University of Illinois Urbana-Champaign

Rates and patterns of temperature mixing at a small stream confluence under variable incoming flow conditions

Lewis, Quinn

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Quinn_Lewis.pdf

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https://hdl.handle.net/2142/50737

Description

Title
Rates and patterns of temperature mixing at a small stream confluence under variable incoming flow conditions
Author(s)
Lewis, Quinn
Issue Date
2014-09-16
Director of Research (if dissertation) or Advisor (if thesis)
Rhoads, Bruce L.
Department of Study
Geography & Geographic InfoSci
Discipline
Geography
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Date of Ingest
2014-09-16T17:26:02Z
Keyword(s)
  • hydrology
  • hydraulics
  • temperature mixing
  • river confluences
Abstract
River confluences are locations in the fluvial network where two incoming flows, often with distinct chemical, thermal, and physical properties, converge and start to mix. The degree of mixing that occurs within a confluence influences ecological and water quality conditions locally as well as farther downstream. Nevertheless, variations in rates and patterns of mixing at confluences under different flow conditions are poorly understood. This study examines the influence of momentum flux ratio, total discharge, and density differences between incoming flows on mixing at a small stream confluence. Temperature data reveal that rates and patterns of mixing depend on event-specific combinations of the three factors. The bottom part of the mixing interface at this asymmetrical confluence is generally distorted towards toward the mouth of the lateral tributary by strong helical motion associated with curvature of flow from the lateral tributary as it turns to become aligned with the direction of the downstream channel. As the relative contribution of lateral momentum flux from the tributary increases, velocities of flow from the lateral tributary tend to increase, the mixing interface is deflected away from the tributary mouth, and helical motion from the curving tributary flow extends over most of the channel cross section within the confluence. These condition enhance lateral mixing. Total discharge and flow depth are negatively correlated with mixing rates, suggesting that that rates of mixing over the fixed control volume at the confluence is inversely related to the scale (volumetric rate) of flow. Density differences between incoming flows may influence mixing under certain conditions, but overall appear to be less important than momentum ratio and total discharge. Results confirm that although mixing rates within the region of confluent flow interaction can be highly variable among flow events with different incoming flow conditions, in general the length scales are small and rates of mixing are large at this small confluence e compared to those typically documented at large river confluences.
Graduation Semester
2014-08
Permalink
http://hdl.handle.net/2142/50737
Copyright and License Information
Copyright 2014 Quinn W. Lewis

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Graduate Dissertations and Theses at Illinois PRIMARY
Graduate Theses and Dissertations at Illinois
Dissertations and Theses - Geography and Geographic Information Science