In case of design of a weir or a barrage by providing a higher afflux, the waterway and, therefore, the length of the weir can be reduced, but it will result in
- Aincreased cost of training worksCorrect
- Breduced risk of failure by outflanking
- Creduced scour
- Dreduced discharge intensity
Solution
Concept
Effects of a higher afflux
Step-by-step solution
1. A higher afflux shortens the weir, which saves cost. 2. But the discharge intensity and scour increase, the risk of outflanking increases, and heavier guide banks and marginal bunds are needed, raising the cost of training works.
Explanation
The higher the afflux, the larger the upstream flood levels, which must be contained by taller and longer marginal bunds and guide banks.
Why the other options are wrong
Options (b), (c) and (d) are the opposite of the actual effects.
Shortcut
More afflux: shorter weir, but more scour, intensity and training works.
Common mistake
Thinking a shorter weir reduces all costs.
Correct answer: A) increased cost of training works