Maria is a teacher and a learning specialist and has master's degrees in literature and education.
A river is a large, flowing waterway. Rivers primarily carry freshwater, which is why people throughout history have made their homes by them. From the Nile River in northern Africa to the Thames flowing through London, rivers have provided people with drinking water, water for crops and easy ways to transport people and goods.
How Rivers Begin
Rivers begin as humble trickles of water from lakes and springs or from melting snow and glaciers. Since they start in higher elevations, rivers can't help but travel downhill, taking in additional streams called tributaries along the way. The Amazon River, one of the longest in the world at over 6,259 kilometers (3,903 miles), is fed by over 1,000 tributaries.
Thanks to gravity, rivers grow in size and speed as they flow downhill. A current is the rate and strength of a river's movement. Rivers, of course, move more than just water. They also carry silt and other bits of earth called sediment. Along with a river's water, sediment shapes the land in its path. For millions and millions of years, the Colorado River has slowly shaped a section of the Rocky Mountains into a steep V-shaped valley called the Grand Canyon.
Humans build dams across rivers to store water in human-made lakes called reservoirs. Since reservoirs usually hold fresh water, that water can be put to farming and household use. There are a few bigger dams, including the Hoover Dam on the Colorado River, where the power of the water current is used to create electricity.
Where Do Rivers Go?
Rivers continue their journey out of the mountains onto more gently-sloping land. Because this terrain is more easily eroded, rivers are able to carve out curved shapes called meanders. Sometimes a meander will be cut off from the rest of the river by sediment, creating a body of water referred to as an oxbow lake.
As rivers move to flatter land, their currents slow even more. Flood plains are created when rivers flow over their banks onto a large, flat area of land. While flooding doesn't sound ideal, flood plains benefit from the additional sediment and water. The San Joaquin Valley in Northern California owes its rich, fertile soil to the large flood plain created by the San Joaquin River.
Rivers eventually flow into other bodies of water like lakes or oceans. With nowhere else to go, the sediment carried by the river is deposited at the river's end, forming a landform called a delta. Deltas develop over time, taking their shape from the unique combination of a river's water current mixed with other forces such as tides and waves. Deltas can be triangular in shape, like the Nile River Delta, or shaped like a bird's foot like the Mississippi River Delta.
After you've completed this lesson, you should be able to:
- Define river and recall how rivers form
- Explain what meanders, oxbow lakes, flood plains and deltas are
- Identify the importance and functions of rivers to people and animals
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