Constructed Stormwater Wetlands Research Articles

Developing simple indicators of nitrogen and phosphorus removal in constructed stormwater wetlands

Quantifying pollutant removal by stormwater wetlands requires intensive sampling which is cost-prohibitive for authorities responsible for a large number of wetlands. Wetland managers require simple indicators that provide a practical means of estimating performance and prioritising maintenance works across their asset base. We therefore aimed to develop vegetation cover and metrics derived from monitoring water level, as simple indicators of likely nutrient pollutant removal from stormwater wetlands. Over a two-year period, we measured vegetation cover and water levels at 17 wetlands and used both to predict nitrogen (N) and phosphorus (P) removal. Vegetation cover explained 48 % of variation in total nitrogen (TN) removal; with a linear relationship suggesting an approximate 9 % loss in TN removal per 10 % decrease in vegetation cover. Vegetation cover is therefore a useful indicator of TN removal. Further development of remotely-sensed data on vegetation configuration, species and condition will likely improve the accuracy of TN removal estimates. Total phosphorus (TP) removal was not predicted by vegetation cover, but was weakly related to the median water level which explained 25 % of variation TP removal. Despite weak prediction of TP removal, metrics derived from water level sensors identified faults such as excessive inflow and inefficient outflow, which in combination explained 50 % of the variation in the median water level. Monitoring water levels therefore has the potential to detect faults prior to loss of vegetation cover and therefore TN removal, as well as inform the corrective action required.

Catchment sourcing urban pesticide pollution using constructed wetlands in Melbourne, Australia

A survey of 111 urban constructed stormwater wetlands (median watershed area = 86.8 ha) was conducted to identify the major pesticides present and to determine their major catchment sources (residential, industrial, commercial, sporting ovals) and associations with catchment imperviousness. Melbourne, Australia, has separate stormwater and sewerage systems and these wetlands are designed to treat urban stormwater. To maximise the pesticides that could be detected, three types of passive samplers (POCIS, Chemcatcher® SDB-XC and Chemcatcher® C18) were deployed, along with collection of fine sediments. A total of 231 pesticides were screened using these methods. Pesticides that were detected in >5 % of wetlands were checked to determine their registered use in urban areas using an Australian government database (PubCris). Twenty-five pesticides were detected in >5 % of wetlands: 4 pesticides were associated with non-urban land uses (agriculture and forests), another 4 pesticides had no known registered use in urban areas and 17 were associated with urban areas. The pesticides associated with urban areas were the herbicides simazine, diuron, metolachlor, bromacil, propyzamide and paclobutrazol, the fungicides tebuconazole, propiconazole, metalaxyl, trifloxystrobin, iprodione and carbendazim and the insecticides fipronil, bifenthrin, chlorantraniliprole, thiamethoxam and permethrin. Atrazine was also detected in 59 % of wetlands but has not been registered for urban uses in Australia since 2010. It's presence in Melbourne may be due to legacy issues or aerial transportation from rural areas where it's still widely used in crop cultivation. Generally, the major urban catchment source of pesticides is from residential areas (particularly fipronil and simazine), most likely in wood preservatives, paints and from weed or insect control. Many of these widely used pesticides were correlated with increased catchment imperviousness. Some pesticides (bromacil and imidacloprid) were correlated with commercial premises and chlorantraniliprole was correlated with the presence of sporting ovals in the catchment. No pesticides were specifically correlated with industrial areas. The use of passive samplers and fine sediments, in conjunction with detailed land use mapping of stormwater wetland catchments is very effective and efficient in monitoring and sourcing pesticide contamination in urban environments.

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.

