Difference between revisions of "Bioretention"

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*Proper spacing must be provided for above-ground and below-ground utilities, and adjacent infrastructure.
 
*Proper spacing must be provided for above-ground and below-ground utilities, and adjacent infrastructure.
  
Tables for identifying ideal species for LID are found [[Bioretention: Plant lists|here]]. See [[Plant standards|plant standards]] for specific plant species and sizes.
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Tables for identifying ideal species for bioretention are found [[Bioretention: Plant lists|here]]. See [[Plant standards|plant standards]] for specific plant species and sizes.
  
 
==Construction==
 
==Construction==

Revision as of 19:37, 8 January 2018

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These bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cells at Edwards Gardens in Toronto receive inflow from hydraulically connected permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.
BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cell capturing and treating runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from adjacent parking lot at the Kortright Centre, Vaughan.

This article is about planted installations designed to capture and filter surface runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. through engineered soil (filter media).
For simple systems (typically without regulatory control), see Rain gardens.
For linear systems, which convey flow, but are otherwise similar see Bioswales.

Overview

BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. systems may be the most well recognized form of low impact development (LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.). They can fit into any style of landscape and encompass all mechanisms of action: infiltration, filtration and evapotranspiration.

BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. is an ideal technology for:

  • Fitting functional vegetation into urban landscapes
  • Treating runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. collected from nearby imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. surfaces

The fundamental components of a bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cell are:

Additional components may include:

Planning considerations

Space

  • For optimal performance bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. facilities should receive runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. 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 catchmentThe land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale. area to the bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. facility.
  • BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cells work best when distributed, so that no one facility receives runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from more than 0.8 Ha.
Although, there is a trade off to be considered regarding distributed collection and treatment against ease of maintenance.
  • BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. can be almost any shape, from very curving, 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.
The maximum width of a facility is determined by the reach of the construction machinery, which must not be tracked into the cell.

Bioretention: Context

InfiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.

Some form of stormwater landscaping (bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.) can be fitted into most spaces. One of the key decisions is whether to infiltrate all of some of the collected water into the native soilThe natural ground material characteristic of or existing by virtue of geographic origin.. Although there are some constraints to infiltrating water, it is preferable to do so where possible. Partial infiltration facilities are a popular choice over 'tight' soils (infiltration ≤ 15 mm/hr).

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

Inlets and pretreatmentInitial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms. options

Options for pretreatment include:

Simple (non-treating) inlets include:

  • Sheet flow from a depressed curb
  • One of more curb cuts
  • Covered drains

Overflow routing

Conceptual diagram of the excess routing alternatives: On the left, excess flow leaves the cell via an overflow; on the right, excess flow is diverted so that only the design volume enters the cell.

Routing

  • Infiltration facilities can be designed to be inlineRefers to a system that accepts all of the flow from a drainage area and conveys larger event flows through an overflow outlet. or offlineRefers to a system that when full, stormwater will bypass the practice. Offline systems use flow splitters or bypass channels that only allow the water quality volume to enter the facility. This may be achieved with a pipe, weir, or curb opening sized for the target flow, but in conjunction, create a bypass channel so that higher flows do not pass over the surface of the filter bed. from the drainage systemA system flow of gully inlets, pipes, overland flow paths, open channels, culverts and detention basins used to convey runoff to its receiving waters. City of Toronto 45 Wet Weather Flow Management November 2006. See Inlets
  • InlineRefers to a system that accepts all of the flow from a drainage area and conveys larger event flows through an overflow outlet. facilities accept all of the flow from a drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds. and convey larger event flows through an overflow outlet. The overflow must be sized to safely convey larger storm events out of the facility.
  • The overflow must be situated at the maximum surface ponding elevation or furthest downgradient end of the facility to limit surface ponding during periods of flow in excess of the facility storage capacity.
  • OfflineRefers to a system that when full, stormwater will bypass the practice. Offline systems use flow splitters or bypass channels that only allow the water quality volume to enter the facility. This may be achieved with a pipe, weir, or curb opening sized for the target flow, but in conjunction, create a bypass channel so that higher flows do not pass over the surface of the filter bed. facilities use flow splitters or bypass channels that only allow the design storm runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. storage volume to enter the facility. Higher flows are conveyed to a downstream storm sewer or other 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. by a flow splitting manhole weir or pipe, or when the maximum surface ponding depth has been reached, by by-passing the curb opening and flowing into a downstream catchbasinBox like underground concrete structure with openings in curb and gutter designed to collect runoff from streets and pavement. connected to a storm sewer.

