Green Stormwater Infrastructure Research Articles

Planning for people and nature: Comparing quality‐of‐life outcomes across environmental systems to inform conservation planning

AbstractConservation programs have been slow to integrate socio‐economic indicators into decision making despite growing recognition that addressing social‐ecological systems improves outcomes for nature and people. Our goal was to identify small, comprehensive sets of socio‐economic indicators for conservation programs designed to (1) improve agricultural soil health and reduce sediment and nutrient loading to freshwater systems, (2) restore Great Lakes coastal wetlands, and (3) implement green stormwater infrastructure in cities. We piloted a structured decision‐making process to select indicators more objectively and transparently. Important elements of our process were (a) using a human quality‐of‐life framework to identify potential indicators and (b) evaluating indicators' relevance to conservation, resonance with communities, and data‐availability. The programs identified 278 potential indicators across seven quality‐of‐life domains, of which 78 were evaluated against six selection criteria. For each program, we developed intended use scenarios, assigned relative weights to selection criteria, and used these weights to calculate a weighted sum of the indicator's criteria scores and rank indicators. Across programs and intended uses, 21 indicators achieved top‐five rankings; indicators for flood risk and damage were common across all three programs. Our collaborative approach provided opportunities to evaluate indicator selections across quality‐of‐life domain, conservation program, and intended uses.

Willingness to pay for ecosystem benefits of green stormwater infrastructure in Chinese sponge cities

Globally, green stormwater infrastructure (GSI) has been adopted to address urban flash flooding and stormwater pollution and provide additional ecosystem benefits such as recreation, education, and aesthetics to urban communities. However, there has been a lack of research on people's preferences for different ecosystem benefits, making it challenging to understand synergies and trade-offs among co-benefits and optimize GSI planning and design. Additionally, urban stormwater management programs commonly face long-term financial challenges, demanding research that investigates the feasibility of public utility programs. This study fills these gaps in a Chinese context by employing a discrete choice experiment (DCE) to compare public preferences and estimate the monetary values of four GSI benefits, including stormwater quantity and quality treatment, educational benefit, aesthetics, and recreational benefits, in four small-to-medium pilot sponge cities. Results show that respondents preferred some kinds of GSI programs to a conventional lawn space in their living environments, and they had significant willingness to pay (WTP) for GSI programs to obtain educational ($14.8 per household per year, p < 0.001) and recreational benefits ($10.8 per household per year, p < 0.001). Stormwater treatment, as the environmental benefit prioritized by governmental agencies, however, did not generate a significant willingness to pay in any studied cities. Residents also showed indifference towards three different planting aesthetic styles (i.e., formal vs. mixed vs. naturalistic). We conclude that providing social-oriented benefits such as education and recreation is more likely to garner urban residents' financial support for GSI development in the chosen sponge cities. While stormwater utility can be a viable funding source to supplement urban stormwater management programs, people's WTP remains limited, and other financial mechanisms need to be explored.

Tracking geomorphic changes after suburban development with a high density of green stormwater infrastructure practices in Montgomery County, Maryland

Stream morphology is affected by changes on the surrounding landscape. Understanding the effects of urbanization on stream morphology is a critical factor for land managers to maintain and improve vulnerable stream corridors in urbanizing landscapes. Stormwater practices are used in urban landscapes to manage runoff volumes and peak flows, potentially mitigating alterations to the flow regime that drive changes in channel morphology. However, there remains a paucity of long-term studies assessing watershed-scale relationships between urbanization and effects on stream morphology where green stormwater infrastructure exists in high densities. This paper evaluates the geomorphic changes across four headwater catchments in the Chesapeake Bay Watershed over the course of >10 yr and relates these changes to urban development. Annual cross-sectional surveys conducted from 2002 to 2019 in one forested catchment, one agricultural catchment, and two treatment catchments were used to understand the relationship between urbanization and changes in stream morphology. Six cross-sectional geomorphic metrics were calculated and compared with development timelines and high flow events. A channel evolution model was then used to understand the status of morphologic stability at sites within the study. Results suggest downstream environments in developing areas are more impacted during early phases of suburban construction. Channel change during construction could be a result of sediment and erosion control efforts' limitations on preventing and controlling overland sediment mobilization or of increased discharge causing widening and thus bank-derived sediment to move to the streambed. Results demonstrate that geomorphic metrics are highly variable within a small area and are not always accurate representations of broader landscape changes but rather of the more localized environment at a specific stream segment. Despite a high density of stormwater management facilities in urban catchments, substantial alterations to cross sections were found at multiple locations in each catchment including the controls.

How much water can bioretention retain, and where does it go?

