Implementation of a Three-Dimensional Hydrodynamic Model to Determine Flushing Rates in Mosquito Lagoon, FL

The Mosquito Lagoon (ML), a sub-basin of the Indian River Lagoon (IRL) system on the East Central Florida coast, is ∼54 km long and ∼4 km wide having an average depth of 1.5 m. Tidal fluctuation varies less than 15 cm seasonally and circulation is wind dominated. Because of the ML configuration and the location of its inlet (Ponce de Leon Inlet), ocean water entering the system with the tide has a limited reach. This makes ML especially sensitive to sudden influxes of pollutants from increasing human activities within its watershed. Previous studies have indicated that water quality in the ML may be declining but these studies are often compartmentalized or restricted in scope.;A three-dimensional hydrodynamic model called the Environmental Fluid Dynamics Code (EFDC) is established for the Mosquito Lagoon and north segment of Indian River Lagoon to study the relationship between the system dynamics and renewal times for hypothetical pollutant (dye tracer) model applications. Simulations were performed for a one year period (May 1998 to May 1999) when synoptic time series of data were the most continuous. The model applications were focused on: (1) establishing a baseline description of the hydrodynamic regime of the study site according to existing conditions; (2) the relevance of groundwater seepage along the deeper section of the domain (following the ICW); and (3) the implications of introducing a hypothetical pollutant (dye tracer) globally and at individual segments to determine the associated renewal (flushing) times. Results indicate that the Mosquito and North Indian River Lagoon are dominated by the nontidal (low frequency) water level oscillations except at the northernmost part of the ML where the influence of tidal renewal dominates.;Results on the flushing time estimates are reported in terms of the R50 which corresponds to the first day the dye tracer concentration drops to 50% from the initial concentration. The global tracer application results show that only the northern segments of Mosquito Lagoon (ML-ac and ML-df) reach R50 within the year of simulation (day 19 and day 176 respectively). The individual segment cases resulted in lower R50 values and all segments cleared up within the year, the corresponding average value of the segmentation applications for the entire Mosquito Lagoon side yields a renewal (flushing) time of 98 days.