Planting Stormwater Solutions: A methodology for siting nature-based solutions for pollution capture, habitat enhancement, and multiple health benefits

Urban areas worldwide must manage stormwater to prevent flooding and reduce pollution. Infrastructure has historically been designed and used for the single purpose of managing stormwater, but this gray infrastructure typically has negative consequences and fails to address other challenges faced by urban areas. As an alternative, vegetated Nature-Based Solutions (NBS) such as bioretention facilities, constructed stormwater wetlands, and outfall retrofits may be used to capture and treat stormwater, while also contributing other benefits, such as reducing urban heat-island effects, increasing carbon sequestration, improving air quality, climate adaptation, and access to open space, and enhancing mental and physical health and urban biodiversity. To optimize these benefits, the siting of NBS can be crucial. We developed a spatially explicit analytical methodology, Planting Stormwater Solutions, to prioritize the siting of vegetated NBS to benefit biological diversity, social and public health, and water quality. Using Los Angeles as a case study, we demonstrate where benefits spatially converge or diverge. We found that while some of the greatest opportunities to benefit biodiversity occur along waterways, the greatest social and public health benefits may be realized for NBS installed in and around heavily developed areas. NBS sited in areas with a high density of commercial and industrial land uses may provide the greatest water quality benefits. Use of our analytical methodology may allow decision-makers with limited resources and multiple challenges to make more informed siting decisions for vegetated NBS.

Dry Wetlands: Nutrient Dynamics in Ephemeral Constructed Stormwater Wetlands.

Constructed stormwater wetlands (CSWs) are used to address contaminants in urban stormwater such as nitrogen (N) and phosphorus (P), but their performance is variable. Ephemeral CSWs tend to be less effective than perennial CSWs at removing N and P. We asked: How does wetland vegetation and sediment affect nutrient cycling/release from sediment and vegetation in ephemeral CSWs? We focused on two ephemeral urban CSWs in Pocatello, ID, USA, one densely vegetated and the other nearly bare. We rewetted intact cores of dry wetland sediments and, separately, senesced vegetation for 1 week at the end of the summer dry period to assess whether wetland sediments and vegetation acted as sources or sinks of N and P. For both CSWs, there was a pulse of nutrients immediately following rewetting, but the magnitude of that pulse and subsequent changes in nutrient concentrations suggest different processes dominate at each wetland, driven by differences in wetland vegetation and associated sediment characteristics. There was evidence of denitrification between and during events at the vegetated wetland, but larger fluxes of P at this site suggests a tradeoff between denitrification and P release. While the experimental results suggested specific biogeochemical controls, CSW nutrient concentrations during three events were more dynamic and suggested more biogeochemical complexity than that represented in our experiment, both within events and seasonally. Ephemeral CSWs may create unique biogeochemical conditions and require careful design to ensure N and P retention. Managers will also need to consider whether perennial water sources would improve CSW function.

A simple and rapid direct injection method for the determination of glyphosate and AMPA in environmental water samples.

Glyphosate is currently the most widely used herbicide in the world, yet screening of environmental waters for this chemical is limited by the need for specialized derivatization and measurement methods that can be tedious and time-consuming. In this work, we present a novel method for the detection and quantification at trace levels of glyphosate and aminomethylphosphonic acid (AMPA) in environmental water samples. The detection and quantification of the analytes was performed by liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS). Chromatographic separation was achieved with an ion-exchange column and a pH-gradient elution of a solution of ammonium hydroxide and ammonium acetate. The limit of detection for glyphosate and AMPA was 0.25 μg L-1 and the limit of quantification was 0.5 μg L-1with a 20-μL injection. The method was used to investigate the levels of glyphosate and AMPA in surface water samples from the Yarra River catchment area and urban constructed stormwater wetlands. The results indicate that at the time of sampling, no glyphosate or AMPA was present in the samples from the Yarra River catchment area (n = 10). However, glyphosate was detected above the limit of quantification in 33% of the wetland samples (n = 12), with concentrations ranging from 1.95 to 2.96 μg L-1. Similarly, AMPA was quantified in 83% of the wetland samples, with concentrations ranging from 0.55 to 2.42 μg L-1. To our knowledge, this is the first report of a pH-gradient LC-MS/MS method for glyphosate and AMPA analysis at ultratrace levels, with minimal sample processing, avoiding costly, time-consuming derivatization and preconcentration steps. Graphical abstract ᅟ.

