Manning’s EquationCE EN 270 – BRIGHAM YOUNG UNIVERSITY
Open Channel Flow
Open Channel Flow
Manning’s Equation
2/1o
3/2h SAR
nuQ
Q = Flow rateu = 1.0 (metric) or 1.49 (English)n = Manning friction factor
concrete0.020earth 0.022streams 0.045pipe 0.013
A = Cross-sectional area of flowRh = Hydraulic radius = A/Pw
Pw = Wetted PerimeterSo = Slope of channel bottom
Trapezoidal Channel
b
yPw z
1A
zyybA 22
w z1y2bP
Rectangular Channel
b
yPw A
ybA
y2bPw
Circular Channel
2Dsin81A
D21Pw
ryrsin2 1
rrysin2 1
If y<r:
If y≥r:
b
q rh
yD
Pw