•Conventional bioretention soil media (BSM) specifications vary by jurisdiction•Conventionally designed BSM struggles to remove dissolved pollutants•Amendments to BSM can improve removal of dissolved ...metals and nutrients in runoff•Amendments are infrequently used at field scale due to lack of regulation, guidance•Guidance is provided for amendments which target specific pollutants of interest
Bioretention systems are widely used green infrastructure elements that utilize engineered bioretention soil media (BSM) for stormwater capture and treatment. Conventional bioretention soil media, which typically consists of sand, sandy loam, loamy sand or topsoil amended with compost, has limited capacity to remove and may leach some stormwater pollutants. Alternative engineered amendments, both organic and inorganic, have been tested to supplement BSM. Yet, municipalities and regulatory agencies have been slow to adopt these alternative amendments into their design specifications, partly because of a lack of clear guidance on how to select the right amendment to treat a target stormwater contaminant under highly variable climatic conditions. This article aims to provide that guidance by: (1) summarizing the current design BSM specifications adopted by jurisdictions worldwide, (2) comparing the performance of conventional and amended BSM, (3) highlighting advantages and limitations of BSM amendments, and (4) identifying challenges for implementing amendments in field conditions. The analysis not only informs the research community of the barriers faced by stormwater managers in implementing BSM amendments but also provides guidelines for their adoption by interested agencies to comply with existing regulations and meet design needs. This feedback loop could catalyze further innovation in the development of sustainable stormwater treatment technologies.
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Road runoff contributes an array of pollutants which degrade the quality of receiving waters. Sediment conveyed in runoff results in loss of habitat and loss of reservoir capacity, among other ...undesirable impacts. To select and design stormwater control measures (SCMs), the sediment particle size distribution (PSD) is needed to quantify the required hydraulic retention time for particle settling and to understand what other treatment processes (e.g., filtration) are needed to meet sediment removal targets. A two-year field monitoring study was undertaken across the state of Ohio, USA, to evaluate the PSD of sediment in runoff at twelve roads. The highest TSS concentrations were observed on interstate highways (highest annual average daily traffic AADT) and minor arterials (low AADT), suggesting factors beyond AADT, such as antecedent dry period, rainfall intensity, and windborne dust and particulates, contribute to the varied sediment characteristics in runoff. The median TSS load across all samples collected was 2.7 kg/ha per storm event, while annual TSS loads for the monitoring sites varied from 98 kg/(ha·yr) to 519 kg/(ha·yr), with a mean value of 271 kg/(ha·yr). Particle size distributions varied across the monitoring sites, with mean and median d
of 48.6 μm and 52.5 μm, respectively. Interstate highways (highest AADT) had significantly finer PSDs than other functional classes, while roads in low density residential areas had coarser PSDs than other land uses. Observed differences in PSD across road characteristics may guide SCM selection; dry detention basins and wet ponds/wetlands were predicted to provide effective removal across a variety of PSDs, while TSS reductions provided by hydrodynamic separators and high-flow media filters (which effectively remove larger particles) may be maximized in areas with coarser PSDs (e.g., roads surrounded by low density residential areas studied herein).
•Field monitoring study of macrodebris conveyed from eleven diverse roads in Ohio.•Mean macrodebris volumetric, mass loading rates of 8.56 L/ha/d and 0.79 kg/ha/d.•Vegetation primary contributor to ...macrodebris volume (80.3%) and mass (79.7%).•Road functional class, land use, and development density influenced macrodebris.•Macrodebris moisture content highly variable; may require drying before disposal.
