A computer program for the calculation of the internal hydraulics of outfalls equipped with multiport diffusers is developed and applied to different geometric configurations. The program calculates the velocities, pressures, head losses and flow rates inside the diffuser pipe and especially at the diffuser port orifices. Possible geometries consider simple ports, high risers and more complex discharge configurations for the openings, as well as various supply pipe configurations. The calculation is based on the application of the continuity and work-energy equations between the ambient fluid at the discharge point and the effluent inside the diffuser pipe. Preliminary calculations show the sensitivity of the geometric manifold features. Further calculations may aim at the design and optimization of the diffuser structure under different ambient and discharge conditions. The overall design objective is a balanced flow distribution under most of the operational conditions with minimized energy losses. @en