Replumbing cities from gray to green: Exploring controls on stormwater infrastructure transitions

Background/Question/Methods

Communities are faced with the challenge of meeting federal mandates that require reductions in pollution from stormwater and combined sewer overflows. Communities can choose between two main approaches to address water quality issues; gray infrastructure (e.g., storage tunnels) or green infrastructure (e.g., bioswales). Transitioning from centralized gray infrastructure, typical in many cities, to decentralized green infrastructure remains challenging because of social and institutional barriers. We explored the human-water system in four U.S. cities and asked; how has the stormwater infrastructure system changed over the last twenty years?; and what socio-political factors influenced a shift in management style from gray to green approaches? Study cities included, Phoenix, AZ, Philadelphia, PA, Portland, OR, and Pittsburgh, PA. In each city, we constructed an infrastructure inventory detailing programmatic goals, investments, and installation of gray and green infrastructure. To explore socio-political factors we developed stormwater governance typologies to group sewer authorities based on the type of government and the complexity and scale of management. 

Results/Conclusions

Our characterization of stormwater governance indicated that Philadelphia and Portland have centralized governance with one authority owning and operating the sewer and stormwater systems within the service area. Phoenix and Pittsburgh have fragmented infrastructure ownership, with multiple authorities at multiple scales owning and operating the sewer and stormwater systems. The infrastructure inventory indicated that Portland and Philadelphia had the highest densities of city-funded green infrastructure that was integrated into city’s overall control plan. In contrast, green infrastructure investments in Pittsburgh and Phoenix were limited and consisted mostly of community-led demonstration projects. Results suggested that the shift from gray to green infrastructure in Philadelphia and Portland was facilitated by a policy window during the NPDES reapplication process, in which both cities incorporated green approaches. Momentum from previously established watershed planning efforts, the creation of inter-bureau working groups, and support from key city champions helped build momentum for green approaches in the years preceding permit reapplication. Our results indicate that integrating characteristics of the physical resource system and the institutions that govern the resource improves our ability to understand the complex feedbacks and processes in coupled human-water systems, particularly in urban ecosystems.