Rain gardens or bioretention cells, green roofs, planter boxes, bioswales, and other bioretention systems are examples of green infrastructure used in low impact development to make city landscapes more permeable to help absorb and control stormwater. Bioretention systems may be used to replace or supplement inadequate gray infrastructure (e.g., gutters, pipes, and tunnels) that would otherwise convey stormwater to water treatment facilities or directly to nearby bodies of water. Rain gardens and other bioretention systems can be implemented on a small scale on individual properties, sites, or neighborhoods, or on a larger scale throughout a city, county, or region. Native and adapted plants can be used in rain gardens and other bioretention systems, since they are tolerant of local climate, soil, and water conditions. Plants and soil layers in such systems filter water before it enters the groundwater system1.
Expected Beneficial Outcomes (Rated)
- Reduced run-off
- Reduced water pollution
- Reduced soil erosion
Other Potential Beneficial Outcomes
- Reduced flooding
- Increased wildlife habitat
- Improved mental health
- Improved health outcomes
- Reduced urban heat island effects
- Improved sense of community
- Reduced crime
Evidence of Effectiveness
There is strong evidence that rain gardens and other bioretention systems reduce stormwater run-off and pollutant concentrations, especially total suspended solids and heavy metals, and reduce soil erosion2, 3, 4, 5, 6, 7, 8, 9. Rain gardens can effectively treat stormwater run-off over the long-term10. Rain gardens and other bioretention systems are also a suggested strategy to protect communities from flooding, improve water quality, recharge groundwater, and preserve habitat, property, and other infrastructure1, 2, 8, 11, 12.
Coordinated efforts to establish many rain gardens throughout an area have a greater effect on water quality than individual rain gardens; combining rain gardens with other low impact development projects such as permeable pavement and infiltration trenches also increases effectiveness13, 14, 15, 16, 17. A San Francisco-based study shows bioretention systems along urban transit corridors can reduce pollutant loads to nearby water bodies and help meet area water quality goals4. Bioretention systems are generally more effective with lighter, steady rainfall rather than extreme storms18, 19. Rain gardens in urban park spaces can also reduce stormwater run-off20. However, individual rain gardens have limited capacity to reduce urban flooding18.
Proper design, implementation, and maintenance of rain gardens maximizes benefits and preserves long-term effectiveness2, 7. In some cases, rain garden effectiveness at capturing nitrogen (N) and phosphorus (P) even improves over time10. Studies show that soils of all types remove N and P from run-off and can retain various levels of N and P, although generally rain gardens retain P more effectively than N3. The amount of soil nutrients captured by rain gardens varies over time, with the intensity and duration of rain events5, and depending on the bioretention system’s design9, 21, 22, 23. Nitrogen retention after capture is especially difficult, since N is highly soluble; however, optimizing rain garden design can prevent N leaching24.
Properly sized and graded water basins can increase residential rain garden water storage capacity, pollutant removal, and erosion control. Deeper rain gardens can also improve effectiveness and capture more run-off; however, deeper rain gardens require more time and labor, more soil disposal, and knowledge of how to avoid safety issues when implemented near buried utilities on private property. Studies suggest most native soil types, except for clay soils, can be used in rain gardens to capture rainwater, with some variation in volume reduction25. Plants used in bioretention systems increase soil permeability, water conductivity, and N removal26. Some studies show using multiple plant species can improve biodiversity, ecosystem resilience, and rain garden functionality, including phosphorus uptake and capture and increased flooding tolerance27. Available evidence has not yet determined if using native plants in rain gardens is more effective than using exotic species; however, native plants may be more resilient and enhance local biodiversity26. In Illinois, rain gardens with native prairie grasses, sedges, and other plantings are associated with improved habitat and a noticeable increase in birds, bees, and butterflies17.
Rain gardens and other bioretention areas increase attractive green spaces, which may improve neighborhood aesthetics and enhance wildlife habitats8, 17. These additional green spaces may also improve mental and physical health for residents, reduce heat island effects, improve sense of community, and reduce crime28, 29. Available evidence shows rain gardens do not serve as mosquito breeding grounds19.
