Dispersion in Rough Rectangular Channels

A three-dimensional numerical model is developed from a two-dimensional solution reported previously by the writers. A rectangular smooth laboratory flume is used to verify the model without dead zones; two series of field experiments carried out in a water race are then used to test the model for two different roughness conditions. Despite the simplifications involved in the numerical model, it provides a reasonable description of the process in the channel examined. Principally, there is a delay before the Fickian-type dispersion and the dispersion coefficients are comparable with those found in the field. Although the theory has not reached a stage where it can be applied to most rivers, it does lend itself to the possibility of a classification system for dead zones in river channels and it demonstrates the importance of the trapping mechanism to the dispersion process in river channels.