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[[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.]]
===Routing===
*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 maximum surface ponding elevation or furthest downgradient end of the facility to limit surface ponding during periods of flow in excess of the facility storage capacity.
*Offline facilities use flow splitters or bypass channels that only allow the design storm runoff storage volume to enter the facility. Higher flows are conveyed to a downstream storm sewer or other BMP by a flow splitting manhole weir or pipe, or when the maximum surface ponding depth has been reached, by by-passing the curb opening and flowing into a downstream catchbasin connected to a storm sewer.
===Overflow elevation===
The invert of the overflow should be placed at the maximum water surface elevation of the practice (i.e. the maximum surface ponding level).
A good starting point is 150 to 350 mm above the surface of the mulch cover. However, consideration should be given to public safety, whether or not an underdrain is included, the time required for ponded water to drain through the filter bed surface, and if no underdrain is present, into the underlying native soil (must drain within 48 hours).
See [[Bioretention: Sizing]] and [[Stormwater planters]] for more details.
===Freeboard===
{{:freeboard}}
===Overflow outlet options===
Metal grates are recommended (over plastic) in all situations.
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===Gallery===
{{:Overflow:Gallery}}