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==Underdrains for infiltrating practices==

==Underdrains for exfiltrating practices==

The pipe within the drain should be elevated from the base to promote infiltration of the water stored beneath. The depth of this internal water storage should be sized according to the desired drainage time and the infiltration rate of the native soils below. An alternative design configuration permits the head of water to be stored by using an upturned outflow pipe.  

The pipe within the drain should be elevated from the base to promote infiltration of the water stored beneath. The depth of this internal water storage should be sized according to the desired drainage time and the infiltration rate of the native soils below. An alternative design configuration permits the head of water to be stored by using an upturned outflow pipe.  

*At least one pair of vertical cleanout pipes/wells should be included in the design, for inspection and periodic flushing of accumulated sediment. As most hydro-jetting apparatus used for this has some trouble accommodating narrow 90 deg bends, it is important that both ends of a perforated pipe be connected with a pair of 45 deg elbows/Y connectors instead.  

*At least one pair of vertical cleanout pipes/wells should be included in the design, for inspection and periodic flushing of accumulated sediment. As most hydro-jetting apparatus used for this has some trouble accommodating narrow 90 deg bends, it is important that both ends of a perforated pipe be connected with a pair of 45 deg elbows/Y connectors instead.  

{| class="wikitable"

{| class="wikitable"

|+Clean out spacing

|+Clean out spacing<ref>Province of Ontario. (2018). O. Reg. 332/12: BUILDING CODE. Retrieved February 23, 2018, from https://www.ontario.ca/laws/regulation/120332</ref>

|-

|-

! Pipe internal diameter (mm)

! Pipe internal diameter (mm)

| 30

| 30

|}

|}

In a [[bioretention]] facility, after the rooting depth of the plants has been accommodated, the reservoir gravel layer can be increased for storage. Reservoir gravel has a void ratio of 0.4, whilst most bioretention [[filter media]] may have a void ratio of 0.3 or lower.  

In a [[bioretention]] facility, after the rooting depth of the plants has been accommodated, the reservoir gravel layer can be increased for storage. Reservoir aggregate has a void ratio of 0.4, whilst most bioretention [[filter media]] may have a void ratio of 0.3 or lower.  

In some cases where the underdrain layer has sufficient depth to accommodate it, a larger bore perforated pipe (e.g. ≥ 300 mm) may be used to add further storage capacity. Ultimately this idea may result in the use of retention chambers to create significant reservoir storage beneath a planted area. Be sure to check with manufacturers about the compatability of their systems with [[trees]].

In some cases where the underdrain layer has sufficient depth to accommodate it, a larger bore perforated pipe (e.g. ≥ 300 mm) may be used to add further storage capacity. Ultimately this idea may result in the use of [[infiltration chambers]] to create significant reservoir storage beneath a planted area. Be sure to check with manufacturers about the compatibility of their systems with [[trees]].

===Spacing drainage pipes to reduce groundwater mounding===

===Spacing drainage pipes to reduce groundwater mounding===

==Maintenance and inspection==

==Maintenance and inspection==

*Well(s), of 100 - 150 mm diameter perforated pipe, should extend to the bottom of the facility.

*Where a horizontal underdrain is being installed, an upstream and a downstream well should be coupled to the underdrain pipe. The pair of wells can then be used to flush out the length of underdrain if required.  

*The exposed tops of all wells should be fitted with lockable caps.  

 

*[[Wells]], of 100 - 150 mm diameter perforated pipe, should extend to the bottom of the facility.  

*The exposed tops of all wells should be fitted with lockable caps.

==Material specifications==

==Material specifications==

==Alternative Technology==

==Alternative Technology==

Smart drain is a polymer ribbon-like material with capillary drains on the underside; it's use has recently been demonstrated in bioretention<ref>Redahegn Sileshi; Robert Pitt, P.E., M.ASCE; and Shirley Clark, P.E., M.ASCE Performance Evaluation of an Alternative Underdrain Material for Stormwater Biofiltration Systems, Journal of Sustainable Water in the Built Environment, 4(2), May 2018 https://doi.org/10.1061/JSWBAY.0000845 </ref>. It's low profile may make it particularly well suited to non-infiltrating practices, such as [[flow-through planters]].  

Smart drain is a polymer ribbon-like material with capillary drains on the underside; it's use has recently been demonstrated in bioretention<ref>Redahegn Sileshi; Robert Pitt, P.E., M.ASCE; and Shirley Clark, P.E., M.ASCE Performance Evaluation of an Alternative Underdrain Material for Stormwater Biofiltration Systems, Journal of Sustainable Water in the Built Environment, 4(2), May 2018 https://doi.org/10.1061/JSWBAY.0000845 </ref>. It's low profile may make it particularly well suited to non-infiltrating practices, such as [[Stormwater planters]].  

[[File:Smart drain.jpg|thumb|Ribbon-like drainage material]]

[[File:Smart drain.jpg|thumb|Ribbon-like drainage material]]

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