Urban stormwater conveys dissolved pollutants, micropollutants, particulate matter, natural debris, and anthropogenic macrodebris to receiving waters. Though it is widely recognized that anthropogenic macrodebris mobilized by stormwater contributes to global pollution management issues (e.g., ocean garbage patches), these materials often are not the focus of stormwater sampling campaigns. Furthermore, macrodebris can cause clogging of sewer systems, exacerbating flooding and public health hazards. Due to their engineered structures draining directly connected impervious areas (e.g., catch basins, inlets, and pipes), roads present a unique opportunity to mitigate the conveyance of macrodebris in stormwater. To optimize control measures, data are needed to understand expected volume and mass of macrodebris in road runoff. To address this gap in knowledge, a field monitoring study was conducted in Ohio (USA) to quantify the mass, volume, and moisture content of macrodebris transported by road runoff. Designed to filter macrodebris (i.e., material with diameter greater than 5 mm) while maintaining drainage, purpose-built inserts were deployed in catch basins at eleven geographically diverse locations across the state. Macrodebris samples were collected from the inserts every 11.6 days (mean) over a two-year monitoring period. Volume and mass of total and categorical (i.e., vegetation, cigarettes, plastic, glass, metal, wood, fabric, gravel, and paper) debris were characterized. Mean total macrodebris volume and mass were 4.62 L and 0.49 kg per sampling window, corresponding to mean volumetric and mass loading rates of 8.56 L/ha/day and 0.79 kg/ha/day, respectively. Natural debris (e.g., vegetation) was the primary contributor to macrodebris (mean 80.3% (i.e., 3.94 L of the mean 4.66 L total sample volume) and 79.7% (i.e., 0.42 kg of the mean 0.53 kg total sample mass) of total volume and mass, respectively), and exhibited seasonal peaks in autumn due to leaf drop. Road functional class (i.e., interstate, principal arterial, and minor arterial routes), land use, and development density significantly impacted macrodebris generation, with increased total and categorical macrodebris along urbanized interstate highways near commercial and residential areas. Macrodebris moisture content was highly variable (ranging from 1.5 to 440%; mean 78.5%), indicating additional management (e.g., drying, solidification) may be required prior to landfilling. Results of this study inform macrodebris mitigation strategies and required maintenance frequencies for pre-treatment devices for other stormwater control measures treating road runoff, including catch basin inserts and hydrodynamic separators, among others.
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Permeable pavements are increasingly implemented to mitigate the negative hydrologic outcomes associated with impervious surfaces. However, the hydraulic function of permeable pavements is hindered ...by clogging in their joint openings, and systematic maintenance is needed to ensure hydraulic functionality throughout the design lifespan of these systems. To quantify the effectiveness of various maintenance measures, surface infiltration rates (SIRs) were measured before and after five different maintenance techniques were applied to five permeable interlocking concrete pavements (PICPs) in central Ohio, USA. Three maintenance techniques, the Municipal Cleaning Vehicle (MCV), the Rejuvenater, and a pressure washer and the Rejuvenater performed in series, significantly improved median SIRs from 16 to 26, 5 to 106, and 11 to 37 mm/min, respectively. However, pressure washing alone resulted in no significant difference to PICP SIR (median SIRs increased from 8 to 20 mm/min). Regenerative air street sweeping significantly worsened SIRs when performed during wet weather (median SIRs decreased from 19 to 4 mm/min) but had no significant impact on SIRs during dry weather (median SIRs decreased from 21 to 18 mm/min). This work captured the maintenance effectiveness of two techniques for the first or second time, namely the Rejuvenater and MCV, to investigate their use as a suitable maintenance technique. Further, the maintenance techniques were tested on multiple PICPs, thus the effect of in-situ pavement conditions had on hydraulic improvement via maintenance could be addressed. Differences in general upkeep, traffic, and runoff routed to a PICP affected the depth of clogging below the pavement surface, which forestalled hydraulic improvement. Though shown to improve the SIR of PICP systems, results indicate that the maintenance techniques were not capable of restoring pavement hydraulics to initial conditions. These results demonstrate the need for regular, routine maintenance and topping up of joint aggregate before clogging migrates deeper into the pavement profile.
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•Assessed pavement conditions and operational factors with maintenance techniques.•Initial hydraulic function was not restored by any maintenance technique studied.•Regenerative air sweeping only improved hydraulic function under ideal conditions.•Best performance observed for techniques combining pressure washing and vacuuming.•Clogging material observed more than 4 cm below pavement surface.
