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→Time to drain the storage reservoir
==To calculate the required storage reservoir depth, where the area is fixed or constrained (3D drainage)==
==To calculate the required storage reservoir depth, where the area is fixed or constrained (3D drainage)==
On densely developed sites, the surface area available for the facility may be constrained. In such cases the required water storage reservoir depth of the bioretention cell or infiltration trench, d, can be calculated assuming three-dimensional drainage as follows
On densely developed sites, the surface area available for the facility may be constrained. In such cases the required water storage reservoir depth of the bioretention cell or infiltration trench, d, can be calculated assuming three-dimensional drainage as follows
:<math>d=a[e^{\left ( -bD \right )} -1]</math>
:<math>d_{r}=a[e^{\left ( -bD \right )} -1]</math>
Where
Where
:<math>a=\frac{Ar}{x}-\frac{i Ai}{x f'}</math>
:<math>a=\frac{A_{r}}{x}-\frac{i\times A_{i}}{x\times f'}</math>
and <br>
and <br>
:<math>b=\frac{xf'}{nAr}</math>
:<math>b=\frac{x\times f'}{n\times A_{r}}</math>
(The rearrangement to calculate the required footprint area of the facility for a given depth assuming three-dimensional drainage is not available at this time. Elegant submissions are invited.)<br>
(The rearrangement to calculate the required footprint area of the facility for a given depth assuming three-dimensional drainage is not available at this time. Elegant submissions are invited.)<br>
It is best applied to calculate the maximum duration of ponding on the surface of [[bioretention cells]], and upstream of the [[check dams]] of [[bioswales]] and [[enhanced grass swales]] to ensure all surface ponding drains within 48 hours.
It is best applied to calculate the maximum duration of ponding on the surface of [[bioretention cells]], and upstream of the [[check dams]] of [[bioswales]] and [[enhanced grass swales]] to ensure all surface ponding drains within 48 hours.
To calculate the time (''t'') to fully drain surface ponded water through the filter media or planting soil:
To calculate the time (''t'') to fully drain surface ponded water through the filter media or planting soil:
<math>t=\frac{dp'}{Kf}</math>
<math>t=\frac{d_{p}'}{K_{f}}</math>
Where <br>
Where <br>
d<sub>p</sub>' is the effective or mean surface ponding depth (mm).<br>
d<sub>p</sub>' is the effective or mean surface ponding depth (mm).<br>
<br>
<br>
To calculate the time (''t'') to fully drain the facility assuming three-dimensional drainage:
To calculate the time (''t'') to fully drain the facility assuming three-dimensional drainage:
<math>t=\frac{nAr}{f'x}ln\left [ \frac{\left (d+ \frac{Ar}{x} \right )}{\left(\frac{Ar}{x}\right)}\right]</math>
<math>t=\frac{n\times A_{r}}{f'\times x}ln\left [ \frac{\left (d_{r} \frac{A_{r}}{x} \right )}{\left(\frac{A_{r}}{x}\right)}\right]</math>
Where "ln" means natural logarithm of the term in square brackets <br>
Where "ln" means natural logarithm of the term in square brackets <br>
Adapted from CIRIA, The SUDS Manual C753 (2015).
Adapted from CIRIA, The SUDS Manual C753 (2015).