FAO BETTER FARMING SERIES

Twenty-eight titles have been published in this series, designed as handbooks for agricultural education and training. They may be purchased as a set or individually.

FIRST YEAR

1. The plant: the living plant; the root

2. The plant: the stem; the buds; the leaves

3. The plant: the flower

4. The soil: how the soil is made up

5. The soil: how to conserve the soil

6. The soil: how to improve the soil

7. Crop farming

8. Animal husbandry: feeding and care of animals

9. Animal husbandry: animal diseases; how animals re-produce

SECOND YEAR

10. The farm business survey

11. Cattle breeding

12. Sheep and goat breeding

13. Keeping chickens

14. Farming with animal power

15. Cereals

16. Roots and tubers

17. Groundnuts

18. Bananas

19. Market gardening

20. Upland rice

21. Wet paddy or swamp rice

22. Cocoa

23. Coffee

24. The oil palm

25. The rubber tree

26. The modern farm business

27. Freshwater fish farming: how to begin

28. Water: where water comes from

Better Farming Series    28

Water

Where water comes from

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS

Rome 1981

FAO Economic and Social Development Series No. 3/28

First printing 1981

P-69
ISBN 92-5-101086-2

© FAO 1981

Contents

1. Preface

2. Outline Of Course

3. Why we study water

1. Rainfall

2. Water in the ground

3. The water table

4. Water on the surface

5. Evaporation

6. Transpiration

7. The process begins again

4. When rain falls

1. How much rain falls

2. Kind of soil

3. Slope the land

4. Plants

5. Water in the ground

1. Water and the soil

2. Water and the subsoil

3. Water and parent rock

6. Where to find water in the ground

1. Wells

2. Springs

7. Water on the surface

1. Groundwater can become surface water

2. Surface water run-off

8. Where to find surface water

1. Swamps, ponds and lakes

2. Streams and rivers

PREFACE

The FAQ Better Farming Series is essentially based on the Cours d’apprentissage agricole prepared in the Ivory Coast by the Institut africain de développement économique et social for use by extension workers in contact with illiterate or semi-literate farmers. The approach is deliberately a general one, the intention being to constitute basic prototype outlines, to be supplemented in each area according lo local conditions of agriculture.

Many of the booklets deal with specific crops, while others, such as this one, are intended to give the farmer information concerning the general agricultural context, and thus to allow him to gain some understanding of why he does what he does, so that he will be able to do it better.

Adaptations of the series, or of individual volumes in it, have been published, among others, in Amharic, Arabic, Bengali, Creole, Hindi, Igala, Indonesian, Kiswahili, Malagasy, SiSwati and Turkish. This impressive list is some indication of the success, and also of the value, of the series. This volume is based on FAO Training Series No. 4/1, Water for Freshwater Fish Culture, prepared by the Inland Water Resources and Aquaculture Service, Fisheries Department, FAO.

Requests for permission to issue this manual in other languages and to adapt it according to local climatic and ecological conditions are welcomed. They should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy.

OUTLINE OF THE COURSE

• Why we study water

Rainfall

Water in the ground

The water table

Water on the surface

Evaporation

Transpiration

The process begins again

• When rain falls

How much rain falls

Kind of soil

Slope the land

Plants

• Water in the ground

Water and the soil

Water and the subsoil

Water and parent rock

• Where to find water in the ground

Wells

Springs

• Water on the surface

Groundwater can become surface water

Surface water run-off

• Where to find surface water

Swamps, ponds and lakes

Streams and rivers

WHY WE STUDY WATER

1. Water is necessary for life. We need water for ourselves and our families to drink and to wash in,

to give to our animals to drink

and to make our crops grow.

2. We should know about water so that we can use water better.

3. This is very important if we do not have much water for long periods of the year.

Rainfall

4. The water we use for ourselves, for our animals and for our crops comes from the rain which falls from the clouds.

5. Even the water in swamps, lakes and streams comes first from the rain. For us, rainfall is very important.

6. In some places it rains very much but only during one or two seasons of the year. During the seasons when it does not rain, we may not have enough water.

7. We must learn how to store water when it rains so that we can have water when it does not rain.

8. In some places it rains very little and only at one season of the year.

In other places, hardly any rain falls at all.

9. In these places, we have too little water and we must learn to find water in the ground or to store water when it does rain to use later.

