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'''The fundamental components of an enhanced grassed swale are:'''
'''The fundamental components of an enhanced grassed swale are:'''
*Graded channel
*Graded channel
*[[Turf| Resilient turf grass]]
*[[Turf| Resilient turf grass]] or [[#Planting_Considerations|other planting]]
*[[Check dams]], to facilitate short term ponding
*[[Check dams]], to facilitate short term ponding
'''Additional components may include:'''
'''Additional components may include:'''
*[[Absorbent landscapes| Amended soil]], to of [[Filter media]] increase infiltration to soils below
*[[Absorbent landscapes| Amended soil]] or [[filter media]] to increase infiltration to soils below
*[[Turf reinforcement]], to prevent scour
*[[Turf reinforcement]], to prevent scour
==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]].
===Best cross sections===
===Best cross sections===
[[File:Best X-section.png|thumb|Both sections a)triangular and, b)trapezoidal, are constrained within ratios of 8:1 H:V]]
[[File:Best X-section.png|thumb|Both sections a)triangular and, b)trapezoidal, are constrained within ratios of 8:1 H:V]]
Enhanced swales aim to both reduce the flow rate and retain a portion of the conveyed water. For these purposes the best x-section is that which maximizes the wetted perimeter for a given area.
Enhanced swales aim to both reduce the flow rate and retain a portion of the conveyed water. For these purposes the best x-section is that which maximizes the wetted perimeter for a given area.
For a given width and depth, the difference between a triangular and trapzoidal section is small. As shown in the diagrams, under low flow conditions the trapezoidal has greater wetted perimeter, and at higher flows the triangular profile does.
For a given width and depth, the difference between a triangular and trapzoidal section is small. As shown in the diagrams, under low flow conditions the trapezoidal has greater wetted perimeter, and at higher flows the triangular profile does.
===Safety===
As shallow grassed swales are a common roadside construction, the Ministry of Transport has created their own guide to maximum flow depth and freeboard<ref>Ontario Ministry of Transportation, & Ontario Ministry for Transportation. (2016). Stormwater Management Requirements for Land Development Proposals. Retrieved February 26, 2018, from http://www.mto.gov.on.ca/english/publications/drainage/stormwater/section8.shtml#controls</ref><ref>Drainage and Hydrology Section Transportation Engienering Branch Quality and Standards Division. (1997). MTO Drainage Management Manual. Retrieved from http://www.ontla.on.ca/library/repository/mon/12000/198363.pdf</ref>. Their advice has been prepared specifically for high risk environments and those stringent constraints should not be applied to all circumstances. In many urban environments the principle of applying check dams to enhance all surface BMPS can be safely used to encourage ponding and subsequent [[infiltration]] for a day or two.
==Design==
==Design==
*33% height of vegetation for infrequently mown swales.
*33% height of vegetation for infrequently mown swales.
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===Planting Considerations===
*[[Grasses]] and herbaceous species with dense root structure cover should be favoured along the bottom of the swale for their ability to increase infiltration, stabilize soils, retain pollutants and assist with suspended solids.
*The plant material on the slopes of grass channels must be capable of withstanding periodic inundation in addition to extended periods of drought. Species include grasses and groundcovers, as well as low shrub species.
*Plants along the exterior of this zone act to slow the flow during stormwater events, reducing sedimentation and increasing infiltration. The root structure of this plant material also acts to reduce erosion.
*Selected grasses or groundcovers for grassed swales should be allowed to grow between 75 to 150 mm to assist in filtering suspended solids from stormwater. Therefore these species are either shorter naturally, or tolerate periodic mowing.
*When grasses grow taller they have a tendency to flatten down from the water flow.
*Fine, close-growing species provide for good soil stabilization.
*Species are salt-tolerant due to the typical location of grass channels along roadways and parking lots.
*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.
==Modeling==
{{:Swales: TTT}}
==Materials==
{{:Turf}}
{{:Turf}}
{{:Stone}}
{{:Check dams}}
[[check dams]]
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