Methodology for the definition of the mixing zones of punctual discharges in coastal waters

Abstract

The European Union allows the designation of mixing zones (MZ) adjacent to a punctual discharge. Concentrations of one or more substances could exceed the environmental quality standards in the MZ if the rest of the water body meets the standards. However, the European Union does not explain how to define it. In this paper, the simulation of the MZ is done through two free software, Discharge Test and Visual Plumes. Discharge Test is used to perform a first analysis of the proposed scenario and to assess the discharge effects on the receiving environment. Visual Plumes is used to analyze in more detail these effects and the behavior of the polluting plume. The results obtained, for a mercury discharge from an outfall that discharges into the coastal zone of the Mediterranean Sea, show that these models could be a useful tool for the determination of MZ. A methodology is defined to delimit the MZ for an outfall. This MZ will be the circular surface, with a radius equivalent to the estimated distance, around the discharge point.