Partially Full Pipe Flow Calculator and Equations

Fluid Flow Table of Contents | Hydraulic and Pneumatic Knowledge
Fluid Power Equipment

This engineering calculator determines the Flow within a partially full pipe using 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 =

Depth of flow, y =

Pipe Radius, r =

(must have y > D/2)

Circ. Segment Height, h =

Full Pipe Manning

roughness, n_full =

Central Angle, q =

radians

Channel bottom

Cross-Sect. Area, A =

ft²

slope, S =

ft/ft

Wetted Perimeter, P =

Calculations

Hydraulic Radius, R =

n/n_full =

Discharge, Q =

cfs

Partially Full Manning

Ave. Velocity, V =

ft/sec

roughness, n =

pipe % full [(A/A_full)*100%] =

r = D/2

h = 2r - y

(hydraulic radius)

R = A/P

(Manning Equation)

Q = (1.49/n)(A)(R^2/3)(S^1/2)

V = Q/A

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

Flow In Partially Full Pipes