Green Stormwater Infrastructure Implementation Research Articles

Lifecycle cost and benefit analysis for parcel-scale implementation of green stormwater infrastructure

Green stormwater infrastructure (GSI) is commonly implemented to reduce excess stormwater runoff while also producing secondary environmental, health, and aesthetic benefits. However, GSI is sometimes perceived to be cost prohibitive for limited-budget site development projects. This study used lifecycle cost analysis (LCCA) and benefit-cost analysis (BCA) to investigate the cost-effectiveness of GSI combined with conventional stormwater infrastructure for a proposed parcel development site in Oxford, Mississippi, USA. Hydrologic modeling was conducted for a conventional underground detention facility as well as three GSIs (permeable pavement, rain garden, and grassy ditch), all of which met regulatory runoff attenuation targets for the site. The LCCA considered capital and operation and maintenance (O&M) costs. Benefits were estimated under six categories–water, energy, climate, air quality, health, and community–based on existing tools for economic analysis of low impact development (LID). Economic benefits and costs over different scenarios of project lifecycles were compared using the present value (PV) approach in the benefit cost analysis (BCA). The lifecycle costs of two of the three GSIs (rain garden and grassy ditch) were lower than for the conventional alternative alone. However, in all three GSI cases, the long-term benefits of GSI features outweighed the costs. The methodology presented can be adapted to other locations to inform analyses of lifecycle costs and benefits and identify GSI and hybrid infrastructure options that are financially and environmentally feasible.

Overarching barriers to mainstream green stormwater infrastructure in Ghana: Towards good green governance

Environmental challenges associated with stormwater management, including flooding, droughts and depleting water quality, are exacerbated in urban areas. Despite growing expertise and policy advocacy for alternatives to conventional stormwater management approaches, Ghanaian cities, like many cities in developing countries, have not adopted governance principles to mainstream green stormwater infrastructure (GSI). There is very limited research which examines the governance barriers to mainstreaming GSI and their nuances within the Ghanaian context. Based on document analysis and interviews, this article explores the governance factors influencing GSI implementation and their associated barriers in Ghana’s most populated water catchment. It analyses the governance dimensions comprising actors, rules of the game, discourse, and resources and power that could influence stormwater management. The article highlights that governance dimensions are currently not framed to facilitate GSI implementation. This shortfall reflects 11 specific barriers, including poverty, unresponsive culture, lack of knowledge, and lack of collaboration. The barriers transcend multiple governance components, particularly the actors. Yet, several governance components, including the specific actors and existing policies, are not currently integrated into stormwater management despite having strong potential to overcome the barriers and facilitate GSI implementation. The article proposes a good green governance framework, which accounts for the holistic nature of the identified barriers and envisages active inclusion and collaboration between diverse actors, including a basin authority as an intermediary, communities, local governments and national-level agencies.

Multi-variable assessment of green stormwater infrastructure planning across a city landscape: Incorporating social, environmental, built-environment, and maintenance vulnerabilities

Green stormwater infrastructure (GSI) is an increasingly popular tool to meet federal water regulations for stormwater quality and quantity, while assuaging urban flooding. While cities across the United States implement GSI into their planning processes, they are also potentially affecting the local communities that are receiving these GSI through social, ecological, physical, and economic impacts. Flooding is impacting urban communities by damaging homes and infrastructure, degrading ecosystems, and exacerbating social inequities. In the planning process, there is an acute need for the consideration of the equitable distribution of GSI in addition to technical and engineering needs. This study examines multiple aspects of vulnerability to local flooding impacts—social, environmental, and infrastructural—across a city landscape to identify those communities that have a greater need for GSI. Given the city of Philadelphia is a leader in GSI implementation in the United States, we use it as our research setting where we create citywide, multifaceted vulnerability indices that account for the spatial distribution of social, built environment, and maintenance vulnerabilities to flooding events. In addition to these indices, a GSI type decision table was created to suggest more equitable placements of different GSI types based on their maintenance needs and expected co-benefits. The results of this study reveal unequal distribution of social and built-environment vulnerabilities in the city at the Census block group scale, with high social vulnerability consistently spread across the central, southwest, and northwest neighborhoods of Philadelphia. Potential areas of severe GSI maintenance impacts appear to be concentrated in the downtown neighborhoods, while overall vulnerability appears elevated throughout the downtown and northwest neighborhoods. These results indicate that some communities in Philadelphia are highly vulnerable and should be prioritized for GSI implementation. In addition, the type of GSI implemented should be optimized to address the specific vulnerability impacts in different areas. A multifaceted vulnerability approach to planning can be applied in multiple areas of climate adaptation equity, with future studies continuing to update and add more dimensions of vulnerability where and when applicable.

