Changes

[[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.]]  

[[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 are a common component of [[underdrains]] used in [[bioretention]], [[permeable paving| permeable pavements]], [[infiltration trenches]] and [[exfiltration trenches| exfiltration systems]].   

Perforated pipes are a common component of [[underdrains]] used in [[bioretention]], [[permeable pavements]], [[infiltration trenches]] and [[exfiltration trenches| exfiltration systems]].   

Pipes should have been manufactured in conformity with the latest standards by the Canadian Standards Association (CSA) or ASTM International.

Pipes should be manufactured in conformity with the latest standards by the Canadian Standards Association (CSA) or ASTM International.

*Perforated pipes should be continuously perforated, smooth interior HDPE (or equivalent material).

*Perforated pipes should be continuously perforated, smooth interior HDPE or PVC.

**Wherever possible pipes should be ≥ 200 mm internal diameter to reduce potential of freezing and to facilitate inspections and maintenance with a push camera.  

**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.  

**Smooth interior facilitates inspection and maintenance activities; internal corrugations can cause cameras or hydrojetting apparatus to become snagged.     

**Smooth interior facilitates inspection and maintenance activities; internal corrugations can cause cameras or hydrojetting apparatus to become snagged.     

**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>.

**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>.

*Non-perforated pipes should be used for conveyance to and away from the facility, including [[overflow]]. It is good practice to extend the non-perforated pipe approximately 300 mm within the reservoir or practice to reduce the potential for native soil migration to clog the pipe at the interface.  

*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.  

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