Question

A triangular irrigation lined canal carries a discharge of 25 $m^3/s$ $\text{at bed slope}=\frac{1}{6000}$. If the side slope of the canal are 1: 1 and Manning's coefficient is 0.018, the central depth of flow is equal to

• A. 2.98 m
• B. 3.62 m
• C. 4.91 m
• D. 5.61 m

Answer 1

The correct option is C 4.91 m

By Manning's equation,
$Q=\frac{1}{n}{R}^{2/3}{S}^{1/2}$ A

$\Rightarrow 25=\frac{1}{0.018}\times {\left(\frac{Y}{2\sqrt{2}}\right)}^{2/3}\times {\left(\frac{1}{6000}\right)}^{1/2}\times (y{)}^2$

$\Rightarrow 25=\frac{1}{0.018}\times (y{)}^{8/3}\times \frac{1}{154.92}$

$\Rightarrow y=4.91m$