SOIL

Erosion
There was once a good farmland. A large family lived well on it. Now the land is useless. What happened? The farm was cut to pieces by rain water that cut deeper and deeper grooves in the land. the good topsoil was washed down into these grooves and carried away. We say the topsoil has been eroded. When running water gets to work on sloping land, the soil is washed away in deep gullies. This is called gully erosion. On almost level land, the soil is washed away in thin layers. This is called sheet erosion. When the topsoil is lost by erosion, it leaves the subsoil exposed. Subsoil is usually rocky and sandy, with very little of the minerals that plants need to grow. Gully erosion has broken the field into narrow pieces. Farm machines cannot work on this broken and eroded land. The full, clear stream that ran through the meadows is now a muddy trickle of water that dries up in the summertime. The fish have died and no cattle can drink from it. This farm is useless now. Erosion by flowing water made it so. There are many ways of protecting soil from water erosion.
Plants and Erosion
Plants soak up water so that it does not pour down the slopes in big, muddy streams. Dead leaves help prevent water erosion, too. The floor of a forest is usually covered with dead leaves which have fallen from the branches above. The leaves protect the soil from the force of falling water. They also act like sponges. They hold back the water and let it trickle off slowly into the basin. Wherever plants grow, there is a tangle of roots in the soil.
Protecting Soil
There is a second way roots help the soil. As roots grow down into the soil, they push the soil aside and create spaces in it. Roots make the soil more porous. Water falling on porous soil sinks into the soil. It will not flow along the surface, carrying away rich topsoil. Plants and soil are partners, in a way. The plants get minerals and water from the soil. The soil is protected by the plants. Without soil plants could not grow. Without plants the soil could not stay in place during heavy rains or windstorms. Sometimes this protection is taken away from the soil.
1. It may happen when a farmer pulls up a crop and leaves the soil bare.
2.It may happen when a lumberman cuts down all the trees on a hillside, or when a forest fire kills all the plants on sloping land.
3. It may happen when a farmer plants a sloping field in such a way that rainwater can wash the soil away.
4. It may happen when a farmer continues to plant crops that use up the minerals of the soil faster than they are replaced. Then crops can't grow and the soil is left bare.

WATER

Controlling Water
Heavy rains may wash away unprotected soil. Rain, the source of precious water, may often do much damage in other ways. When winter snows melt and spring rains fall, rivers may become swollen and overflow their banks. Farms and cities may be flooded. Power and communication are sometimes interrupted by rushing floods. Thousands of people may be left homeless and hungry. Flood water can cause great damage.
            Not enough water can be just as bad. Crops may dry up. Cattle may sicken and die of thirst. Forests may become danger spots where one match can start a huge forest fire. Rivers may dry up and fish die. Not enough water can cause a great deal of trouble.
Storing Water
We can build dams across rivers. Then we can store the water when we have too much of it and let it out as we need it. A dam blocks the flow of water, so that it fills up higher and higher and forms a huge lake. A gate in the dam can be opened to let out just as much water as we need. In times of heavy rains and melting snows, more water than we can use flows into the man-made lake. The lake fills up higher and higher with stored-up water.
            In dry seasons the flow of water into the lake is very little, or none at all. Then water that was stored up in the rainy season is let out as it is needed, and the lake becomes lower and lower. In dry seasons farmers can use the stored water to irrigate their land. Water is let out of man-made lakes into irrigation canals. Stored water is often piped into cities and towns for drinking water. In some water systems, the water is sprayed through the air. This helps oxygen from the air to mix with the water, giving it a fresh, clean taste. Many water storage reservoirs aerate water before it is sent to homes.
Energy from Stored Water
The water dams store can be put to work. As the water flows down, it strikes the blades of huge waterwheels called turbines. The turbines are connected by shafts to electric generators. As the generators are turned, they send out electric current to cities, farms, and factories. Stored water can provide energy for making electricity.
Levees
There is another way to prevent floods. The banks of rivers can be built up higher. In times of heavy rains and melting snows, the rivers may become swollen with too much water. They rise higher and higher, but if the banks are built up high enough, there is less danger of overflow. These built-up river banks, made of earth or concrete, are called levees. But levees that protect the land one year may not prevent floods the next year. As the river rushes down the sides of mountains, it picks up sand and soil. When the water reaches more level places, it slows down and drops the sand and soil. These materials are called silt. The silt settles down on the river bottom, heaping up bit by bit. As the bottom heaps up, there is less room for water above it. Each year the river bottom gets higher and the levees must be built higher.
Underground water
Not all rainwater tears up land. Not all rainwater falls into overflowing lakes and streams. A large amount of rainwater falls on land. If the land is porous, the water soaks in.
Water Table
Many kinds of stone are nonporous. But other stones are porous. They absorb and hold water. When water soaks into the earth, it seeps down through the porous sand and soil and into the porous rocks. When water reaches nonporous rock, it stops. When more water seeps down, it piles up on top of the water already there. The top of this layer of water is called the water table.
High Water Tables
There is underground water almost everywhere in the world. Where the water table comes close to the surface, you have a high water table. Where there is a lot of rainfall there is usually a high water table. It is also usually high where the nonporous rock is near the surface and rainwater cannot go down far. Where the water table is very close to the surface, the ground is wet and soggy. We have a swamp. Swampland is not good for farming. Only certain plants can grow in soggy land. But swamps can be drained and made into good farmland. Pipes or trenches can be used to carry the water into a nearby lake or river.
Low Water Tables
Some land is not good for farming because the water table is too low. Such land is called a desert. In a desert, the soil is dry and sandy. Rain rarely falls to raise the water table level. Yet even in most parts of a dry desert, we can find water if we dig deep enough. In many places in the world the water table is not too high or too low. In these parts of the world there is a good supply of water for plants and animals and people. In these places people do not have to dig very deep to get to the water table.
Wells
Holes that are dug down to reach into the underground water table are called wells. Wells are lined with stones, bricks, or tile pipes. Very deep wells are lined with steel pipes. Wells that go deep beneath the ground need pumps to bring up the water.
Artesian wells
Some rocks are more porous than others. Rain that falls on these rocks is partly absorbed. Sometimes two layers of nonporous rock lie above and below the porous layer. Water entering the porous layer at the surface seeps down through the porous rock. The surrounding nonporous layers cannot absorb the water. This is called an artesian formation. People can drill wells that reach the water stored in the porous rock. Artesian formations may cover hundreds of miles. An artesian well can be located far from the place where the water entered the porous rock. When water can go no further, water piles up. The water at the bottom is under great pressure. When a pipe reaches into the underground water, the water pressure forces the water to flow upward.
Safe Drinking Water
When water is not clean and pure, we say it is polluted. Your Board of Health tests drinking water to be sure it is not polluted. Inspectors may check to see if:
1. Polluted surface water is seeping down from homes into underground water.
2. Sewage pipes are carrying germ-filled wastes into streams.
3. Factories are pouring waste and chemicals into streams.
4. People are polluting town water by swimming and boating.
Filtering Water
Most communities have some kind of water purification system. Sometimes filtering systems are used. Such systems let the water strain through and hold back solids. Water is allowed to filter through layers of sand and gravel. However, some of the smaller disease germs can get through a filter of even the finest sand.
Killing Germs in Water
The look and taste of water cannot always tell you if it is safe. You cannot see typhoid germs, for example. But one sip of water containing them is enough to make you violently ill. Some purification is done with chemicals. This is usually done by adding small amounts of a chemical called chlorine to the water. The small amounts of chlorine in the water are quite harmless for people to drink. You cannot see chlorine kill tiny germs.