Graphical Sizing and Analysis of Ocean Outfalls with Buoyant Plumes

A graphical model is developed that offers a convenient solution to wastewater disposal problems through submarine outfalls. The model is intended to perform preliminary analysis under worst-case dilution conditions for outfalls with line diffusers, currents from any direction, stratified or unstratified ambient, and submerged or surfacing plumes, and it is also valid for outfalls with single horizontal or vertical ports. The model is thus applicable for most outfall configurations and ambient conditions of practical interest. The model simultaneously considers three dilution mechanisms: initial dilution, dilution through dispersion, and effective dilution due to decay of nonconservative substances. This enables analysis of functional dependencies and grouping of model variables in a way that permits a generalized graphical solution. It also allows one to study the sensitivity of the overall dilution to current speeds and compare the relative performance of perpendicular and parallel line diffusers. The results showed that, contrary to what is widely believed, in most situations of practical interest, high rather than low current speeds are critical in outfall design and parallel rather than perpendicular line diffusers often deliver the best overall performance.