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| + | [[File:Perforations.png|thumb|Pipes are available with perforations on just one side, these should be situated on the lower half of the pipe. Pipes with 360° perforations should have a strip of geotextile or membrane placed over the pipe to reduce the migration of fines from overlying media.]] |
− | *Perforated pipes should be continuously perforated, smooth interior HDPE (or equivalent material) with a minimum inside diameter of 100 mm. | + | Perforated pipes are a common component of [[underdrains]] used in [[bioretention]], [[permeable pavements]], [[infiltration trenches]] and [[exfiltration trenches| exfiltration systems]]. |
− | **Where freezing is a concern, horizontal underdrain pipes should be over-sized to a minimum 200 mm diameter. | + | |
− | **Perforations should be 10 mm in diameter and distributed at least every 90 deg around the pipe. | + | Pipes should be manufactured in conformity with the latest standards by the Canadian Standards Association (CSA) or ASTM International. |
− | *All underdrains should be capped on the upstream end. | + | *Perforated pipes should be continuously perforated, smooth interior HDPE or PVC. |
− | *At least one vertical well per BMP is recommended, for inspection and monitoring water level.
| + | **Wherever possible pipes should be ≥200 mm internal diameter to reduce potential of freezing and to facilitate push camera inspections and cleaning with jet nozzle equipment. |
− | **Well(s), of 100 - 150 mm diameter perforated pipe, should extend to the bottom of the facility.
| + | **Smooth interior facilitates inspection and maintenance activities; internal corrugations can cause cameras or hydrojetting apparatus to become snagged. |
− | **Where a horizontal underdrain is being installed, an upstream and a downstream well should be coupled to the underdrain pipe. The pair of wells can then be used to flush out the length of underdrain if required.
| + | **A perforated pipe with many rectangular slots has better drainage characteristics than a pipe with similar open area provided by fewer circular holes <ref>Hazenberg, G., and U. S. Panu (1991), Theoretical analysis of flow rate into perforated drain tubes, Water Resour. Res., 27(7), 1411–1418, doi:10.1029/91WR00779.</ref>. |
− | **The exposed tops of all wells should be fitted with lockable caps.
| + | *Non-perforated pipes should be used for conveyance of stormwater to and from the facility, including [[overflow]]. It is good practice to extend the solid pipe approximately 300 mm within the reservoir or practice to reduce the potential for native soil migration into the pipe. |
− | *Non-perforated pipes should be used for conveyance to and away from the facility, including overflow. | + | |
− | **To function correctly, the capacity of the overflow pipes must be greater than the inlet(s).
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| + | Perforated Pipe 550x550.jpg|Pipe with slotted perforations |
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| + | Pipe with connector.jpg|Perforated pipes awaiting installation, note the 45 degree couplings used to facilitate push camera inspection and jet nozzle cleaning. |
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− | Perforated Pipe 550x550.jpg| Pipe | |
| </gallery> | | </gallery> |
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| + | See also: [[Flow through perforated pipe]] |
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| [[Category:Materials]] | | [[Category:Materials]] |