Which of the following statements are correct about a weir? 1.It is a diversion structure. 2.It raises water level in river. 3.It stores water permanently. 4.It may include shutters or gates.
- A1, 2 and 4 onlyCorrect
- B2 and 3 only
- C1 and 4 only
- DAll of the above
Solution
Concept
A weir acts as a barrier across a river to raise the water level and divert it into canals, featuring optional crest gates, but it does not function as a storage reservoir.
Step-by-step solution
1. A weir is primarily a diversion headwork structure built across rivers. (True) 2. The primary purpose of a weir is to raise the water level on its upstream side so water can enter the canal. (True) 3. Weirs are meant for diversion, not for long-term storage or creation of large reservoirs (which is the function of dams). (False) 4. Many modern weirs (called barrages or concrete weirs with shutters) include adjustable shutters or crest gates to regulate pond level. (True) 5. Conclude that statements 1, 2, and 4 are correct.
Explanation
A weir is a diversion structure constructed across a river to raise the water level and divert water into the off-taking canal. It may include shutters or gates on its crest to control pond level. However, unlike a dam, a weir does not store water permanently for conservation purposes; its live storage is negligible.
Shortcut
Remember the fundamental difference between a weir/barrage and a dam: weirs divert water with little to no permanent storage, whereas dams store water.
Common mistake
Confusing a weir with a dam and assuming it provides permanent, large-scale water storage.
Correct answer: A) 1, 2 and 4 only