DUNE KINEMATICS IN A LARGE ELONGATE MEANDER BEND

Recent advances in hydroacoustic mapping make it possible to obtain high spatial resolution bathymetric data for a variety of natural river channel environments. These detailed bathymetric data allow for accurate mapping and characterization of the overall channel morphology, as well as bedforms ranging from individual ripples to composite dune fields. However, these bathymetric maps only represent a static view of the bed morphology and spatial distribution of bedforms within a particular area of interest. Theoretical models suggest that during steady flow conditions, bed forms will reach an equilibrium morphology based on the hydraulic conditions of the flow. Thus, as discharge and velocities vary during a flood event, it is expected that the bed form geometry will adjust to the local characteristics of the flow, altering rates of sediment transport through the reach. In addition, recent work has shown that the presence of bedforms in meandering channels can locally modify patterns of three-dimensional velocities near the outer bank, increasing peak shear stresses acting upon the channel boundary.

This paper examines the bed morphology, spatial distribution of bedforms, and estimates rates of sediment transport for a large, actively migrating, elongate meander bend. Detailed multibeam echo sounding (MBES) surveys were conducted within Maier Bend, Wabash River, IL-IN, USA for two flood events with different discharge (Feb. 2012 & May 2013). During the May flood event, repeat surveys conducted ~4 hours apart allow for estimates of dune celerity, and thus volumetric rates of sediment transport. Comparisons of the bathymetric maps produced for the two flood events show a large variation in the geometry and spatial distribution of bedforms throughout Maier Bend. The findings from this study are discussed within the context of a recently developed three-dimensional numerical model used to simulate near-bank flow fields and shear stress within Maier Bend.