Impact of blue/green and grey infrastructure interventions on natural capital in urban development

Natural capital can describe the multiple benefits people get from the natural environment. Both global and national trends show that natural capital has been declining overtime due to urbanisation and natural resource depletion. While urban intensification adversely influences natural capital, it is recognised that blue/green infrastructure systems driven by the need to manage stormwater (e.g. rain gardens, swales, ponds etc.) can mitigate such impacts. To capture this potential there is a need to mainstream natural capital assessments at the relevant scales to inform planning decisions and outcomes. The aim of this study is to investigate how future intensification will affect natural capital in a residential area of the London Borough of Sutton. The existing drainage network has exceeded its capacity and recent extreme rainfall events have led to increased flooding incidents. The local authority intends to integrate blue/green infrastructure with the existing grey infrastructure to promote sustainable growth. In this context, this study makes use of the Natural Capital Planning Tool (NCPT) and a GIS-based analysis to inform the impact of proposed developments on natural capital. Hydrodynamic modelling shows that blue/green interventions mitigate flood risk within the intensification zone and beyond. Different natural capital indicators, such as flood risk regulation, are assessed in different spatiotemporal scales and this poses a challenge in producing a coherent natural capital accounting score.