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

人们认识到，三维水流动力学影响河道形态和河道内泥沙的运动和分布。在断面复杂、冲刷顺序型、曲流系发育的河道中，三维速度场对二次流环流的影响对河道水动力和泥沙运动都有着深远的影响。该项目的目标是开发和验证适用于详细现场研究的三维水动力和泥沙输移模型，以调查在高流量事件期间复杂的三维水流结构在以下情况下的影响：(A)池-冲刷序列，(B)复合河道，和(C)曲折复合河道。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。该项目利用现有的非结构网格上非静水静力自由表面流动的半隐式数值模式。该模型以三维N-S方程为基础，采用了一种稳健、稳定、高效的半隐式算法。该模型将与用于悬沙和推移质泥沙输送的流动河床模型相结合。彻底了解复杂河道中的水流和泥沙状况，对于规划和发展成功的河流修复工作至关重要。河流修复失败的主要原因之一是建筑物的布置或渠道设计的建设不适合当前的水文和沉积条件。现有的模型不能准确地预测这些河型在大流量时的水流和泥沙输移，这使得对潜在稳定性的评估变得困难。这项工作的贡献包括：促进了对复杂河道中的河流稳定性、河道形态、洪水输运、泥沙输移和水流变异性的了解，展示了三维速度场对复杂河道中水流和泥沙运动的影响；调查了速度反转假说作为理解高流量时泥沙输移的机制的适用性；模拟了直和曲折复合河道中的二次循环影响，以量化泛滥平原对泥沙运动和洪水输送的影响；展示了水动力模拟的能力，以改进河流修复工程的规划和设计。

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.