# Difference between revisions of "Weirs"

The most common form of weir in 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. 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:

• 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)