Rosgen Stream Classification System

A recently developed system for classifying streams, the Rosgen Stream Classification System (Rosgen 1996), is widely recognized and implemented. Though this system provides a useful framework for communication, it is not universally accepted. One of the major criticisms of this classification method is that it does not incorporate the processes that created and continue to modify the stream. In addition, the system has not been validated in all environments.

Eight major stream classes are defined in this system on the basis of physical characteristics:

The Rosgen Classification System is based on six stream characteristics:

• Entrenchment
• Width/depth ratio
• Sinuosity
• Number of channels
• Slope
• Bedmaterial particle size

The entrenchment ratio of a stream is a measurement of the depth of the stream channel in relation to the uppermost banks. Entrenched streams are said to be disconnected from the adjacent floodplains. When an entrenched stream floods, the water level in the stream channel rises, but is less likely to spill over stream banks than in a less entrenched stream floods.

Left: Slightly entrenched stream. Right: Entrenched stream. Graphics courtesy of U.S. Environmental Protection Agency.

The width/depth ratio is a measurement of channel stability. Wide, shallow channels have high width/depth ratios; bank erosion is high in these channels. A lower width/depth ratio indicates a more stable channel.

The US Environmental Protection Agency has developed an online training module focused on the Rosgen classification system, which can be accessed here.