Hydrodynamic and water quality modelling of Southern Evoikos Gulf, Greece

A mathematical model is presented, consisting of a two-layer, finite difference hydrodynamic submodel
and a compartmental water quality sub-model. The model is calibrated with field data. Then, it
is applied to Southern Evoikos Gulf, an open coastal water body of particular ecological significance in
the region of Attiki, in Greece. The application of the model aims at assessing the effect of three alternative
treatment scenarios (i.e. biological treatment, biological treatment with N removal and biological
treatment with N and P removal) performed in four sewage treatment plants (of a total capacity of
1,000,000 equivalent population) on the water quality of the Gulf. The calculations show that N is the
limiting nutrient and its removal results in an improvement of the quality of the recipient, whereas the
additional implementation of P removal has a rather limited impact.