Experts suggest bioretention systems can be designed to maximize their potential for carbon sequestration in the soil30. However, the effectiveness of bioretention as a means to mitigate climate change may be limited, since biological processes in the soil also produce greenhouse gases, which can include nitrous oxide, methane, and carbon dioxide, in amounts that vary depending on water saturation over time31 and soil temperature32. In general, bioretention systems appear to sequester more carbon and nitrogen than the soil releases as greenhouse gases32.
Models suggest that residential rain garden adoption more than triples with government rebate incentives33. Surveys suggest that non-senior citizen households with higher incomes, higher levels of environmental concern, and more gardening experience are more likely to install rain gardens than other households33. Financial incentives and education also influence the likelihood of adopting green infrastructure34.
On average, residential rain gardens cost $3-4 per square foot and commercial gardens range from $10-40 per square foot; costs vary with plants used and other site specifics. Commercial rain gardens and other bioretention systems can cost less than traditional structural stormwater conveyance systems such as stormwater pipes and retention ponds35, 36. A benefit-cost analysis for Grand Rapids, Michigan suggests many green infrastructure projects are cost-effective, and identifies rain gardens as a low cost and attractive option, especially for small sites such as homes or street corners37.
Impact on Disparities
A few states have regulations that encourage sustainable water management, including techniques such as rain gardens and other bioretention systems; California is one example38. Many states and cities have guidelines encouraging stormwater management best practices that include using low impact development and green infrastructure such as rain gardens, bioswales, permeable pavement, green roofs, and rain barrels. Examples include ConnecticutFuss & O’Neill 2013 (citation unavailable), Minnesota40, Boston41, Los Angeles42, Muncie, Indiana43, New York City44, San Diego45, and Washington, DC46. The US Environmental Protection Agency’s Soak Up the Rain initiative also has many examples of rain gardens, bioretention systems, and other green infrastructure projects in residential developments, elementary schools, college campuses, commercial buildings, federal facilities, and along city streets throughout New England47.
Universities, colleges, and nonprofit organizations provide resources, trainings, information, and tools to support efforts by local governments, businesses, community organizations, and individuals to implement bioretention systems, as in Washington48 and Oklahoma49.
WSU-Rain gardens - Washington State University (WSU), Stewardship Partners. 12,000 Rain gardens in Puget Sound: About rain gardens.
RI DEM-Rain gardens - Rhode Island Department of Environmental Management (RI DEM). Rain gardens.
UCONN Ext-Rain gardens - University of Connecticut Cooperative Extension System (UCONN Ext). Rain gardens: A design guide for Connecticut & New England homeowners.
CDC-Water quality - Centers for Disease Control and Prevention (CDC). Healthy places: Water quality.
US EPA-LID - US Environmental Protection Agency (US EPA). Urban runoff: Low impact development (LID).
US EPA-Soak up the rain - US Environmental Protection Agency (US EPA). Soak Up the Rain: Municipal and community resources and resources for residents.
LSS-Stormwater - Lake Superior Streams (LSS). Tools for stormwater management.
SEMCOG-LID 2008 - Southeast Michigan Council of Governments (SEMCOG). Low impact development (LID) manual for Michigan: A design guide for implementers and reviewers. 2008.
NCSU-Stormwater resources - North Carolina State University (NCSU), Stormwater Engineering Group. NCSU Stormwater publications and resources.
CA DWR-Water efficient - California Department of Water Resources (CA DWR). Model water efficient landscape ordinance.
WEF-Potts 2015 - Potts A, Marengo B, Wible D. The real cost of green infrastructure. Water Environment Federation (WEF), Stormwater Report. 2015.
WMEAC-Calculator - West Michigan Environmental Action Council (WMEAC). Rainwater rewards: Green infrastructure benefits calculator.
McFarland 2019 - McFarland AR, Larsen L, Yeshitela K, Engida AN, Love NG. Guide for using green infrastructure in urban environments for stormwater management. Environmental Science: Water Research and Technology. 2019;5:643-659.
* Journal subscription may be required for access.
1 US EPA-Green infrastructure - US Environmental Protection Agency (US EPA). What is green infrastructure?
2 Sharma 2021* - Sharma R, Malaviya P. Management of stormwater pollution using green infrastructure: The role of rain gardens. WIREs Water. 2021;8.
