Irrigation Engineering Questions and Answers – Tube Well-1

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This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Tube Well-1”.

1. The most widely used type of a deep state tube well in India is __________
a) cavity well
b) strainer tube well
c) slotted pipe gravel packed tube well
d) both cavity and strainer tube well
View Answer

Answer: b
Explanation: Strainer type tubewell is a bored hole in which a metal pipe with suitable perforations is inserted. A strainer type tubewell is suitable when water-bearing stratum is available at less depth and there is a possibility of tapping water through sides. It is generally unsuitable for fine sandy strata.
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2. The general average yield from standard tube wells is of order of____________
a) 5 L/sec
b) 50 L/sec
c) 500 L/sec
d) 5000 L/sec
View Answer

Answer: b
Explanation: Tube well irrigation is very suitable where the subsoil formation is suitable for storing water. The general average yield from the standard deep tube-wells is of the order 40 to 50 liters/sec. Shallow tube-wells may yield as high as 15-20 liters/sec if located at proper places.

3. Which of the following tubewell is suitable when a deep bearing stratum lies below an impervious layer and water contribution can take place through bottom only?
a) Strainer type tubewell
b) Abyssinian tubewell
c) Cavity type tubewell
d) Slotted type tubewell
View Answer

Answer: c
Explanation: A strainer type tubewell is suitable when water-bearing stratum is available at less depth and there is a possibility of tapping water through sides. The slotted type tubewell is intermediate to the strainer and cavity type tubewell and is used where both the above cannot be used.

4. In cavity tubewell, there is a possibility of water tapping through sides and the flow is radial.
a) True
b) False
View Answer

Answer: b
Explanation: In cavity-type tubewell, water contribution to the bored hole takes place through the bottom layer only as is done by screen well. The flow in a cavity well is essentially spherical. In strainer type tubewell, water enters into the well from the sides and the flow is radial.

5. What is the measure of the fineness of an aquifer?
a) Average grain size
b) Effective diameter
c) Mean particle size
d) Uniformity coefficient
View Answer

Answer: b
Explanation: Effective diameter is an index of the measure of the fineness of an aquifer. It is used for designing various intake components of a tubewell. For permeability D10 (i.e. 90% grains retained on the sieve) is taken as the effective size.
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6. What is Pack Aquifer Ratio?
a) D50 of the gravel / D50 of the aquifer
b) D50 of the aquifer / D50 of the gravel
c) D60 of the aquifer material / D10 of the aquifer material
d) D60 of the gravel / D10 of the aquifer
View Answer

Answer: a
Explanation: The gravel pack is usually designed on the basis of Pack Aquifer (PA) ratio. It is usually defined as the ratio of D50 size of the gravel pack material to the D50 size of the aquifer material. It should be designed before designing the size of the slots to be made in the well-screens.

7. According to the Central Board of Irrigation and Power, the PA ratio for graded aquifer should be _______________
a) 9 – 12.5
b) 12 – 15.5
c) > 15.5
d) < 9
View Answer

Answer: b
Explanation: The Central Board of Irrigation and Power suggested the following criteria for PA ratio.
i. For uniform aquifers (having Cu < or = 2.0), the PA ratio should be in between 9 – 15.5
ii. For graded aquifers (having Cu > 2.0), the PA ratio should be in between 12 – 15.5.

8. For good design, the uniformity coefficient (Cu) of the gravel material should preferably be ______
a) > 2.0
b) < 2.0
c) > 2.5
d) < 2.5
View Answer

Answer: d
Explanation: The uniformity coefficient was proposed by Hazen. The value of the coefficient of the gravel material is preferably kept to be equal to or less than 2.5. A higher value may cause segregation of the gravel during pouring which will result in poor efficiency of the well.

9. The efficiency of the centrifugal pumps commonly used for lifting water from wells may be of the order of _____________
a) 30%
b) 65%
c) 90%
d) 95%
View Answer

Answer: b
Explanation: Jet pumps have low efficiency of the order of 35% as compared to 65-85% for other centrifugal pumps. It is not used for irrigation tube-wells.
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10. A tube well is suitable when the subsoil formation is made up of _____________________
a) cracked and faulted rock
b) alluvium
c) alluvium and various layers of sandy soil, clayey soil, and gravel
d) clayey soil
View Answer

Answer: c
Explanation: In India most of the land especially the Indo-Gangetic plains, Narmada valley consists of deep alluvial soils. The sub-soil water slowly penetrates and is stored in porous sand and gravel beds which are extensively found in India. Tube wells can be easily installed in such lands and are useful for irrigation.

11. Bored tube wells in rocky consolidated formations as are encountered in the South Indian States of our country are usually drilled by _____________
a) rotary drilling rigs
b) percussion drilling rigs
c) down the hole hammer (DTH) rigs
d) cable method of drilling
View Answer

Answer: c
Explanation: In rocky areas, down the hole hammer rigs (DTH rigs) are used to drill isolated holes of 10 to 15 cm in diameter. They are usually in the depth range of 100 m and mostly been constructed in southern states of India. This type of wells usually depends on joints and fissures in the rocks for their water supply.

12. Which of the following drilling method is unsuitable in loose formations such as unconsolidated sand and gravel or quicksand?
a) Percussion drilling
b) Wash boring method
c) Rotary boring method
d) Reverse rotary method
View Answer

Answer: a
Explanation: Percussion method of drilling the well hole is also known as the cable method of drilling. It is ineffective in loose material because of slumping and caving of the material around the drilling bit. This method is useful for cutting consolidated rocks from soft clay to hardest rocks.

13. Which drilling method is best suited for underground formations made of gravel, sand and clayey deposits?
a) Percussion drilling
b) Wash boring method
c) Rotary boring method
d) Reverse rotary method
View Answer

Answer: b
Explanation: Percussion method is suitable for soft and fissured rock formations. The rotary boring method can be successfully used for rock as well as unconsolidated formations. The reverse rotary method is used for soft unconsolidated formations made of sand, silt or soft clay.
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14. Which is the fastest method of drilling and especially useful in unconsolidated formations?
a) Cable tool method
b) Water-jet boring method
c) Hydraulic Rotary method
d) Reverse Rotary method
View Answer

Answer: c
Explanation: Hydraulic rotary method can handle hard and soft foundations with ease and the danger of accidents is lesser. The rate of drilling by this method for consolidated rock formation may vary from 10 to 15 m per day and in unconsolidated formations 100 to 150 m per day.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn