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Line 107: − For practices with an underdrain, this includes only the storage reservoir depth that will reliably drain within the specified drainage time:+ − <math>d_{a}=f'\times t \times 1/n</math> − {{Plainlist|1=Where: − *''f''' = Design infiltration rate (mm/h), − *''t'' = [[Drainage time]] (h). Check local criteria for drainage time requirements; and − *''n'' = Porosity of the reservoir aggregate}}
→Determine the active storage depth of the practice
* 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 includes 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. <br>
For practices with an underdrain, this includes only the storage reservoir depth below the invert of the underdrain perforated pipe 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:
*''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}}<br>
*''n'' = Porosity of the reservoir aggregate}}<br>
To boost drainage performance on fine-textured, low permeability soils, consider designing storage reservoirs even deeper than those calculated using the above approach, that many not fully drain between storm events, which increases hydraulic head and infiltration rate at the base of the practice. See [[Low permeability soils]] for more information.
To boost drainage performance on fine-textured, low permeability soils, consider designing storage reservoirs even deeper than those calculated using the above approach, that many not fully drain between storm events, which increases hydraulic head and infiltration rate at the base of the practice. See [[Low permeability soils]] for more information.