A resilient approach to urban flood management: an options value model applied to explore mechanisms of resilience

In large technology systems – such as flood defence and urban drainage and sewerage – the consequences of choices for interventions have to be ‘lived with’ for a long time and touch many aspects of society. This implies that associated uncertainties are likely to grow large and may arise from a number of aspects, such as climate, society and urban land use. Management for long-term, sustainable solutions thus requires a shift in emphasis from risk to uncertainty, and with this the concept of resilience comes into clearer relief. Resilience has been promoted as an aspirational concept or principle to guide new approaches to urban flood management (UFM) and integrated urban drainage management (IUDM) that aim to enhance its capacity to cope with change and to reorganize while undergoing change.

The adoption of a resilient approach in real-world flood management systems has proven difficult because of a limited understanding of effective interventions and their impact on the resilience of the system. A clear framework to formulate management strategies and plans for flood resilience and to assess the contribution of different variables to performance and resiliency has not been devised as yet. This leads to the overall research question (to be detailed below):

- How interventions in urban flood management systems should be planned, designed and managed to contribute to increased resilience?

The objectives of the research in this thesis are to provide (a) insight in the influence of different system structures on the resilience of UFM systems, (b) lessons for the planning, design and management of interventions in UFM systems, and (c) a stochastic dynamic programming model to value adaptation options under uncertainty.

The focus of this thesis is on resiliency of urban water systems. The first two research questions are to establish the object of research:

RQ1: Which definitions of resilience are useful and applicable in the context of UFM systems?

RQ2: What leads to resilience in UFM systems, and which variables should be measured in a study of resilience in UFM systems?

In this thesis, a framework is developed for the planning, design and management of interventions in UFM systems. This framework is intended to provide guidance for the main stakeholders that are able to implement the responses. For the development of this framework the following research questions are defined:

RQ2: How different system structures affect the resiliency of UFM systems?

RQ3: How to include the dynamic context and the sources of uncertainty in the assessment of UFM systems?

RQ4: How to compare solutions when the number of response options is very large?

RQ5: How to address all these issues together?

It is assumed that the answers to the above questions can throw more light to the choice between the range of mitigation measures and the timing of interventions. Secondly, in terms of the tool development, the conclusions would help while analyzing to which extent risk, uncertainty and irreversibility can be modelled by adapting existing flood modelling systems.