Question

In a wide rectangle channel, the normal depth is increased by 20%. This would mean an increase in the discharge of the channel nearly by

• A. 20%
• B. 36%
• C. 56%
• D. 26%

Answer 1

The correct option is B 36%

For very wide rectangular channels,
$R=y$

As per Chezy's equation
$Q\propto y_0^{3/2}\frac{\delta Q}{Q}\times 100=\frac{3}{2}\times 20\%=30\%$

As per Manning's equation
$Q\propto y_0^{5/3}\frac{\delta Q}{Q}\times 100=\frac{5}{3}\times 20\%=33.33\%$

The closest answer is 36%.