Category: Irrigation Engineering Objective Questions

250+ TOP MCQs on Pressure Conduites and Answers

Irrigation Engineering Multiple Choice Questions on “Pressure Conduites”.

1. The flow through the penstocks and pressure conduits is generally ____________________
a) laminar
b) turbulent
c) both laminar and turbulent
d) unpredictable
Answer: b
Clarification: Penstocks are the huge diameter pipe which carries water under pressure and the structural design is similar to that of pressure pipes. Since there is a possibility of sudden load changes in penstocks which changes the pressure and flow velocity which characterizes the turbulent flow in fluid dynamics.

2. The head loss in the flow of water through a penstock pipe of given length ____________
a) increases with the increase in flow velocity
b) decreases with the increase in flow velocity
c) decreases with the increase in the roughness of the pipe surface
d) decreases with time
Answer: a
Clarification: The head loss (HL) by pipe friction is given by Darcy-Weisbach equation –
HL = f’. V2. L / 2gd where L is the length of pipe in meters, d is the diameter of the pipe, V is the velocity of the pipe and f’ is the friction factor which depends on Reynold’s number and the relative roughness of the pipe.
It is clear from the given equation that the head loss is directly proportional to the length of the pipe hence the head loss increases with the increase in the length of the pipe.

3. Hoop’s reinforcement is provided in cement concrete pressure pipes in order to counteract the _________
a) water hammer pressure
b) internal hammer pressure
c) stresses caused by the external backfills
d) both water hammer pressure and internal hammer pressure
Answer: d
Clarification: Hoop’s tension is the internal pressure exerted on the walls of the pipe by flowing water and the circumferential tensile stress (T1) is given by –
T1 = p1 d/2t where p1 is the internal static pressure, d is the diameter of the pipe and t is the thickness of the pipe shell.
Similarly, the circumferential tensile stress caused by water hammer pressure is given by –
T2 = p2 d/2t where p2 is the maximum water hammer pressure developed in pipelines.

4. The more rapid the closure of the valve, greater is the water hammer pressure developed.
a) True
b) False
Answer: a
Clarification: When a liquid is flowing in a pipeline is abruptly stopped by the closing of the valve, it destroys the momentum and retards the velocity of water column behind. This exerts a thrust on the valve, an additional pressure on the pipe shell and it may be so high as to cause bursting of the pipe shell. The more rapid is the closure of the valve, the more rapid is the change in momentum and hence, greater hammer pressure is developed.

5. Which of the following types of pressure conduits is preferably used for large heads?
a) PCC pipes
b) Cast iron pipes
c) Pre-stressed concrete pipes
d) Asbestos pipes
Answer: c
Clarification: Pre-stressed concrete pipes have more strength than RCC pipes and are more economical. The strength can be achieved by circumferential pre-stressing so as to increase the tensile stress. The main advantage is that they offer a cost advantage over other pipes for large diameter and higher pressures.

6. Which head loss formula is also applicable to turbulent flow in pressure conduits?
a) Darch-Weisbach equation
b) Manning’s formula
c) Hazen-Williams formula
d) Both Darch-Weisbach and Manning’s formula
Answer: b
Clarification: Manning’s formula is also applicable to the turbulent flow in pressure conduits. It yields good results provided the roughness coefficient is accurately determined. The head loss is expressed as –
HL = n2. V2. L / R4/3 where, n = manning’s rugosity coefficient, L is the length of pipe, V is the flow velocity through pipe and R is the hydraulic mean depth of the pipe.

7. __________________ joint is often used for connecting cast iron pipes.
a) Flexible joint
b) Expansion joint
c) Collar joints
d) Bell and spigot joint
Answer: d
Clarification: The pipes which are to be joined are made in such a way that one end is enlarged (also called socket or bell) and the other end is normal (i.e. spigot). The spigot end is inserted into the bell and the remaining space is filled with molten lead which gets solidified and thus making a water-tight joint.

