Paper No. JAWRA-07-0009-P of the Journal of the American Water Resources Association (JAWRA).Discussions are open until October 1, 2008
The Role of Observer Variation in Determining Rosgen Stream Types in Northeastern Oregon Mountain Streams1
Article first published online: 21 MAR 2008
© 2008 American Water Resources Association
JAWRA Journal of the American Water Resources Association
Volume 44, Issue 2, pages 417–427, April 2008
How to Cite
Roper, B. B., Buffington, J. M., Archer, E., Moyer, C. and Ward, M. (2008), The Role of Observer Variation in Determining Rosgen Stream Types in Northeastern Oregon Mountain Streams. JAWRA Journal of the American Water Resources Association, 44: 417–427. doi: 10.1111/j.1752-1688.2008.00171.x
- Issue published online: 21 MAR 2008
- Article first published online: 21 MAR 2008
- Received January 18, 2007; accepted August 2, 2007.
- quality control/quality assurance;
- stream classification;
Abstract: Consistency in determining Rosgen stream types was evaluated in 12 streams within the John Day Basin, northeastern Oregon. The Rosgen classification system is commonly used in the western United States and is based on the measurement of five stream attributes: entrenchment ratio, width-to-depth ratio, sinuosity, slope, and substrate size. Streams were classified from measurements made by three monitoring groups, with each group fielding multiple crews that conducted two to three independent surveys of each stream. In only four streams (33%) did measurements from all crews in all monitoring groups yield the same stream type. Most differences found among field crews and monitoring groups could be attributed to differences in estimates of the entrenchment ratio. Differences in entrenchment ratio were likely due to small discrepancies in determination of maximum bankfull depth, leading to potentially large differences in determination of Rosgen’s flood-prone width and consequent values of entrenchment. The result was considerable measurement variability among crews within a monitoring group, and because entrenchment ratio is the first discriminator in the Rosgen classification, differences in the assessment of this value often resulted in different determination of primary stream types. In contrast, we found that consistently evaluated attributes, such as channel slope, rarely resulted in any differences in classification. We also found that the Rosgen method can yield nonunique solutions (multiple channel types), with no clear guidance for resolving these situations, and we found that some assigned stream types did not match the appearance of the evaluated stream. Based on these observations we caution the use of Rosgen stream classes for communicating conditions of a single stream or as strata when analyzing many streams due to the reliance of the Rosgen approach on bankfull estimates which are inherently uncertain.