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*''L'' is the length of perforated pipe (m)
Orifices are simply holes which restrict the flow of water. They may be used at the bottom end of an LID practice to add some [[flow control]].
Orifices are simply holes which restrict the flow of water. They may be used at the bottom end of an LID practice to add some [[flow control]]:
<math>Q= B\times C_{d}\times A_{o}\sqrt{2\cdot g\cdot h}</math>
<math>Q= B\times C_{d}\times A_{o}\sqrt{2\cdot g\cdot h}</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*''B'' is the clogging factor (between 0.5 (for matured installation) and 1 (for a new perfectly performing orifice)),
*''B'' is the clogging factor (between 0.5 (for matured installation) and 1 (for a new perfectly performing BMP)),
*''C<sub>d</sub>'' is the coefficient of discharge (usually 0.61 for a plate, or 0.8 for a pipe),
*''C<sub>d</sub>'' is the coefficient of discharge (usually 0.61 for a plate, or 0.8 for a pipe),
*''A<sub>o</sub>'' is the area of the orifice (m<sup>2</sup>/m),
*''A<sub>o</sub>'' is the area of the orifice (m<sup>2</sup>),
*''g'' is acceleration due to gravity = 9.81 m/s<sup>2</sup>, and
*''g'' is acceleration due to gravity = 9.81 m/s<sup>2</sup>, and
*''h'' is the head of water over the centre of the orifice.
*''h'' is the head of water over the centre of the orifice (m).
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