From LID SWM Planning and Design Guide
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The most common form of weir in LID practices is a rectangular weir, in the form of a check dam or flow control in a swale or other open channel.

The flow (Q), may be calculated by measuring the height of water on the sill of the weir:


  • Cd = discharge coefficient (default 0.62 for a 'sharp edge).
  • L = Length of the weir (m)
  • g = Acceleration due to gravity (9.81 m/s2)
  • H = Height of water over the weir (m)

More flow related pages[edit]