Connecticut Water Trails Program

Watersheds

What Is Stream Order?

Stream ordering is one important method used to describe the components of a watershed and to help look for relationships in its physical and biological attributes. It classifies streams in relation to tributaries, drainage area, total length and age of water. Although there are a few different ordering methods, those of Strahler (1952) are widely accepted. The rules are as follows:

1. The smallest tributaries (i.e., streams without tributaries) are designated first order;

2. Two first-order streams combine to form a second-order stream, two second-order streams combine to form a third-order stream, etc.;

3. When a stream of higher order (e.g., 3) combines with a stream of lower order (e.g., 2) the resulting channel is given the higher order (3). Streams of lower order entering higher-order channels do not influence the order of the channel.

It is important to note that stream order is sensitive to the scale of the watershed map. For example, small streams may be missing on a large-scale map, thus changing the ordering for that map. Most stream orderings also do not include intermittent streams, which are very small streams that form a continuum among headwaters but only occasionally carry water.

Rivers are often roughly grouped into three general categories based on their order: headwaters (stream orders 1 to 3), medium-sized streams (orders 4 to 6) and large rivers (orders greater than 6). These categories are often used when describing general characteristics of the river continuum.

Please Send Feedback To Connecticut Water Trails Association

© 2011 Connecticut Water Trails Association