TRANSVERSE MIXING IN OPEN CHANNELS WITH MULTI-POINTS POLLUTANT SOURCES

Abstract

Stream serve as source of water for various uses like water supply, generation of hydroelectric power, recreation, navigation etc, and also as sink of waste substances resulting from human activities. Wherever streams act as sinks for intentional or accidental spillage of effluents resulting from the activities of society, it becomes necessary to know the concentration of pollutants downstream of its point of injection into the stream to check whether the required environmental standards are being satisfied or not. Although many excellent models are available to make predications for concentration of pollutants in process of transverse mixing in open channel. The present study comprises solution of a two-dimensional transverse mixing equation and its subsequent application to a field problem. The simulation is based upon a finite volume method base numerical solution of two dimensional mixing equations. A computer code has been developed in FORTRAN language to implement the solution. Experiments were carried out to investigate the transverse mixing coefficient and concentrations in an open rectangular channel under uniform flow conditions and tracer (Dye) was continuously injected into the open channel flow at the bank and middle of the channel. The dye concentrations at different downstream longitudinal distances from the point of injection were measured. The work of other researchers, show that the transverse mixing coefficients vary with the product of the shear velocity and flow depth. It was concluded from this study that the dimensionless transverse mixing coefficient remains virtually unchanged under different bottom roughness conditions. Steady state models based on the stream tube concept are presented to predict far-field concentration distributions of pollutants in mixing zones of C rivers. Analytical solutions for pipe and diffuser outfall sources, presented by Yotsukura and Cobb (1972) are modified to account for the reach- dependency of pollutant decay rate, transverse diffusion factor and channel hydraulic parameters.