Addressing the social barriers to green stormwater infrastructure in residential areas from a socio-ecological perspective

Despite the well-recognized financial limitations, social aspects can also impact the adoption of green stormwater infrastructure (GSI) as it is ingrained in the socio-ecological system we live in. Thus, this work focuses on gaining an understanding of the public's perceptions of GSI by considering cognitive biases that hinder its adoption. This work is composed of two forms of human-subject studies, including an online-based survey and a series of semi-structured interviews. The survey (n = 510) was conducted to gauge public opinions toward GSI, whereas the interviews with representatives of major local regulatory agencies were to learn about the logistics for GSI implementation in Mecklenburg County, NC. The results were interpreted using the theory of planned behavior of rational actors. Statistical results showed a weak interpretation through this theory to explain the survey participants' intention to adopt GSI measures. This could suggest that the incorporation of irrationality, such as cognitive biases, could further enhance the predictability of the theory. At the same time, an inconsistency between the findings from the survey and the interviews was identified: most survey participants showed an overall uniform positive attitude, intention, and behavior regarding GSI practice adoption, whereas the interviewed experts all suggested a wide diversity on such terms. Suggestions were made based on the findings for better policy-making on public engagement for local regulatory agencies. This research aims to help local stormwater management authorities explore shortcomings in current stakeholder engagement plans to gain sustainable support for GSI implementation in urbanized areas.

Interdisciplinary Inquiry and Spatial Green Stormwater Infrastructure Research

The use of vegetation and infiltration into soils to manage stormwater and water quality—called green stormwater infrastructure (GSI)—is now widely recognized as a viable alternative or supplement to the pipes and pumps of conventional, or “gray”, drainage infrastructure. Over the years, much research has emerged regarding spatial aspects of GSI implemented at large scales, including where it is located, where it should be located, and what metrics best represent the benefits it brings to different locations. Research in these areas involves expertise from multiple academic disciplines, but it is unclear whether and how researchers from different disciplines identify and approach questions related to the spatiality of GSI. By adopting the explanatory sequential mixed method design, we identified four categories of spatial GSI studies through a literature review of over 120 research papers: empirical, ecological, decision support systems, and optimization. Here, we present representative examples of these categories of spatial GSI studies, as well as associations between the academic disciplines represented in these categories of spatial GSI papers. Then, we conducted semi-structured interviews with a sample of GSI researchers which revealed the value of interdisciplinary training and knowledge. Finally, in this paper, we identify several gaps that could be addressed to improve interdisciplinary research on GSI implementation, and sustainability transitions in general.

Assessing the influence of urban greenness and green stormwater infrastructure on hydrology from satellite remote sensing

Green stormwater infrastructure (GSI), which includes features like rain gardens, constructed wetlands, or urban tree canopy, is now widely recognized as a means to reduce urban runoff impacts and meet municipal water quality permit requirements. Many co-benefits of GSI are related to increased vegetative cover, which can be measured with satellite imagery via spectral indices such as the Normalized Difference Vegetation Index (NDVI). In urban landscapes, there remain critical gaps in understanding how urban greenness and GSI influence hydrology. Here, we quantify these relationships to assess the feasibility of tracking the effectiveness of urban greening for improving downstream hydrologic conditions. We combined hydrologic data from the United States Geological Survey (USGS) gauges with an NDVI time series (1985–2019) derived from Landsat satellite imagery, and synthesis of GSI implementation data from a set of 372 urbanized watersheds across the United States. We used a multivariate panel modeling approach to account for spatial and time varying factors (rainfall, temperature, urban cover expansion) in an effort to isolate the relationships of interest. After accounting for expansion of urban boundaries, only 32 watersheds (9%) showed significant greenness trends, a majority of which were reductions. Urban greenness had significant influences on downstream flow responses, so that on average, a 10% greenness increase showed a corresponding reduction of total flow (−3.8%), flow variance (−7.7%), peak flows (−4.7%), high flows (−7.6%), flashiness (−2.2%), and high flow frequency (−1.5%); and a corresponding increase in baseflow (4.3%). For a subset of these watersheds for which GSI data were available (n = 48), the level of GSI implementation showed a significant, but weak influence on urban greenness with a 20% increase in BMP density corresponding to a greenness increase of 0.9%. The study results may support valuation and verification of GSI co-benefits in urbanized landscapes at the watershed scale.