8. Which of the following conduits is used when large diameter pipes of smaller wall thickness are required?
a) Cast iron conduits
b) Galvanized steel pipes
c) Hume steel conduits
d) Centrifugal type RCC pipe
Answer: b
Clarification: Galvanised steel pipes (with circumferential corrugations) are much stronger than ordinary steel pipes. These are usually manufactured in various sizes varying from 20 cm to 2 meters in diameter. They are lighter and can be more easily transported at distances and are widely used where large pipes of smaller wall thickness are required.

9. A special flexible joint called simplex joint is generally used to join _______________
a) vitrified clay conduits
b) galvanised iron pipes
c) asbestos conduits
d) hume steel conduits
Answer: c
Clarification: Asbestos conduits are highly flexible and may permit as much as 120 deflections in laying them around curves. Expansion joints are not required as the coefficient of expansion is low and the joints are also flexible i.e. simplex joint. Its assembly consists of pipe sleeve and two rubber rings which are compressed between the pipe and the interior of the sleeve.

10. Which of the following statement is incorrect?
a) Steel conduits are lighter than cast iron pipes
b) RCC pipes are generally made from 1:2:4 cement concrete with a maximum size of aggregates as 6 mm
c) RCC pipes and Hume steel conduits are heavy and difficult to handle
d) Riveted pipes are smoother and stronger than welded pipes
Answer: d
Clarification: Steel is strong in tension and even large size diameter pipes can be made of thin shells. They are therefore lighter than cast iron pipes. Welded pipes are smoother and stronger than riveted pipes. But steel pipes get rusted easily and are protected on the inside as well as outside by protective coatings.

11. Which of the following pipes is used for carrying hot water in the interior of the building?
a) Wrought iron pipes
b) Copper pipes
c) Galvanised iron pipes
d) Plastic pipes
Answer: b
Clarification: Copper pipes are very costly but they are highly resistant to acidic as well as alkaline waters. They can be bent easily and do not sag due to heat. Hence, they are very useful in carrying hot waters.

12. Wrought iron pipes are heavier than cast iron pipes and cannot be easily fabricated.
a) True
b) False
Answer: b
Clarification: Wrought iron pipes can be more easily cut threaded and worked but are more costly. They are neat in appearance but are less durable and corrode quickly. These are lighter than cast iron pipes and are generally protected by galvanizing with zinc coatings.

250+ TOP MCQs on Irrigation Canal – Maintenance and Answers

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.

250+ TOP MCQs on Tube Well-2 and Answers

Irrigation Engineering Interview Questions and Answers for freshers on “Tube Well – 2”.

1. A household tube well is called Abyssinian tube well falls under _________
a) strainer type
b) cavity type
c) slotted type
d) both cavity and slotted type
Answer: a
Clarification: Abyssinian tube well is the most common type of tubewell used for household purposes. It is also a strainer type of the tube well and the length of the strainer used here is about 2 meters.

2. Duty of wells expressed in hectares the well can irrigate to bring a crop to maturity because of ___________
a) well irrigation is a minor scheme
b) well water is lifted immediately and cannot be expressed in ha/m3/sec
c) well is situated in the middle of the commanded area
d) wells are owned by cultivators and so the source of supply is a private one
Answer: b
Clarification: In well irrigation water is lifted intermittently. The duty of a well is the area of land in hectares the well can irrigate annually and fully to bring a crop to maturity. It cannot be expressed in hectares/m3/sec for a base period of a crop.

3. Which of the following strainer is used for shallow irrigation tube wells particularly in deltaic regions of developing countries?
a) Continuous slot type of strainer
b) Louver type of strainer
c) Pipe strainer with fine mesh jackets
d) Coir rope strainers
Answer: d
Clarification: Coir rope strainers are low-cost strainers and are generally used for shallow irrigation tube wells. The main disadvantage of such a strainer is its short life of 3 to 5 years. The rusting of the iron bars of the supporting frame and the loosening of the coir rope which expands on wetting are the causes of its failure.

