Do you know where does all the rain go? Two-thirds of the surface of the globe is covered by water. This water is found in the world’s oceans and much of the fresh water which is essential for all life has evaporated forms them.
But what happens to all the rainwater that falls on land? Some are evaporated straight back again, some soak into the ground, some is taken up by the plants of the earth. All the water is the Earth’s rivers and streams, however, comes from meteoric water, that is water that falls from the atmosphere as rain.
Of course, we use a great deal of the rain which falls onto the land surface, not only for washing and drinking but also in our industries and as a mean of transport and disposal of our waste products.
Here is another case where man’s demands on the resources of the planet are beginning to show signs of wear, as you would soon notice if you were to look at the dead, stinking waters of many of the rivers in industrial regions of the United States and elsewhere, where fish can no longer live.
The rain which eventually forms rivers falls onto hills where it first runs downwards as a sheet of water. Soon the water cuts out channels which then come together to form larger streams and rivers. The way in which a river and its valley develop, depends upon the amount, frequency, and violence of the rain, the type of rocks and the slope upon which it falls. It depends also on the plant cover.
When the river flows downhill on a land surface which has been newly uplifted by earth movement, it is called a consequent stream, and the smaller streams which run down its valley sides to join it are called tributaries or subsequent streams. In this way, a river system is formed.
We mentioned that some of the rain soaks into the ground it becomes groundwater. Most rocks, such as sandstone, have many tiny holes between the grains which allow water to pass through them, and they may also be cracked which aids the flow.
Other rocks, like clay, (clay is certainly a rock) do not allow the passage of water, and act as a barrier, so that water may build up against it forming an aquifer. The top surface of this water-bearing layer of rocks (resembling a wet sponge) is called the water table.
We drill our wells providing us with much of our water into this layer, but of course, if we take out more water than is flowing into the aquifer, the well eventually run dry.
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