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>
#REDIRECT [[Enhanced swales]]
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==
<h3>Best X-section</h3>
[[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. The trapzoidal channel has the marginally greater hydraulic radius, but also the greater area.
* Triangle (a), wetted perimeter at full bank depth = 8.25 (unitless)
* Trapezoidal (b), wetted perimeter at full bank depth = 8.32 (unitless)
 
Where the X-section areas are set equal (to demonstrate equivalent flow), the depth of water in the example trapzoidal channel is 4/5 that of the triangular.
 
===Check dams===
{{:Check dams}}
 
==Design==
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
{|class="wikitable"
|+ Slope variations
|-
|< 2 %||Use underdrain to distribute water for infiltration
|-
|2 - 5 %||Design swale for surface flow, consider check dams
|-
||5 %||Check dams required to reduce effective slope to 2 – 3 %
|}
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.
|}}
 
<h3>Modeling</h3>
{{:Swales: TTT}}
 
<h3>Materials</h3>

Latest revision as of 14:23, 12 March 2018

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