Influence of governance structure on green stormwater infrastructure investment
Introduction
The connection of impervious surfaces directly to streams via stormwater infrastructure has resulted in a consistent decline in the ecological integrity of urban aquatic ecosystems (Meyer et al., 2005; Shuster et al., 2005; Walsh et al., 2005a; Schueler et al., 2009). A range of stormwater control measures (SCMs), also referred to as stormwater best management practices (BMPs), can be installed in suburban and urban areas to help mitigate stream water-quality degradation. For the past few decades, urban stormwater control has focused on large, centralized conveyance-based systems. These "gray" infrastructure systems use pipe networks to direct stormwater to a receiving waterway or store and slowly release stormwater using large ponds or storage tanks. Over the last decade, there has been growing recognition that static large-scale infrastructure may not meet current and future needs as urban areas continue to grow and as climate change alters expected precipitation regimes (Ahern, 2011; Palmer et al., 2015). Green stormwater infrastructure has been suggested as a more resilient option to supplement or replace gray infrastructure (e.g., pipes and storage tanks) because it is more flexible and multi-functional in the face of future extreme weather events (Grimm et al., 2016; Moore et al., 2016). We use the term ‘green stormwater infrastructure’ to include practices that manage stormwater runoff at the source where it is generated through the promotion of on-site storage, infiltration, and evapotranspiration. This includes SCMs such as bioretention, infiltration trenches, tree box filters, green roofs, and permeable pavement.
The debate over the use of gray or green infrastructure for stormwater management continues (Palmer et al., 2015). City managers are grappling with how to balance costs with meeting water-quality requirements for Federal National Pollutant Discharge Elimination System (NPDES) permits, calling for improved control of stormwater and an 85% reduction in combined sewer overflows (CSO) into local waterways (US EPA, 1994). Combined sewer systems are those in which one pipe carries both stormwater and wastewater. When the capacity of the combined sewer system is exceeded during storms, CSOs occur, i.e., excess stormwater with mixed sewage is discharged directly to local waterways. For cities with combined sewer systems, meeting reduction targets will require investing millions, and in some cases billions, of public dollars in water infrastructure in the coming decades. The U.S. Environmental Protection Agency (EPA) estimated capital investments of $48.0 billion are needed over the next 20 years for publicly owned treatment works to address CSOs and meet water-quality objectives of the Clean Water Act (US EPA, 2016). Of the $48.0 billion in documented needs, 20 communities indicated $4.2 billion is needed specifically for green infrastructure projects.
Common gray infrastructure solutions to reduce CSOs include the construction of large-scale projects such as underground tunnel or tank storage systems, upsized pipes, and sewer separation. In contrast, green infrastructure solutions require investments in multiple small-scale projects, in which amended soils and vegetation capture and infiltrate stormwater at the source where it is generated. Green stormwater infrastructure solutions include practices such as bioretention (e.g., bioswales and rain gardens) and retention basins. There is an increasing trend in implementing decentralized approaches to water management in local communities, such as green stormwater infrastructure like rain gardens (Walsh et al., 2005b; Gleick, 2003). But widespread adoption of these approaches remains limited due to institutional and organizational barriers, including fragmented responsibilities, lack of coordination among city authorities, limited institutional capacity, resistance to change, and lack of market incentives (Roy et al., 2008; Keeley et al., 2013; Brown et al., 2013; Chaffin et al., 2016). Perceived risk and lack of experience installing green stormwater infrastructure remains another barrier (Oolorunkiya et al., 2012). Even with these uncertainties, several U.S. cities have incorporated a city-wide green infrastructure program to address CSOs (e.g., Philadelphia, PA, Green City Clean Waters Program and Milwaukee, WI, Fresh Coast Green Solutions). The green infrastructure program in Milwaukee was motivated by the need for measures beyond what gray infrastructure could provide, as the city had already invested millions in storage tunnels (Keeley et al., 2013). The green infrastructure program in Philadelphia sparked from experimentation in green infrastructure pilots, billing, and organizational structure (Fitzgerald and Laufer, 2017). These cities have committed to substantial financial investments in green infrastructure approaches.
In this study, we set out to identify “green leader” cities that are planning to invest substantially in green infrastructure to address CSOs and examined if there are common structural aspects of governance in communities that are investing substantially in green stormwater infrastructure to address CSOs. Support for green infrastructure was gauged based on financial commitments for green approaches to address CSOs outlined in control plans. We gathered data on green infrastructure implementation from 25 U.S. cities with combined sewer systems. We characterized two factors associated with governance of the combined sewer system: 1) scale and complexity of system management and 2) the regulatory setting in which stormwater management decisions are made. Two case studies are presented as examples of development of gray and green infrastructure programs in the two cities with the largest proportional investment of green infrastructure in the long-term CSO control plan.
Section snippets
Background
Numerous factors influence local managers' decisions to implement green or gray infrastructure approaches to address CSOs. To explore the factors influencing governance decisions, we examined some of the socio-political drivers of stormwater infrastructure transitions from gray to green approaches in U.S. cities. The water management regime and governance can be characterized according to its structural dimensions, including institutions, vertical and horizontal flows of influence, and policy
Study cities
The majority of cities with combined sewer systems in the United States are located in the Northeast, Upper Midwest, and Pacific Northwest (Fig. 1). To span the range of geographies associated with combined sewer systems, 25 study cities were selected, including the top 10 cities with the greatest number of CSO outfalls (Fig. 1). All study cities have large combined sewer systems serving 50,000 people or more, representing about 24% of all communities with large CSO systems. No small CSO
CSO control plan costs
The total cost of each city's control plan was split into investments in gray and green infrastructure (Fig. 2). Four communities had control plans costing more than $3 billion, including New York City, Chicago, Cincinnati, and Cleveland (Supporting information Table S2). There was a positive linear relation between total control plan cost and baseline CSO volume (R2 = 0.56, p < 0.01), the number of combined sewer outfalls (R2 = 0.59, p < 0.01), and the size of the combined sewer service area (R
Term usage and funding mismatches
Content analysis of gray and green term usage indicated a wide range of term categories used in each control plan (Fig. 3). In some cases, the usage of gray terms aligned fairly well with funds dedicated to gray infrastructure. There was a significant negative correlation (R2 = 0.29, p < 0.05) between the usage of gray terms and the proportion of the control plan budget dedicated to green infrastructure. In contrast, there were no significant relations between green term categories and the
Conclusions
Our synthesis of green infrastructure investments in 25 communities suggests that the scale and complexity of the stormwater management system is less of a barrier than has been suggested. The green leader cities we identified spanned management scales from city to multi-county and municipal complexity from medium to high (Table 3). The scale and complexity of the management system may be a barrier to green infrastructure in some settings; however, our results indicate that transitions to green
Funding source
Funding was provided by the US National Science Foundation (Grant # DBI-1052875) to the University of Maryland. Participation by Grimm and York was also enabled by CAP LTER (NSF grant #DEB-1026865) and UREx SRN (NSF grant # AGS-1444755).
Acknowledgements
We thank two anonymous reviewers and Amanda Cravens for helpful comments that greatly improved this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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