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| {{Plainlist|1=Where: | | {{Plainlist|1=Where: |
| *d<sub>T</sub> = Total depth of the practice, including surface ponding}}<br> | | *d<sub>T</sub> = Total depth of the practice, including surface ponding}}<br> |
− | For practices with the underdrain perforated pipe elevated off the bottom of the storage reservoir: | + | For practices with the underdrain perforated pipe elevated off the bottom of the storage reservoir:<br> |
| d<sub>a</sub>= Depth of storage reservoir below the invert elevation of the underdrain perforated pipe.<br> | | d<sub>a</sub>= Depth of storage reservoir below the invert elevation of the underdrain perforated pipe.<br> |
− | For practices with the underdrain perforated pipe installed on the bottom of the storage reservoir and connected to a riser (e.g., standpipe and 90 degree coupling): | + | For practices with the underdrain perforated pipe installed on the bottom of the storage reservoir and connected to a riser (e.g., standpipe and 90 degree coupling):<br> |
| d<sub>a</sub>= Difference between invert elevations of the reservoir bottom and riser outlet (i.e invert elevation of the 90 degree coupling).<br> | | d<sub>a</sub>= Difference between invert elevations of the reservoir bottom and riser outlet (i.e invert elevation of the 90 degree coupling).<br> |
| | | |
| * Step 5: Calculate the active storage depth of the storage reservoir (''d<sub>a'', mm):<br> | | * Step 5: Calculate the active storage depth of the storage reservoir (''d<sub>a'', mm):<br> |
− | For practices with no underdrain, this is limited to the surface ponding and storage reservoir depth that will reliably drain within the specified drainage time: | + | For practices with no underdrain, this includes the surface ponding and storage reservoir depth that will reliably drain within the specified drainage time: |
| <math>d_{a}=(f'\times t \times 1/n)</math> | | <math>d_{a}=(f'\times t \times 1/n)</math> |
| {{Plainlist|1=Where: | | {{Plainlist|1=Where: |
| *''f''' = Design infiltration rate (mm/hr), | | *''f''' = Design infiltration rate (mm/hr), |
| *''t'' = [[Drainage time]] (hrs). Check local regulations for drainage time requirements; and | | *''t'' = [[Drainage time]] (hrs). Check local regulations for drainage time requirements; and |
− | *''n'' = Porosity of the reservoir aggregate | + | *''n'' = Porosity of the reservoir aggregate}}<br> |
− | *''d<sub>p</sub>''= design surface ponding depth}}<br>
| + | For practices with an underdrain, this includes only the storage reservoir depth that will reliably drain within the specified drainage time: |
− | For practices with an underdrain: | |
| <math>d_{a}=f'\times t \times 1/n</math> | | <math>d_{a}=f'\times t \times 1/n</math> |
| {{Plainlist|1=Where: | | {{Plainlist|1=Where: |