Integrating blue-green and grey infrastructure through an adaptation pathways approach to surface water flooding.

A range of solutions to future flood risk are available ranging from Blue-Green Infrastructure (BGI) as commonly incorporated in Sustainable Drainage Systems (SuDS) and traditional grey infrastructure (e.g. pipe networks, storage tanks, flood walls). Each offers a different profile with respect to costs, flexibility of implementation and the ability to deliver a range of wider benefits beyond their flood protection function. An important question that must be addressed when considering these approaches is what is the most suitable mix of grey and blue-green solutions to urban flooding at any location and at any future time? This paper uses an adaptation pathways approach to compare a range of alternative options to deal with current and expected future flood risk in part of a South London Borough. Solutions considered separately and in combination include grey pipe expansion, bioretention cells, permeable pavements and storage ponds. A methodological framework combines a range of existing tools to develop, assess and characterise each pathway, including a Storm Water Management Model (SWMM), a SuDs opportunity selection tool, an adaptation pathway generator and the CIRIA B£ST tool for monetising multiple benefits. Climate change is represented by the UK Water Industry Research method for establishing future rainfall intensities for sewer and BGI design. Results show combining future Blue-Green interventions with the existing Grey system are more efficient at dealing with flooding and maximising other benefits. This is true for both moderate and high emissions scenarios. The relative contribution of each option’s capital and operation and maintenance costs has implications on where the option is implemented as well as the rate of implementation. The monetisation of the multiple benefits associated with each pathway shows that their economic co-evaluation alongside infrastructure costs can change the preference for one pathway over another.EPSR