This set of Irrigation Engineering Questions and Answers for Aptitude test focuses on “Canal Irrigation System – Losses of Water in Canal”.
1. Loss of canal discharge occurs mainly due to?
a) Seepage and Percolation
b) Percolation and Absorption
c) Seepage and Evaporation
d) Seepage and Absorption
Explanation: Seepage and Evaporation are the two main reasons for loss of canal discharge. Out of these, seepage loss is most significant in the initial stages (about 40%). Evaporation loss may range from 2 to 3% of the total canal discharge.
2. Which of the following factor do not affect seepage loss?
a) Underground water-table condition
b) The porosity of the soil
c) Physical properties of the canal water
d) Prevailing wind velocity in the region
Explanation: The loss due to seepage is the most significant so far as irrigation loss from canals is considered. The porosity of the soil, underground water-table condition, condition of the canal system, and physical properties of the canal water are all factors affecting seepage loss.
3. In which of the following phenomenon there is a continuous direct flow between the canal and the underground water table?
d) Both Absorption and Percolation
Explanation: When the ground water-table is nearer to the natural surface, the water which has entered the subsoil may join the saturation zone or underground reservoir to maintain a continuous direct flow. Due to the difference of level, the water directly flows from the canal to the underground reservoir through the soil pores.
4. Which of the following factor have no influence on evaporation loss?
a) The temperature of the region
b) Prevailing wind velocity in the region
c) Area of water surface exposed to the atmosphere
d) The porosity of the soil
Explanation: Evaporation loss is not that significant and may range from 2-3% of the total canal discharge. The rate of loss depends mainly on temperature and humidity of the region, prevailing wind velocity and the area of water surface exposed to the atmosphere.
5. In the phenomenon of Absorption, the extent of saturation goes on increasing from the ground level below the soil with depth.
Explanation: The soil which is in immediate contact with the channel section forms a bulb of saturated soil. The soil layer below the saturated bulb is partially saturated. Thus the extent of saturation goes on decreasing from the ground level and a zone of unsaturation exists between them.
6. According to Etcheverry and Harding, the range of conveyance loss is highest in which soil?
a) Sandy Loam
b) Loose sandy soil
c) Clay Loam
Explanation: The range of water lost in conveyance for loose sandy soil is 5.18 to 6.10.
For Sandy loam = 3.66 to 5.18
For Clay loam = 1.83 to 3.66
For rocks = about 0.9.
7. Which of the following empirical formula is used in Punjab for calculating channel losses?
a) Q’ = 1.9 Q1/6
b) Q’ = 1/200 x (B+D)2/3
c) Q’ = 1.9 Q
d) Q’ = 1/200 x (B-D)2/3
Explanation: The formula for channel losses used in Punjab and Haryana states is Q’ = 1.9 Q1/6.
Where Q’ = Losses in cumecs per million sq.m of the wetted perimeter, Q = Discharge in cumecs.
The formula is used in U.P is; Q’ = 1/200 x (B + D)2/3 where B is the bed width of channel and D is the depth of water in the channel in meters.
8. Inflow and Outflow method is generally used to measure ____________
a) transpiration loss
b) seepage loss
c) evaporation loss
d) percolation loss
Explanation: Seepage loss is generally measured by Inflow and Outflow method. Regular and simultaneous discharge measurement is done at the entrance and end of the selected reach. Same gauge and discharge are maintained at the entrance during the period of observations. The difference between the inflow and outflow over the reach gives the quantity of water lost.
9. Which of the following statement is incorrect?
a) The seepage loss is very high in black cotton soils and heavy clay as compared to sandy porous soil
b) The seepage through a new canal is more than from a silted canal
c) The more the silt, the lesser are the losses
d) The more the velocity, the lesser will be the losses
Explanation: The seepage losses depend upon all these factors. The seepage loss is very high in sandy or porous soil as compared to black cotton soil or clays. The sandy soil has high permeability so the soil structure allows more water to penetrate and hence there is more seepage.
10. Which soil has the least range of conveyance loss according to Etcheverry and Harding?
a) Sandy Loam
b) Clay Loam
c) Loose sandy soil
d) Impervious clay loam
Explanation: The loss is generally expressed in cubic meters per sec per million square meters of the wetted perimeter. For Impervious clay loam, the range is between 1.02 to 1.22.
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