Journal of Sustainable Water in the Built Environment

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

Drinking water treatment residuals (DWTRs) are a promising media amendment for enhancing phosphorus (P) removal in bioretention systems, but substantial removal of dissolved P by DWTRs has not been demonstrated in field bioretention experiments. We investigated the capacity of a nonamended control media (control) and a DWTR-amended treatment media (DWTR) to remove soluble reactive P (SRP), dissolved organic P (DOP), particulate P (PP), and total P (TP) from stormwater in a 2-year roadside bioretention experiment. Significant reductions in SRP, PP, and TP concentrations and loads were observed in both the control and DWTR media. However, the P removal efficiency of the DWTR cells was greater than those of the control cells for all P species, particularly during the second monitoring season because P sorption complexes likely began to saturate in the control cells. The difference in P removal efficiency between the control and DWTR cells was greatest during large storm events, which transported the majority of dissolved P loads in this study. We also investigated the potential for DWTRs to restrict water flow through bioretention media or leach heavy metals. The DWTRs used in this study did not affect the hydraulic performance of the bioretention cells and no significant evidence of heavy-metal leaching was observed during the study period. Contrasting these results with past studies highlights the importance of media design in bioretention system performance and suggests that DWTRs can effectively capture and retain P without affecting system hydraulics if properly incorporated into bioretention media.

Green stormwater infrastructure, also known as stormwater control measures (SCMs), is a sustainable solution that has been widely used in controlling stormwater runoff in developed areas. Stormwater intensity and land use control the water quality and quantity in urban areas, while soil conditions and the functionality of the outlet structure control enhancement of the water quality and quantity in vegetated basins. The soil conditions and the outlet structure are dubbed geotechnical design characteristics. These parameters impact the basin’s infiltration capacity, volume, and peak flow. In this study, a multistage basin with three cells located at the Pennypack Creek headwaters in Pennsylvania was simulated using the Stormwater Management Model (SWMM). The investigated characteristics of the basin were the gate condition and pipe diameter of the outlet structure and the compaction condition of the soil. The model was calibrated considering opened- and closed-gate setup of the basin. The basin was unintentionally compacted during construction, and this compaction changed the infiltration properties of the basin from sandy loam soil (preconstruction) to sandy clay loam. After basin calibration, it was found that the closed-gate setup induced a high outflow reduction compared to the inflow. A parametric study considering both the outlet pipe diameter and soil type was conducted under both gate setups. The reduction of the outlet pipe diameter was the most effective characteristic in the outflow volume and flow peak reduction under the opened-gate setup, while the soil type was the most effective characteristic in the outflow volume and flow peak reduction under the closed-gate setup.

Vegetated basins are one type of stormwater control measure (SCM) that uses a depression to control runoff volume and enhance water quality. Within this depression, the infiltration and outflow are affected by the infiltration and outlet design characteristics (IODCs) of the basin such as the soil compaction and outlet structure conditions (e.g., opened or closed outlet, and pipe diameter). The distribution of many vegetated basins can mitigate runoff volume to reduce flooding within watersheds. Thus, it is essential to investigate the influence of basin quantity, distribution, and IODC on storm runoff volume, peak flow, and infiltration within watersheds. This study evaluated the influence of vegetated basin quantity, distribution, and IODCs on watershed-scale volume reduction, peak flow attenuation, and stream health using a spatial, hydraulic, and hydrologic framework. One multistage basin with three basins in series located at the Pennypack Creek headwaters in Pennsylvania was simulated using the Storm Water Management Model (SWMM). Then the basins were distributed in different quantities in the three headwater regions using ArcGIS tools. The most effective basin distribution and quantity pattern was used to conduct a parametric study considering different IODCs. The results showed that increasing the quantity of basins within all the headwater regions provided the maximum improvement to the stream volume reduction and peak flow attenuation in the watershed, 31% and 61%, respectively, during a single storm event. This volume reduction also was sensitive to the variation in the IODCs of the basins. Maintaining a fully closed outlet for the watershed basins increased the volume reduction by 78%. Maximizing the number of basins in a headwater can improve the health of receiving water bodies by effectively reducing the percentage of imperviousness. This study provides a framework for utilizing the simulation of a single SCM’s geotechnical and volume control properties using SWMM to optimize the location and quantity of SCMs within watersheds using ArcGIS.

