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{{:Underdrains: Installation}}+
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==Underdrains==
==Underdrains==
+[[File:underdrain-subgrade.jpg|300px|thumb|right|Underdrain installed to subgrade. (Photo Source: CVC, 2010)]]
+[[File:underdrain-with-risers.jpg|300px|thumb|right|Underdrain installed with maintenance risers. Note the 'T' joints, which are no longer recommended. (Photo Source: CVC, 2010)]]
+[[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.
−'''Construction Steps:'''
+#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.
+#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.
+#Use video inspections to confirm that the interior of the underdrain remains free of debris after construction.
+'''Key Inspection Points:'''
+*Size, type, and material of the underdrain conforms to the design specifications.
+*Underdrain is perforated prior to arrival on-site.
+*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.
+*Any manual perforations are approved by the design or field engineer.
+*Pipe grade matches design specifications.
+*Tie-in locations to municipal sewers meet municipal specifications.
+'''Mistakes to Avoid:'''
+*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.
+*Potential for clogging – Remove sock from underdrain prior to installation or geofabric wrap. A choker course is recommended, instead, as field change.
+For more information on the design of underdrains, such as materials and connections, see the page on underdrains linked above.
==Impermeable liners==
==Impermeable liners==