Difference between revisions of "Infiltration: Sizing and modeling"

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     <br> d = Stone reservoir depth (mm)
 
     <br> d = Stone reservoir depth (mm)
 
     <br> q = Infiltration coefficient for native soils (mm/hr) (See [[Infiltration#Planning|Infiltration]] for details on measurement and safety factors)
 
     <br> q = Infiltration coefficient for native soils (mm/hr) (See [[Infiltration#Planning|Infiltration]] for details on measurement and safety factors)
     <br> V<sub>r</sub> = Void space ratio for aggregate(typically 0.4 for 50 mm clear stone)
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     <br> V<sub>r</sub> = Void space ratio for aggregate (typically 0.35 for clear angular stone)
 
     <br> t<sub>s</sub> = Time to drain (48 hour recommended)
 
     <br> t<sub>s</sub> = Time to drain (48 hour recommended)
 
     <br>
 
     <br>
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     </ul>
 
     </ul>
 
</p>
 
</p>
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<p>The ratio of impervious drainage area to infiltration area should be between 5:1 and 20:1 to limit the rate of accumulation of fine sediments and clogging.</p>
The ratio of impervious drainage area to infiltration area should be between 5:1 and 20:1 to limit the rate of accumulation of fine sediments and clogging.</p>
 
 
[[category: Infiltration]]
 
[[category: Infiltration]]
 
[[category: modeling]]
 
[[category: modeling]]

Revision as of 19:22, 8 August 2017

The depth of an infiltration facility is dependent on the native soil infiltration rate, porosity (void space ratio) of the gravel storage layer and the targeted time period to achieve complete drainage between storm events. The depth of the reservoir for designs without an underdrain can be calculated using the following equation:

d = (q × ts)/ Vr

Where:
d = Stone reservoir depth (mm)
q = Infiltration coefficient for native soils (mm/hr) (See Infiltration for details on measurement and safety factors)
Vr = Void space ratio for aggregate (typically 0.35 for clear angular stone)
ts = Time to drain (48 hour recommended)

Notes:

  • The infiltration coefficient (q) used above should incorporate a safety correction factor
  • On highly permeable soils (e.g., infiltration rate of ≥ 45 mm/hr), a maximum depth of 2 m is recommended to prevent soil compaction and loss of permeability from the mass of overlying stone and stored water.
  • For designs that include an underdrain, the above equation can be used to determine the maximum depth of the stone reservoir below the invert of the underdrain pipe.

The ratio of impervious drainage area to infiltration area should be between 5:1 and 20:1 to limit the rate of accumulation of fine sediments and clogging.