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Jefferson County,
Missouri
Est. 1818
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Watersheds and Stream Order

Diagram of a Watershed

The Environmental Protection Agency defines a watershed as "the geographic region within which water drains into a particular river, stream, or body of water."  The boundary of a watershed can be identified by looking at ridges that surround the rivers.  The higher elevations of mountain ridges and peaks define the boundary between watersheds. The diagram at the right was produced by Lane Council of Governments: Source: US EPA.

The watershed contains water in different forms - a tributary, a main channel, and a delta.  A tributary is a small stream or creek.  The watershed is made up of networks of tributaries, each of which flows into a larger stream.  They are identified by stream order, determined by the order of other tributaries that have contributed to their flow.  The start or headwaters of a stream, with no other streams flowing into it, is called the first-order stream.  Two first-order streams flow together to form a second-order stream.  Second-order streams flow into a third-order stream.  This labeling continues until the streams deposit their water into a larger body of water, such as an ocean or a bay. 

 

Stream Orders


Identifying stream order can be useful when studying water quality.  What happens to tributaries affects higher-order streams.  Higher order streams can contain pollutants that originate in each of its contributing tributaries.

(This information was taken from the BioSITE Curriculum website.)