10. To help us know more about the water we use, let us see:

• what happens to the water that falls as rain;

• where water goes after it rains;

• where water can be found when it does not rain.

Water in the ground

11. When it rains, some of the water goes into the ground.

12. This water may stay near the surface or it may go very deep into the ground.

13. The water that goes very deep is called groundwater.

The water table

14. The level at which groundwater is found is called the water table.

15. If there is little groundwater, the water table becomes lower. If there is very much groundwater, the water table becomes higher.

16. If the water table becomes so high that it lies above the surface of the ground, it forms swamps, lakes and streams.

Water on the surface

17. When it rains, all of the water may not go into the ground. Some of it may stay on the surface.

18. Water which stays on the surface will either lie in one place, if the land is flat, or it will run along the surface, if the land is hilly.

19. The water that lies on the surface is called surface water. The water that runs along the surface is called run-off water.

Evaporation

20. At certain times water evaporates from the surface of the soil or from swamps, lakes or streams. It becomes water vapour.

21. We cannot see water vapour. We cannot use it. Water vapour rises into the air to form new clouds.

Transpiration

22. Water vapour is also given off by plants.

23. Plants use the water in the ground to live and grow, and as they live they breathe and give off water vapour from stems and leaves.

24. This is called transpiration.

25. Like vapour given off by evaporation, the water vapour from plants rises into the air to form new clouds.

The process begins again

26. The water we use comes from rain which falls from the clouds.

27. Some of the water stays on the surface. Some of the water goes into the ground and some of the water that goes into the ground may go very deep.

28. Some of the water evaporates from the surface of the soil or from swamps, lakes and streams and some of it is transpired by plants. It becomes water vapour.

29. The water vapour rises into the air to form new clouds.

30. The clouds give up the water vapour as rain and the process begins again.

WHEN RAIN FALLS

31. When it rains, some of the water sinks into the soil and some of the water stays on the surface or runs along the surface.

32. How much water sinks into the soil and how much water stays on the surface depends on several things. It depends on:

• how much rain falls;

• the kind of soil where the rain falls;

• the slope of the land where it falls;

• how many plants there are and what kind of plants they are where the rain falls.

How much rain falls

33. Whether rain goes into the ground or stays on the surface depends on how much rain falls and for how long it falls.

34. If a little rain falls for a long time, more water is likely to go into the ground.

35. If much rain falls for a short time, less water is likely to go into the ground and more will stay on the surface.

Kind of soil

36. Whether water goes into the ground or stays on the surface depends on the kind of soil where the rain falls.

37. In some kinds of soil, very much water sinks in.

In other kinds of soil only a little water sinks in.

38. In some kinds of soil which have a rocky surface, no water at all may sink in.

39. If the structure of the soil is good, water sinks in well. Soil with a good structure can hold more water.

40. The structure of the soil is good when it is made up of sand, clay and silt which are joined together by a mixture of clay and humus.

41. If the structure of the soil is poor, water does not sink in well. Soil with a poor structure holds less water.

42. The structure of the soil is poor when there is no humus and the sand, clay and silt are not joined together.

43. To understand better about good and poor soil structure, see Booklet No. 4, pages 24 and 25.

Slope of the land

44. Whether water goes into the ground or stays on the surface also depends on the slope of the land where the rain falls.

45. If the land is flat, rainwater is more likely to sink into the ground.

46. If the land is flat and the soil structure is good, all of the rainwater will go into the ground until the soil becomes so full of water that it cannot hold more.

47. If the land is flat and the soil structure is poor, water remains in pools on the surface. After a while, part of the water in the pools may sink slowly into the ground and the rest evaporates.

48. If the land is hilly, water will run off more quickly and very little may sink into the ground.

49. Hilly land with poor soil structure holds very little water. Hilly land with good soil structure holds more water. Land that is very hilly holds less water than land that is not very hilly.

Plants

50. Whether water goes into the ground or stays on the surface depends on the number, size and kind of plants that are growing there.

51. When rainfall is heavy and very much water falls in a short time, there may be too much water for the ground to hold and much of the water will stay on the surface.

52. When there are plants present, their limbs, branches and leaves help to slow the water as it falls.

53. Small plants with few leaves will slow rainfall less and more water will stay on the surface.

54. Large plants with many leaves will slow rainfall more and less water will stay on the surface. More water sinks into the ground.

WATER IN THE GROUND

55. The ground is made up of several different layers. To know how water goes into the ground, let us first look at these layers (see Booklet No. 4, pages 6 to 10).

