Sewage outfall plume in the two-layer channel: an example of Istanbul outfall

Abstract

Municipal wastewater from the city of Istanbul is discharged into the Bosphorus Strait through an outfall built on the southern end of the Strait. The behaviour of the wastewater plume in the Bosphorus environment is quite complicated as a result of the two-layer stratification, the rapid currents flowing in opposite directions in each layer, their transverse variations, and the turbulence and entrainment processes in the ambient waters. The wastewater is injected from 22 diffuser ports on each of the two pipelines located in a depth range of 40-60 m. The numerous plumes from the multiple ports combine to yield a line source of plume-like behaviour in the far-field. The plume typically rises due to its buoyancy in the lower layer, and becomes arrested at the interface between the upper and lower layers of the Bosphorus, but the swift undercurrents bend the plume to align it with the interface along the Bosphorus.