Shifts in dissolved organic matter and microbial community composition are associated with enhanced removal of fecal pollutants in urban stormwater wetlands

Constructed stormwater wetlands provide a host of ecosystem services, including potentially pathogen removal. We present results from a multi-wetland study that integrates across weather, chemical, microbiological and engineering design variables in order to identify patterns of microbial contaminant removal from inlet to outlet within wetlands and key drivers of those patterns. One or more microbial contaminants were detected at the inlet of each stormwater wetland (Escherichia coli and Enterococcus > Bacteroides HF183 > adenovirus). Bacteroides HF183 and adenovirus concentrations declined from inlet to outlet at all wetlands. However, co-removal of pathogens and fecal indicator bacteria only occurred at wetlands where microbial assemblages at the inlet (dominated by Proteobacteria and Bacteriodetes) were largely displaced by indigenous autotrophic microbial communities at the outlet (dominated by Cyanobacteria). Microbial community transitions (characterized using pyrosequencing) were well approximated by a combination of two rapid indicators: (1) fluorescent dissolved organic matter, and (2) chlorophyll a or phaeophytin a fluorescence. Within-wetland treatment of fecal markers and indicators was not strongly correlated with the catchment-to-wetland area ratio, but was diminished in older wetlands, which may point to a need for more frequent maintenance.

Phosphate Retention in a Constructed Stormwater Wetland with Low Total Suspended Solids Concentrations

AbstractAlthough constructed stormwater wetlands (CSWs) have been shown to treat stormwater runoff, the mechanisms controlling these water-quality improvements need further study. This research exp...

Adapting the Relaxed Tanks-in-Series Model for Stormwater Wetland Water Quality Performance

Across the globe, water quality standards have been implemented to protect receiving waters from stormwater pollution, motivating regulators (and consequently designers) to develop tools to predict the performance of stormwater control measures such as constructed stormwater wetlands (CSWs). The goal of this study was to determine how well the relaxed tanks-in-series (P-k-C*) model described the performance of CSWs in North Carolina. Storm events monitored at 10 CSWs in North Carolina were used for calibrating the model, and statistical evaluations concluded the model could adequately predict the performance for all pollutants except organic nitrogen. Nash–Sutcliff calibration/validation values were determined to be 0.72/0.78, 0.78/0.74, 0.91/0.87, 0.72/0.62, 0.88/0.73, and 0.91/0.63 for total nitrogen, total ammoniacal nitrogen, oxidized nitrogen, organic nitrogen, total phosphorus, and total suspended solids, respectively. Sensitivity analysis revealed only one calibration parameter with strong sensitivity, the Arrhenius coefficient (temperature dependent model coefficient). With this model, CSWs can be optimized to treat watershed-specific influent concentrations to meet effluent targets. In general, the current design technique used in North Carolina and many other locations (a first flush volume detention method) oversizes CSWs for water quality vis-à-vis the method herein, suggesting improved designs for water quality may be possible through scientifically-informed methods.

Modelling the Hydraulic Processes on Constructed Stormwater Wetland

Constructed stormwater wetlands are manmade, shallow, and extensively vegetated water bodies which promote runoff volume and peak flow reduction, and also treat stormwater runoff quality. Researchers have noted that treatment processes of runoff in a constructed wetland are influenced by a range of hydraulic factors, which can vary during a rainfall event, and their influence on treatment can also vary as the event progresses. Variation in hydraulic factors during an event can only be generated using a detailed modelling approach, which was adopted in this research by developing a hydraulic conceptual model. The developed model was calibrated using trial and error procedures by comparing the model outflow with the measured field outflow data. The accuracy of the developed model was analyzed using a well-known statistical analysis method developed based on the regression analysis technique. The analysis results show that the developed model is satisfactory.

Urban Stormwater Characterization, Control, and Treatment.

The following review presents a synthesis of 181 journal articles published during 2015 that represent progress toward better characterizing, controlling, and treating urban stormwater runoff. The review is structured by general topical areas related to (1) stormwater quality and quantity characterization; (2) engineered stormwater control and treatment practices, including erosion and sediment control, stormwater ponds, constructed stormwater wetlands, bioretention, permeable pavement, greenroofs, and rainwater harvesting systems; and (3) watershed-scale modeling and optimization of stormwater control and treatment practices. Common research themes emerging from this collection of studies include potential to enhance hydrologic and pollutant treatment performance of stormwater practices via media amendments and the use of innovative outlet control structures, as well as development of a more mechanistic understanding of hydrologic and water-quality functions to inform modeling and performance predictions. These studies serve to expand the field's knowledge base and will inform future efforts to further improve stormwater control and treatment at various spatial and temporal scales.

