Modeling the Praia dos Ingleses submarine outfall, Florianópolis, Santa Catarina, Brazil

An outfall 1,800 m long was initially proposed by CASAN (Water and Sanitation Company of Santa Catarina) to dispose of treated domestic residual water effluent from Praia dos Ingleses beach. The final plan average flow, estimated for the summer season is 0.1543 m³/s. The characteristics on the near field of the diffuser were calculated using the NRFIELD model supplied by a series of current profiles and density, gathered at the diffuser location between March and April, 2007. Reliable information of raw sewage fecal coliform concentration and nutrients has been supplied by CASAN, based on continuous monitoring of sewage in its treatment plants. The diffuser was designed in such a way that it maximizes the initial dilution allowing the nutrients concentration to comply with legislation limits. However, results showed that the treatment plant should be designed to mainly reduce total phosphorus. A hydrodynamic model was implemented to generate current fields for the far field modeling. Information gathered in the field on variation in water level, wind, and current velocity and direction was used for boundary and/or initial conditions. Then, a Lagrangian advective–diffusive model was used to evaluate the extent of the plumes. The results of far field modeling showed a need to increase the outfall length. A new location 3,300 m from the beach has been proposed.