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With severely altered rivers throughout the developed world, hydrodynamic processes and floodplain connectivity have changed drastically. The research presented here focuses on quantification of two hydrodynamic processes: flood wave attenuation and channel-floodplain fluxes. Objectives of the three research chapters were to (1) evaluate how the ecosystem service of flood wave attenuation has changed with the implementation of river engineering practices as well as contemporary river restoration efforts, (2) describe the sensitivities of flood wave attenuation to contemporary and altered conditions, and (3) characterize channel-floodplain connectivity through lateral flux metrics. All chapter objectives were met using high-resolution, two-dimensional hydrodynamic modeling techniques conducted on the Rio Grande, New Mexico, USA. Models were created for historical, pre-restoration, contemporary, and altered conditions. Chapter 1 results indicate that historical conditions provided more attenuation than contemporary conditions. Sudden storage of water creates attenuation and alters flood wave shape. Chapter 2 results suggest that attenuation is most sensitive to total area for flow and area available for water storage while also displaying differences in process between topographic and roughness alterations. Chapter 3 flux results show differences in mass and momentum flux due to anthropogenic impacts and inset floodplain feature types provide greater and more heterogeneous lateral connectivity. Results presented here have implications for both anthropogenic flood control strategies and potential application to a myriad of ecological issues based in river connectivity and process-based science. Contributions of the dissertation include new methods for two-dimensional hydrodynamic modeling, improved metrics for attenuation research, and spatiotemporal description of channel-floodplain flux dynamics.