Assessing connectivity between the river channel and floodplains during high flows using hydrodynamic modeling and particle tracking analysis

Abstract

River-floodplain connectivity is vital to hydrological and biogeochemical processes in river corridors over multiple spatiotemporal scales. In the present study, an approach of particle tracking in conjunction with two-dimensional hydrodynamic modeling was developed to study the dynamics of river-floodplain connectivity during flood periods and applied to the study of McCarran Ranch in the lower Truckee River, Nevada, U.S. The hydrodynamic model was calibrated and validated for flood events of different magnitudes of peak flow discharge. The outputs of the hydrodynamic model were further applied to determine the lateral transboundary flux during high flows. Lagrangian particle trajectories were then performed to quantify the flow path length and residence time on floodplains. The exchange frequency between the river mainstem and the floodplain were also examined.The results show that the hydrodynamic model reproduce hydrographs well. The river-floodplain exchange is sensitive to the magnitudes of the flood events. Larger floods cause shorter residence times and flow path lengths on the floodplains but lead to larger transboundary flux within the river reaches. The particle analysis results also show that higher discharge introduces less frequent exchange between the river channel and floodplains. Furthermore, comparison of the river-floodplain exchange properties among river reaches with different levels of sinuosity show that meandering reaches can introduce considerably higher exchange flux than a straight reach, leading to complex exchange behaviors within the river-floodplain system.