Changes

<p>An internal water storage zone  (IWS or IWSZ) is created by including an upturned 90 deg on the outflow pipe to force an elevated outlet. For practical reasons, this is commonly applied within a manhole or other nearby piece of infrastructure, rather than  being buried directly adjacent. The effect  is to create longer term, water-logged, low-oxygen environment within the bottom of the bioretention cell. <br>

<p>An internal water storage (IWS) reservoir or zone is created by including an upturned 90 deg on the outflow pipe to force an elevated outlet. For practical reasons, this is commonly applied within a manhole or other nearby piece of infrastructure, rather than  being buried directly adjacent. The effect  is to create longer term, water-logged, low-oxygen environment within the bottom of the bioretention cell. <br>

This has two primary benefits:

This has two primary benefits:

<ol>

<ol>

<li>Additional infiltration is promoted by holding the water in place over the native soil for longer, </li>

<li>Additional infiltration is promoted by holding the water in place over the native soil for longer, </li>

<li>The types of microbes that grow in a low-oxygen environment are also better at completing the removal of nitrogen compounds from the water. This effect is enhanced by using a low-nutrient carbon source in the bioretention filter media.</li>

<li>The types of microbes that grow in a low-oxygen environment are also better at completing the removal of nitrogen compounds from the water. This effect is enhanced by using a low-nutrient carbon source in the bioretention filter media and storage reservoir aggregate.</li>

</ol>

</ol>

  </p>

  </p>

Nitrogen removal rates are linked to increased depth of IWS, so that a minimum of 45 cm of IWS is recommended where the depth of the native soils and bioretention cell permit<ref>Lynn TJ, Yeh DH, Ergas SJ. Performance of Denitrifying Stormwater Biofilters Under Intermittent Conditions. Environ Eng Sci. 2015;32(9):150710132840004. doi:10.1089/ees.2015.0135.</ref>.  

Nitrogen removal rates are linked to increased depth of IWS, so that a minimum of 45 cm of IWS is recommended where the depth of the native soils and bioretention cell permit<ref>Lynn TJ, Yeh DH, Ergas SJ. Performance of Denitrifying Stormwater Biofilters Under Intermittent Conditions. Environ Eng Sci. 2015;32(9):150710132840004. doi:10.1089/ees.2015.0135.</ref>.  

However, any depth of IWS would be expected to make some improvement on water retention and infiltration. </p>

However, any depth of IWS would be expected to make some improvement on water retention and infiltration. </p>