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[[File:IMG 2457 750X500.jpg|thumb|Bioretention cell capturing and treating runoff from an 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 reservoirs (typically found in 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 that have a gradually sloping filter media bed and 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 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 utilize all of the stormwater treatment mechanisms: [[infiltration]], filtration, attenuation 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 utilize all of the stormwater treatment mechanisms: sedimentation, [[infiltration]], filtration, attenuation and [[evapotranspiration]].

{{textbox|Bioretention is an ideal technology for:  

{{textbox|Bioretention is an ideal technology for:  

*Fitting multi-functional vegetation into urban landscapes  

*Fitting multi-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:'''

*[[Inlets| Inlets]]

*[[Inlets| Inlets]] which may be curb openings (e.g. modified curbs, spillways), pipes, road or side inlet catchbasins, trench drains or other pre-fabricated inlet structures;

*A surface ponding area

*A surface ponding area defined by landscaped side slopes or hardscape structures and the invert elevation of the overflow outlet structure;

*A filter bed containing a [[Bioretention: Filter media| filter media]]

*A filter bed containing [[Bioretention: Filter media| filter media]];

*A filter bed surface cover layer (e.g. [[mulch]] and [[stone]]);

*A filter bed surface cover layer (e.g. [[mulch]] and [[stone]])

*An [[Overflow| overflow outlet]] to limit surface ponding and safely convey excess flow to a downstream storm sewer or the next BMP in the treatment train.

*An [[Overflow| overflow outlet]] to safely convey excess flow to a downstream storm sewer or the next BMP in the treatment train.

'''Additional components may include:'''  

'''Additional components may include:'''  

*An [[underdrain]] to redistribute or remove excess water and structures or standpipe ports for periodic inspection and flushing

*An [[underdrain]] to redistribute or remove excess water and access structures or standpipes for periodic inspection and flushing;

*[[Wells|Monitoring wells]] installed to the base and screened in the internal water storage reservoir to verify and track drainage performance

*[[Wells|Monitoring wells]] installed to the base and screened in the [[underdrain]] aggregate to verify and track [[Drainage time|drainage time]]; and

*Filter media [[additives]] intended to enhance retention of nutrients, metals, petroleum hydrocarbons and/or bacteria.

*Filter media [[additives]] intended to enhance retention of nutrients, metals, petroleum hydrocarbons and/or bacteria.

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.

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 in areas with 'tighter' soils where infiltration rates are ≤ 15 mm/hr. Including a 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.

Bioretention with an [[underdrain]] is a popular choice in areas with 'tighter' soils where infiltration rates are < 15 mm/hr. Including a 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, creating an [[Bioretention: Internal_water_storage| internal water storage reservoir]]. 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 include fresh wood mulch in the storage [[Reservoir aggregate| reservoir aggregate]], which 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 impervious drainage areas between 5 to 20 times their own surface area.  

*For optimal performance bioretention facilities should receive runoff from impervious drainage areas between 5 to 20 times their own permeable footprint surface area.  

*In the conceptual design stage it is recommended to set aside approximately 10 - 20 % of the contributing drainage area for bioretention facility placement.  

*In the conceptual design stage it is recommended to set aside approximately 10 - 20 % of the contributing drainage area for bioretention facility placement.  

*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.  

*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 versus ease of maintenance.  

*Bioretention can be almost any shape, from having very curvilinear, soft edges with variable depth, to angular,  hard-sided and uniform depth.

*Bioretention can be almost any shape, from having very curvilinear, soft edges with variable depth, to angular,  hard-sided and uniform depth.

: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.

*Setback from Buildings: A typical four (4) metre setback is recommended from building foundations. If an impermeable liner is used, no setback is needed.

*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 regarding 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.

*Proximity to underground utilities and overhead wires: Consult with local utility companies regarding 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.

The principles of bioretention can be applied in any scenario where planting or vegetation would normally be found.

!style="background: darkcyan; color: white"|Better design choice: <br> Improves outflow water quality

!style="background: darkcyan; color: white"|Better design choice: <br> Improves outflow water quality

|-

|-

|Single large cell design||Several smaller distributed cells

|Single large cell design||Several smaller distributed or connected cells

|-

|-

|Single concentrated inflow||Forebays or distributed flow

|Single concentrated inflow||Forebays or distributed flow

|-

|-

|No pretreatment||Pretreatment provided as part of treatment train design

|No pretreatment||Pretreatment provided as part of inlet design

|-

|-

|Over-sized underdrain||Moderately sized underdrain (or no underdrain)

|Over-sized underdrain||Moderately sized underdrain (or no underdrain)

Bioretention facilities should be sized to accommodate runoff from approximately 5 to 20 times the footprint area of the facility. i.e. they should have an I/P ratio of 5 to 20.  

Bioretention facilities should be sized to accommodate runoff from approximately 5 to 20 times the footprint area of the facility. i.e. they should have an I/P ratio of 5 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 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 unreasonably costly.   

When the drainage area is relatively small compared to the bioretention facility, it can make the facility unreasonably costly.   

*'''[[Bioretention: Sizing| Sizing]]'''

*'''[[Bioretention: Sizing| Sizing]]'''

*'''[[Bioretention: TTT| Modelling]]'''

*'''[[Bioretention: TTT| Modelling]]'''

===Inlets and pretreatment options===  

===Inlets and pretreatment options===  

Options for [[pretreatment]] include:

Options for [[pretreatment]] include:

*A [[gravel diaphragm]] for sheet flow

*A [[level spreader]], [[gravel diaphragm]] or [[Vegetated filter strip]] for sheet flow

*[[Vegetated filter strips]] for sheet flow

*A [[Forebays|forebay]] for concentrated surface flow

*A [[Forebays|forebay]] for concentrated surface flow

*An [[Oil and grit separators|oil and grit separator]] for concentrated underground flow

*An [[Oil and grit separators|oil and grit separator]] for concentrated underground flow

Simple (non-treating) [[inlets]] include:

Simple (non-treating) [[inlets]] include:

*Sheet flow from a depressed curb

*Sheet flow from a pavement edge or flush curb

*One of more [[curb cuts]]

*One of more [[curb cuts]]

*Covered drains

*Covered drains

#'''Low Zone''' -- This area is frequently inundated during storm events, and is well-drained between rainfall events.

#'''Low Zone''' -- This area is frequently inundated during storm events, and is well-drained between rainfall events.

#*Mineral Meadow Marsh plant community.  

#*Mineral Meadow Marsh plant community.  

#*Grasses, Sedges, rushes, wildflowers, ferns and shrubs that have an ‘obligate’ to ‘facultative’ designation.  

#*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.

#*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 that are likely to occur in wetlands or adjacent to wetlands.  

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==

*[https://hlw.org.au/download/bioretention-technical-design-guidelines/ Bioretention Design Guidelines (2014) Healthy Waterways]

*[https://hlw.org.au/download/bioretention-technical-design-guidelines/ Bioretention Design Guidelines (2014) Healthy Waterways (Australia)]

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[[Category:Infiltration]]

[[Category:Infiltration]]

[[Category:Green infrastructure]]

[[Category:Green infrastructure]]