Considering strong interrelations between hydrodynamic features of the Bosphorus and the tube-tunnel crossing which may affect the performance of marine outfall systems, the Institute of Marine Science and Technology (IMST) conducted a comprehensive meteo-oceanographic data acquisition campaign to collect information both for the reliable design of marine outfall systems and for the environmental impact assessment (EIA) of the railroad tunnel, on the joint request of the owners of the projects.

The main objectives of this paper are to outline the results of the EIA, and also to discuss the newly adopted plan which proposes to divert the sewage collected in the Kadìköy drainage area to Riva, located along the Black Sea. Recent evaluations by the authors on the blocking of lower layer flow, and findings presented on the mixing along the Bosphorus, have been included as scientific evidences in this discussion.