Modelling faecal coliforms dynamics in the Seine estuary, France

A model describing the dynamics of faecal coliforms (FC) in the Seine estuary has been developed and coupled with a three-dimensional hydrodynamic model. As input to this model three types of FC sources were considered: (1) FC transported by the Seine river flow at the estuary entrance at Poses dam; (2) FC brought in through the tributaries of the Seine estuary; and (3) the outfalls of the treated effluents of the WWTPs located along the estuary. As previous studies in the Seine estuary showed that a large proportion of FC was attached to SM, two pools of FC were considered separately in the model: free FC and FC attached to SM. Two main processes controlling the fate of FC in the estuary were considered: mortality and settling. The model calculates for a given discharge of the Seine river at Poses the longitudinal distribution of FC along the estuary. The model was validated by comparison of model calculations with experimental data in various hydrological conditions. The model also correctly reproduced the impact of the main river flow rate on the level of estuarine water's contamination. Finally, the model was used to test different scenarios of sanitation, suggesting priorities for sanitation efforts.