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Swales (view source)

Revision as of 14:49, 26 October 2023

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[[File:20161024 100338 550x550.jpg|thumb|Bioswale, County Court Boulevard, Brampton]]
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[[File:20161024 100338 550x550.jpg|thumb|500px|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 systems which promote 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 of both designs 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>
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'''[[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>
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'''[[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 conveys water and generally contains various water tolerant [[vegetation]],<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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{{float right|{{#widget:YouTube|id=8b3-a_Na1dE}}}}
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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  
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<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 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.
 
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.
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==Inspection and Maintenance==
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Maintenance requirements for [[enhanced swales|enhanced grass swales]], and swales is similar to vegetated filter strips and typically involve a low level of activity after [[vegetation]] becomes established. [[Grasses|Grass]] channel maintenance procedures are already in place at many municipal public works and transportation departments. These procedures should be compared to the recommendations provided on the [[Inspection and Maintenance: Enhanced Swales]] page to assure that the infiltration and water quality
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benefits of enhanced grass swales are preserved.
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Routine roadside ditch maintenance practices such as scraping and re-grading should be avoided at swale locations. Vehicles should not be parked or driven on grass swales. For routine mowing, the lightest possible mowing equipment should be used to prevent soil compaction.
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For swales located on private property, the property owner, resident or manager is responsible for maintenance as outlined in a legally binding maintenance agreement. Roadside
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swales in residential areas generally receive routine maintenance from homeowners who should be advised regarding recommended maintenance activities and ensure they do not build anything within or on the channel of the swale which could result in flooding or pooling on theirs or their neighbours' properties.
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<br>
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Take a look at the [[Inspection and Maintenance: Enhanced Swales]] page by clicking below for further details about proper inspection and maintenance practices:
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{{Clickable button|[[File:Cover Photo swales.PNG|150 px|link=https://wiki.sustainabletechnologies.ca/index.php title=Inspection_and_Maintenance:_Enhanced_Swales&action=edit]]}}
    
==Performance==
 
==Performance==
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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].
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An evaluation of swales and roadside ditches 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].
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===Bioswales===
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===[[Bioswales]]===
 
