Difference between revisions of "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]]
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#REDIRECT [[Enhanced swales]]
[[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]].
 
{{TOClimit|2}}
 
==Overview==
 
'''The fundamental components of an enhanced grassed swale are:'''
 
*Graded channel
 
*[[Turf: List| 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.
 
|}}
 
 
 
===Check dams===
 
{{:Check dams}}
 
 
 
===Modeling===
 
{{:Swales: TTT}}
 
 
 
===Materials===
 
{{:Turf: Roughness}}
 
{{:Turf: List}}
 

Latest revision as of 14:23, 12 March 2018

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