Changes

[[File:underdrain-subgrade.jpg|300px|thumb|right|Underdrain installed to subgrade.]]

[[File:underdrain-subgrade.jpg|300px|thumb|right|Underdrain installed to subgrade.]]

[[File:underdrain-with-risers.jpg|300px|thumb|right|Underdrain installed with maintenance risers. Note the 'T' joints, which are no longer recommended.]]

[[File:underdrain-with-risers.jpg|300px|thumb|right|Underdrain installed with maintenance risers. Note the 'T' joints, which are no longer recommended.]]

[[Underdrains]] are perforated pipes that  collect subsurface water and convey water out of an LID facility once it reaches capacity. Their design is determined by the drainage requirements of the feature.<br>

[[Underdrains]] are perforated pipes that  collect subsurface water and convey water out of an LID facility once it reaches capacity. Their design is determined by the drainage requirements of the feature.<br>

Construction Steps:<br>

'''Construction Steps:'''<br>

#Install the underdrain to grade with a consistent slope of 0.5% to 1.0%

#Install the underdrain to grade with a consistent slope of 0.5% to 1.0%.

#Connect overflow risers with single-elbowed ‘y’ connections or 45° elbows

#Connect overflow risers with single-elbowed ‘y’ connections or 45° elbows.

#Situate maintenance risers where siltation is expected in drain lines (such as at junctions or where grade and direction changes occur), in accordance with the design drawings.

#Situate maintenance risers where siltation is expected in drain lines (such as at junctions or where grade and direction changes occur), in accordance with the design drawings.

#Mark the locations of risers

#Mark the locations of risers.

#Use video inspections to confirm that the interior of the underdrain remains free of debris after construction<br>

#Use video inspections to confirm that the interior of the underdrain remains free of debris after construction.<br>

Key Inspection Points:<br>

'''Key Inspection Points:'''<br>

*Size, type, and material of the underdrain conforms to the design specifications

*Size, type, and material of the underdrain conforms to the design specifications.

*Underdrain is perforated prior to arrival on-site

*Underdrain is perforated prior to arrival on-site.

*Drain material is resistant to UV radiation and any chemicals in the soil and groundwater

*Drain material is resistant to UV radiation and any chemicals in the soil and groundwater.

*Clean-outs are positioned correctly and spaced appropriately for the size of the underdrain

*Clean-outs are positioned correctly and spaced appropriately for the size of the underdrain.

*Any manual perforations are approved by the design or field engineer

*Any manual perforations are approved by the design or field engineer.

*Pipe grade matches design specifications

*Pipe grade matches design specifications.

*Tie-in locations to municipal sewers meet municipal specifications<br>

*Tie-in locations to municipal sewers meet municipal specifications.<br>

Mistakes to Avoid:<br>

'''Mistakes to Avoid:'''<br>

*Incorrect overflow risers – ensure single-elbowed ‘y’ connections or 45° elbows are used for overflow risers instead of ‘T’ connections

*Incorrect overflow risers – ensure single-elbowed ‘y’ connections or 45° elbows are used for overflow risers instead of ‘T’ connections.

*Incorrect drain size – confirm underdrain has an internal diameter greater than or equal to 200 mm to reduce freezing and allow cleaning and camera inspections

*Incorrect drain size – confirm underdrain has an internal diameter greater than or equal to 200 mm to reduce freezing and allow cleaning and camera inspections.

*Potential for clogging – Remove sock from underdrain prior to installation or geofabric wrap. A choker course is recommended, instead, as field change<br>

*Potential for clogging – Remove sock from underdrain prior to installation or geofabric wrap. A choker course is recommended, instead, as field change.<br>

For more information on the design of underdrains, such as materials and connections, see the page on underdrains linked above.<br>

For more information on the design of underdrains, such as materials and connections, see the page on underdrains linked above.<br>