INFLUENCE OF RIPARIAN VEGETATION AND FLOODPLAIN HETEROGENEITY ON THE PLANFORM EVOLUTION OF A LARGE MEANDERING RIVER

Planform evolution and migration rates of meandering channels are dependent upon the dynamic interactions between three dimensional flow structure, sediment transport, and channel form. In addition, channel form is highly dependent upon the characteristics of the channel banks and floodplains. Riparian vegetation can influence channel form by increasing the tensile strength of the banks through root-reinforcement and adding cohesion through soil development. Furthermore, the erosional and depositional history of the floodplain can have an effect on meander migration by introducing spatial heterogeneity of grain size, vegetation, and bedrock. In this paper, migration rates are compared for two meander bends, one forested and one non-forested, on the Wabash River, near Grayville, Illinois. Grain size analyses were conducted on the channel bank sediments at several locations and heights around each bend. The migration history of this reach was determined through time-series aerial photography (1938 – 2011) and recent airborne LiDAR, allowing for centimetric resolution and identification of floodplain features such as scroll bars, abandoned channels, bedrock outcrops. Results from this study show a significant difference in bank material between the forested and non-forested bends. Migration patterns over the last 80 years suggest that the differences in grain size, along with the spatial heterogeneity of vegetation and floodplain features, have greatly influenced migration rates and planform evolution for these two bends.