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The initial instability and finite-amplitude stability of alternate bars in straight channels

January 1, 1990

The initial instability and fully developed stability of alternate bars in straight channels are investigated using linearized and nonlinear analyses. The fundamental instability leading to these features is identified through a linear stability analysis of the equations governing the flow and sediment transport fields. This instability is explained in terms of topographically induced steering of the flow and the associated pattern of erosion and deposition on the bed. While the linear theory is useful for examining the instability mechanism, this approach is shown to yield relatively little information about well-developed alternate bars and, specifically, the linear analysis is shown to yield poor predictions of the fully developed bar wavelength. A fully nonlinear approach is presented that permits computation of the evolution of these bed features from an initial perturbation to their fully developed morphology. This analysis indicates that there is typically substantial elongation of the bar wavelength during the evolution process, a result that is consistent with observations of bar development in flumes and natural channels. The nonlinear approach demonstrates that the eventual stability of these features is a result of the interplay between topographic steering effects, secondary flow production as a result of streamline curvature, and gravitationally induced modifications of sediment fluxes over a sloping bed.

Publication Year 1990
Title The initial instability and finite-amplitude stability of alternate bars in straight channels
DOI 10.1016/0012-8252(0)90030-Y
Authors Jonathan M. Nelson
Publication Type Article
Publication Subtype Journal Article
Series Title Earth-Science Reviews
Index ID 70016019
Record Source USGS Publications Warehouse
USGS Organization WMA - Integrated Modeling and Prediction Division