Conceptual Design of Submarine Outfalls - II: Hydraulic Design of Diffusers

For a given ocean outfall, improvement of dispersal of sewage effluent is accomplished by use of a multiple jet manifold or diffuser at the end of the outfall sewer. If the sewage is discharged at a single port or "en masse", its dispersion and dilution will be slower than if it is discharged over a large area through a number of ports, as explained in the preceding lecture. In fact, without the use of multiple-outlet diffusers, other conditions being equal, much longer outfalls into deeper water are necessary to provide the same degree of dispersion and consequent shore protection. An effective and simple type of diffuser is one which distributes the outflow through many ports over a large area with minimum head loss. The following discussion presumes a diffuser consisting of one long pipe, or several branching ones, with discharge ports at intervals along the pipes.