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→Planning considerations
[[File:Edwards Gardens Bio 2014.JPG|thumb|alt=This is alt text|These bioretention cells at Edwards Gardens in Toronto receive inflow from hydraulically connected permeable paving]]
[[File:Edwards Gardens Bio 2014.JPG|thumb|alt=This is alt text|These bioretention cells at Edwards Gardens in Toronto receive inflow from hydraulically connected permeable paving parking stalls]]
[[File:IMG 2457 750X500.jpg|thumb|Bioretention cell capturing and treating runoff from adjacent parking lot at the Kortright Centre, Vaughan.]]
[[File:IMG 2457 750X500.jpg|thumb|Bioretention cell capturing and treating runoff from an adjacent parking lot at the Kortright Centre, Vaughan.]]
This article is about planted installations designed to capture and infiltrate some or all of the stormwater received.
This article is about planted installations designed to capture and infiltrate some or all of the stormwater received.
<br> For simple systems, without underdrains or storage reservoir (typically found n residential settings), see [[Rain gardens]].
<br> For simple systems, without underdrains or storage reservoir (typically found n residential settings), see [[Rain gardens]].
<br> For linear systems, which convey flow, but are otherwise similar to bioretention see [[Swales|Bioswales]].
<br> For linear systems, which convey flow, but are otherwise similar to bioretention see [[Swales|Bioswales]].
<br> For planted systems that do not infiltrate any water, see [[Stormwater planters]]
<br> For planted systems that do not infiltrate any water, see [[Stormwater planters]].
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==Overview==
==Overview==
Bioretention systems may be the most well recognized form of [[low impact development]] (LID). They can fit into any style of landscape and encompass all mechanisms of action: [[infiltration]], filtration and [[evapotranspiration]].
Bioretention systems may be the most well recognized form of [[low impact development]] (LID). They can fit into any style of landscape and encompass all mechanisms of action: [[infiltration]], filtration, attenuation and [[evapotranspiration]].
{{textbox|Bioretention is an ideal technology for:
{{textbox|Bioretention is an ideal technology for:
*Fitting functional vegetation into urban landscapes
*Fitting functional vegetation into urban landscapes
*Treating runoff collected from nearby impervious surfaces}}
*Treating runoff collected from nearby impervious surfaces}}
'''The fundamental components of a bioretention cell are:'''
'''The fundamental components of a bioretention cell are:'''
*A 'filter bed' containing an [[Bioretention: Filter media| filter media]]
*A 'filter bed' containing a [[Bioretention: Filter media| filter media]]
*A storage layer of [[reservoir aggregate]]
*A storage layer of [[reservoir aggregate]]
*[[Plant lists|planting]], and
*[[Plant lists|planting]], and
'''Additional components may include:'''
'''Additional components may include:'''
*An [[underdrain]] to redistribute or remove excess water
*An [[underdrain]] to redistribute or remove excess water
*Soil [[additives]] intended to enhance nutrient and related water quality pollutant removal
==Planning considerations==
==Planning considerations==
''Note Site Considerations from the Bioretention Fact Sheet [https://sustainabletechnologies.ca/app/uploads/2013/02/Bioretention.pdf] in the 2010 CVC/TRCA LID Stormwater Management Planning Design are detailed below and within links included''
===Infiltration===
===Infiltration===
Some form of stormwater landscaping (bioretention) can be fitted into most spaces. Although there are some [[Infiltration#Constraints|constraints]] to infiltrating water, it is preferable to do so where possible.
Some form of stormwater landscaping (bioretention) can be fitted into most spaces. Although there are some [[Infiltration#Constraints|constraints]] to infiltrating water, it is preferable to do so where possible.
Designing bioretention without an underdrain is highly desirable wherever the soils permit infiltration at a great enough rate to empty the facility between storm events. Volume reduction is primarily through infiltration to the underlying soils, with some evapotranspiration. As there is no outflow from this BMP, it is particularly useful in areas where nutrient management is a concern to the watershed.
Designing bioretention without an underdrain is highly desirable wherever the soils permit infiltration at a rate which is great enough to empty the facility between storm events. Volume reduction is achieved primarily through infiltration to the underlying soils, with some evapotranspiration. As there is no outflow from this BMP under normal operating conditions, it is particularly useful in areas where nutrient management is a concern to the watershed.
