Background Stream Behavior Stream Assessment Stream Classification Regional Guidelines (pdf file 87K)	Food for Thought Contacts Slideshow!
	Natural Channel Design to Restore Native Fish Habitat Regional Policy on Streambank Stabilization Projects (pdf file 145K)

Development pressures have changed river systems throughout the United States. Traditional engineering concepts have been applied to problems of flood control, irrigation, highway construction, and general land management conflicts. This approach has failed to incorporate natural river geometry, channel behavior, riparian function, as well as associated aesthetic and financial value. In Region 6, river and stream alterations have resulted in adverse habitat changes for many fish and wildlife species and have contributed to major declines in native fish populations.

Healthy streams and riparian corridors are rare and dwindling resources, especially in the western U.S. The ability to accurately classify a stream and assess its condition are basic to understanding, restoring, and protecting it. River assessments must go beyond description. Field methods must provide the ability to assess channel morphology and to make some prediction of stream potential.

Natural stream channels are constructed and maintained by the force of the watershed's water and sediment encountering the resistance of bed and bank materials. This complex process forms consistent measurable patterns, described by Luna Leopold in 1964. These patterns are the basis for the bankfull discharge concept.  Bankfull, or channel-forming flow, is the the discharge that defines the morphological characteristics of the channel such as bars, meanders, and bends. The frequent bankfull discharge forms channels, not infrequent flood discharge. 

Leopold's concept has been studied and amplified over the years. In the last decade, Dave Rosgen has developed a system for classifying and assessing rivers based on bankfull channel dimensions. Once bankfull state is accurately identified in the field, it provides a common reference point with which to quantitatively describe and classify channels; and assess river condition.

One problem is that bankfull information is lacking for most rivers. Leopold said in 1978 that "data on the discharge at channel capacity or on the gauge height of the bankfull condition are not published or even determined in a systematic manner despite their importance to planners, environmentalists, and everyone interested in floods and flooding." Although it has been over twenty years since these words were written, the statement is still accurate throughout the United States. A related problem is an information gap among U.S. Fish and Wildlife Service staff. One solution is for field biologists to learn how to collect their own data.  What to collect, how to collect it, and how to interpret it are the subjects of courses taught by Dave Rosgen and Luna Leopold. Service guidance on how to work in rivers will presume that, over time, all Service staff who work to implement the guidance will obtain stream restoration training based on the bankfull concept.

There are eight variables which shape and maintain stream channels:  discharge, width, depth, velocity, slope, channel roughness, bedload size, and bedload volume. Channels are in a continuous state of adjustment to balance these variables. Ideally, a channel will come to a condition of dynamic equilibrium, within a wide range of natural variability.

Leopold says, "Adjustments lead to the most probable state, which is the condition that balances the physical laws of minimum work and even distribution of energy expended, with minimum variance."

A stream manifests these laws of physics through self-stabilization and the natural tendency to evolve into a particular form, the most probable state. However, progression towards stability is often derailed. Natural or man-induced changes cause streams to adjust in order to dissipate energy.

According to Dave Rosgen's definition, a stream functioning best in its most probable state maintains its dimension, pattern, and profile over time, in the present climate, while moving the watershed's sediment and flow without aggrading or degrading.  In a self-stabilized condition, bank erosion and deposition are balanced and the stream at bankfull discharge stays within stable ranges of channel geometry for that stream type.

Rivers, being very dynamic, are subject to change when the variables that shape and maintain the channel are altered. Rivers have accommodated periods of climate change and watershed development. The morphological features of rivers have changed in relation to climate and development.

A classification system quantitatively describes the combination of river features. Stream types, as grouped by morphological similarity, are products of erosional and depositional events over time in certain valley types. Any stream will likely contain more than one stream type along its length. Stream types exhibit similarities in entrenchment, channel form, width to depth ration, sinuosity, slope, and channel materials. Stream classification is accomplished by collecting bankfull data in the field and comparing the bankfull data to known stream types. This task is made easier through the work of Dave Rosgen and Lee Silvey, in their publication, Field Guide for Stream Classification.

