Difference between revisions of "Overflow"
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===Overflow elevation=== | ===Overflow elevation=== | ||
The invert of the overflow should be placed at the maximum water surface elevation of the practice. i.e. the maximum ponding depth. | 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 | 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 for the ponded water to drain. | ||
See [[Bioretention: Sizing#Additional step for system without underdrain|Bioretention]] and [[Stormwater planters]] | See [[Bioretention: Sizing#Additional step for system without underdrain|Bioretention]] and [[Stormwater planters]] | ||
Revision as of 21:09, 14 November 2019
Routing[edit]
- 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.
Overflow elevation[edit]
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 for the ponded water to drain. See Bioretention and Stormwater planters
Freeboard[edit]
- In swales conveying flowing water a freeboard of 300 mm is generally accepted as a good starting point.
- In bioretention the freeboard is the difference between the invert elevation of the overflow structure and the inlet. 150 mm will suffice, so long as the inlet will not become inundated during design storm conditions.
- In above grade stormwater planters, the equivalent dimension would be the difference between the invert elevation of the overflow structure and the lip of the planter (150 mm minimum)
Options[edit]
Metal grates are recommended (over plastic) in all situations.
| Feature | Anti Vandalism/Robust | Lower Cost Option | Self cleaning |
|---|---|---|---|
| Dome grate | x | ||
| Flat grate | x | ||
| Catch basin | x | ||
| Ditch inlet catch basin | x | x | |
| Curb cut | x | x | x |
Gallery[edit]
Flat metal overflow with stone surround to reduce erosion around the cast concrete structure. Mississauga Road, ON
Domed, metal overflow grate
Photo credit: Aaron Volkening Being flush with the surface reduces potential infiltration of ponded water.
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
Flat, metal overflow grate in Emeryville California Stormwater Curb Extension
Note the greyish colour change indicating UV degradation of this plastic overflow inlet in a bioretention cell; metal is recommended instead. Mississauga ON.
