Most Economical Trapezoidal Section

Fig shows the cross-section of a trapezoidal channel.

Let $\quad b=$ Base width of the channel,

$y=$ Depth of flow, and

$\theta=$ Angle made by the sides with horizontal.

Side slope $=1$ vertical to $n$ horizontal. Area of flow, $A=\left(\frac{A B+C D}{2}\right) \times y=\frac{b+(b+2 n y)}{2} …