Changes

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 which promotes infiltration, see [[Exfiltration trenches]].

{{TOClimit|2}}

{{TOClimit|2}}

==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 design of both may increase the benefits:<br>

<strong>[[Bioswales]]</strong> are sometimes referred to as 'dry swales', 'vegetated swales', or 'water quality swales'. This type of structure is similar to a [[Bioretention cells|bioretention cell]] but with a long linear shape (surface area typically >2:1 length:width),<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>

<strong>[[Enhanced grass swales]]</strong> 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.

'''[[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>

<blockquote>Swales are an ideal technology for:  

'''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>

{{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</blockquote>

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

 

{|class="wikitable"

{|class="wikitable"

|+ Types of Swale

|+ Types of Swale

|-  

|-  

!style="background: darkcyan; color: white"|Property

!Property

!style="background: darkcyan; color: white"|Bioswale

!Bioswale

!style="background: darkcyan; color: white"|Enhanced grass swale

!Enhanced grass swale

|-

|-

!Surface water

|Surface water||Minimal<br>Any surface flow can be slowed with check dams||Ponding is encouraged with check dams

|Minimal<br>Any surface flow can be slowed with check dams||Ponding is encouraged with check dams

|-

|-

!Soil

|Soil||Filter media required||Amendment preferable when possible

|Filter media required||Amendment preferable when possible

|-

|-

!Underdrain

|Underdrain||Common||Uncommon

|Common||Uncommon

|-

|-

!Maintenance

|Maintenance||Medium to high||Low

|Medium to high||Low

|-

|-

!Stormwater benefit

|Stormwater benefit||High||Moderate

|High||Moderate

|-

|-

!Biodiversity benefit

|Biodiversity benefit||Increased with native planting||Typically lower

|Increased with native planting||Typically lower

|}

|}

==Planning Considerations==

==Planning Considerations==

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 a 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 is 0.6 m is required for bioswales to have healthy plant growth, and to facilitate construction,

*Grassed swales are usually mown as part of routine maintenance, so the cross section will be parabolic or trapzoidal in shape. The minimum width for this type is 2 m.

*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]]

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

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

*Check dams are required on slopes > 3 %.

*Between 1 - 6 %, check dams are recommended to bring the compensation gradient <1 %.

*Slopes > 6% can accommodate a series of stepped [[bioretention cells]], each overflowing into the next with a weir.

*Slopes > 6% can accommodate a series of stepped [[bioretention cells]], each overflowing into the next with a spillway.

==Design==

==Design==

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 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.

<p>Check dams are a feature of enhanced swales. They promote infiltration and evaporation by promoting limited ponding.

A review of swale-like practices was published by STEP in 1999. The project page and additional tools are available [https://sustainabletechnologies.ca/home/urban-runoff-green-infrastructure/low-impact-development/swales-and-roadside-ditches/ here].

To design check dams into a swale:

#The height of each dam is determined by the depth of ponded water that will infiltrate in 24 hours. The infiltration may be into the native soils, into biomedia, or some other soil amendment may be proposed in the design.

#Dams are usually installed between 10-20 m along the swale. They are distributed such that the crest of each dam is at approximately the same elevation as the toe of the upstream dam.  If the slope along the swale varies, so should the distance between the dams.

The objective of these design recommendations are to maximize the distribution of ponded water along the whole BMP. Detailed design may require iteration of the dam heights and distances along each section of a long swale.

*Dams may be constructed of any resilient and waterproof material, including: rock gabions, earth berms, coarse aggregate or rip-rap, concrete, metal or wood.

*Energy dissipation and erosion control measures should be installed in the 1 - 2 m  downstream of each dam. Examples include large aggregate or [[Turf reinforcement|turf reinforcement]]

<h4>Other components</h4>

*[[Bioretention: Filter media]]

==Performance==

===Bioswales===

{{:Bioswales: Performance}}

{{:Bioswales: Performance}}

<h3>Enhanced grass swales</h3>

===Enhanced grass swales===

==Construction==

==Construction==

==Incentives and Credits==

==Galleries==

{{:Swales: Gallery}}

The City of Mississauga has a stormwater management credit program which includes RWH as one of their recommended site strategies[https://www.mississauga.ca/portal/services/credit-program].

==See Also==

==See Also==

*[[Bioretention cells]]

*[[Bioretention cells]]

*[[Check dams]]

*[[Check dams]]

----

----

[[Category:Infiltration]]

[[Category:Infiltration]]

[[Category:Planted]]

[[Category:Green infrastructure]]

[[Category:Conveyance]]