Suspended solids in runoff were evaluated along the gradient of a bioswale stormwater control measure (SCM), considering storms of varying intensities. Total and size-fractionated suspended solids and their associated metals were used to investigate resuspension or deposition patterns and metal adsorption. Total suspended solids and their associated metal concentrations increased along the gradient of the SCM when average storm intensity was higher than $4.5\mathrm{mm}/\mathrm{h}$, suggesting resuspension was occurring. However, solids and their associated metals for fine size classes ($D<10\mathrm{\mu m}$) revealed that resuspension or ineffective deposition occurred along the SCM regardless of storm intensity, but the degree of resuspension was not related to average storm intensity. Adsorption coefficients derived from analysis of fine sizes were higher compared to coarser sizes by orders of magnitude (10 to 1,000 times), indicating a higher affinity for fine solids. Freundlich isotherm had the best goodness of fit in modeling metal adsorption onto fine solids. The observed resuspension and fine particle–associated metal transport highlight the importance of proper SCM design (e.g., employing forebays and weirs) and maintenance (e.g., vegetative cover and mulching) to address their corresponding challenges.

Stormwater management practices (SMPs) are increasingly being implemented in urban environments to provide water quality and quantity benefits to municipalities. Bioinfiltration systems (e.g., rain gardens) are a common type of SMP that rely on the infiltration of stormwater into the soil to capture and filter stormwater and make water available to plants. Most municipalities require that the maximum time for the ponded water to infiltrate (drain-down time) does not exceed 24–72 h after rainfall. If there is sustained ponding beyond this time period, the bioinfiltration system is considered to be underperforming. Management of such underperforming systems often involves substantial and costly restoration efforts (e.g., reconstruction, soil replacement), forfeiting infiltration benefits to pivot to a bioretention or other SMP approach, or even in some cases abandoning the SMP. A systematic forensic investigation to identify the specific cause(s) of underperformance may allow for more targeted, effective, and economical rehabilitation of the underperforming SMP. In this study, an underperformance assessment framework (UAF) was developed and applied to five underperforming bioinfiltration sites to identify the causes of extended ponding and inadequate water quantity removal relative to design standards. Once likely causes of underperformance were identified, targeted rehabilitation techniques were recommended to restore system performance. Through the use of this comprehensive and systematic tool, isolated SMP components can be identified and rehabilitated, thus avoiding the entire system overhaul, minimizing restoration costs, and avoiding the recurrence of similar issues. Future benefits resulting from the increased knowledge of bioinfiltration systems gained by using this tool include improvements to system design and maintenance, thus ensuring the sustainability and resiliency of urban SMPs.

Successful watershed planning requires a watershed-scale approach to the assessment of erosion hazards. Stream power, or the rate of energy expenditure of flowing water, is a driver of river erosion and morphologic change. Stream Power Index for Networks (SPIN) is a newly developed geographic information system (GIS)-based toolbox that uses simple inputs to calculate total stream power, specific stream power, and their change between past, present, and future land-use conditions. We tested the ability of SPIN to identify areas of erosion risk by comparing its outputs against an independent database of erosion mitigation sites in an urban river. Objectives were to (1) validate the channel slope and threshold particle size calculated by the toolbox against data collected from field sites, (2) assess the utility of the toolbox outputs for interpreting spatial patterns of erosion control structure construction and maintenance, and (3) evaluate how the toolbox can be used to support or enhance current erosion monitoring techniques. Channel slope and threshold substrate size values calculated by SPIN matched those measured in the watershed. Both total and specific stream power increased between the rural (preurban) and urban land-use conditions, and maps generated by the toolbox provided a visual assessment of areas of expected erosion risk. The density of erosion control structures increased with total and specific stream power, and threshold stream power ratio values were identified above which erosion control structures were widespread. Stream power indices were also related to the condition of erosion control structures when defined as the distance between the channel erosion and the infrastructure. The SPIN toolbox makes a novel contribution to erosion hazard assessment at a watershed scale. In combination with existing local monitoring and assessment techniques, this method should improve decision making around erosion mitigation strategies in urban rivers.

Rain gardens are commonly used as green infrastructure to reduce runoff volume and introduce ecological benefits to urban areas. The objective of this study was to evaluate hydrologic performance of a rain garden constructed on low-permeability subsoil with three different drainage systems: no drain, underdrain, and surface drain. A surface-subsurface hydrologic model was implemented in the evaluation. The mathematical model incorporates processes of runoff inflow, direct precipitation, infiltration, evapotranspiration (ET), exfiltration, and outflow. This modeling assessment used a rain garden with subsoil permeability of $1\mathrm{mm}/\mathrm{h}$, ponding and media depth of 304.8 mm each, and loading ratio (contributory catchment area over rain garden area) of 5:1 under rainfalls over an entire year as well as individual design storms in New Jersey. Over an entire year, the longest continual ponding times are 880, 8, and 12 h for design alternatives of no drain, underdrain, and surface drain, respectively. Mosquito issues might arise from long ponding time for the no-drain design. Soil moisture of all three drainage designs never reaches down to the wilting point. Volume reduction of stormwater runoff for the three drainage designs are 89%, 15%, and 58%, respectively. The hydrologic performance for individual design storms (1, 2, 5, 10, 25, 50, and 100 year) was also addressed. Differences of effectiveness in runoff volume reduction for individual storms among the three drainage designs are consistent with those for the entire year. However, the underdrain design has the best performance in peak runoff rate reduction. Taken together, the surface drainage system has the best balance among runoff reduction for flood mitigation, soil moisture for plant survival, and ponding time for mosquito issues. The surface drainage design is recommended for a rain garden if it is installed on subsoil of low permeability and if the runoff captured does not require a substantial water quality improvement.

