8.9: Streams and Rivers

What makes this river so much fun to raft?

Whitewater rafting is a popular recreational activity. The river is fast because its in the mountains traveling downhill. There is a lot of water from snow melt higher up. Sometimes water is added from springs. Did you ever go whitewater rafting? It's fun!

What Are Streams and Rivers?

A stream is a body of freshwater that flows downhill in a channel. The channel of a stream has a bottom, or bed, and sides called banks. Any size body of flowing water can be called a stream. Usually, though, a large stream is called a river.

Features of Streams and Rivers

All streams and rivers have several features in common (Figure below). The place where a stream or river starts is its source. The source might be a spring, where water flows out of the ground. Or the source might be water from melting snow on a mountain top, like the stream pictured below (Figure below). A single stream may have multiple sources.

A stream flows fast and steep where it originates in the mountains. This stream, in Glacier National Park in Montana, is coming from snow melt.

Water in a stream flows along the ground from higher to lower elevation. What force causes the water to keep flowing?

A stream or river probably ends when it flows into a body of water, such as a lake or an ocean. A stream ends at its mouth. As the water flows into the body of water, it slows down and drops the sediment it was carrying. The sediment may build up to form a delta.

Several other features of streams and rivers are also shown above (Figure above).

• Small streams often flow into bigger streams or rivers. The smaller streams are called tributaries. A river and all its tributaries make up a river system.
• At certain times of year, a stream or river may overflow its banks. The area of land that is flooded is called the floodplain. The floodplain may be very wide where the river flows over a nearly flat surface.
• A river flowing over a floodplain may wear away broad curves. These curves are called meanders. Pictured below is an example of this (Figure below).

A river meanders across an estuary in South Carolina.

River Basins and Divides

All of the land drained by a river system is called its basin, or watershed. One river system’s basin is separated from another river system’s basin by a divide. The divide is created by the highest points between the two river basins. Precipitation that falls within a river basin always flows toward that river. Precipitation that falls on the other side of the divide flows toward a different river. A continental divide separates rivers that flow into different oceans.

Pictured below are the major river basins in the U.S. (Figure below).

River basins in the U.S.

Summary

• A moving body of water of any size is a stream. A river is a large stream.
• A tributary begins at its headwaters on one side of a divide. Two tributaries come together at a confluence.
• A river ends at an estuary. If the river drops sediment, it may create a delta.

Review

1. Describe the features of a river from where it begins to where it ends.
2. What happens to two drops of water that fall on opposite sides of a divide?
3. Why does a tributary not cross over a divide?

Explore More

Use the resources below (start at 0:49) to answer the questions that follow.

1. What is the tributary system? What does that mean in simple English?
2. What does a tributary flow into?
3. What do the tributaries in the Rocky Mountains near Woodland Park feed into? What does that flow into? And what does that flow into? And finally what does that flow into?
4. At what point does a tributary meet a river?
5. What is the biggest trunk river in the U.S.?
6. What is the end of the Mississippi River in the Gulf of Mexico?
7. What is a delta?
8. What is found in a delta?
9. How did a delta get its name?