Climate stationarity is a traditional assumption in the design of the urban drainage network, including green infrastructure practices such as bioretention cells. Predicted deviations from historic ...climate trends associated with global climate change introduce uncertainty in the ability of these systems to maintain service levels in the future. Climate change projections are made using output from coarse-scale general circulation models (GCMs), which can then be downscaled using regional climate models (RCMs) to provide predictions at a finer spatial resolution. However, all models contain sources of error and uncertainty, and predicted changes in future climate can be contradictory between models, requiring an approach that considers multiple projections. The performance of bioretention cells were modeled using USEPA's Storm Water Management Model (SWMM) to determine how design modifications could add resilience to these systems under future climate conditions projected for Knoxville, Tennessee, USA. Ten downscaled climate projections were acquired from the North American Coordinated Regional Downscaling Experiment program, and model bias was corrected using Kernel Density Distribution Mapping (KDDM). Bias-corrected climate projections were used to assess bioretention hydrologic function in future climate conditions. Several scenarios were evaluated using a probabilistic approach to determine the confidence with which design modifications could be implemented to maintain historic performance for both new and existing (retrofitted) bioretention cells. The largest deviations from current design (i.e., concurrently increasing ponding depths, thickness of media layer, media conductivity rates, and bioretention surface areas by 307%, 200%, 200%, and 300%, respectively, beyond current standards) resulted in the greatest improvements on historic performance with respect to annual volumes of infiltration and surface overflow, with all ten future climate scenarios across various soil types yielding increased infiltration and decreased surface overflow compared to historic conditions. However, lower performance was observed for more conservative design modifications; on average, between 13-82% and 77–100% of models fell below historic annual volumes of infiltration and surface overflow, respectively, when ponding zone depth, media layer thickness, and media conductivity were increased alone. Findings demonstrate that increasing bioretention surface area relative to the contributing catchment provides the greatest overall return on historic performance under future climate conditions and should be prioritized in locations with low in situ soil drainage rates. This study highlights the importance of considering local site conditions and management objectives when incorporating resiliency to climate change uncertainty into bioretention designs.
•Bioretention climate resiliency analyzed using SWMM models and probabilistic approach.•Climate model bias corrected using novel technique (KDDM); used as SWMM model inputs.•Increasing relative bioretention surface area provided greatest performance returns.•Conservative modifications yielded fewer scenarios surpassing historic performance.•Local site conditions, management objectives key to bioretention climate resiliency.
Mosquitoes (Diptera: Culicidae) are one of the most impactful pests to human society, both as a nuisance and a potential vector of human and animal pathogens. Mosquito larvae develop in still aquatic ...environments. Eliminating these habitats near high human density or managing them to reduce the suitability for mosquitoes will reduce mosquito populations in these human environments and decrease the overall negative impact of mosquitoes on humans. One common source of standing water in urban and suburban environments is the water that pools in stormwater control measures. Previous studies have shown that some stormwater control measures generate large numbers of mosquitoes while others harbor none, and the reason for this difference remains unclear. Our study focuses on elucidating the factors that cause a stormwater control measure to be more or less suitable for mosquitoes. During the summers of 2021 and 2022, we collected and identified mosquito larvae from thirty stormwater control measures across central Ohio to assess variation in mosquito abundance and diversity among sites. Our goal was to determine if specific types of stormwater control measures (retention ponds, detention ponds, or constructed wetlands) harbored different abundances of mosquitoes or different community structures. We also assessed environmental parameters of these sites to elucidate their effects on mosquito abundance and diversity. Overall, we recorded the highest number of mosquito larvae and species in constructed wetlands. However, these sites were dominated by the innocuous species, Culex territans. Conversely, detention ponds held fewer mosquitoes but a higher proportion of known vector species, including Culex pipiens and Aedes vexans. The total number of mosquitoes across all sites was correlated with higher vegetation, more shade, lower water temperatures, and lower pH, suggesting stormwater control measures with these features may also be hotspots for mosquito proliferation.
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•Monitored rainfall-runoff responses from 13 urban and two forested watersheds.•Statistically compared measurements to current and novel hydrologic design models.•Greater uncertainty ...in peak flow predictions compared to runoff volume.•Different design models necessary for specific watershed / rainfall characteristics.
