Journal of Sustainable Water in the Built Environment

Abstract

Best-management practices (BMPs) are widely used to mitigate non-point source pollution from stormwater discharges. However, long-term operation and maintenance of stormwater BMPs have been an afterthought before the compliance requirement detailed in the Municipal Separate Storm Sewer Systems (MS4) permit. As a result, there is limited information available on the actual cost of maintaining BMPs. The objective of this research is to analyze the stormwater maintenance tracking database created by the Virginia Department of Transportation (VDOT) to (1) complete a preliminary cost analysis of routine and non-routine maintenance with respect to VDOT district or practice type and to (2) identify challenges encountered when processing the data for analysis and provide potential solutions relevant to other entities tracking BMP maintenance costs. The cost analyses presented in this study are preliminary based on the currently available data; however, they show insightful trends among the data collected by VDOT from 2018 to 2020. Namely, preventative maintenance actions appeared to greatly lower the need for non-routine or major repairs within the Virginia districts. Routine and non-routine maintenance costs were, on average, $375 per task and $812 per task, respectively. The cost of major repairs was approximately $63,000 per case. The most expensive routine maintenance tasks were basin BMPs (constructed wetlands, wet ponds, and extended detention ponds), averaging $400 per task. The most expensive non-routine maintenance tasks were infiltration BMPs (permeable pavement, infiltration practices, and bioretention), averaging $1,123 per task. Basin BMPs had the largest annual upkeep at $1,100 per year. Approaches for extending the current database design used by VDOT are discussed to address challenges identified through the analysis including data incompleteness, overloaded work orders, and the lack of controlled vocabulary. These lessons learned regarding database design can be useful to other agencies seeking to track and analyze stormwater maintenance activities and associated costs.

Practical Applications

The tracking of stormwater best-management practice (BMP) operation and maintenance (O&M) practices can help reduce the costs associated with stormwater permit compliance. A key factor in the O&M tracking process is the database design, which governs the collection, storage, accessibility, and analysis of the O&M data. However, the database design for BMP O&M tracking is not well documented. An analysis of the Virginia Department of Transportation’s (VDOT’s) O&M collection process and database design indicates that a many-to-many relationship exists between work orders and BMP assets, hindering the cost analysis of the maintenance work. Other challenges observed were a lack of controlled vocabulary when reporting the maintenance activities, assigning maintenance tasks associated with multiple BMPs to a single BMP, and the presence of incomplete work orders. Access to detailed BMP maintenance information can be used to calculate the approximate costs of routine and non-routine maintenance with respect to district or practice type, to determine estimates for BMP inspection frequencies, and to assess the level of effort needed to maintain certain BMPs. A design extension of the VDOT stormwater O&M tracking database is proposed that can inform the design for other states’ and communities’ stormwater BMP O&M tracking databases.

Solar photovoltaic (PV) farms are commonly used for harnessing renewable solar energy, but they will change the natural landscape. Surface depression storage refers to the maximum empty volume that precipitation can fill on a surface before runoff occurs. This study aimed to determine the surface depression storage depths and volumes of a solar PV farm and assess the impact of solar PV panels on them. A solar PV farm with a grassy land surface was chosen and divided into six subwatersheds with varying topographic characteristics. Terrestrial laser scanning (TLS) point cloud and its triangulated irregular network (TIN) were utilized to identify and quantify surface depressions. The results showed that the microtopography of the grassy land surface between and under solar PVPs and the components commonly found in solar PV farms were accurately captured compared with field observations. The rainfall-retaining depression depths at solar PV farms were found to span 0.91–12.63 mm, which, among other applications, would provide new reference values for watershed models. The study also found a positive correlation between the surface depression storage depth and the area ratio of solar PVPs. Moreover, this study isolated the impact of solar PV farms on surface depressions from the underlying grassy surfaces and revealed that a deviation in the area ratio of solar PVP from one-third will result in a deviation of depression depths from the underlying grassy land surfaces. This study provides reference data on rainfall-retaining ground surface depression depths of solar PV farms as well as offers direction for future solar PV farm installations, considering various solar PVP area ratios.

