*For optimal performance bioretention facilities should receive runoff from between 5 to 20 times their own surface area.
*In the conceptual design stage it is recommended to set aside approximately 10 - 20 % of a catchment's total area for bioretention facility placement.
*Bioretention cells work best when distributed, so that no one facility receives runoff from more than 0.8 Ha, although
, there is a trade off to be considered regarding distributed collection and treatment against ease of maintenance.
*Bioretention can be almost any shape, from very curving, soft edges with variable depth, to angular, hard sided and uniform depth.
:For ease of construction and to ensure that the vegetation has adequate space, cells should be no narrower than 0.6 m at any point.