Tributary: Definition, Systems & Examples

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  • 0:02 Background to Tributaries
  • 1:15 Definition of Tributaries
  • 2:07 Tributary Systems
  • 3:12 Some More Examples of…
  • 4:47 Lesson Summary
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Lesson Transcript
Instructor: Suzanne Rebert

Suzanne has taught college economics, geography, and statistics, and has master's degrees in agricultural economics and marine affairs (marine resource management).

A river is rarely as simple as it looks! Most rivers are tributaries and belong to tributary systems. In this lesson, you'll learn about these important natural systems and take a quiz to check your understanding.

Background to Tributaries

Imagine that you're the powerful ruler of an ancient empire. You spend a major part of each day welcoming the leaders of all the smaller nations and tribes within your realm. As you gaze out at the visitors, you see endless lines of them coming to see you with rich gifts to lay at your feet. All these people are bringing you a share of the resources, products, and treasures of their lands. Your visitors are here to pay tribute to you, and this tribute that flows into your palace every day makes you a strong ruler, able to do amazing things.

Like this ruler, a river or lake receives water and other resources from smaller rivers and streams all over its 'empire,' or watershed. These smaller waterways leading to the larger water body are known as tributaries. You can think of them as paying 'tribute' to the larger river or lake, bringing it the precipitation, sediment, and nutrients that originated farther upstream. These 'gifts' make large rivers even more powerful and help large lakes support even bigger ecosystems.

Definition of Tributaries

A tributary is a river or stream that flows into a larger river or a lake. When you think about it, almost every river flows into another river or a lake, and most of the rest flow into an ocean! Since all of this water is part of the earth's water cycle, most bodies of water are both receivers and givers of water to some other body. Evaporation from the world's oceans (and from isolated basins, like the Great Salt Lake, Caspian Sea, and Dead Sea) becomes precipitation that keeps the whole cycle moving.

Wabash River watershed

Take a look at the above image. This is the tributary system of the Vermilion-Wabash River in Indiana. This system is a tributary of the Ohio River, which is in turn a tributary of the Mississippi.

Tributary Systems

A tributary system includes all the streams that collect water over an area and empty it into a particular river or lake. Each tributary collects the precipitation that falls within its own watershed. It doesn't have to go anywhere to collect the water, though - gravity does all the work because the boundaries of a watershed are determined by elevation.

For example, the water that flows into the Missouri River ends up there because it's the easiest river to get to. All the water has to do is flow downhill. The Missouri River has many tributaries, and it, in turn, is a tributary of the Mississippi River. Just by 'going with the flow' in this tributary system, a raindrop can get from eastern Montana (in the upper Missouri watershed) all the way down to the Gulf of Mexico and then the Atlantic Ocean. But what if the raindrop lands in western Montana? If it falls west of the Continental Divide, it will enter a tributary system that takes it to the Pacific Ocean instead!

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