Question

The hydraulic radius for a most economical rectangular open channel with a base width of 5 m is

• A. 1.25 m
• B. 2.5 m
• C. 3.75 m
• D. 5.0 m

Hint:

For a most economical rectangular channel, remember these two simple rules:
1. The depth is half the width: $y = B/2$.
2. The hydraulic radius is half the depth: $R = y/2$.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
Most economical rectangular channel, base 5m. Find hydraulic radius.

Step 2: Key Condition (Alternate):
For best rectangular section: y = B/2. Then R = y/2 = B/4.

Step 3: Detailed Explanation:
y=5/2=2.5m. A=5×2.5=12.5m². P=5+2(2.5)=10m. R=A/P=12.5/10=1.25m. Also R=B/4=5/4=1.25m. Half perimeter equals depth condition.

Step 4: Final Answer:
1.25 m.