2.0

Calculating Weir Values
529
NOTE
The weir coefficients that are provided with Autodesk Civil Design are
samples only. You must determine the weir coefficient based on the
geometry of the weir you are designing.
7 In the Height box, type a height for the weir.
The computed values for the weir display at the bottom left of the dialog box.
The box at the top right area of the dialog box displays a graphic of the
currently defined weir. This information is for display only and cannot be
edited.
NOTE
If the data you entered has an error, the weir graphic image does not
display. Check for an error message at the bottom of the dialog box.
8 Click OK to exit the dialog box.
Triangular Weir Formula
The following formula is used to calculate the design flow rate for triangular
weirs:
Qc g H
8
15 2
25
2tan()
.
T
where:
Q = Design flow rate
c = Weir coefficient
g = Acceleration due to gravity (32.174 ft/s
2
or 9.807 m/s
2
)
T = Notch angle of weir
H = Weir head
Specifying a Triangular Weir Coefficient
The Triangular Weir Coefficient dialog box describes weir structures and the
associated velocity coefficients.
To select a coefficient from the dialog box
1 In the Triangular Weir Calculator dialog box, click the Select button next to the
Coefficient text box to display the Triangular Weir Coefficient dialog box.
2 Select a coefficient by placing your cursor in the appropriate column and
clicking anywhere in the text box that contains the value you want to use.
Use the navigation buttons on the right side of the dialog box to move through
the list of descriptions and coefficients.
You can add a new coefficient:
n
Click Insert to add a new row above the row you currently have selected.
n
To add data, select an empty text box and type the new description and
coefficient.
3 Click OK to return to the Triangular Weir Calculator dialog box.