Flow through an orifice

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Orifices are simply holes which restrict the flow of water. They may be used at the bottom end of an LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. practice to add some flow control.

\(Q= B\times C_{d}\times A_{o}\sqrt{2\cdot g\cdot h}\)


  • L is the length of perforated pipe (m)
  • B is the clogging factor (between 0.5 (for matured installation) and 1 (for a new perfectly performing BMPBest management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.)),
  • Cd is the coefficient of discharge (usually 0.61 for a plate, or 0.8 for a pipe),
  • Ao is the area of the orifice (m2/m),
  • g is acceleration due to gravity = 9.81 m/s2, and
  • h is the head of water over the centre of the orifice.

See also