The need for resilient stormwater infrastructure is increasingly critical as urbanization and climate change continue to threaten water resources. Engineers and practitioners require reliable methodologies to estimate rainfall-runoff responses to adequately size and design sewer pipes and inlets, flood controls, and stormwater control measures (SCMs). The National Resource Conservation Service Technical Release 55 (often referred to as curve number CN method), Simple, and Rational methods are methodologies commonly implemented for such designs by regulatory agencies due to the limited inputs needed to estimate runoff; however, uncertainty is present in each model since they simplify actual hydrological processes. In this study, 13 urban and two forested watersheds were monitored, and their observed hydrologic responses were compared to modeled hydrologic responses utilizing the aforementioned methods. Significant differences in observed normalized runoff volumes (i.e., runoff coefficients) and normalized peak flow rates were found between watersheds with similar watershed characteristics and rainfall patterns, demonstrating the meticulous model inputs required to differentiate hydrologic responses between similar watersheds. A suite of alternative predictive models, informed by feature selection algorithms, were formulated and compared to the performance of standard methods. Results suggested that composite CN methods were the best predictors of event runoff volume across all watersheds (Nash Sutcliffe NSE and Kling Gupta Efficiencies KGE of 0.74 and 0.52, respectively), but were outperformed by the Simple method for watersheds with more than 45% impervious cover (NSE and KGE scores of 0.85 and 0.76, respectively). However, composite CN methods underestimated runoff volume from every watershed, a limitation that was intended to be addressed through the creation of the distributed CN method. In the distributed approach, runoff volume estimations were improved compared to the composite CN approach only when directly connected impervious area in the watershed was extremely high or extremely low. The multi-linear regression runoff volume model created herein did not outperform traditional runoff models except when rainfall depth was less than 12.5 mm (i.e., the storms for which traditional runoff volume estimation methods performed the worst). Uncertainty in modeled peak flow rate was substantially greater than for runoff volume (NSE and KGE scores between 0.48 – 0.55 and 0.39 – 0.67, respectively) across all methodologies. There is a continued need to develop more dependable estimates of peak flow which are critical to the design of pipes, flood routing, and hydrograph prediction. Overall, these results suggest one model is not optimal in all scenarios. Municipalities, regulatory agencies, and stormwater engineers should consider the adoption of multiple methodologies and use guidance from the results herein to provide recommendations as to when each model is most applicable.
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•Four-year monitoring hydrologic changes in four sewersheds within Columbus, OH USA.•Paired watershed approach to assess impacts of green infrastructure (GI) retrofits.•Reductions in ...peak flow rates, increases in lag-to-peak following GI implementation.•Additional improvements to infrastructure increased inflows, countering GI benefits.
Cities across the world are implementing green infrastructure (GI) retrofits to manage stormwater, but limited research has been performed to quantify the hydrologic impact of these efforts at the watershed-scale. To fill this knowledge gap, this study aimed to monitor and evaluate the impact of GI stormwater control measures (SCMs) on sewershed-scale runoff hydrology across multiple treatment sewersheds with varying GI implementation. A paired watershed approach was applied in which a control (i.e., no GI), and three treatment sewersheds (208 bioretention cells and 8,400 m2 of permeable pavement in total) were monitored from 2016 to 2019 in Columbus, Ohio, USA. Further infrastructure changes, such as lining sanitary sewer laterals to prevent infiltration and inflow of stormwater, were anticipated to counterbalance the hydrologic improvements provided by the GI retrofits by routing more stormwater to the storm sewers. Significant decreases in runoff depths and peak flow rates (35–62% and 40–58% respectively) and increases in lag-to-peak (6–64%) were observed in the treatment sewersheds following the installation of GI retrofits. Compared to the control sewershed, the treatment sewersheds had slight increases (1–3 mm) in runoff thresholds and lower runoff coefficients post-GI. Following additional infrastructure changes, increases in volume and rate of flows were observed, but hydrologic indicators did not significantly differ from pre-GI levels (i.e., no net impact of the overall project on runoff hydrology). These responses indicated that sewershed-scale GI implementation successfully mitigated peak flow rates; however, the additional infrastructure improvement projects appear to have neutralized volume reductions by routing additional stormwater to the GI. Results confirm the impacts of sewershed-scale GI retrofits; however, research investigating the optimization of GI retrofit location, climate change impacts, and GI design, construction, and maintenance to maximize benefits of distributed SCMs in urban areas should be further explored.
