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*''D'' = Duration of the design storm event event (hr)
*''D'' = Duration of the design storm event event (hr)
*''i'' = Intensity of the design storm event (m/hr)
*''i'' = Intensity of the design storm event (m/hr)
*''R'' = the ratio of impervious contributing drainage area to permeable pavement area; ''A<sub>i</sub>''/''A<sub>p</sub>''}}
*''R'' = the ratio of impervious contributing drainage area to permeable pavement area; ''A<sub>i</sub>''/''A<sub>p</sub>''
*''A<sub>i</sub> = Impervious contributing drainage area (m<sup>2</sup>)
*''A<sub>i</sub> = Impervious contributing drainage area (m<sup>2</sup>)
*''A<sub>p</sub> = Permeable pavement area (m<sup>2</sup>)
*''A<sub>p</sub> = Permeable pavement area (m<sup>2</sup>)
*''f''' = [[Design infiltration rate]] of underlying native soil (m/hr)
*''f''' = [[Design infiltration rate]] of underlying native soil (m/hr)
*''n'' = Porosity of the stone bed aggregate material (typically 0.4 for 50 mm dia. [[reservoir aggregate|clear stone]])}}
*''n'' = Porosity of the stone bed aggregate material (typically 0.4 for 50 mm dia. [[reservoir aggregate|clear stone]])
It is important to note that R should not exceed 2 to limit hydraulic loading and help avoid premature clogging. Also important to note is that the contributing drainage area should not contain pervious areas that are sources of sediment that can lead to premature clogging.
It is important to note that R should not exceed 1 to limit hydraulic loading and help avoid premature clogging. Also important to note is that the contributing drainage area should not contain pervious areas that are sources of sediment that can lead to premature clogging.
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===For partial infiltration design, to calculate the depth of the storage reservoir needed below the invert of the underdrain pipe===
===For partial infiltration design, to calculate the depth of the storage reservoir needed below the invert of the underdrain pipe===
For designs that include an underdrain, the depth of the storage reservoir below the invert of the underdrain pipe (''d<sub>r'') can be calculated as follows:
For designs that include an underdrain, the depth of the storage reservoir below the invert of the underdrain pipe (''d<sub>r'') can be calculated as follows:<br>
<math>d_{r}=\frac{f'\times t}{n}</math>
<math>d_{r}=\frac{f'\times t}{n}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
Where:<br>
Where:<br>
A<sub>c</sub> = A<sub>i</sub> + A<sub>p</sub>, and
A<sub>c</sub> = A<sub>i</sub> + A<sub>p</sub>, and<br>
A<sub>r</sub> = A<sub>p</sub> (i.e., assumed that the water storage reservoir area and permeable pavement area are the same)
A<sub>r</sub> = A<sub>p</sub> (i.e., assumed that the water storage reservoir area and permeable pavement area are the same)
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Then increase A<sub>r</sub> accordingly to keep R between 0 and 2, which reduces hydraulic loading and helps avoid premature clogging.
Then adjust A<sub>r</sub> accordingly to keep R between 0 and 1, which reduces hydraulic loading and helps avoid premature clogging.
Back to [[Permeable pavements]]
Back to [[Permeable pavements]]
[[Category:Calculations]]
[[Category:Calculations]]