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 [[bioretention]], vegetated systems that infiltrate water to the native soil. <br>
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 not infiltrate water, see advice on [[Planters: Sizing]].
If you are designing a planted system which does infiltrate water, see advice on [[Bioretention: Sizing]].
[[File:Sizing Bioretention.jpg|thumb|The vertical storage zones in a bioretention cell include: ponding, mulch, filter media, choker course, pipe diameter reservoir and the storage reservoir.]]
 
{{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| pipe]] play critical roles for flow control.
Many of the dimensions in a bioretention system can be predetermined according to the function of the component. There is greatest flexibility in the ponding depth and the depth of the storage reservoir beneath the optional underdrain pipe. The order of operations in calculating these dimensions depends on whether an underdrain is desired. 


{| class="wikitable"
{| class="wikitable"
Line 10: Line 9:
! Component
! Component
! Recommended depth (with underdrain pipe)
! Recommended depth (with underdrain pipe)
! Recommended depth (no underdrain pipe)
! Typical porosity (''n'')
! Typical void ratio (''V<sub>R</sub>'')
|-
|-
| Ponding (''d<sub>p</sub>'')
| Ponding (''d<sub>p</sub>'')
| 300 mm
| 150 to 450 mm
| See below
| 1
| 1
|-
|-
| [[Mulch]]
| [[Mulch]]
| colspan="2" |75 ± 25 mm
| 75 ± 25 mm
|  
|  
* 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>'')
| colspan="2" |
|  
* 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
|
|-
* 0.35 for Blend A - Drainage rate priority;
| [[choker layer|Choker course]]
* 0.4 for Blend B - Water quality treatment priority
| colspan="2" |100 mm
| 0.4 typical
|-
|-
| Pipe diameter reservoir
| Pipe diameter reservoir
| Is equal to underdrain pipe diameter
| Is equal to underdrain [[pipe]] diameter
| Not applicable
| 0.4  
| 0.4  
|-
|-
| Storage reservoir (''d<sub>s</sub>'')
| [[Choker course|Pipe bedding]] (''d<sub>b</sub>'')
| See below
| 50 mm (although commonly omitted altogether).
| See below
| 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 01:54, 14 July 2020

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 filter media and the perforations of the pipe play critical roles for flow control.

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
  • 0.35 for Blend A - Drainage rate priority;
  • 0.4 for Blend B - Water quality treatment priority
Pipe diameter reservoir Is equal to underdrain pipe diameter 0.4
Pipe bedding (db) 50 mm (although commonly omitted altogether). 0.4

a top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales.

The engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.

The natural ground material characteristic of or existing by virtue of geographic origin.

A vegetated practice that collects and treats stormwater through sedimentation and filtration. Contributions to water cycle/water balance are through evapotranspiration only; no infiltration.

An underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe.

A perforated pipe used to assist the draining of soils.

The porosity (n) of a mixture is the ratio of the volume of void-space to the total or bulk volume of the mixture. It is closely related to the concept of void ratio (e) where void ratio is the ratio of the volume of void-space to the volume of solids. n = Volume of voids/Total volume of mixture = e/(1+e)

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

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