# Irrigation Engineering Questions and Answers – Channel Cross-sections

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This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Channel Cross-sections”.

1. What types of channel sections are usually adopted?
a) Triangular and Circular channel
b) Triangular and Trapezoidal channel
c) Rectangular and Trapezoidal channel
d) Rectangular and Triangular channel

Explanation: Generally, Triangular and Trapezoidal channel sections are adopted. For smaller discharges, the Triangular channel section is adopted and trapezoidal channel for larger discharges.

2. What is the maximum permissible velocity in Cement concrete lining (Unreinforced) as per Indian Standards?
a) 2 to 2.5 m/sec
b) 1.5 to 2 m/sec
c) 1.2 to 1.8 m/sec
d) 1.5 to 2.5 m/sec

Explanation: The maximum permissible velocity for unreinforced cement concrete lining is 2.0 to 2.5 m/sec. For Boulder lining, the maximum permissible velocity is 1.5 m/sec.

3. What is the minimum value of free-board for Main and Branch Lined canals if the discharge is more than 10 cumecs as per specified by BIS code?
a) 0.60
b) 0.50
c) 0.75
d) 0.30

Explanation: In main and branch canals for discharge more than 10 cumecs, the minimum value of freeboard is 0.75 m. For branch canals and distributaries in which discharge is less than 10 cumecs the value is 0.60 m.
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4. The distance measured above the F.S.L and to the top of the lining is known as free-board.
a) True
b) False

Explanation: The vertical distance between the full supply level (F.S.L) and the top of the bank is called freeboard. It depends on the size of the canal, location of the canal and water level fluctuations.

5. What is the minimum value of inspection bank width recommended by Indian Standards if the discharge is more than 30 cumecs?
a) 8.0
b) 5.0
c) 6.0
d) 7.0

Explanation: The minimum value of the top width of the bank depends on the value of discharge. For discharge greater than 30 cumecs, the minimum value of the top width of the inspection bank is 8.0 m and for Non-inspection bank is 5.0 m.

6. When the concrete lining is not reinforced in a channel, velocities up to 2.5 m/sec are permitted.
a) True
b) False

Explanation: Higher velocities can be safely used in lined canals. The maximum permissible velocities for concrete linings when the lining is not reinforced are up to 2.5 m/sec. The lining can be reinforced if still higher velocities are desired.

7. Calculate hydraulic mean depth for concrete-lined channel to carry a discharge of 350 cumecs at a slope of 1 in 5000. The value of manning’s constant for the lining is 0.015. The side slopes of a channel may be taken as 1.5:1. Assume limiting velocity in the channel as 2m/sec.
a) 2.20 m
b) 2.40 m
c) 2.60 m
d) 2.80 m

Explanation: Using Manning’s equation: V = 1/n.R2/3.S1/2
2 = 1/0.015 x R2/3 x 1/50001/2
R = 2.80 m.

8. Calculate the central depth of a triangular channel section to carry a discharge of 15 cumecs. Consider the available slope as 1 in 9000. Assume the side slopes of the channel be 1.25:1 and manning’s constant is 0.015 for good brick work in lining.
a) 2.94 m
b) 3.14 m
c) 2.25 m
d) 2.77 m

Explanation: Given data- tanQ = 1/1.25; Q = 0.675 radian
A = y2 (Q + cotQ) = 1.925y2 and R = y/2
Q = 1/n.A.R2/3.S1/2
15 = 1/0.015 x 1.925y2 x (0.5y)2/3x 1/90001/2
y = 2.94 m.

Sanfoundry Global Education & Learning Series – Irrigation Engineering.