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[[File:20161024 100338 550x550.jpg|thumb|Bioswale, County Court Boulevard, Brampton]]

[[File:20161024 100338 550x550.jpg|thumb|Bioswale, County Court Boulevard, Brampton]]

This article is about installations designed to capture and convey surface runoff along a vegetated channel, whilst also promoting infiltration. <br>

This article is about installations designed to capture and convey surface runoff along a vegetated channel, whilst also promoting infiltration. <br>

For underground conveyance which promotes infiltration, see [[Exfiltration trenches]].

For underground conveyance systems which promote infiltration, see [[Exfiltration trenches]].

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==Overview==

==Overview==

Swales are linear landscape features consisting of a drainage channel with gently sloping sides. Underground they may be filled with engineered soil and/or contain a water storage layer of coarse gravel material. Two variations on a basic swale are recommended as low impact development strategies, although using a combination design of both may increase the benefits:<br>

Swales are linear landscape features consisting of a drainage channel with gently sloping sides. Underground they may be filled with engineered soil and/or contain a water storage layer of coarse gravel material. Two variations on a basic swale are recommended as low impact development strategies, although using a combination of both designs may increase the benefits:<br>

'''[[Bioswales]]''' are sometimes referred to as 'dry swales', 'vegetated swales', or 'water quality swales'. This type of BMP is form of [[bioretention]] with a long linear shape (surface area typically >2:1 length:width) and a slope which convey water,<br>

'''[[Bioswales]]''' are sometimes referred to as 'dry swales', 'vegetated swales', or 'water quality swales'. This type of BMP is form of [[bioretention]] with a long, linear shape (surface area typically >2:1 length:width) and a slope which convey water,<br>

'''[[Enhanced grass swales]]''' are a lower maintenance alternative, but generally have lower stormwater management potential. The enhancement over a basic grass swale is in the addition of [[check dams]] to slow surface water flow and create small temporary pools of water which can infiltrate the underlying soil.<br>

'''[[Enhanced grass swales]]''' are a lower maintenance alternative, but generally have lower stormwater management potential. The enhancement over a basic grass swale is in the addition of [[check dams]] to slow surface water flow and create small temporary pools of water which can infiltrate the underlying soil.<br>

'''Grass swales''' are a relatively common landscape feature already and a great opportunity for retrofit, to reduce flow and improve water quality by encouraging settling and infiltration behind a series of check dams. <br>

'''Grass swales''' are a relatively common landscape feature already and a great opportunity for retrofit, to reduce flow and improve water quality by encouraging settling and infiltration behind a series of check dams. <br>

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{{textbox|Swales are an ideal technology for:  

{{textbox|Swales are an ideal technology for:  

*Sites with long linear landscaped areas, such as parking lots  

*Sites with long, linear landscaped areas, such as parking lots  

*Connecting with one or more other types of LID}}

*Connecting with one or more other types of LID}}

[[File:Bioswale.png||thumb|Bioswale with check dams<br> (vertical scale exaggerated)]]

[[File:Bioswale.png||thumb|Bioswale with check dams<br> (vertical scale exaggerated)]]

[[File:Stepped cells.png||thumb|Stepped bioretention cells alternative for slopes >6 % <br> (vertical scale exaggerated)]]

[[File:Stepped cells.png||thumb|Stepped bioretention cells alternative for slopes >6 % <br> (vertical scale exaggerated)]]

A linear design (surface area typically >2:1 length:width) is a common feature of a swales:

A linear design (surface area typically >2:1 length:width) is a common feature of swales:

*An absolute minimum width is 0.6 m is required for bioswales to have healthy plant growth, and to facilitate construction,

*An absolute minimum width of 0.6 m is required for bioswales to promote healthy plant growth, and to facilitate construction,

*Grassed swales are usually mown as part of routine maintenance, so the cross section will be triangular or trapzoidal in shape with maximum side slopes of 1:3. The minimum width for this type would be 2 m. See [[Enhanced grass swales#Best cross sections| Best cross sections]]

*Grassed swales are usually mown as part of routine maintenance, so the cross section will be triangular or trapezoidal in shape with maximum side slopes of 1:3. The minimum width for this type would be 2 m. See [[Enhanced grass swales#Best cross sections| Best cross sections]]

Swales may be graded along longitudinal slopes between 0.5 - 6 %:

Swales may be graded along longitudinal slopes between 0.5 - 6 %:

<h3>Pretreatment and inlets</h3>

<h3>Pretreatment and inlets</h3>

To minimize erosion and maximize the functionality of the swale, sheet flow of surface water should be directed into the side of the BMP. [[Gravel diaphragms]], [[vegetated filter strips]] and shallow side slopes are ideal. Alternatively, a series of curb inlets can be employed, where each has some form of flow spreading incorporated. Single point inflow can cause increased erosion and sedimentation which will damage vegetation and contribute to BMP failure. Again, flow spreading devices can mitigate these processes, where concentrated point inflow is required.

To minimize erosion and maximize the functionality of the swale, sheet flow of surface water should be directed into the side of the BMP. [[Gravel diaphragms]], [[vegetated filter strips]] and shallow side slopes are ideal. Alternatively, a series of curb inlets can be employed, where each has some form of flow spreader incorporated. Single point inflow can cause increased erosion and sedimentation, which will damage vegetation and contribute to BMP failure. Again, flow spreading devices can mitigate these processes, where concentrated point inflow is required.

==Performance==

==Performance==