Evaluation of the effectiveness of green infrastructure on hydrology and water quality in a combined sewer overflow community

Authors: CHEN, JINGQIU - Purdue University; LIU, YAOZE - State University Of New York (SUNY); GITAU, MARGARET - Purdue University; ENGEL, BERNARD - Purdue University; Flanagan, Dennis; HARBOR, JONATHAN - Purdue University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2019
Publication Date: 1/31/2019
Citation: Chen, J., Liu, Y., Gitau, M.W., Engel, B.A., Flanagan, D.C., Harbor, J.M. 2019. Evaluation of the effectiveness of green infrastructure on hydrology and water quality in a combined sewer overflow community. Science of the Total Environment. 665:69-79. https://doi.org/10.1016/j.scitotenv.2019.01.416.
DOI: https://doi.org/10.1016/j.scitotenv.2019.01.416

Interpretive Summary: Large urban areas are covered by impermeable surfaces such as roads, buildings, and parking lots, which can generate nearly 100% runoff from rainstorms that occur. This can pose particular problems for cities, especially those which use combined sewer overflow systems (sewer pipes convey both sewage and surface runoff waters during large storm events). These large combined flows are usually released directly into streams or rivers, contributing large amounts of water pollutants. One way for cities to reduce these combined overflows is to reduce the amount of surface runoff by increasing the amount of “green” infrastructure (GI) in their systems, including things such as porous pavements and bioretention areas. In this computer simulation study, we examined the effects of using 8 different GI practices in reducing runoff and pollutant loads for the Darst Sewershed in Peoria, Illinois. We found that combined implementation of GI practices performed better than applying individual practices alone. The adoption levels and combinations of GI practices could potentially reduce runoff volumes by up to 23%, total suspended solids by up to 31%, total nitrogen losses by up to 28%, and total phosphorus losses by up to 28%. Also, adding more practices did not necessarily achieve substantial runoff and pollutant reductions based on the site characteristics. This research impacts cities and towns trying to address combined overflow water quality problems, as well as the public residing there and paying for these systems. The improved model developed here could be applied to other communities with similar concerns.

Technical Abstract: Evaluation of the effectiveness of green infrastructure (GI) practices on improving hydrology and water quality and their associated cost could provide valuable information for decision makers when creating development/re-development strategies. In this study, a watershed scale rainfall-runoff model (the Long-Term Hydrologic Impact Analysis - Low Impact Development model, the L-THIA-LID 2.1 model) was enhanced to improve its simulation of urban management practices including GI practices. The enhanced model (L-THIA-LID 2.2) is capable of: simulating in more detail impervious surfaces including sidewalks, roads, driveways, and parking lots; conducting cost calculations for converting these impervious surfaces to porous pavements; and, considering suitable areas for bioretention in the study area. The effectiveness of GI practices on improving hydrology and water quality in a combined sewer overflow urban watershed - the Darst Sewershed in the City of Peoria, IL - was examined in 11 simulation scenarios using 8 practices. The total cost and the cost effectiveness for each scenario considering a 20-year practice lifetime were calculated. Results showed: combined implementation of GI practices performed better than applying individual practices alone; the adoption levels and combinations of GI practices could potentially reduce runoff volume by 0.2-23.5%, TSS by 0.18-30.8%, TN by 0.2-27.9%, and TP by 0.2 to 28.1%; adding more practices did not necessarily achieve substantial runoff and pollutant reductions based on site characteristics; the most cost-effective scenario out of eleven considered had an associated cost of $9.21 to achieve 1 m^3 runoff reduction per year and $119 to achieve 1 kg TSS reduction per year assuming residents' cooperation in implementing GI practices on their properties; adoption of GI practices on all possible areas could potentially achieve the greatest runoff and pollutant reduction, but would not be the most cost-effective option. This enhanced model can be applied to different locations to support assessing the beneficial uses of GI practices.