Question

The hydraulic mean depth for a circular pipe of diameter 100 mm when running full is:
1. 50 mm
2. 25 mm
3. 100 mm
4. 75 mm

Answer 1

Correct Answer - Option 2 : 25 mm

Concept:

The hydraulic mean depth or also called hydraulic radius is defined as:

\(R = \frac{{\rm{Wetted}\;\rm{Area}}}{{\rm{Wetted}\;\rm{perimeter}}}=\frac{A}{P}\)

Wetted area = \(A = \frac{\pi }{4}{d^2} \)  

Wetted perimeter P = πd

Hydraulic mean deppth = \(R = \frac{A}{P} = \frac{{\pi {d^2}}}{{4\pi d}} = \frac{d}{4}\)

Calculation

Given:

d = 100 mm.

For circular pipe:

\(R = \frac{A}{P} =\frac{d}{4}\)

\(R =\frac{100}{4}=25\;mm\)