Solution :

Given :

Discharge, $ Q=400$ lps $=0.4 \mathrm{~m}^{3} / \mathrm{s}$

Bed slope, $ i=\frac{1}{2000}$

Chezy's constant, $C=50$

(i) Hydraulic mean depth,

$m=\frac{d}{2}$

(ii) Area of flow,(A)

$\quad A=b \times d=2 d \times d=2 d^{2}$

{iii) Discharge,(Q)

$$ Q=A C \sqrt{m i} $$

$$\begin {aligned} 0.4 &=2 d^{2} \times …