Green stormwater infrastructure (GSI) has become a popular alternative to gray infrastructure design by decreasing stormwater pollution and providing a multitude of social, environmental, and economic benefits to communities. Although there has been an increase in the implementation of GSI within the planning and development of communities, little is known about the spatial distribution of maintenance impacts to GSI systems. To address this knowledge gap, a GSI maintenance needs index (MNI) was created for Philadelphia, Pennsylvania using a combination of variables that have been shown to potentially negatively affect the lifespan of GSI, such as litter, leaf litter, and sediment buildup. Philadelphia was used as a case study for creating this index because recently, GSI has been prioritized in the planning and development of projects throughout the city. Our findings suggest that these GSI impact variables are spatially diverse. This newly created GSI MNI is beneficial for decision makers involved in the planning stages of GSI implementation. This, in turn, will allow planners and municipalities to implement siting based on GSI type and local environment and apply targeted maintenance programs to ultimately improve the performance and extend the lifespan of local GSI systems.

Many postindustrial cities are transforming underused areas into urban agriculture, which presents unique stormwater management challenges. One way to manage runoff from urban agriculture is to use green stormwater infrastructure; however, to date, green stormwater infrastructure has largely been applied to treat runoff from impervious surfaces and its application to urban agricultural runoff is underexplored. This study seeks to fill this gap by monitoring two bioswales collecting and treating runoff from an urban farm in Milwaukee, WI. To do so, the influent and effluent at each bioswale was sampled and tested for total suspended solids (TSS), total phosphorus, and total nitrogen. Both bioswales were effective at reducing volume, peak flows, total phosphorus concentrations, and high concentrations of TSS ($>25\mathrm{mg}/\mathrm{L}$) but had mixed results in reducing total nitrogen concentrations and TSS at low influent concentrations ($25\mathrm{mg}/\mathrm{L}$). Large volume capture and exfiltration resulted in load reduction (median 98%) across all pollutants. Overall, this project demonstrates the feasibility of bioswales for reducing pollutant loads from urban farms, which may have different pollutant concentrations within stormwater runoff than other typical urban settings.

There has been a rise in interest to quantify evapotranspiration (ET) in green stormwater infrastructure (GSI), and to do so in easier and cheaper ways than full-scale research sites. This study evaluated using a leaf porometer to estimate ET from plants associated with GSI. The porometer measured water vapor as it transpired from a small portion of a leaf’s surface, which was compared to lysimeter-scale ET calculated via a mass balance method. Twelve vegetated lysimeters planted with black chokeberry, seaside goldenrod, or switchgrass were measured over time for stomatal conductance and lysimeter weight. Fairly strong and statistically significant correlations were observed between ET and stomatal conductance in the lysimeters growing black chokeberry and seaside goldenrod between June 12 and August 28, 2018 [$\mathrm{r}(15)=0.85$, $\mathrm{p}<0.01$]. This study demonstrates the utility of stomatal conductance in describing plant performance in GSI. Conveniently taken stomatal conductance measurements have the capability of being scaled up to describe ET at the GSI scale if they are paired with an approximation of total leaf area.

Permeable Interlocking Concrete Pavement is a type of permeable pavement system that allows surface water to infiltrate through the paver joints into aggregate storage layers below. As they age, sediment and debris accumulate on the surface and within the joints. This accumulation leads to decreased surface infiltration rates, which can ultimately lead to surface ponding. All permeable pavements require maintenance before surface clogging becomes severe. However, researchers still disagree as to the type and frequency of maintenance applied that best enhances the long-term efficiency of the system. This study aims to analyze differences in early and repeated maintenance and restorative maintenance using a regenerative air street sweeper on two identical cells manually clogged with street sweeping material. This study shows that early and repeated maintenance can extend the functional life of permeable pavement as infiltration measurements were similar to the restorative cell even after being clogged with 25% more street sweepings.