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Definition of mixing zones in rivers

Abstract: The adequate definition of the mixing zone generated by the discharge of an effluent is of great importance, as it serves as support for the environmental authorities on the decision-making about the authorization of the discharge. The evolution of the mixing zone of an effluent is affected by different kind of phenomena as temporal variations on the hydrodynamic conditions, spatial variations in the geomorphology and bathymetry of the receiving water, etc. The correct definition of the mixing zone should take into account these factors, for which the use of mathematical modelling is needed. The turbulent hydrodynamic processes in the near field of the discharge and in the far field occur at different spatial and temporal scales. The mathematical model needs to be able of simulating the hydrodynamic and transport processes on both fields. The present paper proposes a methodology to be followed when the prediction of the extents of the mixing zone generated by an effluent discharged into a river is needed. The methodology consists of the obtaining of the necessary hydrodynamic and pollutant concentration data on the effluent and on the receiving water; the building of the adequate calculation meshes for the modelling; the calibration and validation of the model; and finally the definition of the critical conditions for the prediction of the behaviour of the mixing zone. An example of application of the proposed methodology is shown for a real case, the discharge of the WWTP of Casar de Periedo town in the Saja River, Cantabria, Spain, for which field data have been measured. The prediction of the extents of the mixing zone for this case was made using a hydrodynamic two-dimensional depth-averaged long wave model jointly with a transport model. In order to simulate the near field and the far field jointly, an Embedded mesh system was built. For the Embedded mesh system, it was needed the establishment of conditions for the information exchange between the meshes.

 Fuente: Environ Fluid Mech (2016) 16:209–244

 Editorial: Kluwer Academic Publishers

 Fecha de publicación: 01/02/2016

 Nº de páginas: 36

 Tipo de publicación: Artículo de Revista

 DOI: 10.1007/s10652-015-9425-0

 ISSN: 1567-7419,1573-1510

 Url de la publicación: http://link.springer.com/article/10.1007/s10652-015-9425-0