Difference between revisions of "Infiltration: Sizing and modeling"

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<p>The depth of an infiltration facility is dependent on the native soil infiltration rate, porosity (void space ratio) of the [[Reservoir gravel|gravel storage layer]] and the targeted time period to achieve complete drainage between storm events. The depth of the reservoir for designs <em>without an underdrain</em> can be calculated using the following equation:</p>
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<strong>d = (q × t<sub>s</sub>)/ V<sub>r</sub></strong>
 
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<br>
 
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<p>Where:
 
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    <br> d = Stone reservoir depth (mm)
 
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    <br> q = Infiltration coefficient for native soils (mm/hr) (See [[Infiltration#Planning|Infiltration]] for details on measurement and safety factors)
 
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    <br> V<sub>r</sub> = Void space ratio for aggregate (typically 0.35 for clear angular stone)
 
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    <br> t<sub>s</sub> = Time to drain (48 hour recommended)
 
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    <br>
 
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</p>
 
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<p>Notes:
 
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    <ul>
 
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        <li>The infiltration coefficient (q) used above should incorporate a safety correction factor </li>
 
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        <li>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.</li>
 
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        <li>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.</li>
 
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    </ul>
 
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</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>
 
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[[category: Infiltration]]
 
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[[category: modeling]]
 

Revision as of 11:50, 7 September 2017

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