Introduction

This module introduces the basics of the Rosgen classification system, a widely-used method for classifying streams and rivers based on common patterns of channel morphology. The text and visuals presented here are copyrighted material reproduced by permission from the following source:

Rosgen, D.L. and H.L. Silvey. 1996. Applied River Morphology. Wildland Hydrology Books, Fort Collins, CO

This module is a significantly abbreviated version of Chapters 4 and 5 from this publication, and includes only the basics of the Rosgen classification. Readers are referred to the original text for more detail. Additional information on stream stability can be found at the web-based assessment framework Watershed Assessment for River Stability and Sediment Supply (WARSSS), which uses this classification system. More information on stream structure is available at the Watershed Academy Web module Stream Corridor Structure.

Classification systems are used to organize entities into sets on the basis of their similarities or relationships. The main purpose of classifying is to minimize variation by recognizing definable groups with similarities, and increase one's knowledge about a member of such a group by observing the patterns characteristic of the group in general. Often, environmental classifications are based on measurable attributes of physical structure or pattern. Structure, in turn, is usually the result of physical processes and thus structurally-based classification categories are often related to natural processes or functions. Management decisions, as a rule, need to consider and be based on these natural processes or functions to be effective.

The reason for classifying streams on the basis of channel morphology, or form, is to aid the understanding of stream condition and potential behavior under the influence of different types of changes. Specific objectives of the Rosgen stream classification include:

• Predict a river's behavior from its appearance;
• Develop specific hydraulic and sediment relationships for a given stream type and its state;
• Provide a mechanism to extrapolate site-specific data to stream reaches having similar characteristics; and
• Provide a consistent frame of reference for communicating stream morphology and condition among a variety of disciplines.

Section 1 of 25