Overflow elevation

The invert of the overflow should be placed at the maximum water surface elevation of the practice (i.e. the maximum surface ponding level). A good starting point is 150 to 350 mm above the surface of the mulcha top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales. cover. However, consideration should be given to public safety, whether or not an underdrainA perforated pipe used to assist the draining of soils. is included, the time required for ponded water to drain through the filter bed surface, and if no underdrainA perforated pipe used to assist the draining of soils. is present, into the underlying native soilThe natural ground material characteristic of or existing by virtue of geographic origin. (must drain within 48 hours). See Bioretention: Sizing and Stormwater planters for more details.

Freeboard

  • In swales conveying flowing water a freeboard of 300 mm is generally accepted as a good starting point.
  • In bioretention the freeboard is the difference between the invert elevation of the overflow structure and the inlet. 150 mm will suffice, so long as the inlet will not become inundated during design storm conditions.
  • In above grade stormwater planters, the equivalent dimension would be the difference between the invert elevation of the overflow structure and the lip of the planter (150 mm minimum)

Overflow outlet options

Metal grates are recommended (over plastic) in all situations.

Feature Anti Vandalism/Robust Lower Cost Option Self cleaning
Dome grate x
Flat grate x
Catch basinGround depression acting as a flow control and water treatment structure, that is normally dry. x
DitchA long narrow trench or furrow dug in the ground, as for irrigation, drainage, or a boundary line. inlet catch basinGround depression acting as a flow control and water treatment structure, that is normally dry. x x
Curb cut x x x

Gallery

Design for maintenance

Design

Sizing and Modeling

BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. facilities should be sized to accommodate runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from approximately 5 to 20 times the footprint area of the facility. i.e. I/P ratioThe ratio of the impervious catchment (drainage) area to the pervious (footprint) area of the receiving BMP. of 5 to 20.

Sizing

Modeling

Submissions

Bioretention: Drawings

Plant Selection

  1. Exposure to roadway or parking lot runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface.
  • Select salt tolerant grasses, other herbaceous material and shrubs.
  • These can take on several forms, including parking lot islands, traffic islands, roundabouts, or cul-de-sacs and are often used as snow storage locations.
  1. No exposure to roadway or parking lot runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface.
  • Practices allow for a greater range of species selection.
  • These receive runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from rooftops or areas that use no deicing salt and have low pollutant exposure, such as courtyard bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation..

Other selection factors:

  • Most bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cells will be situated to receive full sun exposure. The ‘Exposure’ column in the master plant list identifies the sun exposure condition for each species.
  • Facilities with a deeper media bed (greater than 1 m) provide the opportunity for a wider range of plant species (including trees).
  • The inclusion of vegetation with a variety of moisture tolerances ensures that the bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cell will adapt to a variety of weather conditions.
  • Proper spacing must be provided for above-ground and below-ground utilities, and adjacent infrastructure.

Tables for identifying ideal species for bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. are found here. See plant standards for specific plant species and sizes.

Construction

Bioretention: Construction

Incentives and credits

In Ontario

City of Mississauga
The City of Mississauga has a stormwater management credit program which includes RWHRainwater harvesting. as one of their recommended site strategies [1].


LEED BD + C v. 4

Sustainable sites: Rainwater management (up to 3 points)

  • Two points (or 1 point for Healthcare) will be awarded if the project manages "the runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from the developed site for the 95th percentile of regional or local rainfall events."
  • Three points (or 2 points for Healthcare) will be awarded if the project manages "the runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from the developed site for the 98th percentile of regional or local rainfall events."
    OR
  • For zero-lot-line projects only, 3 points (or 2 points for Healthcare) will be awarded if the project manages "the runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from the developed site for the 85th percentile of regional or local rainfall events."

SITES v.2

See also

External links

Bioretention: External links