Evaluating the effect of city ordinances on the implementation and performance of green stormwater infrastructure (GSI)

The replacement of natural pervious surfaces with impervious surfaces due to urbanization, construction, and development causes excess stormwater runoff and results in cities experiencing localized flooding events. The installation of green stormwater infrastructure (GSI) is one way of reducing flooding events and preventing downstream erosion and damage. In this study, computer rainfall-runoff simulations were performed to analyze GSI's effectiveness in mitigating stormwater runoff when applied to sites with different soil types and for which different design storms were established by regulation. A mixed-use development site was used as a hypothetical site on which to perform the analysis. The study applied the same design to six small- to medium-sized cities in the southeastern United States with different design storm magnitudes. The cities’ ordinances were reviewed, and none required GSI. Therefore, this study revised some of the stormwater management requirements to stress GSI implementation, and then stormwater modeling was conducted to see how regulatory changes would affect runoff. The HydroCAD stormwater modeling tool was used to perform hydrologic simulations for the hypothetical building site in each of the six cities using the design storms and small storms of the cities. Even though GSI has been commonly implemented in large cities, small and medium-sized cities can also prevent excess stormwater by incorporating GSI in their ordinances for new developments and site retrofits. Based on the hydrologic simulation results, municipalities with lower magnitude design storms and low infiltration soils have the most to benefit from GSI and could benefit from ordinances requiring GSI. For smaller, more frequent storms, GSI alone can meet the pre-development peak flow requirements.

Social Barriers and the Hiatus from Successful Green Stormwater Infrastructure Implementation across the US

Green stormwater infrastructure (GSI), a nature-inspired, engineered stormwater management approach, has been increasingly implemented and studied especially over the last two decades. Though recent studies have elucidated the social benefits of GSI implementation in addition to its environmental and economic benefits, the social factors that influence its implementation remain under-explored thus, there remains a need to understand social barriers on decisions for GSI. This review draws interdisciplinary research attention to the connections between such social barriers and the potentially underlying cognitive biases that can influence rational decision making. Subsequently, this study reviewed the agent-based modeling (ABM) approach in decision support for promoting innovative strategies in water management for long-term resilience at an individual level. It is suggested that a collaborative and simultaneous effort in governance transitioning, public engagement, and adequate considerations of demographic constraints are crucial to successful GSI acceptance and implementation in the US.

Social-psychological Determinants of the Implementation of Green Infrastructure for Residential Stormwater Management.

Climate change effects and increasing levels of imperviousness, cause many urban areas globally to experience larger rainfall runoff volumes that need to be managed to protect property and infrastructure, and avoid environmental pollution. Conventionally engineered, 'grey' stormwater infrastructure often is outdated and unable to control these increased runoff volumes. Green stormwater infrastructure (GSI) can complement grey infrastructure, but public land for its installation is limited. Consequently, municipalities often look to residential properties to install GSI at the lot-level. While many studies have been conducted in the engineering aspects of GSI, less is known about what determines residents' decisions to install GSI on their properties. To help close this knowledge gap, we conducted a survey of social-psychological determinants of residential GSI implementation using the Theory of Planned Behavior as theoretical framework, and analyzing our data with partial least squares path modeling. Results from three neighborhoods of our case study area suggest that residents' decisions to install GSI largely are determined by social norms and perceived control factors such as available finances and time. However, residents' beliefs and attitudes toward the effectiveness and attractiveness of GSI did not seem to play a significant role. Neighborhood characteristics including local flooding history did not seem to affect residents' decisions about GSI installation either. We recommend creation of effective municipal education and outreach programs regarding urban stormwater management that speak to residents' shared responsibility and options for addressing this issue, as well as creation of financial instruments that provide meaningful subsidies for residential GSI adoption.

