Technical stream classification systems have been developed to provide a general framework for documenting, evaluating, and understanding different types of stream corridors. These systems are often used by water resources engineers, geomorphologists and stream restoration experts. The classification of a stream often categorizes information about its stability and how it is evolving. This is often referred to as a stream’s evolutionary stage. All of this information can be used as a tool for communication and stream management, especially for projects that require complex engineering.
Two of the most recognized technical stream classification systems are the ‘River Styles Framework’ and ‘Rosgen Stream Classification System’. Though each system has their differences, both are based on assessing the physical characteristics of a reach of stream such as valley type, channel proportions, geomorphic properties and the bed material within the stream. Both the River Styles and the Rosgen systems begin by looking at the larger context in which the stretch of stream lies. This is done by classifying the ‘valley setting’ or ‘valley type.’ The valley type is an important first step because it dictates other characteristics of the stream including its total power and its ability to transport sediment.
Valley Setting/Type
Referred to as the ‘Valley Setting’ in the River Styles Framework and ‘Valley Type’ in the Rosgen Classification System, this characteristic alludes to the overall confinement of the stream corridor. A confined stream is one that is unable to spread across a floodplain area during high flow flood events. Generally, streams in mountainous areas have a more confined valley, whereas reaches along the plains often have a more open valley.
After assessing the valley in which the stream lies, both classifications systems evaluate the characteristics of the channel bed and banks, including the alignment, slope and streambed material. Together, these attributes are used to classify the stream, enhancing our understanding of its processes. Classification can also make it easier to communicate the current state of a stream, understand why things are happening along the stream, and even provide insight into the best restoration practices for that specific site.
River Styles Framework
Rosgen Stream Classification
With the ‘Stream Classification Guide’ in this Handbook, landowners such as yourself can assess the Entrenchment, Slope and Primary Streambed Material on their property. These are three key factors evaluated in both the River Styles and the Rosgen systems, in addition to many more criteria that may not be as easy for a landowner to evaluate on their own. These include the alignment/sinuosity of the stream, a width/depth ratio and channel complexity. These technical classification systems also have more options to choose from. For example, this Handbook’s Stream Classification Guide provides 3 classifications of Stream Slope to choose from; the Rosgen system has 7 options sometimes requiring the evaluator to be able to differentiate between 1% and 0.5% slope. Being able to do this will often require survey equipment to measure accurately.
The Entrenchment, Slope and Primary Streambed Material of your stream can provide insight into its overall characteristic and can help determine appropriate stewardship and restoration techniques. The classification can also be a powerful tool in communicating issues found on your specific site with outside help, as discussed in ‘Chapter 4: Engaging Outside Help’.