The critical depth (yc) for a rectangular channel 2.5 m wide having a specific energy of 1.5 m will be
- A3 m
- B2.5 m
- C2 m
- D1 mCorrect
Solution
Concept
Critical depth from minimum specific energy (rectangular channel)
Formula
Emin = 1.5 yc
Step-by-step solution
1. For a rectangular channel, specific energy at critical depth Emin = 3 yc / 2. 2. yc = 2E / 3 = 2 × 1.5 / 3 = 1 m.
Explanation
At critical flow the velocity head is half the depth, so E = yc + yc/2 = 1.5 yc. The width of the channel is not needed here.
Shortcut
Rectangular: yc = (2/3) E.
Common mistake
Using the channel width (2.5 m) in the calculation.
Correct answer: D) 1 m