|Better Farming Series 28 - Water: Where Water Comes from (FAO, 1981, 31 p.)|
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
First printing 1981
© FAO 1981
The FAO Better Farming Series is essentially based on the Cours d'apprentissage agricole prepared in the Ivory Coast by the Institut africain de dloppement nomique 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 to 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.
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.
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.
Finiding water in the ground
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.
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.
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.
17. When it rains, all of the water may not go into the ground. Some of it may stay on the surface.
Water staying at 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.
Water at surface: staying or running along
19. The water that lies on the surface is called surface water. The water that runs along the surface is called run- on water.
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.
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.
Plants use water
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.
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.
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.
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.
Little rain falls for long time
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.
Much rain falls for short time
6. 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.
Much water sinks in some kinds of soil
In other kinds of soil only a little water sinks in.
Less water sinks in other kinds of soil
38. In some kinds of soil which have a rocky surface, no water at all may sink in.
No water sinks in some kinds of soils
39. If the structure of the soil is good, water sinks in well. Soil with a good structure can held 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 sold 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.
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 around.
Rainwater sinks into around
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 held more.
All rainwater goes in the ground
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.
Very little water sinks in 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.
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 held and much of the water will stay on tile surface.
52. When there are plants present, their limbs, branches and leaves help to slow the water as it falls.
Plants 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.
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.
The parent rock
59. If the soil has very much sand in it, water sinks in quickly and easily.
Water sinks quickly
60. Little water stays on the surface of sandy soils. Because sand has poor texture sandy soils held little water.
61. If the soil has very much clay in it, water does not sink in quickly or easily.
Water does not sink quickly
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 held 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 seeps down into 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.
Little water is holded in the subsoil
68. Sometimes the subsoil is soft and has a structure that holds water well.
Subsoil holds water well
69. If the parent rock that lies below the subsoil is solid and unbroken, water stays on top of the rock
Water stays on top of the parent 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.
Water sinks deep into the rock
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.
Water runs 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.
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.
A dug well
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.
A drilled well
81. Sometimes a water- carrying layer comes to the surface, as in hilly land, and water flows out of the ground.
Water flows out of the ground
2. 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.
86. Water on the surface of the ground comes from both groundwater and from surface water run- off.
Water on the surface
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.
Water lies above the surve of the ground
90. When it does not rain, there is less water in the ground and the water table becomes lower.
There is less water in the ground
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.
The effect is hard to see
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.
The effect is easy to see
96. We can find surface water in
· swamps, ponds and lakes;
· streams and rivers.
97. When surface water gathers in low land and the water cannot flow away, it forms swamps, ponds and lakes.
Surface water gathering in low land
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.
102. Streams and rivers are sources of surface water which has gathered in low land where the water flows away.
Streams and rivers
103. Like swamps, ponds and lakes, the level of water in a stream or river may not stay the same all the time (see Hems 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.
Building an earth dam