4.4.1 Applications & Limitations

While original applications focused primarily on stormwater pollutant removal, bioretention can be highly effective for flow control as well. Where the surrounding native soils have adequate infiltration rates, bioretention can be used as a primary or supplemental retention system. Under-drain systems can be installed and the facility used to filter pollutants and detain flows that exceed infiltration capacity of the surrounding soil. However, an orifice or other control structure is necessary for designs with under-drains to provide significant flow control benefits.

Applications with or without under-drains vary extensively and can be applied in new development, redevelopment, and retrofits. Bioretention areas are most often designed as a multifunctional landscape amenity that provides water quality treatment, stormwater volume reduction, and flow attenuation. Typical applications include:
  • Bioretention systems are applicable to many climatological and geologic situations, with some minor design changes for cold and arid climates (EPA, 2013), as discussed in Section 4.4.2: Design. See Figures 4.4.3 and 4.4.4 for examples of bioretention in arid environments.
  • In cold climates, bioretention areas can be used as a snow storage area. When used for this purpose, or if used to treat parking lot runoff, the bioretention area should be planted with salt tolerant and non-woody plant species.
  • Protection of cold water streams, notably trout streams that are extremely sensitive to changes in temperature. Bioretention has been shown to decrease the temperature of runoff from certain land uses, such as parking lots (EPA, 2013).
  • Individual lots for managing rooftop, driveway, and other on-lot impervious surface.
  • Shared facilities located in common areas for multiple lots.
  • Areas within loop roads or cul-de-sacs.
  • Landscaped parking lot islands.
  • Within right-of-ways along roads (often linear bioretention swales and cells). These facilities are sometimes designed to have traffic-calming functions as well.
  • Common landscaped areas in apartment complexes or other multi-family housing designs.
  • Infiltration planters are often used in highly urban settings as stormwater management retrofits next to buildings or within streetscapes.
  • Stormwater hotspots, or areas where land use or activities generate highly contaminated runoff, such as a gas station. Bioretention can be used to treat stormwater hot spots as long as an impermeable liner is used at the bottom of the treatment media layer (EPA, 2013), appropriate plants are selected that can tolerate contaminants present at the site, and inspection and maintenance plans are adequate to identify and address adaptive measures if needed.

While bioretention is one of the more widely applicable LID BMPs, there are some limitations to its use. Individual bioretention cells should not be used to treat large drainage areas, limiting their uses for some sites. Although bioretention does not typically consume a large amount of space, incorporating bioretention into site designs could impact other site uses, such as sidewalk or parking spaces. In areas where infiltration is not feasible, under-drains may be needed. Under-drained bioretention facilities can provide significant water quality treatment benefits, but typically provide less flow control than non-under-drained facilities. Under-drained facilities are not recommended to be installed if the under-drain discharge would be routed to a phosphorussensitive receiving water body (Ecology, 2013). Also note that under-drains could add complications with regards to conflicts with existing or future utilities. See Section 4.4.5: Infeasibility Criteria, for more discussion of limitations based on infesibility consideration.


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Fig4-4-3_IMG_8870
Fig 4.4.3
Arid climate bioretention example, Spokane. Source: City of Spokane


Fig4-4-4_2012-09-13_14-37-26_52
Fig 4.4.4
Bioretention in arid areas or other parts of the country, Columbus, Ohio. Source: AHBL, Inc.