Bioretention with an [[underdrain]] is a popular choice over 'tighter' soils where infiltration rates are ≤ 15 mm/hr. Including an perforated [[pipe]] in the [[reservoir aggregates|reservoir]] layer help to empty the facility between storm events, even over [[low permeability soils]]. The drain discharges to a downstream point, which could be an underground [[infiltration trench]] or [[chamber]] facility. Volume reduction is gained through infiltration and [[evapotranspiration]]. By raising the outlet of the discharge pipe the bottom portion of the BMP can only drain through infiltration. This creates a fluctuating anaerobic/aerobic environment which promotes denitrification. Increasing the period of storage has benefits for promoting infiltration, but also improves water quality for catchments impacted with nitrates. A complimentary technique is to use fresh wood mulch, which also fosters denitrifying biological processes.
Bioretention with an [[underdrain]] is a popular choice in areas with 'tighter' soils where infiltration rates are ≤ 15 mm/hr. Including an perforated [[pipe]] in the [[reservoir aggregate]] layer helps to empty the facility between storm events, which is particularly useful in areas with [[low permeability soils]]. The drain discharges to a downstream point, which could be an underground [[infiltration trench]] or [[chamber]] facility. Volume reduction is gained through infiltration and [[evapotranspiration]]. By raising the outlet of the discharge pipe the bottom portion of the BMP can only drain through infiltration. This creates a fluctuating anaerobic/aerobic environment which promotes denitrification. Increasing the period of storage has benefits for promoting infiltration, but also improves water quality for catchments impacted with nitrates. A complimentary technique is to use fresh wood mulch, which also fosters denitrifying biological processes.
Where infiltration is entirely impossible, but the design calls for planted landscaping, try a [[stormwater planter]] instead.
Where infiltration is entirely impossible, but the design calls for planted landscaping, try a [[stormwater planter]] instead.
===Space===
===Space===
*For optimal performance bioretention facilities should receive runoff from between 5 to 20 times their own surface area.
*For optimal performance bioretention facilities should receive runoff from between 5 to 20 times their own surface area.
*In the conceptual design stage it is recommended to set aside approximately 10 - 20 % of a catchment area to the bioretention facility.
*In the conceptual design stage it is recommended to set aside approximately 10 - 20 % of a catchment's total area for bioretention facility placement.
*Bioretention cells work best when distributed, so that no one facility receives runoff from more than 0.8 Ha.
*Bioretention cells work best when distributed, so that no one facility receives runoff from more than 0.8 Ha.
:Although, there is a trade off to be considered regarding distributed collection and treatment against ease of maintenance.
:Although, there is a trade off to be considered regarding distributed collection and treatment against ease of maintenance.
:For ease of construction and to ensure that the vegetation has adequate space, cells should be no narrower than 0.6 m at any point.
:For ease of construction and to ensure that the vegetation has adequate space, cells should be no narrower than 0.6 m at any point.
:The maximum width of a facility is determined by the reach of the construction machinery, which must not be tracked into the cell.
:The maximum width of a facility is determined by the reach of the construction machinery, which must not be tracked into the cell.
The principles of bioretention can be applied in any scenario where planting or vegetation would normally be found.
*Setback from Buildings: A typical four (4) metre setback is recommended from building foundations. If an impermeable liner is used, no setback is needed.
*Proximity to Underground Utilities and Overhead wires - consult with local utility companies regards to horizontal and vertical clearance required between storm drains, ditches, and surface water bodies. Further, check whether the future tree canopy height in the bioretention area will not interfere with existing overhead wires
The principles of bioretention can be applied in any scenario where planting or vegetation would normally be found.
===Private sites===
===Private sites===
In single family residential sites [[Rain gardens|rain gardens]] most often take the form of a soft edged, traditional perennial planting bed.
In single family residential sites [[Rain gardens|rain gardens]] most often take the form of a soft edged, traditional perennial planting bed.
===Sizing and Modelling===
===Sizing and Modelling===
Bioretention facilities should be sized to accommodate runoff from approximately 5 to 20 times the footprint area of the facility. i.e. I/P ratio of 5 to 20.
Bioretention facilities should be sized to accommodate runoff from approximately 10 to 20 times the footprint area of the facility. i.e. they should have an I/P ratio of 10 to 20.
When the drainage area is too large, silt can accumulate very rapidly, overwhelm the [[pretreatment]] devices, and lead to clogging of the facility.
When the drainage area is relatively small compared to a bioretention facility, it can make the facility appear unreasonably costly.
*'''[[Bioretention: Sizing| Sizing]]'''
*'''[[Bioretention: Sizing| Sizing]]'''
*'''[[Bioretention: TTT| Modelling]]'''
*'''[[Bioretention: TTT| Modelling]]'''
===Overflow routing===
===Overflow routing===
{{:Overflow}}
{{:Overflow}}
===Design for maintenance===
===Plant Selection===
The nature of bioretention cells is to attenuate stormwater from rainfall events of varying intensities. For this reason, the vegetation used must be suitable for the varying moisture conditions and is often categorized into three zones related to the grading of the feature.
