Fluvial Dynamics of Large River Confluences

汇流处是两条河流交汇的地方，是天然河流网络的基本组成部分，但大多数汇流处的水流，泥沙运动和河道变化的研究都集中在实验室汇流和小型天然汇流。小规模研究得出的结论的相关性知之甚少，大河汇流和一个关键的需要存在的过程为基础的实地调查大河汇流，探讨汇流动态变化与空间尺度和网络规模的水沙运动的影响。本项目将探索各种控制因素，包括汇流几何形状，上游支流的动量比，对大型河流汇流中的水流结构和河道形态变化的影响。将在印第安纳州瓦巴什河系统沿着具有不同几何形状的三个交汇处收集有关河道形态、三维水流结构和河床地形的现场数据。数据收集活动将与厄巴纳的美国地质调查局地区总部合作进行，该总部拥有一整套用于大河研究的最先进仪器。在三年的时间内，将在每个汇合点每年收集一到两个事件的数据。将选择一套抽样事件来代表每个地点的一系列水文条件。数据分析将涉及开发三维计算机绘制的河床形态空间模式、三维速度场和每个地点的水温/混合情况，以探讨汇流平面形状、动量流量比和河床形态对汇流动态的影响。该分析将包括汇流床形态变化的文件，这些变化是由来流动量-流量比的变化引起的，以及流结构和混合对这些变化的响应。通过与英国利兹大学和谢菲尔德大学的研究小组的持续合作，现场数据将被用作三维水流高级数值模型的输入，以测试该模型模拟天然大河汇流水流的能力。数值模拟将补充现场调查，允许现场特定位置的调查结果更完整地理解在理论背景下，并提供解释一般过程如何表现出不同的现场特定的背景下的基础。除了提供对大型河流汇流的动态和汇流在调节河流网络中的水和沉积物通量方面的作用的基本见解外，研究结果有助于改善对与汇流处沉积/侵蚀有关的实际问题的理解和管理，例如河流航行，通过详细界定大河汇流处的自然生境条件，加强河流地貌与生态之间的联系，以及涉及河流系统内污染物和其他溶解或悬浮成分的扩散的应用问题。 这项研究将直接与大学和K-12教育和推广活动联系在一起，通过伊利诺伊大学新成立的水作为一个复杂的环境系统中心。与美国地质调查局的伙伴关系是该项目的一个关键组成部分，通过这种伙伴关系，研究成果有真实的机会融入更广泛的国家利益方案和活动。 (This行动是一个即将离任的机构间协议，以支持美国地质调查局在实地收集数据方面的技术援助。

Confluences, the locations where two rivers join, are fundamental components of natural river networks, yet most studies of flow, sediment movement and channel change at confluences have focused on laboratory confluences and on small natural confluences. Little is know about the relevance of conclusions derived from small-scale studies for large-river confluences and a critical need exists for process-based field investigations of large-river confluences to explore how confluence dynamics change with spatial scale and implications of such changes for network-scale movement of water and sediment. This project will explore the influence of various controlling factors, including confluence geometry, momentum ratio of the upstream tributaries, on flow structure and changes in channel form within large river confluences. Field data on channel form, three-dimensional flow structure and bed topography will be collected at three confluences along the Wabash River system in Indiana that exhibit different geometries. Data-collection activities will be conducted in collaboration with the District Headquarters of the U.S. Geological Survey in Urbana, which maintains a full suite of state-of-the-art instrumentation for large-river research. Data will be collected for one to two events per year at each confluence over a period of three years. The suite of sampled events will be chosen to represent a range of hydrological conditions at each site. Data analysis will involve the development of three-dimensional computer-based renderings of spatial patterns of bed morphology, 3-D velocity fields and water temperature/mixing at each site to explore the influences of confluence planform, momentum-flux ratio and bed morphology on the dynamics of the confluences. This analysis will include documentation of changes in confluence bed morphology resulting from changes in momentum-flux ratio of incoming flows, and the response of flow structure and mixing to these changes. Through an ongoing collaboration with research teams at the University of Leeds and the University of Sheffield in the UK, the field data will be used as inputs to an advanced numerical model of three-dimensional flow to test the capability of the model to simulate flow through natural large-river confluences. The numerical modeling will complement the field investigation by allowing findings for site-specific locations to be understood more completely within a theoretical context and by providing the basis for explaining how general processes manifest themselves differently in site-specific contexts. Besides providing basic insights into the dynamics of large river confluences and the role of confluences in regulating fluxes of water and sediment through river networks, results of the research contribute to improved understanding and management of practical issues related to sedimentation/erosion at confluences, such as river navigation, enhanced linkages between river geomorphology and ecology by defining in detail physical habitat conditions at large-river confluences, and applied problems involving the dispersal of contaminants and other dissolved or suspended constituents within river systems. The research will be tied directly to university and K-12 education and outreach through the newly established Center for Water as a Complex Environmental System at the University of Illinois. A partnership with the U.S. Geological Survey is a critical component of the project and, through this partnership, real opportunity exists for results of the research to become integrated into broader programs and activities of national interest. (This action is an outgoing interagency agreement to support the USGS's technical assistance in the collection of data in the field.)