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To calculate the time (''t'') to fully drain the facility: <math>t=\frac{nd}{q}</math>
For some geometries (e.g. particularly deep facilities or linear facilities), it may be preferred to also account for lateral infiltration. Line 63:
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→Calculate drawdown time
==Calculate drawdown time==
==Calculate drawdown time==
[[file:Hydraulic radius.png|thumb|Three footprint areas of 9 m<sup>2</sup>.<br>
[[file:Hydraulic radius.png|thumb|Three footprint areas of 9 m<sup>2</sup>.<br>
From left to right x = 12 m, x = 14 m, and x = 16 m]]
From left to right x = 12 m, x = 14 m, and x = 16 m]]
The 3 dimensional equations make use of the hydraulic radius (''P''/''x''), where ''x'' is the perimeter (m) of the facility. <br>
The 3 dimensional equations make use of the hydraulic radius (''P''/''x''), where ''x'' is the perimeter (m) of the facility. <br>
Maximizing the perimeter of the facility directs designers towards longer, linear shapes such as [[infiltration trenches]] and [[bioswales]].
Maximizing the perimeter of the facility directs designers towards longer, linear shapes such as [[infiltration trenches]] and [[bioswales]].
:<math>d=a[e^{\left ( -bD \right )} -1]</math>
:<math>d=a[e^{\left ( -bD \right )} -1]</math>
Where
Where
<math>a=\frac{P}{x}-\frac{i I}{P q}</math>
<math>a=\frac{A_{p}}{x}-\frac{i I}{A_{p}q'}</math>
and
and
<math>b=\frac{xq}{nP}</math>
<math>b=\frac{xq}{nP}</math>