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→Spacing drainage pipes
==Spacing drainage pipes==
==Spacing drainage pipes==
[[File:Drain spacing.jpg|thumb|The yellow box represents the recommended hydraulic conductivity of bioretention filter media]]
In most LID underdrain applications, drains should be spaced between 5 - 6 m apart.
In most LID underdrain applications, drains should be spaced between 5 - 6 m apart.
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''q'' is the inflow volume expressed as a depth over the entire surface (m)
''q'' is the inflow volume expressed as a depth over the entire surface (m)
===Example===
===Example===
During a 25 mm storm event, a bioretention cell receives concentrated flow from a catchment 20 times larger than its own footprint (25 x 20 = 500 mm = 0.5 m).
During a 25 mm storm event, a bioretention cell receives concentrated flow from a catchment 20 times larger than its own footprint (25 x 20 = 500 mm = 0.5 m).
The bioretention cell comprises 0.6 m filter media (K = 2.4 m/day), laid over 0.6 m clear, coarse reservoir gravel. The pipes are laid within the reservoir, 0.9 m below the surface.
The bioretention cell comprises 0.6 m filter media (K = 2.4 m/day), laid over 0.6 m clear, coarse reservoir gravel. The pipes are laid within the reservoir, 0.9 m below the surface.