview, insights, results and a classification related to development and analyses of case studies within the scientific networking project COST Action TU1402 on the value of Structural Health Monitoring (SHM) information. With an outline of the framework and approaches, a procedure on how to quantify the value of SHM information on the basis of the Bayesian decision theory is described. Various case studies with different types of structures (e.g. stadium roof, timber structures, offshore wind parks), several types of SHM systems (e.g. structural measurements, damage detection) and with diverse decision scenarios (e.g. structural system properties, SHM system properties, different SHM systems for structural service life extension) are outlined. Approaches for value of SHM information analyses visualisation and classification, both for the purposes of development of decision scenarios and for the comparison of case study results are introduced and described. Whereas the development of value of SHM information analyses is focussed on the establishment of a decision scenario, the comparison of analyses should also include the identification of optimal SHM information acquirement strategies, actions and decision rules beside an indication on which methodological and technological readiness level the analyses has been performed. The paper concludes with open fields identified when applying the visualisation and classification tools.

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For asset management of flood defences a pivotal aspect is the quality and accessibility of available data and information. In the management of flood defences inThe Netherlands, safety assessments are conducted every twelve years. To assure the quality and consistency of these safety assessments, flood defence engineers have to make use of a comprehensive toolbox and a set of guidelines (WBI 2017). The safety assessment is one of the main starting points for the different asset management processes such as day-to-day maintenance and reinforcement/reconstruction. However, there is no clear method available to assess whether the underlying information is sufficient as a basis for decision making. In this study a framework has been developed that consists of methods for an assessment of the quality of information, an assessment of the use and accessibility of information, and a rational framework for assessing the costs and benefits of obtaining additional information. Whereas many frameworks for information management start from the information itself, here the starting point is the extent to which the behavior of a flood defence is understood, in relation to the decision or management process considered. The applicability of the framework is illustrated using various cases and has been tested in multiple workshops with experts in the field.@en

In risk analysis of riverine flood defence systems, sections of flood defences are often considered separately, herewith ignoring their interdependence, e.g. due to the hydraulic response following dike breaches in the system. In previous studies it has been found that such interdependence can have a significant influence on flood risk estimates and the spatial distribution. In this paper a method is proposed for the economic optimisation of riverine flood defence safety levels from a river system perspective. In order to deal with the computational challenge of integrating the hydraulic interactions in an economic optimisation, a surrogate model was developed. Despite the many simplifications, this model yields reasonably accurate results within acceptable time. The application of the model to a case study in the Netherlands has shown that taking into account interactions between flood defences has significant influence on optimal long term strategies for flood defences. The results suggest that accounting for interdependence in setting safety standards and reinforcement prioritisation yields a significant return on investment both in terms of lower investment cost and in terms of reduced risks.@en

Many flood defences in the Netherlands will have to be reinforced in the coming decades. Many dikes do not fulfill the safety standard due to geotechnical failure modes, largely due to epistemic, reducible uncertainties. . The Value of Information is a measure to indicate beforehand whether an investment towards reducing epistemic uncertainty is economically attractive. This paper investigates how reduction of the epistemic uncertainty in aquifer permeability might influence the Total Cost of a dike reinforcement, and the choice of reinforcement method. From the case study it is shown that the Value of Information from measurements strongly depends on firstly, whether the overall prioritization of investment for a larger dike segment is influenced, and secondly, whether the local reinforcement decision is sensitive to the parameter for which uncertainty is reduced. @en

To make informed flood risk management (FRM) decisions in large protected river systems, flood risk and hazard analyses should include the potential for dike breaching. 'Load interdependency' analyses attempt to include the system-wide effects of dike breaching while accounting for the uncertainty of both river loads and dike fragility. The intensive stochastic computation required for these analyses often precludes the use of complex hydraulic models, but simpler models may miss spatial inundation interactions such as flows that 'cascade' between compartmentalised regions and overland flows that 'shortcut' between river branches. The potential for these interactions in the Netherlands has previously been identified, and so a schematisation of the Dutch floodplain and protection system is here developed for use in a load interdependency analysis. The approach allows for the spatial distribution of hazard to be quantified under various scenarios and return periods. The results demonstrate the importance of including spatial inundation interactions on hazard estimation at three specific locations, and for the system in general. The general modelling approach can be used at a local scale to focus flood-risk analysis and management on the relevant causes of inundation, and at a system-wide scale to estimate the overall impact of large-scale measures.@en

