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poly 18 1742 18 2440 1920 1029 2513 530 2131 386 [[Turf|Salt Tolerant Grass Mix]]  

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[[File:Wet swale.png|600px|thumb|The check dams are spaced slightly further apart than would be recommended to maximize infiltration capacity i.e. ponding isn't quite continuous between the dams.]]

[[File:Wet swale.png|600px|thumb|The check dams are spaced slightly further apart than would be recommended to maximize infiltration capacity i.e. ponding isn't quite continuous between the dams.]]

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]].<br>

*For underground conveyance which promotes infiltration, see [[Exfiltration trenches]].<br>

*For conveyance along planted channels, on both surface and underground, see [[Bioswales]].

*For conveyance along planted channels, on both surface and underground, see [[Bioswales]].

==Overview==

==Overview==

==Planning considerations==

==Planning considerations==

When planning a new site, all swales and overground flow paths should be fitted perpendicular to existing contours. See [[Natural drainage]] and [[Existing hydrology]].  

When planning a new site, all swales and overground flow paths should be fitted perpendicular to existing contours. See [[Natural drainage]] and [[Existing hydrology]].  

===Best cross sections===

===Best cross sections===

===Site Topography===

===Site Topography===

Contributing slopes should be between 1 to 5%. Swale longitudinal slopes may range from 0.5 to 6% (this prevents ponding while providing residence time and preventing erosion). On slopes steeper than 3%, check dams should be used. Check the [https://s3-ca-central-1.amazonaws.com/trcaca/app/uploads/2020/01/30145157/ESC-Guide-for-Urban-Construction_FINAL.pdf| Erosion and Sediment Control Guide For Urban Construction] for further details.

Contributing slopes should be between 1 to 5%. Swale longitudinal slopes may range from 0.5 to 6% (this prevents ponding while providing residence time and preventing erosion). On slopes steeper than 3%, check dams should be used. Check the [https://sustainabletechnologies.ca/home/erosion-and-sediment-control/esc-guide/ Erosion and Sediment Control Guide]

===Water Table===  

===Water Table===  

For more information on planning considerations and site constraints see [[Site considerations]].

For a table summarizing information on planning considerations and site constraints see [[Site considerations]].

==Design==

==Design==

*5:1 on low permeability soils, such as [[Soil groups|hydrologic soil group (HSG) C and D]],  

*5:1 on low permeability soils, such as [[Soil groups|hydrologic soil group (HSG) C and D]],  

*20:1 on high permeability soils [[Soil groups|hydrologic soil group (HSG) Aand D]].  

*20:1 on high permeability soils [[Soil groups|hydrologic soil group (HSG) Aand D]].  

===Pre-Treatment===

===Pre-Treatment===

*Erosion protection such as river stone or riprap will be required to dissipate the energy from incoming concentrated flow.  

*Erosion protection such as river stone or riprap will be required to dissipate the energy from incoming concentrated flow.  

*The channel must be vegetated immediately after [[grading]]. Preferably, the swale should be planted in the spring so that the vegetation can become established with minimal irrigation.

*The channel must be vegetated immediately after [[grading]]. Preferably, the swale should be planted in the spring so that the vegetation can become established with minimal irrigation.

==Construction Considerations==

==Construction Considerations==

===Water Balance===

===Water Balance===

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 mai ncontributing factors that influence runoff reduction rates for swales are:   

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:   

* Native [[Soil groups|soil]] types

* Native [[Soil groups|soil]] types

* [[Grading|Slope]]

* [[Grading|Slope]]

|-

|-

|rowspan="8" style="text-align: center;" | Grass Swale

|rowspan="8" style="text-align: center;" | Grass Swale

|style="text-align: center;" |Virginia

|style="text-align: center;" |Brampton

|style="text-align: center;" |0%

|style="text-align: center;" |15 to 35%,

|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>

|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>

|-

|style="text-align: center;" |Various Locations

|style="text-align: center;" |40%

|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>

|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>

|-

|style="text-align: center;" |Maryland

|style="text-align: center;" |59%

|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>

|-

|-

|style="text-align: center;" |Sweden

|style="text-align: center;" |Sweden

|style="text-align: center;" |40 to 75%,  

|style="text-align: center;" |40 to 75%,  

|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>

|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>

|-

|-

|style="text-align: center;" |Los Angeles

|style="text-align: center;" |Los Angeles

|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>

|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>

|-

|-

|style="text-align: center;" |Brampton

|style="text-align: center;" |Various Locations

|style="text-align: center;" |15 to 35%,

|style="text-align: center;" |40%

|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>

|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>

|-

|style="text-align: center;" |France

|style="text-align: center;" |27 to 41%

|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>

|-

|style="text-align: center;" |Virginia

|style="text-align: center;" |0%

|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>  

|-

|-

| 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>'''

| 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>'''

|colspan="2" style="text-align: center;" |'''46% on [[Soil groups|HSG A or B soils]];'''

|colspan="2" style="text-align: center;" |'''45% on [[Soil groups|HSG A or B soils]];'''

'''10% on [[Soil groups|HSG C or D soils]]'''

