A Decision Analysis Approach To A Coastal PollutionProblem: The Sewage System Of The City OfThessaloniki (Greece)

Abstract

Coastal areas (shorelines and waters) are valuable nature resources, but due to their economic importance, are used intensively by mankind (recreation, tourism, aqua-culture, fishing etc.). These uses create pollution problems and the subsequent deterioration of the aquatic ecosystem. The pollution problems are created from the discharge of domestic and industrial waste waters, the drainage waters from agricultural areas, the oil-spills and the construction of coastal works. A methodology towards the management of coastal water quality may be based on the decision analysis approach. This work describes the application of such a methodology to the pollution problem of Thermaikos Bay. The Thermaikos Bay, a semi-enclosed bay in the NW Aegean Sea, with the city of Thessaloniki (about one million inhabitants) in its northern coast, is particularly sensitive to pollution problems. The most important source of pollution is the domestic sewage and the industrial waste waters. The sewage waters are estimated at 160.000 nrVday, of which the 25% are treated, while a new treatment plant is under construction for the whole sewage quantity. An outfall will discharge the waste waters after treatment into the bay, at a depth of 20m. To evaluate the different scenarios of the waste water management and the outfall design, a mathematical model of the baroclinic coastal circulation has been applied to the Thermaikos Bay. A mass balance equation is added to the baroclinic model to simulate the concentration of a conservative tracer. This approach provides the concentrations of the polluting particles dissolved in