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Over-Bank Flows


Project Summary

The primary objective of this project was to expand on current research in the field of solute dispersion during overbank flows. One of the main research papers that analyses the dispersion of a solute in overbank flow conditions was published by Kay (1987). However, this only uses mathematical theory to display results of solute dispersion in an infinitely wide channel. Since then, both Shiono et al. (2003), and Spence and Guymer (2009) have further analysed the effects that compound channel flow has on the transverse dispersion of solutes.

To further investigate solute dispersion, a solute tracer was injected into a compound channel and transverse mixing was observed. To differentiate the experiments from past research, vegetation that is usually present on floodplains was simulated and varied.

The experiments were conducted in a large flume in the laboratory of the School of Engineering at the University of Warwick. Conducting experiments in a simplified channel provided sufficient control to gather results that could be easily applied to a number of different practical situations. To prepare the channel for the experiments that were conducted, a number of modifications were made. Firstly, a gradual slope was created in the channel to ensure that uniform flow conditions could be achieved and that the experiments could be analysed using mathematics.

Having constructed the slope, the next stage was to create the channel bank. For simplicity, this was only constructed on one side of the channel to simulate half of the cross-section of a river. To simulate vegetation on the flood plain, a 10 mm grade of gravel was laid along the length of the flume.

The solute tracer consisted of Rhodamine dye and was injected into the upstream flow at a predetermined location. The dispersion of this dye was then observed by taking readings using a Turner Designs’ fully submersible Cyclops fluorometer. These readings were taken at a number of specific cross-sections at set distances down the channel. The data obtained was then analysed so that a suitable model was produced to predict the dispersion of a pollutant over a larger area of a channel.

The Flume

flume 3