Irrigation Engineering MCQ: Duty, Canal Design, Headworks (NEC Chapter 7)

Chapter 7: Irrigation and Drainage MCQ

192 questions with answers. Practise by sub-section or take a timed test.

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Free practice by EngineeringNepal.com.np. Questions are written and checked by our team; always confirm the current exam format in the official notice.

Irrigation and Drainage MCQ: what this set covers

Irrigation questions lean on a handful of relations, such as D = 8.64B/delta, the Kennedy and Lacey equations, Bligh creep and Khosla exit gradient, plus the purpose of each headwork and canal structure. Use this set for the NEC exam and for the Lok Sewa irrigation group.

There are 192 questions in this chapter, each with the answer and a short explanation. Choose a sub-section, pick how many questions you want, and either see the answer straight away or take it as a timed test. Your mistakes are saved in your browser, so you can come back and practise only those.

Code	Sub-section	Questions here
7.1	Irrigation water demand	32
7.2	Canal design	32
7.3	Diversion headworks	32
7.4	River training works	32
7.5	Regulating and cross-drainage structures	32
7.6	Waterlogging and drainage	32

Sample questions with answers

A few questions from each sub-section are shown below. Tap a question to see the answer. Use the practice tool above for the full set.

7.1 Irrigation water demand

In irrigation engineering, the 'duty' of water is best defined as:

The total depth of water a crop needs during its base period
The area irrigated per unit discharge flowing continuously through the base period
The volume of water stored in the root zone after one irrigation
The discharge needed per hectare during the kor period only

Answer: B. Duty links area to discharge and is usually expressed in hectares per cumec; the depth of water needed is the delta.

The total depth of water required by a crop from its first watering to its last watering before harvest is called:

Duty
Base period
Kor depth
Delta

Answer: D. Delta (Δ) is the total depth of water used by the crop over its base period, usually stated in cm or m.

7.2 Canal design

Kennedy defined the critical velocity in a channel as the mean velocity at which:

The flow becomes supercritical
The channel neither silts nor scours
Bed load movement stops completely
The Froude number equals 1

Answer: B. Kennedy's critical velocity is the non-silting, non-scouring velocity for a channel carrying silty water.

Kennedy's critical velocity relation in SI units (V0 in m/s, depth D in m) is:

V0 = 0.84 D^0.64
V0 = 0.55 D^0.5
V0 = 0.64 D^0.55
V0 = 0.55 D^0.64

Answer: D. V0 = 0.55 m D^0.64 in SI units, where m is the critical velocity ratio; 0.84 is the coefficient in the foot-second form.

7.3 Diversion headworks

The main difference between a weir and a barrage is that in a barrage:

There are no gates at all
The crest is always above the pond level
The pond level is controlled mainly by gates set over a low crest
The floor is never made impervious

Answer: C. A weir raises water mainly by its raised crest (sometimes with small shutters); a barrage has a low crest and the pond is held by a series of gates that can be fully opened in floods.

The rise in the flood water level upstream of a weir caused by its construction is called:

Afflux
Freeboard
Pond level
Hydraulic jump

Answer: A. Afflux is the increase in HFL due to the obstruction; it governs the height of upstream embankments.

7.4 River training works

River training works that aim to provide enough depth of water for navigation during the dry season are called:

High water training
Mean water training
Flood training
Low water training

Answer: D. Low water training (training for depth) concentrates the low flow into a narrower channel to keep navigable depth.

High water training (training for discharge) is mainly intended to:

Improve depth for navigation
Provide enough cross-section to pass floods safely and protect land from flooding
Keep a channel suited to sediment transport
Supply water to canals

Answer: B. High water training uses works such as embankments to carry the flood discharge without spilling over the adjoining land.

7.5 Regulating and cross-drainage structures

A canal fall is required where:

The natural ground slope is steeper than the designed bed slope of the canal
The canal crosses a natural drain
The canal discharge must only be measured
The canal bed is lined

Answer: A. Without falls the canal would go into deep filling as the ground drops away; a fall lowers the bed in a step so the canal follows the ground.

A canal has a bed slope of 1 in 5000 while the ground along its 10 km length falls at 1 in 1000. Ignoring other factors, how many falls of 1 m drop each are needed?

Answer: C. Ground drop = 10000/1000 = 10 m; bed drop = 10000/5000 = 2 m; difference = 8 m, so 8 falls of 1 m.

7.6 Waterlogging and drainage

Agricultural land is said to be waterlogged when:

Its surface is ponded for a few hours after rain
The groundwater table rises so that the root zone becomes saturated and aeration is impaired
It is irrigated by flooding
Its soil moisture is at field capacity

Answer: B. Waterlogging is defined by the effect on crops: a high water table fills the pores of the root zone, cutting off air to the roots.

Which of the following is a common cause of waterlogging in canal-irrigated areas?

Lining of canals
Providing field drains
Seepage from unlined canals and over-irrigation
Lowering the full supply level of canals

Answer: C. Seepage from canals and excess field application recharge the groundwater faster than it can drain, so the water table rises.

Full mock tests

When you have covered every chapter, take a full NEC licence mock test or Lok Sewa model test. The NEC mock follows the real pattern of 80 questions and 100 marks in 2 hours.