Are we planning blue-green infrastructure opportunistically or strategically? Insights from Sydney, Australia

Strategic placement of water-sensitive urban design (WSUD) is essential in optimising its performance and maximising co-benefits. However, little is known about the current placement and interconnectedness between WSUD assets and the performance of current planning strategies. We evaluated the placement of existing WSUDs in a highly urbanised catchment in Sydney, Australia. We used a three-step process: (1) compiling a comprehensive spatial asset database, (2) performing spatial correlation analysis between asset locations and biophysical, urban form and socioeconomic variables and (3) using a novel approach to facilitate holistic understanding through analysing asset locations compared with the outcome of the spatial suitability analysis tool (SSANTO). WSUD coverage was generally low, with clustering in some municipalities. Placement was constrained by physical variables, such as slope, limited space and varying land uses. However, placement was not detectably influenced by most socioeconomic variables. SSANTO's suitability score at asset locations was only slightly higher than average, suggesting that the placement of existing WSUD was opportunistic, rather than strategically planned. Further development and implementation of tools able to account for spatial constraints will help guide future WSUD placement as a component of green urban stormwater management.