Doctoral Dissertation Research: Flow Dynamics and Channel Morphology at Natural Confluent-Meander Bends

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The geometry of river confluences is a controlling factor that influences flow structure, sediment transport and bed morphology at channel junctions. An underlying assumption of previous experimental and theoretical models of confluence dynamics has been that converging rivers have straight channels with angular configurations. However, natural channels, particularly those of meandering rivers, curve and bend. This property has led to the hypothesis that natural stream and river confluences preferentially occur on the concave outer bank of meander bends. The resulting confluence, referred to as a confluent-meander bend, was observed over a century ago but has received little scientific attention. The goal of this doctoral dissertation research project is to advance the understanding of the flow structure and morphology of this possibly common confluence by conducting a field investigation of natural confluent-meander bends. A systematic inventory of confluences throughout selected watersheds will be generated from map and digital ortho-quadrangle interpretation to determine the regularity of confluent-meander bends. Field data collection at confluent-meander bends of varying size and with differing geometric characteristics in east-central Illinois and west-central Indiana will include measuring time-averaged three-dimensional velocity components to discern flow structure, surveying bed and channel morphology to document geomorphic change and recording water temperature and conductivity to reveal spatial patterns of mixing between the confluent flows. Data for a range of flow conditions will be collected to document the effects that variation in momentum flux has on flow structure and channel morphology. Historical aerial photographs will also be interpreted to determine if the confluent-meander bends of the study sites represent a quasi-stable channel configuration in meandering drainage networks.The results of this study will reveal the characteristics of flow and geomorphic structures at confluent-meander bends to provide a basis for management decisions and a contribution to basic knowledge of confluence and meander bend dynamics. This complex hydrodynamic environment has practical ramifications for engineers when assessing channel design criteria and flood routing through drainage networks, as well as for water resource managers concerned about pollutant dispersal and water quality. Flow structure and geomorphic variability at confluences also provide local diversity that disrupts habitat. Functional relations between geomorphology and ecology are increasingly relevant to providing a better assessment of habitat for riverine ecologists. These fluvial and morphological considerations make knowledge of flow dynamics and sediment transport at this possibly common, yet heretofore overlooked, confluence. essential for science and channel management decisions. 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.