Abstract

Abstract A classification system for natural rivers is presented in which a morphological arrangement of stream characteristics is organized into relatively homogeneous stream types. This paper describes morphologically similar stream reaches that are divided into 7 major stream type categories that differ in entrenchment, gradient, width/depth ratio, and sinuosity in various landforms. Within each major category are six additional types delineated by dominate channel materials from bedrock to silt/clay along a continuum of gradient ranges. Recent stream type data used to further define classification interrelationships were derived from 450 rivers throughout the U.S, Canada, and New Zealand. Data used in the development of this classification involved a great diversity of hydro-physiographic/geomorphic provinces from small to large rivers and in catchments from headwater streams in the mountains to the coastal plains. A stream hierarchical inventory system is presented which utilizes the stream classification system. Examples for use of this stream classification system for engineering, fish habitat enhancement, restoration and water resource management applications are presented. Specific examples of these applications include hydraulic geometry relations, sediment supply/availability, fish habitat structure evaluation, flow resistance, critical shear stress estimates, shear stress/velocity relations, streambank erodibility potential, management interpretations, sequences of morphological evolution, and river restoration principles. General statement - It has long been a goal of individuals working with rivers to define and understand the processes that influence the pattern and character of river systems. The differences in river systems, as well as their similarities under diverse settings, pose a real challenge for study. One axiom associated with rivers is that what initially appears complex is even more so upon further investigation. Underlying these complexities is an assortment of interrelated variables that determines the dimension, pattern, and profile of the present-day river. The resulting physical appearance and character of the river is a product of adjustment of its boundaries to the current streamflow and sediment regime. River form and fluvial process evolved simultaneously and operate through mutual adjustments toward self-stabilization. Obviously, a classification scheme risks oversimplification of a very complex system. While this may appear presumptuous, the effort to categorize river systems by channel morphology is justified in order to achieve, to some extent, the following objectives: 1. Predict a river's behavior from its appearance; 2. Develop specific hydraulic and sediment relations for a given morphological channel type and state; 3. Provide 'a mechanism to extrapolate site-specific data collected on a given stream reach to those of similar character; 4. Provide a consistent and reproducible frame of reference of communication for those working with river systems in a variety of professional disciplines. r Stream classification review A definition of classification was offered by Straight, meandering, and braided patterns were described by A descriptive classification was also developed by To cover a wider range of stream morphologies, a descriptive classification scheme was developed for and applied on Canadian Rivers by An attempt to classify rivers in the great plains region using sediment transport, channel stability, and measured channel dimensions was developed by Brice and Blodgett (1978) described four channel types of: braided, braided pointbar, wide-bend point-bar, and equi-width point-bar. A descriptive inventory of alluvial river channels is well documented by Stream classification concepts The morphology of the present day channel is governed by the laws of physics through observable stream channel features and related fluvial processes. Stream pattern morphology is directly influenced by eight major variables including channel width, depth, velocity, discharge, channel slope, roughness of channel materials, sediment load, and sediment size This level delineates homogeneous stream types that describe specific slopes, channel materials, dimensions and patterns from "reference reach" measurements. Provides a more detailed level of interpretation and extrapolation than Level I. The "state" of streams further describes existing conditions that influence the response of channels to imposed change and provide specific information for prediction methodologies (such as stream bank erosion calculations, etc. the others, resulting in channel pattern alteration. Because stream morphology is the product of this integrative process, the variables that are measurable should be used as stream classification criteria. The directly measurable variables that appear from both theory and experience to govern channel morphology have been included in the present classification procedure. These "delineative criteria" interact with one another to produce a stream's dominant features. The present classification system has evolved from field observation of hundreds of rivers of various sizes in all the climatic regions of North America, experience in stream restoration, extensive teaching, and practical applications of the classification system by many hydrologists, geomorphologists, fisheries experts, and plant ecologists. Initial efforts to develop the classification procedure began in 1973, and a preliminary version was presented to the scientific community Stream classification system The classification of rivers is an organization of data on stream features into discreet combinations. The level of classification should be commensurate with the initial planning level objective. Because these objectives vary, a hierarchy of stream classification and inventories is desirable because it allows an organization of stream inventory data into levels of resolution from very broad morphological characterizations to discreet, measured, reach-specific descriptions. Each level should include appropriate interpretations that match the inventory specificity. Further, general descriptions and characteristics of stream types should be able to be divided into even more specific levels. The more specific levels should provide indications of stream potential, stability, existing "states", etc., to respond to higher resolution data and interpretations when planning needs change. A proposed stream inventory system, including an integrated stream classification, is shown in Current river "state" and influences on the modern channel by vegetation, flow regime, debris, depositional features, meander patterns, valley and channel confinement, streambank erodibility, channel stability, etc., comprise additional parameters that are considered critical to evaluate by stream type at a more detailed inventory level (Level III). However, for the sake of brevity and clarity, this paper will focus on the first two levels, the broad geomorphic characterization (Level I) and the morphological description (Level II) which incorporates the general character of channel form and related interpretations. Portions of the data used for detailed assessment levels are contained in the sub-type section of the earlier classification paper Geomorphic characterization (level I) The purpose of delineation at this level is to provide a broad characterization that integrates the landform and fluvial features of valley morphology with channel relief, D.L. Rosgen / Catena 22 (1994) Fig.