Stream power, channel change, and channel geometry in the Blue River, Wisconsin

Abstract

Discharge and bank resistance have long been considered two of the more important factors controlling downstream changes in stream channel geometry. Although stream power has been shown to have an important impact on many components of the fluvial system, it has received little use as an explanatory variable in the consideration of questions related to channel geometry. This study examines spatial and temporal changes in channel geometry and stream power in a moderate-sized watershed in the Driftless Area of Wisconsin, USA. Pre-settlement (~1830) channel geometry and stream power estimates derived from General Land Office survey notes were compared with conditions obtained from modern field surveys. Comparison of pre-settlement and modern channels shows that channel width and cross-sectional area have increased considerably during the post-settlement period, producing on average a threefold increase in cross-sectional stream power. When compared to discharge, slope, and bank sediment variables, cross-sectional stream power is more strongly associated with channel shape, explaining a maximum of 47% of the variance in one of the four study reaches. These results are compared with a reanalysis of previously published data from the midwestern USA, in which cross-sectional power also explains more of the variance in channel shape than discharge or bank sediment.

Keywords:

• stream power
• channel geometry
• channel adjustment
• hydraulic geometry
• Wisconsin

Acknowledgments

This paper is dedicated to Jim Knox, whose passion for channel change in Driftless Area streams inspired me and a generation of geomorphologists. I would also like to thank those whose comments and field assistance are greatly appreciated: Vance Holliday, Tom Vale, Dorothy Sack, Dave Mickelson, Antoinette Winklerprins, Mark Carlson, Duane Griffin, Peter Jacobs, Christopher Woltemade, Bob Pavlowsky, Doug Faulkner, Peter Newall, Mary Braun, Heather Miller, Patti Trocki, Christine Metropolus, and Joe Lecce. Reviews by Bruce Rhoads and two anonymous reviewers greatly improved the manuscript.