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Line 1: − #REDIRECT[[Enhanced grass swales]]+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
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[[File:Dry enhanced swale.png|thumb|Skeleton schematic illustrating the installation of [[check dams]] with centralized, flow concentrating cutouts]]
[[File:Wet swale.png|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>
For underground conveyance which promotes infiltration, see [[Exfiltration trenches]].<br>
For conveyance along planted channels, on both surface and underground, see [[Bioswales]].
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==Overview==
'''The fundamental components of an enhanced grassed swale are:'''
*Graded channel
*[[Turf| Resilient turf grass]]
*[[Check dams]], to facilitate short term ponding
'''Additional components may include:'''
*[[Absorbent landscapes| Amended soil]], to increase infiltration to soils below
*[[Liner|Impermeable membrane]], to prevent infiltration to soils below
*[[Turf reinforcement]], to prevent scour
==Planning considerations==
===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:Sections_perimeters.png|thumb|At lowest flow rates (smallest area) the trapezoidal swale (b) has the greater wetted perimeter; at higher flow rates (greater area) the triangular geometry (a)has a larger wetted perimeter for same area. Both channels modelled using ratios shown in figure above]]
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.
==Design==
All swales should be designed to meet the following criteria:
*Minimum residence time of 5 minutes.
*Maximum flow velocity 0.3 m/s
*Bottom width between 0.6 - 2.4 m
*Minimum length 30 m
Maximum depth of flow
{{plainlist|
*50% height of grass for regularly mown swales, to maximum of 75 mm.
*33% height of vegetation for infrequently mown swales.
|}}
{{:Turf}}
===Check dams===
{{:Check dams}}
===Modeling===
{{:Swales: TTT}}