Changes

===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 aggregate]] layer helps 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.