Analytical Study on Dispersion of Effluent Discharges into Tidal Waters

The number of marine outfall systems along the Omani coastal areas is growing. This outfall disposal system consists of long (submerged) pipelines which terminate in a diffuser that discharges a large volume of municipal wastewaters, cooling waters, or desalination brine effluents to the Oman sea. Major wastewater treatment plants operated by Muscat Municipality are located at As-Seeb, Al-Ansab, and Darsait. Cooling waters are required to cool crude oil stored in PDO tank farms at Mina al Fahal, Muscat and in many industrial facilities at the Port of Sohar. Major power and seawater desalination plants of Oman are located at Sohar, Barka, Al-Ghubrah, Qurayyat, Sur and Salalah. In addition to optimized efficiency, reliability and economical construction costs of marine outfalls, the present day design of outfall systems requires clear proof of minimal adverse environmental and ecological impacts that complies with the water quality standards and minimal public health impacts. A mathematical model for dispersion of effluent discharges under tidal oscillation currents on a sloping beach is studied analytically using the solution of a two-dimensional time-dependent advection-diffusion equation. The solution is presented graphically by contour plots of concentration to visualize the evolution and spreading of effluent discharge plumes in coastal waters. The concentration at the shoreline and at the centerline of the plume are examined by varying the model parameters. A time-varying discharge strategy and compounded concentration from two outfalls, and via multiport diffuser as well, are included in this investigation as practical engineering applications of the model, which illustrate how tidally oscillating currents affect the mixing and spreading of effluent continuously being discharged through marine outfall systems from coastal industrial plants.