Difference between revisions of "Planters: Sizing"

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[[File:Sizing flow-through planter.jpg|thumb|A flow-through planter comprises a ponding zone, mulch layer, filter media for planting, and a supporting gravel drainage layer]]
 
[[File:Sizing flow-through planter.jpg|thumb|A flow-through planter comprises a ponding zone, mulch layer, filter media for planting, and a supporting gravel drainage layer]]
This article is specific to [[Flow-through stormwater planters]], vegetated systems that do not infiltrate water to the native soil. <br>
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This article is specific to flow-through [[Stormwater planters|stormwater planters]], vegetated systems that do not infiltrate water to the native soil. <br>
 
If you are designing a planted system which does infiltrate water, see advice on [[Bioretention: Sizing]].
 
If you are designing a planted system which does infiltrate water, see advice on [[Bioretention: Sizing]].
{{TOClimit|2}}
+
 
The dimensions of a stormwater planter are largely predetermined according to the function of the component. As they do not contain a storage reservoir the planters rely more upon careful selection of materials. Both the filter media and the perforations of the pipe play critical roles for flow control.
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The dimensions of a stormwater planter are largely predetermined according to the function of the component. As they do not contain a storage reservoir the planters rely more upon careful selection of materials. Both the saturated hydraulic conductivity of the filter media and the number and size of perforations of the [[underdrain]] pipe play critical roles for flow control. Options for maintaining separation between filter media and clear stone aggregate surrounding the perforated pipe include a 100 mm deep choker layer or sheet of geotextile filter fabric.
  
 
{| class="wikitable"
 
{| class="wikitable"
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! Component
 
! Component
 
! Recommended depth (with underdrain pipe)
 
! Recommended depth (with underdrain pipe)
! Typical void ratio (''V<sub>R</sub>'')
+
! Typical porosity (''n'')
 
|-
 
|-
 
| Ponding (''d<sub>p</sub>'')
 
| Ponding (''d<sub>p</sub>'')
| ≥ 300 mm
+
| 150 to 450 mm
 
| 1
 
| 1
 
|-
 
|-
Line 19: Line 19:
 
|  
 
|  
 
* 0.7 for wood based
 
* 0.7 for wood based
* 0.4 for aggregate
+
* 0.4 for stone
 
|-
 
|-
| [[Bioretention: Filter media|filter media]] (''d<sub>m</sub>'')
+
| [[Bioretention: Filter media|Filter media]] (''d<sub>m</sub>'')
 
|  
 
|  
 
* 300 mm to support turf grass (and accept only rainwater/roof runoff)
 
* 300 mm to support turf grass (and accept only rainwater/roof runoff)
* 600 mm to support flowering [[perennials]] and decorative [[grasses]]
+
* 600 mm to support shrubs, flowering [[perennials]] and decorative [[grasses]]
 
* 1000 mm to support [[trees]]
 
* 1000 mm to support [[trees]]
| 0.3
+
|
 +
* 0.4 for sandier Blend A - Drainage rate priority;
 +
* 0.35 for more loamy Blend B - Water quality treatment priority
 +
|-
 +
| Choker layer
 +
| 100 mm
 +
| 0.4
 
|-
 
|-
| Pipe diameter reservoir
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| Perforated pipe diameter
| Is equal to underdrain pipe diameter
+
| 150 to 200 mm
 
| 0.4  
 
| 0.4  
 
|-
 
|-
| Pipe bedding (''d<sub>b</sub>'')
+
| Clear stone aggregate layer below perforated pipe
 
| 50 mm (although commonly omitted altogether).  
 
| 50 mm (although commonly omitted altogether).  
 
| 0.4
 
| 0.4
 
|}
 
|}
 
 
==Calculate the maximum overall depth==
 
*Step 1: Determine what the planting needs are and assign appropriate depth of media, using the table above.
 
*Step 2: Select an underdrain pipe diameter (typically 100 - 200 mm), assign this as an 'embedding' depth. 
 
*Step 3: Calculate the maximum possible storage reservoir depth beneath the pipe (''d<sub>s</sub>''):
 
<math>d_{s}=f'\times38.4</math>
 
{{Plainlist|1=Where:
 
*''f''' = Design infiltration rate in mm/hr, and
 
*38.4 comes from multiplying desired drainage time of 96 hours by void ratio of 0.4}}
 
 
===Additional step for system without underdrain===
 
*Step 4: Determine maximum permissible ponding depth (''d<sub>p</sub>''):
 
<math>d_{p}=f'\times19.2</math>
 
{{Plainlist|1=Where:
 
*''f''' = Design infiltration rate in mm/hr, and
 
*19.2 comes from multiplying desired drainage time of 48 hours by void ratio of 0.4. Note that conceptually the drainage of the ponded area is limited by ex-filtration at the base of the practice.}}
 
* Step 5: Sum total depth of bioretention, and compare to available space above water table and bedrock. Adjust if necessary.
 
 
==Calculate the remaining dimensions==
 
* Step 6: Multiply the depth of each separate component by the void ratio and then sum the total to find the 1 dimensional storage (in mm).
 
* Step 7: Calculate the required total storage (m<sup>3</sup>):
 
<math>Storage=RVC_T\times A_c\times C\times 0.1</math>
 
{{Plainlist|1=Where:
 
*''RVC<sub>T</sub>'' is the Runoff volume control target (mm),
 
*''A<sub>c</sub>'' is the catchment area (Ha),
 
*''C'' is the runoff coefficient of the catchment area, and
 
* 0.1 is the units correction between m<sup>3</sup> and mm.Ha.}}
 
* Step 8. Divide required storage (m<sup>3</sup>) by the 1 dimensional storage (in m) to find the required footprint area (''A<sub>p</sub>'') for the bioretention in m<sup>2</sup>.
 
* Step 9. Calculate the peak flow rate (''Q<sub>p</sub>'', in L/s) through the filter media:
 
----
 

Latest revision as of 22:26, 20 May 2022

A flow-through planter comprises a ponding zone, mulch layer, filter media for planting, and a supporting gravel drainage layer

This article is specific to flow-through stormwater planters, vegetated systems that do not infiltrate water to the native soil.
If you are designing a planted system which does infiltrate water, see advice on Bioretention: Sizing.

The dimensions of a stormwater planter are largely predetermined according to the function of the component. As they do not contain a storage reservoir the planters rely more upon careful selection of materials. Both the saturated hydraulic conductivity of the filter media and the number and size of perforations of the underdrain pipe play critical roles for flow control. Options for maintaining separation between filter media and clear stone aggregate surrounding the perforated pipe include a 100 mm deep choker layer or sheet of geotextile filter fabric.

Component Recommended depth (with underdrain pipe) Typical porosity (n)
Ponding (dp) 150 to 450 mm 1
Mulch 75 ± 25 mm
  • 0.7 for wood based
  • 0.4 for stone
Filter media (dm)
  • 300 mm to support turf grass (and accept only rainwater/roof runoff)
  • 600 mm to support shrubs, flowering perennials and decorative grasses
  • 1000 mm to support trees
  • 0.4 for sandier Blend A - Drainage rate priority;
  • 0.35 for more loamy Blend B - Water quality treatment priority
Choker layer 100 mm 0.4
Perforated pipe diameter 150 to 200 mm 0.4
Clear stone aggregate layer below perforated pipe 50 mm (although commonly omitted altogether). 0.4