4. Rewhiding the well involves ____________________
a) heavy pumping of well
b) starting and stopping of pumping intermittently
c) forcing of the well water back into the aquifer
d) jetting with water at high velocity
Answer: b
Clarification: Rewhiding involves starting and stopping of pumping intermittently. It provides a relatively rapid change in the head of the well and can be done with any type of pump. However, the turbine pump installed with a foot valve is the most effective.

5. Which of the following is an effective method for the development of well?
a) Surging
b) Pumping
c) Well development by compressed air
d) Jetting
Answer: d
Clarification: Development of well by high velocity jetting is one of the most effective methods. In this method, the fine particles are washed out of the aquifer due to the shooting of high-velocity water stream through the screen openings. These fines get back into the well due to the turbulence created by the jet. The entire surface of the screen can be covered by gradual raising, lowering and slowly rotating the jetting tool.

6. The appropriate life of a tubewell in India is of the order of ______
a) 1 year
b) 2 years
c) 5 years
d) 15 years
Answer: d
Clarification: A normal tubewell lasts for about 15 to 20 years in Northern India. It may fail due to incrustation and corrosion.

7. Incrustation of the tubewell pipes may lead to _________________
a) reduced discharge from the tubewell
b) excessive discharge of sand with water
c) discharge of highly alkaline water
d) increased pumping rate
Answer: a
Clarification: The deposition of alkali salts on the inside walls of the pipe is called incrustation. It reduces the effective diameter of the well pipe and hence reduces the discharge of the tubewell. It cannot be completely eliminated.

8. Corrosion of tubewell pipes may cause _______________
a) reduced discharge from the tubewell
b) excessive discharge of sand with water
c) discharge of highly alkaline water
d) increased pumping rate
Answer: b
Clarification: Due to the action of acidic water on the pipe, it is gradually destroyed by corrosion. The aquifer sand surrounding the well pipe comes out through the worn-out pipe walls bringing sand along with water. It results in the excessive withdrawal of sand along with the well water.

9. Which of the following pump can effectively lift water under the maximum suction head of 6 to 8 meters?
a) A single-stage centrifugal pump
b) Submersible pumps
c) Turbine pumps
d) Jet pumps
Answer: a
Clarification: A centrifugal pump works effectively under the maximum suction head of 6 to 8 m. Such pumps can be used at places where the fluctuations in water table plus the depression head are limited to a maximum of 8 m. The borehole type pump is used for larger values.

10. The amount of water required from wells to mature a similar crop is more than that required in canal irrigation.
a) True
b) False
Answer: b
Clarification: Delta in well irrigation is the total depth of water required to mature a crop in meters or centimetres. The delta of well water is about 66% of canal water because conveyance losses are minimum and well water is used at the right time in the right quantity.

11. Which of the following gives an indication of the chemical quality of the groundwater?
a) Geological logs
b) Resistivity logs
c) Sonic logs
d) Thermal logs
Answer: b
Clarification: Resistivity surveys are based on the fact that water increases the conductivity of the rocks and thereby reducing their resistivity. Resistivity logs indicate the values of electrical resistivity of the rocks at different depths.

12. Reversing the direction of flow by surging the well does help in removing the bridging.
a) True
b) False
Answer: a
Clarification: The basic principle in well development is to cause reversals of flow that will rearrange the aquifer particles through the screen openings. This breaks down the bridging of the groups of particles. When the flow is in one direction small particles bridge between large particles across the screen openings.

13. Which of the following pumps is also used for testing or development of wells?
a) Vertical turbine pump
b) Submersible motor pump
c) Jet pump
d) Airlift pump
Answer: d
Clarification: Airlift pumps are useful in removing objectionable gas, highly corrosive or abrasive water that damages parts of the pump submerged in the well. It is also used for testing or development of wells but is rarely used due to low efficiency.

