Changes

[[File:underdrain-subgrade.jpg|400px|thumb|right|Underdrain installed to subgrade.]]

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

[[File:underdrain-with-risers.jpg|400px|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.