Abstract Bioretention is a type of green stormwater infrastructure for the urban environment that mimics a natural hydrologic system by reducing peak flows and runoff volumes and encouraging infiltration and evapotranspiration. This study examines the complete water balance of a bioretention system located in Vaughan, Ontario, Canada, between 2018 and 2019. The water balance was further broken down by event size, where the event size was determined by rainfall frequency analysis. Recharge was the largest component of the water balance overall (88% of inflow), as well as by event size. Evapotranspiration was the next largest water balance component (6% of inflow overall), and was a significant component of inflow (19%) when considering only small events (50% probability of recurrence). Evapotranspiration is a slow but consistent process, averaging 2.3 mm/day overall and 2.9 mm/day during the growing season. Climate change is likely to bring more wet days and higher temperatures, which will impact the bioretention water balance by increasing evapotranspiration and inflow. Design standards for retention targets should be updated based on the most recent rainfall frequency analyses to adjust for changing climate conditions.

A Method to Assess Plant Behavior in Green Stormwater Infrastructure

A Method to Assess Plant Behavior in Green Stormwater Infrastructure

Mapping Predicted Areas of Common Maintenance Impacts to Green Stormwater Infrastructure in Philadelphia, Pennsylvania

Mapping Predicted Areas of Common Maintenance Impacts to Green Stormwater Infrastructure in Philadelphia, Pennsylvania

Performance analysis of a stormwater green infrastructure model for flow and water quality predictions

Nature-based solutions or Green infrastructure (GI) used for managing stormwater pollution are growing in popularity across the globe. Stormwater GI models are important tools to inform the planning of these systems (type, design, size), in the most efficient and cost-effective manner. MUSIC, an example of such a tool, uses regression and first order decay models. Studies validating MUSIC model performance are, however, scarce, hindering future model development and transferability of the model for systems operating under different design and climatic conditions. To close this gap, this paper evaluates MUSIC for a field scale bioretention system, stormwater wetland and vegetated swale operating under Singapore tropical climate. The treatment modules were able to simulate outflows and effluent pollutant concentrations reasonably well for cumulative event volumes (mostly within ±25%) and cumulative TP and TN loads (within ±30%). Outflow TSS loads were significantly under-estimated as a result of greater variability in measured TSS concentrations across events. The findings indicate that simple empirical models such as MUSIC can be transferred to different regions provided that management decisions are based on long-term modelling efforts. The modules generally simulated the outflow hydrographs and pollutographs of the different inflow and drying/wetting conditions relatively poorly.

Greening Up For Mosquitoes: A Comparison of Green Stormwater Infrastructure in a Semiarid Region.

Green stormwater infrastructure provides environmental, economic, and health benefits as a strategy for building resilience against climate change impacts. However, it may inadvertently increase vulnerability due to improper design and construction or lack of maintenance. We engaged city stakeholders and a diverse student group to investigate possible maladaptation. After rain events, student interns collected data at green stormwater infrastructure, identified in partnership with city stakeholders, for both water retention and mosquito larvae, if present. During the sampling period in 2018, 24 rain events occurred, with 28 sites visited 212 times including visits to basins (63%), curb cuts (34%), and a bioswale (2%). The largest basin consistently retained water (mean: 3.3 days, SD: 2.3 days) and was a positive site for Culex quinquefasciatus, a West Nile virus vector. We found that while basins can become mosquito breeding habitat, there was no evidence that curb cuts were collecting and retaining water long enough. As cities turn to green stormwater infrastructure to address climate change impacts of increasing drought, flooding, and extreme heat, these findings can help in the selection of appropriate infrastructure design typologies.

Highly variable removal of pathogens, antibiotic resistance genes, conventional fecal indicators and human-associated fecal source markers in a pilot-scale stormwater biofilter operated under realistic stormflow conditions

Green stormwater infrastructure systems, such as biofilters, provide many water quality and other environmental benefits, but their ability to remove human pathogens and antibiotic resistance genes (ARGs) from stormwater runoff is not well documented. In this study, a field scale biofilter in Southern California (USA) was simultaneously evaluated for the breakthrough of a conservative tracer (bromide), conventional fecal indicators, bacterial and viral human-associated fecal source markers (HF183, crAssphage, and PMMoV), ARGs, and bacterial and viral pathogens. When challenged with a 50:50 mixture of untreated sewage and stormwater (to mimic highly contaminated storm flow) the biofilter significantly removed (p < 0.05) 14 of 17 microbial markers and ARGsin descending order of concentration reduction: ermB (2.5 log(base 10) reduction) > Salmonella (2.3) > adenovirus (1.9) > coliphage (1.5) > crAssphage (1.2) > E. coli (1.0) ∼ 16S rRNA genes (1.0) ∼ fecal coliform (1.0) ∼ intl1 (1.0) > Enterococcus (0.9) ∼ MRSA (0.9) ∼ sul1 (0.9) > PMMoV (0.7) > Entero1A (0.5). No significant removal was observed for GenBac3, Campylobacter, and HF183. From the bromide data, we infer that 0.5 log-units of attenuation can be attributed to the dilution of incoming stormwater with water stored in the biofilter; removal above this threshold is presumably associated with non-conservative processes, such as physicochemical filtration, die-off, and predation. Our study documents high variability (>100-fold) in the removal of different microbial contaminants and ARGs by a field-scale stormwater biofilter operated under transient flow and raises further questions about the utility of human-associated fecal source markers as surrogates for pathogen removal.