14. Which log represents the type of strata existing at different depths and encountered during digging or boring of the wells?
a) Well logs
b) Resistivity logs
c) Radiometric logs
d) Sonic logs
Answer: a
Clarification: Resistivity logs indicate the values of the electrical resistivity of rocks at different depths. Sonic logs indicate the value of the velocity of compressional waves at different depths. Radiometric logs indicate the variations of radioactivity with depth.

Irrigation Engineering for Interviews,

250+ TOP MCQs on Regulation Modules – Outlet Types and Answers

Irrigation Engineering Multiple Choice Questions on “Regulation Modules – Outlet Types”.

1. What is the main purpose of the canal outlet?
a) To Connect Head with a Minor Channel
b) To Avoid Leakage
c) To Avoid Exit Gradient
d) For Proper Discharge
Answer: b
Clarification: The canal outlet is a small structure that is built at the head of the watercourse so as to connect it with a distributary channel or a minor channel.

2. How many types of outlets are present?
a) 2
b) 3
c) 4
d) 5
Answer: b
Clarification: The available types of outlets are classified into three classes. These classes are non-modular outlets, semi-modules, and rigid modules.

3. Which structure in the entire network of canals is a link between the government and the cultivators?
a) Weirs
b) Falls
c) Modules
d) Canal Escapes
Answer: c
Clarification: In the entire network of the canals, up to the modules the control and maintenance falls under the jurisdiction of state government, and beyond the modules the entire working of water courses is takencare by the cultivators. Hence the modules are the structures which provide the link between government and the cultivators.

4. The outlet should be cheap and with no moving parts.
a) True
b) False
Answer: a
Clarification: Since these outlets are required in large numbers, they should be cheaply available. And moreover the outlets should be sufficiently strong enough with no moving parts, to avoid periodic maintenance.

5. The outlet should be simple and free from interference by the cultivators.
a) True
b) False
Answer: a
Clarification: The outlet or module should be simple because it can easily be constructed or fabricated by the masons or technicians. Interference with the cultivators should also be avoided to prevent undue tapping of water by the cultivators.

6. Open sluice and drowned pipe outlet come under which class of modules?
a) Modular Outlets
b) Semi Modules
c) Rigid Modules
d) Non-modular Outlets
Answer: d
Clarification: In open sluice or drowned pipe outlet the discharge depends upon the difference between the head in a distributary and the water courses. The discharge in these two also vary widely either with a change in the water level of the distributary or that of a water course. Hence, the open sluice and drowned pipe outlet come under non-modular outlets class.

7. What is the common example of rigid modules?
a) Pipe Outlet
b) Open Sluice
c) Gibb’s Module
d) Venturi Flume
Answer: c
Clarification: In Gibb’s module the discharge is constant within the fixed limits, irrespective of variation of water levels of either the distributary or of a water course or both. Thus Gibb’s module is a common example of a rigid module.

8. In which class of outlets the discharge is independent of water level of the water course?
a) Non-modular Outlets
b) Semi Modules
c) Rigid Modules
d) Modular Outlets
Answer: b
Clarification: The outlets in the class of semi-modules are those in which the discharge is independent of the water level of the water course but depends only on the water level of the distributary as long as a minimum working head is available. Therefore, the discharge is directly proportional to the water surface level in the distributary.

9. When the flexibility of an outlet equals unity, then the outlet is said to be in?
a) Sub-proportional
b) Setting
c) Sensitivity
d) Proportionality
Answer: d
Clarification: An outlet is said to be proportional when the rate of change of outlet discharge equals the rate of change of channel discharge or in other words, we can say when flexibility equals unity then the outlet is proportional or in proportionality. Hence, F = (m/n) x (y/H) = 1.

10. For which type of class of outlets the sensitivity is zero?
a) Rigid Modules
b) Semi Modules
c) Non-modular Outlets
d) Flexible Modules
Answer: a
Clarification: The ratio of rate of change of discharge through the outlet to the rate of change of water level of distributary, to the normal depth of the channel is known as sensitivity. Since the discharge is fixed for rigid modules the sensitivity is zero.

