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→Time for drainage of surface ponded water
<math>Ar=\frac{iDAi}{ndr+f'D}</math>
<math>Ar=\frac{iDAi}{ndr+f'D}</math>
==Time for drainage of surface ponded water==
==Time required to drain surface ponded water==
The following equation assumes one dimensional drainage over the surface ponding area.
The following equation assumes one dimensional drainage over the surface ponding area.
It is best applied to calculate the maximum duration of ponding on the surface of [[bioretention cells]], and upstream of 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 check dams of [[bioswales]] and [[enhanced grass swales]] to ensure all surface ponding drains within 48 hours.
<math>t=\frac{dp'}{Kf}</math>
<math>t=\frac{dp'}{Kf}</math>
Where <br>
Where <br>
d<sub>p</sub>' is the mean or effective surface ponding depth (mm).<br>
d<sub>p</sub>' is the effective or mean surface ponding depth (mm).<br>
K<sub>f</sub> is the minimum saturated hydraulic conductivity of the filter media or planting soil (mm/h).
K<sub>f</sub> is the minimum acceptable saturated hydraulic conductivity of the filter media or planting soil when compacted to 85% maximum dry density (mm/h).
==Drainage time to empty facility==
==Drainage time to empty facility==