LONGITUDINAL DISPERSION OF POLLUTANTS IN OPEN CHANNELS

Abstract

Longitudinal dispersion is the action by which a flowing stream spreads out and dilutes a mass of pollutant. The rate at which the cloud spreads out, the decrease in peak concentration, and the resulting concentration pattern along the stream are of great importance in pollution control. This phenomenon of longitudinal dispersion has been studied in detail by various researchers in the past, but no satisfactory solution of the problem is available for predicting the time variation of the pollutant concentration at a section. The present research program was designed to develop predictive concentration equations for pollutants. The equations of concentration-time variation for instantaneous, continuous and rectangular pulse injection of conservative as well as nonconservative pollutants have been developed. The various parameters involved in the concentration-time equations may be called dispersion parameters. The dispersion parameters have been functionally related to suitable non-dimensional hydraulic and channel parameters for straight laboratory channels, meandering laboratory channels and natural streams. The unknown constants of the functional relationships of the dispersion parameters have been determined using the steepest descent error minimization method. The concentration equation was validated by using a part of laboratory data of straight and meandering channel and available field data of other investigators which were not used in 0) developing the concentration equation. The performance of the present method was compared with other existing methods. The comparison shows that the performance of present method is better than the existing methods. (