CSOs: tools for assessing their operation in our systems.

In recent years, regulations have been introduced under European legislation to govern wastewater discharge into natural environments, with particular provisions for combined sewer overflows. It has therefore become indispensable to control the hydraulic behaviour of these constructions. This article addresses the issue of 1D and 3D hydraulic modelling of CSOs. In the case of 1D modelling, a computational tool that is adapted to the hydraulic complexity of side weirs has been designed. For 3D modelling, the Fluent calculation code has been tested. The two modelling approaches have been validated by the data collected from the small-scale model in Obernai (French).