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Modeling of Dispersion in Natural Streams with Pools and Riffles

by Il Won Seo, Illinois State Water Survey, Champaign, United States,
W. Hall C. Maxwell, Illinois State Water Survey, Champaign, United States,



Document Type: Proceeding Paper

Part of: Hydraulic Engineering

Abstract:

The non-Fickian nature of the dispersion process in natural channels with pools and riffles has been investigated through both laboratory experiments and the numerical solution of a proposed mathematical model that is based on a set of mass balance equations describing mixing and mass exchange mechanisms. Laboratory experiments, which involved collection of data on channel geometry, hydraulics, and dye dispersion, were conducted on a model of four pool and riffle sequences in a 49-m 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. In the pools the recirculating flow, oriented in a horizontal plane, results in a strong storage mechanism for the water and tracer, but no storage zone exists because of vertical location. All concentration-time curves measured, regardless of bed types and flow rates, are significantly skewed with long tails. Comparisons of results of the mathematical model with measurements indicate that the natural process is strongly non-Fickian.

Subject Headings: Mathematical models | Flow measurement | Mathematics | Numerical models | Fluid flow | Water storage | Rivers and streams

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