56. The top layer is the soil. This layer may be very deep or it may be quite shallow. The roots of smaller plants get their water here.

57. Below the soil is the subsoil. The subsoil is much harder than the soil. The roots of larger plants and trees get their water here.

58. Below the subsoil we find stone or rock. This is called parent rock.

Water and the soil

59. If the soil has very much sand in it, water sinks in quickly and easily.

60. Little water stays on the surface of sandy soils. Because sand has poor texture sandy soils hold little water.

61. If the soil has very much clay in it, water does not sink in quickly or easily.

62. It takes a long time for water to go into clay soils and the more clay there is in the soil, the longer it takes. Because clay has good texture, clay soils hold very much water.

63. Some of the water that sinks into the ground is held in the soil.

64. Part of this water is used by plants and part evaporates from the soil at the surface.

65. When water is not held in the soil and used by the plants or evaporated from the surface, it seeps down into the subsoil.

Water and the subsoil

66. How fast and how deep water goes into the subsoil depends on the structure of the subsoil.

67. Sometimes the subsoil is very hard and holds little water.

68. Sometimes the subsoil is soft and has a structure that holds water well.

Water and parent rock

69. If the parent rock that lies below the subsoil is solid and unbroken, water stays on top of the rock.

70. If the rock layer is not too far below the surface, it is not hard to reach this water.

71. If the parent rock that lies below the subsoil is broken, water can sink deep into the rock and becomes hard to reach.

WHERE TO FIND WATER IN THE GROUND

72. We can find water in the ground

• in a water-carrying layer;

• at the level of the water table;

• on top of a solid rock layer;

• in a broken rock layer.

73. If there is a layer of sand, pebbles or small stones in the ground, sometimes water gathers there and begins to run through the layer.

74. This is called a water-carrying layer.

75. A water-carrying layer may lie near the surface or it may lie deep in the ground.

76. A water-carrying layer may be very thin or very thick.

77. A water-carrying layer may be very big or very small.

Wells

78. When the water table is not too deep in the ground, we may be able to dig a hole down to the level of the water.

79. This is called a well.

80. If the water table is very deep in the ground or if the water sinks into broken rock, we may be able to drill a deep well down to the level of the water.

Springs

81. Sometimes a water-carrying layer comes to the surface, as in hilly land, and water flows out of the ground.

82. This is called a spring.

83. How much water we can take from a spring depends on how much and how fast the water runs through the water-carrying layer and the slope of the layer.

84. During how much of the year we can take water from a spring depends on how much it has rained and over how big an area it has rained.

85. Some springs give water all year long and some springs give water during only one or two seasons of the year.

WATER ON THE SURFACE

86. Water on the surface of the ground comes from both groundwater and from surface water run-off.

Groundwater can become surface water

87. When it rains, water sinks into the ground and mixes with the water already in the ground.

88. When there is more water in the ground, the water table becomes higher.

89. If the land is low and the water table is high enough, it may lie above the surface of the ground. Then there is more surface water.

90. When it does not rain, there is less water in the ground and the water table becomes lower.

91. Then there will be less surface water. This can be seen in dry times in swamps, lakes and streams.

92. The effect of groundwater on surface water is hard to see for it happens very slowly.

Surface water run-off

93. When it rains, water which does not sink into the ground runs over the surface into low land.

94. When there is very much rain, more water runs over the surface and low land quickly fills with water. This can be seen during wet seasons in swamps, lakes and streams.

95. The effect of run-off on surface water is easy to see for it happens very quickly.

WHERE TO FIND SURFACE WATER

96. We can find surface water in

• swamps, ponds and lakes;

• streams and rivers.

Swamps, pond and lakes

97. When surface water gathers in low land and the water cannot flow away, it forms swamps, ponds and lakes.

98. The level of water in a swamp, pond or lake may not stay the same all the time.

99. When there is little rain, the level of water is lower.

100. When there is much rain, the level of water is higher.

101. If the water table is very near the surface in a place where water cannot flow away, we can dig a pond where we can go for our water.

Streams and rivers

102. Streams and rivers are sources of surface water which has gathered in low land where the water flows away.

103. Like swamps, ponds and lakes, the level of water in a stream or river may not stay the same all the time (see Items 109 and 110, this Booklet).

104. We can make a better water source in a stream by building an earth dam to store water so that we can use it later.

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