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The Effects of the Width to Depth Ratio on the Process of Transverse Mixing of Pollution in Open Channels

Congress: 2008
M. Pourabadi, E. Amiri, A. Liyaghat Department of Irrigation and Reclamation Eng., College of Agriculture, University of Tehran, Karaj, Iran, P.O. Box: 31587-77871 Tel-Fax: +98-261-2241119

Keyword(s): Transverse Mixing Coefficient, Control Pollution, Tracer, Mixing Process
AbstractAbstract Due to increasing of the world population and the deficiency of the reliable resources of suitable water, there is a highly request for optimal use of both surface and ground water. The continuous growth of the pollution of surface water around the world, especially in developing countries is one of the most critical issues for human communities. In this regard, using the mixing processes and dilatation of the pollutants to refine and to make the possibility of reusing the polluted water, is one of the methods to increase the amount of useable water. Transverse Mixing Coefficient (TMC) is one of the hydraulic parameters of the flow by which the amount of self -refinement and dilatation of the flow inside rivers can be estimated. In this research, the effects of the ratio of width to depth on the hydraulically behaviour of flow and, accordingly, on the TMC has been studied. Using a rectangular straight channel (12 m of length and 0.25 m of width), from a point source with a constant head, a paint material (tracer) has been continuously released into the water flowing inside the canal. Then by measuring the concentration of pollutants in several sections located in different length from the point source, TMC has been determined. Accordingly, the effects of the variation of width to depth ratio in different conditions on TMC have been investigated. The results show that the secondary circulations in narrow waterways have more relative power and hence have more effects on the flow. As a result, the turbulent intensity and accordingly, the turbulent diffusion have been increased. However, due to high shear velocity, the amount of dimensionless transverse mixing coefficient is less than those have been computed by other researchers.
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