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→Underdrains for infiltrating practices
==Underdrains for infiltrating practices==
==Underdrains for infiltrating practices==
The perforated pipe within the drain should be elevated from the base to promote infiltration of the water stored beneath. The depth of this [[Bioretention: Internal_water_storage| internal water storage reservoir]] should be sized to capture and infiltrate the design storm event runoff volume based on the desired [[drainage time]] and the [[design infiltration rate]] of the native soils below. An alternative design configuration is to install the perforated pipe on the base of the practice and using an upturned outflow pipe to permit the required head of water to be stored.
The perforated pipe within the drain should be elevated from the base to promote infiltration of the water stored beneath. The depth of this [[Bioretention: Internal_water_storage| internal water storage reservoir]] should be sized to capture and infiltrate the design storm event runoff volume based on the desired [[drainage time]] and the [[design infiltration rate]] of the native soils below. An alternative design configuration is to install the perforated pipe on the base of the practice and using an upturned outflow pipe to permit the required head of water to be stored.
*Underdrain access structures, which may be maintenance holes or vertical standpipes connected to the perforated pipe, must be included in the design for periodic inspection and flushing of the perforated pipe. Negotiating 90 degree bends will be troublesome for most push camera and jet nozzle cleaning equipment, so it is preferable that 45 degree pipe couplings be used instead.
*Underdrain access structures/cleanouts, which may be maintenance holes or vertical standpipes connected to the perforated pipe, must be included in the design for periodic inspection and flushing of the perforated pipe. Negotiating 90 degree bends will be troublesome for most push camera and jet nozzle cleaning equipment, so it is preferable that 45 degree pipe couplings be used instead.
'''Cleanouts''' are "''a fitting access in a drainage system or venting system that is installed to provide access for cleaning and inspection and that is provided with a readily replaceable air tight cover''" ([https://www.ontario.ca/laws/regulation/120332 O.Reg 332/12: Building Code, 2022])<ref>Province of Ontario. (2018). O. Reg. 332/12: BUILDING CODE. Retrieved February 23, 2018, from https://www.ontario.ca/laws/regulation/120332</ref>.
{| class="wikitable"
{| class="wikitable"
|+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>
|+Clean out spacing<ref>Province of Ontario. (2022). 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)
|}
|}
In some cases where the underdrain layer has sufficient depth to accommodate it, a larger diameter perforated pipe (e.g. ≥ 300 mm) may be used to add further storage capacity to a [[bioretention]] or a [[bioswale]] project. Ultimately this idea may result in the use of [[infiltration chambers]] or other void-forming structures to create significant reservoir storage beneath a bioretention filter media bed or permeable pavement. Be sure to check with manufacturers about the compatibility of their systems with trees.
In some cases where the underdrain layer has sufficient depth to accommodate it, a larger diameter perforated pipe (e.g. ≥ 300 mm) may be used to add further storage capacity to a [[bioretention]] or a [[bioswale]] project. Ultimately this idea may result in the use of [[infiltration chambers]] or other void-forming structures to create significant reservoir storage beneath a bioretention filter media bed or permeable pavement. Be sure to check with manufacturers about the compatibility of their systems with trees.
See the [[Flow through perforated pipe]] for underdrain capacity equation with LID BMPs.
==Underdrains for non-infiltrating practices==
==Underdrains for non-infiltrating practices==
*To permit access by cameras or cleaning apparatus, 90 degree pipe couplings must not be used in subterranean underdrains. Instead 2 x 45 degree couplings, or 3 x 30 degree couplings should be used (see figure to the right).
*To permit access by cameras or cleaning apparatus, 90 degree pipe couplings must not be used in subterranean underdrains. Instead 2 x 45 degree couplings, or 3 x 30 degree couplings should be used (see figure to the right).
*For the same reason, dual walled perforated pipes with smooth internal walls are highly recommended to reduce the potential snagging of maintenance equipment.
*For the same reason, dual walled perforated pipes with smooth internal walls are highly recommended to reduce the potential snagging of maintenance equipment.
*The recommended distances between clean outs is based on advice for filter beds in the Ontario Building Code<ref>Province of Ontario. (2018). O. Reg. 332/12: BUILDING CODE. Retrieved February 23, 2018, from https://www.ontario.ca/laws/regulation/120332</ref>. However, the access capabilities of difference apparatus and contractors varies and designers are advised to take advice from maintenance operators in this matter.
*The recommended distances between [[Wells|clean outs]] is based on advice for filter beds in the Ontario Building Code<ref>Province of Ontario. (2018). O. Reg. 332/12: BUILDING CODE. Retrieved February 23, 2018, from https://www.ontario.ca/laws/regulation/120332</ref>. However, the access capabilities of difference apparatus and contractors varies and designers are advised to take advice from maintenance operators in this matter.
*[[Wells]]
*[[Wells]]