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.

Cost-Benefit Analysis of Green Infrastructure for Sustainable Stormwater Management of the Built Environment

Green infrastructure is a modern network of decentralized stormwater management applications that can capture and infiltrate rain where it falls, thus diminishing stormwater runoff and improving the health of surrounding waterways. While there are unique scales of green infrastructure, such as large swaths of land set aside for preservation. Green infrastructure such as bioretention, green roofs, trees, and permeable pavement is important in today’s world since many municipalities are faced with the issues of aging gray infrastructure, impaired local water way, and projected population growth by 2030. Green stormwater infrastructure helps strengthen communities’ economy while providing environmentally and economically sustainable solutions to stormwater management issues. This study found that current stormwater runoff issues in municipalities across the United States will be substantially decreased with about 1.05 billion gallons diverted from sewer. This will yield about millions of dollars in annual savings and decrease buildings energy metered water use by 1.37 million kWh of carbon dioxide. Green infrastructure is needed to address and plan for the future impacts of climate change by preventing increased flood risks and public health stresses.

A Bayesian modeling framework to predict stormwater pollutant reduction in bioretention media

Bioretention is a green stormwater infrastructure practice that has been shown to reduce some of the harmful effects of urban stormwater on downstream receiving waters. Typically, media used for bioretention consist of high percentages of sand to realize high hydraulic conductivities and smaller percentages of soil or organic materials to improve the retention of stormwater pollutants. The objectives of this study were to evaluate four bioretention media mixes that differed in sand, compost, and water treatment residuals content and to predict pollutant removal based on realistic stormwater concentrations using Bayesian statistics. Pollutants of interest were chemical oxygen demand, ammonia, nitrite, nitrate, total Kjeldahl nitrogen, as well as total and dissolved forms of phosphorus, copper, lead, and zinc. Water quality data were collected for eleven storms, and cumulative rainfall after construction was used as a measure for the media age. The data were evaluated for the probability to observe pollutant reduction and for the probability to observe high-performance reduction (HPR) with a minimum pollutant reduction of 60%. The chemical oxygen demand had a probability for reduction of P = 0.09 and HPR of P = 0.00, resulting in pollutant export in the majority of storms. HPR reduction goals were met for total lead, zinc, and copper, and reduction probabilities were generally P > 0.5 for all total and dissolved metals. Age and media composition affected phosphorus and nitrogen removal, with increased pollutant retention observed as the media aged. Lower compost percentages resulted in less nutrient export. This probabilistic model of realistic stormwater concentrations in combination with bioretention pollutant removal experiments results in a holistic view of credible pollutant outflow concentrations that can be used by stormwater managers to alleviate the effects of stormwater on surface water quality.

Characterization of co-benefits of green stormwater infrastructure across ecohydrologic regions in the United States

Stormwater Green Infrastructure (SGI) systems such as rain gardens, permeable pavement and bioswales are commonly used in municipalities to reduce urban flooding and water pollution. In conjunction with these direct benefits, SGI systems provide additional social and environmental “co-benefits”. Our goal was to investigate the co-benefits of commonly used SGI systems in five cities in the United States, including Baltimore, Denver, New York City, Philadelphia, and Portland. The i-Tree Eco model was used to predict carbon storage and sequestration, air pollution removal, UV reduction, and cooling effects of trees for individual tree species and estimated SGI tree inventories across the five study cities based on observed tree characteristic data. Aspects of SGI design, environmental factors, and model inputs were assessed to understand what parameters impacted SGI co-benefits predicted by the model. We evaluated the most highly influential parameters using a global sensitivity analysis method. As expected, the type of SGI design, and the overall number of trees utilized within those designs, played a large role in determining the overall amount of co-benefits predicted by the model. However, climate also influenced estimation of benefits produced, with similar responses predicted for cities in the same climate zone (e.g. Baltimore, Philadelphia, and New York City). In particular, the global sensitivity analysis showed that variables influencing environmental conditions and tree growth also impacted final co-benefit predictions produced by i-Tree Eco. study revealed how various assumptions and prevailing equations within the i-Tree Eco model can play a major role in the final outcomes predicted by the model. Studies that use i-Tree Eco to analyze potential co-benefits of SGI projects, especially when the goal is to compare projects across climate zones, should consider what aspects of the results are simply a function of the model itself. Overall, the model predicts that more co-benefits are provided in certain climate zones, an assumption currently supported in the literature.

