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GATE 2019 CE (CE1) – Question 38

Hydraulics · Channel hydraulics: specific energy, critical flow, uniform flow, hydraulic jump · 2 marks · Multiple choice

A rectangular open channel is 5 m wide with bed slope 0.001. Uniform flow has depth 2 m and speed 2 m/s. Find Manning’s roughness coefficient.

  1. 0.002
  2. 0.017
  3. 0.033
  4. 0.050

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Correct answer: (B) 0.017

Explanation

Area is $A=5(2)=10$ m² and wetted perimeter $P=5+2(2)=9$ m. Hydraulic radius is R = 10/9 m. Manning’s equation $V=R^{2/3}\sqrt S/n$ gives $$n=\frac{(10/9)^{2/3}\sqrt{0.001}}2=0.01696.$$ Answer **0.017, B**.