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A1) Life-cycle performance

Start: 09/2017
End: 09/2021
Status: Active

Contact details

Wouter Jan Klerk

Delft University of Technology

Outcome

This project developed novel methods for decisions on the life-cycle reliability of flood defence systems. By optimising flood defence reinforcements at a system level, the cost of reinforcement projects can be reduced significantly. Uncertainty reduction through monitoring and proof load testing leads to lower reinforcement and risk costs, both in the short and long term. It has also been demonstrated that imperfect inspections & maintenance of flood defences lead to a failure probability increase. This contribution has not been accounted for up to now, and it demonstrates the importance of including inspection and maintenance in flood risk assessments.

Example of the activities to ensure life-cycle performance: 1) construction, 2) monitoring, 3) inspection, and 4) reinforcement (Photos accordingly by Pascal Ogink, Wouter Jan Klerk, Mark van der Krogt and the Flood Protection Program).

Motivation and practical challenge

The asset management of flood defences in the Netherlands (see Figure 1) has been built upon centuries of experience. We have taken great leaps in quantifying the performance of these structures based on failure probabilities and increased our understanding of many potential failure modes. However, as a researcher, but also as an advisor on flood risk asset management, I saw that there are some missing links in the translation of this knowledge to decisions. In this project, I considered three key topics that I’m convinced will help us take the next step in flood defence asset management. Optimising flood defence reinforcement design at a system level can lead to more effective and efficient reinforcement projects. Countering large reducible uncertainties in dike strength and pore pressures by monitoring and proof load testing can lead to a more cost-effective dike design. And quantifying the accuracy of inspections, and accounting for this in flood defence reliability estimates will greatly improve reliability estimates by itself, but also the decisions that are based on them.

Research challenge

The challenge is, therefore, to develop methods for addressing the missing connections between dike reinforcement, maintenance, monitoring, and inspection at different spatial and temporal scales. By doing so, how does, for example, the reinforcement of a diaphragm wall at one spot (Figure 1 bottom-right) help the safety targets for a larger dike section in the coming decades? How does inspection help in maintaining sufficient reliability?

Components of the research relating decisions at a dike section to a whole segment. (sources: figure 1 adapted from van Beek (2015) including dike segment scheme prepared by Richard Marijnissen.

Innovative components

This research uses smart optimisation techniques to relate measures at different spatial scales. For instance, such a technique was applied to a dike reinforcement project to derive optimal planning of different measures (figure 2.1 and 2.2). By using this technique, the system reliability requirement, incorporating all failure mechanisms, was met optimally when looking at costs and performance.

I use decision trees and Bayesian decision analysis to incorporate monitoring and inspection results to reduce uncertainty in the dike strength parameters (figure 2.3). Moreover, a pivotal part of reducing uncertainty in performance are periodic visual inspections (figure 2.4). However, the accuracy (the inspector sees, i.e., how much?) is unclear and to determine it a field experiment was conducted. The insights can be used in optimising inspection frequencies and methods.

In the last stage of this research, I will develop an approach to consider uncertainty reduction at a system level. For instance, by deriving optimal inspection strategies for revetments a large dike system, such that inspections can be done risk-based.

Relevant for whom and where?

Within the Netherlands, this research is of relevance to the regional water authorities, the Dutch Flood Protection program and the Ministry of Water and Infrastructure. In an international context, anyone with a keen interest in risk/performance-based asset management of flood defences can use it in defining projects and optimising inspections and maintenance.


The research includes key locations for the reinforcement of a dike section and the field experiment to assess the quality of inspections.

Progress and practical application

It is demonstrated that optimisation of flood defence reinforcements at a system level can reduce reinforcement costs by about 40%. For studies on the effectiveness of proof loading and dike monitoring cost savings were in the range of ~25%, due to the achieved uncertainty reduction leading to more efficient designs. However, not only investment costs, but also risk costs can be avoided. For example, when accounting for damage to grass revetments, the estimated failure probabilities differ several orders of magnitude from the estimates from the safety assessment. By including this, effective investments in, for instance, more frequent inspections can be properly valued leading to more effective and efficient asset management. Further improvements can be achieved by improving the collection of inspection data in order to more accurately estimated degradation rates, and by further investigating the impact of damage to for instance revetments on their failure probability. For details about findings, see the related outputs.

