Interactions between near-bank three-dimensional flow structure and large woody debris in an elongate meander bend.

Authors: Kory Konsoer*, Louisiana State University, Bruce Rhoads, University of Illinois, Urbana-Champaign, Jim Best, University of Illinois, Urbana-Champaign, Eddy Langendoen, USDA National Sedimentation Laboratory, Marcelo Garcia, University of Illinois, Urbana-Champaign
Topics: Geomorphology
Keywords: meandering rivers, large woody debris, bank erosion
Session Type: Paper
Day: 4/6/2019
Start / End Time: 8:00 AM / 9:40 AM
Room: Hoover, Marriott, Mezzanine Level
Presentation File: No File Uploaded

The presence of vegetation in river channels can have substantial effects on the magnitude and spatial pattern of three-dimensional velocities, modifying boundary shear stresses and rates of sediment transport and bank erosion. While these interactions have been extensively studied in experimental channels using simulated vegetation or small natural streams, less focus has been given to larger channels with near-bank large woody debris, particularly in meander bends. Here, we present field measurements of near-bank three-dimensional velocities along a forested elongate meander bend with abundant large woody debris on the Wabash River near Grayville, IL. Data were collected using a boat-mounted acoustic Doppler current profiler during a bankfull event along transects perpendicular to the outer bank spaced at roughly 40 m streamwise distance. The measured velocities are used to estimate boundary shear stress and are related to long-term patterns of bank migration observed for this bend. Results show that the near-bank cross-sectional flow fields are highly complex, often exhibiting one or two cells of circulation in addition to the primary curvature-driven helical cell that develops between the point bar and thalweg. The additional flow resistance due to form drag from the large woody debris is also responsible for reducing velocity magnitudes near the outer bank, thereby reducing boundary shear stress and rates of bank erosion.

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