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.

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:

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

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

Key Inspection Points:

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

*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

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

Mistakes to Avoid:

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

*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 under-drains, see the page on under-drains.

For more information on the design of under-drains, see the page on under-drains.<br>