Question

The hydraulic radius of the given rectangular open drainage section (in mm, rounded off to two decimals) is \(\underline{\hspace{2cm}}\).

Hint:

For rectangular channels: $R = \frac{bh}{b + 2h}$. The top free surface is not included in the wetted perimeter.

Answer 1

Correct Answer: 135 - 138

Water depth: \[ h = 250\ \text{mm}. \] Channel width: \[ b = 600\ \text{mm}. \] Hydraulic radius: \[ R = \frac{A}{P}, \] where \(A\) = flow area, \(P\) = wetted perimeter. \[ A = b \times h = 600 \times 250 = 150000\ \text{mm}^2. \] Since this is an open channel, the top surface is free: \[ P = b + 2h = 600 + 2(250) = 1100\ \text{mm}. \] Thus, \[ R = \frac{150000}{1100} = 136.36\ \text{mm}. \] Rounded to two decimals: \[ 136.36\ \text{mm}. \] Final Answer: \[ 136.36\ \text{mm} \]