This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Water Logged Reclamation – Sub-surface or Tile Drainage”.
1. For maximum productivity of crops both surface and sub-surface drains are sometimes needed.
Explanation: Surface drains are needed for crops cultivated on flat lands to remove excess irrigation water, whereas subsurface drains are needed for soils having poor internal drainage and high water table. So, therefore for maximum productivity of crops both surface and subsurface drains are sometimes essential especially in regions of high water table.
2. How can tile drainage help to increase crop yields?
a) Increases Free Gravity Water
b) Increases Volume of Soil
c) Decrease Air Circulation
d) Increases Water Table Level
Explanation: The tile drainage helps in lowering the water table level which in turn increases the crop yields. It also helps in increasing the volume of soil from where the roots of the crops can obtain food.
3. Tile drainage helps to reduce soil erosion.
Explanation: As tile drainage helps in lowering the groundwater level, it gives room for increase in volume of the soil and helps the roots to hold on to the soil very tight. It also provides well drained soil to hold rainfall, resulting in less runoff. Due to these reasons, the soil erosion is reduced by tile drainage.
4. Which type of soils is benefited by using tile drainage?
a) Dry Soils
b) Black Soils
c) Wet Soils
d) Red Soils
Explanation: Tile drainage requires less labour and time in tilling and harvesting the soils as these do not obstruct farming. Planting in wet soils may decrease crop yields. So, therefore the delay in planting and decrease in crop yields in wet soils can be improved by using tile drainage.
5. In what chemical ways does tile drainage help in plant growth?
a) Decreases Alkalinity of Soils
b) Increases salinity of Soils
c) Increases Nitrogen
d) Reduces and Removes Toxic Substances
Explanation: Tile drainage helps in reducing and removal of toxic chemicals and substances like sodium and other soluble salts, which harms the growth of plants.
6. Under what strata the tile drainage should not be placed?
a) In Shallow Depths
b) More Pervious Strata
c) Less Pervious Strata
d) Pervious Strata
Explanation: The tile drainage should not be placed under or below the less pervious strata because in this case, the drains may remain dry even though the land above the impervious strata may be logged as this water will not reach the drains.
7. What structure is surrounded around the tile drains when used in less pervious strata?
a) Envelope Filters
b) French Drains
c) Beehive Grate
d) Surface Inlet
Explanation: Envelope filters surround the tile drains when used in less pervious strata. These filters help in increasing the effective tile diameter and in turn help increasing the inflow rate, and also help in preventing the inflow of soil into the drains.
8. What is the size of the tile at an outlet of a 12 hectare drainage system, if the D.C is 2 cm and the tile grade is 0.5%. Assume the rugosity coefficient as 0.015 for the tile drain material.
a) 10 cm
b) 20 cm
c) 15 cm
d) 25 cm
Explanation: Volume of water passing the drain in one day = (1/100 x 12 x 104) = 1200 m3/day
Volume of water passing the drain in one second = (1200/24 x 3600) = 1/72 m3/sec
Q = 1/72 m3/sec
Q = 1/n x A x R2/3 x S1/2
A = πD2/4, P = πD, R = A/P = D/4
1/72 = (1/0.015) x (πD2/4) x (D/4) x (0.5/100)
On solving the value of D = 17.4 cm
Use D = 20 cm.
9. Which type of alternate layouts system for tile drainage has two mains?
a) Grid Iron System
b) Natural System
c) Double main System
d) Herring Bone System
Explanation: This system has two mains with separate laterals for each main. This type of system is used when the bottom of depression is wide. It also helps in reducing the length of the laterals and eliminates the break in slope at the edge of the depression of the lateral.
10. How many cubic metres of water will be removed for this particular period of a system designed to use a D.C of 1.5 cm draining 20 hectares for a capacity of 5 days?
a) 10000 m3
b) 25000 m3
c) 15000 m3
d) 20000 m3
Explanation: D.C of 1.5 cm means that 1.5 cm of water depth will be removed from the drainage in 24 hours.
Volume of water entering the drain per day = (1.5/100) x 20 x 104 = 3000 m3/day
Volume of water passing the drain within 5 days of flow = 5 x 3000 = 15000 m3.
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