Recommendations All-Risk

Take a system perspective towards flood defence reinforcement projects to achieve more cost-efficient and transparent reinforcement decisions.
• Ensure that reduction of uncertainty is considered properly within and outside the context of dike reinforcements, and ensure that funding arrangements facilitate this.
• Consider uncertainty reduction as effective starting point for longterm adaptation strategies of flood defence systems.
• Improve the collection of inspection data to better understand degradation behavior of flood defences.
• Aim for continuous and targeted improvement of visual inspection of flood defences.

Last modified: 23/11/2021

Main researcher

Wouter Jan Klerk

Delft University of Technology

Contributors

Wim Kanning

Delft University of Technology

prof.dr.ir. Matthijs Kok

Delft University of Technology

prof. Dr. Ir. Rogier Wolfert

Delft University of Technology

Contributing partners

Proof loading and monitoring to optimize flood defence asset management

We calculate the expected value of extra information obtained from proof loading and monitoring. The additional information improves failure probability estimates for slope stability.

Mark van der Krogt

Delft University of Technology

Wouter Jan Klerk

Delft University of Technology

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Project outputs

Accuracy of visual inspection of flood defences

Insights into whether and how we can improve visual inspections, and starting points where other techniques such as drones can be of added value.

17/11/2021

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Bevat: Publication open access journal

Optimal planning of flood defence system reinforcements using a greedy search algorithm

We develop and validate greedy search algorithm that can find (near-)optimal combinations of reinforcement measures for dike segments. The approach was applied to an ongoing reinforcement project, and it was found to reduce investment costs by ~40% compared to the conventional approach.

01/03/2021

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Bevat: Publication open access journal

A framework for assessing information quality in asset management of flood defences

Methodology for scoring quality and use of available information for decision-making and assessing of the value of additional information.

28/10/2018 by Wouter Jan Klerk et al.

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Bevat: Conference proceedings

Risk based inspection of flood defence dams: An application to grass revetments

Method to derive risk-based inspection intervals using visual inspection data and a combined degradation and failure model.

28/10/2018 by Wouter Jan Klerk et al.

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Bevat: Conference proceedings

Value of Information of monitoring in the management of flood defences

Analysis of the Value of Information for different monitoring strategies combined with dike reinforcements to identify the conditions under which monitoring pore pressure is most beneficial for long-term asset management.

30/08/2019 by Wouter Jan Klerk et al.

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Bevat: Publication open access journal

Time-dependent reliability in flood protection decision making in the Netherlands

Exploration of the failure probability definition and the influence of including temporal correlation on failure probability estimates.

17/06/2018 by Wouter Jan Klerk et al.

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Bevat: Conference proceedings

Influence of monitoring on investment planning of flood defence systems

Exploring the value of monitoring for the reinforcement of a dike segment.

11/12/2019 by Wouter Jan Klerk et al.

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Bevat: Conference proceedings

Also applicable to this project

Value of information (VoI) of combinations of proof loading and pore pressure monitoring for flood defences

The decision framework yields insight in total cost and VoI of proof loading and/or pore pressure monitoring to determine the most efficient strategy for a typical river dike with an insufficiently stable inner slope.

18/12/2020

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Contains: Publication open access journal

Blogs

Bringing All-risk to practice: Martin’s recommendations

08/10/2020 by Wim Kanning

This blog is based on an informal interview between Martin Schepers (manager flood safety projects) and Wim Kanning (All-Risk researcher) on the development of...

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Events

10/12/2020

NCR Lecture: A system perspective on flood defence reinforcement projects

Wouter Jan Klerk talked on the NCR December's lecture about the Dutch flood probability standards, and how he works to optimise the way we reach our risk-based target levels. In the dike reinforcement Streefkerk-Ameide-Fort Everdingen a method was developed and applied to optimize flood defence investments at a system level.

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