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→Spacing drain pipe
==Spacing drain pipe==
==Spacing drain pipe==
Laterals drains should be spaced between 3 - 4 m apart. <br>
Laterals drains should be spaced between 3 - 4 m apart.
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This is based on an analysis of Hooghoudt's equation<ref>H.P.Ritzema, 1994, Subsurface flow to drains. Chapter 8 in: H.P.Ritzema (ed.), Drainage Principles and Applications, Publ. 16, pp. 236-304, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands. ISBN 90-70754-33-9</ref>:
This is based on an analysis of Hooghoudt's equation<ref>H.P.Ritzema, 1994, Subsurface flow to drains. Chapter 8 in: H.P.Ritzema (ed.), Drainage Principles and Applications, Publ. 16, pp. 236-304, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands. ISBN 90-70754-33-9</ref>:
<math>Drain\ spacing=\sqrt{\frac{8K_{soil}H\left(D_{i}-D_{d}\right)\left(D_{d}-D_{w}\right)+4K_{soil}\left(D_{d}-D_{w}\right)^{2}}{q}}</math>
<math>Drain\ spacing=\sqrt{\frac{8K_{soil}H\left(D_{i}-D_{d}\right)\left(D_{d}-D_{w}\right)+4K_{soil}\left(D_{d}-D_{w}\right)^{2}}{q}}</math>
''D<sub>w</sub>'' is the minimum acceptable depth to the water table during infiltration
''D<sub>w</sub>'' is the minimum acceptable depth to the water table during infiltration
''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 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 laid over 0.6 m clear, coarse reservoir gravel. The pipes are laid within the reservoir, 0.9 m below the surface:
<math>Drain\ spacing=\sqrt{\frac{4\times 2.4m\left(0.9m-0.3m\right)^{2}}{0.5}}=3.4 m</math>
<math>Drain\ spacing=\sqrt{\frac{4\times 2.4m\left(0.9m-0.3m\right)^{2}}{0.5}}=3.4 m</math>