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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> | | 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]]. |
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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 filter media and the perforations of the pipe play critical roles for flow control. | | 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. |
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| {| 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 |
| |- | | |- |
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| * 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 | | | |
| | * 0.35 for Blend A - Drainage rate priority; |
| | * 0.4 for Blend B - Water quality treatment priority |
| |- | | |- |
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| | Pipe diameter reservoir | | | Pipe diameter reservoir |
| | Is equal to underdrain pipe diameter | | | Is equal to underdrain [[pipe]] diameter |
| | 0.4 | | | 0.4 |
| |- | | |- |
| | Pipe bedding (''d<sub>b</sub>'') | | | [[Choker course|Pipe bedding]] (''d<sub>b</sub>'') |
| | 50 mm (although commonly omitted altogether). | | | 50 mm (although commonly omitted altogether). |
| | 0.4 | | | 0.4 |
| |} | | |} |
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| ==Calculate the maximum overall depth==
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| *Step 1: Determine what the planting needs are and assign appropriate depth of media, using the table above.
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| *Step 2: Select an underdrain pipe diameter (typically 100 - 200 mm), assign this as an 'embedding' depth.
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| *Step 3: Calculate the maximum possible storage reservoir depth beneath the pipe (''d<sub>s</sub>''):
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| <math>d_{s}=f'\times38.4</math>
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| {{Plainlist|1=Where:
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| *''f''' = Design infiltration rate in mm/hr, and
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| *38.4 comes from multiplying desired drainage time of 96 hours by void ratio of 0.4}}
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| ===Additional step for system without underdrain===
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| *Step 4: Determine maximum permissible ponding depth (''d<sub>p</sub>''):
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| <math>d_{p}=f'\times19.2</math>
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| {{Plainlist|1=Where:
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| *''f''' = Design infiltration rate in mm/hr, and
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| *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.}}
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| * Step 5: Sum total depth of bioretention, and compare to available space above water table and bedrock. Adjust if necessary.
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| ==Calculate the remaining dimensions==
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| * 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).
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| * Step 7: Calculate the required total storage (m<sup>3</sup>):
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| <math>Storage=RVC_T\times A_c\times C\times 0.1</math>
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| {{Plainlist|1=Where:
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| *''RVC<sub>T</sub>'' is the Runoff volume control target (mm),
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| *''A<sub>c</sub>'' is the catchment area (Ha),
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| *''C'' is the runoff coefficient of the catchment area, and
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| * 0.1 is the units correction between m<sup>3</sup> and mm.Ha.}}
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| * 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>.
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| * Step 9. Calculate the peak flow rate (''Q<sub>p</sub>'', in L/s) through the filter media:
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