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mLine 3:
Line 3: − According to the storage and infiltration rate of the native soils below, the pipe within the drain should be elevated from the base to promote infiltration of the water stored beneath. An alternative design configuration permits the head of water to be stored by using an upturned outflow pipe. + − A pair of vertical clean out 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. + + + + + + + + + + + + + + + − +
→Infiltrating practices below ground
===Infiltrating practices below ground===
===Infiltrating practices below ground===
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 clean out 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"
!Clean out spacing
|-
! Pipe internal diameter
! Maximum spacing of clean out
|-
| 100 mm
| 15 m
|-
| 200 mm or greater
| 30 m
|}
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 gravel 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 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]].
===Non-infiltrating practices below ground===
===Non-infiltrating practices below ground===