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https://hdl.handle.net/2142/22084
Description
Title
Low flow mixing in open channels
Author(s)
Seo, Il Won
Issue Date
1990
Doctoral Committee Chair(s)
Maxwell, W.H.C.
Department of Study
Civil Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Environmental Sciences
Language
eng
Abstract
In problems involving water quality and pollution in natural streams under low flow conditions, during which pollution problems are most acute, a complete understanding of the effects of variations of flow and channel geometry on mixing and transport of polluted releases is necessary to establish sound water pollution control programs as well as water resources management programs.
In this research, a systematic and comprehensive study of the effects of variations of flow and channel geometry on mixing and transport of polluted releases in natural streams under low flow conditions has been conducted. The non-Fickian nature of the low flow mixing in natural channels has been investigated using both laboratory experiments and the numerical solution of the proposed mathematical model which is based on a set of mass balance equations describing the mixing and mass exchange mechanisms, in which the effect of channel storage zones was included.
Laboratory experiments, which involved collection of channel geometry, hydraulic, and dye dispersion test data, were conducted to obtain sets of experimental data on a model of four pool and riffle sequences in a 161-ft long tilting flume in the Hydrosystems Laboratory at the University of Illinois at Urbana-Champaign. The experimental results indicate that the flow over the model pool-riffle sequences is highly non-uniform. Concentration-time curves are significantly skewed with long tails. The measured dispersion coefficients and the mass exchange coefficients are close to those measured by previous investigators.
The mixing and dispersion in the laboratory channel was simulated using a numerical solution of the proposed mathematical model in which the 6-point finite difference method developed by Stone and Brian was used as a solution technique. The comparison between the measured and predicted concentration-time curves shows that there is a good level of agreement in the general shape, peak concentrations and time to peak. The proposed model shows significant improvement over the conventional Fickian model in predicting the dispersion process in natural channels under low flow conditions.
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