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ABSTRACT: A nontraditional application of the Hydrological Simulation Program - FORTRAN (HSPF) model to simulate freshwater discharge to upper Charlotte Harbor along Florida's west coast was performed. This application was different from traditional HSPF applications in three ways. First, the domain of the model was defined based on the hydraulic characteristics of the landforms using small distributed parameter discretization. Second, broad wetland land forms, representing more than 20% of this area, were simulated as reaches with storage-attenuation characteristics and not as pervious land segments (PERLNDs). Finally, the reach flow-tables (F-Tables) were configured in a unique way to be calibrated representing the uncertainty of the storage-attenuation process. Characterizing wetlands as hydrography elements allows flow from the wetlands to be treated as a stage-dependent flux. The study was conducted for the un-gauged portion of the Peace and Myakka rivers in west-central Florida. Due to low gradient tidal influences, a large portion of the basin is un-gauged. The objective of this study was to simulate stream flow discharges and to estimate freshwater inflow from these ungauged areas to upper Charlotte Harbor. Two local gauging stations were located within the model domain and were used for calibration. Another gauge with a shorter period of record was used for verification. A set of global hydrologic parameters were selected and tested using the parameter optimization software (PEST) during the calibration. Model results were evaluated using PEST and well-known statistical indices. The correlation coefficients were very high (0.899 and 0.825) for the two calibration stations. Further testing of this approach appears warranted for watersheds with significant wetlands coverage. [ABSTRACT FROM AUTHOR]