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Streams and Watersheds - Stream Classification

Method 1 = In relation to other streams

One way to classify streams is by looking at where they lie in relation to other streams in the watershed (Figure 1-3).

  • First order streams ("1" in Figure 1-3) can be thought of as "starter" streams. Most often they are located in the upper parts of a watershed, and water enters them from over land, seeping groundwater, or springs rather than by flowing in from another stream.

  • Second order streams ("2" in Figure 1-3) are fed by two or more first order streams.

  • Third order streams ("3" in Figure 1-3) are formed by the joining of two or more second order streams. Stream orders above 7 are considered large rivers. The highest order stream in North America, the Mississippi River, is a 12th order stream.

Figure 1-3
Streams higher up in a watershed tend to be smaller and of lower order because they are the recipients primarily of seeps and springs and only limited over land flow.

The higher the stream order--the more streams that feed into it--the larger the size of the stream. In general, the higher the order (for example, 3rd order versus 1st order), the more likely the stream is to be influenced by events occurring higher up in the watershed. This also means the more of the watershed you control, the greater the impact--positive or negative--your management decisions have.