Bioretention: Variations

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Types of bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. by underground design
Type Gravel layer UnderdrainA perforated pipe used to assist the draining of soils. Liner Mechanisms Schematic
Rain gardens - - - These are the simplest construction, often used by residents or community groups. Volume reduction is through infiltration and evapotranspirationThe quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/dayThe combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.. Rain Garden Schematic.png
Infiltrating bioretention yes - - This is a highly desirable type of bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. where 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 evapotranspirationThe quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/dayThe combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.. As there is no outflow from this BMPBest management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls., it is particularly useful in areas where nutrient management is a concern to the watershedThe drainage area of a river.An area of land that drains into a river or a lake. The boundary of a watershed is based on the elevation (natural contours) of a landscape.. Full infiltration.png
Partially infiltrating bioretention yes yes - Including an underdrainA perforated pipe used to assist the draining of soils. in the gravel storage layer help to empty the facility between storm events, even over ‘tight soils’. The drain discharges to a downstream point, which could be an underground infiltration facility. Limited volume reduction is gained through infiltration and evapotranspirationThe quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/dayThe combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.. By raising the outlet of the discharge pipe the bottom portion of the BMPBest management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls. can only drain through infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.. This creates a fluctuating anaerobic/aerobic environmentRefers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer. which promotes denitrification. Increasing the period of storage has benefits for promoting infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface., but also improves water quality for catchments impacted with nitrates. A complimentary technique is to use fresh wood mulcha top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales., which also fosters denitrifying biological processes. Partial infiltration.pngPartial with storage.png
Biofilters
(non-infiltrating)
yes yes yes This type may be required over contamination hot-spots or in very dense urban areas with a lot of other underground infrastructure. The design includes an impermeable base and sides, so that volume reduction is made only through evapotranspirationThe quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/dayThe combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.. This type of cell can be constructed above grade in any waterproof and structurally sound container, e.g. in cast concrete or a metal tank. Planter.png