The planform of a river, its geometrical pattern when viewed from above, is a fundamental characteristic of river morphology. River planform develops from mutual interactions among flow, sediment transport and channel form. Anabranching rivers, characterized by multiple channels separated by stable, vegetated islands, occur along otherwise meandering rivers in the intensively managed landscapes of midwestern United States. The Upper Sangamon River (USR) is an example of such a system – and will be the natural field laboratory for this project.
Most of the USR exhibits a meandering planform with a sinuosity between 1.2 to 3, but anabranching occurs locally at ten locations along the river. The causes for such spatial transitions in river planform, and the fluvial dynamics of these systems are unclear. Spatial transitions between multiple-thread anabranching and single thread meandering rivers have been related to differences in energy regimes (valley slope, bankfull discharge), valley width and riparian vegetation. The proposed research aims to answer questions about the development, evolution, and maintenance of anabranching within meandering systems, and will lead to an improved understanding of anabranching dynamics. It will explore the role of natural versus human induced processes including agriculture and riparian corridor alteration in the development of anabranching planform.