Collaborative Research: Mixing at Stream and River Confluences

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

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.