Question

The Froude number of flow in a rectangular channel of width 2 m is 0.7. If the depth of flow is 1.2 m, the critical depth of flow is ____ m.

• A. 0.9

Answer 1

The correct option is A 0.9
Froude number,$F_r=\frac{V}{\sqrt{gy}}$

$0.7=\frac{V}{\sqrt{9.81\times 1.2}}$

$v=2.4\frac{m}{sec}$

Discharge per unit width, q=Vy

$=2.4\times 1.2$

$=2.88\frac{cumecs}{m}$

Critical depth of flow
$y_c=(\frac{q^2}{g}{)}^{\frac{1}{3}}$

$=(\frac{{2.88}^2}{9.81}{)}^{\frac{1}{3}}$

=0.95 m