3 Wadzuk 2021* - Wadzuk B, DelVecchio T, Sample-Lord K, Ahmed M, Welker A. Nutrient removal in rain garden lysimeters with different soil types. Journal of Sustainable Water in the Built Environment. 2021;7(1).
4 Gilbreath 2019* - Gilbreath A, McKee L, Shimabuku I, et al. Multiyear water quality performance and mass accumulation of PCBs, mercury, methylmercury, copper, and microplastics in a bioretention rain garden. Journal of Sustainable Water in the Built Environment. 2019;5(4).
5 Guo 2019* - Guo C, Li J, Li H, Li Y. Influences of stormwater concentration infiltration on soil nitrogen, phosphorus, TOC and their relations with enzyme activity in rain garden. Chemosphere. 2019;233:207-215.
6 Wang 2019* - Wang R, Zhang X, Li MH. Predicting bioretention pollutant removal efficiency with design features: A data-driven approach. Journal of Environmental Management. 2019;242:403-414.
7 Ahiablame 2012* - Ahiablame LM, Engel BA, Chaubey I. Effectiveness of low impact development practices: Literature review and suggestions for future research. Water, Air, and Soil Pollution. 2012;223:4253-4273.
8 Liu 2014 - Liu J, Sample D, Bell C, Guan Y. Review and research needs of bioretention used for the treatment of urban stormwater. Water. 2014;6:1069-1099.
9 LeFevre 2015* - LeFevre GH, Paus KH, Natarajan P, et al. Review of dissolved pollutants in urban storm water and their removal and fate in bioretention cells. Journal of Environmental Engineering. 2015;141(1).
10 Johnson 2019 - Johnson JP, Hunt WF. A retrospective comparison of water quality treatment in a bioretention cell 16 years following initial analysis. Sustainability. 2019;11(7).
11 CDC-Water quality - Centers for Disease Control and Prevention (CDC). Healthy places: Water quality.
12 Morsy 2016* - Morsy MM, Goodall JL, Shatnawi FM, Meadows ME. Distributed stormwater controls for flood mitigation within urbanized watersheds: Case study of Rocky Branch Watershed in Columbia, South Carolina. Journal of Hydrologic Engineering. 2016;21(11):5016025.
13 Roy 2014 - Roy AH, Rhea LK, Mayer AL, et al. How much is enough? Minimal responses of water quality and stream biota to partial retrofit stormwater management in a suburban neighborhood. PLOS One. 2014;9(1):e85011.
14 US EPA-LID - US Environmental Protection Agency (US EPA). Urban runoff: Low impact development (LID).
15 Pennino 2016 - Pennino MJ, McDonald RI, Jaffe PR. Watershed-scale impacts of stormwater green infrastructure on hydrology, nutrient fluxes, and combined sewer overflows in the mid-Atlantic region. Science of The Total Environment. 2016;565:1044-1053.
16 Tredway 2016* - Tredway JC, Havlick DG. Assessing the potential of low-impact development techniques on runoff and streamflow in the Templeton Gap watershed, Colorado. The Professional Geographer. December 2016:1-11.
17 Kim 2018* - Kim J. Exploring green infrastructure benefits at house and neighborhood scale: Case study of Illinois, USA. Landscape and Ecological Engineering. 2018;14:165-174.
18 Qin 2020 - Qin Y. Urban flooding mitigation techniques: A systematic review and future studies. Water. 2020;12.
19 Jennings 2016* - Jennings AA. Residential rain garden performance in the climate zones of the contiguous United States. Journal of Environmental Engineering. 2016;142(12):4016066.
20 Feldman 2019* - Feldman A, Foti R, Montalto F. Green infrastructure implementation in urban parks for stormwater management. Journal of Sustainable Water in the Built Environment. 2019;5(3).
21 Dietz 2007* - Dietz ME. Low impact development practices: A review of current research and recommendations for future directions. Water, Air, and Soil Pollution. 2007;186:351-363.
22 Roy-Poirier 2010* - Roy-Poirier A, Champagne P, Filion Y. Review of bioretention system research and design: Past, present and future. Journal of Environmental Engineering. 2010;136:878-889.
23 Strong 2015* - Strong P, Hudak PF. Nitrogen and phosphorus removal in a rain garden flooded with wastewater and simulated stormwater. Environmental Quality Management. 2015;25(2):63-69.
