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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>
| + | #REDIRECT [[Enhanced swales]] |
− | 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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− | ===Best cross sections===
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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. | |
− | 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.
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− | ==Design==
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− | All 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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− | ===Adding check dams===
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− | To calculate the spacing and sizing of check dams, see [[Check dams: Sizing]]
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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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− | <h3>Modeling</h3>
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− | {{:Swales: TTT}}
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− | <h3>Materials</h3>
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− | {{:Turf: List}}
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