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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:<br>
 
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):<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):<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 includes the combined surface ponding and storage reservoir depth that will reliably drain within the specified drainage time. <br>
 
For practices with no underdrain, this includes the combined surface ponding and storage reservoir depth that will reliably drain within the specified drainage time. <br>

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