The broad crested weir with width B and the height of the liquid surface upstream of weir as H is one for which
- A1.5H ≤ B ≤ H
- B2.5H ≤ B ≤ 10HCorrect
- C2.5H ≤ B ≤ 20H
- Dnone of these
Solution
Concept
Broad-Crested Weir
Step-by-step solution
1. Recall the standard geometric criteria for a broad-crested weir, which requires the crest length B to be related to the upstream head H as 2.5H ≤ B ≤ 10H. 2. Compare the given condition with the options to select Option B.
Explanation
A weir is classified as a broad-crested weir when its width or crest length B is significantly larger than the upstream water depth H. For standard design classifications, the width B must be between 2.5 and 10 times the head H (2.5H ≤ B ≤ 10H) to ensure the water surface stabilizes and flows horizontally over the crest.
Shortcut
To remember a broad-crested weir: think 2.5 to 10. Broad means wide (B is much bigger than H), so width B goes from 2.5 times H up to 10 times H (2.5H ≤ B ≤ 10H).
Common mistake
Students often confuse the limits for broad-crested weir conditions by misremembering the upper bound (confusing 10H with 20H, leading them to select Option C) or confusing the criteria with those for sharp-crested or narrow-crested weirs (where B < 2.5H).
Correct answer: B) 2.5H ≤ B ≤ 10H