[[File:Routing.png|thumb|Conceptual diagram of the excess routing alternatives: On the left, excess flow leaves the cell via an overflow; on the right, excess flow is diverted so that only the design volume enters the cell.]]
*Infiltration facilities can be designed to be inline or offline from the drainage system. See [[Inlets]]
*Inline facilities accept all of the flow from a drainage area and convey larger event flows through an overflow outlet. The overflow must be sized to safely convey larger storm events out of the facility.
*The overflow must be situated at the far end of the facility to prevent any localised ponding to cause bypassing of the infiltration facility.
*Offline facilities use flow splitters or bypass channels that only allow the required water quality storage volume to enter the facility.
:Higher flows are diverted and do not enter the infiltration practice. A pipe can by used for this, but a weir or [[curb cuts|curb cut]] minimizes clogging and reduces the maintenance frequency.
==The invert of the overflow should be placed at the maximum water surface elevation of the
bioretention area. i.e. the maximum ponding depth. A good starting point is around 300 mm over the surface of the practice. However, consideration should be given to public safety and time for the ponded water to drain. See [[Bioretention: Sizing#Additional step for system without underdrain|Bioretention]]
Metal grates are recommended (over plastic) in all situations.