The lining like cement concrete, pre-cast cement concrete, etc. gives a smooth surface to the canal. Smoothness of the canal bed and the sides _______ the discharge of the canal and the duty of water.
- AenhancesCorrect
- Bdoesn't affect
- Creduces
- Dneither reduces nor enhances
Solution
Concept
A smooth lining lowers Manning's n, so velocity and discharge go up. Lower seepage loss raises the duty.
Formula
V = (1/n) R2/3 S1/2; Q = A × V
Step-by-step solution
1. A lined canal has a smooth surface, so the rugosity coefficient n becomes smaller. 2. From Manning's formula V = (1/n) R2/3 S1/2, a smaller n gives a higher velocity. 3. Higher velocity gives higher discharge, Q = A × V. 4. Lining also cuts seepage and other losses, so more water reaches the fields and the duty increases. 5. So smoothness enhances both discharge and duty.
Explanation
A smooth lining reduces friction, so water flows faster and the canal carries more discharge. Lining also reduces seepage loss, so the same water irrigates more area, which means a higher duty. Both are increased.
Why the other options are wrong
B and D: Smoothness clearly changes the friction coefficient, so it does affect the flow. C: Less friction and less loss increase discharge and duty. They do not reduce them.
Shortcut
Smooth surface → less n → more V → more Q; less loss → more duty.
Common mistake
Confusing duty with delta, or thinking smoothness only affects velocity and not duty.
Correct answer: A) enhances