Question

The Froude number of flow in a rectangular channel is 0.8. If the depth of flow is 1.5 m, the critical depth is

• A. 1.80 m
• B. 1.36 m
• C. 1.56 m
• D. 1.29 m

Answer 1

The correct option is D 1.29 m

Froude Number for a rectangular channel is give by
$F=\frac{V}{\sqrt{gy}}$

$\Rightarrow V=0.8\times \sqrt{9.81\times 1.5}$

$=3.07m/s$

$\therefore \text{Discharge per unit width of rectangualr channel is given by}$
$q=Vy=3.07\times 1.5=4.6m^3/s/m$

$\therefore Criticaldepth,$
$y_c={\left(\frac{q^2}{g}\right)}^{1/3}={\left(\frac{{4.6}^2}{9.81}\right)}^{1/3}=1.29m$