During rainfall events, the weirs located in the sewer networks are working in order to limit the flooding risk and the flow at the inlet of the waste water treatment plant. Thus, a part of the polluted water of the sewer networks go directly into the receiving water without any treatment. The European and French legislation requires that the municipalities monitor and control in terms of quantity the biggest weirs. Due to the compexity of these types of ancillaries, the use of CFD software is one interesting way to quantify the flows and quality masses reaching the receiving water without treatment.

Flow pathlines in a combined sewer overflow
Courtesy of Veolia Environnement