Katwijk is a small coastal town located at the old mouth of the River Rhine and along the North Sea. The national flood safety inspection of the coastal area demonstrated the need for the construction of a new sea dike to protect some 4000 people living in the city centre. The dune-covered coastline near the town is a tourist area that lacks sufficient car parking. To make best use of space and funds, the municipality and coastal authorities decided to combine functions and use the dune-area for both flood protection and parking. As this was a first-time project, it was yet unknown how interdepencies of functions would affect the performance of this multifunctional flood defense. In this research project we customized an existing performance analysis method to look into this issue. @en

Multifunctional use of flood defences is proposed in the Netherlands to increase the synergy between flood protection and urbanism and to enhance the cost-effectiveness of flood protection. Once a multifunctional flood defence is constructed, it will become technically and financially hard to modify and adjust the system configuration. Such an infrastructure should maintain its desired performance although the system environment (physical, technical, political) evolves dynamically and steadily. In the presence of uncertainty about the future changes, successful design and management of multifunctional flood defences will require the capability to handle changing conditions. This research focuses on flexibility as a way of increasing the system capability to handle uncertain changes of future. The main objective of the research is thus to systematically explore different aspects related to incorporating flexibility in the design and management of multifunctional flood defences.@en

The very existence of the Netherlands and its prosperity is tightly linked to the provision of sufficient and reliable flood protection. Flood risk can change, as it is influenced by continually changing environmental and socio-economic factors. In such a dynamic situation, maintaining sufficient safety requires continuous investment in maintenance and reinforcement of the flood defenses. Often, flood defense reinforcement requires more space, which is scarce in densely populated urban areas. While the competing needs of housing, commerce, transportation, and agriculture have to fit in a relatively small surface area in the Netherlands, the safety of the living environment and the quality of the landscape have to be maintained as well. One way that has been suggested to deal with the conflict between flood protection and urbanization is by combining activities in the available space. This can be achieved by integrating urban functions into the flood defenses; these are referred to as multifunctional flood defenses. @en

Dike reinforcement decision making under uncertainty is a challenging task. This paper examines whether increasing the managerial flexibility of a reinforcement strategy can improve the lifecycle cost-effectiveness for the Dutch flood defences. Two flexible strategies are developed and compared to an inflexible baseline strategy. The strategies are examined in eight case studies, two sea level rise scenarios, and four discount rates. It is shown that increasing the flexibility of reinforcement can improve the cost-effectiveness for monofunctional dikes. The relative cost-effectiveness of flexible strategies decreases as the dike becomes multifunctional. The results prove to be sensitive to the choice of the scenario and discount rate. It is concluded that reinforcement decision making should address uncertainty explicitly and account for smaller scale developments around the dike. It is suggested that current engineering practice can be improved if the possibility of a variable design lifetime is also addressed in reinforcement decision making.@en

The very existence of the Netherlands and its prosperity is tightly linked to the provision of sufficient and reliable flood protection. Flood risk can change, as it is influenced by continually changing environmental and socio-economic factors. In such a dynamic situation, maintaining sufficient safety requires continuous investment in maintenance and reinforcement of the flood defenses. Often, flood defense reinforcement requires more space, which is scarce in densely populated urban areas. While the competing needs of housing, commerce, transportation, and agriculture have to fit in a relatively small surface area in the Netherlands, the safety of the living environment and the quality of the landscape have to be maintained as well. One way that has been suggested to deal with the conflict between flood protection and urbanization is by combining activities in the available space. This can be achieved by integrating urban functions into the flood defenses; these are referred to as multifunctional flood defenses. @en

Flexibility is often proposed as a valuable capability to cope with uncertainty and change. However, there is no consensus about what constitutes flexibility across the literature. A review of publications on flood management, real options and manufacturing reveals remarkable commonalities along with substantial inconsistencies in the use of flexibility. These observations are used for structuring the discussion of flexibility in this paper. A framework is proposed in the form of four self-consistent and step-wise questions: (Q1) why is flexibility needed; (Q2) what is it that flexibility is required for; (Q3) what are the dimensions of flexibility; (Q4) what needs to change or be adapted? In order to answer the questions in the context of multifunctional flood defences (MFFDs), eight characteristic features of flexibility in connection with the four questions are distilled from the synthesized publications. Subsequently, a working definition of flexibility is developed. An illustrative case study examines the framework’s potential for the development of a MFFD. It is shown that the iterative use of the framework can serve as a guideline for identifying and evaluating flexibility for MFFDs. The paper ends with some challenges for future research.

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