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V-Notch Weir
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Weir flow is calculated using the following formula:
where
Q = Discharge
Cd = Discharge coefficient
b = Weir width
h = Water depth
Coefficient of Discharge - The discharge coefficient depends on the type of weir or flume chosen. A default value of .544 is given and is generally suitable for flow over a flood bank, round nose horizontal - crested weirs and rectangular flumes. Other values may be used and as with the other controls, values for discharge coefficients may be found in any good reference on hydraulic control structures.
A selection of the more common coefficients is given below.
Description | Coefficient | Reference | |
![]() | A round nose horizontal-created weir (or flow over a floodbank) | 0.544 | British Standards Instn (1969) |
A rectangular profile weir | 0.46 | Ackers, White, Perkins, Harrision (1978) British Standards Instn (1969) Crabbe (1974) | |
![]() | Rectangular thin-plate weir full width b with no side contractions | 0.59 | Ackers, White, Perkins, Harrision (1978) British Standards Instn (1965) |
![]() | Rectangular thin-plate weir with side contractions. | 0.56(b +.003) | Ackers, White, Perkins, Harrision (1978) British Standards Instn (1965) |
Crest Level - The crest level of the weir.
Width - Enter the width of the weir. If you are working to a maximum allowable discharge then a Calculator is provided to help size the control. This gives two additional parameters:
Section Pages
Workflow - What's next...?
Connect Inflows to your Stormwater Control, specify Weir or Outlets or connect to another Stormwater Control or Junction.
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V-Notch Weir
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Rainfall Manager
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