11. What is the minimum difference between the upstream and downstream water levels to allow designed discharge through the module?
a) Minimum Modular Depth
b) Efficiency of an Outlet
c) Drowning ratio
d) Proportionality
Answer: a
Clarification: A minimum difference between the water levels of both upstream and downstream is to be maintained so as to enable the module to pass the designed discharge is known as minimum modular head.

12. What is the ratio of the depth of water levels over the crest is called?
a) Efficiency of an Outlet
b) Drowning Ratio
c) Minimum Modular Head
d) Modular Limit
Answer: b
Clarification: The ratio of the depth of water level over the crest on the downstream side to the depth of water level over the crest on the upstream side is called a drowning ratio.

13. What is the ratio of head output to the head input called?
a) Modular Limit
b) Minimum Modular Head
c) Efficiency of an Outlet
d) Drowning Ratio
Answer: c
Clarification: The ratio of head recovered (output) to the head put in (input) is known as efficiency of an outlet. If the head required for the operation that is head put in, is less more will be the efficiency. This efficiency is also a measure of conservation of head by the outlet.

250+ TOP MCQs on Diversion Head Works – Gravity and Non-Gravity Weirs and Answers

Irrigation Engineering Multiple Choice Questions on “Diversion Head Works – Gravity and Non-Gravity Weirs”.

1. When the weight of the weir balances the uplift pressure caused by the head of water seeping below the weir, it is called as ____________
a) gravity weir
b) non-gravity weir
c) vertical drop masonry weir
d) concrete glacis weir
Answer: a
Clarification: In Gravity weir, the weight of the weir balances the uplift pressure caused by the seepage water. In non-gravity weirs, the weight of the concrete slab and the divide piers together keep the structure safe against the uplift.

2. Which weir is also called Dry Stone Slope Weir?
a) Masonry weir
b) Gravity weir
c) Rock-fill weir
d) Concrete weir
Answer: c
Clarification: Rock-fill weir is also called Dry Stone Slope Weir. It is the simplest type of construction and is economical only when the stone is easily available. This type of weir is also becoming obsolete with the development of concrete glacis weir.

3. Which type of weir is suitable for hard clay and consolidated gravel foundations?
a) Gravity weir
b) Non-gravity weir
c) Masonry weir with a vertical drop
d) Rock-fill weirs with sloping aprons
Answer: c
Clarification: This type of weir was used in all the old head-works and is particularly suitable for hard clay and consolidated gravel foundations. Masonry weir is becoming obsolete and all the modern constructions are done by the modern concrete weirs.

4. Which weir is of recent origin and their design is based on modern concepts of sub-surface flow?
a) Gravity weir
b) Non-gravity weir
c) Masonry dam with a vertical drop
d) Concrete weir with sloping glacis
Answer: d
Clarification: The design of concrete weir with sloping glacis is based on the modern concepts of sub-surface flow i.e. Khosla’s theory. Sheet piles are driven at sufficient depths at the upstream and downstream floor end. The hydraulic jump is formed on the downstream sloping glacis to dissipate the energy of the flowing water.

5. Which weir is now extensively used especially on pervious foundations?
a) Vertical drop masonry weir
b) Rock-fill weirs with sloping aprons
c) Concrete weirs with sloping glacis
d) Non-gravity weirs
Answer: c
Clarification: Modern concrete weirs with sloping downstream glacis are generally provided with low crest counter-balanced gates. This is now exclusively used on permeable foundations. Masonry weirs are suitable for hard clay and gravel foundations. Rock-fill weir is suitable for fine sandy foundations.

