Three-Dimensional Hydrodynamic Modeling of Flow and Sediment Transport in Complex River Channels

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0087842KitanidisIt is recognized that three-dimensional flow dynamics influence river channel morphology and the movement and distribution of sediment within the channel. In channels with compound cross-section, pool-riffle sequences, and developed meander systems, the influence of three-dimensional velocity fields on secondary flow circulation has a profound effect on both the river hydrodynamics and the movement of sediment. The goal of this project is to develop and validate a three-dimensional hydrodynamic and sediment transport model suitable for detailed field-scale studies to investigate the influence of complex three-dimensional flow structure during high flow events in: (a) pool-riffle sequences, (b) compound channels, and (c) meandering compound channels. This study will investigate the influence of these flow structures on secondary circulation, and the erosion, deposition, and transport of sediment. The project utilizes an existing semi-implicit numerical model for non-hydrostatic free-surface flows on unstructured grids. The model is based on the three-dimensional Navier-Stokes equations and utilizes a semi-implicit algorithm that is robust, stable, and very efficient. The model will be coupled with a mobile bed model for suspended and bedload sediment transport.A thorough understanding of the flow and sediment regime in complex channels is essential for the planning and development of successful stream restoration efforts. One of the primary causes of failure in stream restoration is the placement of structures or the construction of channel designs that are not suitable for prevailing hydrologic and sedimentologic conditions. Current models cannot accurately predict flow and sediment transport within these channel forms during high flows, which makes it difficult to evaluate potential stability. The contributions of this work include: advancing current understanding of stream stability, channel morphology, flood conveyance, sediment transport, and flow variability in complex river channels, demonstrating the influence of three-dimensional velocity fields on flow and sediment transport in complex channels; investigating the applicability of the velocity reversal hypothesis as a mechanism for understanding sediment transport in pool-riffle sequences during high flows; modeling the influence of secondary circulation in straight and sinuous compound channels to quantify the influence of floodplains on sediment movement and flood conveyance; and demonstrating the capacity of hydrodynamic modeling to improve the planning and design of river restoration projects.