Difference between revisions of "Enhanced grass swales"

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This article is about installations designed to capture and convey surface runoff along a vegetated channel, whilst also promoting infiltration. <br>
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#REDIRECT [[Enhanced swales]]
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For underground conveyance which promotes infiltration, see [[Exfiltration trenches]].<br>
 
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For conveyance along planted channels, on both surface and underground, see [[Bioswales]].
 
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{{TOClimit|2}}
 
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==Overview==
 
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'''The fundamental components of an enhanced grassed swale are:'''
 
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*Graded channel
 
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*[[Turf: List| Resilient turf grass]]
 
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*[[Check dams]], to facilitate short term ponding
 
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'''Additional components may include:'''
 
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*[[Absorbent landscapes| Amended soil]], to increase infiltration to soils below
 
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*[[Liner|Impermeable membrane]], to prevent infiltration to soils below
 
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*[[Turf reinforcement]], to prevent scour
 
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==Planning considerations==
 
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<h3>Best cross sections</h3>
 
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[[File:Best X-section.png|thumb|Both sections a)triangular and, b)trapezoidal, are constrained within ratios of 8:1 H:V]]
 
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[[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]]
 
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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.
 
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===Check dams===
 
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{{:Check dams}}
 
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==Design==
 
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Swales should be designed to meet the following criteria:
 
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*Minimum residence time of 5 minutes.
 
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*Maximum flow velocity 0.3 m/s
 
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*Bottom width between 0.6 - 2.4 m
 
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*Minimum length 30 m
 
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{|class="wikitable"
 
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|+ Slope variations
 
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|-
 
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|< 2 %||Use underdrain to distribute water for infiltration
 
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|-
 
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|2 - 5 %||Design swale for surface flow, consider check dams
 
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|-
 
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||5 %||Check dams required to reduce effective slope to 2 – 3 %
 
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|}
 
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Maximum depth of flow
 
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{{plainlist|
 
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*50% height of grass for regularly mown swales, to maximum of 75 mm.
 
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*33% height of vegetation for infrequently mown swales.
 
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|}}
 
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<h3>Modeling</h3>
 
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{{:Swales: TTT}}
 
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<h3>Materials</h3>
 

Latest revision as of 14:23, 12 March 2018

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