SGER: Fluvial Dynamics of a Large-River Meander Cutoff

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Meandering is a fundamental characteristic of many natural rivers that has yet to be adequately explained. The dynamics of meanders involves the continuous evolutionary development of sequences of meander bends through time as the channel migrates laterally and downstream. Individual bends can evolve into complex forms characterized by multiple arcs of curvature, with these loops evolving to curve back upon themselves at their entrance and exit to form a narrow neck. Flow across the neck during floods eventually leads to the development of a new channel at this location, a process known as a meander cutoff. The old meander loop is then abandoned by the flowing river as sediment plugs the entrance and exit of the loop to form an oxbow lake. Recent research has emphasized the importance of meander cutoffs in the dynamics of meander trains, or sequences of bends. Cutoffs can have a substantial influence on bend interactions, because these events often trigger new patterns of evolutionary development of bends adjacent to the cutoff, which in turn affect other bends throughout a meander sequence. This Small Grant for Exploratory Research will examine the development of a new meander cutoff along the lower reach of the Wabash River on the Illinois-Indiana border. The investigators have been monitoring the new cutoff since the days after it formed in June 2008, and they will use funds from this award to continue to monitor its development and to examine the influence of the cutoff on the dynamics of a large-river confluence immediately downstream where the Wabash flows into the Ohio River. The investigators will focus on how the cutoff affects the three-dimensional flow structure of the river at the upstream and downstream ends of the cutoff channel, the developing flow structure within the cutoff channel and within the meander loop that is being cutoff, and the dynamics at the confluence immediately downstream. They will relate documented patterns of flow structure to patterns of channel erosion and deposition to establish linkages between fluvial processes and fluvial forms within the evolving cutoff. This will be done by (1) mapping the extant morphology of the cutoff channel, the bed morphology of the meander loop, and analyzing ancillary information on the occurrence of the cutoff and its influence on the Wabash River-Ohio River confluence; (2) measuring patterns of three-dimensional flow structure at the upstream and downstream ends of the cutoff, within the cutoff channel and within the meander loop during events of different flow stages; (3) mapping patterns of erosion and deposition at the upstream and downstream ends of the cutoff, within the cutoff channel, and within the meander loop; and (4) measuring the flow structure and mapping patterns of sedimentation at the Wabash-Ohio confluence.This research project will make a substantial field-based contribution to the understanding of the dynamics of meander cutoffs, which can later inform development of general process-based numerical models of meandering. The project also will enhance basic understanding of the ways that the formation of the cutoff affects the changing dynamics of the large Wabash-Ohio river confluence immediately downstream. The project will have positive broader impacts by providing research and training opportunities for graduate and undergraduate students and for providing valuable data to enable local government agencies and other stakeholders to determine how to deal with the land-management implications of the new cutoff and related changes.