Bioretention systems are designed for quality treatment of stormwater. Particulate contaminants are commonly treated efficiently and accumulate mainly in the surface layer of the bioretention filter ...material. However, concerns exist that microplastic particles may not show equal accumulation behavior as other sediment particles. So far only two field and two laboratory studies are available on the fate of microplastics in few relatively newly built bioretention systems. Therefore, this study investigated the abundance and distribution of microplastics in nine 7–12 years old stormwater bioretention systems. It was found that microplastics generally accumulate on the surface of bioretention systems. Microplastic median particle concentrations decreased significantly from the surface layer (0–5 cm) of the filter material to the 10–15 cm depth layer from 448 to 136 particles/100 g, respectively. The distance to the inlet did not significantly affect the surface accumulation of microplastic particles, suggesting modest spatial variability in microplastics accumulation in older bioretention systems. Further, this study investigated the polymer composition in bioretention systems. It was shown that PP, EVA, PS and EPDM rubber are the most abundant polymer types in bioretention systems. Also, it was found that large percentages of microplastic particles are black particles (median percentage of black particles: 39%) which were found in 28 of the 33 investigated samples. This underlines the importance of including black particles in microplastic studies on stormwater, which has been overlooked in most previous studies.
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•Occurrence and accumulation of microplastics in aged bioretention systems.•Determination of polymer types including black particles.•Microplastics are accumulated mainly in the filter media top layer.•Highest microplastic concentrations in the forebays.•Up to 59% of the microplastics in the filter media are black particles.
The discharge of excess nutrients to surface waters causes eutrophication, resulting in algal blooms, hypoxia, degraded water quality, reduced and contaminated fisheries, threats to potable water ...supplies, and decreases in tourism, cultural activities, and coastal economies. An understanding of the contribution of urban runoff to eutrophication is needed to inform management strategies. More broadly, the seasonality in nutrient concentrations and loads in urban runoff needs further analysis since algal blooms and hypoxia are seasonal in nature. This study quantifies the variation of nutrients and sediment in stormwater runoff across seasons from four urban residential sewersheds located in Columbus, Ohio, USA. An average of 62 runoff events at each sewershed were sampled using automated samplers during stormflow and analyzed for nutrients and total suspended solids (TSS). Spring total nitrogen concentrations had a significantly (p < 0.05) higher median concentration (2.19 mg/L) than fall (1.55 mg/L) and summer (1.50 mg/L). Total phosphorus concentrations were significantly higher in spring (0.22 mg/L) and fall (0.23 mg/L) than summer (0.15 mg/L). TSS concentrations were significantly higher in the spring (74.5 mg/L) and summer (56.5 mg/L) than the fall (34.0 mg/L). In contrast, seasonal loading differences for nutrients or sediment were rare because runoff volume varied in such a way as to offset significant concentration differences and significant seasonality in rainfall intensity. Annual pollutant loadings were similar in magnitude to other residential and even some agricultural runoff studies. Although nutrient loads are the key indicator for determining algal biomass, nutrient concentrations are important for real-time algal growth. Future research efforts should be focused not only on understanding how seasonal urban concentrations and loads impact coastal eutrophication, but also developing improved watershed management focused on critical periods. Improved designs for stormwater control measures need to account for seasonality in pollutant discharge.
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•Measured stormwater quality from four residential catchments in Ohio, USA.•Seasonality of nutrients and sediment was observed in residential stormwater runoff.•Springtime pollutant concentrations were higher across all sewersheds.•Runoff pollutant loads of TSS and ammonia were elevated in spring.•Designing for seasonality may require reexamination of stormwater control measures.
