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

0087842 Kitanidi人们认识到，三维流动动力学影响河道形态以及河道内沉积物的运动和分布。 在复式断面、滩槽序列和曲流系统发育的河道中，三维流速场对二次流环流的影响对河流水动力和泥沙运动都有深远的影响。 本项目的目标是开发和验证一个三维水动力和泥沙输运模型，该模型适用于详细的现场规模研究，以调查高流量事件期间复杂的三维水流结构对以下方面的影响：（a）池-浅滩序列，（B）复合河道，和（c）蜿蜒复合河道。 本研究将探讨这些水流结构对二次环流的影响，以及泥沙的侵蚀、淤积和输移。 该项目利用现有的半隐式非结构网格上的非静力自由面流的数值模型。 该模型是基于三维Navier-Stokes方程，并利用半隐式算法，是强大的，稳定的，非常有效的。 该模型将与一个移动的床模型相结合，用于悬浮和推移质泥沙输运。对复杂河道中水流和泥沙状况的透彻了解对于规划和开发成功的河流恢复工作至关重要。 河流恢复失败的主要原因之一是结构的布置或河道设计的建造不适合当时的水文和沉积条件。 目前的模型无法准确预测高流量期间这些河道形式内的水流和泥沙输运，这使得难以评估潜在的稳定性。 本文的贡献包括：提高了对复杂河道水流稳定性、河道形态、洪水输移、泥沙输移和水流变异性的认识，揭示了三维流速场对复杂河道水流和泥沙输移的影响;调查速度反转假设作为理解池中沉积物输运机制的适用性，高流量时的浅滩序列;模拟二次环流在直的和弯曲的复式河道中的影响，以量化洪泛区对泥沙运动和洪水输送的影响;并展示水动力模拟的能力，以改善河流恢复项目的规划和设计。

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.