The correct classification of rivers provides a basis from which to:  1) predict a river's behavior from its appearance; 2) develop empirical relations for individual stream types; 3) stratify and analyze comparison inventory data by stream type; such as fisheries surveys; 4) extrapolate data from other rivers of similar stream type; and 5) communicate more effectively with others who are concerned about rivers. This is a complex subject that will be simplified in this presentation.

Please look at the Rosgen classification system diagram (191k). Use this diagram to classify two streams reaches described below. Follow the diagram from top to bottom. The first delineative criterion on the diagram is single thread versus multiple thread channels. When you have found that location on the diagram, proceed with stream classification in the following two examples.

A stream functioning best in its most probable state maintains its dimension, pattern, and profile over time in the present climate without aggrading or degrading.

The stability of streams is associated with a balance among the variables which shape and maintain stream channels. Changes in streamflow, width, depth, slope, roughness of channel materials, sediment volumes, and sediment sizes induced by watershed changes such as an irrigation diversion, culvert, bridge or a dam directly reflect in the morphology and stability of streams.

A common fate for western streams is to be straightened and relocated along the edge of a valley to make more land available for pasture and hay.  In this example, many of the eight stream-maintaining variables are changed by straightening and relocation of the channel. According to Dave Rosgen, "The response of a stream to natural or imposed changes varies by stream type. The ability to characterize these responses and the associated physical effects by stream type is important to:  a) assess past impacts; b) anticipate future consequences of alternative management strategies; c) evaluate the potential for natural recovery; d) determine the evolutionary stages of channel adjustment; e) determine the feasibility of restoration; f) develop restoration designs that match or accommodate the functioning of a stream's natural stable tendencies."

An assessment, or departure analysis, is the important basis for determining impacts on the fish and wildlife species association that we in the Fish and Wildlife Service are interested in. An assessment based on field measurements is more defensible than an assessment based on  visual characteristics such as "eroded banks" or "straightened channel". Visual characteristics are looked at differently by different people and may have existed for so long that they become to be viewed as "natural". A proper interpretation of a stream's current condition compared to its most probable state will provide the best basis for management direction or restoration.

For example:  when an agency builds an irrigation diversion, changes in flow and sediment regimes are set in motion which affect the channel forming variables in the reach downstream from the diversion. After the diversion is in operation, downstream landowners are likely to experience increased land loss. If landowners complain, an assessment, using traditional engineering concepts, would likely conclude that riprapping is the solution to land loss. A different assessment, based on concepts of the most probable state and self-stabilization, would come to a different conclusion as follows. Measurements taken in the downstream reach and compared to a reference reach might show:  an increasing width to depth ratio; decreased sinuosity; increased slope; increased bar deposition; increased sediment supply; decreased sediment transport capacity; decreased meander width ratio; and channel aggradation.  In general, the stream is adjusting to flow depletions by shifting to a different stream type. This assessment of cause, consequence and correction would help the Service conclude the best solution to land loss is to retain the original stream type. We might conclude the solution is to reconstruct the dimension, pattern, and profile of the reach to handle the changed flow and sediment regime of the benefit of fish and wildlife as well as riparian landowners. In this example, the departure analysis helps develop a defensible decision on impacts and provides leverage for recommending correction action that benefits fish and wildlife.

There are always choices to be made when deciding how to deal with flowing water. The traditional engineering choice has been to contain flows with trapezoidal channels, levees, dams, and rigidly stabilized banks to meet limited objectives. Another choice, as stated by Luna Leopold, is to "incorporate the practical, physical, aesthetic, and financial advantages of approaching river management as maintenance of natural tendencies in river channel behavior."  The Leopold philosophy is in line with meeting multiple objectives, including fish and wildlife habitat objectives. 

Region 6 Partners for Fish and Wildlife
Contacts for Instream Habitat Restoration

Megan Estep
303-236-5322 ext. 232

Greg Neudecker
406-727-7400 ext. 27

Karl Fleming
435-723-5887 ext. *822