This question was previously asked in

UPPSC AE Civil 2013 Official Paper I

Sub-critical

- Super-critical
- Critical
- Not possible

Option 2 : Super-critical

__Concept:__

Any flow in open channel is classified on the basis of Froude’s number.

Froude’s number > 1 ⇒ super critical flow

Froude’s number = 1 ⇒ critical flow

Froude’s number < 1 ⇒ subcritical flow

**For rectangular channel**

Froude’s number \(=\frac{{\rm{V}}}{{\sqrt {\frac{{\rm{g}}}{{\rm{A}}}{\rm{/T}}} }} = \frac{{\rm{V}}}{{\sqrt {{\rm{g}} \times \left( {\frac{{{\rm{By}}}}{{\rm{B}}}} \right)} }} = \frac{{\rm{V}}}{{\sqrt {{\rm{gy}}} }}\)

__Calculation:__

**Given: **y = 1.6 m, and E = 2.7 m

We know, specific energy

\({\rm{E}} = {\rm{y}} + \frac{{{{\rm{v}}^2}}}{{2{\rm{g}}}}\)

\(2.7 = 1.6 + \frac{{{{\rm{v}}^2}}}{{2 \times 9.81}}\)

⇒ v = 4.65 m

Froude’s number \( = \frac{{4.65}}{{\sqrt {9.81 \times 1.6} }}\;\)= 1.17

∵ Froude’s number > 1

⇒ Super critical flow.

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