Highly Resolved Rainfall-Runoff Simulation of Retrofitted Green Stormwater Infrastructure at the Micro-Watershed Scale

Green Stormwater Infrastructure (GSI), a sustainable engineering design approach for managing urban stormwater runoff, has long been recommended as an alternative to conventional conveyance-based stormwater management strategies to mitigate the adverse impact of sprawling urbanization. Hydrological and hydraulic simulations of small-scale GSI measures in densely urbanized micro watersheds require high-resolution spatial databases of urban land use, stormwater structures, and topography. This study presents a highly resolved Storm Water Management Model developed under considerable spatial data constraints. It evaluates the cumulative effect of the implementation of dispersed, retrofitted, small-scale GSI measures in a heavily urbanized micro watershed of Costa Rica. Our methodology includes a high-resolution digital elevation model based on Google Earth information, the accuracy of which was sufficient to determine flow patterns and slopes, as well as to approximate the underground stormwater structures. The model produced satisfactory results in event-based calibration and validation, which ensured the reliability of the data collection procedure. Simulating the implementation of GSI shows that dispersed, retrofitted, small-scale measures could significantly reduce impermeable surface runoff (peak runoff reduction up to 40%) during frequent, less intense storm events and delay peak surface runoff by 5–10 min. The presented approach can benefit stormwater practitioners and modelers conducting small scale hydrological simulation under spatial data constraint.

Quantifying cumulative effectiveness of green stormwater infrastructure in improving water quality

Stormwater runoff is one of the main sources of pollution in streams and receiving water bodies of major cities. Green Stormwater Infrastructure (GSI) is a set of distributed stormwater best management practices that absorb excess water, filter out sediment and pollutants, and help recharge groundwater.Despite the increasing popularity of GSI as means of stormwater management, our knowledge of their cumulative performance is limited. In this research, we apply an empirical approach to study the effectiveness of GSI in improving the water quality of four major receiving water bodies of Seattle, Washington, at the watershed scale. We use a Bayesian structural time series model and synthetic control method to build counterfactual scenarios of water quality in absence of GSI implementation and estimate the causal impact of GSI on water quality. We use monthly time series data of water quality parameters (water temperature, dissolved oxygen, surface PAR, chlorophyll a, Secchi depth, pH, light transmission, and fecal coliform) in Seattle's urban watersheds from 2004 to 2017. We also use a set of nine control variables to estimate the counterfactual water quality parameters. Our findings show that GSI improve some water quality parameters such as chlorophyll a, light transmission and Secchi depth, but increase water temperature and decrease dissolved oxygen in some water bodies.

Changes in event-based streamflow magnitude and timing after suburban development with infiltration-based stormwater management.

Green stormwater infrastructure implementation in urban watersheds has outpaced our understanding of practice effectiveness on streamflow response to precipitation events. Long‐term monitoring of experimental suburban watersheds in Clarksburg, Maryland, USA, provided an opportunity to examine changes in event‐based streamflow metrics in two treatment watersheds that transitioned from agriculture to suburban development with a high density of infiltration‐focused stormwater control measures (SCMs). Urban Treatment 1 has predominantly single family detached housing with 33% impervious cover and 126 SCMs. Urban Treatment 2 has a mix of single family detached and attached housing with 44% impervious cover and 219 SCMs. Differences in streamflow‐event magnitude and timing were assessed using a before‐after‐control‐reference‐impact design to compare urban treatment watersheds with a forested control and an urban control with detention‐focused SCMs. Streamflow and precipitation events were identified from 14 years of sub‐daily monitoring data with an automated approach to characterize peak streamflow, runoff yield, runoff ratio, streamflow duration, time to peak, rise rate, and precipitation depth for each event. Results indicated that streamflow magnitude and timing were altered by urbanization in the urban treatment watersheds, even with SCMs treating 100% of the impervious area. The largest hydrologic changes were observed in streamflow magnitude metrics, with greater hydrologic change in Urban Treatment 2 compared with Urban Treatment 1. Although streamflow changes were observed in both urban treatment watersheds, SCMs were able to mitigate peak flows and runoff volumes compared with the urban control. The urban control had similar impervious cover to Urban Treatment 2, but Urban Treatment 2 had more than twice the precipitation depth needed to initiate a flow response and lower median peak flow and runoff yield for events less than 20 mm. Differences in impervious cover between the Urban Treatment watersheds appeared to be a large driver of differences in streamflow response, rather than SCM density. Overall, use of infiltration‐focused SCMs implemented at a watershed‐scale did provide enhanced attenuation of peak flow and runoff volumes compared to centralized‐detention SCMs.

