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The sizing calculations require that most of the following parameters be known or estimated.  

The sizing calculations require that most of the following parameters be known or estimated.  

The exceptions are the depth (''d'') and Permeable area (''P''), as only one of these is required to find the other.  

The exceptions are the depth (''d'') and Permeable area (''P''), as only one of these is required to find the other.  

<h3>Drawdown time</h3>

<h3>Drawdown time</h3>

The design of infiltration facilities should be checked for [[drawdown time]]. Target drawdown time is between 48-72 hours. <br>

The design of infiltration facilities should be checked for [[drawdown time]]. The target drawdown time for the internal storage of an infiltration facility is between 48-72 hours. <br>

To calculate the time (''t'') to fully drain the facility:  

To calculate the time (''t'') to fully drain the facility:  

<math>t=\frac{nP}{qx}ln\left [ \frac{\left (d+ \frac{P}{x} \right )}{\left(\frac{P}{x}\right)}\right]</math>

<math>t=\frac{nP}{qx}ln\left [ \frac{\left (d+ \frac{P}{x} \right )}{\left(\frac{P}{x}\right)}\right]</math>