Constructing Water Retention Structures

18 Grade 7 Agriculture questions on Constructing Water Retention Structures, with worked marking schemes. 18 questions are available on this topic in full.

1. Question 1

   1 mark

   Why should the soil dug out when making a retention trench be heaped on the LOWER side of the trench?

   A. To make the work look neat

   B. To provide soil for planting seeds

   C. To form a ridge that holds back run-off water

   D. To prevent the trench from collapsing inwards

   (1 mark)

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2. Question 2

   1 mark

   While constructing a water retention structure in the school farm, learners dig small basins around each fruit tree seedling. What is the MAIN purpose of these basins?

   A. To make the seedlings look attractive

   B. To trap and hold rainwater close to the tree roots

   C. To prevent birds from reaching the seedlings

   D. To allow water to drain away quickly

   (1 mark)

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3. Question 3

   1 mark

   When constructing a zai pit for planting maize in a dry area, what is the main reason for placing manure at the bottom of the pit?

   A. To prevent weeds from growing

   B. To keep away termites

   C. To improve soil fertility and hold moisture near the roots

   D. To make the pit deeper

   (1 mark)

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4. Question 4

   6 marks

   A farmer in the dry parts of Kitui notices that whenever it rains, most of the water runs off the sloping farm and very little soaks into the soil for the crops. An agricultural officer advises the farmer to construct water retention structures.

   (a) Name TWO water retention structures the farmer could construct on the sloping land. (2 marks)

   (b) Explain TWO ways in which these structures help the farmer's crops during the dry season. (4 marks)

   (6 marks)

   Marking scheme

   (a) Any TWO: terraces (e.g. fanya juu / fanya chini); cut-off drains; retention ditches/trenches; zai pits / planting pits; gabions; contour bunds/ridges; check dams. (1 mark each = 2 marks) (b) Any TWO well-explained (2 marks each = 4 marks): (1) They slow down and trap the run-off water so that it has time to soak into the soil, increasing the amount of water stored in the soil that crops can use during the dry spell. (2) By holding water and reducing the speed of run-off, they prevent soil erosion so the fertile top soil and its moisture are retained on the farm, keeping the ground moist for longer. (Accept: they recharge the underground water table; they reduce flooding and gully formation that would carry away water and soil.)

5. Question 5

   1 mark

   Which simple instrument can learners make from wood and a stone on a string to mark contours in the field?

   A. A spirit level

   B. A tape measure

   C. An A-frame level

   D. A plumb pendulum clock

   (1 mark)

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6. Question 6

   1 mark

   Cut-off drains constructed above a cultivated field are meant to:

   A. Store water for irrigation

   B. Increase the slope of the land

   C. Provide a path for livestock

   D. Intercept and divert run-off away from the field

   (1 mark)

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7. Question 7

   1 mark

   Which of the following is a benefit of lining the walls of a water pan with clay soil or a liner?

   A. It increases evaporation

   B. It reduces water loss through seepage

   C. It makes the water taste better

   D. It speeds up drainage

   (1 mark)

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8. Question 8

   1 mark

   A learner on a sloping farm in Kitui wants to slow down rain water so that it soaks into the soil instead of washing away topsoil. Which water retention structure should the learner construct across the slope?

   A. A raised footpath

   B. Cut-off drains leading water away quickly

   C. Retention ditches (fanya juu terraces) along the contour

   D. A deep borehole

   (1 mark)

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9. Question 9

   1 mark

   A farmer on a gently sloping piece of land in Kitui keeps losing rainwater and topsoil whenever it rains heavily. A Grade 7 learner advises building a structure that runs across the slope to slow water and hold soil. Which structure is being described?

   A. A vertical drainage channel down the slope

   B. A contour terrace

   C. A raised footpath

   D. A deep storage pit at the lowest point

   (1 mark)

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10. Question 10

    1 mark

    A learner marks out a line across a hillside so that every point on it is at the same height above sea level before digging a retention structure. This line is called a:

    A. Ridge line

    B. Diagonal line

    C. Base line

    D. Contour line

    (1 mark)

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11. Question 11

    3 marks

    State three safety precautions a learner should observe when digging a water retention trench in the school garden.

    (3 marks)

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12. Question 12

    1 mark

    A farmer in a semi-arid part of Kitui wants to trap and store rainwater running off a sloping field for use by crops during dry spells. Which water retention structure is MOST suitable for this purpose?

    A. Drainage channel

    B. Contour ridge for footpaths

    C. Water pan

    D. Terrace riser

    (1 mark)

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13. Question 13

    5 marks

    Describe how a learner can construct a simple zai pit for planting maize in a semi-arid area.

    (5 marks)

    Marking scheme

    Mark out the position; dig a pit about 60 cm wide and 20-30 cm deep (1); place the excavated soil on the lower side to form a ridge/bund (1); mix topsoil with manure/compost and put it at the bottom of the pit (1); plant seeds in the pit; the pit collects and holds run-off water around the seeds (1); several pits are spaced across the slope following the contour (1). Max 5 marks.

14. Question 14

    1 mark

    Which tool would a learner use MOST appropriately to dig a trapezoidal cross-section trench when constructing a water retention structure?

    A. Spade

    B. Watering can

    C. Wheelbarrow

    D. Pruning saw

    (1 mark)

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15. Question 15

    4 marks

    Learners in a school in Machakos were asked to construct water retention structures to conserve water for their crop garden.

    (a) State two water retention structures they could construct.

    (b) Explain two importance of constructing such structures in a dry area.

    (4 marks)

    Marking scheme

    (a) Any two: water pan; zai pits; terraces; contour ridges/bunds; cut-off drains; retention/infiltration trenches (2 marks). (b) Any two, explained: trap and store run-off/rainwater for use by crops during dry spells; reduce soil erosion by slowing run-off; increase water infiltration into the soil raising the water table; conserve moisture around plant roots to improve yields (2 marks).

16. Question 16

    1 mark

    A group of learners planted grass on the edges of a newly dug water retention structure. The MAIN purpose of the grass is to:

    A. Attract rainfall

    B. Provide fodder for animals

    C. Bind the soil and prevent the walls from eroding

    D. Mark the boundary of the structure

    (1 mark)

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17. Question 17

    4 marks

    An A-frame is used to mark out contours before constructing terraces.

    (a) State one material needed to make an A-frame.

    (b) Explain how the A-frame is used to identify points on the same contour.

    (4 marks)

    Marking scheme

    (a) Any one: two long sticks/poles of equal length, one cross-bar/stick, string, a stone/weight, nails or ties (1). (b) Tie the two poles at the top and join them with a cross-bar to form letter A; hang a string with a stone from the apex; first calibrate on level ground and mark where the string crosses the cross-bar (centre point) (1); move the frame across the slope, adjusting each leg until the string hangs on the marked centre point (1); the two feet are then at the same level/on the same contour, and the point is pegged (1). Max 3 for (b).

18. Question 18

    1 mark

    A Grade 7 group is making a structure to harvest and store rain water from a roof for use in the dry season. Which structure are they MOST likely constructing?

    A. A water pan or storage tank fed by gutters

    B. A compost heap

    C. A seedbed

    D. A chicken run

    (1 mark)

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