Role of community participation for green stormwater infrastructure development

The primary objective of this research is to understand the role of community participation in green stormwater infrastructure (GSI) development. There is a lack of understanding about the interactions of technical and non-technical factors that promote or hinder GSI implementation and development. This work uses the qualitative case study methodology to fulfil the objective and answer the research questions. The case study is based on the Proctor Creek Watershed, Atlanta Georgia, a rapidly growing urban area located in the southeastern United States. Data sources include participant interviews, documents, and field notes. Findings reveal that community participation in this case is embedded in collaborative partnership efforts. Also, social conditions highly influence the participation processes by dictating the priorities the community develops during participation processes. Factors such as funding and political support, promote green stormwater infrastructure implementation along with community participation. Additionally, community education addresses the challenge of resistance to change, hence community education plays a role in its development and implementation.

Towards the implementation of green stormwater infrastructure: perspectives from municipal managers in the Pacific Northwest

To mitigate the harmful effects of stormwater runoff, many cities in the United States are constructing green stormwater infrastructure (GSI), yet the varied perceptions of GSI by local municipal managers can make or break the implementation of GSI in any given city. We conducted a series of focus groups with municipal managers from two adjacent regions in the Pacific Northwest (US) – Portland, Oregon and Clark County, Washington – where many of the earliest and most extensive applications of urban GSI have occurred. We aimed to understand the extent to which municipal managers fundamentally differ in their considerations of GSI, even within one metropolitan region. Results indicate that Portland respondents were optimistic about GSI implementation emphasizing stakeholder buy-in and regulatory systems. Alternatively, in Clark County, an unfunded state mandate, public concern, and uncertainties about facility performance culminated in a cautionary approach to GSI. The variation in findings has many implications for implementing GSI.

Utilizing SWMM and GIS to identify total suspended solids hotspots to implement green infrastructure in Lucas County, OH

AbstractThis research demonstrates that modeling approaches can be used to identify priority areas to implement green stormwater infrastructure (GSI) resulting in improved water quality outcomes. The total suspended solids (TSS) washoff loading from watersheds in Lucas County, Ohio due the municipal separate storm sewer system (MS4) was reported based on 2015 rain data. The highest TSS loading was experienced in the winter season in 80% of the watersheds. Subcatchments with the highest predicted TSS washoff loadings were identified as priority areas or hotspots. In subsequent simulations, GSI implementation in hotspots improved water quality by more than twofold as compared to indiscriminate implementation of GSI. These hotspot maps are being used by regional stormwater stakeholders to focus their urban water quality efforts and to identify site characteristics that may be used to inform environmental policy.

Evaluating Green Stormwater Infrastructure strategies efficiencies in a rapidly urbanizing catchment using SWMM-based TOPSIS

The dramatic changes in Land-Use and Land-Cover (LULC) in urbanizing areas have led to problems such as urban flooding and water pollution. Green Stormwater Infrastructure (GSI) has become a new approach to mitigate these problems. The comprehensive assessment of GSI strategies and their combinations is the foundation for decision making regarding GSI implementation. Using the rapidly developing Western New City of Zhuhai in China as an example, this study applies Storm Water Management Model (SWMM) to evaluate Single and Combined GSI strategies. Four indicators—runoff volume control, peak flow reduction, pollutant removal, and economic cost—are selected to conduct a Multi-Criteria Decision Analysis with the use of Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS). The performance evaluation of Single and Combined GSIs suggests that: (i) there may exist linear or nonlinear relation between the efficiency of a Single GSI and the size of its implementation. (ii) the optimal LULC-cost effective range may be identified for certain GSI, and (iii) Distributed-Centralized Combined GSIs are superior to other strategies in regard to reduction of runoff, TSS and peak flow. The TOPSIS assessment indicates that the cost weight (wc) has significant impact on the multi-criteria decision-making, and all strategies may be classified into three categories: effectiveness, cost, and stability. The results of TOPSIS show that the Distributed-Centralized Combined GSIs (scenarios S3, S5) are the best options if wc is not an important factor, while the Centralized Single GSI (S6) is the best option if wc becomes more important. Furthermore, this study can provide the well-informed alternative stormwater management plans and GSI decisions for local planners and water resource managers in the rapidly urbanizing sponge cities.

