# Irrigation Engineering Questions and Answers – Types of Rigid Modules and Cattle Crossings

This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Types of Rigid Modules and Cattle Crossings”.

1. Which of the following is not a type of rigid module?
a) Gibb’s module
b) Khanna’s rigid module
c) Foote module
d) Crump’s proportional module

Explanation: Crump’s Adjustable Proportional Module is also called Adjustable Orifice Semi-Module. In this type, a cast-iron roof block is provided at the entrance end which is screwed to the masonry entrance by the bolts fixed in the masonry. This block is given the lemniscate curve at the lower end on the entrance side.

2. The discharge range of Gibb’s module varies from ____________
a) 0.03 to 0.45 cumec
b) 0.01 to 0.03 cumec
c) 0.45 to 0.55 cumec
d) 0.55 to 0.75 cumec

Explanation: The discharge range of Gibb’s rigid module varies from 1 to 16 cusecs or 0.03 to 0.45 cumecs. It is often economical to construct it in R.C.C for lower values of discharge i.e. 1 to 3 cusecs. For discharge value greater than 3 cusecs it can be constructed in brick masonry.

3. Choose the incorrect statement.
i. Bed bars are constructed in canals at the toe of the canal lining to prevent slippage of the lining.
ii. Cattle crossings also provide safety to cattle that are swept away by currents besides their usual function of helping the cattle to cross the canal.
iii. A canal escape helps in supplying irrigation water to the downstream watercourses.
a) i and ii
b) i only
c) ii only
d) i, ii and iii

Explanation: Canal escape helps in removing surplus water from an irrigation canal into a natural drain. The cattle crossing are not of much use on canals carrying considerable water depths and for the ones who don’t know swimming. Bed bars help in desilting the canal section during its maintenance and indicate the correct alignment and bed levels of the canal.

4. The outlet discharge is maintained constant and it is not at all dependent on the water levels in the parent and the field channels in _________________
a) non-modular outlet
b) modular outlet
c) semi-modular outlet
d) proportional outlet

Explanation: A non-modular outlet is the one in which discharge is directly dependent on the working head. In the semi-modular outlet, the discharge is directly dependent on the water level in the parent channel. A proportional module is a type of semi-module.

5. Gibb’s module is a type of outlet which ensures constant discharge even if the water levels in the supply channel and watercourse fluctuate.
a) True
b) False

Explanation: An upward rotational flow is imparted if the head causing flow increases at the outer wall restricting against the baffles. The water spins round in the compartment between two successive baffles and finally drops on the incoming water stream of water. This dissipates excess energy and helps in maintaining constant discharge for a wide variation in the head.
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6. A baffle wall is a sort of weir constructed at the end of the cistern to:
i. To prevent any excess amount of discharge likely to pass through the module
ii. The baffle plates are inserted in the eddy chamber sloping from the outer wall towards the inner wall
iii. Head up the water to its upstream to such a height that hydraulic jump is formed
Which of the following statement is correct?
a) i only
b) i and iii
c) i and ii
d) i, ii and iii

Explanation: The baffle plates are inserted in the eddy chamber at required height sloping towards the outer wall which helps in preventing any excess discharge to pass through the module. It dissipates the energy by creating an upward rotational flow spinning in between two successive baffles. The number of baffles coming into action depends on the variation in the head.

7. In cattle crossings, the exact distance to be kept between the two ramps on the same side should theoretically be ________
a) 2 BV/U
b) 2 BVU
c) 2 BU
d) 2 BU/ V

Explanation: Theoretically, the exact distance to be kept between the two ramps on the same side should be 2 BV / U where, B = width of the channel, V = average flow velocity of water in the channel and U = the speed with which cattle swim. The distance is kept a little longer than shorter even if the cattle reach the opposite side too nearer they will get at the ramp.

8. For canals carrying smaller water depths, a ramp is provided for the entry and exit as cattle crossings.
a) True
b) False

Explanation: A ramp is provided for the entry and another ramp opposite to it is provided for the exit for smaller water depths or the order 0.75 m or so. The cattle move from one bank on the ramp comes to the bottom of the canal within the water further goes across by walking over the exit ramp.

9. Bed bars are used _______________
i. To serve as permanent reference marks
ii. To correct alignment and theoretical bed levels of the canal
iii. Helps in desilting the canal section during its maintenance
Which of the following function of bed bars is/ are correct?
a) i and ii
b) i and iii
c) ii and iii
d) i, ii and iii

Explanation: These are masonry or concrete toe wall-like structure constructed at suitable intervals, the R.L of which is taken by double levelling accurately. The depth of the block and its cross-section is kept substantial enough so that it is not disturbed by the flowing water and is safe against scoring. The bed bars helps in keeping a check on the behaviour of the canal w.r.t silting and scouring tendencies.

10. Gibb’s module holds good for the standard design in which _________
a) Outlet index m = 2 and H/D = 1/7
b) Outlet index m = 1/3 and H/D = 1/7
c) Outlet index m = 5/3 and H/D = 1/7
d) Outlet index m = 2/3 and H/D = 1/7

Explanation: It is a modular outlet with costly and complicated arrangements. It is based on the free vortex flow and holds good for the standard design in which outlet index = 2 and H/D = 1/7 where H is the head at the outer circumference and D is the difference of the level measured from the minimum water level in the parent channel to the floor of eddy chamber.

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