TRANSFER OF COMBINED SEWER OVERFLOWS IN THE SEINE RIVER

The understanding of transport and dispersion of combined sewer overfl ows (CSOs), containing both dissolved and particulate matters, is a ma jor component of a research program dealing with the assessment of imp acts of CSOs on the Seine River. This study has combined field measure ments and the development of modelling tools. The first experimental r esults stress the fact that predictions of the behaviour of dissolved matter require the use of a fully two-dimensional hydraulic model, bec ause the dispersion process seems to strongly depend on geometrical fe atures of the fiver - meanders and the differential advection they ind uce. Concerning the particulate matter. it appears that different fact ors govern its downstream transport, namely. settling properties. crit ical shear stress, and vertical diffusivity. These factors may produce forces on particles of the same order of magnitude, but in opposite d irections. Special experiments are needed to determine precisely how t hese forces combine.