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Drainage Basins and Watersheds

When rain falls into a valley and on the hills around the valley, it flows down. This often creates a stream or river. Sometimes, overflow can occur and some of the water from the stream or river needs to move somewhere else. This is where drainage basins and watersheds come in. 

An image of a valley with hills on either side and a stream in the middle.

When precipitation falls into a valley and on surrounding hills, it flows down. This can create a stream.

What is a Drainage Basin?

A drainage basin is an area of land that is drained by a river. Often, small drainage basins combine with one another. This creates larger and larger networks of drainage basins. These combine into one large drainage basin. 

What is a Watershed?

If you are currently sitting, stand up and look down. You are standing on a watershed. The area of land that contributes water to a stream or river is a watershed. Watersheds range in size. They can be as small as a footprint or as large as the Chesapeake Bay, which drains into the Atlantic Ocean. 

An image of streams converging into a larger river.

The area of land that contributes water to a stream or river is called a watershed.

Small watersheds generally contribute to streams. The water from larger watersheds come together to form large rivers. From there, the watershed connects these streams and rivers to a common place. These can include the outflow of a reservoir, mouth of a bay, or any point along a stream channel. Some larger watersheds can contain many small watersheds.

The Continental Divide

Ridges and hills separating two watersheds are called drainage divides. A popular example of this is in North America. A massive drainage divide separates the water that flows toward the Pacific Ocean from water that drains towards the Gulf of Mexico and the Atlantic Ocean. This is the Continental Divide. 
For more information on drainage basins and watershed, watch this video:

Other Great Resources:

Kiddle Encyclopedia Entry on Drainage Basins: https://kids.kiddle.co/Drainage_basin

What is a Watershed: https://www.milwaukeeriverkeeper.org/whats-a-river-basin-whats-a-watershed/

USGS on Watersheds: https://water.usgs.gov/edu/watershed.html

 Written by: Lindley Lund