Abstract
Coastal industrial plants dispose of their wastewater effluents into shallow coastal waters through sea outfalls. When two or more outfalls along a coastline are discharging, the long-term impacts are interdependent. Analytical solutions of two-dimensional advection-diffusion equations with a two-point source in a spring-neap oscillating tidal current on a sloping seabed are presented to study the far-field merging and interaction of two discharged effluent plumes in coastal waters. The elongated plumes are spreading towards the shoreline, and thus, asymptotic approximation is made to the analytical solution to assess the long-term build-up of effluent concentration at the shoreline. To show case the applications for effluent disposal, two types of discharge were considered: (i) through two adjacent outfalls and (ii) using a two-port diffuser. In comparison with discharge through a single outfall, it is found that sharing the load of effluent discharges through two adjacent outfalls or using a two-port diffuser could reduce the potential impact on coastal marine environment.