Head or flow over a weir can be determined using the **Weir
Calculations** dialog. If flow is to be calculated then head over
the weir must be entered as an input. If head is to be computed then a
flow rate must be entered as input. The weir calculator uses the standard
equation for computing flow over a weir:

where:

Q - discharge flow (volume/time)

Cw - weir coefficient

L - width of weir (distance, ft or m)

h - head (distance, ft or m)

If a hydrograph has been computed using one of the supported hydrologic model, the peak flow for the hydrograph will be used as the default flow value if the hydrograph is selected prior to opening the dialog.

Selection of one of the predefined weir types automatically assigns the appropriate weir coefficient. A user-defined weir coefficient can also be entered, or the default value for one of the weir types listed modified. Weir calculations can also be used in combination with the detention basin calculator to define any outlet works of the basin/reservoir.

**Related Topics:**

Hydrologic/Hydraulic Calculators