Knowledge of dispersion of pollutants in streams is necessary for the determination of both the acceptable limits of effluent input and the concentration along the river course. In the far-field, the primary variation of concentration is in one direction and termed longitudinal dispersion; it is independent of the geometrical configuration and type of source. The longitudinal dispersion coefficient represents the dispersive characteristics of a stream and is required to compute the pollutant concentration at downstream locations of the streams. The longitudinal dispersion coefficient can be estimated either from the pollutant concentration profile, stream velocity profile or channel and flow parameters. Many laboratory and field studies have been carried out by several investigators to develop relationships for the longitudinal dispersion coefficient in terms of the known hydraulic characteristics of the stream. This paper evaluates the accuracy of the existing empirical relationships for the prediction of longitudinal dispersion coefficient, using a large volume of data that cover a wide range of flow and channel parameters.

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