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→Types of bioretention by underground design
<p>This type may be required over contamination hot-spots or in very dense urban areas with a lot of other underground infrastructure. The design includes an impermeable base and sides, so that volume reduction is made only through evapotranspiration.</p>
<p>This type may be required over contamination hot-spots or in very dense urban areas with a lot of other underground infrastructure. The design includes an impermeable base and sides, so that volume reduction is made only through evapotranspiration.</p>
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<caption><strong>Types of bioretention cell</strong></caption>
<tr class ='success'><th>Form</th><th>Characteristics</th><th>Examples</th></tr>
<tr><td>[[Rain gardens]]</td><td>These are the simplest construction, often used by residents or community groups. Volume reduction is through infiltration and evapotranspiration. </td><td>Image of Raingarden</td></tr>
<tr><td>This is the most highly desirable type of bioretention where the soils permit infiltration at a great enough rate to empty the facility between storm events. Volume reduction is primarily through infiltration to the underlying soils, with some evapotranspiration. As there is no outflow from this BMP, it is particularly desirable in areas where nutrient management is a concern to the watershed.</td><td>Diagram of bioretention without underdrain.</td></tr>
<tr><td>Partially infiltrating bioretention</td><td>Including an underdrain in the gravel storage layer ensures that the facility will empty between storm events even over ‘tight soils’. The drain discharges to a downstream point, which may require a Limited volume reduction is gained through infiltration and evapotranspiration.</td><td>Image here</td></tr>
<tr><td>Bioretention with storage</td><td>By raising the outlet of the discharge pipe the bottom portion of the BMP can only drain through infiltration. This creates a fluctuating anaerobic/aerobic environment which promotes denitrification. Increasing the period of storage has benefits for promoting infiltration, but also improves water quality for catchments impacted with nitrates. A complimentary technique is to use fresh wood mulch, which also fosters denitrifying biological processes. </td><td>Image</td></tr>
<tr><td>Bioretention planters (non-infiltrating)</td><td>This type may be required over contamination hot-spots or in very dense urban areas with a lot of other underground infrastructure. The design includes an impermeable base and sides, so that volume reduction is made only through evapotranspiration.</td><td>Image here</td></tr>
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