Environmental model studies for the Istanbul Master Plan. Part II: water quality and eutrophication

A comprehensive environmental modelling study has been carried out to support the Istanbul Master Plan Study reviewing the waste water strategy for the period up to year 2030, at which time the sewerage system is expected to be extended to serve about 20 million people. Already today the local marine areas suffer from pollution effects caused by sewage discharge. The affected areas in particular are the Bosphorus Strait and the Bosphorus Strait-Sea of Marmara junction area, which are also the natural receiving waters for the sewage from the planned new development areas of Istanbul. The general conditions of the entire Sea of Marmara are also of concern. The object of the study was to determine the effects of the waste water effluent on the marine system and to evaluate alternative plans for sewage treatment and location of outfalls. An advanced 3-Dimensional model of the Black Sea-Bosphorus Strait-Marmara Sea junction area has been set-up and used for studying the immediate effects on oxygen conditions for a two week long design period. A 3-Dimensional model has been set up for the Sea of Marmara with the purpose of studying the effects of eutrophication over a one year period, which is necessary in order to describe the processes involved. These models are based on SYSTEM 3, a general modelling system for baroclinic flow, including modules describing water quality and biological/eutrophication processes. The various loading scenarios evaluated included variation in outfall location horizontally and vertically, e.g. in top layer versus halocline or bottom layer trapping and variation in treatment strategy, e.g. no treatment, biological and tertiary treatment.