Phosphorus Removal in Constructed Stormwater Wetland Mesocosms Amended with Water Treatment Residuals.

Constructed stormwater wetlands (CSWs) reduce stormwater volume and improve water quality. One quality improvement is the removal of soluble reactive phosphorus (SRP). There has been limited study on SRP fate and transport or on the mechanisms to improve SRP removal due to the difficulty in quantifying the complex, spatially heterogeneous removal processes in two-dimensional flow. The present research analyzed the ability of wetland soil (Control) and wetland soil amended with 2%, 5%, and 8% (by mass) of aluminum-based water treatment residuals (AlWTRs) to remove SRP in surface-flow vegetated CSW mesocosms. Batch adsorption experiments showed increasing SRP sorption capacity with increased AlWTR content (590-850 mg/kg soil) compared to the Control (385 mg/kg soil); however, AlWTR-amended flowing mesocosms removed only 6.0-8.8 mg/kg SRP compared to 9.3 mg/kg SRP for the Control. The lack of increased SRP removal in AlWTR-amended mesocosms was attributed to flow dynamics (only 20% of the surface outflow was quantified as subsurface flow). These results suggest the extent of infiltration versus surface flow is key to soil amendments improving SRP removal in a CSW.

Long-term hydraulic and treatment performance of a 19-year old constructed stormwater wetland—Finally maturated or in need of maintenance?

Constructed stormwater wetlands (CSWs) are a commonly used measure for stormwater retention and quality treatment. However, although questions have been raised about the long-term performance of CSWs, only a few studies have targeted this issue and none have evaluated the performance of CSWs more than approximately 5–10 years old. Further, most studies have not examined the development of the long-term performance of CSWs but delivered a snapshot at a certain point of time. The present study investigated the performance of a 19-year-old CSW in Växjö, Sweden, treating stormwater from a 320-ha urban catchment. Besides removal of sediment from the CSW’s forebay, no other maintenance had been conducted. However, regular inspections had been performed. The results of the present sampling campaign were compared to two existing datasets collected at the same CSW after three years of operation in 1997 and nine years of operation in 2003. The CSW was found to provide efficient peak flow reduction and, depending on the event characteristics, also volume reduction. It still treated stormwater effectively: removal of Cd, Cu, Pb, Zn, TSS and TP event mean concentrations were between 89 and 96%, whereas mean concentrations of TN were reduced by 59%. The load removal efficiencies were even higher. Comparative analysis of the three monitoring periods based on the load removal efficiency revealed that the CSW, despite the lack of maintenance, performed more efficiently and stably for most pollutants compared to when newly constructed. This underlines the importance of the establishment and maturation of constructed wetland systems. Overall, the results showed that CSWs are resilient systems, which if designed well and regularly inspected to prevent major issues, can work efficiently for at least two decades.

GREEN INFRASTRUCTURE AND TRANSIT-ORIENTED MIXED USE DEVELOPMENT: THE ALEWIFE AREA OF CAMBRIDGE, MASSACHUSETTS

INTRODUCTION This paper is a case study of the progress on environmental and development fronts in this critical area of Cambridge, Massachusetts. Portions of the riverine system to the north (Little River and Alewife Reservation) have been restored and include public amenities, and the park to the east (Danehy Park) has been realized. The degraded industrial land uses that had comprised the bulk of the land use have made a transition to a dynamic, mixed-used neighborhood. This paper presents both the public and the private strategies undertaken to accomplish these goals. These strategies are presented in three parts: Public Infrastructure: Constructed Stormwater Wetlands and Larger Stormwater Management Goals Site Development: Environmental Strategies Urban Development Goals: Mixed-Use Neighborhood

Stormwater wetlands for the enhancement of environmental ecosystem services: case studies for two retrofit wetlands in Brisbane, Australia

