Partially FULL Pipe Flow Calculator and Equations

Hydraulic and Pneumatic Knowledge
Fluid Power Equipment

This engineering calculator determines the Flow within a partially full pipe (&e1/2 fullusing the Manning equation. This calculator can also be used for uniform flow in a pipe, but the Manning roughness coefficient needs to be considered to be variable, dependent upon the depth of flow.

Partially Full Pipe Flow Calculations  -  U.S. Units
II. Calculation of Discharge, Q, and average velocity, V
for pipes more than half full
Instructions:  Enter values in blue boxes.  Calculations in yellow
Inputs         Calculations

Pipe Diameter, D = in   Pipe Diameter, D = ft
Depth of flow, y = in   Pipe Radius, r = ft
(must have y > D/2)
Circ. Segment Height, h = ft
Full Pipe Manning
roughness, nfull =     Central Angle, q = radians
Channel bottom       Cross-Sect. Area, A = ft2
slope, S = ft/ft
Wetted Perimeter, P = ft
Calculations         Hydraulic Radius, R = ft
n/nfull  =       Discharge, Q = cfs
Partially Full Manning         Ave. Velocity, V = ft/sec
roughness, n =
pipe % full [(A/Afull)*100%] =

r = D/2
h = 2r - y
R = A/P
(Manning Equation)
Q = (1.49/n)(A)(R2/3)(S1/2)
V = Q/A  P

Equation used for n/nfull:  n/nfull = 1.25 - (y/D -0.5)*0.5    (for 0.5  <  y/D  <  1)

Flow In Partially Full Pipes