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→Determine the active storage depth of the practice
==Determine the active storage depth of the practice==
==Determine the active storage depth of the practice==
* Step 4: Determine the active storage depth, d<sub>a</sub> of the practice<br>
* Step 4: Determine the active storage depth, d<sub>a</sub> of the practice<br>
For practices without an underdrain, the active storage depth equals the total depth of the practice, including surface ponding:
For practices without an underdrain, the active storage depth equals the total depth of the practice:
<math>d_{a}=d_{T}</math>
<math>d_{a}=d_{T}</math>
{{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:
d<sub>a</sub>= depth of storage reservoir below the invert 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):
d<sub>a</sub>= Difference between invert elevation of reservoir bottom and outlet of the riser (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 practice (''d<sub>a'', mm):<br>
* Step 5: Calculate the active storage depth of the practice (''d<sub>a'', mm):<br>
For practices with no underdrain:
For practices with no underdrain, this is limited to the depth that will reliably drain within the specified drainage time:
<math>d_{a}=(f'\times t \times 1/n) + d_{p}'</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),