Weirs (SWMM)
Weirs (SWMM) are used in a SWMM network to model outlet and diversion structures in the network, and may also contain a flap gate to prevent blackflow. A weir must be located at an upstream node, and its hydraulic behaviour can be modelled using a weir curve to determine the non-linear relationship between its head and the flow rate through it. Control rules can also be used to adjust the crest height of a weir and the position of its flap gate during a simulation.
The following types of weir can be modelled:
- Transeverse - a sharp or broad crested rectangular weir with an opening perpendicular to the direction of flow
- Sideflow - a sharp or broad crested rectangular weir with a side opening parallel to the direction of flow
- V-notch - a triangular weir
- Trapezodal - a trapezoidal weir
- Roadway - a broad crested rectangular weir normally used to model roadway crossings usually in conjunction with culvert type of conduits
Weirs can either be allowed to surcharge or not. A surcharged weir uses an equivalent orifice equation to compute the flow through it.
The equations used to determine flow through a weir are described in the SWMM5 User Guide and the SWMM Reference Manual, Volume II, Hydraulics.
