A river is a stream of water that flows through a channel in the surface of the ground. The passage where the river flows is called the river bed and the earth on each side is called a river bank. A river begins on high ground or in hills or mountains and flows down from the high ground to the lower ground and it happens because of gravity. A river begins as a small stream and gets bigger the farther it flows. The start of a river is called the source or head water. The part of the river that is near the source is called a young river. A young river is often in a V shaped river bed and flows quickly downhill over stones and around big rocks. Young rivers often have lots of small waterfalls and rapids. As the rivers travel downhill they begin to erode the ground taking small bits of soft rock and soil. The source of a river may be a spring often on a hill and mountain or glacier or another high place. A spring is water that flows out from under the ground. The source of a river may be a lake where lots of water from small streams gathers when it rains or snows. A river may begin in mountains where there is snow. The melting snow runs together to form a small stream that runs down the mountain. As more little streams run in the main stream gets bigger until it forms a river. Some rivers flow from hills where there is no snow but lots of rain. Some rivers only flow after there has been rain near the head water. The middle part of a river is called a mature river. A mature river makes a riverbed that is U shaped. It might be very deep and run fast. It sweeps over small rocks and boulders and makes big turns around hills and mountains. It is much wider than a young river but not as wide as an old river. To cross over a mature river people use bridges. Many cities and towns are built on the banks of mature rivers. Many farms that keep animals such as dairy cows and sheep are along mature rivers because the animals can drink from the river every day. A river usually ends by flowing into an ocean or lake or a bigger river. The place where the river flows out into a bigger body of water is called the mouth of the river. As a river flows towards its mouth the countryside around the river often changes from hilly to flat. As it flows over the flat land the river becomes wider and slower. A wide slow river is called an old river. An old river often floods across the land after there is lots of rain at the headwaters. An old river slowly builds up its banks on either side the high banks are called levees. An old river often meander twists and turns and after a flood it leaves lakes behind which are called oxbows or billabongs. Old rivers are the most useful type of river for growing crops. Corn and rice and fruit and cotton and sugar are some of the crops that are grown near old rivers.