Predicting Dispersion Coefficient of Streams

Using inspectional analysis, a simple formula has been derived which relates the longitudinal dispersion coefficient of natural streams to several bulk flow properties such as the discharge and the hydraulic radius. It is shown that the dimensionless factor, β, of the formula, unlike the dimensionless dispersion coefficient α based on Elder's equation, is independent of the size of natural streams. An analysis of existing data indicates that the value of β for any stream may be predicted within a factor of six from the frictional or resistance factor of the stream. This means the proposed equation for predicting longitudinal dispersion is more accurate than any existing method based on bulk flow properties.