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→Underdrains for exfiltrating practices
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==Underdrains for exfiltrating 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, 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.