'''10% on [[Soil groups|HSG C or D soils]]'''

|-

|-

===Water Quality===

===Water Quality===

Research has shown the pollutant mass removal rates of grass swales are variable, depending on influent pollutant concentrations (Bäckström et al., 2006)<ref>Bäckström, M., Viklander, M. and Malmqvist, P.A. 2006. Transport of stormwater pollutants through a roadside grassed swale. Urban Water Journal, 3(2), pp.55-67. https://www.mdpi.com/2073-4441/6/7/1887/htm</ref>, but generally moderate for most pollutants (Barrett et al., 1998<ref>Barrett, M.E., Walsh, P.M. Malina Jr., J.F. and Charbeneau, R.J. 1998. Performance of Vegetative Controls for Treating Highway Runoff. Journal of Environmental Engineering. November 1998. pp. 1121-1128.</ref>; Deletic and Fletcher, 2006<ref>Deletic, A., and Fletcher, T.D. 2006. Performance of grass filters used for stormwater treatment – a field and modelling study. Journal of Hydrology. Vol. 317. pp. 261-275.</ref>). Median pollutant mass removal rates of swales from available performance studies are 76% for total suspended solids, 55% for total phosphorus, and 50% for total nitrogen (Deletic and Fletcher, 2006<ref>Deletic, A., and Fletcher, T.D. 2006. Performance of grass filters used for stormwater treatment – a field and modelling study. Journal of Hydrology. Vol. 317. pp. 261-275.</ref>). Significant reductions in total zinc and copper event mean concentrations have been observed in performance studies with a median value of 60%, but results have varied widely (Barrett, 2008<ref>Barrett, M.E. 2008. Comparison of BMP performance using the international BMP database. Journal of Irrigation and Drainage Engineering, 134(5), pp.556-561.</ref>). Site specific factors such as slope, soil type, infiltration rate, swale length and vegetative cover also affect pollutant mass removal rates. In general, the dominant pollutant removal mechanism operating in grass swales is infiltration, rather than filtration, because pollutants trapped on the surface of the swale by vegetation or check dams are not permanently bound (Bäckström et al., 2006<ref>Bäckström, M., Viklander, M. and Malmqvist, P.A. 2006. Transport of stormwater pollutants through a roadside grassed swale. Urban Water Journal, 3(2), pp.55-67. https://www.mdpi.com/2073-4441/6/7/1887/htm</ref>). Designers should maximize the degree of infiltration achieved within a grass swale by incorporating check dams and ensuring the native soils have infiltration rates of 15 mm/hr or greater or specifying that the soils be tilled and amended with compost prior to planting. Several of the factors that can significantly increase or decrease the pollutant removal capacity of grass channels are provided in the table below:

Research has shown the pollutant mass removal rates of grass swales are variable, depending on influent pollutant concentrations (Bäckström et al., 2006)<ref>Bäckström, M., Viklander, M. and Malmqvist, P.A. 2006. Transport of stormwater pollutants through a roadside grassed swale. Urban Water Journal, 3(2), pp.55-67. https://www.mdpi.com/2073-4441/6/7/1887/htm</ref>, but generally moderate for most pollutants (Barrett et al., 1998<ref>Barrett, M.E., Walsh, P.M. Malina Jr., J.F. and Charbeneau, R.J. 1998. Performance of Vegetative Controls for Treating Highway Runoff. Journal of Environmental Engineering. November 1998. pp. 1121-1128.</ref>; Deletic and Fletcher, 2006<ref>Deletic, A., and Fletcher, T.D. 2006. Performance of grass filters used for stormwater treatment – a field and modelling study. Journal of Hydrology. Vol. 317. pp. 261-275.</ref>). Median pollutant mass removal rates of swales from available performance studies are 76% for total suspended solids, 55% for total phosphorus, and 50% for total nitrogen (Deletic and Fletcher, 2006<ref>Deletic, A., and Fletcher, T.D. 2006. Performance of grass filters used for stormwater treatment – a field and modelling study. Journal of Hydrology. Vol. 317. pp. 261-275.</ref>). Significant reductions in total zinc and copper event mean concentrations have been observed in performance studies with a median value of 60%, but results have varied widely (Barrett, 2008<ref>Barrett, M.E. 2008. Comparison of BMP performance using the international BMP database. Journal of Irrigation and Drainage Engineering, 134(5), pp.556-561.</ref>). Site specific factors such as slope, soil type, infiltration rate, swale length and vegetative cover also affect pollutant mass removal rates. In general, the dominant pollutant removal mechanism operating in grass swales is infiltration, rather than filtration, because pollutants trapped on the surface of the swale by vegetation or check dams are not permanently bound (Bäckström et al., 2006<ref>Bäckström, M., Viklander, M. and Malmqvist, P.A. 2006. Transport of stormwater pollutants through a roadside grassed swale. Urban Water Journal, 3(2), pp.55-67. https://www.mdpi.com/2073-4441/6/7/1887/htm</ref>). In a recent international research review on processes for improving stormwwater quality treatment of grass swales and vegetated filter strips, Gavric et al. note that while understanding of hydrology and hydraulics of these stormwater control measures is adequate, there are knowledge gaps in understanding water quality treatment processes, particularly for nutrients, traffic associated organic contaminants, and bacteria (Gavric et al., 2019 <ref>Gavric.S, Leonhardt, G., Marsalek, J., Viklander, M. 2019. Processes improving urban stormwater quality in grass swales and filter strips: A review of research findings. Science of the Total Environment. v 669. pp. 431-447. https://www.sciencedirect.com/science/article/pii/S0048969719310502?via%3Dihub</ref>).  Designers should maximize the degree of infiltration achieved within a grass swale by incorporating check dams and ensuring the native soils have infiltration rates of 15 mm/hr or greater or specifying that the soils be tilled and amended with compost prior to planting. Several of the factors that can significantly increase or decrease the pollutant removal capacity of swales are provided in the table below:

{|class="wikitable"

{|class="wikitable"

|}

|}

==References==

==References==