217/33310–15FE Reference Handbook 10.4 · Civil · Open Channel

Handbook formula

Chézy Equation

Chézy is the ancestor of Manning: V=C√(RS). In SI, C=R^{1/6}/n so V=(1/n) R^{2/3} S^{1/2}. USCS uses 1.486/n. Uniform flow: S=So of the bed.

Chézy coefficient
Hydraulic radius A/P
Energy slope

Step-by-step solved example

n=0.020, R=1.0 m, S=0.001. V by Manning/Chézy SI?

yb
Uniform channel: V = C √(RS) = Manning.
  1. 1. Manning

    V=(1/0.02)×1^{2/3}×√0.001=50×0.03162=1.58 m/s.

  2. 2. C

    C=R^{1/6}/n=1/0.02=50, V=50√0.001=1.58 m/s.

Answer: V = 1.58 m/s

10 practice questions

0/10 correct

1.Manning SI V=

2.USCS 1.486 exists because

3.R for a full circle is

4.Rougher n →

5.Uniform flow means

6.C=40, R=2 m, S=0.0004: V=

7.Most efficient rectangle has

8.n for clean earth channel is nearest

9.S must be

10.Darcy-Weisbach in a wide channel can be matched to Manning by