24 Osman 2019 - Osman M, Yusof KW, Takaijudin H, et al. A review of nitrogen removal for urban stormwater runoff in bioretention system. Sustainability. 2019;11.
25 DelVecchio 2020* - DelVecchio T, Welker A, Wadzuk BM. Exploration of volume reduction via infiltration and evapotranspiration for different soil types in rain garden lysimeters. Journal of Sustainable Water in the Built Environment. 2020;6(1).
26 Dagenais 2018* - Dagenais D, Brisson J, Fletcher TD. The role of plants in bioretention systems; does the science underpin current guidance? Ecological Engineering. 2018;120:532-545.
27 Morash 2019 - Morash J, Wright A, LeBleu C, et al. Increasing sustainability of residential areas using rain gardens to improve pollutant capture, biodiversity and ecosystem resilience. Sustainability. 2019;11.
28 Barton 2009 - Barton S. Human benefits of green spaces. University of Delaware Bulletin #137. 2009.
29 UN IL-LHHL - University of Illinois at Urbana-Champaign (UN IL). Landscape and Human Health Laboratory (LHHL).
30 Kavehei 2019* - Kavehei E, Jenkins GA, Lemckert C, Adame MF. Carbon stocks and sequestration of stormwater bioretention/biofiltration basins. Ecological Engineering. 2019;138:227-236.
31 Kavehei 2021* - Kavehei E, Iram N, Rezaei Rashti M, et al. Greenhouse gas emissions from stormwater bioretention basins. Ecological Engineering. 2021;159.
32 Shrestha 2018 - Shrestha P, Hurley SE, Adair EC. Soil media CO2 and N2O fluxes dynamics from sand-based roadside bioretention systems. Water. 2018;10(185).
33 Newburn 2015* - Newburn DA, Alberini A. Household response to environmental incentives for rain garden adoption. Water Resources Research. 2016;52(2):1345-1357.
34 Tayouga 2016 - Tayouga SJ, Gagné SA. The socio-ecological factors that influence the adoption of green infrastructure. Sustainability. 2016;8(12):1277.
35 LIDC-Bioretention costs - Low Impact Development Center (LIDC). Urban design tools: Bioretention costs.
36 Vineyard 2015* - Vineyard D, Ingwersen WW, Hawkins TR, Xue X, Demeke B, Shuster W. Comparing green and grey infrastructure using life cycle cost and environmental impact: A rain garden case study in Cincinnati, OH. Journal of the American Water Resources Association (JAWRA). 2015;51(5):1342-1360.
37 Nordman 2018* - Nordman EE, Isely E, Isely P, Denning R. Benefit-cost analysis of stormwater green infrastructure practices for Grand Rapids, Michigan, USA. Journal of Cleaner Production. 2018;200:501-510.
38 CA SB 7 - California Senate Bill No. 7 (CA SB 7). Part 2.55. Sustainable water use and demand reduction: Chapter 5: Sustainable Water Management. 2009.
39 Fuss & O’Neill 2013 - Fuss & O'Neill. Quinnipac River: Watershed based plan. 2013.
40 MN PCA-Stormwater - Minnesota Pollution Control Agency (MN PCA). Stormwater management: Low impact development and green infrastructure.
41 MAPC-Sustainable water - Metropolitan Area Planning Council (MAPC). Environment: Sustainable water management.
42 LASAN-Green infrastructure - City of Los Angeles, LA Sanitation & Environment (LASAN). Watershed protection program: Low impact development, green infrastructure, and more.
43 MSD-Stormwater management - Muncie Sanitary District (MSD). Stormwater management.
44 NYC-Green infrastructure - New York City (NYC) Environmental Protection. Green infrastructure.
45 San Diego-Water conservation - City of San Diego. Water conservation.
46 DC DDOT-Green infrastructure - Washington DC, District Department of Transportation (DDOT). Green infrastructure.
47 US EPA-Soak up the rain examples - US Environmental Protection Agency (US EPA). See who’s soaking up the rain: Connecticut, Massachusetts, New Hampshire, Rhode Island, Vermont, and Beyond New England.
48 WSC-LID - Washington Stormwater Center (WSC). Low impact development program (LID).
49 OK State-Bioretention - Oklahoma State University (OK State). Bioretention cells and rain gardens.
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