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Flexible Design of Urban Water Management Systems

Why is flexibility required for urban water management?

With increasing global change pressures (urbanisation, climate change, etc.), cities of the future will experience difficulties in managing water supply, drainage and wastewater. Projections of future global change pressures are plagued with severe uncertainties such as unpredictable developments, which cause difficulties when developing urban water management strategies that are sensitive to these global change pressures. Because no sufficient future predictions are possible, it is foreseeable that uncertain future drivers will change the basic conditions of the urban water management systems during their long operational life span. However for the development of urban water management strategies long-lasting decisions have to been taken, even if the future development is uncertain and it is expected that the basic for these decisions will change.

PSGS is doing research in developing a framework to generate urban water management systems that are robust, adaptable and resilient under future global change pressures. These flexible systems are characterized by their ability to cope with uncertainties and have the capability to adapt to new or changing requirements.

PSGS defines the term flexibility as the ability of urban water management systems, to use their active capacity to act, to respond to relevant alterations in a performance-efficient, timely and cost-effective way. There are three core principles of flexible design. Firstly, objective of flexible design is to overcome future uncertainties, which affect the system performance. Flexibility should guarantee the long term performance of urban water management systems by either protecting for downside effects or by capture additional value for the system when upside opportunities occur. Secondly, flexible design provides the system manager with the right but not the obligation to change the urban water management system during operation. There is a differentiation from robustness where the system performance is guaranteed without changes as well as adaptability where the adaptation is initiated from the system itself. Thirdly, flexibility should guarantee the ability to cope with future change requirements with low efforts in cost and time.

PSGS is addressing following research questions about the flexible design of water supply, urban drainage and wastewater systems:

How is flexibility measured?

Flexible Design fig 2

To illustrate the benefits associated with flexible design and to provide the possibility to assess the flexibility of different urban water management systems, approaches for the measurement of flexibility are required. The measurement approaches are precondition for the design, optimization and implementation of flexible urban water management systems.

Up to now for no approach for the measurement of flexibility in urban water management is established as standard. An overview about different measurement approaches is provided here (SWITCH D2.1.4). Measurement methods for different purposes are required. On the one hand approaches are required, which can be applied quick and easily in real world planning situation. The COFAS method developed in the SWITCH project is a pragmatic approach to measure flexibility provides simple results and is designed for quick project assessment (more information about the COFAS approach is available here (Peters et al.)). Furthermore approaches are required, which provide more detailed information to support complex decision and planning processes. At PSGS a more complex approach is developed, which offers a micro-level analysis of flexibility but requires a high amount of work (more information are available here (Eckart et al. 2011)).

How are flexibility options generated?

A significant challenge for the implementation of flexible design for water supply, urban drainage and wastewater systems is the identification of the sources of flexibility. Flexibility options are the ability to modify a system during operation to adapt it to future demands. At present the knowledge about the options, which offer flexibility, is limited. The flexibility options are specific for the kind of system considered. PSGS is doing research to identify specific flexibility options for water supply, urban drainage and wastewater systems. The costs as well as the benefits of these flexibility options are ascertained. Furthermore the best initial design has to be identified, which can be evolved most favourably over time. Information about decision support for flexible design of urban water distribution systems is provided here (Seneshaw et al.). Flexibility options for urban drainage systems are presented here (Eckart et al. 2010).

How is flexibility optimised?

Flexibility is an optimisation task. To much flexibility could cause problems like excessive costs where as to less flexibility could cause problems for the adaptation on uncertain future drivers. PSGS is developing approaches to identify an optimum level of flexibility for water supply, urban drainage and wastewater. Approaches for the optimisation of the flexible design of urban water distribution networks are provided here (Huang et al.).

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