Doctoral Dissertation Research: Influence of Riparian Vegetation on Near-Bank Flow Structure and Erosion Rates on a Large Alluvial River

曲流冲积河流的冲岸过程是通过河道等高线、水流的三维结构、输沙的三维结构以及河道两岸和洪泛平原的岩土力学特征等因素的动态相互作用而发生的。河岸侵蚀的速度还受到河岸上生长的植被类型的影响——这一因素仍然知之甚少，因此在河流形状演变模型中通常被忽视。本博士论文研究项目的目标是通过表征河道堤岸的岩土力学特性以及森林和非森林弯道的近岸水流结构，研究河岸植被对大型冲积河流曲流迁移的影响。通过获得森林和非森林河湾的总体粒度分布、内聚力、根抗拉强度和水力导电性等数据，将对河道堤岸和洪泛平原进行表征。时间平均和瞬时速度测量将在森林和非森林的曲流弯道的不同水流阶段进行，以表征河流弯道附近的水流结构，以及它在不同条件下如何与河道两岸相互作用。此外，将使用最先进的技术对河床和河岸进行重复的详细的水深和形态调查。分析将集中在水流结构、植被和洪泛区沉积物的岩土特性之间的相互作用，以评估森林和非森林弯道中河岸侵蚀的差异。本研究结果将为深入了解大型曲流河流河道形态演变的动力学过程以及植被在这一过程中的影响提供基础。这项研究将产生可用于校准、测试和评估河流形状动力学数值模型的数据，从而更准确地模拟蜿蜒河流的河道变化。河道变化的预测很重要，因为蜿蜒的河流经常形成州和国家之间的政治边界，被用作货物的交通方式，并为水生生物提供了广泛的栖息地。当一条蜿蜒的河流在其泛滥平原上迁移时，它会导致土地的损失，对人类基础设施的破坏，并将大量的沉积物引入河流系统。因此，提高对曲流河流河岸侵蚀过程的理解不仅具有重要的科学意义，而且对环境和社会问题具有重要意义。

The process of bank erosion in meandering alluvial rivers occurs through the dynamic interactions between channel contours, the three dimensional structure of water flow, sediment transport, and the geotechnical characteristics of the channel banks and floodplains. Rates of bank erosion are also influenced by the type of vegetation growing on the banks - a factor that is still poorly understood and therefore commonly neglected in models of river shape evolution. The goal of this doctoral dissertation research project is to examine the influence of bank vegetation on the migration of meanders in large alluvial rivers by characterizing the geotechnical properties of channel banks as well as the near-bank water flow structure for forested and non-forested bends. Channel banks and floodplains will be characterized by obtaining data on the bulk grain size distribution, cohesion, root-tensile strength, and hydraulic conductivity for forested and non-forested river bends. Time-averaged and instantaneous velocity measurements will be taken at various water flow stages in forested and non-forested meander bends to characterize the water flow structure near the river bends and how this interacts with the channel banks under differing conditions. In addition, repeat detailed bathymetric and morphologic surveys of the channel bed and banks will be obtained using state-of-the-art technologies. Analysis will focus on interactions among flow structure, vegetation, and the geotechnical properties of floodplain sediments to evaluate differences in bank erosion in forested and non-forested bends. The results of this research will provide basic insight into the dynamics of how the shapes of channels in large meandering rivers evolve and the influence of vegetation in this process. The research will produce data that can be used to calibrate, test, and evaluate numerical models of river shape dynamics, allowing for more accurate simulations of channel change in meandering rivers. Prediction of channel change is important because meandering rivers often form political boundaries between states and countries, are used as traffic ways for goods, and provide a vast range of habitats for aquatic organisms. As a meandering river migrates across its floodplain, it can result in loss of land, damage to human infrastructure, and introduction of large amounts of sediment into the river system. Thus, an improved understanding of bank-erosion processes in meandering rivers is not only important scientifically, but has important implications for environmental and societal concerns.