Collaborative Research: Mixing at Stream and River Confluences

该研究项目将使用美国和欧洲大小河流汇合处的实地数据和河流流量的数值模型，以检查加强或抑制河流汇合处下游水、溶质、污染物和沉积物混合的机制。该项目将研究溶质和悬浮物在河流系统中混合的过程，这是近几十年来地貌学家、水文学科学家和相关领域学者研究的一个主要问题。该项目将为河流汇合处促进或抑制混合的因素以及不同水动力机制在混合中的作用提供基础理论基础。从该项目中获得的知识将通过确定潜在污染物在河流网络中扩散的机制而造福社会。这些知识还将有助于河流生态系统的管理，因为它显示了混合如何影响汇合处和这些地点下游的生态系统所依赖的生物地球化学条件。调查人员将与国家大河研究和教育中心、刘易斯和克拉克社区学院以及国家密西西比河博物馆合作，加强大学预科和公共教育，让本科生参与，并传播项目发现。将开发教育材料，分享有关河流混合的新知识和用于产生这些见解的科学方法，并将其纳入K-12学生学习和教师培训活动。该项目将涉及跨学科教育和两名研究生的培训，并与德国的国际合作者合作，将加强研究和教育的基础设施。过去关于这一主题的研究表明，一些汇合流在汇合处附近几乎完全混合，而其他汇合流在汇合处下游数百个渠道宽度处通常保持未混合。决定汇流是以大量混合还是少量混合为特征的因素尚未确定。本项目将确定控制流结构的主要机制；大尺度湍流的产生；以及汇合处的水和悬浮沉积物的混合。该项目将确定这些机制如何随着汇合处的形状、形式、流入流特性和大小的变化而变化。研究人员将对几个小溪流汇合处的混合情况进行详细的实地调查，这些汇合处有不同的汇入支流的几何形状。他们还将开发和验证流动和混合的数值模型。详细的实地调查将产生数据，用于严格评估和改进在一系列流动条件和汇流几何形状下汇流混合数值模型的预测能力。将把模拟的预测结果与其他汇流的现有数据进行比较，以确定该模式适应规模效应以及汇流形式和大小差异的能力。经过改进和校准的模型将用于进行数值实验，以评估各种环境条件下汇合处的混合情况。

This research project will use field data for small and large river confluences in the United States and Europe and a numerical model of river flow to examine the mechanisms that enhance or inhibit mixing water, solutes, contaminants and sediment immediately downstream of river confluences. The project will address the processes through which solutes and suspended solids are mixed in river systems, a major issue that geomorphologists, hydrologic scientists, and scholars in related fields have addressed in recent decades. The project will provide fundamental theory-based insight into the factors that promote or inhibit mixing at river confluences and the role of different hydrodynamic mechanisms in mixing. Knowledge gained from the project will benefit society by identifying mechanisms by which potential contaminants are dispersed when moving through river networks. This knowledge will also be useful for management of river ecosystems by showing how mixing influences the biogeochemical conditions on which ecosystems within confluences and downstream of these locations depend. The investigators will collaborate with the National Great Rivers Research and Education Center, Lewis and Clark Community College, and the National Mississippi River Museum to enhance pre-collegiate and public education, involve undergraduate students, and disseminate project findings. Educational materials sharing new knowledge about river mixing and the scientific methods used to generate those insights will be developed and included in K-12 student-learning and teacher-training activities. The project will involve interdisciplinary education and training of two graduate students, and work with an international collaborator in Germany will enhance infrastructure for research and education.Past research on this topic has shown that some confluent flows mix almost completely within the immediate vicinity of the confluence, whereas others remain generally unmixed hundreds of channel widths downstream of a confluence. The factors governing whether a confluence is characterized by large or small amounts of mixing have yet to be determined. This project will identify the main mechanisms that control flow structure; generation of large-scale turbulence; and mixing of water and suspended sediment within confluences. The project will determine how these mechanisms change as the shape, form, incoming flow characteristics, and size of confluences vary. The investigators will conduct detailed field investigations of mixing at several small stream confluences with different geometrical configurations of the incoming tributaries. They also will develop and validate numerical models of flow and mixing. The detailed field investigations will generate data for rigorously evaluating and refining the predictive capabilities of the numerical model of confluence mixing over a range of flow conditions and confluence geometries. Predictions from simulations will be compared to available data for other confluences to ascertain the capabilities of the model to accommodate scale effects and differences in confluence form and size. The refined and calibrated model will be used to perform numerical experiments to evaluate mixing at confluences over a broad range of environmental conditions.