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| <h4>Sizing</h4> | | <h4>Sizing</h4> |
| Bioretention facilities are usually between 0.5 m and
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| <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> |
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