6. Which of the following statement is incorrect about Non-gravity weir?
a) The weir floor is designed continuous with the divide piers as a reinforced structure
b) The weight of the concrete slab balances the uplift pressure
c) The weight of the divide piers also keep the structure against uplift
d) Brick piers have to be used in place of RCC
Answer: d
Clarification: The weir floor and divide-pier are designed as a reinforced structure continuously. The RCC has to be used in place of brick piers and as the weight of the floor can be much less than that of gravity weir, considerable savings are obtained.

250+ TOP MCQs on Channel Cross-sections and Answers

Irrigation Engineering Multiple Choice Questions on “Channel Cross-sections”.

1. What types of channel sections are usually adopted?
a) Triangular and Circular channel
b) Triangular and Trapezoidal channel
c) Rectangular and Trapezoidal channel
d) Rectangular and Triangular channel
Answer: b
Clarification: Generally, Triangular and Trapezoidal channel sections are adopted. For smaller discharges, the Triangular channel section is adopted and trapezoidal channel for larger discharges.

2. What is the maximum permissible velocity in Cement concrete lining (Unreinforced) as per Indian Standards?
a) 2 to 2.5 m/sec
b) 1.5 to 2 m/sec
c) 1.2 to 1.8 m/sec
d) 1.5 to 2.5 m/sec
Answer: a
Clarification: The maximum permissible velocity for unreinforced cement concrete lining is 2.0 to 2.5 m/sec. For Boulder lining, the maximum permissible velocity is 1.5 m/sec.

3. What is the minimum value of free-board for Main and Branch Lined canals if the discharge is more than 10 cumecs as per specified by BIS code?
a) 0.60
b) 0.50
c) 0.75
d) 0.30
Answer: c
Clarification: In main and branch canals for discharge more than 10 cumecs, the minimum value of freeboard is 0.75 m. For branch canals and distributaries in which discharge is less than 10 cumecs the value is 0.60 m.

4. The distance measured above the F.S.L and to the top of the lining is known as free-board.
a) True
b) False
Answer: a
Clarification: The vertical distance between the full supply level (F.S.L) and the top of the bank is called freeboard. It depends on the size of the canal, location of the canal and water level fluctuations.

5. What is the minimum value of inspection bank width recommended by Indian Standards if the discharge is more than 30 cumecs?
a) 8.0
b) 5.0
c) 6.0
d) 7.0
Answer: a
Clarification: The minimum value of the top width of the bank depends on the value of discharge. For discharge greater than 30 cumecs, the minimum value of the top width of the inspection bank is 8.0 m and for Non-inspection bank is 5.0 m.

6. When the concrete lining is not reinforced in a channel, velocities up to 2.5 m/sec are permitted.
a) True
b) False
Answer: a
Clarification: Higher velocities can be safely used in lined canals. The maximum permissible velocities for concrete linings when the lining is not reinforced are up to 2.5 m/sec. The lining can be reinforced if still higher velocities are desired.

7. Calculate hydraulic mean depth for concrete-lined channel to carry a discharge of 350 cumecs at a slope of 1 in 5000. The value of manning’s constant for the lining is 0.015. The side slopes of a channel may be taken as 1.5:1. Assume limiting velocity in the channel as 2m/sec.
a) 2.20 m
b) 2.40 m
c) 2.60 m
d) 2.80 m
Answer: d
Clarification: Using Manning’s equation: V = 1/n.R2/3.S1/2
2 = 1/0.015 x R2/3 x 1/50001/2
R = 2.80 m.

8. Calculate the central depth of a triangular channel section to carry a discharge of 15 cumecs. Consider the available slope as 1 in 9000. Assume the side slopes of the channel be 1.25:1 and manning’s constant is 0.015 for good brick work in lining.
a) 2.94 m
b) 3.14 m
c) 2.25 m
d) 2.77 m
Answer: a
Clarification: Given data- tanQ = 1/1.25; Q = 0.675 radian
A = y2 (Q + cotQ) = 1.925y2 and R = y/2
Q = 1/n.A.R2/3.S1/2
15 = 1/0.015 x 1.925y2 x (0.5y)2/3x 1/90001/2
y = 2.94 m.