- 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 cut minimizes clogging and reduces the maintenance frequency.
The invert of the overflow should be placed at the maximum water surface elevation of the practice. 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 drainage time|time for the ponded water to drain. See Bioretention and Stormwater planters
Where temporary ponded water is being planned for, include a freeboard to reduce the chance of localised flooding.
Metal grates are recommended (over plastic) in all situations.
|Feature||Anti Vandalism/Robust||Lower Cost Option||Self cleaning|
|Ditch inlet catch basin||x||x|
Flat metal overflow with stone surround to reduce erosion around the cast concrete structure. Mississauga Road, ON
Overflow inlet for newly constructed stormwater bioretention areas in median of Bradley Road. Village of Brown Deer, Wisconsin. Bradley Road, east of 51st Street. Photo from October 2015. Constructed summer 2015.
Photo credit: Aaron Volkening