The interaction among channel morphology, turbulent flow structure, and sediment transport often produces complex meander planforms that evolve through lateral and downstream channel migration. As meanders migrate, they tend to increase in sinuosity and curvature, often forming elongate bends with multiple curvature maximums otherwise known as compound loops. Flow moving through simple meander bends is highly three dimensional, but the relationship among 3-D flow structure, turbulence characteristics, and planform evolution in compound loops is poorly understood. In particular, knowledge of the structure of turbulence near the outer bank of meandering rivers, which should be closely related to the erosional forces acting on the bank, is incomplete. The doctoral dissertation research project will conduct a systematic, process-based field investigation of the interactions between near-bank turbulence, the mean flow field, and bank erosion in a compound loop in Central Illinois. Field data on bed and bank morphology, time-averaged flow structure, and near-bank instantaneous flow velocities will be collected at the study site for several flow stages. Monitoring of changes in channel morphology, including bank retreat, will be coupled with repeat flow measurements to facilitate exploration and interpretation of the influence of morphology, flow structure, and the spatial structure of turbulence on the morphodynamics of a compound meander loop. The change in bank position, channel morphology, flow structure, and structure of turbulence will be documented, and the interactions among these processes will be identified.
The results of this project will help fill existing gaps in basic understanding regarding how interactions among meander planform, flow movement through a bend, and bank erosion relate to the development and evolution of complex meander forms. The project will provide high-quality field data to evaluate theoretical models river scientists use to understand and predict planform evolution. In addition to providing new information and insights for basic researchers, greater knowledge of meander planform evolution will have practical utility because of the impacts planform change has on human welfare, such as the threat to structures located along meandering rivers and potential property loss caused by channel migration. Increasing human proximity to meandering rivers is creating a greater need for informed river management practices. By improving scientific understanding regarding how flow stage and near-bank flow turbulence influence bank erosion and channel migration, this project will inform management and policy decisions, including river and habitat restoration practices in or near meandering river systems. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.
Understanding how meandering rivers change through time as they migrate across their floodplains is of interest both to river scientists and to river managers. The movement of meandering rivers involves processes of erosion and deposition within the river channel that are connected to complex patterns of flow. The connection between patterns of flow and the processes of erosion and deposition that lead to channel change are incompletely understood. This field project was undertaken to improve our understanding of the connection between flow within river channels and the processes of erosion and deposition that lead to changes in the form of bends along meandering rivers. In particular, this study examined the connections among patterns of flow, the form of the channel bed, the type of sediment on the channel bed, the amount of erosion along the channel banks, and migration of the river channel along two small meandering rivers in central Illinois. Careful study illuminated the interaction of processes over differing spatial and temporal scales. Findings of the project suggest that patterns of flow, sediment movement, and channel migration in meander bends with complex geometries are more complicated than those in bends with simple geometries. Moreover, interactions among local influences on the flow, such as blocks of failed bank material along the outer bank of meander bends, local topographic steering of the flow by forms on the channel bed, and local increases in curvature of the river channel lead to increases in the complexity of bend geometry over time. . Research undertaken in this project has contributed to basic scientific understanding of how the form of meandering rivers develops through time. In addition to being an important contribution to basic science, the findings of this work are also of practical importance. Human proximity to meandering rivers is increasing—society builds cities close to rivers, practices agriculture on floodplains, and otherwise derives much economic value from water resources and fertile floodplain soils created by meandering rivers. Proper stewardship that balances the needs of protection of property and human welfare with conservation of the environmental functions of riverine ecosystems requires informed river management practices. Advances in scientific understanding of the dynamics of meandering rivers derived from this project can help inform best management practices for river and habitat restoration in or near actively migrating meandering river systems. In addition to these scientific and practical contributions, the research designed and carried out in this Doctoral Dissertation Research Improvement award provided invaluable training and experience for the co-PI, a young environmental professional who has leveraged these skills to start an applied research career in the government sector.