Seasonal Hydroclimatic and Soil Biogeochemical Drivers of N and P Availability in a Constructed Stormwater Wetland

Constructed stormwater wetlands are green stormwater infrastructure (GSI) practices with potential to treat stormwater nutrient pollution. GSI nutrient removal performance is controlled by GSI soil nutrient cycles, which depend on soil hydrologic and biogeochemical conditions. The objective of this study was to characterize spatial and temporal patterns in soil dissolved nutrients, and their relationships with soil conditions, at a constructed stormwater wetland in Milwaukee, Wisconsin. Ion exchange membranes were used to measure soil nutrient availability, which was combined with precipitation, air and soil temperature, soil moisture, and soil oxygen data. Nitrate was intermittent: 17% and 25% of the study period accounted for 50% and 67% of the total nitrate availability in the Upland and Lowland, respectively. Time-series data suggest this intermittency resulted from summertime N mineralization. Orthophosphate was higher in the well-aerated Upland than in the periodically anoxic Lowland with a larger contributing area. Regression results indicate that relationships between nutrient availability and environmental drivers depended on the nutrient and landscape position. Modeling spatiotemporal variability of GSI soil nutrient dynamics may improve system performance and prediction.

The Effects of Eligibility and Voluntary Participation on the Distribution of Benefits in Environmental Programs: An Application to Green Stormwater Infrastructure

The Effects of Eligibility and Voluntary Participation on the Distribution of Benefits in Environmental Programs: An Application to Green Stormwater Infrastructure

"Green Enough Ain't Good Enough:" Public Perceptions and Emotions Related to Green Infrastructure in Environmental Justice Communities.

The concept of biophilic urban planning has inspired neighborhood greening projects in many older urban communities in the USA and beyond. The strengths (e.g., environmental management, biodiversity, heat island mitigation) and challenges (e.g., greenwashing, green gentrification) of such projects are well-documented. Additional research on the relationship between these projects and various social factors (e.g., public perceptions, feelings, and mental health and well-being) is necessary to better understand how people adapt to said projects while struggling to navigate other more pressing socioeconomic issues, especially in communities facing environmental injustice and health inequity. In this article, we focus on one aspect of biophilic urban planning—green stormwater infrastructure (GSI) (e.g., rain gardens, bio-swales, pervious pavements, and wildflower meadows)—in Waterfront South, a post-industrial neighborhood in Camden, NJ, USA, where residents have faced environmental injustices for decades. Our qualitative analysis of in-depth semi-structured interviews of sixteen residents offered a thorough insight into their perceptions and emotions regarding different types of urban GSI projects. Residents acknowledge the many benefits that GSI offers to combat the neighborhood’s social and environmental injustices, but they are cautious about the possibility of some projects prompting new issues and concerns within the community. Our findings reveal potential implications in GSI planning, research, and practice in this neighborhood and similar urban places elsewhere that have yet to undergo gentrification.

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.

Ecosystem Benefits Provision of Green Stormwater Infrastructure in Chinese Sponge Cities.

The Sponge City Development (SCD) concept was initiated in 2012 to address severe urban flooding and water quality challenges in China. Green stormwater infrastructure (GSI) such as rain gardens have been adopted as critical stormwater management tools. Existing GSI research has focused primarily on their environmental performance, overlooking the human dimensions. The co-benefits of GSI have been particularly underinvestigated. We used social surveys (n = 607) and expert interviews (n = 11) to explore public perception of SCD and GSI in four pilot sponge cities, examining flood experience, stormwater concerns, GSI familiarity, institutional trust, and GSI benefit perception. The survey found high exposure to flooding, medium GSI familiarity, and strong institutional trust. The public showed greater concern on stormwater impacts on their quality-of-life than the water environment, rating the less-intended aesthetic and health values as the best-perceived benefits. Experience, familiarity, concern, trust, age, and city significantly affected GSI benefit perception. In contrast, the experts spoke more positively about the environmental benefits while indicating the inadequacy of public participation. The case of GSI in SCD offers broad implications for environmental governance and expert-public relationships in an era of rapid social, technological, and environmental change. Refining policies and regulations to incorporate social goals, bringing the public into the SCD process, and building up the GSI industry's capacity in planning, design, construction, and maintenance are critical to enhancing GSI benefits provision. Adopting the co-benefits approach will be essential to utilizing GSI as a place-making tool to create more sustainable and livable communities.

Programmatic Regimes and the Different Impacts of Public and Redevelopment Driven Green Stormwater Infrastructure (Gsi)

Programmatic Regimes and the Different Impacts of Public and Redevelopment Driven Green Stormwater Infrastructure (Gsi)

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.