Changes

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 include fresh wood mulch in the [[Bioretention: Internal_water_storage| storage reservoir]] aggregate, which 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, 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.