Weirs

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:

$Q={\frac {2}{3}}C_{d}\cdot L{\sqrt {2g}}\cdot H^{\frac {3}{2}}$

Where:

• C_d = 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

• Flow in a swale
• Flow through perforated pipe
• Flow through an orifice

Low 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.