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Line 1: − <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>+ − <strong>d = (q × t<sub>s</sub>)/ V<sub>r</sub></strong> − <br> − <p>Where: − <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> 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> − </p> − <p>Notes: − <ul> − <li>The infiltration coefficient (q) used above should incorporate a safety correction factor </li> − <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> − <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> − </ul> − </p> − <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: modeling]]
Infiltration: Sizing and modeling (view source)
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