Practice Question: Pipe Flow - Open channel

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Solution

Answer: C) 20 in diameter pipe.

Refer to PE Civil Reference Handbook Section 6.4.5.3

Refer to Minimum Diameter of Circular Pipe Under Full Flow Conditions equation

\[D=[ \frac{ C_{0}Qn }{ \sqrt{S} } ]^{3/8}\\\]

where:

\(D = Pipe \ Diameter\)

\(C_{0}=\text{2.16 for USCS units}\\\)

\(Q=Flow = 20 ft^3/sec\ (as\ given)\\\)

\(n = Manning \ Roughness\ Coefficient\)

Refer to PE Civil Reference Handbook Section 6.4.5 for PVC pipe:
\[n = 0.009 \ to \ 0.011 \ \to use \ 0.01\]
\[D= [{\frac{2.16\times20\times0.01}{ \sqrt{1.5/100} }}]^{3/8}=1.604\ ft = 1.604\times12=19.25\ in\]

\[Use \ D = 20 \ in\]
 

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