Three-dimensional hydrodynamic simulation of river channels and floodplains

Three-dimensional hydrodynamic simulation of flow in river channels and on floodplains offers the potential to increase the current understanding of stream stability, channel morphology, flood conveyance, and flow variability in natural rivers. This project develops and validates a three-dimensional hydrodynamic model that is suitable for detailed field-scale studies of rivers. The model development entails the modification and expansion of an existing three-dimensional model. The model is used to simulate flow in pool-riffle sequences, in compound channels, and on a large-scale complex river floodplain.; In pool-riffle sequences, the velocity-reversal hypothesis has been proposed as an important mechanism for the maintenance of channel morphology. For the pool-riffle sequence evaluated, simulation results support the occurrence of a reversal in mean velocity and shear stress. However, results indicate that the effects of flow convergence due to an upstream constriction and the routing of flow through the system may be more significant in influencing pool-riffle morphology than the occurrence of a velocity reversal. The hypothesis of flow convergence-routing is introduced as a more meaningful explanation of the mechanisms acting to maintain pool-riffle morphology.; Compound channels are often constructed in restoration projects on streams that have been channelized or are deeply incised. This study evaluates the effectiveness of a constructed compound channel to reduce channel velocities and bed shear stresses during high flow events using both a one-dimensional and three-dimensional numerical model. The results demonstrate the effectiveness of the compound channel design at reducing maximum channel bed shear stresses, but also indicate the limited capacity of one-dimensional modeling to adequately predict these reductions.; The application of a three-dimensional hydrodynamic model to flooding on a large-scale complex river floodplain demonstrates the utility of using three-dimensional simulations in planning field-scale restoration and management strategies. This modeling effort provides much more detailed information about flood conveyance, and flow variability in the river channel and on the floodplain, than could be obtained from existing one-dimensional models.; These simulations demonstrate the advantages of using a three-dimensional model over more commonly used one-dimensional models and make a strong case for the implementation of more detailed hydrodynamic modeling in evaluating flow in rivers.