Question Bank • QB_EXP_SWCE_OCH_007 NAT • 1 Mark

Section 4: Soil and Water Conservation Engineering

Open Channel Hydraulics & Manning Equation

Subtopic: Most efficient hydraulic cross section

Question Statement:

A trapezoidal channel is designed for maximum hydraulic efficiency with a normal flow depth of $y = 1.40\text{ m}$. The hydraulic radius of this most economical section is ________ $\text{m}$ (round off to two decimal places).

Answer Key:

0.70

Step-by-Step Solution & Explanation

For any most economical / hydraulically efficient trapezoidal channel section, the hydraulic radius $R$ is half of the depth of flow: $R = \frac{y}{2}$ Given $y = 1.40\text{ m}$: $R = \frac{1.40}{2} = 0.70\text{ m}$
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