{{:Bioswales: Performance}}
 
{{:Bioswales: Performance}}
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===Enhanced grass swales===
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Click on the citations above to view the performance of these features based upon specifics (i.e. drainage area to size ratio to achieve the reduction mentioned) in the table.
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===[[Enhanced swales| Enhanced grass swales]]===
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See Performance section on Enhanced swale page link above for additional information.
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Recent research indicates that a conservative runoff reduction rate of 10 to 20% can be used depending on whether soils fall in [[Soil groups| hydrologic soil groups A/B or C/D,]] respectively. The runoff reduction rates can be doubled if the native soils on which the swale is located have been tilled to a depth of 300 mm and amended with compost to achieve an organic content of between 8 and 15% by weight or 30 to 40% by volume. The main contributing factors that influence runoff reduction rates for swales are: 
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* Native [[Soil groups|soil]] types
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* [[Grading|Slope]]
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* [[Vegetation|Vegetative cover]] and,
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* [[Enhanced swales: Specifications|Length of the swale.]]
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{|class="wikitable"
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|+Volumetric runoff reduction from enhanced swales
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|-
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!'''LID Practice'''
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!'''Location'''
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!'''<u><span title="Note: Runoff reduction estimates are based on differences between runoff volume from the practice and total precipitation over the period of monitoring unless otherwise stated." >Runoff Reduction*</span></u>'''
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!'''Reference'''
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|-
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|rowspan="8" style="text-align: center;" | Grass Swale
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|style="text-align: center;" |Brampton
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|style="text-align: center;" |15 to 35%,
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|style="text-align: center;" |[https://sustainabletechnologies.ca/app/uploads/2020/11/CC-Bioswale-Tech-brief-2018-FINAL.pdf| STEP (2018)]<ref>Sustainable Technologies Evaluation Program. Effectiveness of Retrofitted Roadside Biofilter Swales - County Court Boulevard, Brampton. Technical Brief. https://sustainabletechnologies.ca/app/uploads/2020/11/CC-Bioswale-Tech-brief-2018-FINAL.pdf. https://sustainabletechnologies.ca/app/uploads/2020/11/CC-Bioswale-Tech-brief-2018-FINAL.pdf</ref>
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|-
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|style="text-align: center;" |Sweden
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|style="text-align: center;" |40 to 55%,
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|style="text-align: center;" |Rujner ''et al''. (2016)<ref>Rujner, H., Leonhardt, G., Perttu, A.M., Marsalek, J. and Viklander, M. 2016. Advancing green infrastructure design: Field evaluation of grassed urban drainage swales. Modélisation/Models-Contrôle à la source/Source control. http://documents.irevues.inist.fr/bitstream/handle/2042/60477/3B7P03-124RUJ.pdf</ref>
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|-
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|style="text-align: center;" |Seoul, Korea
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|style="text-align: center;" |40 to 75%,
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|style="text-align: center;" |Rujner ''et al''. (2016)<ref>Rujner, H., Leonhardt, G., Perttu, A.M., Marsalek, J. and Viklander, M. 2016. Advancing green infrastructure design: Field evaluation of grassed urban drainage swales. Modélisation/Models-Contrôle à la source/Source control. http://documents.irevues.inist.fr/bitstream/handle/2042/60477/3B7P03-124RUJ.pdf</ref>
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|-
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|style="text-align: center;" |Maryland
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|style="text-align: center;" |59%
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|style="text-align: center;" |Davis ''et al''. (2012)<ref>Davis, A.P., Stagge, J.H., Jamil, E. and Kim, H. 2012. Hydraulic performance of grass swales for managing highway runoff. Water research, 46(20), pp.6775-6786. http://www.jstagge.com/assets/papers/Hydraulic%20performance%20of%20grass%20swales%20for%20managing.pdf </ref>
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|-
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|style="text-align: center;" |Los Angeles
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|style="text-align: center;" |52.5%,
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|style="text-align: center;" |Ackerman and Stein (2008)<ref>Ackerman, D. and Stein, E.D. 2008. Evaluating the effectiveness of best management practices using dynamic modeling. Journal of Environmental Engineering, 134(8), pp.628-639. https://www.researchgate.net/profile/Eric-Stein-2/publication/228910558_Evaluating_the_Effectiveness_of_Best_Management_Practices_Using_Dynamic_Modeling/links/0912f509278915fc77000000/Evaluating-the-Effectiveness-of-Best-Management-Practices-Using-Dynamic-Modeling.pdf</ref>
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|-
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|style="text-align: center;" |Various Locations
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|style="text-align: center;" |40%
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|style="text-align: center;" |Strecker ''et al''.(2004)<ref>Strecker, E., Quigley, M., Urbonas, B., Jones, J. 2004. State-of-the-art in comprehensive approaches to stormwater. The Water Report. Issue 6. August 15,2004. </ref>
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|-
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|style="text-align: center;" |France
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|style="text-align: center;" |27 to 41%
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|style="text-align: center;" |Barrett ''et al''. (2004)<ref>Barrett, M.E. 2008. Comparison of BMP Performance Using the International BMP Database. Journal of Irrigation and Drainage Engineering. September/October. pp. 556-561 </ref>
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|-
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|style="text-align: center;" |Virginia
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|style="text-align: center;" |0%
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|style="text-align: center;" |Schueler (1983)<ref>Schueler, T. 1983. Washington Area Nationwide Urban Runoff Project. Final Report. Metropolitan Washington Council of Governments. Washington, DC. </ref>
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|-
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| colspan="2" style="text-align: center;" |'''<u><span title="Note:This estimate is provided only for the purpose of initial screening of LID practices suitable for achieving stormwater management objectives and targets. Performance of individual facilities will vary depending on site specific contexts and facility design parameters and should be estimated as part of the design process and submitted with other documentation for review by the approval authority" >Runoff Reduction Estimate*</span></u>'''
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|colspan="2" style="text-align: center;" |'''45% on [[Soil groups|HSG A or B soils]];'''
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'''10% on [[Soil groups|HSG C or D soils]]'''
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|-
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|}
    
==Construction==
 
==Construction==
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*[[Check dams]]
 
*[[Check dams]]
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==References==
 
[[Category:Infiltration]]
 
[[Category:Infiltration]]
 
[[Category:Green infrastructure]]
 
[[Category:Green infrastructure]]
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