Irrigation Engineering Multiple Choice Questions on “Irrigation Canal – Maintenance”.
1. The berms help in checking excessive loss of water due to seepage.
a) True
b) False
Answer: a
Clarification: Berms provide a path for inspection. Excessive loss of water due to seepage is checked. It is so because berms are formed of fine silt which makes berms fairly impervious.
2. Which of the following is not a reason which leads to a canal breach?
a) Due to faulty design and construction of banks
b) Due to leakage or piping
c) Due to the maintenance of service roads
d) Due to intentional cuts made by cultivators
Answer: c
Clarification: Breaches are the gaps created in the canal banks due to breaking up of the banks. The maintenance of service roads includes removal of grass and small bushes, levelling and surfacing of roads. The slopes if damaged should be repaired to facilitate drainage of roads.
3. Which of the following is not a preventive measure for the maintenance of the canal?
a) Strengthening of canal banks
b) Formation of berms by internal silting
c) Provision of Pushta or cover to the saturation line
d) Silt removal
Answer: d
Clarification: Preventive measures are aimed at providing additional stability at various components parts of the canal. Remedial measures are aimed at repairing or removing the causes of trouble like aquatic weed control, silt removal, and maintenance of service roads.
4. Internal silting method and external silting method are the methods of _____
a) strengthening of canal banks
b) formation of berms
c) silt removal
d) formation of breaches
Answer: a
Clarification: Internal silting method is adopted only when new canals are constructed as the section has to be sufficiently wide. In the external silting method, subsidiary banks are constructed to hold the water externally in a confined position. Both of these are methods of strengthening of canal banks.
5. Which of the following statement is wrong about the internal silting method?
a) The extra strength is gained by increasing the section of the banks
b) The additional soil is derived from the natural process of silting internally
c) This method of strengthening the canal is very cheap, simple and efficient
d) To decelerate the silting process low submersible spurs may be constructed
Answer: d
Clarification: The spurs project into the canal section from the banks. They provide high silting rate and spurs may be raised after silting has taken place up to the top of spurs. Thus silting takes place in successive layers and finally, silt deposit reaches a predetermined height which is then raised up to the top of the bank.
6. In the external silting method, subsidiary banks are constructed which run parallel to canal main banks.
a) True
b) False
Answer: a
Clarification: It is very essential to bring the flow of water out of the channel section to accomplish silting of banks externally. Subsidiary banks are required to hold the water externally in a confined position and are constructed parallel to the canal main banks.
7. In Long reach system, only a portion of full supply discharge is taken in the compartment.
a) True
b) False
Answer: b
Clarification: Canal water is taken in the compartment through the inlet. When the length of the compartment is between 1200 to 1500 m it is called long reach the system. The whole canal discharge is taken in the compartment and this is done when the water is not required for irrigation purposes.
8. Which of the following combination is incorrect?
a) Silt removal – Silt ejectors and silt escapes
b) Aquatic weed control – Mechanical removal of plants
c) Breach due to piping – provision of a sand core in the bank
d) Breaches in a big canal – Dumping huge quantity of earth
Answer: d
Clarification: This process cannot be adopted for a bigger canal. The outflow from the canal breach will be large and all the soil dumped for closing the breach may be washed off. For bigger canals, the outflow is reduced first followed by cutting the sides of the gap and then driving the double pile in the opening of the breach.
9. Berm is _____________
a) a horizontal strip at the N.S.L
b) a device to remove silt
c) another name of the canal bank
d) a gap created in the bank of the canal
Answer: a
Clarification: It is a narrow horizontal strip of natural ground left between the canal section and inner toe of the bank. This is provided in such a way that the bed line and the bank line remain parallel.
10. The Remodelling of canal system is done to __________
a) beautify the canal surroundings
b) correct deformations in the canal
c) exhibit the canal in exhibition
d) widen up the channel section
Answer: b
Clarification: Remodelling of canal aims at correcting the distribution system as per existing demand. It includes silt clearing operations, remodelling of outlets, the rectification of channels, modification of faulty hydraulic structures etc.