Changes

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 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.

Bioretention with an underdrain is a popular choice over 'tighter' soils where infiltration rates are ≤ 15 mm/hr. Including an underdrain in the [[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 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.

===[[Inlets]] and pretreatment options===  

===[[Inlets]] and pretreatment options===