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Title: Three-dimensional flow structure and bed morphology in large elongate meander loops with different outer bank roughness characteristics

Author
item KONSOER, KORY - Louisiana State University
item RHOADS, BRUCE - University Of Illinois
item BEST, JAMES - University Of Illinois
item Langendoen, Eddy
item ABAD, JORGE - University Of Pittsburgh
item PARSONS, DANIEL - University Of Hull
item GARCIA, MARCELO - University Of Illinois

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2016
Publication Date: 12/27/2016
Publication URL: https://handle.nal.usda.gov/10113/5763088
Citation: Konsoer, K., Rhoads, B.L., Best, J.L., Langendoen, E.J., Abad, J.D., Parsons, D.R., Garcia, M.H. 2016. Three-dimensional flow structure and bed morphology in large elongate meander loops with different outer bank roughness characteristics. Water Resources Research. 52(12):9621–9641. doi:10.1002/2016WR019040.

Interpretive Summary: The role of vegetation on meander migration rates of large, elongate bends of meandering rivers has not been sufficiently documented. Scientists of the USDA-ARS Watershed Physical Processes Research Unit, Oxford, MS, in collaboration with researchers of the Universities of Illinois and Pittsburgh employed high-resolution acoustical measurement techniques to map flow and bed features for two meander bends (one vegetated and one unvegetated) on the Wabash River, Illinois/Indiana. Results showed that in contrast to smaller rivers where the vegetation on the bank significantly controls bank erosion rates, the trees that have fallen in the river during previous bank failures reduce the near-bank flow and bank erosion rates. These findings are significant for river managers as they indicate that for large systems in-stream protection measures are more effective in protecting stream banks.

Technical Abstract: Although the dynamics of meandering rivers have been the focus of considerable research, few studies have examined the three-dimensional flow structure and bed morphology within elongate loops of large meandering channels. The present study focuses on the spatial patterns of three-dimensional flow structure and bed morphology within two elongate loops along the Wabash River, USA. It also examines how differences in outer bank characteristics influence flow structure within these loops. The outer bank of one of the loops is forested, whereas the outer bank of the other loop is unforested. Flow velocities were obtained along cross sections oriented perpendicular to the channel centerline using a boat-mounted acoustic Doppler current profiler during two different events – a near-bankfull flow and an overbank event that extensively inundated the floodplain. Detailed channel bathymetry and bedform geometry were obtained using a multibeam echo sounder during the near-bankfull event. The spatial pattern of depth-averaged velocities and occurrence of multiple outer bank pools within the unforested elongate meander loop are in general agreement with results of previous experimental studies. However, abundant large woody debris along the outer bank of the forested loop produces a zone of reduced velocities that inhibits scour pool development. The positions of pools within both loops are linked to spatial variations in planform curvature. Velocities within the channel during the overbank event are less than those for the near-bankfull flow, highlighting the strong influence of the point bar on convective acceleration of the flow at sub-bankfull stages.