Constructed stormwater wetlands are examples of ‘blue–green’ ecological engineering in the urban environment providing a range of ecosystem services. A study was undertaken in Brisbane, Australia to examine the enhancement of environmental ecosystem services in 2 retrofit wetlands. Originally concrete drainage channels in existing residential catchments, a series of wetlands and ponds were created i.e. green infrastructure in a brownfield setting. Boardwalks, pathways and interpretive signage were incorporated into the design.Golden Pond wetland was only 0.2% of the catchment whereas Bridgewater Creek – Bowie's Flat wetland was 0.4% of the catchment. The larger 0.8 ha Bridgewater Creek wetland had an overflow by-pass channel. Water quality (suspended solids and nutrients) and the diversity of aquatic macroinvertebrates were monitored for 2–4 years after construction.During storm events suspended solids increased at Golden Pond due to resuspension from the high velocities in this small linear flow system. Resuspension was minimised at Bridgewater Creek due to the by-pass channel. During dry weather suspended solids in both wetlands increased due to resuspension from the activity of waterbirds. Both wetlands were effective in reducing nutrient concentrations especially NOx–N and PO4–P, attributed to biological uptake; but during dry periods NH4–N increased within the system. The concept of irreducible background concentrations in wetland systems is discussed.Open water and aquatic vegetation provided habitats for macroinvertebrates. Species richness increased by more than 50% in both stormwater wetlands, compared to the concrete drains.Wetland sizing and design are essential parameters for water quality improvement and biodiversity.

Stormwater control measure (SCM) maintenance considerations to ensure designed functionality

Great investment is made in the design and installation of stormwater control measures (SCMs). Substantial research investment, too, is made to optimise the performance of SCMs. However, once installed, SCMs often suffer from lack of maintenance or even outright neglect. Key maintenance needs for wet ponds, constructed stormwater wetlands, bioretention, infiltration practices, permeable pavement, swales, and rainwater harvesting systems are reviewed with many tasks, such as the cleaning of pre-treatment areas and the preservation of infiltration surfaces, being common maintenance themes among SCMs. Consequences of lacking maintenance are illustrated (mainly insufficient function or failure). Probable reasons for neglect include insufficient communication, unclear responsibilities, lack of knowledge, financial barriers, and decentralised measures. In future designs and research, maintenance (and lack thereof) should be considered. Assessing the performance of SCMs conservatively and including safety factors may prevent consequences of under-maintenance; and requiring regular inspection may help to enforce sufficient maintenance.

Large body size for metamorphic wood frogs in urban stormwater wetlands

Constructed wetlands in urban environments may be used by urban amphibian populations for breeding. Yet, few studies have examined the performance of young-of-the-year from created wetlands even though the success of terrestrial life stages is directly linked to the performance of individuals at the egg and larval stage. We assessed how early-stage amphibians developing within constructed stormwater wetlands compared in body size (one metric of performance) to those in nearby natural wetlands. We conducted surveys for wood frog, Lithobates sylvaticus, larvae and young-of-the-year metamorphs at 13 wetlands located in the City of Edmonton, Alberta, Canada and compared metamorph size (a useful metric for fitness and reproductive success) between constructed stormwater and two types of natural wetlands. We related body size to within-wetland parameters (reflecting water chemistry, thermal regimes and physical characteristics) and used an information-theoretic approach to identify predictors of metamorph body size. Abundances of egg masses, larvae and metamorphs were generally lower at stormwater than natural wetlands. Metamorphs exhibited larger body size in stormwater wetlands compared to natural wetlands. Low metamorph abundances and cool, stable water temperatures best explained large body size in stormwater metamorphs. We propose that with increasing urbanization and associated construction of artificial wetlands, size benefits in early developmental stages may help individuals cope with reduced habitat suitability in the terrestrial environment.

