Should be a minimum of 300 mm deep, and filled with granular material of washed 25 or 50 mm diameter crushed angular stone (max. wash loss of 0.5%). See [[Aggregates]] for further details. Include organic material derived from untreated wood (e.g. chips, mulch or shavings) to enhance nitrogen removal. Also see [[Bioretention: Internal water storage]]. See [[Bioretention: Sizing]] for reservoir sizing guidance, including depth and area of surface ponding and reservoir volume needed to capture and store the design storm. | Should be a minimum of 300 mm deep, and filled with granular material of washed 25 or 50 mm diameter crushed angular stone (max. wash loss of 0.5%). See [[Aggregates]] for further details. Include organic material derived from untreated wood (e.g. chips, mulch or shavings) to enhance nitrogen removal. Also see [[Bioretention: Internal water storage]]. See [[Bioretention: Sizing]] for reservoir sizing guidance, including depth and area of surface ponding and reservoir volume needed to capture and store the design storm. |