Fluvial Dynamics of Large River Secondary Channels: Hydraulic Habitat, Channel Morphology, and Potential for Restoration

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Large rivers have been dramatically altered by modifications driven by socio-economic needs. River managers and communities are seeking restoration alternatives that accommodate significant human impacts while also establishing sustainable, morphologically and hydraulically varied river systems that are capable of supporting healthy ecosystems. Secondary channels, or side channels, represent an opportunity to restore ecosystem functionality to large river systems without seriously affecting floodplain land uses, but restoration of secondary channels is hampered by a lack of knowledge about their geomorphic and hydraulic dynamics. The goal of this research is to advance the understanding of the geomorphic structure and function of large river secondary channels, satisfying the critical need for scientific inquiry to inform the design of secondary channel restoration projects. This will be accomplished by exploring topographic and three-dimensional flow structures present in secondary channels on the Housatonic River in southwestern Massachusetts. This research will: 1) quantify three-dimensional flow structure and channel morphology in secondary and main channel environments using Acoustic Doppler flow meters, 2) evaluate how fluvial processes and forms in secondary channels differ from those in the main channel using hydraulic and topographic metrics, 3) quantitatively identify linkages between morphologic form and functional processes in secondary channels, and 4) inform a new conceptual model for rivers with secondary channels. This work will contribute significantly to theoretical research on the long-recognized, but poorly understood, three-dimensionality of flow in rivers. It will be one of the first studies to directly measure three-dimensional flow structure in unmodified "natural" secondary channels, greatly contribute to our understanding of how channel morphology influence hydraulic habitat variability, and will expand the theoretical understanding of river geomorphological dynamics in the lateral dimension. The results of this study will fill significant gaps in our understanding of how secondary river channels function while at the same time providing extraordinary learning and training opportunities for both graduate and undergraduate students, particularly women. The enhanced scientific understanding of large river secondary channels produced by this project will impact river management throughout the country and beyond by providing a strong basis for evaluating the benefits, costs, and performance of side-channel restoration projects on large, multi-purpose rivers. A better understanding of large-river secondary channels will serve to more efficiently focus river restoration and rehabilitation efforts and resources in the areas of large river systems that can provide the greatest benefits without compromising main channel and floodplain utilization.