This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Water Requirements of Crops – Irrigation Efficiencies”.

1. Which efficiency is also called on-farm efficiency?

a) Water conveyance efficiency

b) Water application efficiency

c) Water storage efficiency

d) Water use efficiency

View Answer

Explanation: The water application efficiency is the ratio of water stored in the root zone to the water actually delivered to the field. It takes into consideration the water lost in the farm hence, it is also known as on-farm efficiency.

2. What is water conveyance efficiency?

a) The ratio of the quantity of water delivered to the field and quantity of water pumped into the canal

b) The ratio of water stored in the root zone and the water delivered to the field

c) The ratio of water used beneficially and the water delivered to the field

d) The ratio of water stored in the root zone and the water needed before irrigation

View Answer

Explanation: It is the ratio of water delivered into the fields to the water entering into the channel. This efficiency accounts for the conveyance or transit losses.

3. The quantity of water beneficially used is the sum of the water used by the crops and the water used for leaching.

a) True

b) False

View Answer

Explanation: The beneficially used water accounts for the water required for leaching and by the crop as well. This is required in calculating water use efficiency.

4. The mean depth of water is 1.5 cm and the mean deviation from the mean is 0.1 cm. Determine its distribution efficiency.

a) 15%

b) 85%

c) 66.66%

d) 93%

View Answer

Explanation: The formula for distribution efficiency is:

N

_{d}= (1- d/D) x 100; where d = mean deviation and D = mean depth of water

Given, d=0.1 cm and D = 1.5 cm

Hence, N

_{d}= 93%.

5. The presence of excess salts in the soil requires _____________

a) high water storage efficiency

b) low water storage efficiency

c) high water application efficiency

d) high water use efficiency

View Answer

Explanation: Leaching is the supply of additional water to wash away the salts in a saline prone area. The presence of excess salts in water requires high water storage efficiency in order to keep the salts washed out of the soil.

6. Which of the following statement is wrong about consumptive use efficiency?

a) It is the ratio of normal consumptive use of water to the net amount of water depleted from the root zone

b) It accounts for the loss of water by deep percolation

c) Evaporation losses are considered

d) The losses due to percolation and evaporation are not considered

View Answer

Explanation: It is the ratio of normal consumptive use of water to the net amount of water depleted from the root zone. It accounts for the loss of water by deep percolation and evaporation following irrigation.

7. The quantity of water that is pumped into a farm distribution system is 2 cumec. 1.6 cumec is delivered to a turn-out, 1km from the well. Compute the conveyance efficiency.

a) 80%

b) 20%

c) 50%

d) 60%

View Answer

Explanation: By definition, Conveyance efficiency N

_{c}= (output/input) x 100

Given, Output = 1.6 cumec and Input = 2 cumec

So, N

_{c}= 80%.

8. If the water losses are more, the output and the efficiency is more.

a) True

b) False

View Answer

Explanation: Efficiency is inversely proportional to the losses. If losses are more, the output is less and therefore, efficiency is less.

9. Determine the distribution efficiency, if the depths of water in the field are 1.1 cm and 1.8 cm.

a) 80%

b) 90%

c) 85%

d) 75%

View Answer

Explanation: Mean depth (D) = (1.1 + 1.80) / 2 = 1.45

Deviation from mean depth (d) = 1.80 – 1.45 = 1.1 – 1.45 = 0.35 (neglecting negative sign)

N

_{d}= (1 – d/D) x 100 = 75%.

10. Uniformity coefficient is also known as ____________

a) water conveyance efficiency

b) consumptive use efficiency

c) water distribution efficiency

d) water storage efficiency

View Answer

Explanation: Water distribution efficiency is also known as the uniformity coefficient. It is the measure of how uniformly water is applied to the area being irrigated. The effectiveness of irrigation is measured by its uniformity coefficient.

11. The water distribution efficiency is 1.0 if _____________

a) the deviation from the mean depth is 1

b) the deviation from the mean depth is 0

c) the deviation from the mean depth is less than 1

d) the deviation from the mean depth is greater than 1

View Answer

Explanation: It represents the extent to which the water has penetrated to a uniform depth throughout the area. If the water penetrates uniformly throughout the field, the deviation from the mean depth is zero and hence, water distribution efficiency is 1.0.

12. What is the correct formula for uniformity coefficient efficiency?

a) N_{d} = 1 – d/D

b) N_{d} = 1 + d/D

c) N_{d} = 1 – D/d

d) N_{d} = 1 + D/d

View Answer

Explanation: The correct representation of the formula is N

_{d}= 1-d/D.

Where N

_{d}= water distribution efficiency, d = deviation from the mean depth and D = mean depth.

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