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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>'') |
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| * 600 mm to support flowering [[perennials]] and decorative [[grasses]] | | * 600 mm to support flowering [[perennials]] and decorative [[grasses]] |
| * 1000 mm to support [[trees]] | | * 1000 mm to support [[trees]] |
− | | 0.3 | + | | |
| + | *[[Bioretention media storage| 0.4]] for sandy mix |
| + | * 0.35 for a more loamy mix. |
| |- | | |- |
| | [[choker layer|Choker course]] | | | [[choker layer|Choker course]] |
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| *Step 2: Select an underdrain pipe diameter (typically 100 - 200 mm), assign this as an 'embedding' depth. *Note that this component does not apply if a downstream riser is being used to control an extended saturation zone. | | *Step 2: Select an underdrain pipe diameter (typically 100 - 200 mm), assign this as an 'embedding' depth. *Note that this component does not apply if a downstream riser is being used to control an extended saturation zone. |
| *Step 3: Calculate the maximum possible storage reservoir depth beneath the pipe (''d<sub>s, max</sub>'', mm): | | *Step 3: Calculate the maximum possible storage reservoir depth beneath the pipe (''d<sub>s, max</sub>'', mm): |
− | <math>d_{s, max}=\frac{f'\times t}{0.4}</math> | + | <math>d_{s, max}=f'\times t</math> |
| {{Plainlist|1=Where: | | {{Plainlist|1=Where: |
| *''f''' = Design infiltration rate (mm/hr), and | | *''f''' = Design infiltration rate (mm/hr), and |
− | *''t'' = [[Drainage time]] (hrs), e.g. 96 hours, check local regulations for drainage time requirements. | + | *''t'' = [[Drainage time]] (hrs). Check local regulations for drainage time requirements.}} |
− | *''0.4'' = Void ratio of [[reservoir gravel|clear stone]]}}
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| ===Additional step for system without underdrain=== | | ===Additional step for system without underdrain=== |
| * Step 4: Determine maximum permissible ponding depth (''d<sub>p, max</sub>''): | | * Step 4: Determine maximum permissible ponding depth (''d<sub>p, max</sub>''): |
− | <math>d_{p, max}=\frac{f'\times48}{0.4}</math> | + | <math>d_{p, max}=f'\times48</math> |
| {{Plainlist|1=Where: | | {{Plainlist|1=Where: |
| *''f''' = Design infiltration rate (mm/hr), and | | *''f''' = Design infiltration rate (mm/hr), and |
| *48 = Drainage time of the ponding (hrs) | | *48 = Drainage time of the ponding (hrs) |
− | *0.4 = Void ratio of [[reservoir gravel|clear stone]] *Note that conceptually the drainage of the ponded area is limited by ex-filtration at the base of the practice.}}
| + | *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. | | * Step 5: Sum total depth of bioretention, and compare to available space above water table and bedrock. Adjust if necessary. |
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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). | | * 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 (S<sub>T</sub>, m<sup>3</sup>): | | * Step 7: Calculate the required total storage (S<sub>T</sub>, m<sup>3</sup>): |
− | <math>S_{T}=RVC_T\times A_c\times C\times 0.1</math> | + | <math>S_{T}=RVC_T\times A_c\times 10</math> |
| {{Plainlist|1=Where: | | {{Plainlist|1=Where: |
| *''RVC<sub>T</sub>'' is the Runoff volume control target (mm), | | *''RVC<sub>T</sub>'' is the Runoff volume control target (mm), |
− | *''A<sub>c</sub>'' is the catchment area (Ha), | + | *''A<sub>c</sub>'' is the catchment area (Ha), and |
− | *''C'' is the runoff coefficient of the catchment area, and
| + | * 10 is the units correction between m<sup>3</sup> and mm.Ha.}} |
− | * 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 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 through perforated pipe|flow rate through the perforated pipe]], | | * Step 9. Calculate the peak [[flow through perforated pipe|flow rate through the perforated pipe]], |
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| Typically, this is only worth exploring over sandy soils with rapid infiltration. | | Typically, this is only worth exploring over sandy soils with rapid infiltration. |
| | | |
− | Note that narrow, linear bioretention features (bioswales) drain faster than round or blocky footprint geometries. | + | Note that narrow, linear bioretention features (or [[bioswales]]) drain faster than round or blocky footprint geometries. |
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| *Begin the drainage time calculation by dividing the area of the practice (''A<sub>p</sub>'') by the perimeter (''P''). | | *Begin the drainage time calculation by dividing the area of the practice (''A<sub>p</sub>'') by the perimeter (''P''). |