2.0

Calculating Pipe Flow and Other Hydraulic Values Using the Mannings n Equations
505
Calculating the Flow for Custom Pipes Using
Mannings Equations
To calculate the flow for custom pipes by using Mannings n equations
1 From the Hydrology menu, choose Pipes ä Manning User to display the
Manning dialog box.
2 From the Solve For list, select the value you want to calculate. The available
values are: Flowrate, Slope, Mannings number, Wetted Area, and Wetted
Perimeter.
NOTE
Do not enter the value for which you are solving. For example, if you select
Flowrate in this step, leave the Flowrate text box at 0. After you enter the
other values, the program solves for the Flowrate.
3 In the Flowrate box, type a flow rate for the pipe (unless you are solving for the
flowrate).
4 In the Slope box, type a slope for the pipe (unless you are solving for the slope).
You can also click Select to specify the slope by selecting points on the drawing.
5 In the Mannings n box, type a roughness value for the pipe (unless you are
solving for the Mannings n).
You can also click Select to select a coefficient from the Pipe - Mannings n
dialog box.
6 In the Area box, type an area for the pipe.
7 In the Wetted Area box, type the flow (wetted) area value (unless you are
solving for the wetted area).
8 In the Wetted Perimeter box, type the wetted perimeter of the pipe (unless you
are solving for the wetted perimeter).
Based on the values that you entered, information about the pipe is calculated
and displayed at the bottom left of the dialog box. This information is for
display only and cannot be edited.
The Percent Full value for user-defined pipes is calculated using the following
formula:
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NOTE
If the data you entered has an error, the pipe graphic image does not
display. Check for an error message at the bottom of the dialog box.
9 Click OK to exit the dialog box.