LIMITATIONS AND IMPLICATIONS OF STREAM CLASSIFICATION¹

Abstract

Stream classifications that are based on channel form, such as the Rosgen Level II classification, are useful tools for the physical description and grouping of streams and for providing a means of communication for stream studies involving scientists and (or) managers with different backgrounds. The Level II classification also is used as a tool to assess stream stability, infer geomorphic processes, predict future geomorphic response, and guide stream restoration or rehabilitation activities. The use of the Level II classification for these additional purposes is evaluated in this paper. Several examples are described to illustrate the limitations and management implications of the Level II classification. Limitations include: (1) time dependence, (2) uncertain applicability across physical environments, (3) difficulty in identification of a true equilibrium condition, (4) potential for incorrect determination of bankfull elevation, and (5) uncertain process significance of classification criteria. Implications of using stream classifications based on channel form, such as Rosgen's, include: (1) acceptance of the limitations, (2) acceptance of the risk of classifying streams incorrectly, and (3) classification results may be used inappropriately. It is concluded that use of the Level II classification for purposes beyond description and communication is not appropriate. Research needs are identified that, if addressed, may help improve the usefulness of the Level II classification.

Évaluation de l’état de l’hydromorphologie des cours d’eau : retour d’expérience sur le bassin Adour-Garonne (France)

“…Ce déficit se retrouve pour la plupart des rivières du bassin Adour-Garonne. Par ailleurs, cette approche diachronique se heurte au fait que, naturellement, un cours d'eau évolue et peut changer de style fluvial, voire se métamorphoser, en fonction des évolutions climatiques, d'événements géologiques ou d'implantations d'espèces exogènes (Juracek et Fitzpatrick, 2003 ;Schumm, 2005). Ainsi, on ne sait pas comment les cours d'eau en tresses du piémont pyrénéen auraient évolué spontanément depuis la fin du présumé Petit Âge Glaciaire (vers 1865) en dehors de toute pression anthropique.…”

How Well Do the Rosgen Classification and Associated ''Natural Channel Design'' Methods Integrate and Quantify Fluvial Processes and Channel Response?

“…definition of the bankfull level (Williams, 1978;Juracek and Fitzpatrick, 2003), and 2. classification of the dominant type of channel materials (Kuhnle and Simon, 2000). The simple definition of "bankfull" by Leopold et al (1964), as the "flow that just spills out onto the floodplain" has produced confusion (Williams, 1978).…”

“…There are, however, crucial differences between Davis' view of geomorphology in the early 20 th century and the classification approach to river restoration today. First, while Davis' approach was scientifically accepted as a valid approach to geomorphology for almost fifty years, the classification approach to restoration design has been criticized since its first introduction to the scientific community, and remains without support in much of the peer-reviewed scientific literature (Kondolf, 1995;Miller and Ritter, 1996;Doyle and Harbor, 2000;Kuhnle and Simon, 2000;Juracek and Fitzpatrick, 2003).…”

“…The bankfull discharge has been ascribed various meanings and levels of importance over the past 50 years since Leopold and Maddock (1953) published their research on hydraulic geometry. Although Dunne and Leopold (1978) described the discharge at the bankfull stage as the most "effective" at forming and maintaining average channel dimensions, given the variation in the recurrence interval of the bankfull discharge (Williams, 1978), others suggest that a more meaningful measure would be one based on flow frequency (Miller and Ritter, 1996;Juracek and Fitzpatrick, 2003;Simon et al, 2004). Nevertheless, considerable resources are being expended by state and federal agencies as well as by academic institutions to determine bankfull channel dimensions and regional curves (based on channel and basin characteristics) to predict the bankfull discharge (eg.…”

Caracterización geomorfológica de los ríos de Galicia mediante unidades litotopográficas

“…y, en segundo término, ¿identifican las escalas espaciales 'ecorregión' y 'cuenca vertiente' áreas en las cuales los procesos y formas ecológicas se comporten de modo similar? Para el primer planteamiento se considera el "sí" como respuesta (Naiman et al, 1992;Juracek y Fitzpatrick, 2003). Las clasificaciones permiten una mejor compresión de las formas y procesos estudiados, promoviendo al mismo tiempo la teorización y empirismo de leyes que expliquen las diferencias de los objetos clasificados (Goodwin, 1999).…”