One of the most rapidly emerging measures in infrastructure asset management is Structural Health Monitoring (SHM), which aims at reducing uncertainty in structural performance by using monitoring equipment. As earthen flood defence structures typically have large strength uncertainties, such techniques can be particularly promising. However, insight in the key characteristics for successful SHM for flood defences is lacking, which hampers the practical implementation. In this study, we explore the benefits of pore pressure monitoring, one of the most promising SHM techniques for earthen flood defences. The approach is based on a Bayesian pre-posterior analysis, and results are evaluated based on the Value of Information (VoI) obtained from different monitoring strategies. We specifically investigate the effect on long-term reinforcement decisions. The results show that, next to the relative magnitude of reducible uncertainty, the combination of the probability of having a useful observation and the duration of a SHM effort determine the VoI. As it is likely that increasing loads due to climate change will result in more frequent future reinforcements, the influence of scenarios of different rates of increase in future loads is also investigated. It was found that, in all considered possible scenarios, monitoring yields a positive Value of Information, hence it is an economically efficient measure for flood defence asset management both now and in the future.@en

In The Netherlands, inspection and maintenance are essential for maintaining stringent flood protection standards. Flood defences are assessed every 12 years to ensure they meet their risk-based safety standards,which are given as legally-binding maximum failure probabilities. Between assessments, flood defence managers are subject to risk-maintenance requirements: they must ensure that the failure probability of the defence does not increase in excess of its safety standard. However, there is no prescribed methodology to meet this requirement. In the study presented here, we developed a method which enables flood defence managers to derive inspection strategies using visual inspection data that will allow them to meet their risk-maintenance requirements.We applied the method to the assessment of grass revetments on the outer slope of the Oesterdam, one of the dams of the Dutch Delta Works. The application illustrates how – using visual inspection data, degradation information, and a failure mechanism model – inspection intervals can be derived that will ensure the risk-maintenance requirements are met.@en

Since 2017 Dutch flood protection standards are defined as target flood probabilities that all primary flood defences have to comply with by 2050. Explicitly accounting for uncertainties in probability distributions of load and resistance is an integral part of estimating the actual flood probability. Based on such estimates, many flood defences will be reinforced in the coming years, for design lifetimes that are generally 25-100 years. Therefore it is important that we correctly take into account time-dependence of both load and resistance during the lifetime. Loads are typically uncorrelated from year to year, whereas strength parameters exhibit significant correlation over time. This correlation over time of strength parameters can significantly reduce the failure rate and increase the lifetime reliability of a flood protection structure. In this paper we show the implications of time-dependent reliability for a set of illustrative cases. We consider the effect of different degrees of temporal dependence on reliability, lifetime and relative cost savings. The cases show that for common configurations, the inclusion of time-dependent effects, especially the correlation in time of strength variables, can increase the lifetime of a flood protection structure by up to 50%.@en

This article highlights recent developments in flood risk management in the Netherlands and presents approaches for reliability analysis and asset management for flood defences and hydraulic infrastructure. The functioning of this infrastructure is of great importance for the country as large parts of it are prone to flooding. Based on a nationwide flood risk assessment, new safety standards for flood defences have been derived in the form of maximal acceptable failure probabilities. A framework for the reliability-based analysis of the performance of hydraulic infrastructure is introduced. Within this context, various challenges are discussed, such as the dynamic nature of loads, resistance and reliability requirements over time. Various case studies are presented to highlight advances and challenges in various application fields. The first case illustrates how structural health monitoring contributes to a better characterisation of the reliability of the defences and how innovative measures can enhance the reliability. The second case discusses how the river system can be managed in the context of the new safety standards. The third case shows how upgrades and reinforcements of hydraulic structures can be evaluated taking into account (uncertain) future developments, such as sea level rise.

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This article highlights recent developments in the flood risk management in the Netherlands and approaches for asset and life cycle management for flood defences and hydraulic infrastructures. The functioning of these infrastructures is of great importance for the country as large parts of it are prone to flooding, and the adequate functioning of several hydraulic structures is vital for safety and other functionalities. The recent transition of the flood management policy toward more risk-based is summarized, resulting in new safety standards for flood defences in the form of tolerable failure probabilities. Using a risk-based framework, challenges in reliability assessment and management are discussed, such as the dynamic nature of loads, resistances and reliability requirements over time. Finally, various case studies are discussed to present advances and challenges in various subfields. Examples illustrate the utilization of risk-based approaches in the evaluation of innovative dike reinforcements and nature based solutions in flood management. In a third case life cycle cost analysis is demonstrated to be used to optimize the management and future proof reinforcement of large structures.@en