The influence of urbanisation on macroinvertebrate biodiversity in constructed stormwater wetlands

The construction of wetlands in urban environments is primarily carried out to assist in the removal of contaminants from wastewaters; however, these wetlands have the added benefit of providing habitat for aquatic invertebrates, fish and waterbirds. Stormwater quantity and quality is directly related to impervious area (roads, sealed areas, roofs) in the catchment. As a consequence, it would be expected that impervious area would be related to contaminant load and biodiversity in receiving waters such as urban wetlands. This study aimed to establish whether the degree of urbanisation and its associated changes to stormwater runoff affected macroinvertebrate richness and abundance within constructed wetlands. Urban wetlands in Melbourne's west and south east were sampled along a gradient of urbanisation. There was a significant negative relationship between total imperviousness (TI) and the abundance of aquatic invertebrates detected for sites in the west, but not in the south east. However macroinvertebrate communities were relatively homogenous both within and between all study wetlands. Chironomidae (non-biting midges) was the most abundant family recorded at the majority of sites. Chironomids are able to tolerate a wide array of environmental conditions, including eutrophic and anoxic conditions. Their prevalence suggests that water quality is impaired in these systems, regardless of degree of urbanisation, although the causal mechanism is unclear. These results show some dependency between receiving wetland condition and the degree of urbanisation of the catchment, but suggest that other factors may be as important in determining the value of urban wetlands as habitat for wildlife.

Comparing Bridge Deck Runoff and Stormwater Control Measure Quality in North Carolina

AbstractBridge deck runoff sometimes directly discharges through deck drains to water bodies. As such, the runoff is usually not treated; however, recent pressures have led Departments of Transportation to install closed pipe drainage systems beneath bridges to deliver stormwater to a stormwater control measure (SCM). This can be costly both in terms of up-front and long-term maintenance capital. This study compared bridge runoff concentrations of nutrients, sediment, and heavy metals to effluent concentrations from six commonly used SCMs. Runoff quality samples from 15 bridges in North Carolina were collected and compared to those from 41 different SCMs across North Carolina. The SCMs examined in this study were permeable friction course (PFC) overlays, wet retention ponds (WP), bioretention cells (BRC), vegetated filter strips (VFS), constructed stormwater wetlands (CSW), and grassed swales (GS). Bridge deck runoff concentrations were not statistically different from SCM effluent concentrations for tota...

Maintenance versus Maturation: Constructed Storm-Water Wetland’s Fifth-Year Water Quality and Hydrologic Assessment

Constructed storm-water wetlands (CSWs) have become popular storm water control measures (SCMs) in low-lying coastal environments, offering a hybrid between larger detention practices (wet ponds) and newer green infrastructure technologies. However, it is relatively rare that CSWs are monitored once the practice has aged 4 years, causing some concern among stakeholders about the long-term performance of CSWs. The specific objective of this research was to investigate the effects that wetland maturation and lack of maintenance have on the ability of a 5-year-old CSW to mitigate hydrology and improve water quality. A CSW was monitored from 2012–2013 that had not been maintained since construction in the spring of 2007. Since then, it has established as a diverse and healthy ecosystem. The monitoring results were compared with the results of a study conducted at the same site for a 1-year period immediately following construction (2007–2008). In 2007–2008, runoff volumes were reduced 54% and peak discharges 80%; whereas in 2012–2013, no change was observed in volume, and peak discharges were reduced by 64%. The stark difference in hydrologic mitigation was attributed to less availability of design volume in 2012–2013 because of (1) organic detritus accumulation during the intervening 5 years measured to be 7 cm; (2) modest siltation; and (3) an upward water-table adjustment owing to differing average antecedent dry periods. The 2012–2013 hydrologic performance of this CSW was similar to other CSWs (that were 2 years of age) studied in North Carolina, indicating that ecological systems should be monitored for performance after the point of establishment (2–3 years) for regulatory purposes. Overall nitrogen event mean concentration (EMCs) were reduced as the wetland matured, but not for total phosphorus (TP), as the effluent concentrations increased from 2007–2008 to 2012–2013. CSW maturation seemed to outweigh the lack of maintenance for both nitrogen treatment and stabilization of internal sediment. Maintenance (removal/replacement of forebay sediments and detritus material) need was apparent, however, for TP treatment and hydrologic mitigation. This appeared to be the only form of maintenance that would have been needed in the last 6 years for an SCM treating a 47-ha watershed. In comparison to the other practices, namely bioretention and permeable pavement, similar CSWs may have much lower operation and maintenance costs. This may make CSWs a viable option in areas where little resources exist for SCM maintenance.