Bioretention practices have been developed to restore natural hydrologic regimes by reducing runoff volume and mitigating the peak flows of urban runoff. This is critical as cities encounter more extreme weather and their aging infrastructure is left ill-equipped to manage new stormwater management challenges. Functional improvements to bioretention through the use of real-time control (RTC) systems may allow more responsive system adjustments to manage incoming runoff volumes; however, minimal research has been performed to understand how various RTC schemes affect hydrologic partitioning and promote runoff volume reductions. A 6-week column study was conducted in which the water balances for static bioretention designs [i.e., free draining (FD) and internal water storage (IWS)] were compared against those of two RTC designs that focused on either regulating soil moisture (SM) or maximizing internal storage volumes (VC). Of the two RTC designs, the SM configuration showed the most storage capability (18%) and the lowest rate of bypass (7%) compared to the VC configuration that showed storage and bypass rates of 11% each. The FD and IWS configurations exhibited storage at 9% and 16% and bypass at 2% and 11%, respectively. This shows the potential for RTC to meet multiple, sometimes conflicting, objectives; in this case, volume reduction and bypass minimization. Correlation analysis revealed strong relationships between storm size and effluent volumes, but no correlation with seepage. Future research into the use of RTC for bioretention should include variable rainfall intensity in lab-scale studies to better understand flow dynamics over time. Studies should also be conducted in field-scale experiments to understand the larger practical implications of their design and implementation.

Stormwater control measures, including green and gray infrastructures, are increasingly used to enhance the level of sustainability of conventional drainage networks in managing rainfall-induced runoff. This paper studies the water quality and hydrologic performances of some bioretention cells and permeable pavements located in a parking lot in Boucherville (near Montreal), Canada, between July 2020 and November 2021. Because plants play a major role in the performance of green infrastructure, plant survival and growth monitoring were also conducted from June to September 2021. The results showed average runoff volume and average peak flow reductions of 91% and 98%, respectively, while the average delay in peak flow, for the few storm events with outflow, was 6.7 h. The average removal rates (in terms of concentration) for suspended solids, chemical oxygen demand, total phosphorus, and total nitrogen were 96%, 79%, 81%, and 90%, respectively, while there was an average increase in electric conductivity of 14%. The survival rate of trees planted in bioretention cells was 100%. For bushes, survival rates indicated a variation between 54% and 100%, while for perennials, survival rates varied between 0% and 100%. The plants with the least survival rates were Alchemilla mollis when planted at the top, with 0%, Rudbeckia fulgida var. ‘Pot of Gold,’ with 74%, and Salix purpurea ‘Gracilis,’ with 54%.

Abstract

Green stormwater infrastructure (GSI) promises to improve stormwater management while making landscapes more sustainable. The ability of GSI to achieve water quality objectives and provide socioeconomic cobenefits depends in part on public perceptions and support. This study contributes to the literature on public perceptions of top-down, municipal-scale GSI. We examined variation in public support for planned rain gardens and the factors associated with support in a large Midwestern city in the US. We collected survey data ($N=588$) in two socioeconomically distinct neighborhoods and fit multivariate linear regression models to explore how variables derived from economics, landscape ecology, and outreach and engagement literatures impact support. There was little difference in support between neighborhoods. The expectation of increased property values and improved neighborhood appearance, alignment with personal norms and experience with conservation landscaping, and satisfaction with outreach and engagement programs were significantly associated with higher support. In addition, strong neighborhood identity magnified the effects of several variables. These results suggest that planners should work with communities to identify rain garden designs and locations that balance functionality with aesthetic preferences to minimize potential negative socioeconomic effects while meeting stormwater management objectives. Proactive community engagement that is attentive to local norms and values and identifies appropriate rain garden maintenance plans could improve the long-term effectiveness of GSI by increasing the likelihood of local support.

Practical Applications

Cities are increasingly using technologies called green stormwater infrastructure (GSI) to manage drainage water, including flooding and sewage overflows to waterways. Common examples of GSI in urban areas are rain gardens and permeable pavement. Vegetated with perennial plants, rain gardens potentially offer additional benefits to urban environments such as pollinator habitat, lower summer heat, and improved community aesthetics, which can enhance health and well-being from activities like increased exercise. However, installing rain gardens alters the landscape, which can be viewed positively or negatively by residents. Public views on rain gardens are important because if viewed negatively, fewer people benefit and otherwise-effective GSI programs could fail to be pursued. On the other hand, community support for GSI could lead to long-term viability of the infrastructure and its benefits. We studied public perceptions of GSI in Columbus, Ohio, where the city planned to install rain gardens throughout residential neighborhoods. Residents were more likely to be supportive of planned rain gardens if they (1) felt they would improve their property values and appearance of the neighborhood, (2) felt sufficiently informed by the city about the rain garden plans, and (3) already had experience with conservation landscaping at home.