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Line 67: − Bioretention facilities are usually between 0.5 m and − + − + − + − + + + +
→Design
<h4>Sizing</h4>
<h4>Sizing</h4>
<ol>
<ol>
<li>Gather preliminary data:
<li>Gather input data:
<ul><li>the applicable infiltration coefficient (q) is calculated by applying the safety factor to the measured infiltration rate. </li>
<ul) >
<li>determine the drainage catchment area, and outline the location of the bioretention facility. The area required for the facility will be at least 5% of the contributing impervious area. </li></li>
<li>The applicable infiltration coefficient (q) is calculated by applying the safety factor to the [[Infiltration testing|measured infiltration rate]].</li>
<li>Unless fill materials (biomedia and gravel) have been tested and certified otherwise, a porosity value of 0.3 may be assumed (i.e. void ratio 30%). </li>
<li>Determine the drainage catchment area (A<sub>D</sub>), and outline the location of the bioretention facility. To begin with, budget for at least 10% of the contributing impervious area to be required for the BMP. </li></li>
<li>Unless the biomedia fill material has been tested and certified otherwise, a porosity value (V<sub>r</sub>) of 0.4 may be assumed (i.e. void ratio 40%). </li>
<li>Bioretention facilities are usually between 0.5 m and 1.25 m deep, owing to construction considerations. Determine the maximum available depth (c<sub>c max</sub>) from the site constraints. The [[Infiltration]] page has some of these listed. </li>
<li>Identify the duration (D) and intensity (i) of design storm(s).
</ol>
</ol>