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Line 1: + − Underdrains comprise a length of perforated pipe embedded into a layer of [[reservoir gravel]]. They are a key component and vary hugely according to the drainage requirements of the installation, and the available maintenance access. Line 17:
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Underdrains comprise a length of perforated [[pipe]] embedded into a layer of [[reservoir aggregate]]. They are an optional component of [[bioretention]] systems, [[stormwater planters]], [[swales]] and [[tree wells]]. Their design varies according to the drainage requirements of the installation, and the available maintenance access.
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==Underdrains for infiltrating practices==
==Underdrains for infiltrating practices==
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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===