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<math>d= \frac{[Qc\times R + P - q\times T ]}{Vr}</math>
 
<math>d= \frac{[Qc\times R + P - q\times T ]}{Vr}</math>
where:{{plainlist|}}
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{{Plainlist|1=Where:
*''d'' &#61; Stone bed depth (m)  
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*''d'' = Stone bed depth (m)  
*''Qc'' &#61; Depth of runoff from contributing drainage area, not including permeable paving surface(m)  
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*''Q<sub>c</sub>'' = Depth of runoff from contributing drainage area, not including permeable paving surface(m)  
*''R'' &#61;  A<sub>c</sub>/A<sub>p</sub> = Ratio of contributing drainage area (A<sub>c</sub>) to permeable paving area (A<sub>p</sub>)
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*''R'' = A<sub>c</sub>/A<sub>p</sub> = Ratio of contributing drainage area (A<sub>c</sub>) to permeable paving area (A<sub>p</sub>)
*''P'' &#61;  Rainfall depth (m)  
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*''P'' = Rainfall depth (m)  
*''q'' &#61;  Infiltration rate for native soils (m/day)  
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*''q'' = Infiltration rate for native soils (m/day)  
*''T'' &#61;  Time to fill stone bed (typically 2 hr)  
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*''T'' = Time to fill stone bed (typically 2 hr)  
*''Vr'' &#61; Void ratio for stone bed (typically 0.4 for 50 mm dia. stone)  
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*''Vr'' = Void ratio for stone bed (typically 0.4 for 50 mm dia. stone)}}
    
Note that the contributing drainage area (Ac) should not contain pervious areas.
 
Note that the contributing drainage area (Ac) should not contain pervious areas.
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