A GIS-Based Framework Creating Green Stormwater Infrastructure Inventory Relevant to Surface Transportation Planning

The stormwater runoff that carries pollutants from the land adjacent to road transportation systems may impair the water environment and threaten the ecosystem and human health. A proper management approach like green stormwater infrastructure (GSI) can help control flooding and the runoff pollutants. One barrier for GSI analysis relevant to system-level surface transportation planning is the lack of the inventory of GSI in many U.S. cities. This study aims to develop a GIS-based framework for creating GSI inventory in a time and labor efficient way, different from the traditional survey-based method. The new proposed framework consists of three steps, including road categorization, GSI mapping, and GSI type identification using the GIS data, high-resolution land-cover image, and Google Earth street view pictures. The new approach was tested in Philadelphia, Pennsylvania and also applied in Tampa, Florida. The results showed that the new GIS-based framework can achieve similar accuracy to the survey-based method while saving time and labor. The GSI inventory created in the study demonstrated the usefulness of the proposed framework for analyzing the status of GSI implementation and identifying gaps for future planning in terms of potential locations and underrepresented GSI types.

Prioritizing Suitable Locations for Green Stormwater Infrastructure Based on Social Factors in Philadelphia

Municipalities across the United States are prioritizing green stormwater infrastructure (GSI) projects due to their potential to concurrently optimize the social, economic, and environmental benefits of the “triple bottom line”. While placement of these features is often based on biophysical variables regarding the natural and built environments, highly urbanized areas often exhibit either limited data or minimal variability in these characteristics. Using a case study of Philadelphia and building on previous work to prioritize GSI features in disadvantaged communities, this study addresses the dual concerns of the inequitable benefits of distribution and suitable site placement of GSI using a model to evaluate and integrate social variables to support decision making regarding GSI implementation. Results of this study indicate locations both suitable and optimal for the implementation of four types of GSI features: tree trenches, pervious pavement, rain gardens, and green roofs. Considerations of block-level site placement assets and liabilities are discussed, with recommendations for use of this analysis for future GSI programs.

Ecosystem services and U.S. stormwater planning: An approach for improving urban stormwater decisions

Green stormwater infrastructure (GI) is gaining traction as a viable complement to traditional “gray” infrastructure in cities across the United States. As cities struggle with decisions to replace deteriorating stormwater infrastructure in the face of looming issues such as population growth and climate change, GI may offer a cost-effective, efficient, and sustainable approach. However, decision makers confront challenges when integrating GI within city plans, including uncertainties around GI capacity and maintenance, resistance to collaboration across city governance, increasingly inflexible financing, accounting practices that do not incorporate the multiple values of GI, and difficulties in incorporating ecological infrastructure into stormwater management. This paper presents an ecosystem services framework for assessing the context-specific needs of decision makers, while considering the strengths and limitations of GI use in urban stormwater management. We describe multiple dimensions of the planning system, identify points of intervention, and illustrate two applications of our framework – Durham, North Carolina and Portland, Oregon (USA). In these case studies, we apply our ecosystem services framework to explicitly consider tradeoffs to assist planning professionals who are considering implementation of GI. We conclude by offering a research agenda that explores opportunities for further evaluations of GI design, implementation, and maintenance in cities.

Temporal Evolution of Green Stormwater Infrastructure Strategies in Three US Cities

Over the last several decades, interest in green stormwater infrastructure (GSI) has rapidly increased, particularly given its potential to provide stormwater management in conjunction with other ecosystem services and co-benefits such as urban heat island mitigation or habitat provision. Here we explore the implementation of GSI in three US cities – Baltimore (Maryland), Phoenix (Arizona), and Portland (Oregon). We examine the trends in GSI construction over several decades, highlighting changes in implementation rates and GSI types with concurrent regulatory and economic changes. Additionally, we discuss the implications of these GSI portfolios for ecosystem service delivery in urban areas. Results indicate that Portland’s quantity of GSI is approximately ten times greater than the quantity of GSI in Phoenix or Baltimore. However, Baltimore has the most diverse portfolio of GSI types. In Phoenix, regional stormwater policies focused on flood control have led to retention basins being the dominant GSI type for decades. In contrast, Portland and Baltimore both have had substantial changes in their GSI portfolios over time, with transitions from detention or retention basins and underground facilities towards filters, infiltration facilities, and swales. These changes favor increased water quality function as well as provision of other ecosystem services. Additionally, we find evidence that each city followed a different GSI implementation pathway, with Portland’s combined sewer overflow program influencing initial development of GSI, while state legislation and regional water quality pressures played a major role in Baltimore’s GSI development. By studying the evolution of GSI in these different cities, we can see the variability in stormwater management trajectories and how they manifest in different suites of benefits. We hope that continued research of GSI implementation and performance will identify opportunities for future improvement of these infrastructures.