Engineering Hydrology Questions and Answers – Evapotranspiration

This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Evapotranspiration”.

1. What does the term consumptive use signify?
a) Evaporation
b) Transpiration
c) Evapotranspiration
d) Either evaporation or transpiration
View Answer

Answer: c
Explanation: The transpiration process can be considered as occurring simultaneously with evaporation of soil moisture from the surrounding land. This is collectively known as evapotranspiration or consumptive use.

2. Which of the following most closely represents the evapotranspiration distribution on a plot with full grown plants?
a) 0% evaporation, 100% transpiration
b) 10% evaporation, 90% transpiration
c) 50% evaporation, 50% transpiration
d) 100% evaporation, 0% transpiration
View Answer

Answer: b
Explanation: The evapotranspiration depends on the amount of soil exposed to radiation and the growth of plants. At the time of sowing, almost all of the ET occurs due to evaporation and as the plant grows, the fraction of evaporation decreases, and transpiration constitutes above 90% of ET.

3. Which of the following is defined as the maximum amount a water that can be retained by the soil against gravity?
a) Potential evapotranspiration
b) Actual evapotranspiration
c) Field capacity
d) Permanent wilting point
View Answer

Answer: c
Explanation: The evapotranspiration (PET and AET) depend on the amount of soil moisture available to the plants. This is represented by quantities known as field capacity, permanent wilting point and available moisture.
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4. What is the minimum value of PET to AET ratio?
a) -1
b) 0
c) 0.5
d) 1
View Answer

Answer: d
Explanation: The actual ET is always lesser than or equal to the potential ET depending on the in situ soil moisture levels. At field capacity, the PET to AET ratio will have a minimum value of 1 and will tend to infinity as the water level drops to permanent wilting point.

5. The change in AET/PET ratio with the available moisture depends on which of the following?
a) Soil type only
b) Field capacity and permanent wilting point
c) Soil type and rate of drying
d) Temperature
View Answer

Answer: c
Explanation: The general trend of AET/PET ratio is that it decreases with decrease in available soil moisture. However, the nature of this decrease is not constant and varies from soil to soil and also depends at what rate the water is lost.

6. Potential evapotranspiration can be used to estimate lake evaporation when pan evaporation data is not available.
a) True
b) False
View Answer

Answer: a
Explanation: In most applications of hydrology, PET is used as the basic parameter for all analysis and calculations related to evapotranspiration. It can be accepted as a good indicator of evaporation from a nearby lake.

7. Identify the correct soils represented by the two curves shown below in the graph of AET/PET vs. available moisture.
AET/PET versus available moisture graph
a) A – Clayey soil, B – Sandy soil
b) A – Sandy soil, B – Silty soil
c) A – Loamy soil, B – Clayey soil
d) A – Silty soil, B – Loamy soil
View Answer

Answer: a
Explanation: The variation of AET/PET ratio with available water depends on the type of soil. Usually for clayey soil, The AET/PET ratio remains one even after the water drops from field capacity to about 50% of initial moisture content. On the other hand, for sands the AET/PET ratio starts dropping as soon as the available moisture start to decrease.
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8. When the moisture content reaches permanent wilting point for a given crop, what will be the AET/PET ratio?
a) AET/PET > 1
b) AET/PET = 1
c) 0 < AET/PET < 1
d) AET/PET = 0
View Answer

Answer: d
Explanation: When the available moisture drops to and below the permanent wilting point for any crop, there wont be any water that the plant will be able to take up and hence the actual evapotranspiration will be zero.

9. The AET variation for a given soil is given as below.
The AET variation graph for a given soil
Estimate the AET/PET ratio when the available moisture reduces to half of its initial value.
a) 0.375
b) 0.5
c) 0.625
d) 0.75
View Answer

Answer: c
Explanation: The AET/PET ratio is constant upto 80% available moisture and then follows a linear decrease. From similar triangles,
\(\frac{100}{80}=\frac{x}{50}\) ⇒ x=62.5 %
Therefore, required ratio is 0.625.
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Sanfoundry Global Education & Learning Series – Engineering Hydrology.

To practice all areas of Engineering Hydrology, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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