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Table Of Contents
Chapter 5 Working with Hydrology Commands
498
n
Use Mannings equation when you want to solve based on gravity for open
flow conditions
n
Use Hazen-Williams or Darcy-Weisbach when you want to solve for pressure
flow conditions.
Calculating Pipe Flow and Other Hydraulic
Values Using the Mannings n Equations
The Manning pipe calculators calculate flowrates and other hydraulic variables
for pipes. The Manning formulas are used to calculate velocity for both imperial
and metric units.
The different menu items provide the variation for the shape of the pipe:
Circular, Rectangular, Elliptical, or Custom (User).
Mannings Formula
Use the commands in the Manning Calculators menu to calculate flows and
other hydraulic variables for pipes. The Mannings formula used to calculate
velocity for both imperial and metric units are:
Imperial Units:
VRs
n
1486
2
3
1
2
.
Metric Units:
VRs
n
1
2
3
1
2
where:
V = Fluid velocity
n = Mannings number
R = Hydraulic radius, which is the area of flow divided by the wetted perimeter.
s = Slope