#'''Low Zone''' -- This area is frequently inundated during storm events, and is well-drained between rainfall events.
#*Mineral Meadow Marsh plant community
#*Grasses, Sedges, rushes, wildflowers, ferns and shrubs that have an ‘Obligate’ to ‘Facultative’ designation
#*Wetland ‘Obligate’ species that are flood tolerant as they will persist in average years and flourish in wetter years.
#*Plants that are likely to occur in wetlands or adjacent to wetlands.
#*Plants with dense root structure and /or vegetative cover are favoured for their ability to act as pollution filters and tendency to slow water velocity
#*Be advised these practices are not constructed wetlands and are designed to fully drain within 48 hours.
#'''Mid Zone''' -- This zone is inundated less frequently (2 – 100 year storm events) and has periodically high levels of moisture in the soil. The ecology of this zone is a transition from the Mineral Meadow Marsh/Beach-type community to an upland community.
#*Plants able to survive in soils that are seasonally saturated, yet can also tolerate periodic drought.
#*Species include grasses and groundcovers, as well as low shrub species.
#'''High Zone''' -- The ecology of this zone is terrestrial due to its elevation in relation to the filter bed. The zone most closely resembles a Cultural Meadow or a Cultural Thicket community, depending on the mix of grasses, herbaceous material, shrubs and trees utilized.
#*Plants should have deep roots for structure, be drought-tolerant and capable of withstanding occasional soil saturation.
#*Trees and large shrubs planted in this zone will aid in the infiltration and absorption of stormwater.
#*This area can be considered a transition area into other landscape or site areas.
#*A variety (min. five) species should be used to prevent a monoculture.
Exposure to roadway or parking lot runoff must be considered.
#Exposure to roadway or parking lot runoff
#Exposure to roadway or parking lot runoff
*Select salt tolerant grasses, other herbaceous material and shrubs.
#*Select salt tolerant grasses, other herbaceous material and shrubs.
*These can take on several forms, including parking lot islands, traffic islands, roundabouts, or cul-de-sacs and are often used as snow storage locations.
#*These can take on several forms, including parking lot islands, traffic islands, roundabouts, or cul-de-sacs and are often used as snow storage locations.
#No exposure to roadway or parking lot runoff
#No exposure to roadway or parking lot runoff
*Practices allow for a greater range of species selection.
#*Practices allow for a greater range of species selection.
*These receive runoff from rooftops or areas that use no deicing salt and have low pollutant exposure, such as courtyard bioretention.
#*These receive runoff from rooftops or areas that use no deicing salt and have low pollutant exposure, such as courtyard bioretention.
Other selection factors:
Other selection factors:
*The inclusion of vegetation with a variety of moisture tolerances ensures that the bioretention cell will adapt to a variety of weather conditions.
*The inclusion of vegetation with a variety of moisture tolerances ensures that the bioretention cell will adapt to a variety of weather conditions.
*Proper spacing must be provided for above-ground and below-ground utilities, and adjacent infrastructure.
*Proper spacing must be provided for above-ground and below-ground utilities, and adjacent infrastructure.
*Where possible, a combination of native trees, shrubs, and perennial herbaceous materials should be used.
*A planting mix with evergreen and woody plants will provide appealing textures and colors year round, but they may not be appropriate for snow storage areas.
*In areas where less maintenance will be provided and where trash accumulation in shrubbery or herbaceous plants is a concern, consider a “turf and trees” landscaping model.
*If trees are to be used, or the bioretention is located in a shaded location, then ensure that the chosen herbaceous plants are shade tolerant.
*Spaces for herbaceous flowering plants can be included. This may be attractive at a community entrance location or in a residential rain garden.
Tables for identifying ideal species for bioretention are found in the [[Plant lists]]. See [[plant selection]] and [[planting design]] for supporting advice.
Tables for identifying ideal species for bioretention are found in the [[Plant lists]]. See [[plant selection]] and [[planting design]] for supporting advice.
==See also==
==See also==
==External links==
==External links==
*[http://hlw.org.au/u/lib/mob/20150715140823_de4e60ebc5526e263/wbd_2014_bioretentiontdg_mq_online.pdf|Bioretention Design Guidelines (2014) Healthy Waterways]
*[https://hlw.org.au/download/bioretention-technical-design-guidelines/ Bioretention Design Guidelines (2014) Healthy Waterways]
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[[Category:Infiltration]]
[[Category:Infiltration]]
[[Category:Green infrastructure]]
[[Category:Green infrastructure]]