  In coastal area, raw wastewater can be directly discharged in the sea during
extreme rain events or failure of the sewage network. The highly urbanized and
touristic area of Nice is directly exposed to this risk. In order to protect
the bathing population and to apply the European regulation (DCE, 2000), Nice
municipality has decided to work on a forecasting tool of transport and fate of
fecal bacterial indicators such as Escherichia Coli. This paper deals with the
first step of this approach which consists in developing a three-dimensional
hydrodynamic simulation coupled with water quality parameters. The model used
is based on Reynolds-Averaged Navier-Stokes's equations for the calculation of
the velocities and water depth (TELEMAC3D), and wave energy balance equation to
account for the wave induced current (TOMAWAC). Two field measurements were
conducted on a real wastewater pollution coming from a sewage pipe located
at-38m depth. The first campaign has validated the vertical diffusion of the
effluent through the water column by the means of variable depth samples and
has stressed the hourly variability of sewage bacterial quality. Due to the
lack of data regarding this last point, the model could not be fully validated.
The second campaign has been designed to overcome this issue and to gather all
the data needed to proceed to the validation of our hydro-ecological
simulation. The comparison of the field measurements and the simulations has
successfully demonstrated the accuracy of the model. But the uncertainty
associated with the laboratory analysis (MPN) are high, making the calibration
and validation processes a complex task. Nevertheless, further research needs
to be done regarding the variability of microbial quality in order to develop
an operational tool allowing the forecast of bacterial pollution. The next step
of this study will be to establish the hourly variation of microbial quality in
the wastewater during dry and raining periods.
